Simultaneous remediation of methylene blue and Cr(VI) by mesoporous BiVO₄ photocatalyst under visible-light illumination

Porous photocatalysts with large surface areas are more photoactive than compact solid counterparts, owing to their larger surface areas and porous structure, which enhance the adsorption and confinement of light, thus improving the reaction between pollutants and photocatalysts. This paper reports the mechanisms involved in the enhanced photocatalytic activity of two kinds of porous BiVO₄ catalysts, named p-BVO-1 and p-BVO-2, which are fabricated by a template-free and alcohol-hydrothermal method, respectively. Characterization, photoelectrochemical and optical measurements, reactive species detection, UV–vis, and XPS analyses were conducted. The results show that the introduction of oxygen vacancies and prolonging effect of light within the pore structure can enhance the photon response and charge separation and transfer, which help to elevate the photocatalytic performance. The simultaneous photocatalysis test of p-BVO-1 for methylene blue (MB) and Cr(VI) showed that the addition of Cr(VI) enhanced MB adsorption by forming an MB-Cr-MB complex, and MB promoted the photoreduction of Cr(VI) by scavenging h⁺ and ⋅O₂⁻, which may oxidize Cr(III) to Cr(VI). The results indicate that ⋅O₂⁻ and h⁺ are mainly deployed to degrade MB, while e⁻ reduces Cr(VI) ions, thereby favoring the separation of electron-hole pairs.