The Preparation And Catalytic Degradation Properties Under Visible Light Of Sulfur Doped G-C₃N₄ Fenton-like Catalysts

With the progress of society and the development of technology,non-biodegradable water pollutants from chemical factories,hospitals and other sources are threatening people’s health.Many advanced oxidation technologies have been applied in wastewater treatment,among which the photo-assisted Fenton-like catalytic technology has attracted wide attention due to its remarkable catalytic efficiency.In this thesis,sulfur-doped g-C₃N₄（SCN）has been chosen as the research object.By designing and improving the surface structure of the material,and using it as the base to synthesize a composite catalyst in order to minimize the defects of SCN and improve its catalytic performance.Three systems have been investigated in this thesis.In the second chapter of this thesis,a porous sulfur-doped g-C₃N₄（P-SCN）was prepared through a one-step calcination route without a template.The in situ doping of sulfur element and the formation of porous morphology were confirmed via various characterization methods.A series of P-SCN with different porous structures were synthesized by adjusting the weight ratio of NH₄Cl to thiourea.When the weight ratio of NH₄Cl to thiourea is 1:1,the specific surface area of the obtained 2P-SCN is almost4 times larger than that of SCN.2P-SCN exhibits the best catalytic activity on rhodamine B decomposition in aid of the photo-assisted PMS activation,which is approximately 6.2-fold and 3.6-fold higher than that of the pristine g-C₃N₄ and SCN,respectively.The superior catalytic activity and high stability of the porous sulfur-doped g-C₃N₄ in a wide p H range are attributed to the features of its higher specific surface area,enriched active sites,efficient photoinduced charge separation,and increased visible light utilization.Meantime,a synergic collaboration between the PMS activation process and photocatalytic process is conducive to the production of abundant radicals for the Rh B degradation.Based on the results of the trapping agent and the literatures,a feasible degradation mechanism of P-SCN in the photo-assisted PMS activation process is proposed.In the third chapter,CoMoO₄ nanoparticles were loaded onto sulfur-doped g-C₃N₄ nanosheets to prepare CoMoO₄/SCN Fenton-like catalysts.Firstly,SCN nanosheets were synthesized by the high temperature calcination and ultrasonic methods and CoMoO₄ were synthesized by the sol-gel method.Then,the SCN nanosheets and CoMoO₄ were mixed and ground uniformly.Finally,the mixture was calcined at high temperature to obtain CoMoO₄/SCN.The catalytic performance of the composite catalyst was studied by activating PMS to degrade Rh B under visible light.By exploring the influence of different loadings of CoMoO₄ on catalytic efficiency of SCN,the optimal loading of CoMoO₄ was determined to be 11%,in which case the catalytic rate is 70-fold and 1.7-fold higher than that of SCN and CoMoO₄.The combination of CoMoO₄ and SCN not only contributes to the separation of photogenerated electrons and holes,but also realizes the efficient activation of PMS.Based on the experimental results and literatures,a feasible degradation mechanism of CoMoO₄/SCN in the photoassisted PMS activation process is proposed.In the fourth chapter,a cobalt-modified sulfur-doped g-C₃N₄（Co-SCN）catalyst was prepared by dispersing cobalt atoms on SCN in the form of coordination based on the principle of single-atomic catalysis.Using ethanol as the solvent,the cobalt atoms are highly dispersed on the SCN nanosheets by the immersion method,and then the cobalt atoms are embedded in the SCN matrix by the high-temperature calcination method to prepare a series of Co-SCN composite catalysts with different cobalt contents.Compared with the pristine SCN,the catalytic activity of the composite catalyst is greatly improved.Among them,2Co-SCN shows the best catalytic activity,by using which the catalytic rate is 79-fold and 46-fold higher than that of g-C₃N₄ and SCN.At the same time,the catalytic performance of 2Co-SCN is better than that of cobalt-doped g-C₃N₄.By comparing the catalytic degradation of each sample under different degradation conditions,a synergy between the Fenton-like process and the photocatalytic process is responsible for the high catalytic efficiency.A reaction mechanism in the photo-assisted Fenton-like process is proposed through the capture agent experiments and literatures,and the cycle experiment proves its good stability.Based on the Fenton-like catalyst with visible light response,this paper aims at the insufficient catalytic performance of bulk SCN.By adjusting the morphology and structure of the catalysts,three novel Fenton-like catalysts were prepared to activate PMS for organic pollutants degradation under visible light irradiation.These catalysts have the advantages of good stability,higher catalytic activity,etc.,and provide some new research ideas for the development of heterogeneous catalysts in the field of the photo-assisted Fenton-like catalysis.