Catalytic performance of CuO-kaolinite composite for norfloxacin degradation by activating peroxymonosulfate
Objective Due to the overuse of pharmaceutical antibiotics,residues have been frequently detected in different environmental matrices,including surface water,sewage,and soils.The presence of antibiotics in environment can cause potential adverse effects on human and ecological system due to their acute and chronic toxicity and the development of antibiotic resistance.How-ever,traditional wastewater purification technologies are ineffective in eliminating antibiotics.In recent years,the advanced oxi-dation process(AOP)based on sulfate radicals has been confirmed as the most suitable and efficient way to remove such pollut-ants from wastewater.The CuO-peroxymonosulfate(PMS)system,in particular,has gained considerable attention due to its strong oxidation ability.Nevertheless,the high surface energy of CuO often leads to aggregation during the synthesis process,reducing the amount of active sites and specific surface area.To address this problem,kaolinite was introduced as a support for CuO in this study,and changes in the structure and catalytic performance of the CuO-kaolinite catalyst were analyzed to achieve efficient degradation of organic pollutants in antibiotic wastewater.Methods In this paper,CuO-kaolinite composite was fabricated using a hydrothermal calcination method.Initially,1.0 g of sepiolite was mixed with 50 mL of distilled water and stirred for 0.5 h.Then,different amounts of Cu(NO3)2·3H2O were added to the solution and stirred for 10 min.Subsequently,an ammonia-water solution(v∶v=1∶1)was added drop-wise to adjust the pH value to 7.5～8 at room temperature.After stirring for 15 min,the mixture was transferred into a 100 mL Teflon-lined stainless-steel autoclave and heated at 150 ℃ for 5 h.The resulting products were washed,dried,ground,and then calcined in a muffle furnace at 250 ℃ for 3 h.Finally,after simple grinding,the CuO-kaolinite composite with different mass ratios of CuO and kaolinite was synthesized.The crystal structure,surface chemical state,microstructure,specific surface area,Results and discussion The effects of different mass ratios of CuO and kaolinite,catalyst dosages,PMS dosages,initial concen-tration of norfloxacin(NOR),initial pH of the solution,and coexisting anions on the degradation efficiency of NOR were investi-gated.The experimental results indicated that higher NOR degradation efficiency was achieved with the CuO-kaolinite-PMS sys-tem compared to other oxidation systems.Specifically,when the mass ratio of CuO and kaolinite was 40％,the CuO-kaolinite composite exhibited optimal catalytic performance.At a catalyst dosage of 1.5 g/L,a PMS dosage of 1.0 mmol/L,and an initial NOR concentration of 10 mg/L,the degradation efficiency of NOR after reacting for 60 min was about 76.21％.An increase in catalyst dosage initially led to a significant enhancement in NOR degradation efficiency,followed by a slight increase,while excessive PMS had an inhibitory effect.A higher initial concentration of NOR gradually decreased its degradation efficiency.Within a wide pH range,high NOR removal efficiency was achieved in the composite-PMS system,demonstrating its good prac-tical application potential.The coexisting Cl-,HCO3-,and H2PO4-in this system exhibited inhibitory effects on the NOR degra-dation,while NO3-had a relatively minor impact.In addition,the catalytic mechanism of the CuO-kaolinite composite for NOR degradation was systematically analyzed,revealing that the valence cycle between the Cu2+and Cu+in CuO-kaolinite composite was involved in the activation of PMS.The main active species in the reaction system were singlet oxygen(1O2),while superox-ide radicals(O2·-),sulfate radicals(SO4·-),and hydroxyl radicals(·OH)also contributed to the NOR degradation.Conclusion The introduction of kaolinite carriers allows for the formation of CuO nanosheets with smaller grain sizes,which are dispersed and deposited on the surface of kaolinite.The specific surface area and pore volume of the composite are greater than those of pure CuO.In CuO-kaolinite composite,CuO nanosheets are uniformly dispersed and deposited on the surface of kaolin-ite carriers,significantly reducing their self-aggregation and exposing more reactive sites,thereby enhancing the activation effi-ciency of PMS.As a result,more active species,such as 1O2,O2·-,SO4·-,and·OH,are continuously produced,which contrib-utes to the NOR degradation.In summary,this work provides a new approach for the structure design and preparation of mineral-based PMS catalysts with efficient catalytic performance and adsorption capacity,guiding their application in antibiotic wastewater treatment.
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