Doped Nitrogen Atoms Research Articles

Activation of Nitrogen-Doped Carbon Materials on the C–N Bond and C–O Bond: Modeling Study Toward Enhanced Pyrolysis Products

The present study investigated the effects of doped nitrogen atoms in carbon materials on the hydrodeoxygenation (HDO) and hydrodenitrogenation (HDN) processes. Density functional theory was used to evaluate the structural stability and catalytic activity of different nitrogen-doped carbon cluster models for HDO and HDN reactions. The results showed that the carbon atom near the nitrogen in graphite is the active center of nitrogen-doped carbon catalytic activation of hydrogen. In the H2-rich system, N@C catalysts can not only activate hydrogen molecules but also directly break the C–O/C–N bond. Results confirmed that the nitrogen assembly structure can affect the performance of C–O/C–N bond activation, and meta-doping nitrogen sites have the highest catalytic activity. This study provides theoretical guidance and views for the development of high-performance carbon catalysts that can replace conventional metal catalysts.

Facile carbon cloth activation strategy to boost oxygen reduction reaction performance for flexible zinc‐air battery application

AbstractFlexible and all‐solid‐state zinc‐air batteries (ZABs) are highly useful and also in demand due to their theoretical high energy densities and special applications. The limitation in their performance arises due to their catalyst‐coated cathode electrodes in terms of catalytic activity and stability as well as cost. In this paper, a novel and environmentally friendly activation strategy is developed to activate the carbon cloth (CC) for the electrodes. The activated CC serves as a catalyst‐free air cathode with high conductivity, excellent mechanical strength, and flexibility, in addition to low cost. The strategy is performed by simply electro‐oxidizing and electroreducing CC under ultrahigh direct current (DC) voltage in a diluted NH4Cl aqueous electrolyte. It is found that the electro‐oxidation not only results in the formation of a graphene‐like exfoliated carbon layer on the surface of CC but also induces the incorporation of oxygen‐containing groups and doping of nitrogen and chloride atoms. After the electroreduction, the π‐conjugated carbon network of CC is partially restored, leading to the recovery of electroconductivity. Such an electroactivated CC shows excellent oxygen reduction reaction activity. The aqueous flexibility and all‐solid‐state ZABs are assembled using such an electroactivated CC cathode without any catalyst loading. Both ZABs can achieve good durability and deliver high peak power density and an energy density as high as 690 Wh kg−1, demonstrating the excellent potential of this electroactivated CC in practical devices.

Sulfur & nitrogen co-doped electrospun carbon nanofibers as freestanding electrodes for membrane capacitive deionization

Capacitive deionization (CDI), especially membrane capacitive deionization (MCDI) technology, is an energy-efficient and environmentally friendly water desalination technology. Tremendous efforts have been devoted to designing and preparing high-performance and applicable electrode materials for CDI and MCDI. In this work, sulfur and nitrogen co-doped carbon nanofibers (SCNFs) are prepared by a facile co-electrospinning strategy coupled with subsequent high-temperature heat treatment, and directly used as monolithic and binder-free electrodes for MCDI. Benefiting from the integrated structural and compositional merits, i.e. 3D network composed of disorderly stacked 1D nanofibers and uniform distribution of nitrogen and sulfur atoms, the as-obtained SCNFs exhibit superior electrosorption ability and excellent cycling stability, with the salt adsorption capacity up to 29.50 mg g−1 and the current efficiency higher than 80% when desalting 500 mg L−1 NaCl solution at the voltage of 1.4 V. The doped nitrogen and sulfur atoms in SCNFs not only effectively improve their electrical conductivity and wettability but also tailor the pore structure, thus providing more active sites for ions adsorption. The heteroatom doping strategy could shed new light on the design of high-performance carbon-based electrodes for the electrochemical MCDI application.

