Hydrogen Nanobubbles Promote As(III) Transformation on the Nanoscale Zero-Valent Iron Interface in an Aquatic System

The efficient detoxification of arsenite (As(III)) in anoxic waters remains a critical challenge. This study investigates the role of hydrogen nanobubbles (HNBs), spontaneously generated during the reaction of nanoscale zero-valent iron (nZVI) with water, in modulating the reactive interfaces of nZVI and enhancing the sequestration of toxic arsenic (As). The presence of HNBs significantly promotes the removal kinetics and capacity of As(III) by nZVI under anoxic aqueous conditions. Mechanistic studies, employing X-ray photoelectron spectroscopy and synchrotron radiation X-ray absorption near-edge structure analysis, reveal that HNBs facilitate the transformation of adsorbed As(III) into less toxic As(0) and As(V) within the iron oxide shell of nZVI. The inherent reducibility of HNBs was confirmed through reactions with 3,3',5,5'-tetramethylbenzidine (TMB, a substrate prone to oxidation) and levofloxacin (LEV, a photosensitizer), as well as by the direct detection of hydrogen radicals (•H) in the system. Furthermore, defects and fractures in the nZVI oxide shell are found to facilitate the interfacial transfer of atomic hydrogen radicals and hydroxyl radicals, thereby mediating the redox reactions of As(III) at the gas-liquid-solid triple interface. This work not only elucidates the mechanism behind the HNB-enhanced reactivity of nZVI but also presents a novel and efficient strategy for the sustainable remediation of water contaminated with heavy metal(loid)s.