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

One-pot synthesis of urea [(NH2)(2)CO] from easily available small molecules, that is, N-2, 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 N-2 and CO2 with H2O to (NH2)(2)CO under visible light. The optimal 40%2D-CdS@3D-BiOBr sample shows up to 15 mu mol.g(-1).h(-1) total yield of NH3 and (NH2)(2)CO, of which (NH2)(2)CO 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 N-2 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)(2)CO molecules. The other is indirect synthesis by photocatalysis and then thermocatalysis. N-2 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)(2)CO by thermocatalysis on 2D-CdS. The former is dominant for urea synthesis. The work confirms that urea could be synthesized photocatalytically from cheap N-2, CO2, and H2O under visible light. A composite heterojunction semiconductor could be a prospective photocatalyst appropriate for the complex reaction.