| Efficient TiO2/solar photocatalysis is one of the most economical and safest methods to degrade organic pollutants.However,in the catalytic system,the crystal phase composition of TiO2 affects its structure and performance.Also,the broadband gap and high electron-hole(e--h+)recombination rate of TiO2 lead to the low catalytic efficiency of visible light,which greatly limit the practical application of TiO2.Therefore,in this paper,taking TiO2 modification and quality improvement method as the main research object,we explored the influence mechanism of different rutile/anatase components on the photodegradation of a variety of aromatic pollutants,and established a quantitative relationship model between pollutant degradation efficiency and rutile ratio(WR)under different environmental conditions.The photocatalytic degradation process of pollutants in solution was studied,the microkinetic mechanism of photocatalytic degradation of pollutants in solution was explored,and the idea of WR affecting the photoreaction pathway in solution was put forward.Furthermore,TiO2 with different crystal phases was used as the catalytic background to improve the catalytic performance of TiO2 by doping modification,and the influence of crystal on the catalytic active components was explored.Finally,the visible light catalytic performance of TiO2 was improved by modification and crystal surface control engineering.The main research contents and results are as follows:1.The structures of TiO2 with different crystalline phases are quite different,so how WR affects the degradation effect of pollutants and the microscopic photodegradation mechanism in the degradation process needs to be explored.We first experimentally determined the effects of TiO2 with different WR on typical aromatic pollutants(rhodamine B[RhB],bisphenol A[BPA]),4-chlorophenol[4-CP],carbamazepine[CBZ],tetracycline[TC]and dimethyl phthalate[DMP]),and then the LogNormal model between k and WR was established.The optimal WR of six typical aromatic pollutants were obtained,which were all within the narrow range of[0.347,0.384].The relationship model between the optimal WR and the chemical structure of pollutants was established.It was found that the molecular weight of pollutants and the number of C=O were negatively correlated with the optimal WR,while the number of benzene ring and C=C was positively correlated with the optimal WR.The linear model of two-factor interaction(2FI)between kinetic k value and photocatalytic performance parameters was established.Combined with Pareto analysis,we found that the interaction between the energy gap(Eg,B)and photoluminescence(PL,C)intensity(B-C)had a great influence on the photocatalytic reaction kinetics.This work can provide effective model support for the synthesis of other TiO2 composite semiconductor materials.2.On the basis of the above crystal phase model study,the photodegradation of tetracycline(TC)by TiO2 with different crystalline phases was further studied.The hypothesis that the total degradation process(kT)of pollutants in solution can be divided into dry degradation(in solid,ka)and wet degradation(in solution,kb)wasproposed,and the high initial concentration(>40 mg L-1)was suitable for step photodegradation study.The total reaction rate constant kT and wet reaction rate constant kb of TC degraded by different WR were calculated by photodegradation and quenching experiments,and then the dry reaction rate constant ka was determined by dry photocatalytic degradation experiments.The relationship equations of kT=aka+bkb+c(c as the correction constant,represents the influence of other factors on kT)were obtained respectively,and the microscopic kinetic mechanism of TiO2 photocatalytic degradation of TC in solution was explored.Furthermore,the relationship model between kinetic fitting parameters and WR was constructed,and it was found that the coefficients a,b and correction constant c had good linearity with lnWR,indicating that lnWR showed a good consistency with the photocatalytic kinetic parameters,which verified that there was some inevitable relationship between the photocatalytic reaction mechanism of pollutants in aqueous solution and WR.This work can provide a basis for further elucidation of photocatalytic micro-reaction mechanism.3.The influence of TiO2 with different crystalline phases as catalytic background needs to be further explored.For example,TiO2 rutile phase helps to reduce metal oxides at low temperatures in appropriate proportions and form metal-metal oxide heterojunction structures,which may affect the catalytic performance of catalysts.Therefore,we first prepared TiO2(Ni-NiO/TiO2-Re450)catalyst by optimizing the composition of anatase and rutile crystal phase under the condition of 10%H2/Ar gas calcination.Under mild reaction conditions(1 MPa,140℃,6 h),the complete transformation of furfural(FFA)was achieved with 87.4%cyclopentanone(CPO)yield.The cyclic experiment showed that the conversion rate of FFA remained at 95.4%at the fifth reaction,indicating that Ni-NiO/TiO2-Re450 had high stability.A series of characterization,control experiments and DFT theoretical calculation proved that the synergistic effect of TiO2 crystal composition and Ni-NiO heterojunction structure were main reasons to improve the hydrogenation performance of the catalyst.This work may facilitate the practical application of mixed crystalline TiO2 as a mass transfer substrate for biomass-derived chemicals.4.For photocatalytic degradation of new organic pollutants,different crystal phase TiO2 needs to be further modified.Different from traditional quantum dots modified different crystal phase TiO2,biomass-based quantum dots with multifunctional groups were combined with TiO2 to degrade favipiravir(FAV),a novel COVID-19 drug.Firstly,we prepared blue algae biochar quantum dots CQDs(QAB)with high solid yield by ball milling oxidation method,and developed a simple method to load QAB onto TiO2 with different crystalline phases to obtain a novel TiO2 composite material(TiO2-700-QAB).In a peroxymonosulfate(PMS)photocatalytic system,TiO2-700-QAB with high visible light catalytic performance was prepared by adjusting rutile ratio and doping amount of QAB,and the visible light reaction rate k was about 10 times of TiO2-QAB.Compared with conventional carbon quantum Qc doping(TiO2-700-Qc),the k value of TiO2-700-QAB is about 16 times that of TiO2-700-Qc,which reflects the obvious advantages of QAB biomass derived quantum dots.The main activation mechanism of singlet oxygen(1O2)was confirmed by quenching experiments and spin capture techniques.Based on three-dimensional excited emission matrix(3D-EEM),high performance liquid chromatography-mass spectrometry(HPLC-MS)and DFT calculations,the potential degradation pathways of FAV were elucidated in detail.This work not only provided new ideas for TiO2 modification by biomass quantum dots,but also proposed the photoreactive degradation pathway of FAV for the first time,and expanded the research scope of emerging COVID-19 drug degradation.5.It is similar to the principle that the mixed crystal phase of rutile/anatase improves the catalytic performance of TiO2,crystal planes with different energy band locations can not only improve the band structure of TiO2,but also efficiently promote charge separation in the process of photoreaction.First,TiO2(001)was synthesized successfully through the crystal surface control project.Then,based on Px+and Fcharge compensation effect,an F and P dual ion co-doping method was proposed,which could significantly improve the visible light catalytic efficiency and cycling stability of TiO2(001).The degradation rate constant of methylene blue(MB)by the optimized FP3-TiO2(001)catalyst was 14 times more than that of TiO2(001).A series of photochemical characterization proved that the synergistic effect of F and P3 co-doping improved the visible light response and photogenic charge separation efficiency of TiO2(001).The cyclic experiments showed that the cyclic stability of FP3-TiO2(001)was excellent,and the efficient degradation effect could still be maintained after 15 cycles.The newly formed surface ≡TiⅣ-OOH and the constant transformation between its precipitation state([≡TiⅣ-OOH]*)may be important reasons why FP3-TiO2(001)had good cyclic stability.The environmental suitability of the catalyst had been tested by changing environmental conditions and using actual wastewater,and the results showed that FP3-TiO2(001)still exhibited excellent visible-light catalytic performance.This work paves the way for the preparation of TiO2 materials with high visible light performance by crystal surface engineering and non-metallic doping,which can be widely used in the field of environmental photocatalytic degradation. |
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