Two-dimensional Carbon Nitride Research Articles

Improved Adsorption and Migration of Divalent Ions Over C4N Nanosheets: Potential Anode for Divalent Batteries

Divalent ion batteries are potential substitutes to existing rechargeable batteries because of the high-energy density, safety, and low cost. However, the applications of divalent batteries are strongly dependent on the availability of efficient electrode materials. We herein report the adsorption and migration mechanism of divalent ions like Mg+2 and Ca+2, on two-dimensional carbon nitride monolayer (C4N). The adsorption of both Mg and Ca ions are much stronegr on C4N saturated with functional groups like hydrogen (-H), hydroxyl (-OH), and carboxylic (-COOH) as compared to the pristine monolayers, which implies the improvement in metal storage caused by the functional groups. On functionalized C4N, the first Mg binds within the binding energy range of 1.5-2.2 eV having migration barrier, at the saturated sites, of around 0.5 eV, which indicates desirable binding and robust diffuse. However, the functional groups tend to act as the trapping sites for Ca ions and the diffusion might get hindered as compared to Mg ions. In addition to binding and diffusion mechanism, charge transfer, electronic structures and open circuit volatges have also been calculated for both Mg and Ca on pristine and functionalized C4N monolayers. We find that -H, -OH, and -COOH play important role for the cyclic performance of C4N as the prospective anode material for divalent ion batteries.

Molten salt synthesis of carbon-doped boron nitride nanosheets with enhanced adsorption performance

Owing to their large specific areas, high thermal stability and chemical inertness, two-dimensional boron carbon nitride nanosheets (BCNNs) have captured much attention in recent years in the field of adsorption of pollutants. The formation of BCNNs via incorporating carbon into boron nitride (BN) can effectively improve the photoelectric and adsorption properties of the latter. In this work, carbon-doped BN (BCN) nanosheets were prepared at 1100 °C via a molten salt route using boric acid, melamine and glucose as the main starting materials. The effects of molten salt type and carbon doping level on the formation of BCN were investigated, and their isothermal adsorption properties in a methylene blue (MB) aqueous solution were evaluated based on the Langmuir and Freundlich models. The results indicated that using molten LiCl-KCl as a liquid medium was more favorable than NaCl-KCl to the formation of BCNNs. As-prepared BC0.4N sample possessed a sheet-like structure of about 10 nm thick and a specific surface area as high as 484 m2 g−1. Moreover, the adsorption test of MB demonstrated a high adsorption capacity of 249.04 mg g−1, which was about 14 times higher than that in the case of the pristine BN, and the kinetic rate constant value in the case of using BC0.4N is about ten times as high as that of BN following a pseudo-second-order model, suggesting that the as-formed BC0.4N nanosheets could be potentially used as a value-added effective adsorbent for future wastewater remediation.

Theoretical design of two-dimensional carbon nitrides

The study of two-dimensional (2D) materials has attracted considerable attention owing to their unique but fascinating properties. Here we systematically explored 2D carbon nitride monolayer sheets via the particle swarm optimization algorithm in combination with density functional theory. As a result of structural searches, four carbon nitride monolayers are predicted with stable stoichiometries of C5N2, C2N, C3N2 and CN. These predicted structures are semiconductors with an optimal band gap for solar cell application as indicated in our electronic simulations. Our current results also reveal the high tensile strengths of the predicted structures compared to known porous carbon nitride monolayer sheets. This work may provide a route for the design of 2D candidates in the application of photovoltaic materials.

Visible-light-induced controlled ATRP by modified N-rich holey carbon nitride nanosheets in natural solvent

The design and preparation of green and recyclable catalysts for improving the selectively and efficiency of atom transfer radical polymerization reactions is a critical challenge in polymerization scope. Herein, two-dimensional N-rich carbon nitride nanosheets (g-C3N4 NSs) with high surface area and chemical stability were synthesized. Then, the surface of g-C3N4 NSs was modified with N-(2-acetamido)-2-aminoethanesulfonic acid as a chelating agent to obtain ACES@ g-C3N4 NSs. Finally, copper (II) was introduced to the ACES@ g-C3N4 NSs. The as-synthesized Cu-ACES@g-C3N4 NSs were characterized by various analyses. The ionic interaction, arising from sulfonate and iminium ions, increases the dispersity and stability of the catalyst in a deep eutectic solvent (DES). So, the photocatalyst was successfully utilized for “green” atom transfer radical polymerization of styrene and methyl methacrylate by the irradiation of the reaction mixture under sunlight and visible light in deep eutectic solvent as a green polymerization reaction media. The polymers with good conversions and relatively low polydispersity were obtained which characterization analyses confirmed their structure and properties. Notably, the advantages of the presented photocatalyst include easy separation and reusability without loss of activity due to its heterogeneous nature, as well as using DES as a green solvent which promotes the reaction efficiency.

