Polymeric Graphitic Carbon Nitride Research Articles

Metal Doped-C3N4/Fe2O4: Efficient and Versatile Heterogenous Catalysts for Organic Transformations

The polymeric graphitic carbon nitride (g-C3N4) has been one of the interesting earth abundant elements. Though g-C3N4 finds application as a photocatalyst, its photocatalytic behaviour is limited because of low efficiency, mainly due to rapid charge recombination. To overcome this problem, several strategies have been developed including doping of metal/non-metal in the cavity of g-C3N4. Moreover, the CoFe2O4 NPs have been used in many organic transformations because of its high surface area and easy separation due to its magnetic nature. This review describes the role of cobalt ferrite as magnetic nanoparticles and metal-doped carbon nitride as efficient heterogeneous catalysts for new carbon-carbon and carbon-hetero atom bond formation followed by heterocyclization. Reactions which involved new catalysts for selective activation of readily available substrates has been reported herein. Since nanoparticles enhance the reactivity of catalyst due to higher catalytic area, they have been employed in various reactions such as addition reaction, C-H activation reaction, coupling reaction, cyclo-addition reaction, multi-component reaction, ring-opening reaction, oxidation reaction and reduction reactions etc. The driving force for choosing this topic is based-on huge number of good publications including different types of spinels/metal doped-/graphitic carbon nitride reported in the literature and due to interest of synthetic community in recent years. This review certainly will represent the present status in organic transformation and for exploring further their catalytic efficiency to new organic transformations involving C-H activation reaction through coupling, cyclo-addition, multi-component, ring-opening, oxidation and reduction reactions.

Incorporating p-Phenylene as an Electron-Donating Group into Graphitic Carbon Nitride for Efficient Charge Separation.

Low charge-separation transport efficiency resulting from structural defects largely limits photocatalytic hydrogen production over polymeric graphitic carbon nitride (PCN) photocatalyst. Herein, an electron-donating group, namely p-phenylene, is incorporated into PCN by a polycondensation reaction between carbon nitride and p-phenylenediamine (or p-benzoquinone) to repair the structural defects. The p-phenylene-modified PCN exhibits an almost fivefold increase in H2 evolution, a threefold increase in photocurrent density, and higher nonradiative rate (0.285 ns-1 ). Spectroscopic studies confirm that p-phenylene tends to bridge the heptazine-based oligomers through a polycondensation reaction. Theoretical calculations reveal that anchoring of the heptazine units by p-phenylene induces localization of h+ and e- on the phenylene and melem moieties, respectively, which effectively separates the charge carriers. This strategy provides an opportunity to overcome structural defects in carbon nitride for efficient photocatalytic solar energy conversion.

CsPbBrCl2/g-C3N4 type II heterojunction as efficient visible range photocatalyst.

Photocatalytic activity of low band gap semiconductor largely restrained by high recombination rate of photogenerated charge carriers. To enhance the catalytic performance numerous protocols were adopted amongst which designing of novel hybrid via coupling of semiconductors are very intriguing from modest application point of view. Here, we report facile realization of type II heterojunctions embracing polymeric graphitic carbon nitride (g-C3N4/GCN) and all-inorganic cesium lead halide perovskite (CsPbBrCl2) for degradation complex organic effluents under visible-light illumination. Synthesized hybrid presented much improved performance in toxic cationic and anionic dyes degradation as compared to individual building units. Signature of favorable staggered gap junction's formation at interface was confirmed via Mott-Schottky analysis. Such kind of junctions delay the recombination of photogenerated electron holes and facilitates active radical generation at catalyst surface thereby ensures improved photocatalytic performance. Charge transfer process in heterojunction further illustrated via Density functional theory (DFT) based calculations. Several scavenger tests have been performed to examine the impact of different active radicals in the photocatalysis which suggests manifold performance improvement in the presence of very small concentrations of EDTA. A plausible photocatalytic mechanism in accordance with the type II junction has been proposed.