Preparation of activated coke by carbonization, activation, ammonization and thermal treatment of sewage sludge and waste biomass for SO2 absorption applications

Flue gas desulfurization of coal-burning power plants is imperative to mitigate pollution and acid rain. Use of activated coke as a sulfur dioxide adsorbent is a promising technology, particularly since activated coke can also effectively remove other emissions, such as mercury. In this manuscript, a modified method of ammonia water was used to prepare activated coke for flue gas desulfurization. The feedstock is a blend of sewage sludge and waste biomass, at a mass ratio of 2:1. This material was carbonized prior to activation and ammonization; in some cases, additional thermal treatment was applied. The products were successfully tested for sulfur dioxide adsorption. A graphene model incorporating nitrogen-containing functional groups was used to simulate the sulfur dioxide adsorption process. Thereby, the effects of different ammonia modification concentrations on the physical and chemical properties of activated coke were studied, and the sulfur dioxide adsorption process of nitrogen-containing functional groups (such as pyridine and pyrrole) in activated coke, during flue gas desulfurization, was simulated. This study confirmed that the method of ammonization and heating can introduce nitrogen-containing functional groups on the surface of the activated coke. This greatly improves its chemical properties and, as a result, it markedly improves its SO2 adsorption capacity. It was found through simulation that the doping of nitrogen atoms changes the uniform electrostatic potential distribution and changes the surface polarity. H2O, pyridine functional groups and pyrrole functional groups can promote the adsorption of SO2 on the graphene surface. The pyrrole functional group showed selective adsorption for both SO2 and H2O, but it was predicted to be more effective in adsorbing SO2 than in adsorbing H2O. The pyridine functional group showed no selective adsorption for SO2 and H2O, and it was predicted to be more active in adsorbing SO2 when compared with the pyrrole functional group. The O2 had no effect on the physical adsorption of SO2 on the graphene.

Self-supporting nitrogen-doped reduced graphene oxide@carbon nanofiber hybrid membranes as high-performance integrated air cathodes in microbial fuel cells

The traditional air cathode in microbial fuel cell (MFC) usually consists of catalyst layer (CL), supporting layer (SL) and conductive gas diffusion layer (GDL), the overall MFC performance is inevitably affected by the additional and expensive adhesives and conductive agents. Here, we developed an integrated air cathode in MFC without any additional SL, GDL or adhesives. The integrated air cathode was self-supporting nitrogen-doped reduced graphene oxide@carbon nanofiber (N-rGO@CNF) hybrid membranes fabricated by electrospinning with subsequent heat-treatment under ammonia atmosphere. The as-fabricated N-rGO@CNFs possessed far superior MFC performance and oxygen reduction reaction (ORR) activity to the pristine nitrogen-doped carbon nanofibers (NCNF) and commercial activated carbon (CAC). The amount of rGO embedded into CNF had prominent influence on their ORR activities and MFC performances. N-5-rGO@CNF had the lowest resistance and the maximal exchange current density, exhibiting desirable oxygen reduction performance via a four-electron pathway. The maximum power density of N-5-rGO@CNF can reach 826 mW m−2 in MFC, which is approximately 9, 2.53 and 1.82 times of pristine NCNF, CAC and Pt/C with values of 91, 327 and 454 mW m−2. The outstanding performance of the integrated air-cathodes originates from the integrality, brevity and hybrid composition of the electrospun nanofiber membrane. The appropriate embedded rGO not only improves the bulk conductivity of the rGO@CNF to promote ion adsorption, but also provides vacancies to accommodate ions, the doped nitrogen atoms facilitate O2 adsorption and/or subsequent O–O bond breaking, thus improving the electrochemical performance of N-rGO@CNF in MFC.

Hydrogen Generation from Methane on FeN3 and FeN4 Embedded Graphene Surface Using DFT Method with Grimme-D3 Dispersion Correction

