Interactions between nanoscale zerovalent iron (NZVI) and silver nanoparticles alter the NZVI reactivity in aqueous environments

The increasing production and broad application of engineered nanoparticles (ENPs) have led to a substantial release of ENPs into natural systems. Despite their different utilization prospects, ENPs such as nanoscale zero-valent iron (NZVI) and silver nanoparticles (AgNPs) have been co-found in aquatic environments. This study comprehensively examined the effect of AgNPs on the reductive ability of NZVI, which was probed through the conversion of p-nitrophenol (p-NP) to p-aminophenol (p-AP). Electron microscopic and spectroscopic investigations and Derjaguin-Landau-Verwey-Overbeek (DLVO) calculations showed that the aggregation of NZVI with a low dose of AgNPs dramatically decreased the NZVI reactivity. In contrast, enhanced NZVI reactivity was observed when a high dose of AgNPs was used. The collision between self-assembled aggregates of AgNPs and NZVI can lead to the exposure of inner Fe(0), thereby improving the reductive ability of NZVI. The same behavior was observed for other nanosized (e.g., TiO2) and microsized (e.g., quartz sand) particles, which suggests the predominance of physical processes in NZVI peeling. Further investigations showed that the presence of sulfate and humic acid enhanced the p-NP removal in the NZVI-AgNP suspension, in contrast to other groundwater constituents. Our findings provide a better under-standing of potential ENP interactions, particularly in the context of groundwater remediation.