Boosting exciton dissociation and molecular oxygen activation by in-plane grafting nitrogen-doped carbon nanosheets to graphitic carbon nitride for enhanced photocatalytic performance

The metal-free graphitic carbon nitride (g-C3N4) polymer is a promising photocatalyst for energy production and environmental protection. However, attempts to intrinsically improve its low activity in photooxidation are rarely effective for the poor molecular oxygen (O2) activation. Here we report a synthesis of directionally nitrogen-doped in-plane metal-free heterostructure, through coplanar grafting nitrogen-doped carbon nanosheets (NDCN) to g-C3N4. The in-plane grafted NDCN not only promoted exciton dissociation and charge transfer but also enhanced activating O2 to reactive oxygen species, including superoxide radicals (O2−) and H2O2. The optimal C3N4-NDCN coplanar heterojunction (C3N4-NDCN-3) photocatalytically degraded 96.3% of sulfamethoxazole (SMX) under visible light irradiation at a low light intensity of 14.5 mW cm−2 in 4 h, whose SMX degradation rate was 37.7-fold higher than that of pure g-C3N4. Furthermore, C3N4-NDCN-3 exhibited 95.3% removal of SMX under sunlight irradiation (59.8 mW cm−2) in 1 h, higher than the 58.0% of pristine g-C3N4. First-principles calculations and material characterizations demonstrated that the coplanar NDCN served as electron sink and catalytic center for hot-electron involved O2 activation. The improved charge carrier separation and O2 activation promoted generation of photoexcited hole and superoxide for photocatalytic degradation of SMX. The design strategy in this work inspires a new approach for high-performance polymer photocatalysts in solar energy storage and environmental remediation.

Shape-controlled assemblies of graphitic carbon nitride polymer for efficient sterilization therapies of water microbial contamination via 2D g-C3N4 under visible light illumination.

Bacterial pathogens of water origin have potential public threats thus suggesting the need of developing efficient and sustainable water disinfection strategies from waterborne pathogens. We set out to synthesize different controlled morphologies of graphitic carbon nitride (g-C3N4) polymer, evaluate their comparative effects on the generation of reactive oxygen species (ROS), and investigate potential applications in water purification systems. Characterization of the synthesized microstructures of g-C3N4, such as melamine-cyanuric acid (MCA)-based rosette-type, rod-type, 2D hexagonal, and 3D cubic mesoporous silica was accomplished using Fourier transform infrared (FT-IR), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffractometry (XRD), and transmission electron microscopy (TEM). The microbial inhibitory potential of 2D g-C3N4 photocatalyst against waterborne Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium was evaluated based on the effective activity of 2D g-C3N4 upon visible light excitations. The microbicidal efficiency of 2D g-C3N4 was evident within 30 min of visible light exposure via direct interaction, while other microstructures of g-C3N4 demonstrated only slight antimicrobial effects after 120 min, with insufficient ROS generation. The antimicrobial and ROS-generating effects of 2D g-C3N4 depended on the type and surface area of the synthesized 2D g-C3N4 material. Considering its availability and excellent disinfection activity, 2D g-C3N4 obtained from simple and convenient facile synthesis is a promising solar-driven photocatalyst for clearing microbial contamination from water.

Doping-Induced Hydrogen-Bond Engineering in Polymeric Carbon Nitride To Significantly Boost the Photocatalytic H2 Evolution Performance.

Unlike graphene, graphitic carbon nitride (CN) polymer contains a weak hydrogen bond and van der Waals (vdWs) interactions besides a strong covalent bond, which controls its final morphology and functionality. Herein, we propose a novel strategy, hydrogen-bond engineering, to tune hydrogen bonds in polymeric CN through nonmetal codoping. Incorporation of B and P dopants breaks partial hydrogen bonds within the layers and simultaneously weakens the vdWs interaction between neighboring layers, resulting in ultrathin codoped CN nanosheets. The two-dimensional structure of the ultrathin sheet, broken hydrogen bonds, and incorporated dopants endow them with efficient visible light harvesting, improved charge separation, and increased active edge sites that synergistically enhance the photocatalytic activity of doped CN. Specifically, the B/P-codoped CN exhibits an extremely high hydrogen-evolution rate of 10877.40 μmol h-1 g-1, much higher than most reported values of CN. This work demonstrates that hydrogen bond engineering is an effective strategy to modify the structure and properties of polymers for various applications.

