Two-dimensional Carbon Nitride Research Articles

Recent progress in synthesis and properties of two-dimensional boron carbon nitride for application in energy storage devices

Abstract Two-dimensional (2D) Boron Carbon Nitride (BCN) has recently gained significant attention as a convoluted ternary system owing to its remarkable capability to exhibit a wide range of finely tunable physical, chemical, optical, and electrical properties. In this review, we discuss a variety of stable structure forms of BCN nanosheets. In addition, this review provides recent approaches for synthesizing BCN nanostructures, and properties of BCN derivatives. BCN is a promising material for sustainable energy and energy storage devices. Since BCN application is a challenge in the field of energy, we present potential applications of BCN in the field of energy including supercapacitors and batteries, wastewater treatment, electrochemical sensing, and gas adsorption.

Monodispersed Cu sites assembled on ultrathin 2D C3N4 for efficient electrocatalytic CO2 methanation

Electrocatalytic CO2 reduction (ECO2R) to methane is a promising technology that could effectively realize carbon resource integration and energy recycling. Currently, Cu-based catalysts are the most effective catalysts for this process, and a long-term goal of high selectivity and high stability still remains elusive. In this study, a controllable and multistep solid-state pyrolysis route is implemented to successfully introduce atomically dispersed Cu sites (Cu SA) into the two-dimensional carbon nitride (2D C3N4) matrices. The active site density and morphology structure of the Cu SA-2D C3N4 catalyst could be precisely controlled by adjusting the calcination process. Through the strategic combination of an ultrathin 2D structure and uniformly dispersed active sites, the Cu SA-2D C3N4 maximizes the exposure of active sites while suppressing competitive C–C coupling reactions. Ultimately, the optimized Cu SA-2D C3N4-30 exhibit a Faradaic efficiency of 62.9 % for CO2-to-CH4 conversion with a partial current density of 172.4 mA cm−2 at −1.68 V vs. RHE. This work demonstrates an advanced Cu-based electrocatalyst that effectively improves the performance of electrocatalytic CO2 methanation.

High density cobalt single atom catalysts for H2O2 electrosynthesis: A critical design of carbon nitride skeleton

Direct hydrogen peroxide (H2O2) electrosynthesis via the two-electron oxygen reduction reaction (ORR) provides aburgeoning alternative to the industrial anthraquinone process.In this work, based on first-principles calculations and a targeted structural search, we predicted a new two-dimensional (2D) carbon nitride monolayer, PH-CN, accompanied by high mechanical stability and adequate intrinsic pyrrolic N-rich network, such remarkable merits ensure its greatpotential as substrates. Herein, we demonstrate how the coordination environment regulates the electronic structure of the Co central atom and thus steers the ORR selectivity and activity using a series of control samples based on the most prevalent CoN4 moiety. As expected, the acquired P-CoN4 and PH-CoN4 show excellent H2O2electrosynthesis performance with low thermodynamic overpotential of 0.02 and 0.07 V, as well as extremely high Co loadings of 26.28 and 27.42 wt%, respectively. This work sheds light on how the carbon nitride skeleton affects catalytic activities on Co-N-C catalysts.

Two-dimensional tetragonal carbon nitride semiconductors with fascinating electronic/optical properties and low thermal conductivity

Abstract Exploring two-dimensional (2D) tetragonal carbon nitride materials is significant for unlocking new physical properties beyond those offered by traditional hexagonal lattices. In this work, we propose three theoretically stable 2D carbon nitride monolayers with tetragonal lattices, namely T-C3N, P-C3N, and PH-C5N4. Electronic structure calculations indicate that all three monolayers exhibit semiconducting characteristics, with T-C3N showing interesting flat band features. Additionally, these three carbon nitrides exhibit anisotropic and high carrier mobilities and excellent light absorption capabilities in the visible-light and near-infrared regions. Meanwhile, the calculated thermal conductivity (κp) of PH-C5N4 is 63.9 Wm−1K−1 at room temperature, significantly outperforming T-C3N (12.2 Wm−1K−1) and P-C3N (18.9 Wm−1K−1). Phonon scattering rates and Grüneisen parameters confirm the origin for the relatively high κp in PH-C5N4. Our study proposes three tetragonal carbon nitride structures with novel physical properties, which lays a theoretical foundation for the multifunctional applications of 2D carbon nitride materials.

