Role of nanomaterials in advanced membrane technologies for groundwater purification

Abstract

Access to clean and potable groundwater is paramount for sustaining human health and ecological balance. Traditional groundwater purification techniques often fall short in addressing emerging contaminants and increasing water scarcity challenges. As per the World Health Organization (WHO), around 2 billion individuals worldwide rely on a drinking water source that is contaminated with faeces. In India, approximately 163 million individuals do not have access to potable water, rendering it a notable concern. Advanced membrane technologies have emerged as promising solutions for groundwater purification due to their efficiency, cost-effectiveness, and adaptability. In recent years, the incorporation of nanomaterials such as graphene, carbon nanotubes, metal nanoparticles, and nanocomposites into membrane structures has revolutionized the field of groundwater purification. These nanomaterials offer unique properties, including a high surface area, tuneable surface chemistry, and exceptional mechanical strength, which significantly enhance membrane separation processes. Their application has resulted in improved removal efficiencies for various contaminants, including heavy metals, organic pollutants, and microorganisms. This review provides an overview of recent advancements in membrane-based groundwater purification, with a specific focus on the integration of nanomaterials to enhance membrane performance. It explores the key mechanisms by which nanomaterial-enhanced membranes enhance groundwater purification, including increased adsorption capacity, reduced fouling, and improved selectivity. Moreover, the environmental sustainability of these advanced membranes is discussed, highlighting their potential to reduce energy consumption and chemical usage compared to conventional purification methods. Additionally, this review sheds light on the challenges and prospects associated with implementing nanomaterial-enhanced membranes at a larger scale, considering factors such as scalability, cost-effectiveness, and regulatory compliance. It also emphasizes the need for interdisciplinary research collaborations among materials scientists, engineers, and environmental experts to address these challenges effectively.

---

Water impact

Our water treatment project significantly contributes to the local water quality, guaranteeing the community's safe drinking water. By utilizing economical, sustainable adsorption methods with agricultural waste, we improve public health and lessen harm to the environment. By creating jobs, this project also promotes economic growth and upholds India's commitment to water conservation and sustainable development.

1. Introduction

Access to clean and safe drinking water is crucial for the well-being of both individuals and communities.¹ With growing industrialization and urbanization, conventional water treatment methods are struggling to keep pace with the escalating levels of pollution, particularly in groundwater sources.² Emerging contaminants, such as industrial chemicals, pharmaceuticals, and heavy metals, pose a significant challenge to traditional water purification techniques.^3,4 This paradigm shift has led to the exploration and utilization of nanotechnology in water treatment, opening new possibilities for enhancing the efficiency and efficacy of water purification processes.⁵ Nanomaterials, with their unique properties and high surface area-to-volume ratio, offer immense potential to address the limitations of conventional treatment methods.⁶ By harnessing these characteristics, researchers and practitioners aim to innovate and refine membrane-based water purification systems. The realm of water purification has witnessed a transformative shift with the advent of nanotechnology. Nanomaterials, at the nanoscale, exhibit unique and superior properties compared to their bulk counterparts.⁷ These properties include a high surface area-to-volume ratio, exceptional mechanical strength, unique optical and catalytic properties, and enhanced reactivity.⁸ Such characteristics make nanomaterials highly promising for various applications, particularly in the domain of water treatment.⁹ The integration of nanomaterials into membrane-based water purification systems offers immense potential to enhance efficiency, selectivity, and sustainability. The key to ensuring access to clean and safe drinking water for communities worldwide lies in the ongoing research, innovation, and responsible implementation of filtration systems improved with nanotechnology.

Objectives

• Analyze and synthesize the current state of research and applications for nanotechnology-integrated membrane technologies in groundwater purification.

• Explore the fundamental properties of nanomaterials that make them promising for membrane integration in water purification, including the surface area, size, morphology, and surface charge.

• Investigate the diverse applications of nanotechnology in water treatment, highlighting how nanomaterials address various water quality challenges and contaminants.

• Provide a comprehensive understanding of membrane-based water purification, including membrane types, structures, and mechanisms, as well as the advantages and limitations of conventional membrane technologies.

• Examine techniques and approaches for integrating nanomaterials with membranes to enhance their permeability, selectivity, mechanical strength, and anti-fouling properties.

• Assess the sustainability, environmental impact, and economic feasibility of implementing nanomaterial-enhanced membrane technologies for large-scale groundwater purification.

2. Nanotechnology in water treatment

Nanotechnology, a cutting-edge multidisciplinary field, has revolutionized water treatment methodologies.⁷ At the nanoscale, materials possess unique and advantageous properties such as a large surface area, high reactivity, exceptional strength, and enhanced adsorption capabilities.¹⁰ These properties enable the development of novel materials and technologies that address longstanding challenges in water treatment. Nanotechnology offers innovative solutions for the removal of contaminants, disinfection, and efficient water purification processes.

2.1. Nanomaterials and their properties

Nanomaterials refer to materials with at least one dimension in the nanoscale range (approximately 1–100 nm). Their properties are significantly different from bulk materials due to their increased surface area-to-volume ratio and quantum effects as shown in Table 1.¹¹ Bulk materials in the given content are materials whose size is larger than nanoscale, usually more than 100 nm in at least one dimension. The special qualities of nanomaterials, like a higher surface area-to-volume ratio and quantum effects, are not present in these materials.¹² Reactivity is increased by a high specific surface area because it offers more active locations for interactions.¹³ When compared to their bulk counterparts, these materials have a higher percentage of atoms on their surface at the nanoscale, which increases surface energy and the number of sites available for chemical reactions.¹⁴ Due to their enhanced surface area, nanomaterials are very useful for catalysis and pollutant removal, among other surface-dependent processes including adsorption and catalysis.⁹

Table 1 Physicochemical properties of nanomaterials, innovative engineering approaches and applications

Property	Innovative approach	Application
Properties
High surface area	Functionalization with nanoparticles for enhanced surface area	Adsorption of contaminants
Selective pore size	Tuneable pore size through nanopatterning	Size based filtration
Surface functionalization	Modification with tailored functional groups	Targeted adsorption
Mechanical strength	Reinforcement with nanofibers or nanocomposites	Robust and durable membranes
Chemical resistance	Incorporation of chemically resistant nanomaterials	Harsh chemical environments

---

Application
Water purification	Nanomaterial-enhanced membranes for improved filtration	Removal of contaminants
Desalination	Development of nanocomposite membranes for enhanced desalination	Conversion of seawater to freshwater
Gas separation	Functionalized nanomembranes for improved gas selectivity	Separation of gases
Biomedical implants	Surface-modified nanomembranes to reduce tissue response	Improved biocompatibility

---

Innovative approaches
Photocatalytic membranes	Integration of photocatalytic nanomaterials for pollutant degradation	Water purification
Catalytic membrane	Integrates the benefits of both catalysis and membrane filtration	Water purification
Self-healing membranes	Introduction of self-healing nanofillers for membranes	Enhanced durability
Biomimetic membranes	Design inspired by biological membranes for advanced separation	Improved selectivity
Sensing nanomembranes	Incorporation of sensing elements for on-site detection	Real-time water quality monitoring

---

The antibacterial and improved membrane antifouling properties of nanomaterials are attributed to their large surface area, size-dependent characteristics, and unique surface charges. Diverse morphologies and surface functionalization make it easier for pollutants to interact with membranes in specific ways, which enhances membrane performance in water treatment and other applications.¹⁵

2.2. Mechanism

Metal oxide nanoparticles (NPs) can be included in polymers to improve hydrophilicity due to their capability to adsorb hydroxyl groups and create a hydration layer on the surface.¹⁶ This can lead to an improvement in membrane performance through higher water flux and improved rejection/adsorption capacity. Moreover, intrinsic magnetic, antibacterial, and antifouling characteristics of metal oxide nanoparticles add to the functional improvement of membranes. Carbon nanostructures can provide superior water flux, strong ion rejection, and antifouling qualities because of their high specific surface area, mechanical strength, homogeneous porosity, thermal stability, surface reactivity, and chemical stability under adverse conditions.¹⁷ However, surface functionalization is required to solve their poor dispersibility and agglomeration concerns. Furthermore, the structure, morphology, stacking configuration and surface functional groups of carbon nanostructures and polymer membranes can all affect how they adsorb pollutants; a thorough investigation of these mechanisms would be beneficial. Also, the well-defined porous structure of zeolite-based nanocomposites, which has negatively charged surfaces, voids, and flow channels, improves membrane performance by facilitating ion exchange processes that are made possible by the exchangeable ions present in the zeolite structure.¹⁸

2.3. Applications of nanotechnology in water treatment

Nanotechnology has spurred a range of applications revolutionizing water treatment methodologies (Fig. 1). Nanotechnology has revolutionized the field of water purification by enabling the integration of nanomaterials into filtration systems, greatly enhancing their efficiency in removing a wide range of contaminants such as heavy metals, bacteria, viruses, and organic pollutants.¹⁹ This integration brings about unique characteristics and capabilities to conventional filtration technologies, making them more effective and sustainable in addressing the growing concerns regarding water quality and safety.

Fig. 1 Applications of nanotechnology in water treatment.

• Improved removal of heavy metals: nanomaterials, particularly nanoparticles like graphene oxide, carbon nanotubes, and various metal oxides, have high adsorption capacities due to their large surface area and unique surface properties.²⁰ When incorporated into filtration membranes or adsorbent filters, these nanomaterials significantly improve the removal of heavy metals like lead, arsenic, mercury, and cadmium from water.

