Visible-Light Photocatalytic CO₂–N₂–H₂O to Urea with CdS@Bi₂WO₆

Direct synthesis of urea from CO2, N2, and H2O through photocatalysis stands out as an effective solution to mitigate the over-release of CO2 and alleviate the high costs associated with nitrogen fertilizer production. The 20% CdS@Bi2WO6 sample exhibits optimal activity under visible light, achieving a urea yield of 10.0 μmol·g–1·h–1. The photocatalytic efficacy of this composite is attributed to its S-type heterojunction, which can significantly enhance the redox capacity and the efficiency of photogenerated charge separation compared to individual semiconductor components. CdS appears to be responsible for the photocatalytic reduction of N2 and urea synthesis, while Bi2WO6 is involved in the oxidation of H2O to form O2 and H+. It is suggested that urea is synthesized on the surface of CdS through two mechanisms: (I) the reaction between the activated intermediates of CO2 and N2 (mainly) and (II) the reaction of the in situ formed NH3 with the feed CO2.