Photocatalytic conversion of CO2 and H2O is an interesting route to produce fuels and chemicals [1]; this process is also known as Artificial Photosynthesis (AP). In last years, extensive efforts have been made to develop efficient catalytic systems capable of harvesting light absorption and reducing CO2 especially when using water as the electron donor. Several modification pathways of inorganic semiconductors have been performed to improve the reaction efficiencies, including tailoring of the band structure, doping with metals and non-metallic elements and deposition of metal nanoparticles, etc [1-2].

Herein, we report different strategies and modifications of photocatalysts to increase process performance. Among them, an interesting approach to improve charge separation in photocatalytic systems is the use of heterojunctions. In this line, the combination of different semiconductors with noble metal nanoparticles or organic semiconducting polymers leads to a separation of the photogenerated charge carriers and thus to increasing their life time, facilitating charge transfer to adsorbed molecules.

The main products, using bare TiO2, were CO and H2, with low concentrations of CH4. The deposition of surface plasmon nanoparticles (SP-NPs) leads to changes in the selectivity to higher electron-demanding products, such as CH4. TAS measurements confirm that this behaviour is due to the electron scavenging ability of SP-NPs.

The H2 evolution rates of organo-inorganic hybrid materials, is increased with the polymer content reaching the optimum with IEP-1@T-10 which improves the activity of TiO2 by a factor of 40. These hybrid materials also show a dramatic reactivity improvement in CO2 photoreduction. Hybrid materials also show a great change in the selectivity, enhancing the relative production of methane vs. carbon monoxide, and largely promoting selectivity towards hydrogen. Meanwhile, bare TiO2 gives rise to the formation of CO, a small amount of CH4 and H2 and traces of CH3OH and higher hydrocarbons (C2 mainly). To explain this behaviour a combination of in-situ NAP-XPS, FTIR, TAS spectroscopies and theoretical tools has been used, showing a more efficient light absorption and charge transfer in the hybrid photocatalyst compared with bare materials.

References

[1] V. A. de la Peña O’Shea, D. P. Serrano, J. M. Coronado, “Current challenges of CO2 photocatalytic reduction over semiconductors using sunlight”, in Molecules to Materials—Pathway to Artificial Photosynthesis, Ed. E. Rozhkova, K. Ariga (Eds.), Springer, London, 2015.

[2] L. Collado, A. Reynal, J.M. Coronado, D.P. Serrano, J.R. Durrant, V.A. de la Peña O'Shea, Appl. Catal. B: Environ. 178, 177, 2015