The electron bridge of Ti–O–Cu on well-integrated core–shell TiO 2@Cu nanorod for efficient and stable photocatalytic urea synthesis

The photocatalytic co-reduction of CO2 and NO3⁻ is a sustainable method for urea synthesis under mild condition. However, the low photocatalytic yield of urea is a challenge, due to the sluggish kinetics of the C-N coupling reaction. Herein, we have successfully engineered a TiO2 nanoparticle modified Cu nanorod photocatalyst (TiO2@Cu) for simultaneously promoting the NO3⁻ reduction and CO2 reduction reaction in the photocatalytic synthesis of urea. The TiO2 nanoparticles are uniformly covered onto the surface of the Cu nanorod via a simple one-pot strategy, and the as-prepared well-integrated core-shell TiO2@Cu showed excellent efficiency in photocatalytic urea synthesis, reaching up to 72.8 μmol g-1 h-1 of urea yield. The turnover frequency of TiO2@Cu is 30.1 times higher than that of pure TiO2. Furthermore, the photocatalytic performance of TiO2@Cu remains stable after 10 photocatalytic cycles, with no significant decline in urea yield. The remarkable photoactivity is attributed to the unique Ti-O-Cu bond in heterojunction interface of TiO2@Cu, and Ti-O-Cu bond provides a favorable electron transfer pathway from TiO2 to Cu, which accelerates the transfer of photogenerated charge and reduces the recombination of hole and electron. Meanwhile, the introduction of Cu alters the energy band structure of TiO2, resulting in a smaller band gap and further improving the utilization of light. The energy barrier of the C-N coupling reaction in Ti-O-Cu site (-3.22 eV) is much lower than individual Cu site (1.21 eV). This work provides important inspiration and guiding significance towards highly efficient photocatalytic synthesis of urea.