Emerging Chemical Functionalization of g-C3N4: Covalent/Noncovalent Modifications and Applications

Atomically 2D thin-layered structures, such as graphene nanosheets, graphitic carbon nitride nanosheets (g-C₃N₄), hexagonal boron nitride, and transition metal dichalcogenides are emerging as fascinating materials for a good array of domains owing to their rare physicochemical characteristics. In particular, graphitic carbon nitride has turned into a hot subject in the scientific community due to numerous qualities such as simple preparation, electrochemical properties, high adsorption capacity, good photochemical properties, thermal stability, and acid-alkali chemical resistance, etc. Basically, g-C₃N₄ is considered as a polymeric material consisting of N and C atoms forming a tri-s-triazine network connected by planar amino groups. In comparison with most C-based materials, g-C₃N₄ possesses electron-rich characteristics, basic moieties, and hydrogen-bonding groups owing to the presence of hydrogen and nitrogen atoms; therefore, it is taken into account as an interesting nominee to further complement carbon in applications of functional materials. Nevertheless, g-C₃N₄ has some intrinsic limitations and drawbacks mainly related to a relatively poor specific surface area, rapid charge recombination, a limited light absorption range, and a poor dispersibility in both aqueous and organic mediums. To overcome these shortcomings, numerous chemical modification approaches have been conducted with the aim of expanding the range of application of g-C₃N₄ and enhancing its properties. In the current review, the comprehensive survey is conducted on g-C₃N₄ chemical functionalization strategies including covalent and noncovalent approaches. Covalent approaches consist of establishing covalent linkage between the g-C₃N₄ structure and the chemical modifier such as oxidation/carboxylation, amidation, polymer grafting, etc., whereas the noncovalent approaches mainly consist of physical bonding and intermolecular interaction such as van der Waals interactions, electrostatic interactions, π-π interactions, and so on. Furthermore, the preparation, characterization, and diverse applications of functionalized g-C₃N₄ in various domains are described and recapped. We believe that this work will inspire scientists and readers to conduct research with the aim of exploring other functionalization strategies for this material in numerous applications.

Bio-inspired honeycomb-like graphitic carbon nitride for enhanced visible light photocatalytic CO2 reduction activity

Graphitic carbon nitride (g-C₃N₄) is paying attention lately owing to its interesting characteristics and substantial application in improving environmental and energy concerns. Nevertheless, the photocatalytic activity of g-C₃N₄ is constrained by the inertness of the surface and particle aggregation during photocatalytic activity. Herein, we report the preparation of g-C₃N₄ with honeycomb-like morphology (HC-C₃N₄) via thermal condensation of prepared SiO₂ templates and dicyandiamide. The etching out of the SiO₂ templates by NH₄HF₂ created hollow or macropores in the C₃N₄ matrix resulting in its structural changes. Similar, to the bulk C₃N₄, the HC-C₃N₄ exhibited higher photocatalytic CO₂ reduction in hydrocarbons. This improved photocatalytic achievement is associated with higher specific surface area, excellent visible light absorption capability, higher electron donor density, easy mass diffusion of materials for surface reaction, and effective segregation of photogenerated charge carriers. Furthermore, the HC-C₃N₄ honeycomb structure was deposited with Ni(OH)₂ clusters which showed remarkable CO₂ reduction activity of 1.48 μmolh^-1 g^-1 of CH₄ and 0.73 μmolh^-1 g^-1 of CH₃OH generation which is 3.5 and 4.3 times higher CO₂ reduction activity compared with bulk C₃N₄ clustered with Ni(OH)₂ particles. This comprehensive study demonstrated that HC-C₃N₄ nanostructured polymeric semiconductor is envisaged to have great potential in the application of a variety of fields such as photocatalysis, sensor technology, and nanotechnology.

In situ synthesis of highly dispersed Co–N–C catalysts with carbon-coated sandwich structures based on defect anchoring

Highly dispersed Co–N–C catalysts were prepared via a defect strategy to anchor metal atoms with a carbon coating and were applied for the selective oxidation of ethylbenzene.

Fabrication of surface hydroxyl modified g-C3N4with enhanced photocatalytic oxidation activity

Photocatalytic activity of C₃N₄in the decomposition of phenolic compounds in water was significantly improved with hydroxyl surface modification.

A Metal-Free Carbon-Based Catalyst: An Overview and Directions for Future Research

Metal-free carbon porous materials (CPMs) have gained the intensive attention of scientists and technologists because of their potential applications, ranging from catalysis to energy storage. Various simple and facile strategies are proposed for the preparation of CPMs with well-controlled sizes, shapes, and modifications on the surface. The extraordinary tenability of the pore structure, the environmental acceptability, the unique surface and the corrosion resistance properties allow them to be suitable materials for a large panel of catalysis applications. This review briefly outlines the different signs of progresses made towards synthesizing CPMs, and their properties, including catalytic efficiency, stability, and recyclability. Finally, we make a comparison of their catalytic performances with other nanocomposites, and we provide an outlook on the expected developments in the relevant research works.

Synthesis of efficient Co and N co-doped carbon catalysts with high surface areas for selective oxidation of ethylbenzene

In this manuscript, Co and N co-doped carbon catalysts with high surface areas were prepared via the pyrolysis of cobalt nitrate and 1,10-phenanthroline monohydrate, using Mg(OH)₂ as a pore former, followed by acid etching.

Synthesis of N-doped Carbon Xerogel (N-CX) and its Applications for Adsorption Removal of Microcystin-LR

N-doped carbon xerogel (N-CX) is synthesized and used for adsorption removal of microcystin-LR (MC-LR) from aqueous solution. Characterizations including N2 physisorption, TEM and XPS indicate that N atoms are doped into the N-CX and the material has porous structure. Adsorption tests show that the N-CX is efficient for MC-LR adsorption, with adsorption capacity of 1916.2 μg g−1, which is higher than that of commercial activated carbon (1034.13 μg g−1) and graphene oxide (1700 μg g−1). The material is recyclable after desorption treatment by washing with NaOH solution, with no loss of uptake within five cycles. Effect of initial MC-LR concentration, temperature, and pH on the adsorption behavior is further investigated, to realize the adsorption process, showing that the adsorption process obeys the Langmuir isotherm and pseudo-second-order equation. Thermodynamical calculation indicates that the adsorption of MC-LR onto N-CX is a spontaneous and exothermic process, with the Gibbs free energy (ΔG) of −16.1 kJ mol−1 and enthalpy (ΔH) of −18.45 kJ mol−1.

Preparation of CoNC catalysts via heating a mixture of cobaltporphyrin and casein for ethylbenzene oxidation

Biomass-derived cobalt-coordinated N-doped carbon (CoNC) for C–H bond oxidation is synthesized by a facile procedure based on pyrolysis of cobaltporphyrin with natural, amino acid-rich biomass casein as a supplementary nitrogen source.

Dehydrochlorination of polyvinylchloride using Al-modified graphitic-C3N4

The increased dehydrochlorination activity for PVC over Al-modified g-C₃N₄is due to the larger number of basic sites and higher crystallinity of g-C₃N₄.

Graphitic carbon nitride for photocatalytic degradation of sulfamethazine in aqueous solution under simulated sunlight irradiation

Graphitic carbon nitride is active and stable for sulfamethazine (SMT) degradation under simulated sunlight irradiation, with 70% SMT conversion obtained within 90 min and no loss of activity observed within 5 cycles.