Preparation Of Cu₂O/TiOF₂/TiO₂ Composite Photocatalyst And Its Photocatalytic Performance

Antibiotics wastewater has always been a hot and difficult point in the field of water environment,which is difficult to be completely degraded by the conventional municipal sewage treatment system.Tetracycline antibiotics are widely used in our country,and their wastewater has negative effects on human health and ecological environment.Photocatalytic technology has many advantages,such as economy and energy saving,non-toxic and harmless,no secondary pollution,and has the development advantages in removing antibiotic wastewater.TiOF2 is a new type of semiconductor material that can absorb sunlight,However,its development in the field of photocatalysis is limited due to its low utilization rate of visible light,low photocatalytic degradation efficiency and insufficient stability.Cu2O is widely used in the field of photocatalytic treatment of water pollution due to its outstanding characteristics such as narrow forbidden band gap,strong response to sunlight,good thermal stability,and low preparation cost.This thesis aimed to improve the photocatalytic activity of TiOF2,dope the Cu2O and TiOF2 with complementary advantages and disadvantages to form a Cu2O/TiOF2 heterostructure,and improve the photocatalytic activity and stability of TiOF2 under visible light.On the basis of Cu2O/TiOF2 composite photocatalyst,the conversion of TiOF2 to TiO2 was realized by changing the relative content of NaOH to form TiOF2/TiO2 heterostructure with higher activity.Finally,a series of Cu2O/TiOF2/TiO2 ternary composite photocatalysts were formed.The photocatalytic activity of Cu2O/TiOF2/TiO2 was further enhanced by improving the specific surface area and electron-hole pair recombination properties of the composite catalyst.In this thesis,the photocatalytic activity of Cu2O/TiOF2 and Cu2O/TiOF2/TiO2 in tetracycline antibiotic wastewater were investigated under simulated sunlight(500W xenon lamp).Firstly,XRD,FESEM,BET,FT-IR,UV-Vis DRS and PL techniques were used to systematically analyze the crystal morphology,surface morphology,elemental composition,specific surface area,surface functional groups,light absorption characteristics and electron-hole pair composition of the samples.Secondly,the effects of composite ratio of photocatalyst,dosage,pollutant type and initial concentration on photocatalytic performance were studied.Then the kinetics of degradation process and the stability of materials were explored.Finally,the degradation mechanism of the composite photocatalyst was preliminarily analyzed by free radical trapping experiment and liquid ultraviolet test.The main results are as follows:(1)A series of Cu2O/TiOF2 composite photocatalysts with different molar ratios(Cu2O:TiOF2=1:1、Cu2O:TiOF2=1:4、Cu2O:TiOF2=1:8)were synthesized by low temperature hydrothermal method using TiOF2 as precursor.When the initial concentration of antibiotic wastewater was 10 mg/L,the dosage of Cu2O/TiOF2 was 300 mg/L,and the simulated sunlight was irradiated for 2.5 hours,the degradation activity of Cu2O:TiOF2=1:4 was the highest.The removal rates of Cu2O:TiOF2=1:4 for pollutants was tetracycline hydrochloride(86.93%)>oxytetracycline(82.20%)>chlortetracycline hydrochloride(80.65%).Through the free radical capture experiment,it can be known that the order action of the active factor was:·O2->h+>·OH.Cu2O:TiOF2=1:4 can still maintain a removal rate of more than 80%after repeated use for five times.The degradation process of the Cu2O/TiOF2 composite photocatalyst to antibiotic wastewater conformed to the first-order kinetic model(L-H model).(2)During the formation of Cu2O/TiOF2 composite photocatalyst,the morphology of Cu2O changed from irregular cube structure to spherical structure.Compared with pure Cu2O(SBET=8.39 m2/g)and pure TiOF2(SBET=4.80 m2/g),the specific surface area of Cu2O:TiOF2=1:4(SBET=14.53 m2/g)was increased by 2 to 3 times.Compared with pure TiOF2,the forbidden band gap of Cu2O:TiOF2=1:4 decreased from 3.09 eV to 2.45 eV,and the absorption in the visible light region was significantly enhanced,and the absorption threshold showed varying degrees of red shift.The fluorescence intensity of Cu2O/TiOF2 composite catalyst had decreased.(3)A series of Cu2O/TiOF2/TiO2 composite photocatalysts with different material ratios(Cu:Ti=1:4,Cu:Ti=1:8,Cu:Ti=1:10)were synthesized by low-temperature hydrothermal method.When the dosage of Cu2O/TiOF2/TiO2 was 400 mg/L and the simulated sunlight was exposed for 2.5 hours,the removal rate of Cu:Ti=1:8 to 10 mg/L tetracycline hydrochloride was 96.86%,which was the highest removal rate than Cu2O/TiOF2 The rate(86.93%)was about 10%higher.Through the free radical capture experiment,it can be known that the action sequence of the active factor was:·O2->·OH>h+.Cu:Ti=1:8 can still maintain a removal rate of more than 80%after repeated use for five times.The degradation process of the Cu2O/TiOF2/TiO2 composite photocatalyst to antibiotic wastewater conformed to the first-order kinetic model(L-H model).(4)Compared with Cu2O/TiOF2,the morphology of Cu2O did not change during the formation of Cu2O/TiOF2/TiO2 composite photocatalyst,but the particle size was slightly smaller.The specific surface areas of Cu:Ti=1:4,Cu:Ti=1:8,and Cu:Ti=1:10 were respectively(26.87,42.31,34.42)m2/g,and the specific surface area of Cu:Ti=1:8 was the largest,which was nearly 3 times larger than Cu2O:TiOF2=1:4(SBET=14.53 m2/g).Compared with Cu2O:TiOF2=1:4,the band gap of Cu:Ti=1:8 decreased from 2.45 eV to 2.19 eV,and the absorption of visible light was slightly improved.The fluorescence intensity of Cu2O/TiOF2/TiO2 composite catalyst had decreased.