Preparation Of Heterogeneous Catalysts And Their Use In The Degradation Of Tetracycline Hydrochloride Wastewater

Over the last few decades,water pollution has become one of the most serious threats to human health and ecosystems.The second largest group of antibiotics in the world is tetracycline,which is widely used in aquaculture,animal husbandry and medicine.However,with rapid urbanisation and industrialisation,the misuse of tetracycline antibiotics is increasing,leading to more serious water pollution and posing a great threat to the natural environment and human health.The need for efficient and simple removal of tetracycline residues from wastewater has therefore become very urgent.Advanced oxidation processes（AOPs）have attracted a lot of attention in recent years as a new technology for the formation of highly reactive species that can then degrade and even mineralise pollutants.Advanced oxidation technologies based on peroxynitrite（PS-AOPs）have received a lot of attention for their high redox potential and wide environmental applicability in the p H range 2 to 10.Transition metal Co and Cu ions can efficiently activate PS to produce active species to degrade pollutants,but homogeneous catalysis is often difficult to recover and can cause leaching of metal ions,whereas multiphase catalysis can effectively alleviate or avoid these problems.Therefore,this paper investigates the effect of different reaction conditions on the activation of peroxynitrite in different systems,as well as the stability of the catalysts and the reaction mechanism of each system,using highly efficient and stable Co-doped carbon nitride,CuO and CoS catalysts.The main studies in this thesis are summarised as follows:（1）Cobalt-doped g-C₃N₄ was investigated as a multiphase catalyst for the light-assisted activation of peroxynitrite for the degradation of tetracycline hydrochloride.The cobalt-doped g-C₃N₄ photocatalyst was prepared by calcination and used as a visible light catalyst for TC degradation in the presence of PMS.The Co-CN-70/PMS/Vis system showed the highest photocatalytic degradation performance for TC under 9 min of light.The active cobalt on g-C₃N₄ effectively activated PMS and accelerated the degradation of organic matter.there was a synergistic effect between the PMS activation process and the photocatalytic process,and this synergy promoted the generation of active species,with h⁺and ¹O₂ being the main active species.（2）The preparation of CuO nanosheets and their performance in the degradation of tetracycline hydrochloride by activated peroxymonosulfate were investigated.Rectangular CuO nanosheets were prepared by a one-step hydrothermal method and the morphological structure and chemical composition of the materials were analysed to demonstrate that the catalyst was successfully synthesised.The removal effect of activated PMS from copper oxide materials on the target pollutant TC was also investigated.The experimental results showed that the CuO/PMS system could efficiently remove the contaminant from water.98.8%degradation of tetracycline hydrochloride was achieved within 5 min at an initial concentration of TC of 30 mg/L under the investigated optimal reaction conditions（1.0 m M PMS,0.3 g/L CuO,p H 4.6）,and the complete degradation of tetracycline hydrochloride was basically achieved within 30 min.degradation within 30 min.After four cycles,the TC removal rate still reached 92.5%and the crystal structure remained unchanged.EPR tests and bursting experiments showed that ¹O₂,·OH and SO₄·^-were all involved in the degradation of TC,and ¹O₂ was the main active substance generated by the activated PMS.（3）The preparation of CoS catalysts and their performance for the degradation of tetracycline hydrochloride by activated peroxymonosulfate were investigated.A floral non-homogeneous catalyst CoS,consisting of flakes,was prepared by a one-step hydrothermal method using thiourea and Cobalt（II）acetate tetrahydrate as raw materials and used as an activated PMS for the degradation of TC.The effects of factors such as catalyst addition,PMS addition,p H,initial TC concentration,inorganic anion and temperature on the degradation of tetracycline hydrochloride by the CoS/PMS system were investigated.The results showed that the CoS/PMS system was able to degrade the contaminants in water rapidly and efficiently.The removal rate of 30 mg/L tetracycline hydrochloride within one minute already reached 96.8%,and the complete degradation of tetracycline hydrochloride was basically achieved within 20 min.In addition,based on the efficient removal of TC,the CoS/PMS system has excellent cycling performance,achieving more than 90%TC removal within 20 min even in the fourth cycle.A comprehensive analysis of the EPR tests and the results of the bursting experiments showed that the reactive oxygen species involved in the degradation process included·O₂^-,·OH and SO₄·^-,with·O₂^-playing a major role,followed by·OH and SO₄·^-Further,to understand the degradation pathway of TC in the CoS/PMS system,the degradation process of TC at natural p H was investigated by LC-MS.In addition,XPS characterisation of the CoS catalyst before and after the reaction revealed that the nature of the efficient and rapid degradation of TC is the electron-giving nature of S^2-which accelerates the cycling of Co²⁺/Co³⁺on the catalyst surface.