Cu/PCN Metal-Semiconductor Heterojunction by Thermal Reduction for Photoreaction of CO 2 -Aerated H 2 O to CH 3 OH and C 2 H 5 OH.

g-C 3 N 4 -based materials show potential for photoreduction of CO 2 to oxygenates but are subjected to fast recombination of photogenerated charge carriers. Here, a novel Cu-dispersive protonated g-C 3 N 4 (PCN) metal-semiconductor (m-s) heterojunction from thermal reduction of a Cu 2 O/PCN precursor was prepared and characterized using in situ X-ray diffraction, scanning transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible (UV-vis) spectra, photoluminescence (PL) spectra, transient photocurrent response, and electrochemical impedance spectroscopy (EIS). The Cu amount in Cu/PCN and the reduction temperature affected the generation of CH 3 OH and C 2 H 5 OH from the photoreaction of CO 2 -aerated H 2 O. During calcination of Cu 2 O/PCN in N 2 at 550 °C, Cu 2 O was completely reduced to Cu with even dispersion, and a m-s heterojunction was obtained. With thermal exfoliation, Cu/PCN showed a specific surface area and layer spacing larger than those of PCN. Cu/PCN-0.5 (12.8 wt % Cu) exhibited a total carbon yield of 25.0 μmol·g -1 under UV-vis irradiation for 4 h, higher than that of Cu 2 O/PCN (13.6 μmol·g -1 ) and PCN (6.0 μmol·g -1 ). The selectivity for CH 3 OH and C 2 H 5 OH was 51.42 and 46.14%, respectively. The PL spectra, transient photocurrent response, and EIS characterizations indicated that Cu/PCN heterojunction promotes the separation of electrons and holes and suppresses their recombination. The calculated conduction band position was more negative, which is conducive to the multielectron reactions for CH 3 OH and C 2 H 5 OH generation.