State Key Laboratory of Separation Membranes and Membrane Processes/National Center for International Joint Research on Separation Membranes, Department of Chemical Engineering, Tiangong University, Tianjin 300387, China; School of Materials Science and Engineering, Tiangong University, Tianjin 300387, China.
State Key Laboratory of Separation Membranes and Membrane Processes/National Center for International Joint Research on Separation Membranes, Department of Chemical Engineering, Tiangong University, Tianjin 300387, China; School of Environmental Science and Engineering, Tiangong University, Tianjin 300387, China.
J Colloid Interface Sci. 2022 Feb 15;608(Pt 2):1334-1347. doi: 10.1016/j.jcis.2021.10.118. Epub 2021 Oct 23.
Acid treatment serves as an effective engineering strategy to modify the structure of graphitic carbon nitride (g-CN) for enhanced metal-free photocatalysis, while their lacks a comprehensive understanding about the impacts of different acid species and acid treatment approaches on the intrinsic structure and properties of g-CN and structure-activity relationships are ambiguous. Employing inorganic/organic acids including hydrochloric acid (HCl), nitric acid (HNO), acetic acid (HAc), sulphuric acid (HSO), or oxalic acid (HCO) as treatment acids, herein, we compare the impacts of different acid pretreatment approaches on the structure and properties of g-CN. Due to different acid-melamine interaction modes and the activation roles of various acids, the obtained g-CN samples exhibit varied structures, physiochemical properties and photocatalytic activities. Compared with bulk graphitic carbon nitride (BCN), g-CN prepared by acid pretreatment show enhanced photocatalytic performance on bisphenol A (BPA) degradation. The photocatalytic degradation rates of BPA by g-CN prepared by HNO, HAc, HSO, HCO, or HCl pretreatment are about 2.2, 2.7, 2.8, 3.2 and 3.8 folds faster than that by BCN. HCl pretreatment proves to be the optimal approach, with the derived g-CN (HTCN) showing more intact heptazine structural units, and increased specific surface area, which promote the exposure of more active sites, accelerate charge transfer, and give rise to a notable improvement in photocatalysis, eventually. Mechanistic investigations through quenching experiments and electron paramagnetic resonance (EPR) characterization unveil that superoxide ion radical (O) and photo-induced holes (h) worked principally in the photodegradation reaction. This work provides new insights for the rational selection of acid types and treatment methods to synthesize metal-free carbon nitrides with improved activity for photocatalytic applications.
酸处理是一种有效的工程策略，可以用来修饰石墨相氮化碳（g-CN）的结构，以增强无金属光催化性能，然而，人们对不同酸种类和酸处理方法对 g-CN 的本征结构和性质的影响缺乏全面的了解，结构-活性关系也不明确。本文采用无机/有机酸（包括盐酸（HCl）、硝酸（HNO）、乙酸（HAc）、硫酸（HSO）或草酸（HCO）作为处理酸，比较了不同酸预处理方法对 g-CN 结构和性质的影响。由于不同的酸-三聚氰胺相互作用模式和各种酸的活化作用，得到的 g-CN 样品表现出不同的结构、物理化学性质和光催化活性。与块状石墨相氮化碳（BCN）相比，经酸预处理制备的 g-CN 在双酚 A（BPA）降解方面表现出增强的光催化性能。经 HNO、HAc、HSO、HCO 或 HCl 预处理制备的 g-CN 对 BPA 的光催化降解速率分别比 BCN 快 2.2、2.7、2.8、3.2 和 3.8 倍。HCl 预处理被证明是最佳方法，所得的 g-CN（HTCN）具有更完整的六嗪结构单元和增加的比表面积，这促进了更多活性位点的暴露，加速了电荷转移，并导致光催化性能显著提高。通过猝灭实验和电子顺磁共振（EPR）表征的机理研究表明，超氧阴离子自由基（O）和光致空穴（h）在光降解反应中起主要作用。这项工作为合理选择酸类型和处理方法提供了新的见解，以合成具有改善的光催化应用活性的无金属碳氮化物。
