Zn–Cr LDH/Graphene Oxide Composites for Selective Photocatalytic CO₂ Reduction toward CO under Visible Light Irradiation

The direct conversion of solar energy to chemical energy represents a substantial scientific challenge in contemporary society. The levels of carbon dioxide (CO2), the main gas responsible for the greenhouse effect, are increasing. Consequently, there is growing interest in the photocatalytic transformation of CO2 into valuable products to reduce its environmental impact. In this context, sunlight, as a clean and sustainable energy source, is harvested for CO2 photoreduction (CO2PR). Additionally, high selectivity for carbon monoxide (CO) may be desirable because it can be further converted via well-known processes into chemical fuels such as methanol, hydrogen, or liquid hydrocarbons. Layered double hydroxides (LDH) are excellent candidates as catalysts due to their unique layered structures and redox activity. In the past decade, scientists have endeavored to improve the properties of LDH to increase the overall efficiency of CO2 conversion. In this work, Zn–Cr LDH and their composites with graphene oxide (GO) were prepared by a coprecipitation method, characterized by different techniques, and tested as catalysts in a three-component system using [Ru(bpy)3]2+ as a photosensitizer (PS) and triethanolamine (TEOA) as a sacrificial electron donor (ED). This is the first use of Zn–Cr LDH/GO composites as catalysts in CO2PR under visible light irradiation. The results were outstanding (13,933 μmol of CO g–1 at 24 h). The amount of GO in the composite is crucial to achieve a synergistic effect with the LDH, resulting in an increased efficiency in the photoreduction of CO2 to CO.