Single-atom nickel on defective g-C4N3 as a promising bifunctional electrocatalyst for the OER and ORR: a first-principles analysis

Searching for inexpensive and highly active materials to replace noble metals for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is an important challenge. The two-dimensional semi-metallic carbon nitride g-C4N3 is an excellent candidate for electrochemical reactions owing to its eminent conductivity and stability. Here, using density functional theory (DFT) a series of low-budget non-noble transition metal single-atom (SAC) loaded on the g-C4N3 (named as TM@C4N3, TM = Cr, Mn, Fe, Co, Ni, Cu) were investigated as electrocatalysts for OER and ORR. Ni@C4N3 shows an enormous application potential as electrode material, with OER and ORR overpotentials of 0.59 V and 0.23 V, respectively. The second lowest binding energy between Ni and support g-C4N3 indicates that Ni@C4N3 possesses good overall stability. The d-band center as well as metal valence as the descriptor exhibit good agreement with the adsorption energy of the intermediate. A linear relationship exists among the adsorption energies of the three intermediates O, OH, and OOH, given the similarity that they are all bonded to the metal through one oxygen atom. By adjusting the adsorption energy of these intermediates, the catalytic activity of electrocatalysts can be tuned for OER and ORR. This study confirmed that Ni@C4N3 is a good bifunctional catalyst and provides important guidance for the design of bifunctional electrocatalysts for OER and ORR.

Layered conjugated porous fused aromatic network structures of two-dimensional carbon nitride: a first-principles calculation of optoelectronic properties

Layered conjugated porous fused aromatic network structures of two-dimensional carbon nitride: a first-principles calculation of optoelectronic properties

Prediction of two-dimensional carbon nitride materials with semimetal states and flat bands

The search for new two-dimensional (2D) carbon nitride (CN) materials with desirable properties is an important and critical area of research. This study presents a series of 2D CN materials with appealing features such as semimetal or flat bands. By utilizing group theory and graph theory, we perform a random search of the configurational space of 2D CN monolayers, leading to the identification of 721 new CN materials. Extensive density functional theory calculations were then conducted to evaluate their properties. We found that 57 materials exhibit semimetal behavior, while 664 display characteristics of semiconductors and normal metals. Notably, materials such as 51-5-16-C3N-r568 and 55-5-20-C4N-r568 feature topological Dirac semimetals with protected 1D topological boundary states. Moreover, 31 materials possess flat bands near their Fermi level, including two with kagome-like flat bands that induce intrinsic spontaneous magnetization due to partially-occupied flat bands. Our results offer several promising candidates for exploring physical phenomena related to semimetals or flat bands in 2D CN materials.

Semimetallic state transition in Two-Dimensional carbon nitride covalent networks and enhanced electrocatalytic activity for nitrate to ammonia conversion

Single-atom catalysts (SACs), due to their maximum atomic utilization rate, show tremendous potential for application in the electrocatalytic synthesis of ammonia from nitrate. Yet, the development of superior supports that preserve the high selectivity, activity, and stability of SACs remains an imperative challenge. In this work, based on first-principles calculations and tight-binding (TB) model analysis, a new two-dimensional (2D) carbon nitride monolayer, C7N6, is proposed. The C7N6 structure exhibits a strong covalent network, with dynamical, thermal, and mechanical stability. Surprisingly, the structural transition from C9N4 to C7N6 corresponds to a semimetallic state transition. Further symmetry analysis unveils that the Dirac states in C7N6 are protected by space–time inversion symmetry, and the physical origin of the Dirac cone was confirmed using the TB model. Additionally, a non-zero Z2 invariant and significant topological edge states demonstrate its topologically nontrivial nature. Considering the excellent structural and topological properties of C7N6, a three-step screening strategy is designed to identify eligible SACs for electrochemical nitrate reduction reaction (NO3RR), and Ti@C7N6 is identified as possessing the best activity, with the last proton-electron coupling step *NH2→*NH3 being the potential-determining step (PDS), for which the limiting potential is 0.48 V. Moreover, a free energy diagram shows that the *NOH reaction pathway is energetically preferred on Ti@C7N6, and ab initio molecular dynamics (AIMD) calculations at 500 K confirm its good thermal stability. Our study not only provides excellent CN-based support material but also offers theoretical guidance for constructing highly active and selective SACs for nitrate reduction.

