He Qingshen, Yi Yuyan, Shi Wenjun, Sun Pengfei, Dong Xiaoping
Department of Chemistry, Zhejiang Sci-Tech University, No.928, Second Avenue, Xiasha Higher Education Zone, Hangzhou, 310018, China.
Postdoctoral Workstation, Zhejiang Huachuan Industrial Group Co., Ltd., No.72, Huachuan South Road, Yiwu, 322003, China.
Chemosphere. 2023 Mar;317:137828. doi: 10.1016/j.chemosphere.2023.137828. Epub 2023 Jan 11.
Graphitic carbon nitride (g-CN) has been proved to possess intrinsic piezoelectricity and its two-dimensional (2D) nanosheets present piezocatalytic activity to produce hydrogen from water splitting and eliminate organic pollutants in wastewater. Specific surface area and piezoelectric polarization are of great significance to achieve high piezocatalytic activity, but it is difficult to simultaneously improve both of them. Herein, to reveal the dominant role in the piezocatalysis of g-CN, we investigated the effect of exfoliation level on the piezocatalytic activity for degrading tetracycline hydrochloride (TC). Characterization results indicated that the specific surface area of the bulk g-CN was much lower than those of exfoliated g-CN samples due to the decrease of size and thickness. However, piezoresponse force microscopy (PFM) and kelvin probe force microscopy (KPFM) examinations suggested the bulk g-CN possessed the biggest piezoelectric polarization that gradually declined as increasing the exfoliation temperature. Through testing the piezocatalytic abatement of TC, the activity decline following the order of decrease in polarization was confirmed, which demonstrated the piezoelectric polarization was the dominant factor in the piezocatalysis of g-CN. This conclusion was also verified by the step-by-step performance decrease of the bulk g-CN during the successive four piezocatalytic runs, where the ultrasound treatment promoted the delamination of g-CN. In addition, superoxide (·O) radical, hydroxyl (·OH) radical and polarized positive charge were determined to be main active species, and accordingly the bulk g-CN had the highest ·OH and ·O concentrations, as well as the highest piezocurrent response. This work reveals the main role to affect the piezocatalytic performance of g-CN, and also provides a possible strategy to design piezocatalysts with optimized piezocatalytic activity.
石墨相氮化碳（g-CN）已被证明具有本征压电性，其二维（2D）纳米片具有压电催化活性，可通过水分解产生氢气并去除废水中的有机污染物。比表面积和压电极化对于实现高压电催化活性具有重要意义，但同时提高两者却很困难。在此，为了揭示g-CN在压电催化中的主导作用，我们研究了剥离程度对降解盐酸四环素（TC）的压电催化活性的影响。表征结果表明，由于尺寸和厚度的减小，块状g-CN的比表面积远低于剥离后的g-CN样品。然而，压电响应力显微镜（PFM）和开尔文探针力显微镜（KPFM）检测表明，块状g-CN具有最大的压电极化，且随着剥离温度的升高逐渐下降。通过测试TC的压电催化降解效果，证实了活性随极化程度降低的顺序下降，这表明压电极化是g-CN压电催化的主导因素。在连续四次压电催化运行过程中块状g-CN的性能逐步下降也验证了这一结论，其中超声处理促进了g-CN的分层。此外，超氧（·O）自由基、羟基（·OH）自由基和极化正电荷被确定为主要活性物种，因此块状g-CN具有最高的·OH和·O浓度以及最高的压电电流响应。这项工作揭示了影响g-CN压电催化性能的主要作用，也为设计具有优化压电催化活性的压电催化剂提供了一种可能的策略。
