Preparation Of TiO₂/Graphene Composites And Their Photocatalytic Properties

Nowadays, the environmental pollution does affect people’s lives. Among the numerous environment management techniques, the photocatalytic technique has a great potential in the widespread applications because of its high efficient and non-toxic advantages. It is very important to synthesize the photocatalysts with high catalytic activity and stability. In this dissertation, we study the design and synthesis of titanium dioxide（TiO₂） based photocatalysts, such as TiO₂ microspheres, Ti O₂/graphene composites, and TiO₂/graphene aerogels using the hydrothermal and solvothermal methods, together with thermal treatment. The morphologies and structures of the prepared photocatalysts were characterized, and the effects of experimental conditions on morphologies and structures were demonstrated. The photocatalytic performances of resultant materials were characterized using degradation efficiency of materials toward methylene blue（MB）, and the relationship between structure and photocatalytic activity was also discussed. The main content and conclusions are summarized as follows:（1） The flower-like TiO₂ microspheres were synthesized by solvothermal method without adding of any chelating agent and surfactant. The results showed that the prepared TiO₂ microspheres have a typical flower-like morphology constructed with TiO₂ nanosheets and anatase crystal structure. The particle size is about 2 μm. The TiO₂ microspheres showed the highest photocatalyst activity under the experimental condition of solvothermal reaction of 6 h at 180℃ and calcining for 2 h at 500℃. The 81.6% MB can be degraded within 30 min by such photocatalyst.（2） On the basis of the above experiments, the graphene oxide was introduced into above experiments, and the TiO₂/graphene composites were obtained. By adjusting the amount of graphene oxide, TiO₂/graphene composites with different graphene contents were obtained. The results showed that the TiO₂ microspheres remained a typical flower-like structure and the graphene sheets successfully coved on the surface of the TiO₂ microspheres. The band gap of the TiO₂ in composites was reduced from 3.2 eV to 2.64 eV compared with that of pure TiO₂ microspheres. Besides, the recombination rate of photon-generated carrier was reduced and the special surface area increased from 49.6 m2/g to 95.3 m2/g. The photocatalytic performances of the composites were significantly enhanced using introducing of graphene. The photocatalytic degradation efficiency of MB was 98.9% within 30 min that was higher than that of P25 or TiO₂ microspheres. The photoreaction kinetics constant value was 3.22 times and 2.79 times as high as that of the P25 and TiO₂ microspheres, respectively.（3） The TiO₂/graphene aerogel was prepared by self-assembly process of graphene oxide and TiO₂ mixture using the hydrothermal method at low temperature. The results showed that the aerogel has a typical three-dimensional network structure. The TiO₂ particles were dispersed into graphene backbones. The TiO₂/graphene aerogels have a large specific surface area of 225 m2/g and high pore volume of 0.352 cm3/g. The aerogel presented an excellent degradation efficiency of MB with the synergy of adsorption and photocatalytic properties. The 95.5% MB can be degraded after 60 min adsorption and 30 min illumination. Furthermore, the TiO₂/graphene aerogel exhibited good cycle stability.