Abstract
A series of composite materials based on titania and growing quantities of the (NH4)4[NiMo6O24H6]·5H2O heteropolyacid (NiMo6 HPA) was tested in the gas-phase toluene photo-oxidation reaction. Materials were characterized with the help of chemical analysis, X-ray diffraction, porosimetry, electron transmission and scanning microscopies, as well as X-ray photoelectron and UV–visible diffuse-reflectance spectroscopies. Photo-activity performance was assessed under UV and sunlight-type illumination conditions through the calculation of the true quantum efficiency to measure activity as well as the analysis of the selectivity of the reaction. The composite system having a 3 wt. % of the NiMo6 component presents improved performance with respect to well defined titania references (parent nanosized anatase or P25) under all illumination conditions tested. The characterization of the solids indicates that the NiMo6 component supported on titania suffers a significant modification of its physico-chemical properties as a function of the loading of the composite system. Such modification appears as a consequence of the interface interaction between the components of the composite system. An electron paramagnetic resonance study of the radical species formed under illumination shows that charge handling through the NiMo6 – TiO2 interface controls the photo-catalytic properties.
Highlights
Heterogeneous photocatalysis is a relatively well established technology based in the use of semiconductors and light to create charge carrier species able to transform chemical molecules [1,2]
To confirm the last point and considering that toluene photo-oxidation is a hole-driven mechanism [12,40,43], we studied the formation of hydroxyl radicals by the samples using electron paramagnetic resonance (EPR) with the help of a probing molecule, dimethyl-1-pyrroline N-oxide (DMPO), which selectively interacts with radical hydroxyl entities rendering an adduct product (DMPO-octahedron whose vertices are (OH))
In this work we synthesized NiMo6-TiO2 composite materials with different chemical composition defined by the loading of the minor NiMo6 component
Summary
Heterogeneous photocatalysis is a relatively well established technology based in the use of semiconductors and light to create charge carrier species able to transform chemical molecules [1,2]. The utilization of POMs together with titanium oxide appears as the most successful combination for their application in the photocatalytic field The usefulness of such composite materials is based in a number of potential interesting facts. As we will show here, the composite system joining NiMo6 with a high surface area anatase renders highly active systems under UV, visible, and sunlight-type illumination conditions in gas-phase toluene photo-oxidation. The improvement with respect to the titania references indicates the potential utility of such composite in a broad number of photo-catalytic reactions concerning organic molecules (pollutants or not) degradation and/or transformation processes This occurs under UV and under Sunlight-type illumination, indicating the suitability of the system for solar-assisted processes
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