Split second: The photocatalytic activity of gallium oxide (β-Ga₂O₃) depends strongly on the co-catalysts CuO_x and chromia, which can be efficiently deposited in a stepwise manner by photoreduction of Cu²⁺ and CrO₄^2-. The water-splitting activity can be tuned by varying the Cu loading in the range 0.025–1.5 wt %, whereas the Cr loading is not affecting the rate as long as small amounts (such as 0.05 wt %) are present. Chromia is identified as highly efficient co-catalyst in the presence of CuO_x: it is essential for the oxidation of water

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Titania exhibits unique photo-physical and -chemical properties and can be used for potential applications in the field of photocatalysis. The control of TiO2 in terms of phase, shape, morphology, and especially nano-scale synthesis of TiO2 particles still remains a challenge. Ti-containing metal-organic frameworks (MOFs), such as MIL-125, can be used as sacrificial precursors to obtain TiO2 materials with diverse phase compositions, morphologies, sizes and surface areas. MIL-125 is composed of Ti/O clusters as the secondary building units (SBUs) bridged by 1,4-benzene-dicarboxylate (bdc). In this study, pre-formed and surfactant stabilized gold nanoparticles (GNPs) were deposited onto the surface of amino functionalized NH2-MIL-125 during solvothermal synthesis. Targeted gold/titania nano composites, GNP/TiO2, were fabricated through the pyrolysis of GNP/NH2-MIL-125 nanocrystals. The modification of TiO2 with GNPs significantly increased the photocatalytic activity of the MOF derived TiO2 material for the reduction of CO2 to CH4 as compared to TiO2 reference samples such as P-25 and Aurolite (Au/TiO2). The new materials GNP/TiO2 and TiO2 derived by the MOF precursor route were thoroughly characterized by PXRD, FTIR and RAMAN, TEM and N2 adsorption studies.

Using a high-purity gas phase photoreactor and highly sensitive trace gas analysis, new insights into the mechanism of photocatalytic CO2 reduction on TiO2 P25 have been obtained. The reactor design and sample pretreatment excludes product formation from intermediates. Apart from CO2, the only other reactant offered to the catalyst is water. The main products found on this prominent photocatalyst are methane and carbon monoxide. To distinguish between the three possible mechanisms reported in previous studies, likely intermediates of the reaction were added to the TiO2 photocatalyst and their reactivity was followed by gas chromatographic analysis. Based on the results, we can clearly rule out CO as intermediate of any photocatalytic reaction pathway on TiO2, because CO was not converted at all within a course of six hours. An improvement of carbonate formation on TiO2 brought about by surface-doping with sodium decreased product yields, so carbonates are unlikely intermediates as well. Methanol, formaldehyde and formic acid were exclusively oxidized back to CO2. We thus support a mechanism running over C2-intermediates, and we tested our hypothesis by reacting glyoxal, glyoxylic acid, acetic acid and acetaldehyde on TiO2. The reactions of acetaldehyde and acetic acid led to product distributions very similar to those obtained from CO2 under the standard reaction conditions, strongly supporting the C2 mechanism. This mechanism can also explain the small amounts of ethane usually found in the product mixture.

Mesoporous silica (SBA-15) loaded with TiO x species was synthesized by anhydrous grafting of titanium isopropoxide, and a novel procedure for the preparation of ZnO x /SBA-15 materials by grafting of Zn(acac) 2 was explored.The TiO x /SBA-15 and ZnO x /SBA-15 materials as well as subsequently prepared bifunctional ZnO x -and TiO x -containing SBA-15 materials were characterized in depth by combining N 2 physisorption measurements, UV−vis, X-ray photoelectron and Xray absorption spectroscopy, and CO 2 and NH 3 temperatureprogrammed desorption experiments. The characterization results confirmed a close proximity of ZnO x and TiO x in the subsequently grafted materials. Because of strong interactions between the Zn precursor and the SiO 2 surface, the order of the ZnO x and TiO x grafting steps affected the amount of Ti−O−Zn bonds formed in the materials. When ZnO x is present in SBA-15, subsequently grafted TiO x is higher coordinated and more Ti−O−Zn bonds are formed compared to SBA-15 in which TiO x was introduced first, indicating strong interactions between the Ti precursor and ZnO x . While all TiO x and ZnO x -containing samples exhibit a large amount of acidic sites, ZnO x present as isolated species or small clusters in SBA-15 significantly improves the CO 2 adsorption capacity by introducing basic sites. In the subsequently grafted samples the amount of acidic and basic sites is found to be unaffected by the order in which the two transition metals are introduced.