Iron oxide nanoparticles confined in mesoporous silicates for arsenic sequestration: effect of the host pore structure

Iron oxide nanoparticles (NPs) exhibit great potential in water decontamination from arsenic. Embedding NPs inside porous hosts is a very promising approach to inhibit their undesirable but inherent aggregation as well as the subsequent capacity drop during application. In this study, we confined iron oxide NPs inside inert silicates (MPS) of varying pore sizes (3.0, 5.7 and 15.7 nm) and obtained three nanocomposite adsorbents. The effect of MPS pore size on As(V) adsorption by the resultant nanocomposite adsorbents was particularly focused. The maximum As(V) adsorption capacity of the nanocomposites was negatively correlated with their host pore size. Based on the in situ Gran plots of the nanocomposites, the narrower pore size of the host resulted in a higher surface hydroxyl density of the confined iron oxide NPs. More interestingly, the reactivity of the hydroxyl groups binding smaller NPs was significantly enhanced compared to the larger one, as indicated by the higher molar ratio of the adsorbed As to the hydroxyl groups. The effect of pH and competitive anions on As(V) adsorption was also studied to further examine the role of the host pore in tuning the properties of the resultant composites.