Preparation Of Modified Titanium Dioxide And Study On Photocatalytic Degradation Of Dyes

Nowadays,water pollution is becoming more and more serious.Dye wastewater in particular,is a kind of wastewater that will cause severe pollution and is difficult to treat due to its characteristics including high chromaticity,high chemical oxygen demand,toxicity,and hard-to-achieve biodegradation.However,the approach of Photocatalytic Oxidation has attracted great attentions of scholars from all over the world due to its mild reaction conditions and low secondary pollution.As for titanium dioxide?TiO₂?,though it is deemed as a promising photocatalyst because of its advantages like low price,high catalytic activity,corrosion resistance,stable chemical properties,and non-toxic properties,it is restricted in practical use due to the narrow band gap and high photocarrier recombination rate.Therefore,the research on expanding TiO₂ response range to visual lights and inhibiting recombination of electron-hole pairs by means of modification,has become the hotspot of TiO₂ photocatalysis study.In this paper,the hydrothermal method was applied to prepare TiO₂,the orthogonal test was designed and the range analysis method was adopted to optimize the process conditions;then,proper doping proportion of iron and nitrogen was determined as well to study the dye degradation under ultraviolet and visible light conditions.Finally,the TiO₂ was characterized,and the dynamic analysis was carried out on the test results,aiming to offer certain theoretical basis and technological support to the study of TiO₂ modification and dye photocatalysis degradation.In the orthogonal test,four influencing factors were selected,including:hydrothermal reaction temperature,time,ratio of tetra-n-butyl titanate to water volume,and pH value of precursor solution.Meanwhile,the methyl orange solution was taken as the target degradant to study the photocatalysis performance of the catalyst.And the range analysis method was applied to optimize the process conditions.The results showed that the pH value of the precursor solution influenced the TiO₂ photocatalytic activity the most.The degradation rate of methyl orange solution was subject to the applied amount of TiO₂ and the initial concentration of the solution.Too high or too low concentration was both not conductive to photocatalytic reaction.As for 5mg/L methyl orange solution,the optimal TiO₂ dosage should be 3.75 g/L.For the TiO₂ prepared by the optimized process,the degradation rate of its methyl orange solution under the irradiation of halogen lamp was quite low,and the degradation rate under the irradiation of ultraviolet light for 2h turned out to be 86.48%.The doping modification carried out on TiO₂ which was prepared by taking iron nitrate as the iron source and urea as the nitrogen source,could help to improve the TiO₂ photocatalytic activity.TiO₂ photocatalyst of different proportions of iron doping and iron-nitrogen doping were prepared in this study,among which,TiO₂ photocatalyst with 0.01% iron doping,and 0.01% and 0.7%iron-nitrogen doping showed the greatest TiO₂ photocatalytic activity.Being placed in ultraviolet light conditions for 2h,the degradation rate of methyl orange solution reached 96.05%.And under the visible light conditions for 6h,the degradation rate of methyl orange solution increased from 19.36% to 94.52%.According to the analysis results for XRD,SEM,XPS,and UV-vis,the prepared TiO₂ sample was presented in anatase nano-scale irregular spherical particles.The doping did not change the crystal form of TiO₂,but the iron doping inhibited the growth of TiO₂ particle size while the nitrogen doping having little impact on the particle size of TiO₂.Then for the TiO₂ prepared with iron-nitrogen doping showed better particle dispersibility and red shift of absorption spectrum.Fe³⁺replaced part of Ti⁴⁺ to combine with oxygen.After nitrogen doping,TiO₂ entered the crystal lattice and replaced O inside the lattice,thereby forming the O-Ti-N bonds.The doping could help to reduce the recombination rate of photoelectron and holes effectively.Results of degradation tests carried out on other dyes showed that the photocatalytic reaction of TiO₂ had good degradation effects on neutral red and crystal violet,reaching 93.47%and 99.11%respectively;but seemed not so effective in degrading Safranine T and bromophenol blue,reaching 78.45% and 73.73%respectively;and showed bad degradation effect on Methylene blue,which was only 52.17%.The kinetic equation of TiO₂ photocatalytic reaction was in line with the L-H model.And the methyl orange degradation process by photocatalysis was a first-order reaction.The size of k,which was the kinetic constant of the first-order reaction,was subject to the initial concentration of the methyl orange solution,the amount of added catalyst,and the element doping.The kinetic analysis results were consistent with the conclusions of photocatalytic reaction experiment.