G-C3N4-heme bound to amyloid β peptides: In-situ generation of the secondary co-reactant for dual-enhanced electrochemiluminescence assay of amyloid β detection

Heme binds to amyloid β-peptide (Aβ) in the brain of Alzheimer΄s disease (AD) patients, thus forming heme-Aβ complexes and leading the characteristic pathological features of AD. The heme-Aβ complexes reduce O2 by 2e− to obtain co-reactant H2O2. In this work, two-dimensional graphite-like carbon nitride (g-C3N4) was hybridized with heme via π-π interaction to construct an electrochemiluminescence (ECL) biosensor for detection of Aβ peptides. The capture aptamer was firstly immobilized on the gold electrode, and then incubated with target Aβ peptides and g-C3N4-heme. The g-C3N4-heme-Aβ composite was subsequently anchored on the electrode and showed a signal-on, label-free ECL emission based on dual co-reactants enhancement attributed to in-situ generated H2O2 and original K2S2O8 in PBS buffer. Under the optimum experimental conditions, the ECL biosensor has a sensitive response to Aβ peptides with a linear range of 10 fM-0.1 μM and a detection limit of 3.25 fM. Considering prominent specificity, reproducibility, and stability, the proposed biosensor was used to assess recovery of Aβ peptides in human serum and the result was satisfactory. We believe that the established method would offer a useful analytical means for quantifying Aβ peptides in a biological matrix.

Understanding interfacial interaction characteristics of carbon nitride reinforced epoxy composites from atomistic insights

Two-dimensional carbon nitride (C3N) is a promising alternative to graphene (GN) as the reinforcement in epoxy composites, yet the complicated interfacial interactions have not been fully understood, which restricts the application of using C3N for enhancing the mechanical properties of thermosetting polymers. To explore its functionality, we undertake this work aims to overcome the obstacles and uncover the interfacial interaction mechanism between C3N and epoxy chains through density function theory (DFT) and molecular dynamics (MD) simulations. We discover, for the first time, that C3N sheet exhibits outstanding performances on improving the thermal-mechanical properties of epoxy composites. The Young’s modulus and glass transition temperature of C3N reinforced epoxy are 20% and 26 K (7%) larger than that of GN filled epoxy, respectively. Our findings conclude that the interfacial interaction mechanisms behind the superlative thermal-mechanical properties are: (1) the C3N sheet exhibits a better adhesion with aromatic rings of epoxy chains, which is attributed to preferred parallel alignment of aromatic rings and C3N surface, and (2) the C3N sheet induces a higher capacity of hydrogen bonding at the interface, leading to better load transfer. The superior reinforcing efficiency of C3N over GN opens extensive applications of it in the next-generation thermomechanical systems.

Design of two-dimensional carbon-nitride structures by tuning the nitrogen concentration

Nitrogen-doped graphene (NG) has attracted increasing attention because its properties are significantly different to pristine graphene, making it useful for various applications in physics, chemistry, biology, and materials science. However, the NGs that can currently be fabricated using most experimental methods always have low N concentrations and a mixture of N dopants, which limits the desirable physical and chemical properties. In this work, first principles calculations combined with the local particle-swarm optimization algorithm method were applied to explore possible stable structures of 2D carbon nitrides (C1−xNx) with various C/N ratios. It is predicted that C1−xNx structures with low N-doping concentration contain both graphitic and pyridinic N based on their calculated formation energies, which explains the experimentally observed coexistence of graphitic and pyridinic N in NG. However, pyridinic N is predominant in C1−xNx when the N concentration is above 0.25. In addition, C1−xNx structures with low N-doping concentration were found to have considerably lower formation energies than those with a high N concentration, which means synthesized NGs with low N-doping concentration are favorable. Moreover, we found the restrictions of mixed doping and low N concentration can be circumvented by using different C and N feedstocks, and by growing NG at lower temperatures.

