Study On Fabrication And Modification Of TiO₂ Photocatalyst With Tunable Morphology

With the progress of society and the development of technology,environmental pollution and the energy crisis are becoming increasingly serious.In order to solve these problems,researchers have studied photocatalytic reactions and photocatalytic semiconductors inspired by photosynthesis in nature.Among different photocatalytic materials,titanium dioxide（Ti O₂）is considered to be the most promising photocatalyst due to its non-toxicity,environmental friendliness,low cost,stable physical and chemical properties and excellent catalytic oxidation ability.However,considering their drawbacks of unsatisfactory solar energy absorption and rapid electron-hole recombination efficiency,the photocatalytic activity of Ti O₂ material is very limited.In this paper,we try to provide new approaches for the development of high-efficiency Ti O₂ photocatalysts by altering morphology,doping non-metal elements and combining with a second substance.The relationship between formula,process conditions,morphology,structure and photocatalytic performance was discussed in detail.The efficiency and high-performance Ti O₂ photocatalyst provide new ideas and ways,and have social and economic significance for promoting the practical application of Ti O₂.Our work provides a new practical way for the preparation of Ti O₂photocatalyst and has a great significance on broadening the application of Ti O₂ materials.Firstly,a basic synthetic framework is set up,that is,titanium dioxide is prepared by one-step solvothermal route with Ti OSO₄ as titanium source and a mixed solution of deionized water and n-propanol as a solvent.The effects of hydrothermal temperature and hydrothermal time on the morphology and photocatalytic performance of Ti O₂ were studied.The results showed that the obtained Ti O₂ has a spherical shape with particle size of 1-2μm.When the reaction temperature was 90°C and the reaction time was 14 h,Ti O₂ achieves best performance.The photocatalytic degradation efficiency for rhodamine B（Rh B）was better than that of commercial P25 under visible light.This basic synthesis framework provided an ideal synthesis scheme for subsequent morphology control,element doping and composite modification.Secondly,by changing the content of Ti OSO₄ and the volume ratio of deionized water and n-propanol,the morphology control from solid microspheres to core-shell structure and from core-shell structure to rod-like structure was successfully achieved.Related synthesis mechanisms were explored:the morphologies,rod-like structure and core-shell structure are caused by in situ growth and Ostwald ripening,respectively.Among the obtained five different micro-morphologies,the rod-shaped and core-shell structure Ti O₂ had the best photocatalytic performance and the reaction rate constant of the photodegradation for Rh B reached 3.1 and 2.5 times,respectively,compared with P25.Therefore,Ti O₂ samples with these two morphologies were selected for subsequent nitrogen doping.Subsequently,urea as a N source was added to the Ti O₂ precursor solution.The resulting rod-like and yolk-like N-doped Ti O₂ hierarchical architectures were denoted as N-TR and N-TYS,respectively.A comparative study on morphological,structural and optical behavior of N-TR and N-TYS are conducted by SEM,TEM,BET,XPS,UV-Vis DRS,photoelectrochemical and photodegradation experiments.The resultant N-doped Ti O₂ with specific surface area of 190.8 m²g^-1 and 166.6 m²g^-1 for rod-like structure and yolk-like structure,respectively,exhibited excellent photocatalytic performance using Rhodamine B（Rh B）,Methylene blue（MB）and phenol as the degraded pollutants under visible light irradiation.And the photodegradation rate:N-TR>N-TYS>TR>TYS>P25,especially N-TR is12 times than P25 for the photodegradation of Rh B.Finally,N-TR was selected for composite modification.Through the reaction of N-TR and additive solution at room temperature,an a-MOTi@N-TR composite sample was successfully prepared.The effects of the concentration of additive and reaction time on morphology and performance of the samples were investigated.The results show that the sample with the additive concentration of 0.86 mol L^-1 and the reaction time of 30 min has the best performance,which degradation rate is 2.6 times than N-TR and 30.1 times than P25.In this study,a mild and efficient Ti O₂ synthesis system was established.The free regulation of Ti O₂ micromorphology can be realized via changing the process parameters.Through modification strategies of N-doped and introduction of co-catalyst,photocatalytic degradation performance has been greatly improved.Moreover,the synthesis mechanism and photocatalytic mechanism of doping and composite modification was also discussed.