• Bacterial and viral disinfection: silver nanoparticles (AgNPs) and titanium dioxide nanoparticles (TiO₂NPs) are well-known for their antibacterial and antiviral properties.²¹ Integration of these nanoparticles into filtration systems results in efficient disinfection of water by inactivating and deactivating bacteria and viruses.²²

• Selective filtration and size exclusion: nanomaterials can be engineered to have specific pore sizes and surface functionalities, allowing for selective filtration based on the size, charge, or chemical properties of the contaminants.²³ This enables precise removal of targeted pollutants while allowing the passage of safe water molecules.

• Self-cleaning and anti-fouling properties: certain nanomaterials exhibit self-cleaning and anti-fouling properties due to their hydrophilicity and unique surface structures. This reduces the fouling of membranes, extends their lifespan, and reduces the need for frequent maintenance and cleaning, thereby enhancing the overall efficiency and sustainability of filtration systems.²⁴

• Environmental compatibility and sustainability: nanomaterial-enhanced filtration systems are designed to be environmentally friendly and sustainable. The use of nanomaterials often results in reduced chemical usage, lower energy consumption, and decreased waste generation, aligning with sustainable practices and minimizing the environmental footprint.²⁵

• Scalability and technological integration: nano-enhanced filtration technologies are scalable and adaptable for various applications, including household water filters, industrial wastewater treatment, desalination processes, and point-of-use systems.²⁶ The integration of nanomaterials into existing filtration infrastructure is achievable, making it a viable solution for widespread implementation.²⁶ It is essential to establish standardized protocols for biomass preparation, optimize cost-effective pretreatment methods, and develop reliable supply chains. Working with industry partners can also help with the transition from pilot to commercial-scale applications. In terms of regulations, the authors need to emphasize the importance of conducting thorough safety and toxicity testing to meet the requirements of current water treatment standards.²⁷ It is crucial to prioritize the establishment of precise guidelines for the utilization of nanomaterials in water treatment. In addition, collaborating with policymakers to advocate for favourable regulations and incentives can expedite the implementation of these technologies. Ultimately, raising public awareness and involving the community can help generate support and acceptance, leading to the successful implementation and long-term sustainability of nanomaterial-based membrane technologies for purifying groundwater.²⁷

2.3.1. Nanoscale adsorbents and catalysts. Nanomaterials have emerged as promising tools in water treatment, functioning as highly efficient adsorbents and catalysts for contaminant degradation.²⁸ Their nanoscale dimensions, high surface area, and tuneable surface chemistry make them exceptional in adsorption and catalytic processes, leading to a significant reduction in pollutant concentrations within water.²⁹

• Enhanced adsorption capacity: nanomaterials possess an extraordinary surface area-to-volume ratio, providing a vast number of active sites for adsorption. This leads to significantly enhanced adsorption capacities compared to conventional adsorbents.³⁰ Various nanomaterials, such as carbon nanotubes, graphene oxide, and metal–organic frameworks (MOFs), exhibit outstanding adsorption properties for a wide array of pollutants, including heavy metals, dyes, pharmaceuticals, and organic compounds.³¹

• Tailored surface functionalization: nanomaterials can be precisely functionalized by modifying their surface properties through doping, functional groups, or coatings. This tolerability allows for the selective adsorption of specific pollutants based on charge, size, and chemical affinity, thus optimizing the adsorption process, and improving overall efficiency.³²

• Regenerability and reusability: the design of nanomaterial-based adsorbents allows for regeneration and reuse, contributing to their sustainability. After adsorbing contaminants, these nanomaterials can often be regenerated through desorption,³³ thermal treatment, or other means, restoring their adsorption capacity, and ensuring prolonged usage.

• Catalytic degradation of pollutants: nanomaterials, especially metal and metal oxide nanoparticles, exhibit remarkable catalytic activity for degrading organic pollutants and facilitating oxidation processes. Through catalytic reactions, nanocatalysts can break down complex organic molecules into less harmful or non-toxic byproducts, thus effectively treating wastewater and mitigating environmental pollution.³⁴

• Photocatalysis for water remediation: nanomaterials like titanium dioxide (TiO₂) and zinc oxide (ZnO) nanoparticles are well-known photocatalysts. When exposed to light, these nanoparticles generate reactive oxygen species (ROS) that degrade organic pollutants and disinfect water.³⁵ Photocatalytic processes are particularly effective in treating organic pollutants and microbial contaminants.

• Synergistic approaches: combining nanomaterials with other water treatment technologies, such as membranes or activated carbon, creates synergistic effects that significantly enhance the overall water treatment efficiency.³⁶ For example, incorporating nanomaterials into membrane matrices can improve membrane fouling resistance and separation efficiency.

• Real-time monitoring and remediation: nanotechnology allows for the development of real-time, in situ monitoring systems using nanosensors. These nanosensors can detect and quantify pollutants at very low concentrations, enabling timely and targeted remediation strategies.³⁷

The integration of nanoscale adsorbents and catalysts into water treatment processes represents a paradigm shift, offering unprecedented efficiency in pollutant removal and degradation. As ongoing research advances our understanding of nanomaterial properties and behaviour in water treatment contexts, we can expect even more innovative and sustainable solutions to address the global water crisis.

2.3.2. Nano-enabled disinfection. Nanotechnology has revolutionized water disinfection by introducing innovative approaches utilizing nanoparticles and nanomaterial-based photocatalysts.³⁷ These advancements present efficient and eco-friendly alternatives for water sterilization, effectively addressing microbial contamination concerns.

• Photocatalytic disinfection mechanism: nanomaterials, such as titanium dioxide (TiO₂) and zinc oxide (ZnO) nanoparticles, demonstrate excellent photocatalytic properties under light exposure.³⁷ When illuminated, these nanoparticles produce reactive oxygen species (ROS), including hydroxyl radicals (·OH), which possess strong oxidative potential. ROS attack and disrupt the cell membranes of microorganisms, effectively inactivating them.

• Broad-spectrum microbial inactivation: nano-enabled photocatalysts exhibit broad-spectrum antimicrobial activity against a wide range of microorganisms, including bacteria, viruses, fungi, and algae.³⁸ The photocatalytic process ensures effective disinfection, making it a promising approach for treating diverse water sources with varying microbial contamination.

• Enhanced disinfection efficacy: nano-enabled photocatalysis significantly enhances the disinfection efficacy compared to traditional disinfection methods. It enables rapid inactivation of microbes and can achieve higher log reductions in microbial populations within a shorter time frame, providing a quick and efficient means of water sterilization.³⁹

• Reduced microbial regrowth: unlike some traditional disinfection methods, nano-enabled disinfection reduces the possibility of microbial regrowth.³⁸ The oxidative damage caused by ROS disrupts microbial cell structures, making it difficult for microorganisms to recover or develop resistance, ensuring sustained disinfection effects.³⁸

• Eco-friendly approach: nano-enabled disinfection processes are environmentally friendly as they utilize light energy to activate the photocatalytic properties of nanomaterials. This approach eliminates the need for additional chemicals, making it a sustainable and green solution for water treatment.⁴⁰

• Potential for point-of-use systems: the development of portable and cost-effective point-of-use systems incorporating nano-enabled disinfection technology holds great promise.⁴¹ These systems can provide safe drinking water at the household level, especially in areas with limited access to centralized water treatment facilities.

• Long-term stability and durability: nanomaterial-based photocatalysts demonstrate long-term stability and durability, ensuring sustained disinfection performance over extended periods. Their robust nature makes them suitable for continuous water disinfection applications.²⁸

• Scalability and integration: the scalability of nano-enabled disinfection processes allows for integration into existing water treatment systems or the design of standalone disinfection units.⁴² This versatility facilitates their deployment in various settings, from small-scale community water supply systems to large municipal treatment facilities.

2.3.3. Nano-sensors for water quality monitoring. The integration of nanotechnology in the field of water quality monitoring has led to the development of advanced nano-sensors, offering real-time and precise detection of pollutants.⁴³ These nano-sensors enable continuous monitoring of water quality parameters, facilitating timely interventions and ensuring safe and sustainable water resources (Fig. 2).

Fig. 2 Water quality monitoring structure.⁴⁴

Ultra-sensitivity and selectivity: nano-sensors demonstrate ultra-sensitivity, capable of detecting pollutants at extremely low concentrations. Their high surface area-to-volume ratio and unique surface properties enhance adsorption, making them highly selective in identifying specific pollutants amidst a complex mixture of compounds.⁴⁵

• Multiparametric analysis: nano-sensors can be engineered to detect multiple parameters simultaneously. This includes heavy metals, organic compounds, microbial contaminants, and more.⁴⁶ Their ability to perform multiparametric analysis in real time provides a comprehensive understanding of water quality and pollution levels.

• Real-time monitoring: nano-sensors offer real-time monitoring capabilities, allowing for continuous data collection and immediate feedback. This enables prompt responses to any water quality deviations, facilitating timely interventions to mitigate potential risks to public health and the environment.

• Wireless communication and connectivity: nano-sensors can be integrated with wireless communication technologies, enabling remote monitoring and data transmission.⁴⁷ This connectivity facilitates centralized data collection, analysis, and decision-making, enhancing the efficiency and effectiveness of water quality management.

• Long-term stability and reliability: nano-sensors exhibit long-term stability and reliability, ensuring consistent and accurate monitoring over extended periods. Their robustness makes them suitable for deployment in various environmental conditions, including challenging or remote locations.

