Z-Scheme Cu₂O Nanoparticle/Graphite Carbon Nitride Nanosheet Heterojunctions for Photocatalytic Hydrogen Evolution

A recrystallization-assisted way was developed to create Z-scheme Cu2O nanoparticle/g-C3N4 nanosheet layered heterostructures using melamine and copper salts by a two-step polymerization procedure. The recrystallization of melamine was carried out by adding different Cu salts. These copper salts not only influenced the recrystallization process of melamine but also resulted in the introduction of a little amount of Cu ions in the melamine crystals. The two-step polymerization procedure at 650 and 700 °C produces superior thin Cu2O/g-C3N4 nanosheets. The decrease of the thickness of the nanosheets increased specific surface areas. Cu2+ ions were reduced into Cu2O after heat treatment. Cu2O/g-C3N4 nanosheets revealed expanded visible light absorption and a decreased band gap. Cu2O/g-C3N4 nanosheets prepared by optimized preparation conditions (sample 650-700-Cu2O/RCNs) exhibited the best H2 generation of 5776.4 μmol/g/h with 3 wt % Pt as a cocatalyst and triethanolamine (TEOA) as a sacrificial reagent, which was about 3 times that of pure g-C3N4 nanosheets (sample 650-700-CN, 1912.6 μmol/g/h). Without the Pt cocatalyst, the photocatalytic H2 evolution of the sample 650-700-Cu2O/RCNs was 266.3 μmol/g/h, which was ∼18 times that of the sample 650-700-CN. The excellent performance is ascribed to the formation of Z-scheme heterostructures. This work provides a strategy to prepare highly efficient photocatalysts.