C3N Nanosheet Research Articles

Comparative investigation of the mechanical, electrical and thermal transport properties in graphene-like C3B and C3N

By using state-of-the-art first-principles calculations based on density functional theory (DFT), we conduct a comparative study of the mechanical, electrical, and in-plane thermal transport properties of recently synthesized graphenelike C3B and C3N nanosheets. Our DFT results reveal that the monolayer C3B remarkably possesses a lower elastic modulus and in-plane stiffness as well as ultimate tensile strength compared to C3N, while obviously stronger anisotropy in failure behavior is found in C3B sheets. Both monolayer materials are found as semiconductors with indirect bandgaps of about 1.78 eV and 1.15 eV at the HSE06 level, and their carrier mobilities demonstrate remarkable anisotropy. Additionally, the electron mobility of C3B is found to be much higher than its hole mobility, while for C3N, the reverse is true. For the thermal transport properties, as expected, the intrinsic lattice thermal conductivity of the monolayer C3B (301 W/m K at 300 K) is also lower than that of C3N (380 W/m K at 300 K), while much great anisotropy of in-plane thermal conductivity is found in C3B. The underlying mechanisms governing the phonon thermal transport of these two graphenelike monolayers are thoroughly discussed and compared. Our research will benefit future theoretical research and practical application of these two novel boron-carbide and carbon-nitride materials.

Doping-induced enhancement of CO2 adsorption on negatively charged C3N nanosheet: Insights from DFT calculations

It is an increasing need to explore advanced materials and technologies for CO2 capture to weaken its impact on the environment. For the first time, it is demonstrated that a suitable doping can dramatically increase CO2 adsorption capacity of negatively charged C3N nanosheets using density functional theory calculations. For example, the CO2 adsorption energy on 2e− negatively charged P doped C3N (P-C3N) nanosheet can reach −2.233 eV, which is about 600% larger than that on 2e− negatively charged C3N nanosheet. Additionally, the negatively charged P-C3N nanostructure exhibits good CO2/CH4, CO2/H2 and CO2/N2 selectivity. Therefore, P-C3N nanosheet may be a very promising negatively charge-regulated CO2 sorbent. More importantly, charge modulation strategies offer the potential for spontaneous, controllable CO2 storage and release. Furthermore, it is manifested that the increased interactions between CO2 and negatively charged P-C3N monolayer are attributed to the heterogeneous charge density distribution of P-C3N monolayer and the hybridization of p orbits of C and P atoms. These theoretical predictions could shed new light on designing feasible high-performance CO2 sorbents.

Two-dimensional carbon nitride (C3N) nanosheets as promising materials for H2S and NH3 elimination: A computational approach

Abstract Motivated by the increased emission of pollutant in the atmosphere, we explore the promise of pristine and defect carbon nitride (C 3N) monolayers for H2S and NH3 capture by means of van der Waals corrected density functional theory (DFT) calculation. Our results reveal that the adsorption energies ( Eb) of pristine C3N towards H2S and NH3 are 0.610 eV and 0.444 eV, respectively. However, a spontaneous partial dissociation of H2S is observed in case of single C and N vacancy in C3N monolayer with minimum Eb values of 1.90 and 1.577 eV, respectively. Furthermore, by using transition states (TS) calculation, we predicted a complete dissociation path of H2S by ab-initio molecular dynamics simulation at 1000 K. Results show complete dissociation of H2S molecule on C3N–C system. In addition, the trend of our results has demonstrated that O2 and H2O contaminations in our sample could barrier H2S adsorption. However, we also observed a physisorption phenomenon in the case of the interaction between NH3 and C3N. In addition, the binding energy of NH3 at C and N vacancies resulted in Eb values of 0.45 and 0.30 eV, respectively. This proves that the mono vacancy defect is highly selective toward H 2S gas than NH3. This study reveals a future for Two-Dimensional C3N nanosheets as H2S sensor.

