Aerobic oxidation of benzyl alcohols to benzaldehydes using monoclinic bismuth vanadate nanoparticles under visible light irradiation: Photocatalysis selectivity and inhibition

- Oxidation occurs selectively with high conversion using simple LED light source.
- The reaction is inhibited by the aldehyde product and benzoic acid byproduct.
- Surface effects dominate. Nanostructuring does not improve photophysical properties.

Monoclinic bismuth vanadate nanoparticles (nan-BiVO4) have been used for the selective photo-oxidation of benzyl alcohols (13 examples) to benzaldehydes under visible light irradiation using dioxygen as oxidant. Illumination with a blue LED (λmax = 470 nm) gave yields more than 30 times greater than bulk BiVO4 with >99% selectivity for several cases. Photo-oxidation of PhCH2OH/PhCD2OH isotopomers gave a kinetic isotope effect of 1.3 indicating that CH bond activation is not the rate determining step in contrast to other reported photocatalysts including TiO2 and carbon nitride. Collectively, structural characterisation, spectroscopic, and reactivity data are correlated with the greater surface area of nan-BiVO4 compared to bulk BiVO4. Furthermore, conversion is shown to be limited as reaction progresses. Control experiments indicate that photo-oxidation is retarded by product aldehyde and that trace amounts (<1%) of the corresponding benzoic acid, from over-oxidation, result in significant reduction in conversion.

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