Robust Carbon Nitride-Based Thermoset Coatings for Surface Modification and Photochemistry

Light-Mediated Polymerization Catalyzed by Carbon Nanomaterials

Carbon nanomaterials, specifically carbon dots and carbon nitrides, play a crucial role as heterogeneous photoinitiators in both radical and cationic polymerization processes. These recently introduced materials offer promising solutions to the limitations of current homogeneous systems, presenting a novel approach to photopolymerization. This review highlights the preparation and photocatalytic performance of these nanomaterials, emphasizing their application in various polymerization techniques, including photoinduced i) free radical, ii) RAFT, iii) ATRP, and iv) cationic photopolymerization. Additionally, it discusses their potential in addressing contemporary challenges and explores prospects in this field. Moreover, carbon nitrides, in particular, exhibit exceptional oxygen tolerance, underscoring their significance in radical polymerization processes and allowing their applications such as 3D printing, surface modification of coatings, and hydrogel engineering.

Captopril supported on magnetic graphene nitride, a sustainable and green catalyst for one-pot multicomponent synthesis of 2-amino-4H-chromene and 1,2,3,6-tetrahydropyrimidine

Captopril (CAP) is a safe, cost-effective, and environmentally organic compound that can be used as an effective organo-catalyst. Functional groups of captopril make it capable to attach to solid support and acting as promoters in organic transformations. In this work, captopril was attached to the surface of magnetic graphene nitride by employing a linker agent. The synthesized composite efficiently catalyzed two multicomponent reactions including the synthesis of 1,2,3,6-tetrahydropyrimidine and 2-amino-4H-chromene derivatives. A large library of functional targeted products was synthesized in mild reaction conditions. More importantly, this catalyst was stable and magnetically recycled and reused for at least five runs without losing catalytic activity.

Synthesis and up-to-date applications of 2D microporous g-C3N4 nanomaterials for sustainable development

In recent years, with the development of industrial technology and the increase of people's environmental awareness, the research on sustainable materials and their applications has become a hot topic. Among two-dimensional (2D) materials that have been selected for sustainable research, graphitic phase carbon nitride (g-C3N4) has become a hot research topic because of its many outstanding advantages such as simple preparation, good electrochemical properties, excellent photochemical properties, and better thermal stability. Nevertheless, the inherent limitations of g-C3N4 due to its relatively poor specific surface area, rapid charge recombination, limited light absorption range, and inferior dispersion in aqueous and organic media have limited its practical application. In the review, we summarize and analyze the unique structure of the 2D microporous nanomaterial g-C3N4, its synthesis method, chemical modification method, and the latest application examples in various fields in recent years, highlighting its advantages and shortcomings, with a view to providing ideas for overcoming the difficulties in its application. Furthermore, the pressing challenges faced by g-C3N4 are briefly discussed, as well as an outlook on the application prospects of g-C3N4 materials. It is expected that the review in this paper will provide more theoretical strategies for the future practical application of g-C3N4-based materials, as well as contributing to nanomaterials in sustainable applications.

Polymer Coated Functional Catalysts for Industrial Applications

Surface engineering of conventional catalysts using polymeric coating has been extensively explored for producing hybrid catalytic material with enhanced activity, high mechanical and thermal stability, enhanced productivity, and selectivity of the desired product. The present review discusses in detail the state-of-the-art knowledge on surface modification of catalysts, namely photocatalysts, electrocatalysts, catalysts for photoelectrochemical reactions, and catalysts for other types of reactions, such as hydrodesulfurization, carbon dioxide cycloaddition, and noble metal-catalyzed oxidation/reduction reactions. The various techniques employed for the polymer coating of catalysts are discussed and the role of polymers in enhancing the catalytic activity is critically analyzed. The review further discusses the applications of biodegradable and biocompatible natural polysaccharide-based polymers, namely, chitosan and polydopamine as prospective coating material.

Synergistic effects of the hybridization between boron-doped carbon quantum dots and n/n-type g-C3N4 homojunction for boosted visible-light photocatalytic activity

Dye wastewater has raised a prevalent environmental concern due to its ability to prevent the penetration of sunlight through water, thereby causing a disruption to the aquatic ecosystem. Carbon quantum dots (CQDs) are particularly sought after for their highly tailorable photoelectrochemical and optical properties. Simultaneously, graphitic carbon nitride (g-C₃N₄) has gained widespread attention due to its suitable band gap energy as well as excellent chemical and thermal stabilities. Herein, a novel boron-doped CQD (BCQD)-hybridized g-C₃N₄ homojunction (CN) nanocomposite was fabricated via a facile hydrothermal route. The optimal photocatalyst sample, 1-BCQD/CN (with a 1:3 mass ratio of boron to CQD) accomplished a Rhodamine B (RhB, 10 mg/L) degradation efficiency of 96.8% within 4 h under an 18 W LED light irradiation. The kinetic rate constant of 1.39 × 10^-2 min^-1 achieved by the optimum sample was found to be 3.6- and 2.8-folds higher than that of pristine CN and un-doped CQD/CN, respectively. The surface morphology, crystalline structure, chemical composition and optical properties of photocatalyst samples were characterized via TEM, FESEM-EDX, XRD, FTIR, UV-Vis DRS and FL spectrometer. Based on the scavenging tests, it was revealed that the photogenerated holes (h⁺), superoxide anions (∙O₂^-) and hydroxyl radicals (∙OH) were the primary reactive species responsible for the photodegradation process. Overall, the highly efficient 1-BCQD/CN composite with excellent photocatalytic activity could provide a cost-effective and robust means to address the increasing concerns over global environmental pollution.

