Experimental and theoretical elucidation of adsorption performance and mechanism of surface-engineered BiVO4 hollow cuboids for removing MB and other pollutants

Abstract

To expand the application of BiVO4 (BVO) in removing environmental pollutants as an adsorbent, it is imperative to develop an efficient way to engineer its adsorption performance and understand the underlying mechanism. To achieve this aim, herein we have firstly synthesized a new type of BVO hollow cuboids (length 1.8–4 μm, width 1–1.5 μm) via a hydrothermal reaction route, and then created O vacancies on their surface via NaBH4 treatment. The adsorption experiment for removal of methylene blue (MB) demonstrates that the surface-engineered BVO using 0.4 M NaBH4 solution exhibits an adsorption performance about 96.4 times greater than that of pristine BVO; and the value of qe is predicted by response surface methodology (RSM) to be 74.115 mg g−1 at the operation parameters CBVO = 0.1 g L−1, CMB = 40 mg L−1 and T = 10 °C. The adsorption kinetics, isotherms and thermodynamics analyses manifest that the dye adsorption process is a spontaneous, exothermic and heterogeneous multilayer adsorption process. Density functional theory (DFT) calculations suggest the creation of O vacancy significantly increases the adsorption energy of MB on the BVO surface, from −0.0375 eV for perfect BVO to −0.1204 eV for O1-vac-BVO. The adsorption mechanism of the surface-engineered BVO was elucidated based on the experimental data and theoretical calculations. Furthermore, their adsorption behaviors in removing various cationic and anionic organic dyes in different acidic-alkaline environments were evaluated.