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

Abstract

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.

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