• Integration with IoT and AI: nano-sensors can be integrated into the Internet of Things (IoT) platforms and artificial intelligence (AI) systems. This integration enhances data analysis and interpretation, allowing for predictive modelling, anomaly detection, and intelligent decision support systems. Nano-sensors revolutionize water quality monitoring by providing accurate, real-time data crucial for effective water resource management and pollution control.⁴⁸ As ongoing research continues to refine nano-sensor designs, optimize their performance, and expand their applications, the potential for these advanced sensors to address water quality challenges on a global scale becomes increasingly promising.

2.3.4. Nanotechnology in desalination. Nanotechnology has emerged as a game-changer in the field of desalination, addressing the critical challenge of freshwater scarcity through innovative nanostructured membranes and other nanomaterial-based approaches. These advancements enhance desalination efficiency, lower energy consumption, and ultimately contribute to the sustainable production of freshwater.⁴⁹ Let's explore the notable findings and data associated with nanotechnology's role in desalination:

• Enhanced membrane performance: nanostructured membranes, often made using nanomaterials like carbon nanotubes, graphene oxide, and nanoporous materials, exhibit enhanced performance in desalination.⁵⁰ Their unique nanoarchitecture significantly improves water permeability and salt rejection rates, making desalination processes more efficient and cost-effective.

Selective ion transport: nanotechnology enables the design of membranes with precise nanopores that allow for selective ion transport. This selectivity enhances the efficiency of salt removal, ensuring that only ions are transported through the nanopores, leaving behind clean water.⁵¹ It's a promising approach to optimize desalination processes.

• Antifouling properties: nanomaterials integrated into membranes have inherent antifouling properties due to their surface properties and charge distribution.⁵² This antifouling characteristic reduces membrane fouling, prolongs membrane lifespan, and decreases the need for frequent maintenance and cleaning, resulting in considerable cost savings.

• Reduced energy consumption: nanostructured membranes possess improved permeability, requiring less hydraulic pressure to drive water through the membrane.⁵³ Consequently, desalination processes powered by these membranes consume less energy compared to traditional methods, contributing to sustainable and energy-efficient freshwater production.

• Scalability and feasibility: nanotechnology facilitates the scalability of desalination technologies. The production of nanostructured membranes and their integration into desalination plants can be efficiently scaled up to meet the growing demand for freshwater, especially in water-scarce regions. Combining nanotechnology with other desalination techniques, such as reverse osmosis (RO), allows for the development of hybrid nano-membrane systems.⁵⁴ These systems leverage the strengths of both approaches, achieving higher desalination efficiency, improved water quality, and reduced environmental impact.

• Sustainable desalination: by integrating nanotechnology, desalination processes become more sustainable. The reduction in energy consumption, improved membrane durability, and decreased need for chemical cleaning agents contribute to a more environmentally friendly and sustainable desalination industry.⁵⁵

• Real-world applications: nanotechnology-based desalination is finding applications in various regions facing freshwater scarcity, including arid and coastal areas.⁵⁶ These applications underscore the practicality and effectiveness of nano-enhanced desalination technologies in addressing water shortages and improving water security. Nanotechnology has paved the way for transformative advancements in desalination technologies, making them more efficient, cost-effective, and environmentally sustainable.⁵⁷ The integration of nanomaterials into desalination processes holds immense promise for addressing the global freshwater crisis and ensuring a sustainable future with abundant freshwater resources.

3. Fundamentals of membrane-based water purification

Membrane-based water purification is a widely used technology for treating various water sources, ensuring access to clean and safe drinking water.⁵⁸ The fundamental principle involves using semi-permeable membranes to separate contaminants from water based on their size, charge, or other specific properties.⁵⁹ Nanoscale materials are used in nanotechnology-enabled water purification to effectively remove pollutants. The technique entails the utilisation of nanoparticles that possess distinct properties at the nanoscale, including carbon nanotubes or metal oxides. Through adsorption, catalytic degradation, or filtration, these particles engage in interactions with contaminants.⁶⁰ For example, nanoparticles can adsorb heavy metals and pathogens or function as catalysts to degrade organic contaminants. Cleaner water is ensured by advanced nanomaterials that can trap pollutants at a tiny level, such as nano-filters or membranes. Additionally, by increasing their efficiency and lowering their energy requirements, conventional purification techniques can benefit from the application of nanotechnology.⁶¹

3.1. Membrane types and structures

Microfiltration (MF) membranes: these membranes have relatively large pore sizes ranging from 0.1 to 10 μm (Fig. 3). The porous structure of MF membranes makes them suitable for removing larger particles, suspended solids, bacteria, and some protozoa from water.⁶²

Fig. 3 Technologies based on membrane processes that utilise pressure.⁶³

Ultrafiltration (UF) membranes: UF membranes have smaller pore sizes compared to MF membranes, typically ranging from 0.001 to 0.1 μm. They effectively remove colloidal particles, macromolecules, proteins, and some viruses.⁶²

Nanofiltration (NF) membranes: NF membranes have even smaller pores, usually between 0.001 and 0.01 μm. They can remove multivalent ions, small organic compounds, and organic matter.⁶⁴

Reverse osmosis (RO) membranes: RO membranes have the smallest pores, less than 0.001 μm. They are highly effective in rejecting salts, ions, and small organic molecules, making them suitable for the desalination and purification of various contaminants.⁶⁵ Membranes can have different structures, including asymmetric, symmetric, composite, and thin-film composite (TFC) membranes. TFC membranes, for instance, consist of a thin selective layer that enhances separation efficiency and permeability.⁶⁶

Size exclusion: membranes function as sieves, allowing smaller water molecules to pass through while blocking larger contaminants based on the membrane's pore size. This is particularly significant in MF and UF membranes.

Electrostatic interaction: some membranes have charged surfaces that attract ions and molecules with opposite charges, effectively removing charged particles from water.⁶⁷

Adsorption: certain membranes possess specific surface properties that allow them to adsorb contaminants onto their surfaces, providing an additional mechanism for water purification.⁶⁸

Diffusion and permeation: molecules and ions diffuse or permeate through the membrane based on concentration gradients, allowing for the separation of different substances in the water.⁶⁹

4. Integration of nanomaterials with membranes

Nanotechnology has revolutionized membrane-based water purification by offering innovative approaches to enhance membrane performance. Integration of nanomaterials into membranes has shown tremendous potential in improving permeability, selectivity, anti-fouling properties, and overall efficiency of water treatment systems.

4.1. Nanomaterials for enhanced membrane performance

Nanotubes and nanofibers: carbon nanotubes and nanofibers possess unique structural properties, such as a high aspect ratio and large surface area, making them effective reinforcements for membranes (Fig. 4). Incorporating these nanomaterials enhances mechanical strength and water flux while inhibiting biofouling.

Fig. 4 Nanomaterials-based membrane structures.

Nanoparticles: there has been a growing interest in the antimicrobial properties of metal and metal oxide nanoparticles such as silver, titanium dioxide, and zinc oxide. Using a scientific approach, the incorporation of nanoparticles into membranes has been found to have a significant impact on the elimination or suppression of bacteria and other microorganisms, leading to notable enhancements in water quality.⁷⁰ Zinc oxide (ZnO) nanoparticles increase membrane hydrophilicity and photocatalyzed pollutant degradation. Montagnillonite clay nanoparticles improve membrane durability and operational longevity by increasing structural stability and mechanical strength.⁷¹ These nanomaterials address fouling, permeability, and pollutant removal to make groundwater purification membrane systems more efficient, durable, and sustainable.

Nanocomposites: combining nanoparticles with polymers to create nanocomposites provides membranes with enhanced properties.⁷² These composites can exhibit improved structural stability, anti-fouling capabilities, and specific functionalities based on the chosen nanoparticles.

Graphene and graphene oxide: graphene-based nanomaterials possess exceptional mechanical strength, high surface area, and excellent conductivity.⁷³ When incorporated into membranes, they enhance both permeability and selectivity, making them promising for various water purification applications.

Nanomaterials can be categorized based on their structure: 1D, 2D, or 3D. Titanium dioxide (TiO₂) and zinc oxide (ZnO) nanoparticles are 0D due to their nanoscale dimensions in all directions. Carbon nanotubes (CNTs) are 1D, with elongated structures offering high tensile strength and electrical conductivity.⁶⁹ Graphene oxide is 2D, featuring a single-layer atomic structure with remarkable thermal and electrical properties. Metal–organic frameworks (MOFs) are 3D, with a porous structure ideal for gas storage and separation due to their high surface area and tuneable pore sizes.⁵⁰

4.2. Techniques for incorporating nanomaterials into membranes

In situ synthesis: nanomaterials can be synthesized directly within the membrane matrix during its formation.⁷³ This technique ensures uniform distribution and strong bonding between the nanomaterials and the membrane structure.

Physical blending: nanomaterials, in the form of nanoparticles or nanofillers, can be physically mixed with polymer solutions before membrane casting. This method allows for straightforward incorporation of nanomaterials into the membrane structure.⁵

Layer-by-layer assembly: alternating layers of nanomaterials and oppositely charged polyelectrolytes are deposited on the membrane surface, providing precise control over the nanomaterial distribution and layer thickness.