Orientation and crystal structure of two-dimensional carbon nitride films

In this work, thermal CVD from a melamine source produces two-dimensional carbon nitride films with high orientation. The diffraction pattern from a θ/2θ scan shows two peaks at 27.77° and 57.3°, corresponding respectively to the (001) and (002) orientations. The pole figure of (001) indicates that the carbon–nitrogen layer in the film is stacked parallel to the substrate with a mosaic spread of 8.0°. We use an in-plane scan to successfully measure the pattern of (hk0) diffractions excluding and diffractions. Most of the observed diffraction peaks can be identified with polymeric melon Miller indices.

Design of p-n homojunctions in metal-free carbon nitride photocatalyst for overall water splitting

Two-dimensional (2D) carbon nitride (CN) photocatalysts are attracting extensive attention owing to their excellent photocatalytic properties. In this study, we successfully prepared CN materials with heterogeneous structures via hydrothermal treatment, high-temperature roasting, ball milling, sintering, and other processes. Benefitting from interface interactions in hybrid architectures, the CN photocatalysts exhibited high photocatalytic activity. The rate of hydrogen production using these CN photocatalysts reached 17028.82 μmol h−1 g−1, and the apparent quantum efficiency was 11.2% at 420 nm. The ns-level time-resolved photoluminescence (PL) spectra provided information about the time-averaged lifetime of fluorescence charge carriers; the lifetime of the charge carriers causing the fluorescence of CN reached 9.99 ns. Significantly, the CN photocatalysts displayed satisfactory results in overall water splitting without the addition of sacrificial agents. The average hydrogen and oxygen production rates were 270.95 μmol h−1 g−1 and 115.21 μmol h−1 g−1 in 7 h, respectively, which were promising results for the applications of the catalysts in overall water splitting processes. We investigated the high efficiency of the prepared CN photocatalysts via a series of tests (UV-vis diffuse reflectance spectroscopy, photocurrent response measurements, PL emission spectroscopy, time-resolved PL spectroscopy, and Brunauer-Emmett-Teller analysis). Furthermore, the Mott-Schottky plot and current-voltage curve were acquired via electrochemical tests. The fabricated CN photocatalyst had a small p-n junction in its heterogeneous structure, which further enhanced its photocatalytic efficiency. Therefore, this work can promote the development of CN photocatalysts.

Development of CuAg/Cu2O nanoparticles on carbon nitride surface for methanol oxidation and selective conversion of carbon dioxide into formate

Herein we report a catalyst consisting of CuAg/Cu2O nanoparticles (NPs), synthesized on the two-dimensional carbon nitride (CN) surface via galvanic exchange route for electrocatalytic methanol oxidation and carbon dioxide reduction. The lower reduction potential of copper ([Cu+(aq) + e− → Cu(s)], + 0.52 eV) compared to Ag ([Ag+(aq) + e− → Ag(s)], +0.80 eV) makes Cu(0) easily exchangeable by Ag+ ions via galvanic exchange without applying any external bias. In a two-step process, the Cu NPs are synthesized first on CN surface by adsorbing Cu2+ precursors and reducing them by NaBH4. Due to unstable nature of Cu2+ in aqueous medium some Cu2O NPs (a mixed phase of Cu/CuO) were also formed. Thereafter in the second step, Ag+ precursors are brought in contact with the already synthesized Cu and Cu2O nanoparticles (NPs). The Cu and Cu2O NPs present on the surface of CN are partially exchanged by Ag atoms to generate bimetallic CuAg/Cu2O NPs. Two atoms of Ag are expected to be deposited for every Cu atom replaced. As galvanic replacement occurs on the solid surface of carbon nitride, there is only a partial replacement of Cu and Cu2O atoms. The catalysts CN/Cu/Cu2O and CN/CuAg/Cu2O were evaluated for their performance towards methanol oxidation and carbon dioxide reduction. CN/CuAg/Cu2O showed twice the current density for methanol oxidation than CN/Cu/Cu2O in a 0.5 M methanol solution. Probably the reason for high activity of Ag than Cu is related to the weak bond of oxygen on silver substrate for oxidation reactions and strong binding affinity on copper substrate. In case of carbon dioxide reduction (CO2 reduction) the product was identified to be formate by oxidizing the product (formate) on a Pt ring electrode. The results revealed CN/CuAg/Cu2O shows a better selectivity towards formic acid formation than CN/Cu/Cu2O using the rotating ring disc electrode (RRDE). A probable reason may be the strain induced by alloy formation which could favor a reduced coverage of adsorbed hydrogen and a decrease in oxophilicity of the compressively strained copper.

