Graphitic Carbon Nitride Materials Research Articles

Enhanced Electron Delocalization Induced by Ferromagnetic Sulfur doped C 3 N 4 Triggers Selective H 2 O 2 Production

For the 2D metal‐free carbon catalysts, the atomic coplanar architecture enables a large number of pz orbitals to overlap laterally, thus forming π‐electron delocalization, and the delocalization degree of the central atom dominates the catalytic activity. Herein, designing sulfur‐doped defect‐rich graphitic carbon nitride (S‐Nv‐C3N4) materials as a model, we propose a strategy to promote localized electron polarization by enhancing the ferromagnetism of ultra‐thin 2D carbon nitride nanosheets. The introduction of sulfur (S) further promotes localized ferromagnetic coupling, thereby inducing long‐range ferromagnetic ordering and accelerating the electron interface transport. Meanwhile, the hybridization of sulfur atoms breaks the symmetry and integrity of the unit structure, promotes electron enrichment and stimulating electron delocalization at the active site. This optimization enhances the *OOH desorption, providing a favorable kinetic pathway for the production of hydrogen peroxide (H2O2). Consequently, S‐Nv‐C3N4 exhibits high selectivity (>95%) and achieves a superb H2O2 production rate, approaching 4374.8 ppm during continuous electrolysis over 300‐hour. According to theoretical calculation and in‐situ spectroscopy, the ortho‐S configuration can provide ferromagnetic perturbation in carbon active centers, leading to the electron delocalization, which optimizes the OOH* adsorption during the catalytic process.

Enhanced Electron Delocalization Induced by Ferromagnetic Sulfur doped C 3 N 4 Triggers Selective H 2 O 2 Production.

For the 2D metal-free carbon catalysts, the atomic coplanar architecture enables a large number of pzorbitals tooverlap laterally,thus formingπ-electron delocalization, and the delocalization degree of the central atom dominates the catalytic activity. Herein, designing sulfur-doped defect-rich graphitic carbon nitride (S-Nv-C3N4) materials as a model, we proposea strategy to promote localized electronpolarization by enhancing the ferromagnetism of ultra-thin 2D carbon nitride nanosheets.The introduction of sulfur (S)further promotes localized ferromagnetic coupling,thereby inducing long-range ferromagnetic ordering and accelerating the electron interface transport. Meanwhile, the hybridization of sulfur atoms breaks the symmetry and integrity of the unit structure, promoteselectron enrichment and stimulating electron delocalization at the active site. This optimization enhances the *OOH desorption, providing a favorable kinetic pathway for the production of hydrogen peroxide (H2O2). Consequently, S-Nv-C3N4exhibits high selectivity (>95%)and achieves a superb H2O2production rate,approaching4374.8ppm duringcontinuous electrolysisover 300-hour. According to theoreticalcalculationand in-situspectroscopy,the ortho-S configurationcan provide ferromagnetic perturbation incarbon active centers, leading to the electron delocalization, which optimizes the OOH* adsorption during the catalytic process.

Highly Sensitive Diethylamine Detection at Room Temperature Using g-C3N4 Nanosheets Decorated with CuO Hollow Polyhedral Structures.

Chemiresistive-based metal oxide semiconductor (MOS) gas sensors are widely used in gas sensing due to their advantageous properties. Graphitic carbon nitride (g-C3N4) and metal oxide heterostructure materials can improve charge transport properties, selectivity, and sensitivity in MOS gas sensor materials. Herein, for the first time, CuO hollow polyhedral structures (HPSs) were synthesized via a hydrothermal technique and annealed at different temperatures, with the 400 °C annealed (CuO-400 HPSs) demonstrating remarkable sensing capabilities for diethylamine (DEA) gas at room temperature (RT). The x-g-C3N4 nanosheets were decorated with CuO HPSs in varying amounts (x = 0.8, 1.8, 2.1, and 3.1 wt %) and then annealed at 400 °C for x-g-C3N4-CuO-400 hollow polyhedral heterostructures (HPHSs). Indeed, among the synthesized samples, the 1.8%-g-C3N4-CuO-400 HPHSs have a higher sensitivity to DEA (resistance change in gas (Rg) and air (Ra); Rg/Ra= 65 @ 20 ppm), a low detection limit (Rg/Ra= 6 @ 500 ppb), wide dynamic response (Rg/Ra= 190 @ 80 ppm), strong stability (30 days), and 21.6 times higher sensitivity than pure CuO at RT toward 20 ppm of DEA. The exceptional gas-sensing behavior can be attributed to various factors, including controlled annealing conditions that result in the formation of well-defined structures and greater porosity, efficient charge transfer properties resulting from an optimized ratio of g-C3N4 to CuO in HPHSs, an abundance of defects, unsaturated Cu sites, and synergistic effects. The study presents a universal strategy for generating sensitive and selective g-C3N4-based composite materials for low-temperature gas sensors.

