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

Abstract

Direct synthesis of urea from CO₂, N₂, and\nH₂O through photocatalysis stands out as an effective solution\nto mitigate the over-release of CO₂ and alleviate the high\ncosts associated with nitrogen fertilizer production. The 20% CdS@Bi₂WO₆ sample exhibits optimal activity under visible\nlight, achieving a urea yield of 10.0 μmol·g^–1·h^–1. The photocatalytic efficacy of this\ncomposite is attributed to its S-type heterojunction, which can significantly\nenhance the redox capacity and the efficiency of photogenerated charge\nseparation compared to individual semiconductor components. CdS appears\nto be responsible for the photocatalytic reduction of N₂ and urea synthesis, while Bi₂WO₆ is involved\nin the oxidation of H₂O to form O₂ and H⁺. It is suggested that urea is synthesized on the surface\nof CdS through two mechanisms: (I) the reaction between the activated\nintermediates of CO₂ and N₂ (mainly) and (II)\nthe reaction of the in situ formed NH₃ with the feed CO₂.