Zuoyu
Wang
a,
Lu
Han
c,
Gaolei
Xi
c,
Tao
Jia
*ab,
Yi
Liu
a,
Xiao
He
a,
Hongxia
Wang
*c and
Bin
Li
*ab
aKey Laboratory of Forest Plant Ecology, Ministry of Education, Engineering Research Center of Forest Bio-Preparation, Heilongjiang Provincial Key Laboratory of Ecological Utilization of Forestry Based Active Substances, College of Chemistry, Chemical Engineering and Resource Utilization, Northeast Forestry University, 26 Hexing Road, Harbin 150040, P. R. China. E-mail: jiataopolychem@nefu.edu.cn
bPost-doctoral Mobile Research Station of Forestry Engineering, Northeast Forestry University, Hexing Road 26th, Harbin, Heilongjiang 150040, P. R. China
cTechnology Center for China Tobacco Henan Industrial Limited Company, Zhengzhou, Henan Province 450000, P. R. China
First published on 4th March 2024
Interfacial solar-driven evaporation technology has attracted widespread attention. The core technology of photothermal conversion is photothermal materials and biomass photothermal materials are characterized by low cost, large specific surface area, environmental friendliness, and renewability. Low-grade tobacco leaves (LTLs) are harmful to the environment; however, they also have good recycling potential. In this work, a high-performance, low cost, and environmentally friendly solar steam generation material was fabricated by combining polyvinyl alcohol hydrogels and biomass photothermal material LTL. The photothermal conversion efficiency can reach 14.33% for LTL under sunlight irradiation, and the evaporation rate reached 1.07 kg m−2 h−1 with an evaporation efficiency of 74.3%. The waste heat generated during solar water evaporation can be effectively used for synergistic water-electricity cogeneration, thus achieving an evaporation rate and voltage of 0.83 kg m−2 h−1 and 38.7 mV under sunlight irradiation, respectively. This work enhances the prospects for the comprehensive utilization of biomass resources and provides effective application methods for the development of seawater desalination technology.
Sustainability spotlightIn recent years, under the influence of climate issues, the construction of a clean, low-carbon, and efficient energy system has become a global consensus and inevitable trend. Solar energy is a type of renewable energy. Referring to solar thermal radiation energy, the main performance is often said to be sun rays. In modern times, it is commonly used to generate electricity or provide energy for water heaters. In addition, by 2025, the total consumption of biomass energy will reach 180 million tons of standard coal. Biomass energy should account for more than 14.5% of total renewable energy consumption. Increasing the development of biomass energy and promoting the industrialization process of the comprehensive utilization of biomass resources are important measures to implement the green development strategy and promote the construction of ecological civilization and sustainable development. In this work, a high-performance, low-cost, and environmentally friendly solar steam generation material was fabricated by combining polyvinyl alcohol (PVA) hydrogels and biomass photothermal material from low-grade tobacco leaves. The photothermal conversion efficiency can achieve 14.33% for abandoned tobacco leaves under sunlight irradiation, and the evaporation rate reached 1.07 kg m−2 h−1 with an evaporation efficiency of 74.3%. The waste heat generated during solar water evaporation can be effectively used for synergistic water-electricity cogeneration. This work enhances the prospects for the comprehensive utilization of biomass resources, provides effective application methods for the development of seawater desalination technology, and can also achieve sustainable energy utilization and reduce environmental pollution. |
Biomass-based materials contain many organic compounds, some of which have strong absorbance. Therefore, biomass-based materials are considered excellent photothermal materials for seawater desalination.21 Inspired by this, low-grade tobacco leaves (LTL) were selected as the photothermal material in this study. Approximately 0.9 million tons to 1.5 million tons of tobacco in the world's annual tobacco production are discarded due to their inability to be used in cigarette production. These discarded tobacco leaves are collectively referred to as LTL. Simultaneously, the tobacco production and processing process generates tobacco leaf fragments and tobacco dust, and according to incomplete statistics, nearly 2 million tons of tobacco dust are generated annually. Although some LTL and tobacco residues are currently used in the production of tobacco flakes,22 there are still a large number of LTL and tobacco residues that have not been fully utilized.23 This not only caused certain pressure on the environment but also caused a serious waste of resources. Therefore, developing comprehensive utilization technologies for LTL and tobacco fragments is a major issue that the tobacco industry urgently needs to solve.24
A large amount of pigments are distributed in the LTL, which makes them have good light-absorbing properties. By analyzing the infrared range, it can be proven that the main components of light-absorbing pigments in LTL are carotenoids and chlorophyll.25 Among them, chlorophyll is a necessary pigment for plants to carry out photosynthesis, which can convert light energy into chemical energy.26 In addition, due to the cooperative part of carotenoids, light absorption is further improved. On the one hand, carotenoids collect light and transmit it to chlorophyll. On the other hand, they are important antioxidants for reducing light damage and photoinhibition.27–29 Besides, they can efficiently absorb light because of the dispersion of these light-absorbing components in LTL. For example, chlorophyll molecules are widely distributed in the chloroplasts of leaves, which allows lighter to be absorbed and converted into other forms of energy.