Fabrication of spinel SrBi2O4 nanomaterials anchored on g-C3N4 nanosheets with enhanced performance of electrode material for energy storage application

Graphitic carbon nitride (g-C3N4) material with a similar structural phase to graphite opens new opportunities in energy conversion storage systems. The g-C3N4 sheets offered many defected sites that enhanced the adsorption and diffusion of electrolyte ions. High nitrogen concentration in g-C3N4 was ideal for increasing the binding energy between metals and carbon. The stability of pseudo-active metal oxides/chalcogenides supported by carbon results in improved capacitive performance. This study used a hydrothermal route to fabricate binary SrBi2O4/g-C3N4 composite onto g-C3N4 sheets. The SrBi2O4/g-C3N4 nanocomposite was characterized through various techniques including different analytical analyses. Among all evaluated electrodes for the electrochemical experiment binary composite SrBi2O4/g-C3N4 demonstrated the highest electrochemical activity and showed the capacitive of 777.2 F g−1 at 1 A g−1. Moreover, binary composite SrBi2O4/g-C3N4 was shown to have a lesser charge transfer resistance (Rct) of 0.87 Ω as compared to other bare fabricated materials. The exceptional electrochemical capability of SrBi2O4/g-C3N4 can be due to the combined effect of SrBi2O4 and g-C3N4 which included various redox state enhanced electrode wettability and superior structural and chemical stability. The composite material shows excellent power and high energy density of 319.95 W Kg−1 and 44.20 Wh Kg−1. Based on the findings our study suggested a practical approach to fabricated hybrid electrode materials that have optimum properties for use in energy storage devices in future supercapacitors.

Enhancing the Photoluminescence and Electroluminescence of Graphitic Carbon Nitride via Atomic and Molecular Co-modification.

Graphitic carbon nitride (g-CN) materials exhibit attractive optoelectronic physical properties; however, their low photoluminescence quantum yields (PLQYs) limit their applications in luminescent devices. Here, boron-doped aromatic carbon nitride (B-PhCNx) was synthesized for the first time via direct thermal polymerization of 2,4-diamino-6-phenyl-1,3,5-triazine and boric acid. The impact of B doping and phenyl modifying on the structural and optical characteristics of the samples was investigated in detail. The highest PLQY of 40.7% was achieved in B-PhCN20, which is 6.8 times that of pristine carbon nitride (p-CN). The B-PhCN20-based light-emitting diode demonstrates a maximum luminance of 1494 cd m-2 and a maximum external quantum efficiency of 1.03%, which are 3.5 and 4.9 times that of the p-CN-based device, respectively. Our findings will provide a reference for rationally designing low-cost and high-performance carbon-nitride-based optoelectronic devices.

Enhanced conversion from H2O2 to 1O2 on Cu–N centers: Investigation of mechanisms and application in alkaline wastewater treatment