Electrospinning: nanofibers containing nanomaterials can be electrospun to form composite membranes with improved structural characteristics and functionalities.⁷⁴

Methods for integrating nanomaterials into different membranes have some advantages and disadvantages. In situ synthesis ensures uniform distribution and strong bonding but may complicate membrane fabrication.⁷³ Physical blending offers straightforward incorporation but can result in uneven distribution.⁵ Layer-by-layer assembly provides precise control over nanomaterial distribution but is time-consuming and complex.⁷⁵ Electrospinning creates nanofiber membranes with enhanced properties but requires specialized equipment.⁷⁴ These techniques improve MF, UF, NF, and RO membranes by addressing fouling, permeability, and selectivity challenges, but each method has trade-offs in complexity, uniformity, and control over nanomaterial integration.

These techniques offer flexibility in tailoring the properties of the resulting membranes, allowing for optimization according to specific water treatment requirements. Incorporating nanomaterials into membranes represents a pivotal advancement in membrane technology. The resulting nanocomposite membranes hold immense promise for addressing the persistent challenges in water treatment, including fouling, low permeability, and inadequate selectivity. By capitalizing on the unique properties of nanomaterials, these membranes are poised to significantly enhance water purification processes, bringing us closer to sustainable and efficient solutions for clean water accessibility.

5. Enhanced membrane permeability and selectivity

Membrane permeability and selectivity are paramount in achieving efficient water purification processes. The integration of nanomaterials with membranes has emerged as a transformative approach to enhance both permeability and selectivity simultaneously, resulting in highly efficient water treatment systems.⁷⁶ Improving water permeability through nanomaterial integration, often characterized by flux or the rate of water passage through a membrane, is a critical factor influencing the efficiency and cost-effectiveness of membrane-based water purification systems. Membranes experience significant enhancements in their properties thanks to the incorporation of nanomaterials like carbon nanotubes (CNTs), graphene oxide (GO), and titanium dioxide (TiO₂). These improvements occur through a range of different mechanisms. The enhanced membrane permeability and selectivity can be attributed to the high surface area and distinct structure of CNTs and GO. These properties enable more efficient water transport and effective removal of contaminants. Titanium dioxide (TiO₂) possesses unique properties that allow it to act as a photocatalyst. This means that it can facilitate the breakdown of organic pollutants when exposed to ultraviolet (UV) light. As a result, TiO₂ helps to prevent fouling and maintain the efficiency of membranes. Silver nanoparticles have been found to possess antimicrobial properties, effectively inhibiting the growth of microorganisms on the surface of membranes and preventing biofouling. In addition, the use of zeolites and silica nanoparticles can improve the adsorption capacity and enhance mechanical strength. These advancements result in membranes that exhibit greater efficiency, durability, and versatility in dealing with a broader spectrum of contaminants. As a result, the overall performance of water purification systems is greatly enhanced. Further investigation into these particular mechanisms would offer a more thorough comprehension of the progress made in membrane technology with the aid of nanomaterials (refer). Nanomaterial integration offers several pathways to enhance water permeability:

■ Pore size engineering: nanomaterials can be strategically incorporated to modify the membrane's pore structure, effectively reducing the effective pore size.¹⁰ This controlled alteration enhances permeability by allowing faster water flow while maintaining the membrane's selectivity towards contaminants. Many nanomaterials exhibit inherent hydrophilic properties. Integration of hydrophilic nanomaterials enhances the wettability of the membrane surface, reducing energy barriers for water molecules to pass through, thus improving permeability.

■ Surface functionalization: functionalization of membranes with nanomaterials alters the surface properties, minimizing surface resistance to water flow. The increased surface area provided by nanomaterials promotes efficient water transport, thereby enhancing permeability.⁷⁷ A material's hydrophilicity can be increased through surface functionalization. A material's affinity for water can be raised by adding hydrophilic functional groups or molecules to its surface, improving its wetting and water absorption qualities. This is especially helpful for applications where water contact is required or desired, like membranes, coatings, and biological materials.⁷⁸

■ Reduced thickness: utilizing ultrathin nanomaterials or incorporating nanoparticles can decrease the membrane's effective thickness. This reduction in thickness reduces diffusional resistance, consequently enhancing permeability.

■ Enhanced structural support: certain nanomaterials, like carbon nanotubes and nanofibers, when integrated, provide mechanical reinforcement to the membrane structure.⁷⁹ This reinforcement allows for thinner yet mechanically robust membranes to be fabricated, improving permeability.

5.1. Reducing fouling and enhancing mechanical strength

Membrane fouling and mechanical strength are critical aspects influencing the efficiency and durability of membrane-based water purification systems. Fouling, the accumulation of unwanted substances on the membrane surface, hampers performance, while mechanical strength ensures the longevity and stability of the membrane structure.⁸⁰ Anti-fouling coatings lessen fouling and extend the surface life by preventing pollutants from sticking to surfaces. To reduce the need for manual cleaning, self-cleaning surfaces use hydrophobic or photocatalytic qualities to help remove dirt and organic matter through natural processes like rain or sunlight.¹⁵

5.2. Strategies to mitigate membrane fouling

Fouling poses a substantial challenge in membrane processes, diminishing water flow rates and necessitating frequent cleaning or replacement of the membrane. Integration of nanomaterials offers effective strategies to mitigate fouling as shown in Fig. 5.

Fig. 5 Key strategies to mitigate membrane fouling.⁸¹

Nanomaterials enhance membrane antifouling by modifying surface properties and improving durability. They reduce organic fouling by creating hydrophilic or oleophobic surfaces that repel organic matter. For inorganic fouling, nanomaterials like nanoparticles can disrupt scale formation or enhance self-cleaning. Biofouling is mitigated through antimicrobial properties or surface modifications that inhibit microorganism attachment.⁸²Fig. 6 illustrates nanomaterial layers on membranes, showing their interactions with foulants and the resulting clean, functional surface.

Fig. 6 Schematic diagram of the mechanism of nanomaterials using adsorption (A) and separation (B) in wastewater purification.⁶¹

• Anti-fouling coatings: nanomaterials with anti-fouling properties, such as hydrophilic nanoparticles or zwitterionic coatings, can be incorporated into membranes. These coatings repel foulants, reducing the accumulation of contaminants on the membrane surface.⁸²

• Self-cleaning surfaces: nanostructured materials with unique surface properties, like hierarchical surface roughness, promote self-cleaning behaviour. When integrated into membranes, these materials dislodge foulants, maintaining membrane efficiency.

• Surface modification for charge repulsion: functionalized nanomaterials can modify the membrane surface to carry a charge that repels foulants with similar charges, minimizing fouling due to electrostatic interactions.⁸³

• Pore size control: integration of nanomaterials can be tailored to control pore sizes at the nanoscale. This precise control impedes the entry of larger foulants while permitting the passage of water molecules.

• Zwitterionic nanocoatings: incorporating zwitterionic nanomaterials with dual positive and negative charges mitigates fouling by forming a hydration layer that repels foulants, preventing their adhesion to the membrane.

5.3. Reinforcing mechanical strength of membranes with nanomaterials

Mechanical strength is crucial to ensure the structural integrity and longevity of membranes. The incorporation of nanomaterials significantly contributes to reinforcing the mechanical strength of membranes:

• Nanofiber reinforcement: nanofibers, especially those made of materials like carbon nanotubes or nanocellulose, can be added to membrane matrices during fabrication to enhance mechanical strength without compromising flexibility.⁷⁹

• Layer-by-layer assembly: nanomaterials can be assembled layer-by-layer to create a strong, flexible multilayer structure that reinforces the membrane and improves its mechanical properties.

• Cross-linking with nanoparticles: nanoparticles can be used as cross-linkers to form covalent bonds within the membrane structure, enhancing mechanical stability and resilience to physical stress.

• Nanocomposite membranes: incorporating nanoparticles into the membrane matrix creates nanocomposite membranes with superior mechanical properties, including enhanced tensile strength and tear resistance.

• Hybrid polymer–nanomaterial matrices: hybrid matrices formed by integrating polymers with nanomaterials offer a synergistic effect, combining the mechanical strength of the nanomaterial with the processability of the polymer.

By adopting these strategies and integrating nanomaterials, we pave the way for highly resilient membranes that resist fouling and maintain mechanical stability under diverse operating conditions. The amalgamation of anti-fouling properties and enhanced mechanical strength significantly prolongs the membrane lifespan and reduces maintenance, ultimately contributing to sustainable and cost-effective water treatment technologies.⁸⁴ The successful implementation of these strategies represents a significant advancement in membrane-based water purification, ensuring reliable access to clean and safe drinking water for populations worldwide.

6. Applications of nanomaterial-integrated membranes in groundwater remediation

Nanomaterial-integrated membranes present a paradigm shift in groundwater remediation, offering efficient, cost-effective, and environmentally friendly solutions to address water contamination challenges. Some research findings are shown in Table 2. The cost associated with the production of various nanoparticles through different techniques is shown in Table 3.

Table 2 Finding on nanomaterial-integrated membranes in groundwater remediation

Contaminant type	Nanomaterials used	Membrane functionality	Reference
Arsenic removal	Iron oxide or titanium dioxide	Adsorption and removal of arsenic from groundwater	85
Pesticide and herbicide removal	Activated carbon nanoparticles or graphene oxide	Adsorption of pesticides and herbicides from contaminated groundwater	86
Heavy metal removal	Zeolites or carbon nanotubes	Adsorption properties for heavy metals like lead, cadmium, and mercury	87
Pathogen and microbial contaminant removal	Silver nanoparticles	Antimicrobial properties for removal of microbial contaminants from groundwater	88

---

Table 3 Analysis of the production costs for various types of nanoparticles

Name of nanoparticle	Production technology	Total production cost (USD per year)	Reference
ZnO	—	57 124.32	89
Copper oxide	Green synthesis	2 219 500	90
TiO2 nanoparticles	CMTiO2 process	64 792 191.25	91
Chitosan	Topologies	37 838 536.68
Cu/Zn	Biosynthesized	131 387.20	92

---

7. Environmental and economic implications

Nanomaterial-integrated membranes in groundwater purification offer a dual advantage by not only addressing environmental concerns but also exhibiting potential economic benefits.⁹³ Environmental impacts of nanomaterial-enhanced membranes are listed in Table 4.

