Maarisetty Dileep, Mahanta Sasmita, Sahoo Akshaya Kumar, Mohapatra Priyabrat, Baral Saroj Sundar
Department of Chemical Engineering, BITS Pilani KK Birla Goa Campus, South Goa 403726, Goa, India.
Department of Chemistry C.V.Raman College of Engineering, Bhubaneswar 752054, India.
ACS Appl Mater Interfaces. 2020 Mar 11;12(10):11679-11692. doi: 10.1021/acsami.9b22418. Epub 2020 Feb 27.
Developing an efficient photocatalyst for concurrent hydrogen production and environmental remediation by using solar energy is a challenge. Defect engineering, although it offers a strategical promise to enhance the photocatalytic performance, has limitations that come from the ambiguity surrounding its role. In the current work, a comprehensive study on defects in promoting the charge transfer, band edge modulation, and surface reaction was carried out. The excess electrons springing from defects act like donor states and cause band bending at the junction interface. Characterization techniques such as X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, electron spin resonance, and photoluminescence were employed to investigate defect functionality, and its ultimate effect on photocatalytic performance was studied by simultaneous H production and methylene blue degradation. The role of graphene in optoelectronics and defect formation in the composite catalysts was explored. In addition, efforts have been made to unveil the reaction pathway for hydrogen evolution reaction and oxygen evolution reaction where excess defect density greatly hampered the quantum yield of the process. Results suggest that maintaining optimal defect concentration aborts the undesired thermodynamically favored back reactions. The conduction band and valence band values of the catalysts indicate that the photocatalytic mechanism was dominated by the electron pathway. Graphene acted as an effective electron sink when its concentration was around 2.5-3%. The superior activity of TiO-ZnS-rGO was attributed to the narrow bandgap, rapid separation of photo-excited charge carriers, and favorable conduction band position for photocatalytic reactions. This work may assist in exploring the fundamental role of defects in driving the photocatalytic reactions and improve the selectivity in heterogeneous photocatalysis.
开发一种利用太阳能同时制氢和进行环境修复的高效光催化剂是一项挑战。缺陷工程虽然为提高光催化性能提供了一种战略前景，但存在局限性，因为其作用尚不明确。在当前工作中，对缺陷在促进电荷转移、能带边缘调制和表面反应方面进行了全面研究。缺陷产生的多余电子起到施主态的作用，导致结界面处的能带弯曲。采用X射线光电子能谱、紫外光电子能谱、电子自旋共振和光致发光等表征技术来研究缺陷功能，并通过同时制氢和亚甲基蓝降解来研究其对光催化性能的最终影响。探索了石墨烯在光电子学中的作用以及复合催化剂中缺陷的形成。此外，还努力揭示析氢反应和析氧反应的反应途径，其中过高的缺陷密度极大地阻碍了该过程的量子产率。结果表明，保持最佳缺陷浓度可避免不希望的热力学有利的逆反应。催化剂的导带和价带值表明光催化机理以电子途径为主导。当石墨烯浓度约为2.5 - 3%时，它作为有效的电子阱。TiO-ZnS-rGO的优异活性归因于其窄带隙、光激发电荷载流子的快速分离以及光催化反应有利的导带位置。这项工作可能有助于探索缺陷在驱动光催化反应中的基本作用，并提高多相光催化中的选择性。