Electronic and Molecular Adsorption Properties of Pt-Doped BC6N: An Ab-Initio Investigation.

In the last two decades, significant efforts have been particularly invested in two-dimensional (2D) hexagonal boron carbon nitride h-BxCyNz because of its unique physical and chemical characteristics. The presence of the carbon atoms lowers the large gap of its cousin structure, boron nitride (BN), making it more suitable for various applications. Here, we use density functional theory to study the structural, electronic, and magnetic properties of Pt-doped BC6N (Pt-BC6N, as well as its adsorption potential of small molecular gases (NO, NO2, CO2, NH3). We consider all distinct locations of the Pt atom in the supercell (B, N, and two C sites). Different adsorption locations are also considered for the pristine and Pt-doped systems. The formation energies of all Pt-doped structures are close to those of the pristine system, reflecting their stability. The pristine BC6N is semiconducting, so doping with Pt at the B and N sites gives a diluted magnetic semiconductor while doping at the C1 and C2 sites results in a smaller gap semiconductor. We find that all doped structures exhibit direct band gaps. The studied molecules are very weakly physisorbed on the pristine structure. Pt doping leads to much stronger interactions, where NO, NO2, and NH3 chemisorb on the doped systems, and CO2 physiorb, illustrating the doped systems' potential for gas purification applications. We also find that the adsorption changes the electronic and magnetic properties of the doped systems, inviting their consideration for spintronics and gas sensing.

Biaxila strain modulated high anisotropic gas-sensing performance of C5N-based two-dimensional devices: A first-principles study

Two-dimensional carbon nitride materials have been widely used in many applications such as device fabrication, gas adsorption and separation due to their abundant element resources, high physicochemical stability and excellent electronic properties. In this paper, density functional theory and non-equilibrium Green's function method are used to study the electronic structure, transport characteristics and gas sensitivity of C5N-based structures. The results show that the electron transport exhibits obvious anisotropy, in which the electron transport in the armchair direction is more conductive than that in the zigzag direction. It is worth noting that the negative differential resistance effect exists in both directions. Furthermore, the transport and sensing characteristics of inorganic molecules (NO, CO, NO2, SO2, and NH3) adsorbed on the C5N monolayer are studied. The results show that CO, SO2 and NH3 exist on the surface of C5N in the form of physical adsorption, while NO and NO2 adhere to the surface of C5N in the form of chemical adsorption. The designed C5N gas sensor exhibits high sensitivity to NO and NO2 molecules, reaching 81 % sensitivity to NO2 at a 0.1 V bias voltage. Finally, the effect of strain on the adsorption properties of gas sensing devices is studied. Studies have shown that the application of -4 % strain in the armchair direction significantly increases the current of NO and NO2, significantly improving the performance of the gas sensor. Whether strain is applied to the device or gas adsorption, C5N materials always maintain significant anisotropy. This study shows that C5N is a highly anisotropic and sensitive two-dimensional material, which has broad application potential in the field of electronic properties and gas sensing.

Strong mechanical anisotropy and an anisotropic Dirac state in 2D C5N3.

Two-dimensional (2D) carbon nitride materials have emerged as a versatile platform for the design of high-performance nanoelectronics, but strong anisotropy in 2D carbon nitrides has rarely been reported. In this work, a 2D carbon nitride with strong anisotropy composed of tetra-, penta-, and hexa-rings (named as TPH-C5N3) is proposed. This TPH-C5N3 exhibits both dynamical and mechanical stability. Furthermore, it also showcases remarkable thermal stability, reaching up to 2300 K, as evidenced by AIMD simulations conducted in an NVT environment utilizing the Nosé-Hoover thermostat. Significantly, TPH-C5N3 demonstrates high anisotropic ratios in its mechanical properties, positioning it as the frontrunner in the current carbon nitride systems. In addition, a Dirac cone with an anisotropic ratio of 55.8% and Fermi velocity of 7.26 × 105 m s-1 is revealed in TPH-C5N3. The nontrivial topological properties of TPH-C5N3 are demonstrated by a non-zero Z2 invariant and topologically protected edge states. Our study offers theoretical insights into an anisotropic 2D carbon nitride material, laying the groundwork for its design and synthesis.