Influence of Stone-Wales defects on the mechanical properties of graphene-like polyaniline (PANI) C3N nanosheets

Today, Graphene-based 2D materials, i.e. those hexagonal arrangements that can be produced by making slight changes to graphene, are amongst the most interesting nanostructures for science and industry. Carbone nitrides (CNs) i.e. CxNy is one of the most important types of graphene-like materials, and C3N is the first two-dimensionally synthesized and most widely used of these materials. In this paper, the properties of C3N monolayer in the presence of Stone-Wales (7-5-7) defects, have been studied. After validating the model used for this purpose, by comparing the results with those of other works, the structures and arrangements that can be anticipated for Stone-Wales (SW) defects have been predicted. Then the effects of different SW defects, their position and density, and the effect of loading direction on elastic properties of pristine and defected sheets, have been simulated. The obtained results indicate that by increasing the number of SW defects, the failure stress and the failure strain of single-layer C3N nanosheets are generally reduced, while its modulus of elasticity does not vary significantly. Generally, the defective armchair C3N nanosheet is more resistant than the zigzag configuration.

An effective approach for tuning catalytic activity of C3N nanosheets: Chemical-doping with the Si atom

It is well-known that the catalytic oxidation of CO molecule into CO2 is one of the most important strategies for the removing of this toxic gas from the atmosphere. In the present study, we investigate the reaction pathways and energy barriers for the oxidation of CO by O2 molecule over the Si-doped C3N nanosheet. According to our results, doping of C3N nanosheet with a Si atom could greatly modify its surface reactivity and electronic structure. Due to the large positive charge on the Si, this atom acts as the most active site to adsorb CO and O2 molecules. Three possible reaction mechanisms are studied for the CO oxidation, namely the Eley–Rideal (ER), Langmuir-Hinshelwood (LH) and new Eley–Rideal (NER). Comparing the activation energies indicates that the CO oxidation reaction proceeds via the LH mechanism over the title surface. The energy barrier needed to remove the activated oxygen atom (O*) from the Si atom is only 0.22 eV, which is most likely to overcome at room temperature. The results of this study may be useful to fabricate noble-metal free catalysts to remove toxic CO molecules from the atmosphere.

Adsorption of molecules on C3N nanosheet: A first-principles calculations

Using first-principles calculations we investigate the interaction of various molecules, including H2,N2,CO,CO2,H2O,H2S,NH3,CH4 with a C3N nanosheet. Due to the weaker interaction between H2,N2,CO,CO2,H2O,H2S,NH3 and CH4 molecules with C3N, the adsorption energy is small and does not yield any significant distortion of the C3N lattice and the molecules are physisorbed. Calculated charge transfer shows that these molecules act as weak donors. However, adsorption of O2,NO,NO2 and SO2 molecules are chemisorbed, they receive electrons from C3N and act as a strong acceptor. They interact strongly through hybridizing its frontier orbitals with the p-orbital of C3N, modifying the electronic structure of C3N. Our theoretical studies indicate that C3N-based sensor has a high potential for O2,NO,NO2 and SO2 molecules detection.

Catalytic reduction of nitrous oxide over boron-doped C3N monolayers: A DFT study

Abstract Using DFT calculations, a novel metal-free catalyst is proposed for reduction of nitrous oxide (N2O). It is found that the presence of a B impurity can modify the surface reactivity of C3N and promote the effective adsorption of N2O. The reduction of N2O over B-doped C3N nanosheets starts with the adsorption of this molecule, followed by its decomposition into N2 and an active oxygen atom (O*). By overcoming a small activation energy, the O* moiety can be then eliminated by a CO molecule. The results suggest that B-doped C3N nanosheets are promising catalysts to remove the environmentally harmful N2O molecules.