Table 4 Environmental and economic implications of nanomembranes

Implication	Environmental impact	Economic impact	Reference
Resource efficiency	Reduced raw material usage due to efficient design	Lower material costs due to reduced consumption	94
Energy efficiency	Lower energy consumption in water treatment	Significant operational cost savings over time	95
Waste reduction	Reduced waste generation through efficient processes	Lower disposal costs and potential recycling/reuse benefits	96
Greenhouse gas emission	Lowers carbon emissions due to reduced energy usage	Potential eligibility for carbon credit programs	97
Pollution prevention	Prevents pollutants from entering natural water sources	Potential cost savings on environmental remediation	98
Capital investment	Initial high investment in research and development	Potential for high returns on investment in the growing market	99
Operating costs	Lower operational costs due to energy and material savings	Continuous cost reduction as the technology matures	100
Market competitiveness	Competitive edge through advanced technology	Enhanced market position, leading to increased sales	101
Regulatory compliance	Compliance with environmental standards and regulations	Avoidance of fines and legal costs associated with non-compliance	102

---

• Resource efficiency: nanomaterial-integrated membranes typically require lower quantities of materials due to their enhanced efficiency, contributing to resource conservation.⁹³

• Reduced footprint: the improved performance of these membranes leads to reduced plant size, minimizing land requirements and, consequently, less habitat disruption.

• Energy efficiency: enhanced membrane properties translate to lower energy consumption, making nanomaterial-integrated membranes more energy-efficient compared to traditional methods.

• Reduced chemical usage: nanomaterial-enhanced membranes often require fewer chemicals for effective water treatment, lowering the overall environmental impact associated with chemical usage and disposal.

• Longevity and durability: the longer lifespan of nanomaterial-enhanced membranes means fewer replacements and, consequently, less waste generation, contributing to sustainability.

7.1. Cost–benefit analysis and feasibility for large-scale implementation

• Cost savings in the long run: while initial implementation costs may be higher due to nanomaterial integration, the enhanced efficiency and longer lifespan of these membranes result in significant cost savings over their operational lifetime.

• Healthcare savings: access to clean drinking water achieved through nanomaterial-enhanced membranes can lead to reduced healthcare costs associated with waterborne diseases, thus indirectly contributing to economic savings.

• Market potential and job creation: the burgeoning market for nanotechnology in water treatment offers substantial economic potential, fostering technological advancements and job creation in the field.

• Attracting investments and grants: innovative technologies, especially those with clear environmental benefits, are often eligible for various grants and investments, supporting their implementation on a larger scale.

• Economic growth: the successful integration and widespread adoption of nanomaterial-enhanced membranes in groundwater purification can bolster economic growth by stimulating research, innovation, and industry development.

Striking a balance between environmental sustainability and economic viability is crucial for the successful deployment of nanomaterial-integrated membranes in groundwater purification.

8. Future prospects and emerging trends

As we move forward, the field of nanomaterial-integrated membrane technologies is poised for remarkable advancements. This section explores the potential advancements within these technologies and the anticipated developments in groundwater purification, outlining the exciting future that lies ahead.

8.1. Potential advancements in nanomaterial-integrated membrane technologies

Recent advancements in membrane technologies are leveraging the unique properties of nanomaterials to address challenges in water treatment. By integrating multifunctional nanomaterials, developing responsive and smart membranes, and engineering precise nanostructures, researchers are pushing the boundaries of membrane performance.⁶⁰ Additionally, bioengineering approaches that combine nanomaterials with biological elements or systems are opening new possibilities for more effective and sustainable water treatment solutions. These innovations promise to enhance efficiency, versatility, and adaptability in managing diverse water sources.

• Multifunctional nanomaterials: the integration of multifunctional nanomaterials with membranes, capable of simultaneously targeting multiple contaminants and adjusting membrane properties, is a promising advancement.¹⁰³ This could lead to more efficient water treatment processes and greater versatility in handling diverse water sources.

• Responsive and smart membranes: the development of membranes that respond to specific conditions such as pollutant concentration or pH changes will enhance adaptability and efficiency. Smart membranes can modify their permeability or selectivity based on real-time needs, improving overall water treatment effectiveness.

• Nanostructured membranes: engineering membranes with well-defined nanostructures allow precise control over transport properties, leading to enhanced permeability, selectivity, and fouling resistance. Tailoring these nanostructures could revolutionize membrane performance in water treatment.

• Membrane bioengineering: integrating nanomaterials with biological components or designing membranes inspired by biological systems may pave the way for advanced bioengineered membranes. Bioengineered membranes could mimic biological processes and exhibit improved selectivity and sustainability.

8.2. Anticipated developments in groundwater purification

Anticipated advancements in groundwater purification are set to transform the field with innovative approaches and technologies. Decentralized water treatment systems are emerging as a key trend, offering localized purification solutions through nanomaterial-integrated membranes. The convergence of nanotechnology with cutting-edge technologies such as IoT and AI will enable real-time monitoring and control, enhancing system efficiency.⁹ Additionally, customization of treatment solutions to meet specific local needs and increased global collaboration will drive progress in nanomaterial-integrated membranes, collectively advancing water treatment strategies and sustainability.

• Decentralized water treatment systems: future trends suggest a shift towards decentralized water treatment systems, bringing treatment closer to the point of use. Nanomaterial-integrated membranes are ideal for such systems, providing efficient, on-the-spot purification solutions.

• Technological convergence: integration of nanotechnology with other cutting-edge technologies like the Internet of Things (IoT) and Artificial Intelligence (AI) is on the horizon. Smart monitoring systems utilizing nanomaterial-enhanced membranes will enable real-time tracking and control of water quality, ensuring optimized performance.³

• Customization and personalization: tailoring water treatment solutions to specific local conditions and contaminants is an emerging trend. Nanomaterial-integrated membranes can be customized for various geographical and water quality scenarios, allowing for more effective purification.

• Global collaborations and knowledge sharing: the future involves enhanced global collaboration and knowledge exchange, accelerating research and development. International partnerships will drive innovations in nanomaterial-integrated membrane technologies for widespread use and impact.

The future of water treatment through nanomaterial-integrated membrane technologies holds immense promise. The envisioned advancements in both nanomaterial technology and water treatment strategies will collectively contribute to addressing water challenges and ensuring a sustainable and safe water future for all. Continued research, interdisciplinary collaborations, and sustained investments will be key to realizing this vision.

9. Conclusion

9.1. Key findings

The state-of-the-art field of nanotechnology combined with membrane technologies for groundwater purification has been thoroughly examined in this extensive report. The journey began with an understanding of nanomaterials and their properties, and their applications in water treatment, and delved into the fundamental mechanisms of membrane-based water purification. For the sake of both human health and environmental preservation, nanotechnology provides a revolutionary response to the global problem of water pollution. Water can be purified with amazing efficiency using techniques including adsorption, nanofiltration, photocatalysis, disinfection, sensing, and monitoring. The integration of nanomaterials with membranes was examined, highlighting strategies to enhance membrane permeability, selectivity, and mechanical strength. Comprehending the viability and sustainability of these cutting-edge technologies is essential for their appropriate incorporation into groundwater treatment procedures, guaranteeing a more efficient and eco-friendly method of water remediation. Moreover, we discussed applications through case studies and research findings, demonstrating the success and challenges of groundwater purification. The environmental and economic implications were also scrutinized, emphasizing sustainability and the need for cost–benefit analysis. Looking forward, we envisioned potential advancements and emerging trends in this field.

9.2. Call to action for sustainable groundwater remediation

The critical insights derived from this review underscore a compelling call to action for sustainable groundwater remediation. With escalating water pollution and increasing water stress, adopting innovative and sustainable technologies is imperative. The integration of nanomaterials with membrane technologies offers a powerful solution, enabling efficient removal of contaminants while maintaining eco-friendliness.

• Advocating research and innovation: researchers and stakeholders should prioritize research and innovation in nanotechnology-integrated membrane systems. Collaborative efforts must be encouraged to expedite technological advancements and overcome existing limitations.

• Policy and regulation implementation: governments and regulatory bodies should play a pivotal role in formulating and implementing policies that promote the development and deployment of nanomaterial-enhanced membrane technologies. Regulations must ensure the safe production, use, and disposal of nanomaterials.

• Public awareness and education: raising public awareness about the significance of clean groundwater and the role of nanotechnology in achieving it is crucial. Educational campaigns and programs can empower communities to actively participate in sustainable groundwater management.

• Cross-sectoral partnerships: collaboration between academia, industry, governments, and non-governmental organizations is fundamental. Such partnerships can foster interdisciplinary approaches, innovative funding models, and technology transfer, expediting the translation of research into scalable solutions.

• Investment in infrastructure: adequate funding and investment in infrastructure are pivotal for the successful implementation of nanotechnology-integrated membrane systems. Governments and investors should allocate resources for research, pilot projects, and large-scale deployment.

