| In recent years,with the rapid development of human society,fossil fuels shortage and environmental pollution are gradually becoming the two major problems.The environment and human health are thr-eatened due to the increased levels of refractory organic pollutants such as Pharmaceutical and Personal Care Products(PPCPs),Endocrine Disrupting Chemicals(EDCs)and Volatile Organic Compounds(VOCs)in air and water.The grim situation of atmosphere and water environment puts forward higher requirements for environmental treatment technology.Recent studies show that photocatalysis has a promising prospect in the field of liquid and gas phase organic pollutant degradation.Among many types of photocatalysts,TiO2 is one of the most promising photocatalysts.Although nano-TiO2 photocatalytic oxidation technology has been applied to water pollutant treatment,volatile organic compounds treatment,antibacterial and bacteriostasis,hydrogen production,carbon dioxide reduction,nitrogen fixation and other fields at the research level,there are still some drawbacks in real industry including low solar energy utilization efficiency,low quantum efficiency,easy agglomeration,low surface area and adsorption ability,difficulty in separation and recycling,etc.As a natural layered mineral,kaolinite has many excellent properties,including good dispersion,catalysis promotion effect and easy recovery,which could reduce the secondary pollution and cost.Nano-TiO2 was successfully immobilized on the surface of kaolinite to prepare nano-TiO2/kaolinite composites for controlling air and water pollution.It can not only solve the problems of poor dispersion,high cost,low efficiency of photo-generated carriers and difficult recycling of nano-TiO2,but also solve the problem that kaolinite can only adsorb pollutants.To maximize the advantages of both materials,in this paper,nano TiO2/kaolinite composite photocatalytic materials were prepared by sol-gel method,and the impact of different influence factors was determined by orthogonal test.Afterwards,the influence of preparation process on the structure and photocatalytic activity of the composite and the structure-activity relationship within the composite were systematically studied.The effect of application conditions on the degradation of ciprofloxacin under ultraviolet light and its reusability were also investigated.Furthermore,the coupling mechanism of kaolinite adsorption and nano-TiO2 photocatalysis within the composite was revealed,and the optimized preparation technology of TiO2/kaolinite composite as well as the application basis of ciprofloxacin degradation was also obtained.On the basis of controllable preparation technology,structure-activity relationship and ultraviolet photocatalytic activity of nano-TiO2/kaolinite composites,the nano-TiO2/kaolinite composites were modified by acetic acid protonation,generation of oxygen vacancies induced by nitrogen atmosphere,and assembled with lamellar graphite-like carbon nitride in acid solution to form sandwich-like structure,controllable preparation of enhanced visible-light-driven composite photocatalysts were achieved.By characterizing the effects of three innovative modification methods on the crystal structure and composition,optical absorption properties,valence states and changes of elements,pore structure characteristics,micro-morphologies,electrochemical properties and visible light photocatalytic properties of the composites,the corresponding visible light photocatalytic enhancement mechanisms were proposed.And the relationship between the preparation process,material structure and photocatalytic activity of the modified nano-TiO2/kaolinite composites were also revealed.The visible light enhancement mechanism of acetic acid protonated TiO2/kaolinite composites is as follows:acetic acid modification reduces the grain size of TiO2 within the composites,increases the degree of lattice distortion,enlarges the overall specific surface area,reduces the average pore size and increases the degree of surface hydroxylation,all of them are beneficial for the transition and transfer of electrons,and promotes the overall photocatalytic performance.The degradation rate of ciprofloxacin(CIP)of CH3COOH protonated TiO2/kaolinite composites is higher than that of pure TiO2 or TiO2/kaolinite composites under ultraviolet and visible light.The pseudo-first-order kinetic constants are 1.57 and 3.82 times higher than that of TiO2/kaolinite composites under ultraviolet and visible light.respectively.The visible light enhancement mechanism of the modified TiO2/kaolinite composites under nitrogen atmosphere is as follows:carrier structure effect,reduction of band gap energy,formation of intermediate oxygen vacancy energy level,enhancement of light absorption capacity and enhancement of carrier separation and utilization efficiency.The reaction rate constants of nitrogen-treated TiO2/kaolinite composites were 7.00,2.54 and 3.13 times higher than those of air-treated TiO2 under ultraviolet,sunlight and visible light,respectively.In addition,compared with air-treated TiO2,the degradation rate of formaldehyde in the wide spectral range by the prepared composite material increased nearly two times.The visible light enhancement mechanism of graphite-like carbon nitride modified TiO2/kaolinite composites is as follows:the construction of sandwich-like structure(g-C3N4/TiO2/kaolinite)effectively promoted the reduction of band gap(band gap 2.72 eV),the decrease of TiO2 grain size(grain size 14.21 nm),the increase of specific surface area(specific surface area 51.596 m2/g),the enhancement of light absorption ability,and the improvement of separation and transmission efficiency of photogenerated carriers.The g-C3N4/TiO2/kaolinite composite exhibited strong photocatalytic activity and good reusability towards ciprofloxacin under visible light.Its apparent rate constants were 5.35,6.35 and 4.49 times than those of pure TiO2,g-C3N4 and P25,respectively.At the same time,the composites had high inactivation ability towards Staphylococcus aureus under visible light. |
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