固溶体内电场调控增强Bi24O31ClxBr10-x体相电荷流动和光催化活性

光催化是一种在能源和环境领域有着重要应用前景的绿色技术,在光照射下可将有机污染物彻底降解为二氧化碳和水,但因缺乏精确调控电荷流动的方法,导致大多数光催化剂活性不高.因此,促进光生电荷的高效分离一直是光催化研究的重要方向.目前多数电荷分离调控研究集中于表面修饰、表面缺陷设计、异质结构建等表面电荷分离改善策略,而对于体相电荷分离调控研究相对较少.卤氧化铋固溶体光催化材料由于独特的层状晶体结构、可调节的带隙结构和优化的电荷分离效率,近年来受到广泛关注.目前对固溶体的体相电荷分离机理尚不清楚.内电场作为一种新的增强光催化反应活性的有效调控途径,通过定向促进体相电荷的分离和转移,使光生载流子快速参与氧化还原反应.然而,通过调控内电场来增强卤氧化铋固溶体光催化活性的报道较少,且缺乏从理论和实验的角度对固溶体内电场大小以及电荷分离机理的分析.本文构建了具有相同形貌和晶体结构的Bi₂₄O₃₁Cl_xBr_10-x固溶体光催化剂,并考察了其催化性能.密度泛函理论计算、开尔文探针力显微镜(KPFM)和Zeta电位测试结果表明,通过改变卤素类型和比例可增加晶体结构单元的不对称性,从而调节Bi₂₄O₃₁]和X]层之间的电势差,增强光催化材料的内电场强度,促进体相电荷分离和转移效率,进而提高酚类有机污染物的降解活性.光电化学测试发现,相较于Bi₂₄O₃₁Cl₁₀和Bi₂₄O₃₁Br₁₀,Bi₂₄O₃₁Cl₄Br₆固溶体体相电荷分离效率显著提高,表面和界面上的电荷转移效率以及载流子密度增加.Bi₂₄O₃₁Cl₄Br₆的载流子密度分别是Bi₂₄O₃₁Cl₁₀和Bi₂₄O₃₁Br₁₀的33.1倍和4.7倍,Bi₂₄O₃₁Cl₄Br₆固溶体降解双酚A活性分别是Bi₂₄O₃₁Cl₁₀和Bi₂₄O₃₁Br₁₀的6.21倍和2.71倍.此外,其它酚类的降解实验也证明了光催化活性和内电场强度以及电荷分离效率成正相关.综上所述,本文从内电场的角度揭示了固溶体策略对光催化性能增强的内在机理,这些发现将进一步加深对体相电荷运动行为的理解,为设计高活性光催化剂提供一条新的途径.

Enhancing an internal electric field by a solid solution strategy for steering bulk-charge flow and boosting photocatalytic activity of Bi24O31ClxBr10-x

Constructing bismuth oxyhalide solid solutions with a single homogeneous phase have intrigued the research community; however, a deeper understanding of the intrinsic origin for improved bulk-charge separation is still unclear. Herein, a series of Bi24O31ClxBr10-x solid solutions with the same structural characteristics were synthesized by crystal structure regulation. Combining density functional theory calculation, Kelvin probe force microscopy, and zeta potential testing results, an enhanced internal electric field (IEF) intensity between Bi24O31] and X] layers was achieved by changing halogen types and ratios. This greatly facilitated bulk-charge separation and transfer effi-ciency, which is significant for the degradation of phenolic organic pollutants. Owing to the en-hanced IEF intensity, the charge carrier density of Bi24O31Cl4Br6 was 33.1 and 4.7 times stronger than that of Bi24O31Cl10 and Bi24O31Br10, respectively. Therefore, Bi24O31Cl4Br6 had an optimal photo-activity for the degradation of bisphenol A, which was 6.21 and 2.71 times higher than those of Bi24O31Cl10 and Bi24O31Br10, respectively. Thus, this study revealed the intrinsic mechanism of the solid solution strategy for photocatalytic performance enhancement with respect to an IEF.