B-doped C3N monolayer: a robust catalyst for oxidation of carbon monoxide

The catalytic oxidation of carbon monoxide (CO) on B-doped C3N nanosheet is investigated by first-principle density functional theory calculations. According to our results, the incorporation of a B atom can induce a noticeable charge redistribution into C3N monolayer, which results in the enhancement of O2 adsorption. The activation energy for the rate-determining step of CO + O2 reaction via the Langmuir–Hinshelwood (LH) mechanism is calculated to be 0.32 eV, which is 0.24 eV smaller than that of the Eley–Rideal (ER) mechanism. This can be mainly related to the more favorable CO-5σ → O2-2π* orbital interaction in the former mechanism, which facilitates the formation of OCOO intermediate over B-doped C3N. The results of this study provide a theoretical evidence for the potential of B-doped C3N as a novel and metal-free catalyst in the CO oxidation reaction.

Effects of vacancies and divacancies on the failure of C3N nanosheets

Two-dimensional materials, and especially carbon-based 2D materials, have gained a special reputation and status in many engineering fields and applications recently; because they can be engineered by various methods to precisely yield the properties desired by the designers. One of the most important techniques used for engineering these structures is to create nanopores in them. The varied effects of nanopores in graphene sheets and some other 2D materials have already been studied. In this work, for the first time, the effects of nanopores on the mechanical properties of C3N sheets have been evaluated. Using the molecular dynamics method, various types of achievable vacancy and divacancy pores in C3N sheets have been specified, and the formation energy for each type has been calculated. The formation energy for a vacancy formed by removing a carbon atom or a nitrogen atom is 2.63 eV or 1.31 eV, respectively. In comparing the formation energies for different types of vacancies and divacancies, it was observed that the removal of carbon atom in the structure of C3N requires much more energy, and that the highest amount of energy is needed for removing two carbon atoms in two types of divacancies. Since graphene sheets with a large number of vacancies do not fail easily and remain intact, these sheets can be considered as suitable candidates for ‘straintronic’ applications. By studying the effect of pore density on the mechanical properties of C3N sheets it was observed that at pore densities lower than 5%, C3N sheets exhibit better mechanical properties than graphene, and thus, they can be a better option for straintronic applications.

Stable H-Terminated Edges, Variable Semiconducting Properties, and Solar Cell Applications of C3N Nanoribbons: A First-Principles Study.

Motivated by the recent synthesis of the graphene-like C3N nanosheet, the geometrical structures and electronic properties of its ribbon form, that is, C3N nanoribbons (C3NNRs), are investigated by first-principles calculations. It is found that there are five types of energetically favorable H-terminated edges in the C3NNRs. Different from graphene nanoribbons, the corresponding stable C3NNRs are all nonmagnetic semiconductors regardless of the edge shape and termination. However, their band feature and gap size can be modulated by the ribbon width and edge termination, which brings direct-, quasi-direct-, and indirect-band-gap semiconducting behaviors in the nanoribbons. Comparing to the C3N nanosheet, the work function is reduced in the C3NNRs with fully di- and monohydrogenated edges, which results in a type-II band alignment with SiC and silicane nanosheets. More interestingly, the combined hetero-nanostructures will be promising excitonic solar cell materials with high power conversion efficiencies up to 17–21%. Our study demonstrates that the C3NNRs have distinct edge stabilities and variable semiconducting behaviors, which endow fascinating potential applications in the fields of solar energy and nanodevices.

Mechanical responses of pristine and defective C3N nanosheets studied by molecular dynamics simulations

The purpose of this study is to investigate the mechanical properties of a new two-dimensional graphene like material, crystalline carbon nitride with the stoichiometry of C3N. The extraordinary properties of C3N make it an outstanding candidate for a wide variety of applications. In this work, the mechanical properties of C3N nanosheets have been studied not only in the defect-free form, but also with critical defects such as line cracks and notches using molecular dynamics simulations. Different crack lengths and notch diameters were considered to predict the mechanical response at different temperatures under the uniaxial tensile loading. Our simulation results show that larger cracks and notches reduce the strength of the nanosheets. Moreover, it was shown the temperature rise has a weakening effect on the tensile strength of C3N. Our study can provide useful information with respect to the thermo-mechanical properties of pristine and defective graphene like C3N 2D material.