Heterogeneous Fenton-like systems using H2O2 as an oxidant have been extensively investigated in acidic and neutral conditions, but usually, they become ineffective under alkaline conditions. In this study, a cuprous graphitic carbon nitride material (Cu–CN) was prepared that can generate singlet oxygen (1O2) from H2O2. The results demonstrate that at pH 11, 95 % of 50 mg/L p-chlorophenol (4-CP) can be effectively eliminated within 120 min. Through semi-quantitative analysis and density functional theory calculations, it has been confirmed that 1O2 is the dominant reactive oxygen species in this system under alkaline conditions. The main pathway for 1O2 generation involves the formation of a complex between ·O2– and Cu(II)-N sites, and the subsequent intramolecular electron transfer. To enhance the stability and separation performance of this catalyst, polyethylene glycol (PEG) was employed as a binder to combine Cu–CN with Fe3O4. The terminal hydroxyl groups in PEG were cross-liked by metals, thus forming a solid and magnetic composite (CuFe@PEG). Compared to Cu–CN, CuFe@PEG exhibited remarkable performance with 93 % retention of its original capacity for 4-CP removal at pH 11. Furthermore, after seven cycles, the degradation efficiency only decreased by 6.36 %. This study introduces a novel approach for utilizing Fenton-like reactions in treating alkaline wastewater.

Efficient Strategies to Use β-Cationic Porphyrin-Imidazolium Derivatives in the Photoinactivation of Methicillin-Resistant Staphylococcus aureus.

Bacterial resistance to antibiotics is a critical global health issue and the development of alternatives to conventional antibiotics is of the upmost relevance. Antimicrobial photodynamic therapy (aPDT) is considered a promising and innovative approach for the photoinactivation of microorganisms, particularly in cases where traditional antibiotics may be less effective due to resistance or other limitations. In this study, two β-modified monocharged porphyrin-imidazolium derivatives were efficiently incorporated into polyvinylpyrrolidone (PVP) formulations and supported into graphitic carbon nitride materials. Both porphyrin-imidazolium derivatives displayed remarkable photostability and the ability to generate cytotoxic singlet oxygen. These properties, which have an important impact on achieving an efficient photodynamic effect, were not compromised after incorporation/immobilization. The prepared PVP-porphyrin formulations and the graphitic carbon nitride-based materials displayed excellent performance as photosensitizers to photoinactivate methicillin-resistant Staphylococcus aureus (MRSA) (99.9999% of bacteria) throughout the antimicrobial photodynamic therapy. In each matrix, the most rapid action against S. aureus was observed when using PS 2. The PVP-2 formulation needed 10 min of exposure to white light at 5.0 µm, while the graphitic carbon nitride hybrid GCNM-2 required 20 min at 25.0 µm to achieve a similar level of response. These findings suggest the potential of graphitic carbon nitride-porphyrinic hybrids to be used in the environmental or clinical fields, avoiding the use of organic solvents, and might allow for their recovery after treatment, improving their applicability for bacteria photoinactivation.

Atomic Cu Sites Engineering Enables Efficient CO2 Electroreduction to Methane with High CH4/C2H4 Ratio

HighlightsThe Cu-doped graphitic carbon nitride (g-C3N4) material is synthesized by an in situ thermal polymerization strategy, through which the atomic dispersion and coordination structure of Cu on g-C3N4 are realized by regulating the doping level of Cu.High Faraday efficiency of CH4 of 49.04% and a maximum CH4/C2H4 ratio up to 35.03 are achieved for the first time on g-C3N4-supported Cu single-atom catalyst.Structure–activity relationship analysis based on experimental and theoretical studies demonstrates the well-defined Cu single atoms coordinated with N atoms in the nitrogen cavity of g-C3N4 are active sites for CO2-to-CH4.

Long-Term Characterization of Oxidation Processes in Graphitic Carbon Nitride Photocatalyst Materials via Electron Paramagnetic Resonance Spectroscopy.

Graphitic carbon nitride (gCN) materials have been shown to efficiently perform light-induced water splitting, carbon dioxide reduction, and environmental remediation in a cost-effective way. However, gCN suffers from rapid charge-carrier recombination, inefficient light absorption, and poor long-term stability which greatly hinders photocatalytic performance. To determine the underlying catalytic mechanisms and overall contributions that will improve performance, the electronic structure of gCN materials has been investigated using electron paramagnetic resonance (EPR) spectroscopy. Through lineshape analysis and relaxation behavior, evidence of two independent spin species were determined to be present in catalytically active gCN materials. These two contributions to the total lineshape respond independently to light exposure such that the previously established catalytically active spin system remains responsive while the newly observed, superimposed EPR signal is not increased during exposure to light. The time dependence of these two peaks present in gCN EPR spectra recorded sequentially in air over several months demonstrates a steady change in the electronic structure of the gCN framework over time. This light-independent, slowly evolving additional spin center is demonstrated to be the result of oxidative processes occurring as a result of exposure to the environment and is confirmed by forced oxidation experiments. This oxidized gCN exhibits lower H2 production rates and indicates quenching of the overall gCN catalytic activity over longer reaction times. A general model for the newly generated spin centers is given and strategies for the alleviation of oxidative products within the gCN framework are discussed in the context of improving photocatalytic activity over extended durations as required for future functional photocatalytic device development.

