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

Direct synthesis of urea from CO 2, N 2, and H 2 O through photocatalysis stands out as an effective solution to mitigate the over-release of CO 2 and alleviate the high costs associated with nitrogen fertilizer production. The 20% CdS@Bi 2 WO 6 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 N 2 and urea synthesis, while Bi 2 WO 6 is involved in the oxidation of H 2 O to form O 2 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 CO 2 and N 2 (mainly) and (II) the reaction of the in situ formed NH 3 with the feed CO 2 .