Enhanced visible-light H2 evolution of g-C3N4 photocatalysts via the synergetic effect of amorphous NiS and cheap metal-free carbon black nanoparticles as co-catalysts

•A 2.51-fold enhancement in H2 production was obtained via the loading of carbon black.•The synergetic effect between the CB and NiS as co-catalysts achieved the enhanced activity.•The promoted charge separation and enhanced H2-evolution kinetics are the key factors.•Conductive carbon black as co-catalyst is promising in enhancing H2-evolution rate. In this report, g-C3N4-based photocatalysts with dual co-catalysts of amorphous NiS and carbon black were firstly synthesized through a facile two-step process. The g-C3N4/carbon black/NiS composite photocatalyst were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV–vis), N2 adsorption, photoluminescence (PL) spectra and transient photocurrent responses. The photocatalytic activities for photocatalytic hydrogen evolution under visible light irradiation (λ≥420nm) were measured using an aqueous solution containing triethanolamine as an electron donor. Moreover, the results showed that the ternary g-C3N4 photocatalyst loaded by 0.5wt% carbon black and 1.5wt% NiS could achieve the highest H2-production rate of 992μmolg−1h−1 under visible-light irradiation (>420nm), which is about 2.51 times higher than that of the corresponding binary g-C3N4/1.5% NiS photocatalyst. It is believed that the enhanced photocatalytic H2-evolution activities could be attributed to the excellent synergetic effect between the carbon black and NiS as co-catalysts on the surface of g-C3N4, leading to the improved visible light absorption, promoted charge separation and enhanced the following H2-evolution kinetics. This work would not only demonstrate the promising potentials of carbon black as co-catalyst for applications in visible-light H2 generation, but also offer a new insight into the construction of highly efficient and stable g-C3N4-based hybrid semiconductor nanocomposites with dual co-catalysts for diverse photocatalytic applications.