Preparation, degradation pathway and mechanism of Ag-TiO2/g-C3N4 photocatalyst for formaldehyde removal

spherical Ag-TiO2/g-C3N4 composite photocatalysts were prepared on activated alumina carriers using thermal condensation synthesis and impregnation methods. The optimal preparation conditions were determined based on the formaldehyde degradation rate, with pH 2, roasting temperature of 525°C, Ag/TiO2 doping ratio of 1:3, 18 wt% Ag-TiO2 doping, and loading temperature of 500°C being preferred. Formaldehyde photocatalytic degradation experiments were conducted using the prepared photocatalysts in a homemade simulated photocatalytic experimental chamber under weak UV irradiation, with a catalyst usage of 4g, initial formaldehyde concentration of 0.8 mg/m3, and reaction time of 30 minutes. The obtained formaldehyde degradation rate was 28.56%. Structural, morphological, optical absorption, and photocatalytic active substance analyses were performed using various characterization methods. It was found that the enhancement in photocatalytic ability resulted from the formation of the tubular g-C3N4 carrier structure, which increased the catalyst loading area, exposing more active sites. Additionally, g-C3N4 promoted the generation of more active radicals, while the incorporation of silver nitrate and TiO2 facilitated photogenerated carrier separation, enhancing visible light absorption by the catalyst. The composite photocatalytic material exhibited only a 0.07% reduction in adsorption rate after three cycles of recycling, indicating its good stability in formaldehyde degradation. In conclusion, the advantages of Ag-TiO2/g-C3N4 photocatalytic degradation of formaldehyde lie in the generation of superoxide radicals and fewer electron-hole complexes.

采用热凝合成和浸渍法，在活化铝载体上制备了球形Ag-TiO2/g-C3N4复合光催化剂。制备条件优化依据为甲醛降解速率，最佳条件为pH值为2，煅烧温度525°C，Ag/TiO2掺杂比为1:3，掺杂18 wt% Ag-TiO2，负载温度500°C。在自制的模拟光催化实验室内，利用制备的光催化剂在弱紫外照射下进行甲醛光催化降解实验，催化剂用量为4g，初始甲醛浓度为0.8 mg/m³，反应时间为30分钟，甲醛降解率为28.56%。采用多种表征方法对结构、形貌、光学吸收和光催化活性物质进行了分析。研究发现，光催化能力的提升源于管状g-C3N4载体结构的形成，这增加了催化剂的负载面积，暴露出更多的活性位点。此外，g-C3N4促进了更多活性自由基的生成，而银硝酸和TiO2的引入则促进了光生载流子的分离，增强了催化剂对可见光的吸收。复合光催化材料在三次循环回收后吸附率仅降低0.07%，表明其在甲醛降解方面具有良好的稳定性。总之，Ag-TiO2/g-C3N4光催化降解甲醛的优势在于超氧自由基的产生和电子-空穴对的减少。