| Two TiO2/graphene composites were synthesized using the graphene oxide and Ti(SO4)2 as the initial reactants by the different reaction routes. The first route: TiO2/graphene oxide composite was prepared by nucleation growth of nanometer TiO2 particles in the graphene oxide interlayer after Ti(SO4)2 hydrolysis. Then, TiO2/graphene composite (TiO2-GRl) was prepared through reduction reaction. The other route:graphene oxide was reduced to prepare graphene, in whose interlayer TiO2/graphene composite (TiO2-GR1) was prepared by nucleation growth of nano-TiO2 after Ti(SO4)2 hydrolysis. Chloroplatinic acid as the metal ion source, TiO2/graphene composite Pt doping (Pt-TiO2/GR1) was prepared through the first route.The composites were characterized by XRD, FE-SEM, HR-TEM, FTIR, UV-Vis, BET and the electrochemical measurements(CV, EIS). Under visible light irradiation(λ>420nm), using the composite as working electrode, platinum electrode as counter electrode, and saturated calomel electrode as reference electrode, the catalytic activity and reaction kinetics of the composite for the photocatalytic and photoelectrocatalytic decomposition of acid red B(ARB) which contains azo chemical health were studied. The influence of different reaction on the composites, the factors affected catalytic reaction, the stability of the composites, the mechanism of photoelectrocatalytic reaction was studied. Through experiment and theoretical analysis, the results showed that:(1) the different reaction had great influence on the morphological characteristics, crystal structure, specific surface area, electrochemical measurements of the composites. Crystal structure was high purity anatase type of TiO2-GRl composite which prepared by the first route. While, the crystal type structure was mixed crystal(anatase type and rutile type) of TiO2-GR2 composite which prepared by the second route. And its anatase type is the main type. And it showed that the visible light response ability, specific surface area, electrochemical measurements of TiO2-GRl was superior to TiO2-GR2.(2) the photocatalytic and photoelectrocatalytic experiment showed that:the catalytic performance of composite(TiO2-GR1、TiO2-GR2) was significantly superior to TiO2. It illustrated that the catalytic efficiency was improved by the coordination effect of graphene and TiO2. And it also demonstrated that the nature of the graphene of the excellent electrical properties and large specific surface area had played a positive role in photoelectric catalysis.(3) The catalytic performance of TiO2-GR1 was superior to TiO2-GR2 under the same reaction conditions. The reason may be that the crystal structure, visible light response ability, specific surface area, electrochemical measurements of TiO2-GR1 was superior to TiO2-GR2. It illustrated that the catalytic performance of the composites were greatly affected by different reaction routes.(4) The photoelectrocatalytic performance of composite (TiO2-GR1) was superior to its photo catalytic performance. It showed that:On the one hand, the applied electrode potential caused the light electron of TiO2 transfer to the graphene and directional movement happened. And graphene provided favorable conditions for the light electron to move quickly. On the other hand, excellent performance of electric double layer of composite materials, making the solution ion in plus under the action of electrode voltage to the electrode diffusion dynamics of setback was lesser, can more easily spread, moved to the electrode active substances, such as hydroxyl radicals in the reaction.(5) The active material of working electrode, initial concentration of target degradation content, electrode potential and initial reaction of pH had great influence on the catalytic properties of the composite. By the TiO2-GR1 composite as the research object, at room temperature(25℃), the optimization of conditions was:The active material of working electrode W=0.5 g, initial concentration of target degradation content C0=100 mg/L, electrode potential ξ= 0.05 V, initial reaction of pH= 5.0. Under the optimization of conditions and visible light irradiatiation(λ>420nm), the photoelectrocatalytic activity of composite was studied through the decomposition of ARB. It showed that the degradation efficiency was 1.08 mg·min-1·g-1 as within 30 min. And reaction 240 min could make the degradation efficiency of ARB reached 93.6%.(6) From using frequency, placement time and degradation of different target of three aspects such as object to study the stability of the composite catalytic properties. Experiments showed that the composite material has excellent catalytic stability.(7) COD digestion experiment showed that the composite (TiO2-GR1) for a variety of operations on the target degradation of organic pollutants degradation, the COD digestion reaction process was in good condition, and the degradation efficiency curve were identical with each other.(8) Composites (TiO2-GRl) of ARB degradation process of ultraviolet visible spectra analysis shows that degradation of target chromophore and aromatic structure was eventually degradation of organic matter for inorganic small molecule compounds.(9) photoelectrocatalytic reaction mechanism of the composites was discussed, and through the relation between the reaction processes were described.(10) The reaction kinetics of photocatalytic and photoelectrocatalytic reaction of composites (TiO2-GR1, TiO2-GR2) could be described by the Langmuir-Hinshelwood model. And all the reaction was conformed to the first order reaction kinetics, good linear relationship. Photocatalytic and photoelectrocatalytic reaction kinetics constants of composites were greater than the kinetic constants of TiO2, and Photocatalytic and photoelectrocatalytic reaction kinetics constants of TiO2-GR1 composite were greater than the kinetic constants of TiO2-GR2. Under the optimization of conditions, Photoelectrocatalytic reaction kinetics constants of TiO2-GR1 composite k=12.3×10-3 min-1, and its activation energy Ea=24.55 kJ/mol at 25℃.(11) Pt-TiO2-GRl Composite as a catalyst, in this experiment to optimize the conditions to investigate the photocatalytic and photoelectrocatalytic performance. It showed that 240 min of photocatalysis, photoelectrocatalysis can make the ARB decomposition rate reached 61.9%,97.3% respectively. Degradation efficiency is superior to the same condition of TiO2-GR1 composite materials. The reaction kinetics of photocatalytic and photoelectrocatalytic reaction of composites (Pt-TiO2-GR1) could be described by the Langmuir-Hinshelwood model. And all the reaction was conformed to the first order reaction kinetics, good linear relationship. Photocatalytic reaction kinetics constants of Pt-TiO2-GRl composite k=4.6×10-3 min-1, photoelectrocatalytic reaction kinetics constants of Pt-TiO2-GRl composite k= 13.8×10-3 min-1. And the kinetics constants is superior to the same condition of TiO2-GR1 composite materials.(12) Through PwPP method calculation of DFT total energy, it showed that after Pt doping TiO2 band gap (Eg) decreases, the forbidden band formed the impurity level, lower the Fermi level, enhance the catalytic activity. |
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