Design of Boron and Transition Metal Embedded Two-Dimensional Porous Carbon Nitride for Electrocatalytic Synthesis of Urea.

Electrocatalytic coupling of CO and N2 to synthesize urea under ambient conditions is considered a promising strategy to replace traditional industrial technology. It is crucial to find efficient electrocatalysts that can adsorb and activate N2 and promote the C-N coupling reaction. Herein, a new two-dimensional porous carbon nitride material with multiactive sites is designed, in which boron and transition metal are embedded. Through a series of screening, B2Cr2, B2Mn2, and B2Os2 are predicted to be potential electrocatalysts for urea synthesis. Mechanistic studies are performed on bidentate metal-metal and metal-boron sites, and both NCON and CO mechanisms are explored. The electronic structure analysis shows that there is a strong N2 chemical adsorption within the bidentate site and that the N≡N bond is significantly activated. A new mechanism where free CO is inserted for C-N coupling within the two-dimensional porous structure is proposed.

Two-Dimensional Carbon Nitride as a Support of Single Metal Atom for Carbon Dioxide Reduction Reaction

Electrochemical conversion of CO2 into added-value chemicals is an important approach to recycle CO2. Heterogeneous catalysis is widely used in industrial applications because of the possibility of facile separation, which reduces the operating costs, although heterogeneous catalysts often have limited selectivity. In contrast, homogeneous catalysts are very selective although they have limited industrial applications due to their cost, the use of precious metals, and the difficulty in separating and recovering the catalysts. Currently, the research community is trying to combine the properties of homogeneous and heterogeneous catalysts. From the heterogeneous catalyst perspective, research has been focused on creating smaller and dispersed catalyst particles. Single-atom catalysts (SACs), which comprise atoms of metal species dispersed on a solid support, are expected to bridge the homogeneous and heterogeneous catalyst properties.The work described herein explores, by means of density functional simulations, the electrocatalytic CO2 reduction reaction (CO2RR) using several single transition metal atoms anchored in 2D graphitic carbon nitride (g-C3N4),1 focusing on the group XI transition metals since they include Cu, the only transition metal capable of reducing CO2 to hydrocarbons and alcohols with acceptable faradaic efficiencies. Moreover, the Cu1/g-C3N4 system has been experimentally evaluated as CO2RR electrocatalysts. 2D g-C3N4 has been demonstrated to be a competitive candidate for electrocatalytic CO2 reduction since it can act as an active support for single metal-atom catalysts, mainly Cu, Pd, and Pt, and the deposition of Au single atom was experimentally characterized.The computational hydrogen electrode model has been used to explore the suitability of several transition metals atoms anchored to C3N4, showing that single atoms enhance the catalytic activity of the system as the first proton–electron transfer is thermodynamically favored in comparison to bare carbon nitride support. Our theoretical interpretations are consistent with the experimental results using Cu1/g-C3N4,2 revealing that the competitive H2 generation is favored due to the strong CO binding energies. This fact reinforced the capability of our computational models to predict the behavior of several single metal atom electrocatalysts to reduce CO2, for instance, predicting that Au can promote the methane formation after eight electron-proton transfer processes. Our computational study paves the road to finding suitable metals that catalyze the first proton–electron transfer in the carbon dioxide reduction reaction. Posada-Pérez, A. Vidal-López, M. Solà, and A. Poater, 2023, Phys. Chem. Chem. Phys, 25, 8574.Cometto, A. Ugolotti, E. Grazietti, A. Moretto, G. Bottaro, L. Armelao, C. Di Valentin, L. Calvillo and G. A. Granozzi, npj 2D Mater. Appl., 2021, 5, 63. Figure 1

A composite coating based on Ti3C2Tx MXene and M16 corrosion inhibitor for self-healing anti-corrosion and wear resistance

