Sustainable Photocatalytic Reduction of Maleic Acid: Enhancing CuxO/ZnO Stability with Polydopamine

The development of effective photocatalysts for environmental applications is still a critical aspect of green chemistry. This study explores copper oxide (CuxO) catalysts supported on titanium dioxide (TiO2) and zinc oxide (ZnO) for the photocatalytic reduction of maleic acid to succinic acid under ultraviolet (UV) light in water. The main goal was to evaluate the performance of CuO/ZnO compared to CuO/TiO2 in photoreduction. In order to improve the efficiency of the first catalyst, an environmentally friendly synthesis, assisted by polydopamine (PDA), was tested, obtaining the Cu2O/ZnO-PDA catalyst. The results showed that CuO/TiO2 exhibited the highest activity for maleic acid reduction, obtaining a succinic acid yield and a selectivity of 32% after 24 h of reaction time, but comparable results could be reached even with Cu2O/ZnO-PDA increasing the reaction time. Furthermore, the addition of sodium ascorbate as a co-catalyst in the reaction mixture allowed us to overtake the previous results, leading to a succinic acid yield of 61% and a selectivity of 67%. These findings suggest that the PDA shell can be a solution for CuxO photodegradation, making Cu2O/ZnO-PDA an alternative to the toxic CuO/TiO2.