In this article, the catalytic effect of Nx graphene embedded by Fe metal has been conducted for methane (CH4) decomposition reaction using Density Functional Theory (DFT) calculations with Grimme-D3 dispersion correction. Recently, the catalytic activities of TMNx (x=3→4) graphene surfaces on chemical reactions have attracted a lot of attention. In particular, the activities of graphene surfaces can be increased by different numbers of doped nitrogen atoms on the graphene surface. For analyzing the adsorption mechanism, adsorption energy, BBader charge, charge density difference and the partial density of state have been calculated. CH4 molecule is attached into FeN3 embedded graphene physically with higher adsorption energy (-0.41 eV) than that of FeN4 graphene. Their charge transfers from the molecule to the surface are quite small 0.0041e^- for FeN3 and 0.0003 e^- for FeN4 graphene. The decomposition of methane has been calculated using the nudged elastic band method. There are the sequential four steps (CHx → CH(x-1)+H, x=4,3,2,1). All reactions in these steps are endothermic. The activation energy of the first hydrogen production from methane (CH4 →CH3 +H) on FeN3 surface is 0.39 eV while the barrier energy is 0.20 eV. However, the same reaction on FeN4 graphene has a quitequite high activation energy same as its barrier energy (1.84 eV), and its initial state switches directly to the final state without the transition state. The activation energies of most steps on FeN3 embedded graphene are much lower than that of FeN4 graphene surface. Therefore, dehydration reactions can occur with lower energy on FeN3 surface. This study can assist to discover a promising catalyst for methane dissociation through their finding.

Effect of dopant gas pressure on the growth of magnetron sputtered CuO thin films for electrical and optical applications

Tunability offers in the optoelectronic properties of TCOs open up the way to advanced applications in the field of photovoltaics. However, the conductivity of p-type TCOs remains an unresolved problem. In this work, an advantage of RF magnetron sputtering is employed to obtain polycrystalline CuO film at room temperature with better conductivity and optimum bandgap by controlling nitrogen gas pressure. Doping of N2 gas pressure has a significant influence on the morphology of CuO films, resulting in improved electrical and optical properties of films at room temperature. The variation of structural characteristics with respect to N2 gas pressure is discussed in detail using XRD, AFM, SEM, and EDX measurements, and these results confirm nitrogen's impact in improving the property of the fabricated film. The results show that the crystalline size, as well as the crystalline quality of the film, was found to increase with the increase in N2 gas pressure at room temperature. Atomic force microscope (AFM) shows that all the deposited films are well adherent and grains are uniformly distributed over the surface of the substrate. The simultaneous effect of doping and grain boundary migration of nitrogen atom into CuO lattice increases crystallinity and the mobility of charge carriers at room temperature. This experimental strategy made CuO a good p-type material with mobility of 2.17 × 103cm2/Vs and bandgap of 2.44eV at N2 gas pressure of 2 × 10−2mbar and resistivity is decreased due to high mobility obtained by tuning N2 gas pressure. These results suggest that the electrical and optical properties of CuO thin films can be modulated by optimizing the carrier concentration and thus mobility by controlling the N2 gas pressure.

Density functional theory investigation of As4 adsorption on Ti, V, Cr, Mn-doped graphene

Coal gasification technology can effectively solve the problem of clean coal utilization, but the problem of volatilization of harmful metals such as arsenic in the coal gasification process cannot be underestimated. In this paper, based on DFT (density functional theory), the adsorption characteristics of As4 on the surface of different carbon-based single-atom Ti/V/Cr/Mn adsorbents (nitrogen atom-doped, single vacancy and double vacancy) were studied. The single-atom adsorbent geometry, adsorption configuration, adsorption energy, electronic structure, electron density and other data were analysed. By comparing and analysing the calculation results of sixteen adsorbents, it is found that the catalyst with the double-deficient nitrogen-doped substrate has higher stability. Through the analysis of charge transfer and density of state, it was found that the adsorption of a single-atom adsorbent catalyst to As4 is related to charge transfer and hybridization. In particular, doped nitrogen atoms can enhance the charge transfer and hybridization of the system. amongst the sixteen adsorbents, the double-vacancy nitrogen-doped Ti catalyst is a promising As4 adsorbent, which provides a reference for further research on the adsorption of toxic gases on the surface of single-atom catalysts and the design of new nonnoble metal adsorbents.

