Graphitic carbon Nitride (g-C₃N₄) is one of the most utilized graphitic materials in hydrogen (H₂) production via photocatalytic water splitting. Thus, a detailed critical overview, updated with the most recent works, has been performed on the synthesis methods, modification techniques, characterization, and mechanisms of g-C₃N₄ and g-C₃N₄-based composite materials, with the aim of clarifying the optimum course towards highly efficient hydrogen-producing photocatalysts based on this promising material. First, the synthesis methods for different morphologies of pure g-C₃N₄ (bulk, nanosheets, nanotubes and nanodots) are critically analyzed in detail for every step and parameter involved, with special mention regarding the modification methods of g-C₃N₄ (doping and composite formation). Next, the most common results of g-C₃N₄ characterization, regarding structural, morphological, optical, and electrical properties, are presented and analyzed. Then, a detailed critical survey of the mechanisms, using g-C₃N₄ and g-C₃N₄-based composites during photocatalytic activity, is performed with a focus on their effect on their hydrogen production capabilities via water splitting. This review aims to provide a clear image of all aspects regarding the use of g-C₃N₄ for photocatalysis, as well as a comprehensive guide for research targeted towards this promising graphitic material.

In the current study, CoFe₂O₄ and TiO₂ nanoparticles were primarily made using the sol-gel method, and subsequently, the hybrid magnetic composites of TiO₂ loaded with CoFe₂O₄ (5–15 percent w/w) were made using a hydrothermal procedure. X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) were all used to thoroughly characterize the materials. Additionally, the zero-charge point (ZCP) determination, the examination of the pore structure by nitrogen adsorption, and an evaluation of magnetic properties were performed. Six organic dye pollutants were selected to evaluate the performance of the synthesized nanocomposites toward photocatalytic degradation, including methylene blue (MB), methyl orange (MO), crystal violet (CV), acridine orange (AO), rhodamine B (RhB), and rhodamine 6G (R-6G). Photodegradation of tetracycline (TL), a model pharmaceutical pollutant, was also studied under UV and visible light. The composites exhibited a high degradation performance in all cases without using any oxidants. The photocatalytic degradation of tetracycline revealed that the CoFe₂O₄/TiO₂ (5% w/w) composite exhibited a higher photocatalytic activity than either pure TiO₂ or CoFe₂O₄, and thus attained 75.31% and 50.4% degradation efficiency under UV and visible light, respectively. Trapping experiments were conducted to investigate the photodegradation mechanism, which revealed that holes and super oxide radicals were the most active species in the photodegradation process. Finally, due to the inherent magnetic attributes of the composites, their easy removal from the treated solution via a simple magnet became possible.

In this review, the most recent advances in the field of magnetic composite photocatalysts with integrated plasmonic silver (Ag) is presented, with an overview of their synthesis techniques, properties and photocatalytic pollutant removal applications. Magnetic attributes combined with plasmonic properties in these composites result in enhancements for light absorption, charge-pair generation-separation-transfer and photocatalytic efficiency with the additional advantage of their facile magnetic separation from water solutions after treatment, neutralizing the issue of silver’s inherent toxicity. A detailed overview of the currently utilized synthesis methods and techniques for the preparation of magnetic silver-integrated composites is presented. Furthermore, an extended critical review of the most recent pollutant removal applications of these composites via green photocatalysis technology is presented. From this survey, the potential of magnetic composites integrated with plasmonic metals is highlighted for light-induced water treatment and purification. Highlights: (1) Perspective of magnetic properties combined with plasmon metal attributes; (2) Overview of recent methods for magnetic silver-integrated composite synthesis; (3) Critical view of recent applications for photocatalytic pollutant removal.