Repairing single and double atomic vacancies in a C3N monolayer with CO or NO molecules: a first-principles study

Confined and spontaneously transformed oxidation structures due to the intrinsic heterogeneous surface morphology of C3N monolayer

Identifying the oxidation structure of two-dimensional interfaces is crucial to improve surface chemistry and electronic properties. Beyond graphene with only phenyl rings, a novel carbon-nitrogen material, C3N, presents an intrinsic heterogeneous surface morphology where each phenyl ring is encircled by six nitrogen atoms, yet its atomistic oxidation structure remains unclear. Here, combining a series of density functional theory calculations and ab initio molecular dynamics simulations, we demonstrate that thermodynamically favorable oxidation loci are confined to the phenyl ring, and kinetic transformations of oxidation structures are feasible along the phenyl ring, whereas those toward nitrogen atoms are proven to be extremely difficult. These results are attributed to the lower barrier of oxygen atom migration along the phenyl ring, while the significantly high barriers toward nitrogen atoms are due to the heterogeneous potential energy surface for oxygen-C3N interaction. This work highlights the significance of surface morphology on the characteristics of oxidation structure, offering insights into tunable electronic properties via confined interfacial oxidation.

Unravelling the adsorption and electroreduction performance of CO2 and N2 over defective and B, P, Si-doped C3Ns: a DFT study

Two-dimensional carbon-based materials have great potential for electrocatalysis. Herein, we screen 12 defective and doped C₃N nanosheets by evaluating their CO₂RR and NRR activity and selectivity vs. the HER based on density functional theory calculations. The calculation results suggest that all 12 C₃Ns can enhance CO₂ adsorption and activation. And P_N-V_C-C₃N is the best electrocatalyst for the CO₂RR towards HCOOH with U_L = -0.17 V, which is much more positive than most of the reported values. B_N-C₃N and P_N-C₃N are also good electrocatalysts that promote the CO₂RR towards HCOOH (U_L = -0.38 V and -0.46 V). Moreover, we find that Si_C-C₃N can reduce CO₂ to CH₃OH, adding an alternative option to the limited catalysts available for the CO₂RR to CH₃OH. Furthermore, B_C-V_C-C₃N, B_C-V_N-C₃N, and Si_C-V_N-C₃N are promising electrocatalysts for the HER with |ΔG_H*| ≤ 0.30 eV. However, only three C₃Ns of B_C-V_C-C₃N, Si_C-V_N-C₃N, and Si_C-V_C-C₃N can slightly improve N₂ adsorption. And none of the 12 C₃Ns are found to be suitable for the electrocatalytic NRR because all the Δe_NNH* values are larger than the corresponding ΔG_H* values. The high performance of C₃Ns in the CO₂RR stems from the altered structure and electronic properties, which result from the introduction of vacancies and doping elements into C₃N. This work identifies suitable defective and doped C₃Ns for excellent performance in the electrocatalytic CO₂RR, which will inspire relevant experimental studies to further explore C₃Ns for electrocatalysis.

Effect of vacancy defect and strain on the structural, electronic and magnetic properties of carbon nitride 2D monolayers by DFTB method

We investigate the electronic and magnetic properties of CnNm(C₆N₆, C₂N, C₃N and C₃N₄) using density functional tight-binding (DFTB) method. We find that these compounds are dynamically stable and their electronic band gaps are in the range of 0.59-3.28 eV. We show that the electronic structure is modulated by strain and the semiconducting behavior is well preserved except for C₃N at +5% biaxial strain, where a transition from semiconductor to metal was observed. Under +3% biaxial strain, C₃N₄undergoes a transition from an indirect (K-Γ) to a direct (Γ-Γ) band gap. Moreover, band gap of C₂N transforms from direct (Γ-Γ) to indirect (M-Γ) under +4% biaxial strain. However, no change in the nature of the band gap of C₆N₆. Further, when the studied materials under uniaxial tensile strain, their bandgaps reduce. Our theoretical study showed that an indirect-to-direct nature transition may occur for C₆N₆and for C₃N₄, which broadens their applications. On the other hand, magnetism is observed in all N-vacancy defected CnNm, which encourages its application in spintronic. Moreover, calculations of formation energies indicate that N-vacancy is energetically more favorable than C-vacancy in both C₂N and C₃N₄. Opposite behavior found for C₆N₆and C₃N.

