Earth-abundant NiS co-catalyst modified metal-free mpg-C3N4/CNT nanocomposites for highly efficient visible-light photocatalytic H2 evolution

Abstract

In the present work, the earth-abundant NiS co-catalyst modified mesoporous graphite-like C₃N₄ (mpg-C₃N₄)/CNT nanocomposites were prepared via a two-step strategy: the sol–gel method and the direct precipitation process. The mpg-C₃N₄/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 H₂-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-C₃N₄/CNT nanocomposites can remarkably enhance their photocatalytic H₂-production activity. The optimal loading amount of NiS on metal-free mpg-C₃N₄/CNT nanocomposites was about 1 wt%. The as-obtained mpg-C₃N₄/CNT/1% NiS ternary composite photocatalyst exhibits the best H₂-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-C₃N₄/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 H₂-evolution kinetics. The co-loading of nanocarbon materials and earth-abundant co-catalysts onto metal-free mpg-C₃N₄ photocatalysts offers great potential for practical applications in photocatalytic H₂ evolution under visible light illumination.