Light-driven transformation of biomass into chemicals using photocatalysts - Vistas and challenges.

Lignocellulosic biomass has become an important sustainable resource for fuels, chemicals and energy. It is an attractive source for alternative fuels and green chemicals because it is non-edible and widely available in the planet in huge volumes. The use of biomass as starting material to produce fuels and chemicals leads to closed carbon cycle and promotes circular economy. Although there are many thermo-chemical methods such as pyrolysis, liquefaction and gasification close at hand for processing lignocellulosic biomass and transforming the derived compounds into valuable chemicals and fuels, the photocatalytic method is more advantageous as it utilizes light and ambient conditions for reforming the said compounds. Appraisal of recent literature indicates a variety of photocatalytic systems involving different catalysts, reactors and conditions studied for this purpose. This article reviews the recent developments on the photocatalytic oxidation of biomass and its derivatives into value-added chemicals. The nature of the biomass and derived molecules, nature of the photocatalysts, efficiency of the photocatalysts in terms of conversion and selectivity, influence of reaction conditions and light sources, effect of additives and mechanistic pathways are discussed. Importance has been given also to discuss the complementary technologies that could be coupled with photocatalysis for better conversion of biomass and biomass-derived molecules to value-added chemicals. A summary of these aspects, conclusions and future prospects are given in the end.

Pt/TiO2 nanotube photocatalyst - Effect of synthesis methods on valance state of Pt and its influence on hydrogen production and dye degradation.

Direct conversion of solar energy into clean fuels is emerging as an efficient way for the future energy generation and solving environmental issues. Especially, photocatalytic splitting of water into H2 under solar light irradiation is one of the best techniques for clean energy production. Also, decomposition of organic pollutants using solar light is an urgent need to protect the environment. Hence, in the present study, we studied Pt-TiO2 nanotubes based composites for H2 generation and methyl orange dye degradation under solar light irradiation and compared the effect of deposition methods namely photo-deposition and chemical reduction methods. We have achieved the highest rate of H2 generation activity compared to other Pt-TiO2 based composite photocatalysts reported previously, and it is ≈173 mmol·h-1·g-1cat for both photo-deposited and chemically reduced Pt/TiO2 nanotubes. This is about 46.8 folds higher than the pristine TiO2 nanotubes at the same experimental conditions. The selected catalysts were tested for degradation of methyl orange dye, where the catalyst prepared by chemical reduction method showed improved activity (94% degradation in 30 min) compared to the one which is prepared by photo-deposition method (50.5% degradation in 30 min). XPS analysis revealed that the photo-deposited catalyst consist only metallic Pt°, while the chemical-reduction yielded Pt with multiple oxidation states, Pt°, Pt2+ and Pt4+.