Toward the understanding of surface phenomena involved in the photocatalytic performance of amorphous TiO2/SiO2 catalyst – A theoretical and experimental study

Abstract

In this contribution, the behavior of a photocatalytic CO2 reduction (PCO2R) employing an amorphous-TiO2 modified with silica (SiO2) supported on polyethylene terephthalate film-coated with indium tin oxide (AM-TiO2-SiO2/ITO-PET) catalyst was studied. The AM-TiO2-SiO2/ITO-PET synthesized via soft method exhibited a high performance toward the production of CH4, H2 and CO gases, a decrease of the gases production after being used once. This behavior was analyzed and explained from surface phenomenon approaches employing experimental and theoretical means XRD (experimental and theoretical), Raman, FTIR, PL, binding energies (Ebinding), DFT-Koopman descriptors and theoretical Gibbs free energy. The analysis proposes that surfaces with superficial SiO2 groups are more affine to some target molecules (T-M). This affinity promotes faster adsorption and reaction, but contributes to the obstruction in the mechanizing reaction. The formation of second-order links (Van der Waals and Hydrogen bonds) between affine T-M and catalytic surfaces will result in molecular blocking and will lead to catalyst deactivation. Finally, the production of CO on AM-TiO2-SiO2/ITO-PET is kinetically favorable due to the disorder on the AM-TiO2 surface. This specific chemical photoreduction pathway, promoted by the superficial disorder, is also assisted by second-order links (Van der Waals and Hydrogen bonds).