First-Principles Insight into Pd-Doped C3N Monolayer as a Promising Scavenger for NO, NO2 and SO2

The adsorption and sensing behavior of three typical industrial toxic gases NO, NO₂ and SO₂ by the Pd modified C₃N monolayer were studied in this work on the basic first principles theory. Meanwhile, the feasibility of using the Pd doped C₃N monolayer (Pd-C₃N) as a sensor and adsorbent for industrial toxic gases was discussed. First, the binding energies of two doping systems were compared when Pd was doped in the N-vacancy and C-vacancy sites of C₃N to choose the more stable doping structure. The result shows that the doping system is more stable when Pd is doped in the N-vacancy site. Then, on the basis of the more stable doping model, the adsorption process of NO, NO₂ and SO₂ by the Pd-C₃N monolayer was simulated. Observing the three gases adsorption systems, it can be found that the gas molecules are all deformed, the adsorption energy (E_ad) and charge transfer (Q_T) of three adsorption systems are relatively large, especially in the NO₂ adsorption system. This result suggests that the adsorption of the three gases on Pd-C₃N belongs to chemisorption. The above conclusions can be further confirmed by subsequent deformable charge density (DCD) and density of state (DOS) analysis. Besides, through analyzing the band structure, the change in electrical conductivity of Pd-C₃N after gas adsorption was studied, and the sensing mechanism of the resistive Pd-C₃N toxic gas sensor was obtained. The favorable adsorption properties and sensing mechanism indicate that the toxic gas sensor and adsorbent prepared by Pd-C₃N have great application potential. Our work may provide some guidance for the application of a new resistive sensor and gas adsorbent Pd-C₃N in the field of toxic gas monitoring and adsorption.

Fadlallah M, V. Chuong N, Ghergherehchi M, Faraji M, Feghhi SAH, Oskoeian M. Electronic and optical properties of two-dimensional heterostructures and heterojunctions between doped-graphene and C- and N-containing materials

The electronic and optical properties of vertical heterostructures (HTSs) and lateral heterojunctions (HTJs) between (B,N)-codoped graphene (dop@Gr) and graphene (Gr), C₃N, BC₃ and h-BN monolayers are investigated using van der Waals density functional theory calculations.

Theoretical insights into oxygen reduction reaction catalyzed by phosphorus-doped divacancy C3N nanosheet

The catalytic reduction of O₂ molecule into H₂O is investigated over a P-doped divacancy C₃N nanosheet (P-Dv-C₃N) by using density functional theory calculations. A negative formation energy is calculated for P-Dv-C₃N, suggesting that the introduction of a P atom into divacancy defective C₃N would be thermodynamically favorable. The oxygen reduction reaction (ORR) over P-Dv-C₃N would proceed via a 4e^- pathway (O₂ + 4H⁺ + 4e^-→ 2H₂O) at room temperature. The rate-determining step of the ORR on P-Dv-C₃N is O + H⁺ + e^- → OH which requires an activation energy of 1.21 eV. These results provide helpful insights into design novel metal-free catalysts to improve the kinetics of ORR in fuel cells.

Heteroatom-doped C3N as a promising metal-free catalyst for a high-efficiency carbon dioxide reduction reaction

Converting CO₂ into useful fuels and chemicals offers a promising strategy for mitigating the issues of energy crisis and global warming.

Repairing the N-vacancy in an InN monolayer using NO molecules: a first-principles study

The synthesis of a perfect InN monolayer is important to achieve desirable properties for the further investigation and application of InN monolayers. However, the inevitably existing defects, such as an N-vacancy, in the synthesized InN nanomaterials would significantly impair their geometric and electronic behaviors. In this study, we proposed to repair the N-vacancy in the InN monolayer using NO molecules through NO disproportionation, which was verified to be energetically favorable according to our first-principles calculations. The repaired InN monolayer was similar to the perfect counterpart in terms of the geometric and electronic aspects. In this study, a promising strategy is presented for repairing the N-vacancy in the InN monolayer to perfect its physicochemical properties effectively, which may also be used to repair N-vacancies in other materials.

Transition metal embedded C3N monolayers as promising catalysts for the hydrogen evolution reaction

Transition metal-embedded C₃N monolayers as efficient catalysts for the electrocatalytic hydrogen evolution reaction are investigated, and the underlying electronic mechanisms are revealed.

Introducing novel electronic and magnetic properties in C3N nanosheets by defect engineering and atom substitution

Using first-principles calculations the effects of topological defects, vacancies, Stone–Wales and anti-site and substitution of atoms, on the structure and electronic properties of monolayer C₃N are investigated.

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.