Titania Cowrapped α-Sulfur Composite as a Visible Light Active Photocatalyst for Hydrogen Evolution Using in Situ Methanol from CO2 as a Sacrificial Agent

With an increase in global warming due to an increase in CO 2 emission, there have been immense efforts to convert CO 2 into either renewable fuels or useful chemicals. At the same time, because hydrogen is a clean energy source, there has been much interest in the hydrogen evolution reaction (HER). In this paper, we report a titania cowrapped α-sulfur composite material that under a light-emitting diode light source showed the highest level of hydrogen evolution reported for any elemental material. In situ methanol from CO 2 photoreduction conversion was used as a sacrificial agent for the hydrogen evolution reaction. The effect of in situ methanol on hydrogen production was around 165 times stronger than the effect of ex situ methanol as a sacrificial agent. A plausible mechanism was proposed to explain the higher level of hydrogen production with in situ methanol as a sacrificial agent. The S 8 –TiO 2 –Au photocatalysts were thoroughly characterized by powder X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflection spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and N 2 sorption studies. Photocatalytic products were analyzed using a gas analyzer (gas chromatograph with a thermal conductivity detector and a flame ionization detector). In situ, in operando FT-IR spectroscopy established the formation of formaldehyde and methanol as intermediate products. Density functional theory calculations showed the creation of additional density of states in the band gap of the photocatalyst, as well as a shift in the conduction band to the energy potential for hydrogen formation.