Atomically Anchored Cu on MXene-Derived TiO₂/Ti₃C₂ Enables Cu-Ti Dual Sites for Selective Urea Photosynthesis from CO₂ and Nitrate

Abstract

Urea photosynthesis from CO₂ and nitrate presents a sustainable solution to mitigate carbon and nitrogen pollution. Nonetheless, simultaneously activating both substrates and directing selective C–N coupling remains challenging. In this study, we present the first construction of atomically coordinated Cu–Ti dual sites on a MXene-derived TiO₂/Ti₃C₂ heterostructure for direct urea synthesis. Asymmetric Cu–O–Ti dual sites are engineered by anchoring isolated Cu single atoms. HAADF-STEM and in-situ XPS/XAFS analyses confirm atomically dispersed Cu and light-induced, reversible Cu⁺/Cu²⁺ cycling. In-situ FTIR and DFT studies reveal that Cu sites convert CO2 to *CO, Ti sites catalyze the eight-electron nitrate reduction to *NH2, and the Cu-O-Ti bridge reduces the energy barrier for C-N coupling to urea intermediates, thereby suppressing CO and NH3 by-products. Under simulated sunlight, the optimized catalyst (0.5 wt% Cu) achieves a urea production rate of 11.57 μmol·gcat−1·h−1, which is 2.2 times higher than that of TiO2/Ti3C2, with excellent cycling stability. This MXene-enabled single-atom coordination strategy provides a general approach for renewable-energy-driven C-N coupling and pollutant valorization.