The Preparation Of WO₃/Graphene Composite Photocatalysts And Their Photocatalytic Activities

The development of new photocatalytic materials and their application have beenresearch hot in recent years. WO3possesses a narrower band gap of2.5~2.8eV,which provides the possibility of the effective utilization of the visible light accountingfor almost half of the solar radiation energy. Materials can be composited with WO3inorder to improve its photocatalytic activity. The hybridation of graphene make metalnanoparticles disperse well on the surface of the nano-materials and restrain theirreunion to get bigger specific surface area, higher reaction activity and selectivity.In this paper, the pure WO3, WO3/graphene and WO3-TiO2-RGO nanomaterialswere successfully prepared by hydrothermal method. The photocatalytic activitieswere evaluated by using rhodamine B as target degradation. The influence of synthesistemperature, preparation time, the amount of graphene and material ratio of sampleswere mainly inspected. The obtained specimens were characterized X-ray diffraction(XRD), X-ray energy spectrum (EDS), scanning electron microscope (SEM), UV-visdiffuse reflection spectrum (DRS) and transmission electron microscope (TEM),respectively. Researches have showed that:(1) The WO3photocatalyst series were prepared via hydrothermal method underthe facile condition. The crystal size, type and morphology of samples have beencharacterized by XRD, SEM, EDS, TEM and DRS methods. Results showed that thenano-WO3photocatalysts fabricated at160℃for48h has best morphology and thehighest degree of crystallinity. The (001) diffraction peak was the sharpest andstrongest, which had the greatest intensity in the best position of23.101°.The lightabsorption redshifts was the biggest with the band gap of2.67eV, and WO3nanosheetswas with a regular crystal morphology. Potocatalytic activities of samples were studied on the degradation of rhodamine B. The results showed that the degradation rate of theas-prepared samples reached60%after illumination for5h. First-principles densityfunctional theory (DFT) calculations were performed to study the band structure anddensity of states, which accounted for the experimental phenomena.(2) The series of flake WO3/graphene composite photocatalysts were prepared byultrasonic assisted hydrothermal method, using Na2WO4·2H2O and graphene oxide asrough material, and its photocatalytic performance was examined via the degradationof rhodamine B. The influence of synthesis temperature, preparation time and theamount of graphene material were mainly inspected. The studies found that thereaction conditions of WO3composited with graphene has reduced. The photocatalyticactivity of products synthesized at120℃for12h was best, and its degradation rate ofrhodamine B reached91%after illumination for1h. The crystallinity ofWO3/graphene composites is pretty high. Compared with the pure WO3, the lightabsorption of all the samples occurred redshifts and the band gap of the as-preparedproducts was the smallest (2.44eV).(3) The WO3-TiO2-RGO composite nanomaterials were fabricated by ultrasonicassisted hydrothermal method, using sodium tungstate, tetrabutyl titanate andhomemade graphene oxide as raw material. The best molar ratio was1:1, the bestresponse time was24h and to the optimum quality of graphene oxide was0.1g. Thecrystal form of tungsten trioxide and titanium dioxide was monoclinic crystal andanatase phase, respectively. All samples presented square of the lamellar structure. Theapplication of flake WO3-TiO2-RGO composites was explored via the adsorption ofrhodamine B, and the results showed that all samples presented very good adsorptionrate. Especially, the adsorption rate of rhodamine B of the as-prepared specimen hasreached more than95%in5min.