Protonated supramolecular complex-induced porous graphitic carbon nitride nanosheets as bifunctional catalyst for water oxidation and organic pollutant degradation

Polymeric graphitic carbon nitride (g-C3N4) materials are promising catalysts to compete with precious metals, but they mostly only show moderate catalytic activity, particularly low oxidation power for oxygen evolution reaction (OER). Although activating strategies, such as nanostructure designing and band structure engineering, have led to remarkable activity gains, there remains considerable room to improve performance that aims for real applications. We report here a novel strategy—protonating supramolecular aggregates followed by thermal polycondensation—to prepare porous g-C3N4 nanosheets (SH-g-C3N4) with high oxidation power, which employ as bifunctional OER catalyst and highly efficient photocatalyst material. The OER onset potentials of 1.47 V and Tafel slope of 128 mV dec−1 over SH-g-C3N4 are superior to the g-C3N4 obtained from supramolecular aggregates without protonation (S-g-C3N4). Furthermore, its Tafel slope would be reduced to 63.6 mV dec−1 under visible light irradiation, which is comparable to that of the active commercial RuO2 and IrO2 catalysts. Interestingly, the achieved nanosheets display enhanced visible light photocatalytic activity. The striking catalysis performance of SH-g-C3N4 can be ascribed to the unique advantage of its highly porous structure and favorable electronic structure and the generation of lots of ·O 2 − and ·OH radicals promoting the kinetic process. Our theoretical calculations reveal the mechanism of photoelectric catalyst for oxygen evolution reaction. This work provides a facile and scalable method to design highly efficient polymeric catalysts.

In situ reduction and exfoliation of g-C3N4 nanosheets with copious active sites via a thermal approach for effective water splitting

Poor optical absorbance and charge recombination are the major drawbacks of polymeric graphitic carbon nitride (g-C3N4)-based photocatalysts.

Semiconductor polymeric graphitic carbon nitride photocatalysts: the “holy grail” for the photocatalytic hydrogen evolution reaction under visible light

Graphitic carbon nitrides and their composites with various morphologies and bandgaps engineered for the hydrogen evolution reaction under visible light are reviewed.

Porous graphitic carbon nitride with lamellar structure: Facile synthesis via in-site supramolecular self-assembly in alkaline solutions and superior photocatalytic activity

The development of highly active photocatalysts is the primary goal in the field of photocatalysis. We herein first develop a facile and scale up approach to synthesize porous polymeric graphitic carbon nitride (g-C3N4) with lamellar structure through thermal polycondensation of supramolecular aggregates. The feature of this approach lies in the directed in-situ self-assembly of cyanuric acid molecules, converted from the hydrolysis of melamine in NaOH solution, with the residual melamine molecules to form supramolecular aggregates, which lead to the formation of porous g-C3N4 with lamellar structure. The synthesized lamellar g-C3N4 exhibit superior photocatalytic activity as demonstrated by the complete degradation of methylene blue (MB) under one hour’s visible light irradiation, as well as excellent stability with high activity retained after four runs of MB degradation testing. The enhancement in photocatalytic performance can be attributed to its unique lamellar structure with high surface area, narrow bandgap, and efficient separation of photogenerated electron-hole pairs. This work shows that the alkaline solutions can be used as the molecular self-assembly medium and opens a new avenue towards designing highly active g-C3N4-based photocatalyts for energy and environmental applications.

