In Situ Creation of Oxygen Vacancies in Porous Bimetallic La/Zr Sorbent for Aqueous Phosphate: Hierarchical Pores Control Mass Transport and Vacancy Sites Determine Interaction.

Abstract

Porous materials constructed from hierarchical pores are beneficial for the mass transport during the aqueous adsorption process. To achieve high performance, it is important to create adequate numbers of active centers to anchor the target ions in the solution. Synchronous construction of powerful bonding sites in the surface area amplification process should be a promising path for developing outstanding sorbents. By in situ evaporation of reductive soft organic templates, we successfully confined oxygen vacancies (VO) in porous La/Zr bimetallic oxides. For aqueous phosphate contaminants, the as-produced porous sorbent exhibited superior removal performance, with equilibrium adsorption capacities almost ∼2 times higher those that of the VO-free counterpart. Based on mass transfer model analysis, pore structure has the potential to buffer external influence on mass transfer. Under an adverse condition (pH 9.0), the mass transfer was ∼2.5 times higher than that in the pore-free one (0.10 min-1 vs 0.04 min-1), ensuring the possibility of diffusing phosphate in further contact with these active sites. According to results of orbital interaction analysis and X-ray spectroscopy measurements, VO-dominated active sites not only enhanced attractive orbital bonding interaction toward phosphate but also converted repulsive interaction into attractive reaction, thereby eliminating this kinetics barrier and promoting the rate of phosphate chemisorption reaction.