| Energy shortage and environmental pollution are two major problems for the development of human society,especially for environmental pollution,such as water pollution.The existence and elimination of pharmaceuticals and personal care products（PCCP）have become a hot research spot in the field of environmental biology.Ciprofloxacin（CIP）,a kind of fluoroquinolone antibiotics used to treat bacterial infections,is difficult to be completely decomposed and metabolized in vivo.The detection concentration of CIP in water environment ranges from ng/L toμg/L,even to mg/L.The residual CIP even at the trace level in water can lead to microbial resistance,seriously threatens the ecological environment and human health.Therefore,the removal of trace CIP in water has practical significance for environmental protection.The photocatalytic oxidation technology is an effective and green method for degradation of organic pollutants.Different performance of the photocatalysts produces different treatment results.Among them,the new BiOX has attracted wide attention due to its unique layered structure and excellent optical properties.However,how to prepare and develop high-efficiency BiOX and how to apply it economically are still the main problems that needs to be solved now.However,the performance of the photocatalysts is largely affected by the preparation process.In this paper,BiOCl with ultra high degradation activity for CIP was prepared by hydrolysis process under low temperature.In order to further improve the catalytic performance,the diatomite as a carrier and carbon quantum dots（CQDs）were introduced in the preparation of BiOCl to form BiOCl/diatomite or CQDs/BiOCl/diatomite composite photocatalysts,and achieve the purpose of synergistic and rapid degradation of CIP under different light source conditions.At the same time,the relationship between the transformation of CIP molecular structure and its antibacterial activity during the degradation process was deeply studied by confirming the CIP decay pattern,identifying the existence state of the transformation intermediates and clarifying the antibacterial property of CIP treated solution to the microbial model Escherichia coli（E.coli）,which provide a reliable theoretical basis and important reference for the practical application of photocatalytic degradation technology.The main research contents are as follows:1.BiOCl nanospheres were synthesized by a facile hydrolysis method via adjusting the EG-H2O ratio under the assistance of ultrasound.BiOCl exhibited excellent degradation activity of 92.9%for CIP within 3 min simulated solar light irradiation.Based on trapping agent experiment,electron spin resonance（ESR）and electron paramagnetic resonance（EPR）,the degradation mechanism of CIP was proposed.The outstanding photocatalytic performance of BiOCl was ascribed to the exposed（001）surface of the nanosphere,large specific surface area,high adsorption properties,large amount of oxygen vacancies（OVs）and high separation ability of electron-hole pairs（e--h+）.However,the mineralization rate of CIP was only 30.8%after 1 h,indicating that some intermediates were relatively stable and difficult for elimination.The antibacterial performance of the CIP solution before and after photodegradation was evaluated using E.coli as the microorganism model.The results indicated that CIP intermediates had also certain antimicrobial potency,which could be negligible after 3 min irradiation.In order to explore the nature of the photocatalytic degradation reaction,the identification of intermediate products and their corresponding concentration evolution process were analyzed by using liquid chromatography-mass spectrometry（LC-MS）and ion chromatography（IC）from the microscopic point of view.The correlation was established between the toxicity of the intermediates and the molecular structure transformation of CIP.Finally,combined with the degradation activity experiment,the degradation pathways of CIP were proposed and the criterion of“effective degradation”was further given.2.A series of the BiOCl/diatomite composite photocatalysts were prepared with diatomite as a carrier for the CIP degradation.The results showed that the composites had high photocatalytic degradation performance with the diatomite content ranged from 0～70%under the same catalyst dosage（0.05 g/L）.Among them,BiOCl/20%D exhibited degradation rate of 96%within 3 min simulated solar light irradiation.The diatomite was not only a carrier,but also a dispersant.Moreover,the synergistic effect between diatomite and BiOCl could transfer e-better and improve the separation ability of photogenerated e--h+pairs.If the theoretically calculated value of BiOCl in the composite catalysts was the standard for degradation comparison,BiOCl/60%D had the most significant activity in these composites.The degradation rate of CIP could reach 94%under10 min illumination.At the same time,the antibacterial activity of degradation solution at different reaction time points over BiOCl/60%D was tested using E.coli as the model microorganism,it was found that the degradation solution at10 min could completely lose the antibacterial property and achieve the purpose of effective degradation.The degradation pathways and mechanism were proposed by trap experiments,ESR,EPR,LC-MS and IC.3.The initial pH of CIP solution has a great influence on its photocatalytic degradation.Therefore,the effects of pH on the CIP existence form,and photolysis,BiOCl adsorption-degradation and recycling performance,diatomite adsorption performance,BiOCl/diatomite adsorption-degradation and recycling performance were systematically investigated,meanwhile,the differences of degradation intermediates and pathways under different acid-base conditions were investigated by LC-MS.The results showed that there were five existing forms of CIP in the pH range of 3～11,and the maximum photolysis rate occurred near the CIP isoelectric point of pH=7.4.Diatomite had only adsorption effect on CIP,which gradually increased with the initial pH increase of CIP solution,then decreased after pH>7.The adsorption of BiOCl and BiOCl/60%D for CIP was also affected by pH and showed a tendency to increase first and then decrease,and the turning point appeared at the pH=9.Both them had the same degradation trends in different pH value:under acidic conditions,the oxidation of piperazine ring was dominant reaction process but the defluorination of the quinolone ring was difficult to occur;under neutral conditions,the oxidation reaction of the piperazine ring and quinolone ring was the main process and defluorination of the intermediates easily occurred;Under alkaline conditions,the role of hydroxyl radicals（?OH）was significantly enhanced,but the overall degradation rate of CIP was less than that of neutral conditions,at the same time,BiOCl would undergo phase transformation.Finally,the optimal degradation effect of CIP was obtained when the initial pH of the solution was neutral.4.In order to broaden the response range of BiOCl/diatomite to visible light,the CQDs/BiOCl/diatomite composite photocatalysts were prepared by adding CQDs with up conversion function in BiOCl/diatomite and used for CIP photodegradation.The results showed that the photodegradation rate of CIP over3%CQDs/BiOCl/20%D reached 90%within 90 min visible light irradiation.Based on various modern spectroscopic characterizations,the high photocatalytic performance of 3%CQDs/BiOCl/20%D was attributable to the exposed（001）surface and moderate OVs of BiOCl,strong adsorption capacity,up conversion function and electron transfer ability of CQDs,dispersity of diatomite and synergistic effect among BiOCl,CQDs and diatomite.The antibacterial activity of the degraded CIP solution over 3%CQDs/BiOCl/20%D under visible light at different times was tested,the results showed the degradation solution at 80 min could completely lose the antibacterial property.The degradation pathways and mechanism were proposed by fluorescence experiment（PL）,capture agent experiment,ESR,EPR,LC-MS,IC,etc. |
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