New evidence for the photocatalytic efficiency of natural raw vermiculites to produce hydrogen from aqueous methanol solution.

The potential of vermiculites as environmentally friendly photocatalysts for hydrogen production and pollutant degradation was demonstrated by a photocatalytic test in an aqueous 50 % methanol solution (MeOH50). After 4 h of irradiation with the commercial TiO2 Evonik P25 catalyst, the H2 yield was of 656.9 ± 4.2 μmol/gcat. For vermiculites Vm1, Vm3, and Vm4, hydrogen yields were comparable (H₂ = 420.6 ± 5.8 μmol/gcat; H₂ = 414.2 ± 1.8 μmol/gcat, and 449.3 ± 1.8 μmol/gcat, respectively) but were lower in the presence of vermiculite-chlorite intermediate Vm2 (H₂ = 385.1 ± 6.6 μmol/gcat). After the extended 24-h irradiation, hydrogen yield was promoted by the negative tetrahedral charge, while the positive octahedral charge inhibited the photocatalytic decomposition of the MeOH50 into hydrogen in favor of the formation of CO and CH4 byproducts. The decrease in methanol yield in the MeOH50 was effectively assessed by the red shift of the C-O and C-H bands in the Raman spectrum, corresponding to the photocatalytic production of H2.