There is no doubt that an efficient and environmentally friendly method of photosynthesis converts solar energy into chemical energy, which is further converted into heat energy and releases heat from plants. Importantly, this thermal effect can be utilized to save energy and accelerate seawater desalination. Therefore, the development of biomass-based materials for water and electricity cogeneration has broad application prospects in the field of solar-driven seawater desalination.30
The core of solar-driven evaporation water technology is one of the photothermal materials and the other is the carrier. In the continuous development and innovation of technology,31,32 hydrogel as a new evaporation carrier material has broad application prospects because of its low cost, efficient operation, and strong sustainability.33 At present, researchers have successfully developed different types of hydrogel carriers, which show good application potential in evaporation technology, and some encouraging research results have been obtained.34 Compared with traditional evaporation carriers, polyvinyl alcohol (PVA) hydrogel is a polymeric network with a three-dimensional porous structure, with a large surface area and numerous channels.35–37 The hydrogel carrier possesses high water absorption capacity and good water retention. Moreover, the water in a PVA hydrogel has almost the same properties as bulk liquid water. Water easily escapes from the hydrogel surface and evaporates into the air, which can achieve a large amount of water evaporation in a relatively short time.
In this work, LTL powder was applied as biomass photothermal materials for photothermal conversion experiments (Scheme 1). Herein, to achieve a high-performance, low-cost, and ecofriendly device, using LTL powder as a photothermal material and PVA hydrogel as a water carrier, an LTL-based photothermal hydrogel was prepared. The results show that the low-grade tobacco leaves hydrogel (LTL/H) showed a broad absorption spectrum ranging from 300 to 1000 nm. The LTL powder has a high photothermal conversion efficiency of 14.33% under 1.0 kW m−2 simulated solar irradiation. The water evaporation rate of LTL/H was 1.07 kg m−2 h−1 under 1.0 kW m−2 simulated solar irradiation, and the water evaporation efficiency reached 74.3%.
Furthermore, the water and electricity co-generation device was constructed by applying LTL/H and thermoelectric modules to maximize the utilization of waste heat energy produced during evaporation, aiming to generate electricity based on temperature differences. The evaporation rate of the water-electric cogeneration device and the stable output voltage are 0.83 kg m−2 h−1 and 38.7 mV under solar irradiation, respectively. Based on the good experimental results, it is confirmed that the complex formed by PVA hydrogel and LTL has superior photothermal conversion ability, which can be applied to seawater desalination. Simultaneously, the biomass-based hydrogel solar evaporator was designed to solve the situation of rapid growth in tobacco production and oversupply. This strategy for the comprehensive utilization of resources, energy conversion, and clean energy-related issues, implementing the use of biomass resources as photothermal materials for water and electricity integration, has a series of guiding significance.38
Due to the excellent photothermal performance of LTL and the superior water supply performance of hydrogel, an eco-friendly and efficient solar-driven interfacial evaporation device was constructed (Fig. 2e). The whole used LTL powder as the photothermal layer of photothermal conversion and PVA hydrogel as the support carrier for water. The LTL/H evaporator is fixed with polystyrene (PS) foam in a plastic container filled with water. The solar-driven water evaporation rate and water evaporation efficiency were systematically studied, and the simulation equipment was used to measure the mass change varying with time under one solar irradiation in real time. The effective projection area is about 9.18 cm2. It is worth noting that the LTL/H with 0.30 g of LTL powder has a high water evaporation rate and good performance. The water evaporation rate of this material reaches 1.07 kg m−2 h−1, and the water evaporation efficiency is η = 74.3%. However, under the same environmental conditions, the evaporation efficiencies of pure water and blank hydrogel were only 28.5% and 47.1%, respectively (Fig. 2f), which are much lower than those of LTL/H, further proving the excellent water evaporation performance of LTL/H. The specific experimental method and calculation process are provided in the ESI.† To highlight the advantages of LTL, 0.02 g carbon black (CB) powder was mixed with 0.3 g LTL powder to prepare the hydrogel. By measuring the surface temperature and water evaporation performance, it was found that the surface temperature of the LTL + CB hydrogel (LTL + CB/H) increased from 12.2 °C to 39.2 °C within 20 minutes (Fig. S5, ESI†). The evaporation water rate was 1.15 kg m−2 h−1 with an efficiency of 80.0% (Fig. S6, ESI†) under sunlight irradiation. This confirmed that the water evaporation property of LTL/H with CB slightly increased. However, this work highlights the use of LTL without any treatment for photothermal conversion properties and its application in the field of water purification and energy conversion. Therefore, subsequent experiments are based on the material of the LTL.
