Promotion of Nickel-Modified Titanium Dioxide Photocatalysts with Graphene and Graphitic Carbon Nitride for Hydrogen Production from Water–Glycerol Mixtures

In photocatalytic hydrogen production, the influence of different promoters on the charge transfer behavior in nickel-modified titanium dioxide remains insufficiently understood, particularly in direct comparisons under the same catalyst platform. This study aimed to compare graphene and graphitic carbon nitride as promoters in Ni-G/TiO₂ and Ni-g-C₃N₄/TiO₂ composites and to elucidate their effects on the photocatalytic hydrogen evolution from water–glycerol mixtures. The composites were synthesized by wet impregnation followed by calcination and characterized using X-ray diffraction, ultraviolet–visible spectroscopy, and Fourier transform infrared spectroscopy to evaluate their structural and optical properties. Photocatalytic hydrogen production was tested under ultraviolet irradiation for 4 h in a batch photoreactor. Among the investigated materials, Ni-G/TiO₂ exhibited the highest hydrogen production of 12.8 mL, outperforming TiO₂ (8.3 mL), graphitic carbon nitride (7.4 mL), and Ni-g-C₃N₄/TiO2 (9.0 mL). The superior performance of Ni-G/TiO₂ is attributed to the higher conductivity of graphene, which promotes more efficient electron migration and suppresses charge recombination more effectively than the band-alignment-dominated charge transfer in Ni-g-C₃N₄/TiO₂. These findings demonstrate that promoter selection governs electron transfer pathways and strongly influences photocatalytic performance. This study provides comparative insight into promoter-dependent electron transfer and establishes a design basis for improving the hydrogen production of titanium dioxide-based photocatalysts.

g-C3N4; Graphene; Hydrogen production; Nickel; Photocatalysis; TiO2

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