Surface modification of nanoscale zero-valent iron for controlled corrosion and enhanced anaerobic digestion: mechanisms, modification strategies, and future perspectives

Abstract

Nanoscale zero-valent iron (nZVI) has emerged as a promising nanomaterial for enhancing anaerobic digestion (AD) owing to its strong reducing capacity and potential to stimulate microbial activity. However, its effects on methane production remain inconsistent, with both enhanced and inhibited performance reported. These contradictory findings mainly arise from the uncontrolled corrosion of bare nZVI, which causes the rapid release of electrons, Fe²⁺/Fe³⁺, hydrogen, and reactive oxygen species, together with nanoparticle aggregation and surface passivation. Surface modification has therefore emerged as an effective strategy for regulating nZVI corrosion. To the best of our knowledge, this is the first review to specifically examine surface modification of nZVI as a strategy for controlled corrosion and enhanced AD performance. The review evaluates carbon-supported materials, polymer coatings, inorganic shells, transition-metal modifications, and bio-inspired surface engineering. Particular attention is given to how surface properties, including dispersion, surface accessibility, coating permeability, conductivity, and coating thickness, influence corrosion kinetics, electron release, microbial interactions, and methane production. Individual studies have reported substantial improvements in methane production following the application of surface-modified nZVI, including a 120% increase under semi-continuous operation. These improvements were associated with enhanced microbial interactions, regulated electron transfer and redox processes, and improved substrate degradation. Finally, future research priorities are discussed, including adaptive dosing, multifunctional surface coatings, green synthesis, predictive corrosion engineering, and techno-economic and environmental assessments. Overall, controlled corrosion is proposed as a central design principle for developing stable, efficient, and sustainable surface-modified nZVI systems for AD.