Towards a high-performance anode for zinc metal batteries: A tri-functional nitrogen-defective graphitic carbon nitride material for anode protection

As an important potential candidate for large-scale energy storage, rechargeable zinc metal batteries have become a research hotspot. Zn metal anodes are an extremely crucial component of rechargeable Zn metal batteries. However, the Zn dendrites, the evolution of hydrogen and side reactions on the surface of the Zn metal anodes severely hinder its commercial use. Here, we report a modified Zn metal anode with a layer of nitrogen-defective graphitic carbon nitride (NDCN) nanosheets coated onto a commercial Zn foil by a simple spraying method. The NDCN coating on the anode’s surface not only provides zincophilic sites, but also drives the deposition of zinc with a particular crystallographic orientation. At the same time, the formation of zinc dendrites and the evolution of hydrogen were suppressed, which enhanced the reversibility of the anode. Thus, the symmetric cells with the NDCN-protected zinc foil (NDCN@Zn) electrodes remained stable for 2000 h at a current density of 5 mA cm−2. More importantly, the long-term cycling performance of the full cell tested at 1 A g−1 retained approximately 88 % of its capacity even after 2300 cycles. This simple but effective method will provide a reference for future studies on protecting the anodes of zinc metal batteries.

Solvent‐free selective oxidation of ethylbenzene with molecular oxygen catalyzed by cobalt catalysts supported on exfoliated carbon nitride

AbstractExfoliated graphitic carbon nitride (eg‐C3N4) material was applied as a support to load cobalt catalysts (CoOx/eg‐C3N4) through a simple impregnation method. The physical and chemical properties of the synthesized CoOx/eg‐C3N4 materials were characterized by a series of analytic techniques including XRD, SEM, FT‐IR, UV–vis, and XPS. The characterization results revealed that the introduction of Co2+ species had not altered the graphitic structure of eg‐C3N4. The Co2+ species probably coordinatively interact with the nitrogen‐containing group of eg‐C3N4. The catalytic performances of the CoOx/eg‐C3N4 were evaluated in the solvent‐free selective oxidation of ethylbenzene (EB) using molecular oxygen as an oxidant. Among the 3CoOx/eg‐C3N4 materials with various preparation temperatures, 3CoOx/eg‐C3N4‐400 exhibited the highest EB conversion, which was owing to its superior percentages of Co2+ and tertiary nitrogen species.

Synthesis of 3‐Arylquinoxalin‐2(1H)‐ones under Visible‐Light Irradiation with Oxygen‐Doped Carbon Nitride as Heterogenous Photocatalyst

AbstractA novel oxygen‐doped graphitic carbon nitride (OCN) material was designed and synthesized via the hydrothermal‐calcination method with melamine and hydroperoxide as starting materials. The OCN material was utilized as a highly efficient solid metal‐free photocatalyst for the synthesis of 3‐arylquinoxalin‐2(1H)‐ones via the catalytic decomposition of aryl diazonium salts under blue light irradiation. Following this approach, various 3‐arylquinoxalin‐2(1H)‐one derivatives could be obtained in moderate to excellent yields with broad substrate scope under mild conditions. Also, the OCN solid photocatalyst shows good recyclability in the reaction, there was no appreciable loss in yields observed even after 5 cycles. This methodology offers a practical, mild, and metal‐free alternative to the preparation of 3‐arylquinoxalin‐2(1H)‐ones.

