Effective CO2 Capture and Selective Photocatalytic Conversion into CH3OH by Hierarchical Nanostructured GO-TiO2-Ag2O and GO-TiO2-Ag2O-Arg.

Abstract

The attenuation of greenhouse gases, especially CO2, as one of the main causes of global warming and their conversion into valuable materials are among the challenges that must be met in the 21st century. For this purpose, hierarchical ternary and quaternary hybrid photocatalysts based on graphene oxide, TiO2, Ag2O, and arginine have been developed for combined CO2 capture and photocatalytic reductive conversion to methanol under visible and UV light irradiation. The material's band gap energy was estimated from the diffuse reflectance spectroscopy (DRS) Tauc analysis algorithm. Structural and morphological properties of the synthesized photocatalysts were studied using various analytical techniques such as Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The calculated band gaps for GO-TiO2-Ag2O and GO-TiO2-Ag2O-Arg were 3.18 and 2.62 eV, respectively. This reduction in the band gap showed that GO-TiO2-Ag2O-Arg has a significant visible light photocatalytic ability. The investigation of CO2 capture for the designed catalyst showed that GO-TiO2-Ag2O-Arg and GO-TiO2-Ag2O have high CO2 absorption capacities (1250 and 1185 mmol g-1, respectively, at 10 bar and 273 K under visible light irradiation). The amounts of methanol produced by GO-TiO2-Ag2O and GO-TiO2-Ag2O-Arg were 8.154 and 5.1 μmol·gcat1·h-1 respectively. The main advantages of this study are the high efficiencies and selectivity of catalysts toward methanol formation. The reaction mechanism to understand the role of hybrid photocatalysts for CO2 conversion is deliberated. In addition, these catalysts remain stable during the photocatalytic process and can be used repeatedly, proving to be enlightening for environmental research.