In conclusion, the potential of nanomaterial-enhanced membrane technologies for groundwater purification is vast and transformative. Embracing this potential requires a collective and concerted effort from all stakeholders. By integrating cutting-edge research, responsible policies, public awareness, and collaborative actions, we can ensure sustainable groundwater remediation, securing a cleaner and healthier future for our communities.

Consent to participate

This research does not involve human participants and/or animals.

Consent for publication

All authors agreed with the content, and all gave explicit consent to submit.

Data availability

The authors affirm that the data supporting the outcomes of this study are available in the manuscript.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this work.

Acknowledgements

This research received no external funding.

References

1. J. Qian, X. Gao and B. Pan, Nanoconfinement-Mediated Water Treatment: From Fundamental to Application, Environ. Sci. Technol., 2020, 54(14), 8509–8526,  DOI:10.1021/acs.est.0c01065.
2. S. Kumari, J. Chowdhry and M. Kumar, et al., Machine learning (ML): An emerging tool to access the production and application of biochar in the treatment of contaminated water and wastewater, Groundw. Sustain. Dev., 2024, 26, 101243,  DOI:10.1016/j.gsd.2024.101243.
3. C. Geng, D. Lu and J. Qian, et al., A Review on Process-Based Groundwater Vulnerability Assessment Methods, Processes, 2023, 11(6), 1610,  DOI:10.3390/pr11061610.
4. S. Kumari, J. Chowdhry and P. Sharma, et al., Integrating artificial neural networks and response surface methodology for predictive modeling and mechanistic insights into the detoxification of hazardous MB and CV dyes using Saccharum officinarum L. biomass, Chemosphere, 2023, 344, 140262,  DOI:10.1016/j.chemosphere.2023.140262.
5. S. Al Aani, C. J. Wright and M. A. Atieh, et al., Engineering nanocomposite membranes: Addressing current challenges and future opportunities, Desalination, 2017, 401, 1–15,  DOI:10.1016/j.desal.2016.08.001.
6. N. Maroufi and N. Hajilary, Nanofiltration membranes types and application in water treatment: a review, Sustain. Water Resour. Manag., 2023, 9(5), 142,  DOI:10.1007/s40899-023-00899-y.
7. A. A. Ansari, M. A. Shamim and A. M. Khan, et al., Nanomaterials as a cutting edge in the removal of toxic contaminants from water, Mater. Chem. Phys., 2023, 295, 127092,  DOI:10.1016/j.matchemphys.2022.127092.
8. X. Zhao, W. Liu and Z. Cai, et al., An overview of preparation and applications of stabilized zero-valent iron nanoparticles for soil and groundwater remediation, Water Res., 2016, 100, 245–266,  DOI:10.1016/j.watres.2016.05.019.
9. W. Liu, S. Tian and X. Zhao, et al., Application of Stabilized Nanoparticles for In Situ Remediation of Metal-Contaminated Soil and Groundwater: a Critical Review, Curr. Pollut. Rep., 2015, 1(4), 280–291,  DOI:10.1007/s40726-015-0017-x.
10. S. Poornima, S. Manikandan and V. Karthik, et al., Emerging nanotechnology based advanced techniques for wastewater treatment, Chemosphere, 2022, 303, 135050,  DOI:10.1016/j.chemosphere.2022.135050.
11. V. K. Khanna, Nanomaterials and Their Properties, 2016, pp. 25–41,  DOI:10.1007/978-81-322-3625-2_3.
12. R. Gusain, N. Kumar and S. S. Ray, Recent advances in carbon nanomaterial-based adsorbents for water purification, Coord. Chem. Rev., 2020, 405, 213111,  DOI:10.1016/j.ccr.2019.213111.
13. D. D. Suppiah, N. M. Julkapli and S. Sagadevan, et al., Eco-friendly green synthesis approach and evaluation of environmental and biological applications of iron oxide nanoparticles, Inorg. Chem. Commun., 2023, 152, 110700,  DOI:10.1016/j.inoche.2023.110700.
14. P. Makvandi, S. Iftekhar and F. Pizzetti, et al., Functionalization of polymers and nanomaterials for water treatment, food packaging, textile and biomedical applications: a review, Environ. Chem. Lett., 2021, 19(1), 583–611,  DOI:10.1007/s10311-020-01089-4.
15. X. Li, H. Liu and Y. Zhang, et al., Durable, self-cleaning and anti-fouling superhydrophobic coating based on double epoxy layer, Mater. Res. Express, 2022, 9(2), 026404,  DOI:10.1088/2053-1591/ac5074.
16. H. M. Mousa, M. Hamdy and M. A. Yassin, et al., Characterization of nanofiber composite membrane for high water flux and antibacterial properties, Colloids Surf., A, 2022, 651, 129655,  DOI:10.1016/j.colsurfa.2022.129655.
17. E. M. M. Wanda, B. B. Mamba and T. A. M. Msagati, Comparative analysis of performance of fabricated nitrogen-doped carbon-nanotubes, silicon/germanium dioxide embedded polyethersulfone membranes for removal of emerging micropollutants from water, Physics and Chemistry of the Earth, Parts A/B/C, 2022, 127, 103164,  DOI:10.1016/j.pce.2022.103164.
18. A. Sahu, R. Dosi and C. Kwiatkowski, et al., Advanced Polymeric Nanocomposite Membranes for Water and Wastewater Treatment: A Comprehensive Review, Polymers, 2023, 15(3), 540,  DOI:10.3390/polym15030540.
19. A. B. Machado, G. Z. P. Rodrigues and L. R. Feksa, et al., Applications of nanotechnology in water treatment, Rev. Conhecimento Online., 2019, 1, 03,  DOI:10.25112/rco.v1i0.1706.
20. T. S. Vo, M. M. Hossain and H. M. Jeong, et al., Heavy metal removal applications using adsorptive membranes, Nano Convergence, 2020, 7(1), 36,  DOI:10.1186/s40580-020-00245-4.
21. M. I. Rahmah, Study the effect of graphene and silver nanoparticles on the structural, morphological, optical, and antibacterial properties of commercial titanium oxide, Inorg. Chem. Commun., 2023, 149, 110441,  DOI:10.1016/j.inoche.2023.110441.
22. A. Gordano, Polymer-Based Nano-Enhanced Microfiltration/Ultrafiltration Membranes, in Advancement in Polymer-Based Membranes for Water Remediation, Elsevier, 2022, pp. 81–118,  DOI:10.1016/B978-0-323-88514-0.00015-2.
23. B. Kowalczyk, I. Lagzi and B. A. Grzybowski, Nanoseparations: Strategies for size and/or shape-selective purification of nanoparticles, Curr. Opin. Colloid Interface Sci., 2011, 16(2), 135–148,  DOI:10.1016/j.cocis.2011.01.004.
24. Y. Zhao, J. Wen and H. Sun, et al., Thermo-responsive separation membrane with smart anti-fouling and self-cleaning properties, Chem. Eng. Res. Des., 2020, 156, 333–342,  DOI:10.1016/j.cherd.2020.02.006.
25. R. S. Varma, Greener approach to nanomaterials and their sustainable applications, Curr. Opin. Chem. Eng., 2012, 1(2), 123–128,  DOI:10.1016/j.coche.2011.12.002.
26. L. Xu, W. Ma and L. Wang, et al., Nanoparticle assemblies: dimensional transformation of nanomaterials and scalability, Chem. Soc. Rev., 2013, 42(7), 3114,  10.1039/c3cs35460a.
27. A. Thirunavukkarasu, R. Nithya and R. Sivashankar, A review on the role of nanomaterials in the removal of organic pollutants from wastewater, Rev. Environ. Sci. Biotechnol., 2020, 19(4), 751–778,  DOI:10.1007/s11157-020-09548-8.
28. M. Saeed, H. M. Marwani and U. Shahzad, et al., Nanoscale silicon porous materials for efficient hydrogen storage application, J. Energy Storage., 2024, 81, 110418,  DOI:10.1016/j.est.2024.110418.
29. N. Puri, A. Gupta and A. Mishra, Recent advances on nano-adsorbents and nanomembranes for the remediation of water, J. Cleaner Prod., 2021, 322, 129051,  DOI:10.1016/j.jclepro.2021.129051.
30. Y. Yu, Z. Liu and X. Chen, et al., Water-based synthesis of nanoscale hierarchical metal-organic frameworks: Boosting adsorption and catalytic performance, Nano Mater. Sci., 2022, 5(4), 361–368,  DOI:10.1016/j.nanoms.2022.09.002.
31. S. Liu, W. Peng and H. Sun, et al., Physical and chemical activation of reduced graphene oxide for enhanced adsorption and catalytic oxidation, Nanoscale, 2014, 6(2), 766–771,  10.1039/C3NR04282K.
32. M. S. Sri Abirami Saraswathi, A. Nagendran and D. Rana, Tailored polymer nanocomposite membranes based on carbon, metal oxide and silicon nanomaterials: a review, J. Mater. Chem. A, 2019, 7(15), 8723–8745,  10.1039/C8TA11460A.
