Preparation Of Immobilized Photocatalyst Coatings And Study On The Performance For The Degradation Of Organic Pollutants

Environmental pollution has become a worldwide issue that hinders the development of human civilization.How to effectively solve this problem and achieve the goal of sustainable development has become the primary task of researchers.In recent years,semiconductor photocatalysis technology has been considered as an effective and environmental-friendly method without secondary pollution.TiO2 has become a research hotspot in the field of photocatalysis due to low cost,low toxicity and excellent ultraviolet absorption ability.The powder-type semiconductor photocatalyst such as TiO2 shows excellent performance in removing pollutants under ultraviolet light irradiation.However,the organic-wastewater is discharged without filtration and recycling the photocatalyst,it will cause secondary pollution of the aquatic environment.Immobilized photocatalyst materials such as photocatalytic coatings supported on the surface of some hard materials(such as pumice,glass)can effectively solve the problem of filtering catalysts.In view of this,this article takes PDMS-SiO2 hybrid material as the photocatalyst recovery body,embeds the photocatalyst(TiO2,Cs@TiO2 and BiPO4)into PDMS-SiO2 hybrid to form a photocatalytic coating.And the photocatalytic coating is loaded on the surface of pumice stone and glass as the carrier to achieve continuous removal of organic pollutants,eliminating the step of filtering the catalyst.Different characterization methods were used to analyze the composition,crystal,morphology,thermal stability and hydrophobicity of the photocatalyst coating.At the same time,the influence of process parameters on the photocatalytic performance,the cycle catalytic stability of the photocatalytic coating,and the main active matters in the photocatalytic reaction process were also discussed.The main research contents of this article are as follows:(1)Using commercial TiO2(P25)as photocatalyst,a crack-free PDMS-SiO2-TiO2 photocatalytic coating was obtained by a sol-gel method.The PDMS-SiO2-TiO2 photocatalytic coating is supported on different supports(pumice stone,maifan stone and glass fiber).Compared with the maifan stone or glass fiber as carriers,the PDMS-SiO2-TiO2 photocatalytic coating loaded on pumice stone exhibited the best photocatalytic performance under ultraviolet light irradiation,and achieved the degradation rate of golden orange ?(AO7,20 mg/L)up to 98%in 12 h.In addition,after five cycles of UV photocatalytic processes(6 h each time),the removal efficiency of AO7 by PDMS-SiO2-TiO2 photocatalytic coating can still reach more than 90%.The photocatalytic performance of PDMS-SiO2-TiO2 photocatalytic coating toward actual wastewater was also investigated under ultraviolet light irradiation.The results showed that the COD removal rate of actual wastewater by PDMS-SiO2-TiO2 photocatalytic coating was 65%,which was 23%higher than the blank experiment.The contact angle test shows that the PDMS-SiO2-TiO2 photocatalytic coating has a high contact angle(101°),thereby has high hydrophobicity.(2)Chitosan-doped TiO2(Cs@TiO2)was prepared by a hydrothermal-calcination method.The photocatalytic performance of Cs@TiO2(which calcined at 200,300,400,500 and 600?)toward methylene blue(MB)was investigated under visible light irradiation.The results showed that Cs@TiO2 calcined at 300 ?(Cs@TiO2-300)had the best adsorption efficiency and photocatalytic degradation efficiency toward MB.Therefore,using Cs@TiO2-300 as the visible light photocatalyst of photocatalytic coating,a crack-free PDMS-SiO2-Cs@TiO2 photocatalytic coating was obtained by a sol-gel method.The photocatalytic coating was loaded on the surface of pumice stone,and the removal efficiency of MB by PDMS-SiO2-Cs@TiO2 photocatalytic coating under simulated sunlight irradiation was studied.The results show that the PDMS-SiO2-Cs@TiO2 photocatalytic coating has a higher removal efficiency of MB of 59%compared to the PDMS-SiO2-TiO2 coating(MB removal efficiency is 34%),which is attributed to the Cs@TiO2 composite which has an ability of absoring visible light.Through characterization techniques include DRS and XPS?we can found that the doped of chitosan reduces the band gap of the original TiO2 and increases the light absorption range.The photocatalytic cycle test and the contact angle test show that Cs@TiO2 is stably combined with the PDMS-SiO2 hybrid material to form a crack-free photocatalytic coating.(3)Using bismuth bromide oxide as the Bi source,a crack-free PDMS-SiO2-BiPO4 photocatalytic coating was prepared by a sol-gel assisted precipitation method.The PDMS-SiO2-BiPO4 photocatalytic coating was loaded on the surface of borosilicate glass.Under ultraviolet light irradiation,the effect of the mass ratio of BiPO4 on the degradation of MB by the PDMS-SiO2-BiPO4 photocatalytic coating was investigated.The data shows that when the mass ratio of BiPO4 is 18 wt%,PDMS-SiO2-BiPO4 photocatalytic coating has the highest degradation efficiency of MB compared with other mass ratios(9 wt%,12 wt%,27 wt%),and the corresponding first-order kinetic constant is 2.2 times that of PDMS-SiO2-TiO2 coating.ESEM-EDX and XRD characterization revealed that the monoclinic BiPO4 particles were deposited on the PDMS-SiO2-BiPO4 coating surface and wrapped with a layer of PDMS-SiO2 hybrid,which effectively prevented the shedding of BiPO4 particles.The addition of inorganic ions(NO3-,SO42-,Cl-,H2PO4-,HCO3-,Na+,Ca2+,Mg2+,NH4+and Al3+)has an inhibitory effect on the removal efficiency of MB by PDMS-SiO2-BiPO4,which is attributed to the-OH radical capture and competitive adsorption of additional ions.The photocatalysis experiment of radical scavenging shows that-OH and·O2-are the main radicals on the surface of PDMS-SiO2-BiPO4 photocatalytic coating under ultraviolet light irradiation.