EVALUATION OF THE PHOTOCATALYTIC ACTIVITY OF SiO2@TiO2 HYBRID SPHERES IN THE DEGRADATION OF METHYLENE BLUE AND HYDROXYLATION OF BENZENE: KINETIC AND MECHANISTIC STUDY

Abstract Silica spheres coated with titania (SiO2@TiO2) were synthesized using chitosan as template. The N2 adsorption/desorption isotherms of the spheres point to meso and macroporous characteristics and the elemental mapping by EDS shows uniform distribution of Ti on the surface of the silica spheres, leading to formation of an amorphous structure (XRD). The results from the model reaction of photocatalytic degradation of methylene blue (MB) show a good stability of the spheres regarding their reuse. The tests with various additives pointed to hydroxyl radical production as the main via of MB degradation. The photocatalytic activity of the spheres in the hydroxylation of benzene to form phenol, hydroquinone and benzoquinone was assessed. The kinetic data point to the formation of phenol as the limiting step; in addition, the phenol consumption occurs by parallel and consecutive reactions producing benzoquinone.

摘要 以壳聚糖为模板，合成了二氧化钛包覆二氧化硅微球（SiO2@TiO2）。氮气吸附-脱附等温线表征结果表明，该微球兼具介孔与大孔结构特征；能量色散X射线光谱（EDS）元素面扫描成像显示，钛元素在二氧化硅微球表面均匀分布，X射线衍射（XRD）测试证实其为无定形结构。以亚甲基蓝（MB）为模型底物的光催化降解实验结果显示，该微球具备优异的循环使用稳定性。通过多种添加剂的测试实验证实，羟基自由基的生成是亚甲基蓝降解的主要途径。本研究评估了该微球在苯羟基化制备苯酚、对苯二酚与苯醌反应中的光催化活性；动力学数据表明，苯酚的生成是该反应的限速步骤，此外苯酚可通过平行与连续反应被消耗，生成苯醌。