Elaboration of interconnected mixed oxides nanotubes as photocatalytic materials

Details

Supervisors

Hermans, Sophie ; Demoustier-Champagne, Sophie

Faculty

Faculté des sciences

Degree label

Master [120] en sciences chimiques, à finalité approfondie

Abstract

The increasing discharge of wastewater containing polluting persistent organic molecules by industries is a real environmental disaster. To address this problem, research is being conducted on the catalytic degradation of persistent molecules. One approach involves using nanostructured photocatalysts that are active in the visible part of the solar spectrum, which is the most intense. Nanostructuring photocatalytic materials in a 3D network of interconnected nanotubes would enable pollutants to be degraded in a continuous flow. TiO2 is an abundant and inexpensive photocatalyst but, has the disadvantage of absorbing in the ultra-violet range, which represents only 5% of the solar spectrum. The formation of a mixed oxide SiO2-TiO2 could be one of the solutions for shifting absorption into the visible range. In addition to its intrinsic photocatalytic activity, thanks to nanostructuring into nanotubes, it can also serve as a support for complexes or nanoparticles that are also photoactive, and give synergistic effects. In this context, the aim of this work was to synthesise, in a controlled way, 3D networks of interconnected photocatalytic nanotubes composed of SiO2-TiO2 mixed oxide and to use them in continuous flow for the degradation of methylene blue, an organic pollutant that can be considered as a model-molecule. This study is part of the CaScadOS project; the ultimate aim of this project being to develop multifunctional nanostructured photocatalysts to carry out complex cascade reactions in continuous flow. Initially, the synthesis conditions for obtaining 1D TiO2 nanotubes in an alumina template by means of sol-gel impregnation were optimised for the use of polycarbonate templates. Thanks to the optimisation of these conditions, 1D TiO2 nanotubes with dimensions corresponding to the characteristics of the template used were obtained. By combining this TiO2 synthesis with the SiO2 synthesis developed earlier in the project, and by controlling the molar ratios engaged, various mixed oxides were obtained: SiO2:TiO2=10:90, 25:75, 50:50 and 75:25. Samples were analysed by XPS and ICP to verify if the Si and Ti content incorporated in the nanotubes was similar to the Si:Ti ratio in the precursor solutions. The effect of calcination on the crystalline or amorphous structure of the obtained oxides was also investigated. All these syntheses were transposed to obtain 3D networks of interconnected nanotubes. Finally, flow and batch photocatalytic tests for methylene blue degradation were carried out on 1D SiO2 nanotubes, TiO2 nanotubes and different compositions of mixed oxide nanotubes. Although the bandgaps measured by UV-vis spectroscopy did not shift, an improvement in photocatalytic activity was observed with an optimum for the mixed oxides with a SiO2:TiO2 composition between 75:25 and 50:50.