Efficient visible-light photocatalytic H2 evolution over metal-free g-C3N4 co-modified with robust acetylene black and Ni(OH)2 as dual co-catalysts

Abstract

In this work, a novel g-C₃N₄/acetylene black (AB)/Ni(OH)₂ ternary composite photocatalyst with dual robust electron co-catalysts was successfully synthetized using a facile two-step strategy: ultrasonic dispersion treatment and a subsequent precipitation process. The photocatalytic H₂-production activity over the composite photocatalyst was also evaluated using an aqueous solution containing triethanolamine under visible light (λ ≥ 420 nm). For the first time, it was revealed that the robust AB can be utilized as a co-catalyst to significantly enhance the photocatalytic H₂-evolution activity of g-C₃N₄. The results also demonstrated that the ternary g-C₃N₄/AB/Ni(OH)₂ nanocomposite exhibited enhanced photocatalytic H₂-evolution activity as compared to bulk g-C₃N₄ and binary hybrids. The g-C₃N₄–0.5% AB–1.0% Ni(OH)₂ (weight ratio) composite shows the highest H₂ evolution rate of 240 μmol g⁻¹ h⁻¹ under visible light irradiation, which is 320, 100 and 3.31 times higher than that of pure g-C₃N₄, g-C₃N₄–0.5% AB and g-C₃N₄–1.0% Ni(OH)₂, respectively. It is believed that the excellent synergetic effect between the robust AB and Ni(OH)₂ as dual electron co-catalysts on the surface of g-C₃N₄ can achieve the effectively promoted separation of photo-generated electron–hole pairs and enhance the following H₂-evolution kinetics, thus resulting in a significant enhancement of the photocatalytic H₂ evolution activity over g-C₃N₄. It is expected that the combination of nano-carbons such as AB and other earth-abundant co-catalysts can become a general strategy to improve the H₂-evolution activity over various kinds of conventional semiconductors.