Preparation And Photocatalytic Properties Of Doped TiO₂/Reduced Graphene Oxide Composites

Since the unprecedented discovery of photocatalytic activity in early 1970 s, TiO2 has drawn much attention in catalytic field during the past few decades. Compared with other semiconductors, TiO2 has a number of potential advantages, like inexpensive cost, high chemical stability and environment friendly. Nevertheless the wide band gap and rapid recombination of the photoexcited electron-hole pairs result in the lack of visible light absorption(λ<380 nm) and the loss of practically 90% of the excited carriers, thus hindering its application greatly in the field of photocatalytic degradation. In addition, the absorbing capacity of TiO2 for organic pollutant is also crucial to the photocatalytic degradation process. In the appropriate range, better absorbing capacity can achieve superior photocatalytic reaction rate. Therefore, in order to overcome the two shortcomings we mentioned above as well as strengthen the absorbing capacity of TiO2 for organic pollutant, modifications of TiO2 were carried out in this thesis. The synthesis and characterizations of doped TiO2/reduced graphene oxide composites were mainly studied, and the photocatalytic degradation properties of the composites were evaluated by measuring the photodegradation of methylene blue et al. organic pollutants with irradiation of visible light. The specific research details are listed below:(1) Synthesis and photocatalytic properties of Ni-doped TiO2 nanoparticles/reduced graphene oxide composites. Firstly, Graphene Oxide(GO) was prepared by a modified Hummer’s method, in which natural graphite flakes were used as the raw material. Ni-doped TiO2 nanoparticles(Ni-TiO2NPs) were synthesized by the solvothermal method, in which tetrabutyl titanate and Ni(NO3)2·6H2O were used as the sources of Ti and Ni respectively. Then, Ni-TiO2NPs/reduced graphene oxide composites(Ni-TiO2NPs/RGO) were prepared using the hydrothermal reaction of GO and Ni-TiO2 NPs. The prepared catalysts were characterized by X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), Raman spectra(Raman), scanning electron microscope(SEM) and UV-vis diffuse reflectance spectroscopy(UV-vis DRS). The photocatalytic degradation performances of the catalysts were evaluated by measuring the photodegradation of methylene blue with irradiation of visible light. It turned out that, compared with TiO2 NPs, Ni-TiO2NPs/RGO showed much higher photocatalytic activity, the photocatalytic degradation rate in photodegrading of methylene blue was about 4.7 times higher than that of TiO2 NPs. Furthermore, the mechanism of the improved photocatalytic activity, which aroused from the collaborative effect of Ni doping and graphene incorporation, was also put forward in this thesis.(2) Synthesis and photocatalytic properties of Cr-doped TiO2 nanowires/reduced graphene oxide composites. Firstly, Cr-doped TiO2 nanowires/reduced graphene oxide composites(Cr-TiO2NWs/RGO) were successfully synthesized using a alkaline hydrothermal method followed by a calcination treatment, in which GO(the preparation method had been mentioned above) and commercial TiO2 nanoparticles(Degussa P25) were used as the precursors while Cr(NO3)3·9H2O was used as the Cr source. For comparison, TiO2 nanowires(TiO2NWs), Cr-doped TiO2 nanowires(Cr-TiO2NWs) and TiO2 nanowires/reduced graphene oxide composites(TiO2NWs/RGO) were also synthesized using the similar method. The synthesized catalysts were characterized by a variety of methods including XRD, Raman, FTIR, X-ray photoelectron spectroscopy(XPS), SEM, transmission electron microscope(TEM) and UV-vis DRS. The photocatalytic degradation properties of the samples were evaluated by measuring the photodegradation of methylene blue with irradiation of visible light. It turned out that, compared with TiO2 NWs, Cr-TiO2NWs/RGO showed much higher photocatalytic activity, the photocatalytic degradation rate in photodegrading of methylene blue was about 4.8 times higher than that of TiO2 NWs. Furthermore, the mechanism of the enhanced photocatalytic activity, which aroused from the synergistic effect of morphology modification, Cr doping and graphene incorporation, was also put forward in this thesis.(3) Synthesis and photocatalytic properties of Mo-doped TiO2 nanowires/reduced graphene oxide composites. Firstly, Mo-doped TiO2 nanowires/reduced graphene oxide composites(Mo-TiO2NWs/RGO) were successfully synthesized using a alkaline hydrothermal method followed by a calcination treatment, in which GO(the preparation method had been mentioned above) and commercial TiO2 nanoparticles(Degussa P25) were used as the precursors while(NH4)6Mo7O24·4H2O was used as the Mo source. For comparison, TiO2 NWs, Mo-doped TiO2 nanowires(Mo-TiO2NWs) and TiO2NWs/RGO were also synthesized using the similar method. The obtained samples were characterized by XRD, Raman, thermogravimetric analysis(TGA), FTIR, XPS, SEM, TEM and UV-vis DRS. The photocatalytic properties of the samples were evaluated by measuring the photodegradation of methylene blue and Rhodamine B under visible light irradiation. It turned out that, compared with TiO2 NWs, Mo-TiO2NWs/RGO-5 showed much higher photocatalytic activity, the photocatalytic degradation rate in photodegrading of methylene blue was about 5.5 times higher than that of TiO2 NWs. And Mo-TiO2NWs/RGO-5 showed excellent photocatalytic activity for Rhodamine B as well, the photodegradation efficiency could reach up to 96.8% in 120 min. Furthermore, the mechanism of the enhanced photocatalytic activity, which aroused from the collaborative effect of morphology modification, Mo doping and graphene incorporation, was also put forward in this thesis.