Synthesis Of Pt-graphene/TiO₂ Nanofilm Electrode And Its Photoelectrocatalytic Performance

Recently,Titanium dioxide （TiO₂）,as a kind of photocatalysts, which has high photocatalytic activity, low cost, easy to industrialization produce, stable performance and non-toxicity, has been widely attracted researchers’ attention. In this study, two kinds of visible-drivenPt/RGO/TiO₂ film electrodes were synthesized by electrochemical deposition and vacuum evaporation technology on the anodizing titanium substrate.Respectively the mixture solution of chloroplatinic acid,ammonium hydrogen phosphate,disodium hydrogen phosphate and water was used as electrolyte in the electrochemical deposition.In the vacuum evaporation process, the electric current was kept at 0.5 A/S, while adjusted the time of evaporation.The morphology structure, crystal structure and optical absorption characteristics of Pt/RGO/TiO₂ film electrode were investigated by SEM,XRD, UV-vis-NIR, XPS, Raman and other analysis methods. Moreover, the photoelectrocatalytic activity was evaluated by the degradation of methyl orange （MO）. And the influence of different microstructure on macro photoelectric catalytic activity was researched.On this basis,the factors that influenced the photoelectriccatalytic activity were investigated,and the mechanism for excellent photoelectricatalytic degradation of MO was analyzed. This research has obtained the following results:（1） The controllable preparation of RGO/TiO₂ films was obtained by optimizing the preparation conditions, such as anodic oxidation voltage, oxidation time, electrode distance and the annealing condition.The optimal preparation condition was obtained:electrolyte composed of a certain amount of graphene and 50ml of 100mg/L Mg（NO₃）₂·6H₂O,the anodic oxidation voltage of 40V, oxidation time for 2min, and calcined at 450℃ for 2h.The controllable preparation of Pt/RGO/TiO₂ films was obtained by optimizing the preparation conditions, such as electrochemical deposition voltage, oxidation time, electrode distance and the hydrogen reduction condition.The optimal preparation condition was obtained:electrolyte composed of Mchloroplatmic acid:Mdiammomum hydrogen phosphate:Mdisodium hydrogen phosphate=1:10:30,the electrochemical deposition voltage of 30V, oxidation time for 90min, H₂:N₂=1:3,and hydrogen reduction at 550℃ for 2h.（2） The SEM images indicated thatcataphracted cataphractus-like structures of GO/TiO₂, grew on the surface after anodizing, and platinum clusters irregular deposition on the surface of GO/TiO₂.The XRD results showed that Pt/RGO/TiO₂ has a mixed crystal structure of anatase and rutile, and the ratio of anatase and rutile changed with the different calcination temperature.The sample calcinated at 450℃ for 2hours possessed of 32.3% of anatase phase.The XPS results showed that Pt/RGO/TiO₂ thin film electrode consisted of Ti,O,C,and Pt four elements.C element was derived from the graphene;The mass fraction of Pt was 11.2% and it exists in three states. Pt0 as maximum, which had 7.0%. That because parts of PtO and PtO2 turned into Pt0 after high temperature hydrogen reduction.The Raman results showed that GOwas decreased in the composite material,but RGO was increased,after deposition of Pt on the surface of RGO/TiO₂ thin film.UV-vis-NIR results showed that the Pt/RGO/TiO₂ film electrode had a wide absorption from ultraviolet to near-infrared light （200-2500nm）, and the bandgap calculation displayed that two impurity energy levels existed in the forbidden band of TiO₂, one was introduced by graphene, the other one was introduced by Pt loading.Especially,the film showed excellent optical absorption capacityand photocurrent density after deposition ofPt, which greatly reduced the time of photoelectrocatalytic.（3） The vacuum evaporation method need less platinum content （6.2%） than electrochemical deposition method, and the thin film electrode does not contain Pt（Ⅱ）and Pt（Ⅳ）. Under the same conditionof photoelectrocatalytic degredation of MO, the samples prepared by the vacuum evaporation method need less time than that of electrochemical deposition method.（4） The photoelectrocatalytic activity of Pt/RGO/TiO₂ film electrode was evaluated by photoelectrocatalytic degradation of MO under fluorescent lamp.The results indicated that the sample showed excellent photoelectrocatalytic activity, the MO degradation rate can reach up to 95% only 10 min under fluorescent lamp.The main factors in the photoelectrocatalytic process, such as bias, the initial pH of solution, light intensity and so on, had a great influence on the degradation efficiency of MO.What’s more, Pt/RGO/TiO₂ film electrode exhibited a good stability and efficiency. It remained high photoelectrocatalytic activity after repeating 10 times and the photoelectrocatalytic activity of the electrode had no decay.