CO₂ Photoreduction Product Selectivity with TiO₂−Cu Nanocatalysts under Different Reaction Media

Abstract

This study explores photocatalytic conversion of CO2 using TiO2‐Cu heterojunctions with different Cu contents and investigates influence of different reaction media on the process efficiency. The use of KOH favored liquid products, especially ethanol. An analysis of H2 production as the main competitive reaction was done. Sodium oxalate led to an increase in H2 evolution by approximately 600 µmol g‐1 compared to pure water, in the presence of CO2 in the reaction medium, but the blank test (without CO2) indicates a lower H2 yield (~136 µmol g‐1), which suggests that the competitive reaction with CO2 also plays a role in H2 production. This role was related to the decrease of the initial pH from approximately 8.5 to 5.2, stabilizing at 5.5 at the end of the 6h reaction. In an environment saturated with N2, the pH increases to 9 and stabilizes at 7.8 at the end of the process. In the presence of acetic acid, both CO and H2 production were suppressed, with a significant increase in the selectivity for methane via cleavage of the acid's carbon bond. The findings underscore the importance of optimizing reaction conditions to achieve higher yields of desired products in the photocatalytic conversion of CO2.