Monolayer C7N6 : Room-temperature excitons with large binding energies and high thermal conductivities

Two-dimensional (2D) carbon nitrides compounds have attracted wide attention in recent years due to their diverse structures and excellent electronic, thermal, and optical properties. Here, by using first-principles approach, we investigate in details the stability, many-body effect, electronic/thermal transport properties, and thermoelectric performance of monolayer ${\mathrm{C}}_{7}{\mathrm{N}}_{6}$, as a new kind of 2D carbon nitride compounds composed of $s{p}^{2}\text{\ensuremath{-}}\mathrm{hybridized}$ carbon atoms forming hexagonal lattice. Our results show that ${\mathrm{C}}_{7}{\mathrm{N}}_{6}$ monolayer is a direct band-gap semiconductor with a band-gap value of 3.56 eV under the accurate ${G}_{0}{W}_{0}$ method. Ab initio molecular dynamics simulations demonstrate that ${\mathrm{C}}_{7}{\mathrm{N}}_{6}$ maintains stable up to $1500\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Two exciton absorption peaks can be observed within the band gap with the respective large binding energies of $0.84$ and $0.09\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$, which means both excitons can exist at room temperature. Monolayer ${\mathrm{C}}_{7}{\mathrm{N}}_{6}$ possesses high carrier mobility with the order of ${10}^{2}--{10}^{3}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. Moreover, we find that the lattice thermal conductivity for ${\mathrm{C}}_{7}{\mathrm{N}}_{6}$ is as high as $134.55\phantom{\rule{0.28em}{0ex}}\mathrm{W}/\mathrm{mK}$ at room temperature, thus the thermoelectric figure of merit for ${\mathrm{C}}_{7}{\mathrm{N}}_{6}$ is relatively low. Our work suggests that ${\mathrm{C}}_{7}{\mathrm{N}}_{6}$ is a promising candidate for nanoscale (opto-)electronic and heat transport devices.

Single cobalt atom anchored on carbon nitride with well-defined active sites for photo-enzyme catalysis

By analogy to mono-nuclear metalloenzymes, single-atom dispersed catalysts (SACs) demonstrate very promising performance for many conventional heterogeneous and homogeneous reactions. However, the prospect of integrating SACs with enzymatic catalysis is still unexplored. Herein, atomically dispersed Co sites on ultrathin two-dimensional (2D) carbon nitride nanosheets (Co 1 /C 3 N 4 ) were constructed and applied for efficiently photochemical cofactor (NADH) regeneration. The NADH regeneration yield reached as high as 99%. Subsequently, the in-situ regenerated-NADH triggered alcohol dehydrogenase for enzymatic reduction of aldehyde where 100% alcohol yield was achieved. Using atomic spectroscopy characterization and theoretical calculation, the genuine active sites of Co 1 /C 3 N 4 catalyst in reaction system were revealed in the form of CoN 3 - Cp* moieties ( Cp* , 1,2,3,4,5-pentamethylcyclopentadiene). Such a well-defined atomic catalyst opens a new avenue for the organic transformation application of single-atom catalysts in enzyme catalysis. • Atomically dispersed Co sites on carbon nitride nanosheets (Co 1 /C 3 N 4 ) were synthesized by crystal-assisted confinement pyrolysis approach. • Co 1 /C 3 N 4 manifested extraordinary performance for photocatalytic NADH regeneration, which could integrate the photo and enzyme catalysis. • The Co 1 in Co 1 /C 3 N 4 catalyst was found to interact with Cp* of Rh-based redox mediator in the form of CoN 3 - Cp* moieties.

Mass difference and polarization lead to low thermal conductivity of graphene-like carbon nitride (C3N)

The newly synthesized two-dimensional polyaniline (C3N) of graphene family attracted extensive research attention due to extraordinary electrical and electron-related properties, but its thermal properties have still been in its infancy although the thermal management is of critical importance for the performance and reliability of electron-related devices. Herein, we investigated the thermal transport properties of single-layer C3N with different system size by utilizing non-equilibrium molecular dynamics simulations. Compared with the graphene, the analysis of lattice dynamics and electron density distribution revealed that the lower thermal conductivity of single-layer C3N stems from the disorders from mass difference and the polarization from asymmetric electrical difference density. Moreover, the temperature dependence of thermal conductivity of single-layer C3N approaches κ ∼ T−1 when the system size increases. Our studies provide more physical insights into the thermal transport of emerging two-dimensional polymeric carbon nitride materials.