Tuning azulene defects and doping of N atoms in graphene nanosheets: Improving nonlinear optical properties of carbon-based nano materials

Recent successful syntheses of azulene-defect graphene nanosheets (GNSs) pave a path for the applications of those GNSs in nonlinear optics, since azulene-defect GNSs maintains the thermal stability of carbon-based nanomaterials and possesses potential large nonlinear optical (NLO) responses. In the present work, azulene-defect GNSs with different relative position and orientation are designed for applications in optoelectronics and nonlinear optics. The all-carbon azulene-defect GNS Paral-2 with parallel orientated azulenes has good electronic kinetic stability as well as a large static first hyperpolarizability (<β0>) of 1032.28 × 10−30 esu (18.43 × 10−30 esu per heavy atom). The Paral-0-4N, formed by replacing four edge C atoms with N atoms in the GNS Paral-0, has the largest <β0> (1247.68 × 10−30 esu, 22.28 × 10−30 esu per heavy atom) due to the charge transfer based electron excitations and the polar structure while with enhanced electronic kinetic stability. The two-dimensional second order NLO spectra of those azulene-defect GNSs provide vital information for further experimental exploration and applications. The introduction of polar azulene in GNSs to improve the NLO responses and doping of nitrogen atoms to enhance the electronic kinetic stability of GNSs provide a practical strategy and useful information for future NLO materials design.

Effect of N-doping on tribological properties of graphene by molecular dynamics simulation

Graphene has attracted a lot of attention due to its excellent electrical properties, however, the gapless nature of graphene limits its further applications. Doping is an effective way to open the bandgap, in which nitrogen-doped (N-doped) graphene has potential applications, but the study of its tribological properties is still lacking. In this work, the effects of nitrogen doping on the tribological properties of graphene under different interfacial structures are investigated by molecular dynamics simulation. The simulation models include a hexagonal graphene sheet, graphene or N-doped graphene substrate. The results show that the nitrogen doping has different effects on friction when interface structure is in a commensurate state and an incommensurate state. In a commensurate state, N-doping reduces the friction between interfaces in all cases, but the friction first goes up and then decreases with the increase of doping ratio of nitrogen. The local maximum value of friction occurs at a doping ratio of 7.5%. This phenomenon results from the interface structure and the change of van de Waals force between interfaces. The introduction of nitrogen atoms causes the lattice of graphene to distort, which results in the formation of local incommensurate state, thus reducing the interfacial potential barrier and friction. However, the van der Waals force between nitrogen atom and carbon atom between layers is stronger than that between carbon atoms and carbon atoms, which causes the friction to increase. When the doping ratio is low or high, lattice distortion plays more important role. The friction of N-doped graphene shows much smaller increase with load than that of ideal graphene, which indicates that the N-doped graphene possesses a better performance under high load. When the interface structure is in an incommensurate state, the introduction of nitrogen atoms shows slight influence on lattice mismatch, therefore, the change of atomic type plays a dominant role in determining the friction between interfaces, which goes up with the increase of N-doping ratio. When the substrate is graphene with vacancy defects, the value of friction between interfaces is larger than the ideal graphene substrate or N-doped graphene substrate, which indicates that the doping of nitrogen atoms has positive effect on reducing the friction of graphene with defects.

Converting amorphous kraft lignin to hollow carbon shell frameworks as electrode materials for lithium-ion batteries and supercapacitors

Lignin has been widely used as a high-quality carbon source in the preparation of carbon electrodes. Because the skeleton of lignin molecules is an unordered three-dimensional network structure, it is difficult to obtain high-performance porous carbon electrode materials with regular structures by conventional carbonization methods. To improve the electrochemical performance of lignin-based carbon, green, convenient and mass-produced lignin-based porous hollow carbon shell frameworks (HCSFs) were proposed. With the help of electrostatic forces, lignin/silica nanocomposites were generated by an insitu self-assembly and coprecipitation method using quaternary ammonium lignin and sodium silicate as raw materials. After carbonization and activation, HCSFs with hollow porous frame structures rich in nitrogen were obtained. The prepared HCSFs can maintain a reversible specific capacity of 480 mA h g−1 after 200 cycles at 200 mA g−1 as a lithium-ion battery anode, and they can also maintain a specific capacity of 180.4 mF g−1 after 10,000 cycles at 1 A g−1 as a supercapacitor electrode. Their better energy storage performance is mainly attributed to the special hollow shell structure of HCSFs, which can provide channels for rapid ion transport, and the doping of nitrogen atoms can also provide an increase in the number of storage sites. This work provides a theoretical basis for the preparation of carbon shells from biomass and widens the application field for the high value utilization of industrial lignin.

