A critical review of nitrate reduction by nano zero-valent iron-based composites for enhancing N₂ selectivity

Due to the highly reductive capacity of nano zero-valent iron (nZVI) nanoparticles, the reduction of nitrate (NO₃^--N) is prone to produce ammonia nitrogen (NH₄⁺-N) as a by-product and has low selectivity for nitrogen gas (N₂). Water and dissolved oxygen (DO) in the solution consume electrons from nZVI, decreasing the efficiency of NO₃^--N reduction. In order to overcome the drawbacks of plain nZVI being used to remove NO₃^--N pollution, nZVI-based multifunctional materials have been constructed to realize the selective conversion of NO₃^--N to N₂ as well as the efficient removal of NO₃^--N. Therefore, advanced research on the reduction of NO₃^--N by nZVI-based composites has been comprehensively reviewed. Strategies to improve NO₃^--N reduction efficiency and N₂ selectivity are proposed. Moreover, the shortcomings of iron-based nanomaterials in NO₃^--N pollution control have been summarized, and some suggestions for future research directions provided.