Mechanochemistry-driven synthesis of Cu/P25/g-C₃N₄ photocatalysts for sustainable CO₂ reduction

A systematic series of advanced photocatalysts featuring heterojunctions between commercial titanium dioxide (P25, TiO₂) and graphitic carbon nitride (g-C₃N₄) have been synthesised via a robust and scalable mechanochemical technique, incorporating 1 wt% of copper precursor to facilitate direct interaction at the TiO₂/g-C₃N₄ interface. Extensive structural, chemical, and spectroscopic characterisation was conducted, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (DRS), and gas physisorption, revealing highly crystalline nanometre-scale particles and homogeneous Cu dispersion. The photocatalytic activity was evaluated by conducting CO₂ photoreduction experiments in a custom-designed, continuous-flow, two-dimensional gas-phase reactor, using 40 mg of catalyst, a simulated sunlight source (UV LED lamp, 5.6 W, 368 nm), and ethanol (100 µL in 2.5 mL H₂O) as a sacrificial hole scavenger. By optimising the TiO₂ to g-C₃N₄ ratio with copper content kept constant, the best-performing sample, 1Cu/3P1D, exhibited outstanding CH₄ and CH₃CHO production rates of 550 μmol/g·h and 20 μmol/g·h, respectively—values that surpass those of benchmark commercial P25 TiO₂ (16.9 μmol CH₄/g·h and 20.4 μmol CH₃CHO/g·h). The superior performance is attributed to enhanced charge separation, increased visible-light absorption, and efficient utilisation of the Cu/TiO₂/g-C₃N₄ interfaces. Long-term stability tests confirmed the reliable and repeatable catalytic efficiency of the material, showcasing its durability for extended operations. Reproducibility and stability tests confirmed consistent yields across multiple runs for the best-performing sample (1Cu/3P1D). These findings elucidate the crucial influence of co-catalyst dispersion and interface engineering on photocatalytic efficiency, providing new insights and a versatile synthetic route for high-performance CO₂ photoreduction systems. • Heterojunctions between TiO₂, g-C₃N₄ and Cu have been synthesised via a robust and scalable mechanochemistry-based approach. • Photocatalytic activity in CO₂ photoreduction was evaluated in a continuous-flow, two-dimensional gas-phase reactor. • High catalytic activity was measured due to enhanced charge separation and visible-light absorption at the interfaces.