The role of g-C3N4 as nanofiller in improvement of mechanical, thermal, and X-band wave absorption properties of epoxy vinyl ester coating

The present work has been focused on the development of nanocomposites based on epoxy vinyl ester (EVE) matrix and some kinds of polymeric graphitic carbon nitride (g-C3N4) as a reinforcing agent. At first, the obtained solids were characterized by X-ray diffraction analyzer (XRD) and scanning electron microscope (SEM). Then, water absorption properties and mechanical properties for nanocomposites consist of g-C3N4 nanosheets were investigated. The results showed that the most appropriate amount of nanofiller (NF) (i.e., g-C3N4 nanosheets (CN-500)) is 0.5%wt. Then, the comparison between neat EVE and nanocomposites consist of CN-500 (0.5%wt) was studied by Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA), and the results showed that the thermal properties had been improved. The effects of embedment (dope process) with atoms like sulfur, chlorine, phosphorus, Fe3+ ion and couple with Fe3O4 was investigated by the vector network analyzer. Data analysis indicated that among the prepared nanocomposites with 0.5%wt of NFs, the phosphorus-doped g-C3N4 (PCN) sample (with 2 mm thickness) reflection loss (RL) spectrum is less than -10 dB (absorption >90%) at the frequency range of 8–12 GHz (X-band). Also, the area under the RL curve for the best nanocomposite sample was calculated 67.42 GHz.dB, and it was suggested that PCN could be a good candidate for microwave (MW) absorption purposes. Also, this sample has shown interesting results in the tensile strength test which makes it an appropriate choice for using it as rigid coating with MW absorption ability.

Cyano group modified carbon nitride with enhanced photoactivity for selective oxidation of benzylamine

Polymeric graphitic carbon nitride (g-C3N4) is a promising photocatalyst but suffers from the high recombination rate of photogenerated carriers. Many strategies for introducing active “sites”, such as heteroatom doping and defect creation, which can hinder recombination by capturing the separated electrons or holes, have been developed to solve the problem. As a polymeric organic material, it is possible to alter the electron structure and improve the charge separation by introducing organic groups with different electronegativities or conjugation properties to the side chains. Herein, we report a facile and efficient CN group modification strategy using the thermal condensation of the thiocyanuric acid (TA) precursor. The sulfur content in the precursor forms CNS and then transforms to CN. The CN group introduced catalyst exhibits enhanced light absorption and a low carrier recombination rate based on optical and photoelectrical measurements. This is due to the formation of a CN group related midgap state between the bandgap of g-C3N4, according to a density functional theory (DFT) calculation. The CN groups can also loosen the stacking texture of g-C3N4 and result in a thinner layer structure during the post-thermal treatment, which can shorten the distance of photogenerated carrier transfer from the bulk to the surface. The CN group introduced photocatalyst is efficient for the selective oxidation of benzylamine to imine, even under green light irradiation. This result demonstrates that the introduction of an electron rich conjugation group such as CN into the edge chain of polymeric carbon nitride is efficient for better photoactivity.

Vertically Aligned Porous Organic Semiconductor Nanorod Array Photoanodes for Efficient Charge Utilization

Because of inefficient charge utilization caused bylocalizedπ-electron conjugation and large exciton binding energy, the photoelectrochemical water-splitting efficiency of organic polymers is seriously limited. Taking the graphitic carbon nitride (g-CN) polymer as an example, we report a novel photoanode based on a vertically aligned g-CN porous nanorod (PNR) array prepared in situ, using a thermal polycondensation approach, with anodic aluminum oxide as the template. The g-CN PNR array exhibits an excellent photocurrent density of 120.5 μA cm-2 at 1.23 VRHE under one sun illumination, the highest reported incident photon-to-current efficiency of ∼15% at 360 nm, and an outstanding oxygen evolution reaction stability in 0.1 M Na2SO4 aqueous solution, which constitutes a benchmark performance among the reported g-CN-based polymer photoanodes without any sacrificial reagents. When compared with its planar counterpart, the enhanced performance of the PNR array results principally from its unique structure that enables a high degree of aromatic ring π-electron conjugation for higher mobility of charge carriers, provides a direct pathway for the electron transport to the substrate, produces a large portion of hole-accepting defect sites and space charge region to promote exciton dissociation, and also withstands more strain at the interface to ensure intimate contact with the substrate. This work opens a new avenue to develop nanostructured organic semiconductors for large-scale application of solar energy conversion devices.