Ethanol Solvothermal Treatment on Graphitic Carbon Nitride Materials for Enhancing Photocatalytic Hydrogen Evolution Performance

Recently, Pt-loaded graphic carbon nitride (g-C₃N₄) materials have attracted great attention as a photocatalyst for hydrogen evolution from water. The simple surface modification of g-C₃N₄ by hydrothermal methods improves photocatalytic performance. In this study, ethanol is used as a solvothermal solvent to modify the surface properties of g-C₃N₄ for the first time. The g-C₃N₄ is thermally treated in ethanol at different temperatures (T = 140 °C, 160 °C, 180 °C, and 220 °C), and the Pt co-catalyst is subsequently deposited on the g-C₃N₄ via a photodeposition method. Elemental analysis and XPS O 1s data confirm that the ethanol solvothermal treatment increased the contents of the oxygen-containing functional groups on the g-C₃N₄ and were proportional to the treatment temperatures. However, the XPS Pt 4f data show that the Pt²⁺/Pt⁰ value for the Pt/g-C₃N₄ treated at ethanol solvothermal temperature of 160 °C (Pt/CN-160) is the highest at 7.03, implying the highest hydrogen production rate of Pt/CN-160 is at 492.3 μmol g⁻¹ h⁻¹ because the PtO phase is favorable for the water adsorption and hydrogen desorption in the hydrogen evolution process. In addition, the electrochemical impedance spectroscopy data and the photoluminescence spectra emission peak intensify reflect that the Pt/CN-160 had a more efficient charge separation process that also enhanced the photocatalytic activity.

Low-Temperature Synthesis of Solution Processable Carbon Nitride Polymers

Carbon nitride materials require high temperatures (>500 °C) for their preparation, which entails substantial energy consumption. Furthermore, the high reaction temperature limits the materials' processability and the control over their elemental composition. Therefore, alternative synthetic pathways that operate under milder conditions are still very much sought after. In this work, we prepared semiconductive carbon nitride (CN) polymers at low temperatures (300 °C) by carrying out the thermal condensation of triaminopyrimidine and acetoguanamine under a N2 atmosphere. These molecules are isomers: they display the same chemical formula but a different spatial distribution of their elements. X-ray photoelectron spectroscopy (XPS) experiments and electrochemical and photophysical characterization confirm that the initial spatial organization strongly determines the chemical composition and electronic structure of the materials, which, thanks to the preservation of functional groups in their surface, display excellent processability in liquid media.

Molding and Encoding Carbon Nitride-Containing Edible Oil Liquid Objects via Interfacial Toughening in Waterborne Systems

Charge interaction-driven jamming of nanoparticle monolayers at the oil-water interface can be employed as a method to mold liquids into tailored stable 3D liquid objects. Here, 3D liquid objects are fabricated via a combination of biocompatible aqueous poly(vinyl sulfonic acid, sodium salt) solution and a colloidal dispersion of highly fluorescent organo-modified graphitic carbon nitride (g-C₃N₄) in edible sunflower oil. The as-formed liquid object shows stability in a broad pH range, as well as flexible pathways for efficient exchange of molecules at the liquid-liquid interphase, which allows for photodegradation of rhodamine B at the interface via visible light irradiation that also enables an encoding concept. The g-C₃N₄-based liquid objects point toward various applications, for example, all-liquid biphasic photocatalysis, artificial compartmentalized systems, liquid-liquid printing, or bioprinting.

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.

Colloidal properties of the metal-free semiconductor graphitic carbon nitride

The metal-free, polymeric semiconductor graphitic carbon nitride (g-CN) family is an emerging class of materials and has striking advantages compared to other semiconductors, i.e. ease of tunability, low cost and synthesis from abundant precursors in a chemical environment. Efforts have been done to improve the properties of g-CN, such as photocatalytic efficiency, designing novel composites, processability and scalability towards discovering novel applications as a remedy for the problems that we are facing today. Despite the fact that the main efforts to improve g-CN come from a catalysis perspective, many fundamental possibilities arise from the special colloidal properties of carbon nitride particles, from synthesis to applications. This review will display how typical colloid chemistry tools can be employed to make 'better g-CNs' and how up to now overseen properties can be levered by integrating a colloid and interface perspective into materials chemistry. Establishing a knowledge on the origins of colloidal behavior of g-CN will be the core of the review.

