Abstract
Recently, the engineering of optical bandgaps and morphological properties of graphitic carbon nitride (g-C3N4) has attracted significant research attention for photoelectrodes and environmental remediation owing to its low-cost synthesis, availability of raw materials, and thermal physical–chemical stability. However, the photoelectrochemical activity of g-C3N4-based photoelectrodes is considerably poor due to their high electron–hole recombination rate, poor conductivity, low quantum efficiency, and active catalytic sites. Synthesized Ni metal-doped g-C3N4 nanostructures can improve the light absorption property and considerably increase the electron–hole separation and charge transfer kinetics, thereby initiating exceptionally enhanced photoelectrochemical activity under visible-light irradiation. In the present study, Ni dopant material was found to evince a significant effect on the structural, morphological, and optical properties of g-C3N4 nanostructures. The optical bandgap of the synthesized photoelectrodes was varied from 2.53 to 2.18 eV with increasing Ni dopant concentration. The optimized 0.4 mol% Ni-doped g-C3N4 photoelectrode showed a noticeably improved six-fold photocurrent density compared to pure g-C3N4. The significant improvement in photoanode performance is attributable to the synergistic effects of enriched light absorption, enhanced charge transfer kinetics, photoelectrode/aqueous electrolyte interface, and additional active catalytic sites for photoelectrochemical activity.
Highlights
Over the past few decades, energy and environmental issues have become the most important and popular topic worldwide
The XRD analysis of the Ni-doped g-C3 N4 samples revealed that there were no characteristic peaks related to metallic nickel, nickel oxides (NiO and Ni2 O3 ), nickel nitrides (Ni3 N), and nickel carbides (Ni3 C) in any of the Ni-doped g-C3 N4 nanostructures, even at a high Ni dopant concentration of 0.5 mol%, which designates the substitution of Ni ions into the host g-C3 N4 matrix, possibly in the form of Ni–N bonds due to the high affinity among the Ni2+ ions and negatively charged N atoms in the N pots of g-C3 N4 [28]
The major peak intensity of Ni-doped g-C3 N4 gradually decreased with increasing Ni dopant concentration, indicating that the deterioration of the (002) reflection plane was related to the inhibition of the polycondensation of g-C3 N4 nanostructures upon increasing the dopant concentration of Ni
Summary
Over the past few decades, energy and environmental issues have become the most important and popular topic worldwide. As a metal-free photocatalyst, graphitic carbon nitride (g-C3 N4 ) has attracted significant interest owing to its remarkable physical and chemical properties, such as reliable thermal and chemical endurance, super hardness, high efficiency, stability, nontoxic photocatalysis, low density, water resistivity, and biocompatibility [6]. Of the various semiconductors investigated [9,10,11,12], g-C3 N4 is characteristically nontoxic and metal-free, with a comparatively narrow bandgap (2.7 eV), high thermal and chemical stability, and attractive electronic properties It is considered as a promising material owing to its reasonable bandgap and electron localization properties or appropriate microstructural active site anchoring with surface dissolution as well as nitrogen atom water-splitting defect [13,14]. It is evident that Ni-based g-C3 N4 catalysts exhibit good catalytic activity; a methodical study on Ni-doped g-C3 N4 photoelectrodes for PEC water-splitting activity remains unavailable. The incorporation of Ni improved the photoanode performance and enhanced the charge transfer kinetics between the photoelectrode/aqueous electrolyte interface
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