Bi₄O₇的可控合成与调控及其近红外光催化性能研究

Research on Controlled Synthesis and Regulation of Bi₄O₇ and Its Near-Infrared Photocatalytic Performance

摘要: 近红外光在太阳光谱中约占50%，因此开发高效的近红外响应光催化材料对提高太阳能利用效率和去除有机污染物具有重要意义。Bi₄O₇是一种典型的混合价态铋氧化物，因其具有Bi³⁺/Bi⁵⁺共存特征和可调的缺陷结构，在近红外光催化领域表现出较好的应用潜力。本文选取Bi₄O₇作为研究对象，通过调节水热反应中的碱浓度和后续退火温度，系统研究材料价态分布、缺陷结构与近红外光催化性能之间的关系。结果表明，适中的碱浓度(1~2 M)有利于纯相Bi₄O₇的生成。随着碱浓度的升高，样品中的缺陷浓度增加，Bi³⁺/Bi⁵⁺比值降低，材料对近红外光的吸收能力也逐渐减弱。在不同碱浓度条件下所得的样品中，1 M NaOH条件下所得的Bi₄O₇表现出最佳的近红外光催化活性，对磺胺嘧啶的降解率为91.67%，矿化率为16.57%。选取碱浓度调控后的最佳样品继续进行退火处理，材料的价态分布和缺陷结构得到了进一步调节。随着退火温度的升高，Bi³⁺/Bi⁵⁺比例和氧空位浓度都逐渐增加。其中，230℃退火样品表现最好，其吸收边由724 nm红移至762 nm，禁带宽度由1.54 eV降低到1.40 eV，对磺胺嘧啶的降解率达到100%，矿化率提高到36.40%。结合XPS、DRS和光电化学测试结果可知，230℃下退火处理能够较好地协调价态分布与氧空位浓度的变化。一方面，它拓宽了材料的光响应范围；另一方面，也促进了光生载流子的分离与迁移，因此材料的光催化性能得到了提升。该研究为混合价态铋氧化物近红外响应光催化材料的结构设计和性能优化提供了理论依据。

Abstract: Near-infrared (NIR) light accounts for approximately 50% of the solar spectrum. Therefore, the development of highly efficient NIR-responsive photocatalytic materials is of great significance for improving solar energy utilization and removing organic pollutants. Bi₄O₇ is a typical mixed-valence bismuth oxide. Owing to the coexistence of Bi³⁺ and Bi⁵⁺ and its tunable defect structure, it exhibits considerable potential in the field of NIR photocatalysis. In this work, Bi₄O₇ was selected as the target material, and the relationships among valence-state distribution, defect structure, and NIR photocatalytic performance were systematically investigated by tuning the alkali concentration during the hydrothermal process and the subsequent annealing temperature. The results showed that a moderate alkali concentration (1~2 M) was favorable for the formation of pure-phase Bi₄O₇. As the alkali concentration increased, the defect concentration in the samples increased, the Bi³⁺/Bi⁵⁺ ratio decreased, and the NIR light absorption ability gradually weakened. Among the samples prepared under different alkali concentrations, the Bi₄O₇ obtained at 1 M NaOH exhibited the best NIR photocatalytic activity, achieving a sulfadiazine degradation efficiency of 91.67% and a mineralization rate of 16.57%. The optimal sample obtained from alkali concentration regulation was then further subjected to annealing treatment, which enabled additional tuning of its valence-state distribution and defect structure. With increasing annealing temperature, both the Bi³⁺/Bi⁵⁺ ratio and the oxygen vacancy concentration gradually increased. Among these samples, the one annealed at 230˚C showed the best performance. Its absorption edge red-shifted from 724 nm to 762 nm, and its band gap decreased from 1.54 eV to 1.40 eV. Meanwhile, the degradation efficiency for sulfadiazine reached 100%, and the mineralization rate increased to 36.40%. Combined analyses of XPS, DRS, and photoelectrochemical measurements indicated that annealing at 230˚C effectively balanced the changes in valence-state distribution and oxygen vacancy concentration. On the one hand, it broadened the light-response range of the material; on the other hand, it promoted the separation and migration of photogenerated charge carriers. As a result, the photocatalytic performance of the material was significantly enhanced. This study provides a theoretical basis for the structural design and performance optimization of NIR-responsive mixed-valence bismuth oxide photocatalysts.