Visible light photoreforming of greenhouse gases by nano Cu–Al LDH intercalated with urea-derived anions

Abstract

The accumulation of anthropogenic greenhouse gases (GHGs) in the atmosphere causes global warming. Global efforts are carried out to prevent temperature overshooting and limit the increase in the Earth's surface temperature to 1.5 °C. Carbon dioxide and methane are the largest contributors to global warming. We have synthesized copper–aluminium layered double hydroxide (Cu–Al LDH) catalysts by urea hydrolysis under microwave (MW) irradiation. The effect of MW power, urea concentration, and M^II/M^III ratios was studied. The physicochemical properties of the prepared LDH catalysts were characterized by several analysis techniques. The results confirmed the formation of the layered structure with the intercalation of urea-derived anions. The urea-derived anions enhanced the optical and photocatalytic properties of the nano Cu–Al LDH in the visible-light region. The photocatalytic activity of the prepared Cu–Al LDH catalysts was tested for greenhouse gas conversion (CH₄, CO₂, and H₂O) under visible light. The dynamic gas mixture flow can pass through the reactor at room temperature under atmospheric pressure. The results show a high conversion percentage for both CO₂ and CH₄. The highest converted amounts were 7.48 and 1.02 mmol mL⁻¹ g⁻¹ for CH₄ and CO₂, respectively, under the reaction conditions. The main product was formaldehyde with high selectivity (>99%). The results also show the stability of the catalysts over several cycles. The current work represents a green chemistry approach for efficient photocatalyst synthesis, visible light utilization, and GHGs' conversion into a valuable product.