Synthesis Of TiO₂-based Composite Materials And Their Photocatalytic Performances

With the rapid development of human civilization,the sustainable development of human society has been seriously affected by energy shortage and environmental pollution.The photocatalytic degradation technology,which is driven by the clean solar energy,has been an effective way to solve these problems.Among the various photocatalytic materials,the semiconductor of Ti O₂,which has been commercially produced,is widely used as the classic"star"photocatalyst due to its stable chemical properties,easy preparation,low cost,non-toxic and environmental protection.However,powdered Ti O₂ suffers those disadvantages such as the wide band gap,high recombination rate of photogenerated electron hole pair,low quantum yield,and the easy agglomeration,which would result in the need of the only UV light irradiation and the reducing of active sites.To overcome the above shortcomings of Ti O₂ that really limit its practical application,in this paper,Ti O₂ based photocatalysts will be prepared by compounding Ti O₂ with conductive polyaniline or silver-based semiconductor,or by adjusting the morphology of Ti O₂,or by loading it on some suitable carrier materials.The purpose is to extend the scope of Ti O₂ light absorption,improve the photoelectron-hole separation efficiency,and also to solve the difficulties of powdered samples in the separation and the low cycle performance.The details are as follows:（1）Synthesis of CC/PANI/Ti O₂ composite material and its photocatalytic performance:Polyaniline was firstly grown on carbon cloth by in-situ polymerization.The final composite material of CC/PANI/Ti O₂ was then successfully synthesized via solvothermal method,during which the tetrabutyl titanate was hydrolyzed to form Ti O₂ nanosheets on the carbon cloth/polyaniline（CC/PANI）composite material.The synthesized photocatalysts were characterized using SEM,XRD,UV,Raman,FTIR,XPS and so on.With Rhodamine B（Rh B）as pollutant model,the photocatalytic degradation performance of CC/PANI/Ti O₂ composite under UV-visible irradiation was evaluated.The results showed that CC/PANI/Ti O₂ composite had better adsorption-photocatalytic degradation performance than Ti O₂.After UV-visible irradiation for 120 min,the degradation rate of Rh B was 96.5%,much higher than that of Ti O₂ without supported（80.5%）.Photoluminescence spectra,transient photocurrent response and EIS curves verified that the reasons for such enhanced photocatalytic activity were the accelerated mobility of photogenerated carriers and the lower recombination rate of photogenerated electrons and holes.The capture of active pieces experiments indicated that the free·OH radicals and·O₂^-radicals were the main active oxidizing species involved in the Rh B photoreaction process of CC/PANI/Ti O₂.CC/PANI/Ti O₂ composite has easy separation and good regeneration property,after six cycles of degradation of Rh B,its photocatalytic degradation rate is only reduced by about 13.69%.（2）Synthesis of CC/Ti O₂/Ag@Ag Cl composite material and its photocatalytic performance:Ti O₂ nanoparticles were first loaded onto the surface of CC to form CC/Ti O₂ composites via chemically coupled method,and then the Ag@Ag Cl was further grown on the surface of CC/Ti O₂ by in-situ deposition and the followed photogenic reduction method.The final photocatalysts of CC/Ti O₂/Ag@Ag Cl was characterized by SEM,XRD,UV,XPS and so on,and its performance of photocatalytic degradation over Rh B under UV-visible light irradiation was also evaluated.The experimental results showed that CC/Ti O₂/Ag@Ag Cl composites had better performance of adsorption-photocatalytic degradation than Ti O₂ and Ag@Ag Cl,the degradation rate of Rh B can reach 96.9%after the UV-visible irradiation for 120min,which is much higher