Investigation on the effect of an anion layer on photocatalytic activity: carbonate vs. oxalate

Abstract

In a layer structure, the influence of an anion layer on the photochemical property is still unknown. In this study, we mainly investigated the photochemical properties of Bi₂O₂CO₃ and Bi(C₂O₄)OH. It has been found that although they have similar layer structures, Bi₂O₂CO₃ shows activities 1.15 and 2.48 times higher than those of Bi(C₂O₄)OH for the degradation of phenol and rhodamine B (RhB) under UV light irradiation (λ ≤ 400 nm), respectively; these high activities have been mainly attributed to their different anion layers. For Bi₂O₂CO₃, CO₃²⁻ ions connect with one another to form a linked anion layer, whereas the alternating [Bi₂O₂]²⁺ and CO₃²⁻ layers are completely separate; however, for Bi(C₂O₄)OH, C₂O₄²⁻ ions do not link with each other, whereas oxygen bridges are formed between the [Bi₂O₂]²⁺ and C₂O₄²⁻ layers. The results demonstrate that an internal electric field (IEF) is favored by the separate [Bi₂O₂]²⁺ and CO₃²⁻ layers, which can greatly improve the charge separation rate. In contrast, the oxygen bridges between the [Bi₂O₂]²⁺ and C₂O₄²⁻ layers do not favor the formation of an IEF, resulting in a low charge separation rate. This finding suggests that layer semiconductors with completely separate cation and anion layers can be developed as efficient photocatalysts.