Designing porous nickel architectures for adsorptive removal of Cr(VI) to achieve drinking water standard

摘要

Adsorption is evolving as a front line of water purification in recent years. Unfortunately, it is generally the case that residual pollutant concentrations in treated water still exceed the water quality standards set by WHO. In this work, we devoted to designing and synthesizing porous nickel adsorbents. Their large size and spherical shape made them mechanically tough to sustain water flow sufficiently, while their surface pores and wrinkles provided high surface areas as well as low-resistance diffusion pathways for pollutants. Besides, their high saturation magnetization above 44 emu g(-1) endowed them with quick magnetic response and easy separation from contaminated water, and their low coercivities (< 132 Oe) facilitated their good redispersibility in regeneration and reuse procedures. Our carefully-designed cycling Cr(VI) adsorption kinetic studies showed that Cr(VI) adsorption on these adsorbents conformed the pseudo-second-order kinetic model and intra-particle diffusion model, suggesting that the adsorption rate-controlling step depended on both intra-particle diffusion and ion exchange between Cr(VI) species and the adsorbent. Most notably, these adsorbents could reduce Cr(VI) concentration from 100 mg L-1 down to ca. 20 mu g L-1 within merely four adsorption cycles, making the goal of 50 mu g L-1 (drinking water standard from WHO) readily attainable.