Xiaoli Li,Ting Wang,Xueqin Tao,Ganhua Qiu,Can Li,Benxia Li
Metal-modified semiconductors are being deemed as one of the most promising photocatalysts for various applications. Although great efforts have been devoted to developing a variety of metal-modified semiconductor photocatalysts, the exact functions of their interfaces in governing photocatalytic processes still remain elusive. Herein, the interfacial synergy of metal sites and defective semiconductor with oxygen vacancies (VOs) was investigated toward the photocatalytic selective oxidation of toluene, by taking the Pd/BiOBr photocatalyst as an example. The presence of Pd induces the generation of more VOs on the BiOBr surface due to the electronic interaction at the Pd–BiOBr interface. The coexistence of the Pd and VO sites on BiOBr enables the favorable adsorption of O2 and toluene molecules. The Pd–BiOBr interface governs the charge separation and prompts the activation of O2 and toluene, leading to 1.5 times the activity of BiOBr–VO for the photocatalytic selective oxidation of toluene to benzaldehyde with a high selectivity (>99%). Moreover, the typical influencing factors, such as the illumination intensity and toluene concentration, were optimized to improve the photocatalytic efficiency. The active species and intermediates in the photocatalytic reaction were identified by a series of controlled experiments, as well as in situ ESR measurements. Therefore, both experimental and theoretical results provide the direct evidence to understand the key roles of the interfacial Pd and VO sites in enhancing photocatalysis toward the selective oxidation of toluene.
Ye Xinhui,Li Yu,Luo Peipei,He Bingcai,Cao Xinxing,Lu Tongbu
Sunlight-driven activation of molecular oxygen (O 2 ) for organic oxidation reactions offers an appealing strategy to cut down the reliance on fossil fuels in chemical industry, yet it remains a great challenge to simultaneously tailor the charge kinetics and promote reactant chemisorption on semiconductor catalysts for enhanced photocatalytic performance. Herein, we report iron sites immobilized on defective BiOBr nanosheets as an efficient and selective photocatalyst for activation of O 2 to singlet oxygen ( 1 O 2 ). These Fe 3+ species anchored by oxygen vacancies can not only facilitate the separation and migration of photogenerated charge carrier, but also serve as active sites for effective adsorption of O 2 . Moreover, low-temperature phosphorescence spectra combined with X-ray photoelectron spectroscopy (XPS) and electronic paramagnetic resonance (EPR) spectra under illumination reveal that the Fe species can boost the quantum yield of excited triplet state and accelerate the energy transfer from excited triplet state to adsorbed O 2 via a chemical loop of Fe 3+ /Fe 2+ , thereby achieving highly efficient and selective generation of 1 O 2 . As a result, the versatile iron sites on defective BiOBr nanosheets contributes to near-unity conversion rate and selectivity in both aerobic oxidative coupling of amines to imines and sulfoxidation of organic sulfides. This work highlights the significant role of metal sites anchored on semiconductors in regulating the charge/energy transfer during the heterogeneous photocatalytic process, and provides a new angle for designing high-performance photocatalysts.
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