Application and mechanism of various modified nano zero-valent iron in wastewater treatment: A critical review

Abstract

The rising productivity and continuous discharge of inorganic/organic wastewater pose significant threats to human health and environmental safety, making contamination control an urgent priority. Nano zero-valent iron (nZVI) demonstrates exceptional adsorption and reductive capabilities, and nanoscale size, making it a promising solution for wastewater treatment. However, practical applications face challenges such as particle agglomeration, rapid surface passivation and inefficient electron utilization. Various modification methods including surface coating, supporting, coating-support, sulfidation, bimetallic, and bio-integrated methods have been developed to overcome these limitations. This review summarizes the advantages and operational principles of these modification methods while proposing standardized nomenclature for modified nZVI composites. Each modification method exhibits distinct strengths and constraints, suggesting that combined methodologies can compensate for individual limitations and achieve "1+1>2" synergistic effects. The review further includes contaminant removal mechanisms: heavy metals are primarily eliminated via adsorption, reduction, complexation, and co-precipitation; nitrate removal occurs through three steps (rapid adsorption, chemical reduction, and re-adsorption); while organic pollutants are degraded through advanced oxidation processes (AOPs) involving reactive species (·OH, ·SO4-, ·O2-, 1O2, RO·), with adsorption and direct reduction playing minor roles. These organics are either detoxified into less harmful intermediates or completely mineralized into CO2 and H2O. Finally, current challenges in nZVI-based remediation and improvement strategies are outlined. This paper serves as a reference for advancing research and applications in the field.