than Ti O₂（83.8%）and Ag@Ag Cl（78.6%）.Photoluminescence spectra,transient photocurrent response and EIS curves verified that the reasons for such enhanced photocatalytic activity were more efficient photocarrier separation and transfer efficiency,beneficial to inhibit the electron-hole pair recombination.The capture of active pieces experiments indicated that the free·OH radicals and·O₂^-radicals were the main active oxidizing species involved in the Rh B photoreaction process of CC/Ti O₂/Ag@Ag Cl.CC/Ti O₂/Ag@Ag Cl composite material also has a simple separation process and good cycling stability.After 6 cycles of degradation of Rh B,its photocatalytic degradation rate is only reduced by about9.75%,and the comparison of SEM images before and after the cycles shows that there is no morphological change,which shows a good application prospect in the field of sewage treatment.（3）Preparation and photocatalytic performance of 2D Ti O₂/Ag₃PO₄heterojunction composite catalyst:Heterostructured 2D Ti O₂/Ag₃PO₄ photocatalyst was synthesized by in-situ growth of Ag₃PO₄ on the surface of two dimensional Ti O₂nanosheets（2D Ti O₂）prepared via solvothermal method.The synthesized 2D Ti O₂/Ag₃PO₄ photocatalyst was characterized by TEM,SEM,XRD,UV,FTIR,XPS,N₂ adsorption-desorption and so on.Still using Rh B as pollutant model,the photocatalytic degradation performance of 2D Ti O₂/Ag₃PO₄ under visible light irradiation was evaluated.The results indicated that the adsorption-photocatalytic degradation performance of the prepared 2D Ti O₂/Ag₃PO₄ was improved with the increase of Ag₃PO₄ content,and that a small amount of H₂O₂ can greatly improve the photocatalytic activity of 2D Ti O₂/Ag₃PO₄.Compared with 2D Ti O₂,2D Ti O₂/Ag₃PO₄ has better adsorption-visible light catalytic degradation activity due to the formation of heterojunction between 2D Ti O₂ and Ag₃PO₄,which can more effectively promote the separation of electron-hole pair,improve electron transfer efficiency,and inhibit the recombination of photogenerated carriers.Combined with electrochemical test,the 2D Ti O₂/Ag₃PO₄ composite has enhanced photoinduced carrier migration and separation efficiency.The capture of active pieces experiments indicated that the free·OH radicals and·O₂^-radicals were the main active oxidizing species involved in the Rh B photoreaction process of 2D Ti O₂/Ag₃PO₄,and the mechanism of photocatalytic degradation of Rh B by 2D Ti O₂/Ag₃PO₄ was proposed.（4）Synthesis of Ti O₂@Ag/Ag Br nanofibers and its photocatalytic performance:Ti O₂ nanofibers were first fabricated by an electrospinning technology and the photocatalyst of Ti O₂@Ag/Ag Br nanofibers was synthesized via an in-situ precipitation method followed by photo-assisted reduction.The synthesized Ti O₂@Ag/Ag Br photocatalyst was characterized by SEM,XRD,UV,XPS,PL and so on.Employed rhodamine B（Rh B）and Cr（VI）as pollutant models,the photocatalytic activities of the proposed Ti O₂@Ag/Ag Br nanofibers were investigated under UV-visible light irradiation.The results showed that Ti O₂@Ag/Ag Br had better photocatalytic degradation performance than Ti O₂ and Ag Br,and the catalytic degradation rate of Rh B solution was 98%within 10 min,significantly higher than Ti O₂（70%）and Ag Br（38%）.And the catalytic degradation rate of Cr（VI）within 40min was 94%,which was also higher than Ti O₂（72%）and Ag Br（61%）.The photocatalytic activity of Ti O₂@Ag/Ag Br was still high after five cycles of degradation of Rh B and Cr（VI）.The capture of active pieces experiments indicated that the free h⁺radicals and·O₂^-radicals were the main active oxidizing species involved in the Rh B and Cr（VI）photoreaction process of Ti O₂@Ag/Ag Br.Fluorescence and electrochemical test results showed that Ti O₂@Ag/Ag Br composite had the enhanced photoinduced carrier migration and separation efficiency.