FeO-decorated hollow porous silica spheres assisted by waste gelatin template for efficient purification of synthetic wastewater containing As(V).

Purification of As(V)-contaminated water through adsorption by FeO-based materials is a promising technology due to its low-cost and high efficiency. Dispersing the FeO phase on silica supports can improve both the adsorption rate and capacity due to the reduction in FeO particle sizes and the prevention of clumping of the FeO particles. However, the clusters in conventional silica materials largely impede the diffusion of As(V) to reach the FeO sites dispersed inside the clusters. Here, by applying a gelatin template strategy, the structure of silica materials was tailored by changing the gelatin-to-silica ratio (0, 0.6, 1.2 and 1.8) and hydrothermal temperature (60 °C, 100 °C and 140 °C). The silica cluster size could be reduced using either a low gelatin-to-silica ratio (0.6) or a low hydrothermal temperature (60 °C). Increasing the gelatin-to-silica ratio to 1.2 created porous silica spheres with a hollow structure. The FeO-loaded hollow porous silica spheres with a shell thickness of 280 nm had twice the maximum As(V) adsorption capacity (7.66 mg g) compared to the FeO-loaded silica product prepared in the absence of gelatin (3.82 mg g). The maximum As(V) adsorption capacity could be further enhanced to 9.94 mg g by reducing the shell thickness to 80 nm through increasing the gelatin-to-silica ratio to 1.8 and the hydrothermal temperature to 140 °C. In addition, the best FeO-loaded hollow porous silica spheres had rapid As(V) adsorption and showed excellent durability as the As(V) removal efficiency slightly decreased to 98.9% subsequent to five adsorption-regeneration cycles.