A new bifunctional nanostructure based on Two-Dimensional nanolayered of Co(OH)2 exfoliated graphitic carbon nitride as a high performance enzyme-less glucose sensor: Impedimetric and amperometric detection

A novel non-enzymatic glucose sensor was constructed based on the nanolayered Co(OH)2 deposited on polymeric graphitic carbon nitride (Co(OH)2-g-C3N4) via chemical bath deposition. The two-dimensional nanocomposite was used to modify a carbon paste electrode and its electrochemical performance of electrode was carefully evaluated. The electrochemical oxidation of glucose at modified electrode was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in 0.2 M KOH. It revealed a remarkable electrocatalytic behavior and noticeably synergistic effect as a result of decent exfoliation of graphitic carbon nitride in the presence of Co(OH)2. The amperometric response achieved by the modified electrode showed two calibration ranges with an excellent selectivity. A single-frequency impedance method was applied for glucose determination as an alternative to conventional EIS methods. The developed sensor represents a high sensitivity, wide concentration range (25 μM - 420.0 mM by impedimetry and 6.6–9800 μM by amperometry), and high reproducibility. The modified electrode showed a good selectivity for glucose over potentially interfering materials such as dopamine, ascorbic acid, urea, and uric acid. Finally, the Co(OH)2-g-C3N4-CPE was utilized for quantification of glucose in blood serum samples.

Polymeric graphitic carbon nitride–barium titanate nanocomposites with different content ratios: a comparative investigation on dielectric and optical properties

Absorption capability of barium titanate (BaTiO3) was enhanced by coupling it with graphitic carbon nitride (g-C3N4) a polymeric semiconducting material. g-C3N4–BaTiO3 nanocomposite was prepared with different weight percentage of g-C3N4 (3–18%) by simple solution method and was further characterized for analysing the properties of prepared material like structural and morphological properties were examined utilizing scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and FTIR spectroscopy. Photoluminescence and UV–Vis spectrophotometers were used for studying the optical properties and impedance analyser was used for measuring the dielectric constant, loss factor and charge transfer resistance. From the optical and dielectric studies we can predict that absorption was slightly enhanced toward visible region, recombination loses were reduced and the band gap values calculated were in close approximation with the dielectric constant data. On the basis of above studies we can say that optimum concentration was 3 and 6% g-C3N4 nanocomposite.

Polymeric graphitic carbon nitride nanosheet-coated amorphous carbon supports for enhanced fuel cell electrode performance and stability

Carbon blacks, which consist of the assemblies of small graphene clusters having a spherical concentric packing structure, are amorphous and have widely been used as catalyst supports for proton exchange membrane fuel cell (PEMFC) electrodes. However, poor electrochemical corrosion resistance during extended use and repeated cyclic operation of PEMFCs shortens their practical device lifetime; surface defects, such as nanosized disordered domains, have been established as the most influential factors. Herein, we coupled polymeric graphitic carbon nitride (pg-CN) with amorphous carbon black (a-CB) in a core@shell structure to produce an electrochemically efficient and stable electrocatalyst support. Our protocol allowed for the simultaneous optimization of uniformly thin graphitic shell structures for electrochemical corrosion stability and nitrogen-enriched functionalities on the carbon surfaces for electrocatalyst (e.g., platinum) nucleation. The newly prepared a-CB@pg-CNs enhanced the stable fuel cell devices operation and remained invariant even at high potential (1.2–1.7 V). Significantly, when used for constructing the PEMFC electrode, a-CB@pg-CN support-based Pt catalyst electrodes outperformed and exhibited superior stability over state-of-the-art commercial a-CB-based counterparts. Experimental observations and density functional theory (DFT) calculations revealed that the unusual electrocatalytic properties of as-prepared a-CB@pg-CNs originated from an intrinsic chemical and electronic coupling that synergistically reduced electrochemical corrosion kinetics and promoted catalyst–support interactions.