In this study, two-dimensional transition metal carbides and carbon nitride (MXene) and mesoporous silica nanoparticles (SiO2) loaded with corrosion inhibitor 1-(3-((N-n-butyl) aminecarboxamido) propyl)-3-hexadecyl imidazolidin bromide (M16) were used to prepare a M16@MXene-SiO2 nanocomposite with good anti-corrosion and wear resistance. The structure and composition of the nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The synthesized M16@MXene-SiO2 nanocomposite was then added to an epoxy coating on Q235 carbon steel. The uniform distribution of M16@MXene-SiO2 in the coating was confirmed by SEM and atomic force microscopy (AFM). The electrochemical impedance spectroscopy (EIS) test showed that the corrosion resistance of epoxy coating was the best when the addition amount of M16@MXene-SiO2 was 5 wt%, and its electrochemical impedance could reach 5.98 × 109 Ω∙cm2. After 144 h immersion, the coating resistance (Rc) of the epoxy coating decreased to 3.88 × 103 Ω∙cm2, and that of the epoxy coating with M16@MXene-SiO2 increased to 1.01 × 104 Ω∙cm2. The corrosion inhibition efficiency of M16@MXene-SiO2 was tested by potentiodynamic polarization. After immersion for 24 h, the corrosion current density (Icorr) of the epoxy coating was 2.23 × 10−7 A∙cm−2, which reduced to 4.38 × 10−8 A∙cm−2 after adding M16@MXene-SiO2 and the corrosion inhibition efficiency increased by 80.36 %. In addition, the wear resistance of the epoxy coating was tested by reciprocating friction experiment. The friction coefficient of the epoxy coating decreased from 0.44 to 0.12 after adding 5 wt% M16@MXene-SiO2. The results showed that the composite coating had excellent corrosion resistance, self-healing properties and wear resistance. The improvement in corrosion could be explained by the filling of coating defects with MXene-SiO2 and the formation of corrosion inhibitor films. The improvement of friction performance was mainly attributed to the friction transfer film formed by MXene-SiO2 and M16.

Photocatalytic aqueous environmental remediation via two-dimensional carbon nitride nanosheets

Graphitic carbon nitride (GCN) has garnered considerable attention across diverse fields, particularly in photocatalysis for energy and environmental applications, due to its unique physicochemical properties. Among the various structural engineering strategies applied to GCN, two-dimensional (2D) nanosheet design stands out as a fascinating direction due to the 2D geometric advantages. This review explicitly explores the various synthetic (classified as bottom-up and top-down) and physicochemical structural modification methods of GCN-NS matrix and their based composites, as well as their application in photocatalytic remediation of aqueous pollutants. The features of these synthetic strategies in the formation of 2D GCN-NS are first compared. Different modification strategies of GCN-NS, such as surface modification, crystal structure design, doping and heterojunction construction, are summarized. Furthermore, the structure-activity relationship of GCN-NS in various photocatalytic water treatments regarding light absorption, carrier transport and catalytic reaction paths is discussed. Lastly, the developed perspectives are described, including the challenge of GCN-NS-based materials. We expect this review to provide guidelines and inspirations for preparing, modifying, and utilizing two-dimensional GCN materials in the photocatalytic field.

Fe-doped two-dimensional graphite carbon nitride: An effective nanozymetic catalyst for electrochemical detection of cell-released H2O2

In this work, a simple one-step pyrolysis process was designed to synthesize Fe-doped graphite carbon nitride (Fe–C3N4) nanosheets with FeCl3 as Fe source. The resulted samples were characterized by various characterization techniques, and the results showed that Fe species might form Fe–N bonds with N atoms of C3N4, which was similar to the iron (II) porphyrin active center of horseradish peroxidase. Then Fe–C3N4 nanosheet was further mixed with carbon nanotube (CNT) to obtain Fe–C3N4@CNT nanocomposite, which was further modified on the self-made flexible printed electrode (PE) to construct the flexible working electrode. Fe–C3N4 nanosheets show good catalytic activity for H2O2 and the introduction of CNT can effectively improve the electron transfer efficiency at the modified electrode interface. By combining with wireless portable electrochemical workstation, the sensor shows a wider detection range (10.0 μmol L−1–20.0 mmol L−1) and a lower limit of detection (0.38 μmol L−1, S/N = 3) for the H2O2 analysis. Furthermore, the sensor can be applied to the real time and in-situ analysis of H2O2 secreted from live cells. In word, this self-supported sensing electrode shows great potential applications in monitoring the pathological and physiological dynamics of cancer cells.

