Titanium dioxide (TiO2) is one of the most used photocatalysts, but it has some limitations, such as its low surface area and high electron-hole recombination rate. These limitations can be resolved by the coupling of a metal-organic framework (MOF). In contrast to monofunctional photocatalysts, MOF-based composites can yield improved molecule selectivity and visible light activity. MIL-101(Cr) was chosen as the MOF component due to ease of modifications to its framework and its enhanced CO2 uptake capacity. In this work, two different strategies to mediate MOF growth onto the surface of TiO2 are being investigated and will be presented. Following a direct interface approach, core-shell particles were obtained by a hydrothermal synthesis composed of MOF starting materials and anatase TiO2, in which a MOF shell grew directly in contact with the semiconductor. The effect of the concentration of TiO2 on the formation of core-shell particles was investigated. As the concentration of TiO2 increased from 20% to 60% compared to a fixed concentration of MIL-101(Cr) starting materials, more MOF@TiO2 particles with flower-like morphology were seen throughout the sample. Moreover, the second strategy investigated followed an indirect approach, which consisted of growing MOF particles on carboxylate terminated TiO2 by applying a step-by-step self-assembly process. Here, metal ions were coordinated to the carboxylate terminated TiO2 followed by addition of the organic ligand. Further investigations will be conducted by using hollow TiO2 and amine modified MIL-101(Cr), which has been a successful material to mitigate the photocatalyst limitations and enhancement of CO2 binding sites on MIL-101(Cr), respectively. As a result of the MOF-based materials design that combines the properties of MOF and TiO2, this work provides the means for improving photocatalytic CO2 conversion.

Preparation of MOF@TiO2 via self-assembly approach

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