When a thermoelectric material is heated, the electrons in it are excited, creating a stream of electrons. This flow of electrons creates an electric field inside the material, which creates an electric potential difference. When two thermoelectric materials with different temperatures are joined together, the temperature difference causes electrons to flow from the hot side to the cold side, which generates an electric current. By connecting the thermoelectric material into a loop and introducing the current into an external circuit, the conversion of heat energy into electricity can be achieved.42 Therefore, to fully utilize the waste heat generated by solar-driven interface evaporation, a solar-driven water-electricity integrated generation device is designed, as shown in Fig. 3a. This integrated water-electricity generation system helps address the current water-energy challenges, surpassing the limitations of traditional single-source energy conversions, thereby supporting sustainable development. In the study, the LTL/H cut to a size consistent with the shape of the thermoelectric module (area ≈ 16 cm2) is coated on the upper surface of the thermoelectric module (TE module), and both LTL/H end in contact with water; a PS foam frame is used to hold the thermoelectric device (Fig. 3b). Under solar light densities of 1, 2, and 5 suns, a temperature difference of approximately 3.8 °C, 7.1 °C, and 14.9 °C was generated on both sides of the TE module (Fig. 3c). Correspondingly, the maximum open circuit voltages generated by the thermoelectric device are approximately 38.7 mV, 45.4 mV, and 97.4 mV, respectively (Fig. 3d). Compared with the blank hydrogel thermoelectric module exposed to one sunlight density (temperature difference = 1.7 °C, voltage = 22.6 mV), the LTL/H performance was much better than that of the uncoated thermoelectric device, with the temperature difference increased by about 2.2 times and the maximum open circuit voltage increased by about 1.7 times, confirming the feasibility of the LTL/H to improve thermoelectric power generation. It was found that under continuous solar irradiation, the voltage produced by the water-electricity cogeneration device increased rapidly within two minutes and reached a stable state at three minutes. The temperature difference curves during the thermoelectric power generation under different solar radiation densities are demonstrated as shown in Fig. 3e, which clearly compares the temperatures between the hot and cold ends of the thermoelectric sheet. Simultaneously, under 1.0 kW m−2 simulated solar irradiation, the water-electricity integrated device achieved a water evaporation rate of 0.83 kg m⁻2 h⁻1 and a vapour conversion efficiency of 57.9% (Fig. 3f). More interestingly, these experimental results show that the photothermal conversion of the LTL/H and the water cooling coupled with the TE module can be effectively used for collaborative thermoelectric power generation, providing potential opportunities for freshwater resources and power supply in remote areas. According to the comprehensive experimental investigation results, combined water and electricity cogeneration can fully use the waste heat in solar thermal evaporation water to achieve energy diversification and reduce dependence on a certain energy source. The use of LTL/H to build solar evaporators has achieved the transportation of water and simulated its future practical application in the water environment,43 and its thermal energy generation can be effectively applied to water and electricity cogeneration, achieving sustainable development in resource and energy environmental utilization research, and has broad application prospects in the field of solar photothermal conversion.
Footnote |
† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4su00005f |
This journal is © The Royal Society of Chemistry 2024 |