Construction Of Heterogeneous Tin-Based Catalysts And Their Application In Efficient Activation Of PMS For The Removal Of Organic Pollutants In Water

BackgroundDrugs and personal care products（PPCPs）are a kind of emerging environmental pollutants with large production and use,complex chemical composition and biological activity.After use,they often enter the urban domestic sewage in the form of mother or active metabolites,which poses a great threat to the ecological environment and people’s health.In recent years,advanced oxidation technology based on transition metal oxide activated peroxymonosulfate（PMS）considered to be a powerful means to treat typical PPCPs in the environment.Among them,tin dioxide（SnO₂）has attracted extensive attention because of its wide source and good photoelectric and electrical conductivity,but there is still the problem of insufficient activation ability of PMS.Therefore,developing a PMS activator with good performance,low cost and low secondary pollution based on tin oxide has good application potential.ObjectiveBuild an efficient and stable binary tin-based composite photocatalyst activated PMS catalytic system,explore the degradation efficiency and degradation mechanism of the catalytic system for PPCPs pollutants,and provide new ideas for the development of efficient activated PMS catalytic system and its application in water PPCPs pollution control.MethodUsing tin tetrachloride as tin source and nitrogen doped carbon quantum dots(N-CDs/cobalt chloride/nickel chloride as exogenous doping,binary tin based composite catalysts（N-CDs/SnO₂,Co₃O₄/SnO₂,NiO/SnO₂,NiCo₂O₄/SnO₂）were prepared by one-step hydrothermal method.The micro morphology,crystal structure,element composition and photoelectric response of the composite catalyst were tested by various characterization methods.Taking typical PPCPs such as dye（Rhodamine B）,quinolone antibiotics（ofloxacin）,tetracycline antibiotics（tetracycline）and other antibiotics（metronidazole）as degradation objects,the catalytic degradation experiment of activated PMS was carried out under visible light.The light intensity,reaction temperature,PPCPs type and concentration,catalyst dosage,solution p H value and the effects of coexisting inorganic salts and other reaction conditions and external environmental factors on the degradation performance of the catalytic system are analyzed.The degradation reaction kinetics in the catalytic process is analyzed,the formation law of active species in the photocatalytic system and the acute toxicity changes of intermediate products are analyzed.Through multiple degradation cycle experiments,the leaching rate of metal ions in the catalyst and the changes of catalytic activity are analyzed,and the stability and reusability of the catalytic system are investigated.Result1.Compared with pure SnO₂（nano square box）,the photocatalytic degradation efficiency of Rh B in the activated PMS system with the best composite amounts of N-CDs/SnO₂-3%composite is 100%after 25 min visible photocatalytic reaction,indicating that the doping of N-CDs enhances the light absorption capacity of SnO₂,accelerates the electron transfer efficiency and improves the activation efficiency of PMS.2.Compared with pure SnO₂（solid sphere）,Co₃O₄/SnO₂composite nano materials show strong PMS activation performance and produce active species such as SO₄^·-,O₂^·-,OH^· and ~1O₂.The degradation efficiency of ofloxacin is 92.6%within 30 minutes,and the catalytic system is stable in the range of p H（5-11）.3.Flower like SnO₂and semiconductor NiO were combined to form heterojunction photocatalytic material.The degradation efficiency of activated PMS to tetracycline was up to 90%within 30 minutes under visible light.It was found that the toxicity of the intermediate was much less than that of tetracycline.4.NiCo₂O₄/SnO₂composite catalyst has regular spherical structure and shows excellent light response ability.Activated PMS can completely remove metronidazole within 30min under visible light irradiation,and the element leaching rates of Niand Co are very low.In the system,~1O₂was identified as the main reactive substance,while O₂^·-,OH^· and SO₄^·-played a secondary role.ConclusionIn this study,a photocatalytic oxidation PMS technology based on modified tin-based oxide semiconductors with different morphology and structure was established.Through the optimization of reaction conditions and the exploration of external environmental factors,a series of visible light catalysts N-CDs/SnO₂,Co₃O₄/SnO₂,NiO/SnO₂and NiCo₂O₄/SnO₂were prepared.The results show that,SnO₂based catalyst activated PMS system can achieve more than 90%degradation efficiency for a variety of typical PPCPs（such as dyes,antibiotics,etc.）within 30 minutes,and the toxicity of intermediate products is significantly reduced.It has a certain purification effect on different water quality in the actual environment,which confirms the application potential of the system in the field of photocatalysis and provides theoretical guidance and technical support for the practical application of typical PPCPs in the treatment environment.