Superior stiffness and vibrational spectroscopic signature of two-dimensional diamond-like carbon nitrides

Abstract Carbon nitride materials are promising for applications in electronics, clean energy production, and heat dissipation. Two-dimensional (2D) diamond-like carbon nitrides α -C 2 N 2 , β -C 2 N 2 , and γ -C 4 N 4 rise as beyond graphene semiconductors. Here, we apply first-principles calculations and group theory to study their structure, mechanical properties, and vibrational signature. The α -C 2 N 2 is the strongest among them, with a 2D Young’s modulus E 2D equal to 616(6) N/m, followed by the γ -C 4 N 4 with an E 2D equal to 632(6) N/m and 581(7) N/m along its zigzag and armchair directions, respectively, and the β -C 2 N 2 with an E 2D equal to 582(9) N/m. These materials are about 2 times stiffer than graphene, and are the stiffest among 2D networks of carbon and nitrogen atoms. The zigzag direction of 2D γ -C 4 N 4 is approximately 8% stronger than its armchair direction, unusual for in-plane anisotropic 2D materials, where the armchair direction is considerably weaker than the zigzag direction. These findings from stress–strain analysis are consistent with the high sound speed and elastic constants values we found by using 2D density-functional perturbation theory framework, suggesting them for mechanical reinforcement. We report the phonon wavenumber, atomic vibrational pattern, and Raman and infrared spectra for all polytypes. The longitudinal and transverse optical modes of the in-plane isotropic polytypes display the breakdown of LO–TO splitting, characteristic of 2D polar crystals. We found that the difference between their phonon wavenumbers can be probed in their unpolarized Raman and infrared spectra. The simulated angular dependency of the Raman intensity under backscattering parallel and cross polarizations show how to assign the A 1 ′ and E ′ modes of the α -C 2 N 2 , the A 1 g and E g modes of the β -C 2 N 2 , and of the A g and B 1 g modes of the γ -C 4 N 4 , being key for polytype identification. These results provide comprehensive information on the emerging 2D diamond-like carbon nitrides, necessary for further developments on their synthesis, characterization, and future device fabrication.

Metal-free highly efficient photocatalysts for overall water splitting: C3N5 multilayers.

As a promising means of renewable energy storage, the production of molecular hydrogen and oxygen from photocatalytic water splitting has gained increasing interest. The optimal photocatalyst for water splitting should have high solar energy conversion efficiency and strong photocatalytic redox ability to drive the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, few photocatalysts have been reported to fulfil these two contradictive requirements. Here, we demonstrated from first-principles calculations that the recently synthesized two-dimensional carbon nitride (C3N5) multilayers can serve as promising candidates to reach this goal. The intrinsic electric field which is more pronounced in the multilayers alters the band alignment of the photocatalysts, making the HER and OER be driven solely by the photogenerated carriers. The thickness-dependent electronic band gap (2.95-2.16 eV) along with the high carrier mobility broadens the energy range of light absorption and promotes carrier separation and transfer, leading to high solar energy conversion efficiency. Our computational results offer not only low-cost, Earth-abundant and environmentally friendly photocatalysts but also a promising strategy for the design of photocatalysts for highly efficient overall water splitting without using sacrificial reagents.

Remarkable improvement in hydrogen storage capacities of two-dimensional carbon nitride (g-C3N4) nanosheets under selected transition metal doping

We have performed DFT simulations to quest for an optimal material for onboard hydrogen (H2) storage applications. Using first-principles calculations, we established that the selected transition metals (M: Sc, Ti, Ni, V) decorated two-dimensional (2D) g-C3N4 sheets as optimal materials with reversible and significantly high H2 gravimetric densities. By effectively avoiding metal-metal (M-M) clustering effect in case of mono doping, up to four molecules of H2 per dopant could be adsorbed with an average binding energy of around 0.30–0.6 eV/H2, which is ideal for practical applications. Decorating the g-C3N4 sheet with (M-M) dimers, the systems are found to be even more efficient for H2 binding than single dopant decoration. The stability of these M decorated g-C3N4 sheets have been confirmed with ab-initio molecular dynamics simulations. We have further calculated the H2 desorption temperatures of metal decorated g-C3N4 sheets, which confirms the practical application of these metal decorated sheets at ambient working conditions.