3D structured photocatalysts for sustainable H2O2 generation from saccharides derivatives

The possibility of using hydrogen peroxide (H2O2) as a chemical oxidizer or as a green liquid fuel to produce electricity has encouraged both the scientific and industrial communities to investigate green technologies aimed at the sustainability of the production process. In particular, the light-induced synthesis of H2O2 from water and oxygen has attracted significant attention using optical semiconductors.An exfoliated metal-free graphitic carbon nitride material (GCN-T) was prepared and tested for the photocatalytic production of H2O2 using five saccharides (arabinose, cellobiose, fructose, glucose, and sorbitol) as sacrificial electron donors. The results showed that the scavenging efficiency of the photogenerated holes rapidly increases with the number of –OH groups in the molecular structure of these sacrificial agents. Among the polyhydroxy compounds tested, the highest concentration of H2O2 was achieved using cellobiose.To develop a technological approach for H2O2 production, the GCN-T photocatalyst was immobilized on a 3D printed structure (GCN-T/3D structure), which showed high stability with both ultrapure water and seawater after several reusability runs. This innovative photocatalytic structure enables remarkable efficiency for H2O2 production, with an apparent quantum efficiency (AQE) of 17% at 412 nm radiation, compared to 12% obtained with GCN-T in suspension.

Porous graphitic carbon nitride nanosheets with three-dimensional interconnected network as electrode for supercapacitors

Graphitic carbon nitride material with hierarchical porous structure and high doping level has been reported to exhibit superior capacitive properties due to the facilitated electrolyte migration and redox process. In this work, porous graphitic carbon nitride layers (UMCN-A1.25) with typical three-dimensional (3D) network were prepared through a facile calcination process. For its preparation, NH4HCO3 was used as the pore generator and glucose was used as the carbon precursor. Urea and melamine, which worked as the binary precursors for sacrificial template, played important roles in the formation of the final 3D interconnected structure. The hierarchical pore structure and high nitrogen-doping level endow UMCN-A1.25 with high specific capacitances (520 F g−1 at 0.1 A g−1 and 219.4 F g−1 at 20 A g−1) and stable charge-discharge behavior with no capacitance declination after 10,000 cyclic tests. This work proposed an efficient route for the construction of inter-connected carbon nitride layers, and also revealed the importance of both lamellar morphology and interwoven structure for the acquisition of high capacitive properties.

Investigation of structural, optical and thermal properties of TiO2 reinforced g-C3N4 nanocomposite for emissive layer application

TiO2 incorporated graphitic carbon nitride (g-C3N4) material have sought huge attention in the field of optoelectronic applications. Pristine g-C3N4 and g-TiO2 nanocomposite were prepared via one step calcination method. The nanocomposite formation was confirmed by X-ray diffraction (XRD) and Raman analysis. The uniform distribution of the TiO2 nanoparticles in g-C3N4 was confirmed by Field Emission Scanning Electron Microscope (FESEM). Elemental analysis (C, N, Ti, O) was done by Energy Dispersive X-ray Spectroscopy (EDS). UV–VIS analysis was done to calculate the optical band gap of the nanocomposites. Direct optical band gaps were calculated as 2.85, 3.42 and 2.94 eV for g-C3N4, TiO2 and g-TiO2 nanocomposite, respectively. Photoluminescence intensity was enhanced in g-TiO2 nanocomposite compare to pure g-C3N4 which indicated that the rate of electron-hole (e--h+) recombination in nanocomposite was increased. Thermogravimetric analysis (TGA) was done to investigate the thermal stability of the nanocomposite. After incorporation of TiO2 into the g-C3N4, thermal stability of the nanocomposite was improved. These improved results suggest that nanocomposite is suitable material for an emissive layer in optoelectronic device application.

Rapid chemical vapor deposition of graphitic carbon nitride films

Rapid chemical vapor deposition of continuous thin films of graphitic carbon nitride (g-CN) material with stoichiometry close to its ideal g-C3N4 form on silicon and glass substrates is demonstrated. It allows fabrication of 200–1200 nm g-CN films within 3–5 min at 500–620 °C instead of earlier reported few hours. SEM, XRD and EDX analysis of the films revealed their grain-layered structure and high crystallinity. The film thickness and crystallinity were found to have maximum at synthesis temperature of 575–600 °C. Energy band gap of the material changes with the deposition temperature too and reaches its maximum of 2.98 eV at 600 °C. Dependence of the film properties on the deposition temperature evidences competition between the rates of synthesis and evaporation of the synthesized material. The developed approach is energy budget saving and could be scaled up using conventional rapid thermal processing equipment opening a way to practical g-CN based electronics and optoelectronics.