33. S. P. Goutam, G. Saxena and D. Roy, et al., Green Synthesis of Nanoparticles and Their Applications in Water and Wastewater Treatment, in Bioremediation of Industrial Waste for Environmental Safety, Springer Singapore, Singapore, 2020, pp. 349–379,  DOI:10.1007/978-981-13-1891-7_16.
34. I. Som, M. Roy and R. Saha, Advances in Nanomaterial-based Water Treatment Approaches for Photocatalytic Degradation of Water Pollutants, ChemCatChem, 2020, 12(13), 3409–3433,  DOI:10.1002/cctc.201902081.
35. C. Mendes-Felipe, A. Veloso-Fernández and J. L. Vilas-Vilela, et al., Hybrid Organic–Inorganic Membranes for Photocatalytic Water Remediation, Catalysts, 2022, 12(2), 180,  DOI:10.3390/catal12020180.
36. S. Dahiya, A. Singh and B. K. Mishra, Capacitive deionized hybrid systems for wastewater treatment and desalination: A review on synergistic effects, mechanisms and challenges, Chem. Eng. J., 2021, 417, 128129,  DOI:10.1016/j.cej.2020.128129.
37. S. Das, B. Sen and N. Debnath, Recent trends in nanomaterials applications in environmental monitoring and remediation, Environ. Sci. Pollut. Res., 2015, 22(23), 18333–18344,  DOI:10.1007/s11356-015-5491-6.
38. R. Nawab, A. Iqbal and F. Niazi, et al., Review featuring the use of inorganic nano-structured material for anti-microbial properties in textile, Polym. Bull., 2023, 80(7), 7221–7245,  DOI:10.1007/s00289-022-04418-5.
39. S. P. Deshmukh, S. M. Patil and S. B. Mullani, et al., Silver nanoparticles as an effective disinfectant: A review, Mater. Sci. Eng., C, 2019, 97, 954–965,  DOI:10.1016/j.msec.2018.12.102.
40. M. N. Abd El-Ghany, R. A. Yahia and H. A. Fahmy, Nanosensors for Agriculture, Water, Environment, and Health, in Handbook of Nanosensors, Springer Nature Switzerland, Cham, 2024, pp. 1–29,  DOI:10.1007/978-3-031-16338-8_53-1.
41. C. K. Pooi and H. Y. Ng, Review of low-cost point-of-use water treatment systems for developing communities, npj Clean Water, 2018, 1(1), 11,  DOI:10.1038/s41545-018-0011-0.
42. A. A. Ahuchaogu, O. J. Chukwu, A. I. Obike, C. E. Igara, I. C. Nnorom and J. B. O. Echeme, Reverse Osmosis Technology, its Applications and Nano-Enabled Membrane. International Journal of Advanced Research, Chem. Sci., 2018, 5(2), 20–26,  DOI:10.20431/2349-0403.0502005.
43. N. H. H. Hairom, C. F. Soon and R. M. S. R. Mohamed, et al., A review of nanotechnological applications to detect and control surface water pollution, Environ. Technol. Innovation, 2021, 24, 102032,  DOI:10.1016/j.eti.2021.102032.
44. A. Oukhatar, M. Bakhouya and O. D. El, Electromagnetic-Based Wireless Nano-Sensors Network: Architectures and Applications, J. Commun., 2021, 8–19,  DOI:10.12720/jcm.16.1.8-19.
45. A. Thakur and A. Kumar, Recent advances on rapid detection and remediation of environmental pollutants utilizing nanomaterials-based (bio)sensors, Sci. Total Environ., 2022, 834, 155219,  DOI:10.1016/j.scitotenv.2022.155219.
46. N. Colozza, S. Tazzioli and A. Sassolini, et al., Multiparametric analysis by paper-assisted potentiometric sensors for diagnostic and monitoring of reinforced concrete structures, Sens. Actuators, B, 2021, 345, 130352,  DOI:10.1016/j.snb.2021.130352.
47. O. Gulec, Extending lifetime of Wireless Nano-Sensor Networks: An energy efficient distributed routing algorithm for Internet of Nano-Things, Future Gener. Comput. Syst., 2022, 135, 382–393,  DOI:10.1016/j.future.2022.05.009.
48. M. Fawzy, A. E. D. Mahmoud and A. M. Abdelfatah, Environmental and Industrial Applications Using Internet of Things (IoT), in, A Roadmap for Enabling Industry 4.0 by Artificial Intelligence, Wiley, 2022, pp. 141–167,  DOI:10.1002/9781119905141.ch9.
49. Z. M. Mumtaz, N. Hussain and H. M. Husnain Azam, Applications of Novel Nanomaterials in Water Treatment, in Nanomaterials for Bioreactors and Bioprocessing Applications, Elsevier, 2023, pp. 217–243,  DOI:10.1016/B978-0-323-91782-7.00002-3.
50. K. Selatile, S. S. Ray and N. Kumar, et al., Fabrication of Advanced 2D Nanomaterials Membranes for Desalination and Wastewater Treatment, 2023, pp. 245–268,  DOI:10.1007/978-3-031-28756-5_8.
51. N. Khanna, S. Singh and T. Chatterji, Potential application of nanotechnology in wastewater management: A paradigm shift, Mater. Lett., 2022, 315, 131975,  DOI:10.1016/j.matlet.2022.131975.
52. K. S. Nishu, Smart and innovative nanotechnology applications for water purification, Hybrid Advances, 2023, 3, 100044,  DOI:10.1016/j.hybadv.2023.100044.
53. I. A. Said, N. Fuentes and Q. Li, Energy recovery in electrified capacitive deionization systems for wastewater treatment and desalination: A comprehensive review, Chem. Eng. Process., 2022, 178, 109030,  DOI:10.1016/j.cep.2022.109030.
54. A. K. Priya, L. Gnanasekaran and P. S. Kumar, et al., Recent trends and advancements in nanoporous membranes for water purification, Chemosphere, 2022, 303, 135205,  DOI:10.1016/j.chemosphere.2022.135205.
55. K. S. Ahmad, M. Nawaz and S. B. Jaffri, Role of renewable energy and nanotechnology in sustainable desalination of water: mini review, Int. J. Environ. Anal. Chem., 2022, 102(19), 7700–7719,  DOI:10.1080/03067319.2020.1837121.
56. R. A. McIntyre, Common Nano-Materials and Their Use in Real World Applications, Sci. Prog., 2012, 95(1), 1–22,  DOI:10.3184/003685012X13294715456431.
57. S. Palit, P. Das and P. Basak, Application of Nanotechnology in Water and Wastewater Treatment and the Vast Vision for the Future. in, 3D Printing Technology for Water Treatment Applications, Elsevier, 2023, pp. 157–179,  DOI:10.1016/B978-0-323-99861-1.00005-9.
58. S. Majidi, H. Erfan-Niya and J. Azamat, et al., Membrane Based Water Treatment: Insight from Molecular Dynamics Simulations, Sep. Purif. Rev., 2023, 52(4), 336–352,  DOI:10.1080/15422119.2022.2111263.
59. J. M. Gohil and R. R. Choudhury, Introduction to Nanostructured and Nano-Enhanced Polymeric Membranes: Preparation, Function, and Application for Water Purification. in, Nanoscale Materials in Water Purification, Elsevier, 2019, pp. 25–57,  DOI:10.1016/B978-0-12-813926-4.00038-0.
60. Y. Ji, W. Qian and Y. Yu, et al., Recent developments in nanofiltration membranes based on nanomaterials, Chin. J. Chem. Eng., 2017, 25(11), 1639–1652,  DOI:10.1016/j.cjche.2017.04.014.
61. T. S. Vo, K. M. Lwin and K. Kim, Recent developments of nano-enhanced composite membranes designed for water/wastewater purification—a review, Adv. Compos. Hybrid Mater., 2024, 7(4), 127,  DOI:10.1007/s42114-024-00923-5.
62. T. Urošević and K. Trivunac, Achievements in Low-Pressure Membrane Processes Microfiltration (MF) and Ultrafiltration (UF) for Wastewater and Water Treatment. in, Current Trends and Future Developments on (Bio-) Membranes, Elsevier, 2020, pp. 67–107,  DOI:10.1016/B978-0-12-817378-7.00003-3.
63. M. K. Selatile, S. S. Ray and V. Ojijo, et al., Recent developments in polymeric electrospun nanofibrous membranes for seawater desalination, RSC Adv., 2018, 8(66), 37915–37938,  10.1039/C8RA07489E.
64. V. Madhavi and T. Ramesh, Introduction and Basic Principle of Nanofiltration Membrane Process, 2023, pp. 1–15,  DOI:10.1007/978-981-19-5315-6_1.
65. Z. Yang and Z. Feng, et al., A Review on Reverse Osmosis and Nanofiltration Membranes for Water Purification, Polymers, 2019, 11(8), 1252,  DOI:10.3390/polym11081252.
66. P. Karami, B. Khorshidi and M. McGregor, et al., Thermally stable thin film composite polymeric membranes for water treatment: A review, J. Cleaner Prod., 2020, 250, 119447,  DOI:10.1016/j.jclepro.2019.119447.
67. Z. Wang, A. Wu and L. Colombi Ciacchi, et al., Recent Advances in Nanoporous Membranes for Water Purification, Nanomaterials, 2018, 8(2), 65,  DOI:10.3390/nano8020065.
68. T. Yu, J. Zhou and F. Liu, et al., Recent Progress of Adsorptive Ultrafiltration Membranes in Water Treatment—A Mini Review, Membranes, 2022, 12(5), 519,  DOI:10.3390/membranes12050519.
69. M. Sajid, M. Asif and N. Baig, et al., Carbon nanotubes-based adsorbents: Properties, functionalization, interaction mechanisms, and applications in water purification, J. Water Process Eng., 2022, 47, 102815,  DOI:10.1016/j.jwpe.2022.102815.