Graphitic Carbon Nitride Stabilizers Meet Microfluidics: From Stable Emulsions to Photoinduced Synthesis of Hollow Polymer Spheres

Graphitic carbon nitride (g-CN) has been utilized as a heterogeneous catalyst, but is usually not very well dispersible. The amphiphilic character of g-CN can be altered by surface modifications of g-CN nanopowders. Introducing hydrophilicity or hydrophobicity is a promising avenue for producing advanced emulsion systems. In this study, a special surface-modified g-CN is used to form stable Pickering emulsions. Using a PDMS-based microfluidic device designed for stable production of both single and double emulsions, it is shown that surface-modified g-CNs allow the manufacture of unconventionally stable and precise Pickering emulsions. Shell thickness of the double emulsions is varied to emphasize the robustness of the device and also to demonstrate the extraordinary stabilization brought by the surface-modified carbon nitride used in this study. Due to the electrostatic stabilization also in the oil phase, double emulsions are centered. Finally, when produced from polymerizable styrene, hollow polymer microparticles are formed with precise and tunable sizes, where g-CN is utilized as the only stabilizer and photoinitiator.

Polymer Brushes on Graphitic Carbon Nitride for Patterning and as a SERS Active Sensing Layer via Incorporated Nanoparticles

Graphitic carbon nitride (gCN) has a broad range of promising applications, from energy harvesting and storage to sensing. However, most of the applications are still restricted due to gCN poor dispersibility and limited functional groups. Herein, a direct photografting of gCN using various polymer brushes with tailorable functionalities via UV photopolymerization at ambient conditions is demonstrated. The systematic study of polymer brush-functionalized gCN reveals that the polymerization did not alter the inherent structure of gCN. Compared to the pristine gCN, the gCN-polymer composites show good dispersibility in various solvents such as water, ethanol, and tetrahydrofuran (THF). Patterned polymer brushes on gCN can be realized by employing photomask and microcontact printing technology. The polymer brushes with incorporated silver nanoparticles (AgNPs) on gCN can act as a multifunctional recyclable active sensing layer for surface-enhanced Raman spectroscopy (SERS) detection and photocatalysis. This multifunctionality is shown in consecutive cycles of SERS and photocatalytic degradation processes that can be applied to in situ monitor pollutants, such as dyes or pharmaceutical waste, with high chemical sensitivity as well as to water remediation. This dual functionality provides a significant advantage to our AgNPs/polymer-gCN with regard to state-of-the-art systems reported so far that only allow SERS pollutant detection but not their decomposition. These results may provide a new methodology for the covalent functionalization of gCN and may enable new applications in the field of catalysis, biosensors, and, most interestingly, environmental remediation.

Graphitic Carbon Nitride Nanosheets Covalently Functionalized with Biocompatible Vitamin B1: Synthesis, Characterization, and Its Superior Performance for Synthesis of Quinoxalines

The physical properties of two-dimensional nanosheet materials make them promising candidates as active materials in the areas of photoelectronics, fuel cells, sensors, water splitting, solar energy conversion, CO2 reduction, and heterogeneous catalysis. Among two-dimensional nanosheet materials, graphitic carbon nitride due to its electronic structure and high chemical and thermal stability possesses unique properties. Covalent functionalization of graphitic carbon nitride could be the key step in modifying its ability and significantly improving its properties. To this purpose, a novel strategy for the covalent functionalization of g-C3N4 nanosheets (CN) with vitamin B1 (VB1) by using 1,3-dibromopropane as a covalent linker for the first time is demonstrated. The obtained CN-Pr-VB1 exhibits increased thermal stability compared to the VB1 which is important in the practice application and can be easily dispersed in common organic solvents. The efficacy of the CN-Pr-VB1 as a heterogeneous organocatalyst was evaluated in the quinoxaline synthesis under solvent-free conditions and afforded good isolated yield with high purity. Moreover, the prepared catalyst could be facilely recycled and reused for seven consecutive cycles without a noticeable decrease in the catalytic activity. Extensive characterization confirmed the stability of morphology and chemical structure after recyclability of the CN-Pr-VB1.

Grafting Polymers onto Carbon Nitride via Visible-Light-Induced Photofunctionalization

Metal-free graphitic carbon nitride (g-CN) has attracted significant attention recently due to its multiple applications, such as photocatalysis, energy storage and conversion, and biomaterials, albeit formation of g-CN films is challenging. Herein, a “grafting to” route to graft polymer brushes onto g-CN via visible-light irradiation is described. Afterward, g-CN/polymer films can be obtained through spin coating on glass substrates. As such, the present material provides an improved process toward further application of g-CN in thin films. Moreover, an improved dispersibility in organic solvent was realized after grafting and functional groups (such as epoxides) were introduced to g-CN. Subsequently, the epoxy groups were utilized for further functionalization to adjust the surface polarity.

Visible-light induced emulsion photopolymerization with carbon nitride as a stabilizer and photoinitiator

Graphitic carbon nitride is utilized as a stabilizer and photoinitiator for surfactant-free emulsion polymerization under visible light.

Polymer grafted graphitic carbon nitrides as precursors for reinforced lubricant hydrogels

Carbon nitride-based hydrogels are formed in a two-step procedure and feature significant toughness, compressibility and lubricant properties.