Me–N–C (Me = Fe, Cu, and Co) nanosheet as a promising charge-controlled CO2 capture material

This figure represents a controlled CO2 adsorption and desorption process on C3N nanosheet by tuning charge state, demonstrating M–C–N nanosheet is a promising candidate for CO2 capture.

Charge-modulated CO2 capture of C3N nanosheet: Insights from DFT calculations

Increasing concerns about the atmospheric CO2 concentration and its impact on the environment promote developing new materials and technologies for efficient CO2 capture and conversion. Here, for the first time we investigate the CO2 adsorption on C3N nanosheet with different charge states by means of density functional theory calculations. It is found that injecting extra negative electrons instead of positive electrons can extremely improve CO2 adsorption capacity of C3N nanomaterial. The adsorption strength of CO2 molecules on this 3 e− negatively charged nanomaterial is 20 times of that on neutral surface while there is little difference between these on positively charged surface and the neutral surface. Interestingly, CO2 molecules can spontaneously adsorb and desorb from C3N sorbent with appropriate charge density range by injecting and removing extra negative charges. Importantly, this negatively charged C3N exhibits highly selective adsorption for CO2/C2H2, CO2/CH4, CO2/H2, C2H2/CH4 and C2H2/H2 mixtures through tuning charge density. Our theoretical results could provide guidance for designing high-capacity and high-selectivity CO2 capture materials.

Ultra high stiffness and thermal conductivity of graphene like C3N

Recently, single crystalline carbon nitride 2D material with a C3N stoichiometry has been synthesized. In this investigation, we explored the mechanical response and thermal transport along pristine, free-standing and single-layer C3N. To this aim, we conducted extensive first-principles density functional theory (DFT) calculations as well as molecular dynamics (MD) simulations. DFT results reveal that C3N nanofilms can yield remarkably high elastic modulus of 341 GPa nm and tensile strength of 35 GPa nm, very close to those of defect-free graphene. Classical MD simulations performed at a low temperature, predict accurately the elastic modulus of 2D C3N with less than 3% difference with the first-principles estimation. The deformation process of C3N nanosheets was studied both by the DFT and MD simulations. Ab initio molecular dynamics simulations show that single-layer C3N can withstand high temperatures like 4000 K. Remarkably, the phononic thermal conductivity of free-standing C3N was predicted to be as high as 815 ± 20 W/mK. Our atomistic modelling results reveal ultra high stiffness and thermal conductivity of C3N nanomembranes and therefore propose them as promising candidates for new application such as the thermal management in nanoelectronics or simultaneously reinforcing the thermal and mechanical properties of polymeric materials.

Adsorption of carbon monoxide on the pristine, B- and Al-doped C3N nanosheets.

The potential application of the intrinsic and extrinsic (8,0) zigzag single-walled C3N nansheets as chemical sensor for CO molecules has been investigated using density functional theory calculations. The calculation shows that the pristine sheet is a semiconductor with a HOMO-LUMO gap (Eg) of about 2.19eV. The pristine and B-doped sheets can weakly adsorb a CO molecule with the adsorption energies of -4.8 and -4.6kcal mol(-1), and their electronic properties are not sensitive to this molecule. By replacing a C atom with an Al atom, localized impurity states are induced under the conduction level of the sheet. The binding interaction between the CO molecule and the Al-doped sheet becomes much stronger (Ead = -17.8kcal mol(-1)). After the adsorption of CO on the Al-dope sheet, the Eg of the sheet is significantly decreased from 1.07 to 0.73eV. This leads to a sizable increase in the resistance of the tube. Thus, the Al-doped sheet can show the presence of CO molecules by an electronic signal because of the change in its resistance and conductivity.