Ternary catalysts based on amino-functionalized carbon quantum dots, graphitic carbon nitride nanosheets and cobalt complex for efficient H2 evolution under visible light irradiation

Preparation of earth-abundant and noble-metal-free transition metal complexes serving as photocatalytic hydrogen evolution co-catalysts is of great challenge and significance. Here, ternary photocatalysts Co(dcbpy)(2)(NCS)(2)/CQDs/CN by amide bonds coupling Co(dcbpy)(2)(NCS)(2)[dcbpy = (4,4'-dicarboxy-2,2'-bipyridine)] with amino-functionalized carbon quantum dots (CQDs) or graphitic carbon nitride nanosheets (CN) were developed for efficient solar-to-hydrogen conversion. The amide bonds accelerate the combination of Co(dcbpy)(2)(NCS)(2) and CQDs/CN and improve the dispersion of Co(dcbpy)2(NCS)(2) on CN framework, thus leading to enhanced migration of charge carriers and absorption of visible light. In addition, the optimum photocatalytic hydrogen evolution activity of Co(dcbpy)(2)(NCS)(2)/CQDs/CN catalyst reaches 295.9 mmol h(-1) g(-1) with excellent stability after four cycling tests under visible light irradiation. The hydrogen evolution activity of 3Co(dcbpy)(2)(NCS)(2)/CQDs/CN catalyst reaches 75.02 mmol h(-1) g(-1) under monochromatic light irradiation (lambda = 450 nm) and the apparent quantum efficiency reaches 14.11%, whereas pure CN is inactive under the same condition. The amide bond between cobalt-based complex and CN plays an important role for excellent photocatalytic performance. More importantly, the composite catalysts give a new insight for designing noble-metal-free co-catalysts with excellent photocatalytic activity and high stability towards solar-to-hydrogen conversion. (c) 2019 Elsevier Ltd. All rights reserved.