Ma Zhongmin, Zhang Ling, Zang Lihua, Yu Fei
School of Environmental Science and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China.
Materials (Basel). 2025 Jul 17;18(14):3350. doi: 10.3390/ma18143350.
The efficient depolymerization of lignin has become a key challenge in the preparation of high-value-added chemicals. Graphitic carbon nitride (g-CN)-based photocatalytic system shows potential due to its mild and green characteristics over other depolymerization methods. However, its inherent defects, such as a wide band gap and rapid carrier recombination, severely limit its catalytic performance. In this paper, a g-CN modification strategy of K⁺ doping and surface alkalinization is proposed, which is firstly applied to the photocatalytic depolymerization of the lignin β-O-4 model compound (2-phenoxy-1-phenylethanol). K⁺ doping is achieved by introducing KCl in the precursor thermal polymerization stage to weaken the edge structure strength of g-CN, and post-treatment with KOH solution is combined to optimize the surface basic groups. The structural/compositional evolution of the materials was analyzed by XRD, FTIR, and XPS. The morphology/element distribution was visualized by SEM-EDS, and the optoelectronic properties were evaluated by UV-vis DRS, PL, EIS, and transient photocurrent (TPC). K⁺ doping and surface alkalinization synergistically regulate the layered structure of the material, significantly increase the specific surface area, introduce nitrogen vacancies and hydroxyl functional groups, effectively narrow the band gap (optimized to 2.35 eV), and inhibit the recombination of photogenerated carriers by forming electron capture centers. Photocatalytic experiments show that the alkalinized g-CN can completely depolymerize 2-phenoxy-1-phenylethanol with tunable product selectivity. By adjusting reaction time and catalyst dosage, the dominant product can be shifted from benzaldehyde (up to 77.28% selectivity) to benzoic acid, demonstrating precise control over oxidation degree. Mechanistic analysis shows that the surface alkaline sites synergistically optimize the C-O bond breakage path by enhancing substrate adsorption and promoting the generation of active oxygen species (·OH, ·O). This study provides a new idea for the efficient photocatalytic depolymerization of lignin and lays an experimental foundation for the interface engineering and band regulation strategies of g-CN-based catalysts.
木质素的高效解聚已成为制备高附加值化学品的关键挑战。基于石墨相氮化碳（g-CN）的光催化体系因其相对于其他解聚方法具有温和且绿色的特性而展现出潜力。然而，其固有的缺陷，如宽带隙和快速的载流子复合，严重限制了其催化性能。本文提出了一种K⁺掺杂和表面碱化的g-CN改性策略，并首次将其应用于木质素β-O-4模型化合物（2-苯氧基-1-苯基乙醇）的光催化解聚。通过在前驱体热聚合阶段引入KCl实现K⁺掺杂，以削弱g-CN的边缘结构强度，并结合用KOH溶液进行后处理来优化表面碱性基团。通过XRD、FTIR和XPS分析了材料的结构/组成演变。通过SEM-EDS可视化了形态/元素分布，并通过UV-vis DRS、PL、EIS和瞬态光电流（TPC）评估了光电性能。K⁺掺杂和表面碱化协同调节材料的层状结构，显著增加比表面积，引入氮空位和羟基官能团，有效窄化带隙（优化至2.35 eV），并通过形成电子捕获中心抑制光生载流子的复合。光催化实验表明，碱化的g-CN可以使2-苯氧基-1-苯基乙醇完全解聚，并具有可调节的产物选择性。通过调整反应时间和催化剂用量，主要产物可以从苯甲醛（选择性高达77.28%）转变为苯甲酸，证明了对氧化程度的精确控制。机理分析表明，表面碱性位点通过增强底物吸附和促进活性氧物种（·OH、·O）的产生，协同优化C-O键断裂路径。本研究为木质素的高效光催化解聚提供了新思路，为基于g-CN的催化剂的界面工程和能带调控策略奠定了实验基础。