Excited‐state nonadiabatic dynamics simulations on the heptazine and adenine in a water environment: A mini review

AbstractStudying the excited‐state decay process is crucial for materials research because what happens to the excited states determines how effective the materials are for many applications, such as photoluminescence and photocatalysis. The high computational cost, however, limits the use of high‐accuracy theoretical approaches for analyzing research systems containing a significant number of atoms. Time‐dependent density functional theory is a practical approach to investigate the photorelaxation processes in these systems, as demonstrated in the studies of the excited‐state decays of heptazine‐water clusters and adenine in water described in this review. Here, we highlight the importance of conical intersections in the excited‐state decay processes of these systems using the aforementioned examples. In the heptazine‐water and adenine‐water systems, these intersections are associated with the photocatalytic water splitting reaction, caused by a barrierless reaction called water to adenine electron‐driven proton transfer. We expect the result would be helpful for researching the excited‐state decays of graphitic carbon nitride materials and DNA nucleotides.

Preparation and characterization of Ce-MOF/g-C3N4 composites and evaluation of their photocatalytic performance

In this study, unique hybrid structures were constructed between a Ce-based metal-organic framework (Ce-MOF) and graphitic carbon nitride (g-C3N4) materials. In addition, the g-C3N4 materials used for these heterostructures were prepared by five different methods, namely the conventional pyrolysis method, chemical exfoliation by a strong acid, activation by an alkaline hydrothermal treatment, melamine-cyanuric acid supramolecular assembly with a mechanochemical method, and by the solvothermally pre-treated method. The structural and morphological properties of the resulting g-C3N4 sheets and their composites were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis-derivative thermogravimetry (TGA-DTG), diffuse reflectance UV–vis spectroscopy (UV–vis DRS) and N2 sorption-desorption isotherms (BET). Finally, the photocatalytic performance of the composites was determined by following the photocatalytic degradation of methylene blue (MB) in an aqueous solution under UV–visible light irradiation. It was found that the photocatalytic efficiency of the Ce-MOF/g-C3N4‒TS composite was significantly higher than that of their counterparts (Ce-MOF or g-C3N4‒TS) for the photocatalytic degradation of MB. When employing the composite, UV light-induced degradation of MB yielded an efficiency of 96.5% after 120 min for a dye solution containing 10 mg/L MB. This corresponds to a 5-fold or 2-fold improvement of the rate constant (k) when compared to the Ce-MOF or g-C3N4, respectively.

Functionalized Graphitic Carbon Nitrides for Photocatalytic H<sub>2</sub>O<sub>2</sub> Production: Desired Properties Leading to Rational Catalyst Design

Photocatalytic H2O2 production based on graphitic carbon nitride (g-C3N4) materials has been attracting increasing attention. However, it is difficult to reveal the inner relationships among the structure, properties and performance of a g-C3N4-based photocatalyst by simply summarizing preparation methods, properties and performances in previous works. In this review, the three most important issues for improving H2O2 generation based on the band diagram and physicochemical properties of pristine g-C3N4 are proposed. Improvement of the charge separation, promotion of the light absorption and introduction of active sites for 2e− oxygen reduction reaction to suppress side reactions are the most three attractive strategies for enhancing the activities. Following discussion of these strategies, representative functionalization methods are summarized on the basis of the most desired properties for improving the photocatalytic activities for H2O2 production. Other influence factors for improving H2O2 production such as addition of electron donors and adjustment of pH value of the solution are also discussed. Future challenges for photocatalytic H2O2 based on g-C3N4 materials are also summarized to provide future directions in this field.

Graphitic carbon nitride materials in dual metallo-photocatalysis: a promising concept in organic synthesis

Discussion of the recent reports on dual metallo-photocatalytic strategies using graphitic carbon nitride materials in organic syntheses.