Earth-abundant NiS co-catalyst modified metal-free mpg-C 3 N 4 /CNT nanocomposites for highly efficient visible-light photocatalytic H 2 evolution

In the present work, the earth-abundant NiS co-catalyst modified mesoporous graphite-like C 3 N 4 (mpg-C 3 N 4 )/CNT nanocomposites were prepared via a two-step strategy: the sol–gel method and the direct precipitation process. The mpg-C 3 N 4 /CNT/NiS composite photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis absorption spectroscopy, photoluminescence spectroscopy (PL), photoelectrochemical (PEC) and electrochemical impedance spectra (EIS) experiments. The photocatalytic H 2 -production activity over the composite catalysts was also evaluated by using an aqueous solution containing triethanolamine under visible light ( λ ≥ 420 nm). The results showed that the loading of earth-abundant NiS co-catalysts onto metal-free mpg-C 3 N 4 /CNT nanocomposites can remarkably enhance their photocatalytic H 2 -production activity. The optimal loading amount of NiS on metal-free mpg-C 3 N 4 /CNT nanocomposites was about 1 wt%. The as-obtained mpg-C 3 N 4 /CNT/1% NiS ternary composite photocatalyst exhibits the best H 2 -evolution activity with the highest rate of about 521 μmol g −1 h −1 under visible light ( λ ≥ 420 nm), which is almost 148 times that of a pure mpg-C 3 N 4 /CNT sample. The enhanced photocatalytic activity can be mainly attributed to the synergistic effect of effectively promoted separation of photo-generated electron–hole pairs and enhanced H 2 -evolution kinetics. The co-loading of nanocarbon materials and earth-abundant co-catalysts onto metal-free mpg-C 3 N 4 photocatalysts offers great potential for practical applications in photocatalytic H 2 evolution under visible light illumination.