Graphene oxide/TiO(2) composites were prepared by using TiCl(3) and graphene oxide as reactants. The concentration of graphene oxide in starting solution played an important role in photoelectronic and photocatalytic performance of graphene oxide/TiO(2) composites. Either a p-type or n-type semiconductor was formed by graphene oxide in graphene oxide/TiO(2) composites. These semiconductors could be excited by visible light with wavelengths longer than 510 nm and acted as sensitizer in graphene oxide/TiO(2) composites. Visible-light driven photocatalytic performance of graphene oxide/TiO(2) composites in degradation of methyl orange was also studied. Crystalline quality and chemical states of carbon elements from graphene oxide in graphene oxide/TiO(2) composites depended on the concentration of graphene oxide in the starting solution. This study shows a possible way to fabricate graphene oxide/semiconductor composites with different properties by using a tunable semiconductor conductivity type of graphene oxide.

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Co3O4/BiVO4 composite photocatalyst with a p-n heterojunction semiconductor structure has been synthesized by the impregnation method. The physical and photophysical properties of the composite photocatalyst have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transimission electron microscopy (TEM), BET surface area, and UV-visible diffuse reflectance spectra. Co is present as p-type Co3O4 and disperses on the surface of n-type BiVO4 to constitute a heterojunction composite. The photocatalyst exhibits enhanced photocatalytic activity for phenol degradation under visible light irradiation. The highest efficiency is observed when calcined at 300 degrees C with 0.8 wt % cobalt content. On the basis of the calculated energy band positions and PL spectra, the mechanism of enhanced photocatalytic activity has been discussed.

The visible light induced photoelectrochemical properties of the pressed powder electrodes n-BiVO 4 , p-Co 3 O 4 , and n-BiVO 4 /p-Co 3 O 4 containing 0.8 wt % cobalt were investigated. At pH 7 flatband potentials of -0.30 and +0.54 V vs NHE were measured for the bismuth vanadate and cobalt oxide, respectively, whereas -0.31 V was obtained for BiVO 4 /Co 3 O 4 . At a bias of 0.1 V vs Ag/AgCl the n-type photocurrent of BiVO 4 changes to p-type upon prolonged irradiation, whereas it remains n-type at the much higher bias of 1.0 V vs Ag/AgCl. The change in conductivity type can be rationalized by invoking oxidation of water to a surface peroxide species. From the photocurrent decay of BiVO 4 under chopped irradiation the presence of efficient charge recombination is indicated. It can be suppressed by addition of iodide, thiocyanate, or methanol, leading to about twice as large incident-photon-to-current efficiencies (IPCE). Different from that, in the case of the BiVO 4 /Co 3 O 4 electrode the IPCE values do not change in the presence of iodide or thiocyanate and are 4 times higher. This distinct difference is rationalized by the assumption that the photogenerated charges are efficiently separated at the BiVO 4 -Co 3 O 4 interface forming a type of n-/p-junction. Whereas electrons migrate to the n-type component, holes move to the p-type material. In summary, modification of n-BiVO 4 by p-Co 3 O 4 stabilizes the photocurrent, increases the efficiency of its generation, and leads to a compartmentalization of interfacial reduction and oxidation at the n-type component and p-type component, respectively.