Photocatalytic Coreduction of N2 and CO2 with H2O to (NH2)2CO on 2D-CdS/3D-BiOBr

One-pot synthesis of urea [(NH2)2CO] from easily available small molecules, that is, N2, CO2, and H2O, is an extremely attractive but very challenging reaction. 2D-CdS@3D-BiOBr composites with S-scheme heterojunctions are constructed via a facile hydrothermal technique followed by a self-assembly method and shown to be an excellent photocatalyst enabling the reduction of N2 and CO2 with H2O to (NH2)2CO under visible light. The optimal 40%2D-CdS@3D-BiOBr sample shows up to 15 μmol·g–1·h–1 total yield of NH3 and (NH2)2CO, of which (NH2)2CO accounts for 54%. The apparent quantum efficiency (AQE) is 3.93% for urea production. On the photocatalyst, urea is speculated to form by two possible chemical routes. One is direct photocatalytic synthesis. Both N2 and CO2 molecules are activated by the Cd2+ ion of 2D-CdS and the oxygen defect of 3D-BiOBr at the edges of the heterojunction interface of 2D-CdS/3D-BiOBr, respectively. *HNCONH* is the key intermediate of the formation of (NH2)2CO molecules. The other is indirect synthesis by photocatalysis and then thermocatalysis. N2 is reduced into NH3 and CO2 is reduced into CO on 2D-CdS by the photogenerated electrons and protons, and then the formed NH3 reacts with the reactant CO2 or the product CO to form (NH2)2CO by thermocatalysis on 2D-CdS. The former is dominant for urea synthesis. The work confirms that urea could be synthesized photocatalytically from cheap N2, CO2, and H2O under visible light. A composite heterojunction semiconductor could be a prospective photocatalyst appropriate for the complex reaction.