Synthesis Of G-C₃N₄/MIL-68（In）-NH₂ And Their Photocatalytic Performance For Ibuprofen

China is a major producer and consumer of pharmaceuticals and personal care products（PPCPs）.Due to the lack of effective control measures and treatment technology,a large amount of PPCPs residues are continuously exported to water bodies,resulting in microbial drug resistance and biological toxicity,which poses a direct threat to human health and ecological environment safety.Therefore,the research on the treatment of PPCPs wastewater has received more and more attention in recent years.Relevant studies have shown that photocatalytic technology is able to thoroughly and effectively treat PPCPs wastewater,while the conventional photocatalysts commonly used at present cannot meet the requirements of large-scale application due to their own limitations（prone to photochemical corrosion,small specific surface area,low photocatalytic activity,etc.）.Hence,this study started from the construction of metal-organic frameworks（MOFs）photocatalysts with high efficiency and good stablity,took the removal of a typical non-steroidal anti-inflammatory drug pollutant—ibuprofen in water as the application goal,developed the synthesis technology of graphite-like nitrogen carbide/In-based MOFs（g-C₃N₄/MIL-68（In）-NH₂）heterojunction photocatalysts.At the same time,the structure and performance differences of as prepared materials were compared and analyzed by means of systematic characterization.In addition,photocatalytic experiments were carried out to evaluate the performance of the synthesized materials,which mainly included:photocatalytic degradation of ibuprofen experiment,the single factor effect experiment,the response surface model research as well as the mechanism and degradation path analysis.The specific research contents and conclusions are as follows:（1）The g-C₃N₄/MIL-68（In）-NH₂ composites with high photocatalytic activity were prepared using in-situ solvothermal method.The characterization results showed that MIL-68（In）-NH₂ needle-like crystals in the composites were tightly coated on the rough surface of g-C₃N₄layer.The crystal structure of MOFs in g-C₃N₄/MIL-68（In）-NH₂ was not changed,and the functional groups were well maintained.Compared with the single material,the visible light absorption capacity and photocatalytic performance of the composites were significantly improved.This is due to the heterojunction formed between the materials,which promoted the transfer and separation of photogenerated carriers.（2）The experimental results of photocatalytic performance tests showed that g-C₃N₄/MIL-68（In）-NH₂exhibited excellent photocatalytic degredation and mineralization capacity toward ibuprofen,and the composites had good structural stability and reusability.The removal efficiency of ibuprofen by 10wt%g-C₃N₄/MIL-68（In）-NH₂ was 93%,which was much higher than that of g-C₃N₄（9%）and MIL-68（In）-NH₂（68%）.Meanwhile,the TOC removal rate of the g-C₃N₄/MIL-68（In）-NH₂ photocatalytic system was as high as70%,which was 1.56 times than that of MIL-68（In）-NH₂ system.The solution p H had an important effect on the photocatalytic process,and the high-efficiency degradation of ibuprofen was acheived when the p H was 4～5,the initial concentration of ibuprofen was10～40 mg/L,and the catalyst dosages were 30～40 mg.（3）The results of response surface model analysis showed that the order of the significant effects of various factors on the photocatalytic system was:p H（A）>catalyst concentration（C）>initial concentration of ibuprofen（B）,and the premise of improving the degradation rate of ibuprofen in the system was to adjust the reaction solution to the optimal range.After the optimization of the model,the optimal operating conditions of the system were:the p H of the reaction solution was 4.56,the initial concentration of ibuprofen was20.77 mg/L,and the concentration of catalyst was 0.20 g/L.Under this condition,the removal rate of ibuprofen was up to 94.19%,and the difference between the measured value and the predicted value was less than 0.50%,which indicated that the response surface model established was highly reliable.（4）In this study,h⁺,·OH,and·O₂^-were main active species in the photocatalytic system,and h⁺played a major role in the process of ibuprofen degradation.The heterojunction formed between g-C₃N₄ and MIL-68（In）-NH₂could promote the separation of photogenerated electron-hole pairs and accelerate the formation of free radicals,thereby significantly improving the degradation efficiency of ibuprofen.The photocatalytic degradation of ibuprofen by g-C₃N₄/MIL-68（In）-NH₂ composites mainly occurred in the side chain and showed a trend of gradual degradation.The photocatalytic degradation process mainly involved hydroxylation,decarboxylation,dehydrogenation and side chain breaking reactions.