Visible-Light\nPhotocatalytic CO<sub>2</sub>–N<sub>2</sub>–H<sub>2</sub>O to Urea with CdS@Bi<sub>2</sub>WO<sub>6</sub>

Direct synthesis of urea from CO<sub>2</sub>, N<sub>2</sub>, and\nH<sub>2</sub>O through photocatalysis stands out as an effective solution\nto mitigate the over-release of CO<sub>2</sub> and alleviate the high\ncosts associated with nitrogen fertilizer production. The 20% CdS@Bi<sub>2</sub>WO<sub>6</sub> sample exhibits optimal activity under visible\nlight, achieving a urea yield of 10.0 μmol·g<sup>–1</sup>·h<sup>–1</sup>. 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 N<sub>2</sub> and urea synthesis, while Bi<sub>2</sub>WO<sub>6</sub> is involved\nin the oxidation of H<sub>2</sub>O to form O<sub>2</sub> and H<sup>+</sup>. It is suggested that urea is synthesized on the surface\nof CdS through two mechanisms: (I) the reaction between the activated\nintermediates of CO<sub>2</sub> and N<sub>2</sub> (mainly) and (II)\nthe reaction of the in situ formed NH<sub>3</sub> with the feed CO<sub>2</sub>.