Two-dimensional carbon nitride (2DCN) nanosheets: Tuning of novel electronic and magnetic properties by hydrogenation, atom substitution and defect engineering

By employing first-principles calculations within the framework of density functional theory, we investigated the structural, electronic, and magnetic properties of graphene and various two-dimensional carbon-nitride (2DNC) nanosheets. The different 2DCN gives rise to diverse electronic properties such as metals (C3N2), semimetals (C4N and C9N4), half-metals (C4N3), ferromagnetic-metals (C9N7), semiconductors (C2N, C3N, C3N4, C6N6, and C6N8), spin-glass semiconductors (C10N9 and C14N12), and insulators (C2N2). Furthermore, the effects of adsorption and substitution of hydrogen atoms as well as N-vacancy defects on the electronic and magnetic properties are systematically studied. The introduction of point defects, including N vacancies, interstitial H impurity into graphene and different 2DCN crystals, results in very different band structures. Defect engineering leads to the discovery of potentially exotic properties that make 2DCN interesting for future investigations and emerging technological applications with precisely tailored properties. These properties can be useful for applications in various fields such as catalysis, energy storage, nanoelectronic devices, spintronics, optoelectronics, and nanosensors.

Exfoliation and Sensitization of 2D Carbon Nitride for Photoelectrochemical Biosensing under Red Light.

Two-dimensional carbon nitride (CN) has drawn increasing attention as a conjugated metal-free polymer for photoelectrochemical (PEC) biosensing. However, CN only absorbs ultraviolet and very limited visible light (λ<460 nm), which poses potential risks for biomolecules and also cannot pass through tissue for in vivo detection. Herein, simultaneous exfoliation and functionalization of CN nanosheets (CNNS) with copper phthalocyanine (TsCuPc) simply by mechanical milling, thanks to the delicate π-π interaction between them, is reported. Moreover, due to energy-level matching, an effective donor-acceptor (D-A) interaction with much-improved photocurrent under irradiation with red light (λ>630 nm) was observed for the as-prepared CNNS-TsCuPc. As an example, dopamine in blood was detected by using red light by a CNNS-TsCuPc photoelectrode with uncompromised linear range and detection limit, as well high selectivity. As one of the few successful demonstrations of red-light-responsive PEC sensing systems, this work takes a first step toward future in vivo applications by enriching the optoelectronic properties of CN with task-specific antenna molecules via D-A interaction.

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.

Metal-Oxide-Mediated Subtractive Manufacturing of Two-Dimensional Carbon Nitride for High-Efficiency and High-Yield Photocatalytic H2 Evolution.

g-C3N4 is a promising visible-light-driven photocatalyst for H2 evolution reaction; however, the achievement of the high photocatalytic performance is primarily limited by the low separation efficiency of the photogenerated charge carriers and partly restricted by the slow kinetics of charge transfer. 2D g-C3N4 can significantly improve the charge generation, transfer, and separation efficiencies. The 2D g-C3N4-based Z-scheme heterostructure can further enhance the charge-carrier separation and simultaneously increase the redox ability, thereby further boosting the photocatalytic performance. Here we report a transition-metal-oxide (TMO)-mediated subtractive manufacturing process toward the large-scale synthesis of 2D g-C3N4 and the simultaneous formation of a 2D/2D TMO/g-C3N4 Z-scheme heterojunction. The TMOs serve as catalysts to facilitate the hydrolysis reaction of the bulk g-C3N4 in the presence of moist air, forming 2D g-C3N4. The resulting 2D/2D TMO/g-C3N4 catalysts, in particular, 2D/2D Co3O4/g-C3N4, exhibit high-efficiency and high-yield photocatalytic H2 evolution due to the suppression of electron-hole pair recombination and enhanced redox ability. The 2D/2D Co3O4/g-C3N4 photocatalyzes the H2 evolution with a rate of ∼370 μmol h-1 within λ > 400 nm. The external quantum efficiency of 2D/2D Co3O4/g-C3N4 at λ = 405 nm reaches 53.6%, which is among the highest values for g-C3N4-based catalysts.