Environmentally Sustainable Fabrication of Ag@g-C3N4 Nanostructures and Their Multifunctional Efficacy as Antibacterial Agents and Photocatalysts

Noble-metal silver (Ag) nanoparticles (NPs) anchored/decorated onto polymeric graphitic carbon nitride (g-C3N4) as nanostructures (NSs) were prepared using modest and environment-friendly synthesis method with a developed-single-strain biofilm as a reducing implement. The as-fabricated NSs were characterized using standard characterization techniques. The nanosized and uniform AgNPs were well deposited onto the sheet-like matrix of g-C3N4 and exhibited good antimicrobial activity and superior photodegradation of dyes methylene blue (MB) and rhodamine B (RhB) dyes under visible-light illumination. The Ag@g-C3N4 NSs exhibited active and effective bactericidal performance and a survival test in counter to Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. The as-fabricated NSs also exhibited superior visible-light photodegradation of MB and RhB in much less time as compared to other reports. Ag@g-C3N4 NSs (3 mM) showed superior photocatalytic measurements under visible-light irradiation: ∼1...

Facile synthesis of highly reactive and stable Fe-doped g-C3N4 composites for peroxymonosulfate activation: A novel nonradical oxidation process

Ferrous ions (Fe2+) are environmentally friendly materials but show extremely inefficient persulfate activation. Polymeric graphitic carbon nitride (g-C3N4) has recently shown potential to activate persulfates, but the process requires intense light irradiation. To overcome these drawbacks, we designed an innovative heterogeneous iron catalyst by doping Fe into g-C3N4 (Fe-g-C3N4) and used it to activate peroxymonosulfate (PMS) for degradation of pollutant phenol. The catalysts synthesized were fully characterized with various techniques, such as X-ray diffraction, Mössbauer spectroscopy, and X-ray photoelectron spectroscopy. Fe was found to be coordinated with the framework of g-C3N4. Approximately 100% degradation of phenol was achieved with Fe-g-C3N4 after 20 min of reaction, whereas less than 5% degradation of phenol was achieved with Fe2+. Fe-g-C3N4-PMS had a wide effective pH range, and its reactivity was nearly independent of natural illumination. In contrast to the previously proposed radical mechanisms, quenching experiments revealed that nonradical oxidation contributed to the observed degradation. The OO bond in the activated PMS likely underwent heterolysis, producing high-valence iron species (FeIVO) as the primary active species. These findings have important implications for the development of a selective heterogeneous nonradical-oxidation process.

Post-activation of in situ B[sbnd]F codoped g-C3N4 for enhanced photocatalytic H2 evolution

Porous graphitic carbon nitride polymer (p-CN-BF) with enhanced photoproduction of H2 from water was prepared by a two-step treatment process including in-situ Boron and fluorine codoping using [Emim]BF4 as dopants followed by post-calcination in air. Several techniques were employed to characterize the modified structure and elucidate the doping state of B and F. It was shown that in-situ doping method is necessary for efficient doping of heteroatoms into the molecular composition of CN. The difference of doping state of B and F was that B doping primary existing in the inside skeleton of CN, but F doping merely presents in the surface layer. The inside doped B made for the enhanced visible light absorption and the production of uniform porous structure during post-sintering process. By the synergistic effect of BF codoping and post-activation, p-CN-BF showed much enhanced photoelectron generation, transmission and separation, therefore, it performs high photocatalytic activity for H2 evolution (351 μmol h−1), which was 13 and 5 times higher than samples only modified by BF codoping (CN-BF) or post-annealing (P-CN).

Template-Free Synthesis of Hollow G-C3N4 Polymer with Vesicle Structure for Enhanced Photocatalytic Water Splitting

As always, layered graphitic carbon nitride (g-C3N4) polymer demonstrated importance in the field of artificial photocatalysis. Many modified works have been operated on defected g-C3N4 to improve ...