Degradation Of Organic Pollutants By Photocatalysts Based On MOF-derived Porous Carbon

Tetracycline（TC）is widely used to treat human microbial infections and promote animal growth.However,due to its poor absorption and irrational utilization,serious TC residues have been detected in water sources,soil and other ecological environments,leading to the proliferation of antibiotic-resistant bacteria,which may cause ecological and health risks.Therefore,further research is needed on how to improve the removal rate of antibiotics in wastewater treatment process.Photocatalytic technology has gained the attention of research scholars because of its high efficiency,low energy consumption and no secondary pollution.So far,various semiconductor materials have been widely used for photocatalytic degradation of water pollutants,which can use light to generate reactive oxygen radicals to remove TC.however,relevant studies have shown that most single-phase photocatalysts have problems such as small specific surface area,lack of pore structure and poor photocatalytic stability.Therefore,the development of green,efficient and economical multiphase catalysts has become a popular research topic nowadays.In recent years,metal organic framework materials（MOFs）have attracted much attention in the fields of catalysis,gas storage and energy storage because of their high specific surface area,ordered pore channels,and tunable structural properties.MOF-derived nanomaterials can effectively retain the high porosity and large specific surface area of MOFs,improve the adsorption and mass transfer of reactive substances,and expose more catalytically active sites.Zeolite imidazolate frameworks（ZIFs）are a subclass of MOFs formed by imidazolate linkers and metal ion coordination,with high nitrogen content,three-dimensional flexible structure,and good chemical and thermal stability,and they are widely used as precursors for the preparation of porous carbon catalysts.Based on this,in this paper,ZIFs were selected as the precursor to prepare porous carbon by roasting carbonization,and the transition metal elements Co and Fe were introduced to modify them.The morphological and optical properties of the material were investigated based on the experimental instrumentation,and the catalytic activity of the material was investigated by using the results of photocatalytic degradation of simulated tetracycline wastewater,and the possible mechanism of photocatalytic degradation of TC was initially explored by radical capture experiments.The research mainly focused on:（1）The zeolite imidazole skeleton ZIF-8 was prepared by ambient liquid-phase synthesis,and the N-doped porous carbon material（NC）was roasted by the programmed warming method using it as a template.UV-vis and PL characterization results showed that the roasted carbonization significantly improved the UV-light absorption and carrier separation efficiency of the material.First,the formation of carbon groups improved the UV absorption of NC,and the porous structure increased the specific surface area of the composites,which was favorable for the adsorption of tetracycline.Secondly,the doping of C and N elements narrowed the material band gap value,enhanced the dispersion and transfer of photogenerated electrons,and effectively hindered the carrier complexation.The results of photocatalytic experiments showed that the removal rate of TC by NC reached 87.34%.The capture experiments show that h⁺is the main active substance for TC degradation,while·O₂^-and·OH also play a synergistic role in TC removal.（2）The zeolite imidazole skeleton ZIF-67 was prepared and the N-doped hollow carbon cage HCo@NC was fabricated by high-temperature pyrolysis using it as a template,and the particle size of the prepared material was controlled by regulating the molar ratio of Co²⁺to methanol to investigate its effect on photocatalytic performance.The carbon skeleton makes an outstanding contribution to accelerating mass transfer due to its good electrical conductivity,reducing carrier complexation and prolonging lifetime.The included N sites not only enhance the chemical stability of carbon,but also promote the formation of active sites on the carbon surface.The results showed that the prepared cobalt-based porous carbon material HCo@NC exhibited the optimal photocatalytic performance when the molar ratio of Co²⁺to methanol was197.63:1,and the removal rate of TC was 96.71%within 150 min.The capture tests showed that·O₂^-and·OH are the main reactive groups for the degradation of TC.（3）Ferrocene was introduced for modification during the high-temperature pyrolysis of ZIF-67,and traces of isolated Fe active centers were deposited on the formed N-doped porous carbon carriers by diffusion vapor of ferrocene ligands to improve their photocatalytic activity,and the ratio of ferrocene to ZIF-67 during calcination was also regulated.Finally,the iron-modified porous carbon materials Fe/HCo@NC based on ZIFs materials were obtained,and the morphology and structure of the materials were further analyzed by XRD and TEM characterization methods,and their photocatalytic activities were investigated.The results showed that the iron-modified cobalt-based porous carbon material Fe/HCo@NC obtained with the molar ratio of ZIF-67 to ferrocene of 1:1 had the highest removal rate of tetracycline,which could reach 96.66%within 90 min.