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Artificial photosynthesis that converts CO2 and H2O into compounds with added value is a viable method for reducing atmospheric CO2 concentration. In this study, we investigated the photocatalytic activity of ultrathin indium tin oxide (ITO) films on rigid and flexible substrates for CO2 reduction in water vapor and batch and flow setups. To explain a viable reaction mechanism for the 2760 ± 10 % μmol.gcat-1.hr-1 production rate achieved in a continuous reaction system, several theoretical models were developed. According to DFT simulation results, oxygen vacancy might be regarded as the main reaction site for CO2 to CO conversion. Moreover, a viable reaction pathway leading to CH4 formation is proposed. The catalyst’s lower rate of CO2 reduction in the batch reactor as compared with the flow reactor was justified via surface affinity simulation. Our findings highlight the significance of the catalyst’s structural design and reaction media configuration for stability and high activity.

The performance of two TiO2 catalysts, anatase powder (ALD) and Degussa P25 (DP25), was evaluated through photodegradation of Acid Blue 9 (AB9). The results were used to exhibit a sort of selectivity identified in these systems. The photodegradation was performed through a batch annular non-sleeve photoreactor. The kinetic constant values (k) and discolouration profiles exhibited a sort of catalytic selectivity. The results were explained by surface phenomena approach through experimental and theoretical means, employing UV–Vis, X-ray diffraction, Z potential, DFT-Koopman’s descriptors and the catalyst total binding energy ((EBin,T)i,j). This contribution propose (EBin,T)i,j equation, which involves theoretical (binding energies (Ebinding)) and experimental (relative intensity of the main crystalline catalyst planes) variables. The photocatalysis using ALD showed the highest k; but the photocatalysis with DP25 exhibited a linear discolouration profile, indicating a complete degradation of AB9 and their by-products. The k values agreed with (EBin,T)i,j, so the performance of TiO2 catalysts was attributed to Ebinding; these energies are product of the hydrogen bonding between the catalyst crystalline planes and AB9, in aqueous medium. Also, two different AB9 pathways were identified through DFT-Koopman’s descriptors. The theoretical tools showed in this contribution are useful to understand the catalyst affinity and degradation pathways of pollutants.