70. Y. Ji, W. Qian and Y. Yu, et al., Recent developments in nanofiltration membranes based on nanomaterials, Chin. J. Chem. Eng., 2017, 25(11), 1639–1652,  DOI:10.1016/j.cjche.2017.04.014.
71. S. S. Vedula and G. D. Yadav, Wastewater treatment containing methylene blue dye as pollutant using adsorption by chitosan lignin membrane: Development of membrane, characterization and kinetics of adsorption, J. Indian Chem. Soc., 2022, 99(1), 100263,  DOI:10.1016/j.jics.2021.100263.
72. S. Bandehali, F. Parvizian and H. Ruan, et al., A planned review on designing of high-performance nanocomposite nanofiltration membranes for pollutants removal from water, J. Ind. Eng. Chem., 2021, 101, 78–125,  DOI:10.1016/j.jiec.2021.06.022.
73. L. Y. Ng, H. S. Chua and C. Y. Ng, Incorporation of graphene oxide-based nanocomposite in the polymeric membrane for water and wastewater treatment: A review on recent development, J. Environ. Chem. Eng., 2021, 9(5), 105994,  DOI:10.1016/j.jece.2021.105994.
74. A. Escribá, B. A. T. Thome Da Silva and S. A. Lourenço, et al., Incorporation of nanomaterials on the electrospun membrane process with potential use in water treatment, Colloids Surf., A, 2021, 624, 126775,  DOI:10.1016/j.colsurfa.2021.126775.
75. M. Khraisheh, S. Elhenawy and F. AlMomani, et al., Recent Progress on Nanomaterial-Based Membranes for Water Treatment, Membranes, 2021, 11(12), 995,  DOI:10.3390/membranes11120995.
76. X.-H. Ma, Z.-K. Yao and Z. Yang, et al., Nanofoaming of Polyamide Desalination Membranes To Tune Permeability and Selectivity, Environ. Sci. Technol. Lett., 2018, 5(2), 123–130,  DOI:10.1021/acs.estlett.8b00016.
77. S. R. Lakhotia, M. Mukhopadhyay and P. Kumari, Surface-Modified Nanocomposite Membranes, Sep. Purif. Rev., 2018, 47(4), 288–305,  DOI:10.1080/15422119.2017.1386681.
78. B. Niemczyk-Soczynska, A. Gradys and P. Sajkiewicz, Hydrophilic Surface Functionalization of Electrospun Nanofibrous Scaffolds in Tissue Engineering, Polymers, 2020, 12(11), 2636,  DOI:10.3390/polym12112636.
79. X. Yang, Y. Chen and C. Zhang, et al., Electrospun carbon nanofibers and their reinforced composites: Preparation, modification, applications, and perspectives, Composites, Part B, 2023, 249, 110386,  DOI:10.1016/j.compositesb.2022.110386.
80. B. Díez and R. Rosal, A critical review of membrane modification techniques for fouling and biofouling control in pressure-driven membrane processes, Nanotechnol. Environ. Eng., 2020, 5(2), 15,  DOI:10.1007/s41204-020-00077-x.
81. M. Bagheri and S. A. Mirbagheri, Critical review of fouling mitigation strategies in membrane bioreactors treating water and wastewater, Bioresour. Technol., 2018, 258, 318–334,  DOI:10.1016/j.biortech.2018.03.026.
82. P. S. Goh, W. J. Lau and M. H. D. Othman, et al., Membrane fouling in desalination and its mitigation strategies, Desalination, 2018, 425, 130–155,  DOI:10.1016/j.desal.2017.10.018.
83. V. Kochkodan and N. Hilal, A comprehensive review on surface modified polymer membranes for biofouling mitigation, Desalination, 2015, 356, 187–207,  DOI:10.1016/j.desal.2014.09.015.
84. S. Manikandan, R. Subbaiya and M. Saravanan, et al., A critical review of advanced nanotechnology and hybrid membrane based water recycling, reuse, and wastewater treatment processes, Chemosphere, 2022, 289, 132867,  DOI:10.1016/j.chemosphere.2021.132867.
85. T. Siddique, N. K. Dutta and C. N. Roy, Nanofiltration for Arsenic Removal: Challenges, Recent Developments, and Perspectives, Nanomaterials, 2020, 10(7), 1323,  DOI:10.3390/nano10071323.
86. K. V. Plakas and A. J. Karabelas, Removal of pesticides from water by NF and RO membranes — A review, Desalination, 2012, 287, 255–265,  DOI:10.1016/j.desal.2011.08.003.
87. M. A. Hashim, S. Mukhopadhyay and J. N. Sahu, et al., Remediation technologies for heavy metal contaminated groundwater, J. Environ. Manage., 2011, 92(10), 2355–2388,  DOI:10.1016/j.jenvman.2011.06.009.
88. A. M. Nasir, M. R. Adam and S. N. E. A. Mohamad Kamal, et al., A review of the potential of conventional and advanced membrane technology in the removal of pathogens from wastewater, Sep. Purif. Technol., 2022, 286, 120454,  DOI:10.1016/j.seppur.2022.120454.
89. G. Yashni, A. Al-Gheethi and R. M. S. Radin Mohamed, et al., Bio-inspired ZnO NPs synthesized from Citrus sinensis peels extract for Congo red removal from textile wastewater via photocatalysis: Optimization, mechanisms, techno-economic analysis, Chemosphere, 2021, 281, 130661,  DOI:10.1016/j.chemosphere.2021.130661.
90. A. S. Mahmoud, M. K. Mostafa and R. W. Peters, A prototype of textile wastewater treatment using coagulation and adsorption by Fe/Cu nanoparticles: Techno-economic and scaling-up studies, Nanomater. Nanotechnol., 2021, 11, 184798042110411,  DOI:10.1177/18479804211041181.
91. S. I. Meramo-Hurtado and Á. D. González-Delgado, Application of Techno-economic and Sensitivity Analyses as Decision-Making Tools for Assessing Emerging Large-Scale Technologies for Production of Chitosan-Based Adsorbents, ACS Omega, 2020, 5(28), 17601–17610,  DOI:10.1021/acsomega.0c02064.
92. E. Noman, A. Al-Gheethi and B. A. Talip, et al., Inactivating pathogenic bacteria in greywater by biosynthesized Cu/Zn nanoparticles from secondary metabolite of Aspergillus iizukae; optimization, mechanism and techno economic analysis, PLoS One, 2019, 14(9), e0221522,  DOI:10.1371/journal.pone.0221522.
93. S. D. Alexandratos, N. Barak and D. Bauer, et al., Sustaining Water Resources: Environmental and Economic Impact, ACS Sustainable Chem. Eng., 2019, 7(3), 2879–2888,  DOI:10.1021/acssuschemeng.8b05859.
94. N. Mpongwana and S. Rathilal, A Review of the Techno-Economic Feasibility of Nanoparticle Application for Wastewater Treatment, Water, 2022, 14(10), 1550,  DOI:10.3390/w14101550.
95. S. Ahmad, H. Jia and Z. Chen, et al., Water-energy nexus and energy efficiency: A systematic analysis of urban water systems, Renewable Sustainable Energy Rev., 2020, 134, 110381,  DOI:10.1016/j.rser.2020.110381.
96. H. Saleem and S. J. Zaidi, Developments in the Application of Nanomaterials for Water Treatment and Their Impact on the Environment, Nanomaterials, 2020, 10(9), 1764,  DOI:10.3390/nano10091764.
97. S. M. Rahman and A. N. Khondaker, Mitigation measures to reduce greenhouse gas emissions and enhance carbon capture and storage in Saudi Arabia, Renewable Sustainable Energy Rev., 2012, 16(5), 2446–2460,  DOI:10.1016/j.rser.2011.12.003.
98. R. Ningthoujam, Y. D. Singh and P. J. Babu, et al., Nanocatalyst in remediating environmental pollutants, Chem. Phys. Impact., 2022, 4, 100064,  DOI:10.1016/j.chphi.2022.100064.
99. E. Machairas and E. A. Varouchakis, Cost–Benefit Analysis and Risk Assessment for Mining Activities in Terms of Circular Economy and Their Environmental Impact, Geosciences, 2023, 13(10), 318,  DOI:10.3390/geosciences13100318.
100. S. Kumar, T. Baalisampang and E. Arzaghi, et al., Synergy of green hydrogen sector with offshore industries: Opportunities and challenges for a safe and sustainable hydrogen economy, J. Cleaner Prod., 2023, 384, 135545,  DOI:10.1016/j.jclepro.2022.135545.
101. I. Corsi, I. Venditti and F. Trotta, et al., Environmental safety of nanotechnologies: The eco-design of manufactured nanomaterials for environmental remediation, Sci. Total Environ., 2023, 864, 161181,  DOI:10.1016/j.scitotenv.2022.161181.
102. R. J. Feliciano, P. Guzmán-Luna and G. Boué, et al., Strategies to mitigate food safety risk while minimizing environmental impacts in the era of climate change, Trends Food Sci. Technol., 2022, 126, 180–191,  DOI:10.1016/j.tifs.2022.02.027.
103. A. A. Yaqoob, A. Kanwal and M. N. M. Ibrahim, et al., Application and Fabrication of Nanofiltration Membrane for Separation of Metal Ions from Wastewater. in, Emerging Techniques for Treatment of Toxic Metals from Wastewater, Elsevier, 2023, pp. 365–398,  DOI:10.1016/B978-0-12-822880-7.00009-1.

---