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As one of the best sustainable approaches for visible-light production of hydrogen (H2) to meet energy demands, semiconductor-based photocatalysis has received broad interest in recent decades. The fundamental restrictions of graphitic carbon nitride (g-C3N4) as a promising metal-free photocatalytic semiconductor in water splitting, like insufficient visible-light harvesting and high electron–hole (e/h) pairs recombination, have limited its applications for this goal. In this regard, the optical, charge separation, and surface features of g-C3N4can be tuned via engineering C/N vacancies, which is reviewed here for water splitting by g-C3N4. Reports confirm that the enhanced surface features of g-C3N4resulting from the engineering of C/N vacancies are helpful for water adsorption on its surface, improving the water-splitting kinetics. First in this Review, recent improvements to the structural and optical characteristics of g-C3N4by introducing C/N vacancies, especially nitrogen vacancies, will be discussed to illustrate its better photocatalytic performance. Then, various strategies for creating and controlling C/N vacancies will be reviewed. The critical roles of C/N vacancies for optimizing photocatalytic performance will also be described, and finally advances in defective photocatalysis water oxidation will be addressed.

In recent decades, a great interest in photocatalytic water splitting has been due to the importance of sunlight water splitting hydrogen production as a renewable energy source to reduce global warming effects. The photocatalytic water splitting applications of metal sulfide semiconductors photocatalysts, as chalcogenide compounds, with advantages of the wide range for light harvesting and tunable bandgap, may be restricted by the limited active sites, poor conductivity, photo corrosion, and charge recombination. The sulfur vacancy (SV) effectively addresses these issues and generates H2and O2by attaining adequate water-splitting because of the improved optoelectronic features. This review article aims to comprehensively highlight the synergistic roles of SV in metal sulfides for amended overall water-splitting activity. The SV-modulated metal sulfides’ photocatalytic features are deliberated, followed by different advanced synthetic techniques for effectual vacancy defect generation. The specific SV aspects in refining the optical harvesting range, dynamics of charge carrier, and photoinduced surface chemical reactions are deeply described for overall water splitting applications. Finally, summarized vouchsafing outlooks and opportunities confronting the S-vacancy engineered metal sulfides-based photocatalysts are elucidated. It would be expected and hoped that this review will help researchers design/fabricate better metal sulfide-based photocatalytic systems.