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 and organic wastewater pose significant threats to human health and environmental safety, making contamination control an urgent priority. Nano zero-valent iron (nZVI), coupled with nanoscale size, demonstrates exceptional adsorption and reductive capabilities, 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-supporting, 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 and proposes a 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. This review further discusses contaminant removal mechanisms: heavy metals are primarily eliminated via adsorption, reduction, complexation, and co-precipitation; nitrate removal can be achieved through reduction to N₂, adsorption, or electrochemical conversion to NH₃ via electrocatalysis; and organic pollutants are degraded through advanced oxidation processes (AOPs) involving reactive species (˙OH, ˙SO₄⁻, ˙O²⁻, ¹O₂, and 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, the current challenges in nZVI-based remediation and improvement strategies are outlined. This review serves as a reference for advancing research and applications in this field.