Built-in electric field leverages synergistic thermodynamic-kinetic enhancement for superior fixed-bed oxyanion adsorption.

Abstract

Fixed-bed adsorption is a widely adopted method for the removal of diverse aqueous pollutants at the industrial scale, including oxyanions such as arsenite [As(III)], arsenate [As(V)], and phosphate [P(V)]. However, owing to the inherently unsteady operating conditions, effective strategies that synergistically coregulate thermodynamics and kinetics to enhance adsorption performance remain limited. Here, we propose a generalizable approach that leverages a built-in electric field (BEF) around nanoconfined metal oxides to stabilize metastable pollutant-surface complexes, thereby optimizing both the adsorption capacity and kinetics of oxyanions to substantially improve working capacity. As a proof of concept, nanoscale hydrous zirconium oxide (HZO) was embedded inside quaternized poly(styrene-co-divinylbenzene) beads (PS⁺) to prepare HZO@PS⁺ for As(III) removal. The positively charged PS⁺ matrix electrostatically attracts the negatively polarized oxygen atoms of adsorbed As(III), stabilizing a metastable monodentate-mononuclear As(III)-HZO complex instead of the conventional bidentate-binuclear configuration. This BEF-induced modulation maintains high adsorption selectivity while enhancing both adsorption capacity and rate. In fixed-bed column tests, the working capacity increased dramatically from 160 bed volumes (BV) for a BEF-free analogue (HZO@PS⁰) to 1,790 BV for HZO@PS⁺, driven by concurrent improvements in adsorption thermodynamics and kinetics. Similar metastable surface complexes, along with substantial enhancements in adsorption performance, were also preliminarily indicated in other metal oxide-oxyanion systems, suggesting that this BEF-enabled strategy may provide a broadly applicable design principle for high-performance adsorbents suitable for fixed-bed operation.