Boron carbon nitride nanosheets via induction plasma: Insights on synthesis, characterization, and control of band gap

Band gap-controlled two-dimensional boron carbon nitride nanosheets (BCNNS) were synthesized via a scalable one-step thermal plasma-based process near atmospheric pressure. Monotonic change in the band gap of BCNNS from 2.4 to 4.1 eV was achieved through manipulating the carbon loading during the nanosheet formation from ammonia borane and methane. Electron microscopy images showed 2D structures with sizes of 100–200 nm and 1.1–3.7 nm in sheet thickness (3–10 atomic layers). The sheets displayed non-uniformity in layer stacking and dislocation-type defects indicating the inclusion of BN in the C framework. Quasi-uniform distribution of the B/N/C was shown through energy dispersive X-ray spectroscopy. The presence of these elements as well as the sp2 hybridization of the bonding were confirmed using electron energy loss spectroscopy. Fourier Transform infrared spectroscopy showed the presence of B–N/BN, C–N/CN, and C–B/CB groups, and Raman spectroscopy showed progressive graphitization across the BCNNS samples as the BN content is decreased. The optical band gap of various samples is estimated using the Tauc method and found to increase as the carbon content decreased.

Amphoteric dissolution of two-dimensional polytriazine imide carbon nitrides in water.

Crystalline two-dimensional carbon nitrides with polytriazine imide (PTI) structure are shown to act amphoterically, buffering both HCl and NaOH aqueous solutions, resulting in charged PTI layers that dissolve spontaneously in their aqueous media, particularly for the alkaline solutions. This provides a low energy, green route to their scalable solution processing. Protonation in acid is shown to occur at pyridinic nitrogens, stabilized by adjacent triazines, whereas deprotonation in base occurs primarily at basal plane NH bridges, although NH2 edge deprotonation is competitive. We conclude that mildly acidic or basic pHs are necessary to provide sufficient net charge on the nanosheets to promote dissolution, while avoiding high ion concentrations which screen the repulsion of like-charged PTI sheets in solution. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

Исследование миграции протона на поверхности двумерного карбонитрид бора

One of the specific electrical properties of hexagonal two-dimensional boron carbon nitride (h-BCN) is proton conductivity, which solid electrolytes possess. Proton conductors are widely used as components of electrochemical devices such as gas sensors, electrolyzers, fuel cell membranes, etc. A key feature of the h-BCN layer is that it actually consists of a mixture of C-C carbon bonds and B-N boron nitride bonds. This makes it possible to change the conductive properties of the material by changing the concentration of the B-N bonds, which makes this material one of the most attractive to study at the moment. The adsorption of atomic hydrogen on the surface of a two-dimensional BCN layer is studied using density functional theory. The migration process of a single proton along the surface of a two-dimensional BCN layer has been studied, and the most probable path of its movement has been established. The density of states of a BCN layer with a proton on the surface is estimated. It is proved that the two-dimensional BCN layer is a promising material for using it as a functional element of devices with conductivity.

Rational design of α-MnO2/HT-GCN nanocomposite for effective photocatalytic degradation of ciprofloxacin and pernicious activity.

The present study is mainly concerned with the development of cost-efficient composite material utilized to produce one-dimensional manganese oxide (α-MnO2) nanoparticles coated on two-dimensional graphitic carbon nitrides (HT-GCN) as nanocomposite (α-MnO2/HT-GCN) for highly efficient CIP degradation. The α-MnO2 nanoparticles (NPs) were prepared by a simple hydrothermal technique before being decorated on HT-GCN (H denotes protonation and T represents thermal-decomposition-graphitic carbon nitride). Tauc plots were used to calculate the band gap values of the photocatalysts α-MnO2 (1.74eV), GCN (2.84eV), HT-GCN (2.63eV), and α-MnO2/HT-GCN (2.31eV). The mechanism was investigated by various scavengers, particularly isopropanol (•OH) makes a significant role in the photodegradation process. The degradation percentage for ciprofloxacin was 89.2% and the rate of reaction R2 = 0.9913. This study demonstrates a unique method for developing a heterojunction-based nanocomposite of α-MnO2/HT-GCN, which exhibit better light absorption performance.