Insights of Pt Stabilization by Nitrogen-Doped Carbon for Oxygen Reduction Reaction

Highly dispersed and uniformly distributed platinum nanoparticles (Pt NPs) supported on carbon are highly desirable for oxygen reduction reaction (ORR), especially in fuel cell application. When oxygen is flown across the catalysts, the smaller particles prone to oxidation even at ambient conditions, which was demonstrated in recent x-ray diffraction (XRD) studies using synchrotron radiation [1] and benchtop powder XRD with a high sensitivity silicon strip detector [2-4]. Additionally, these oxidized Pt NPs lead to sintering of Pt phase into larger particles and a corresponding loss in catalytic active sites, which eventually causes the loss in catalyst reactivity. Systematic doping of nitrogen atoms into carbon matrix is a promising method to improve the ability to control of such oxidation and sintering of Pt NPs during ORR. This study derived a N-doped carbon by high temperature pyrolysis of poly-phenylporphyrin to investigate the effects of N atoms inside the carbon structure in Pt NPs stabilization against oxidation and thermal sintering. Strong electrostatic adsorption technique (SEA) was used to synthesize ultra-small (<2 nm) particle with uniform size distribution and improved dispersion. To compare the results obtained for N-doped carbon supported catalyst, similar studies were conducted for a N-free carbon supported catalysts. It was hypothesized that ultra-small Pt NPs prepared by SEA onto N-doped carbon will exhibit superior resistance to oxidation and sintering vis-à-vis N-free carbon support. In this study, with an in-situ high sensitivity powder XRD that allows the observation of 1 nanometer-sized NPs, we demonstrated the stabilizing effect of N-doped carbon on Pt NP oxidation as well as thermal sintering and were able to isolate the effect of Pt NP size on both properties. Although in the prior X-ray photoelectron spectroscopy (XPS) work, the appearance of higher Pt valances in N-doped carbon supported Pt catalysts was attributed to the electron transfer from Pt NPs to the underlying support via Pt-N interactions, with in-situ XPS this work clearly revealed that Pt-N bonds are not associated with higher Pt valences, but instead, with a shift in the Pt0 binding energy ( Figure 1).

Nitrogen-Doped Reduced Graphene Oxide Supported Pd4.7Ru Nanoparticles Electrocatalyst for Oxygen Reduction Reaction.

It is imperative to design an inexpensive, active, and durable electrocatalyst in oxygen reduction reaction (ORR) to replace carbon black supported Pt (Pt/CB). In this work, we synthesized Pd4.7Ru nanoparticles on nitrogen-doped reduced graphene oxide (Pd4.7Ru NPs/NrGO) by a facile microwave-assisted method. Nitrogen atoms were introduced into the graphene by thermal reduction with NH3 gas and several nitrogen atoms, such as pyrrolic, graphitic, and pyridinic N, found by X-ray photoelectron spectroscopy. Pyridinic nitrogen atoms acted as efficient particle anchoring sites, making strong bonding with Pd4.7Ru NPs. Additionally, carbon atoms bonding with pyridinic N facilitated the adsorption of O2 as Lewis bases. The uniformly distributed ~2.4 nm of Pd4.7Ru NPs on the NrGO was confirmed by transmission electron microscopy. The optimal composition between Pd and Ru is 4.7:1, reaching −6.33 mA/cm2 at 0.3 VRHE for the best ORR activity among all measured catalysts. Furthermore, accelerated degradation test by electrochemical measurements proved its high durability, maintaining its initial current density up to 98.3% at 0.3 VRHE and 93.7% at 0.75 VRHE, whereas other catalysts remained below 90% at all potentials. These outcomes are considered that the doped nitrogen atoms bond with the NPs stably, and their electron-rich states facilitate the interaction with the reactants on the surface. In conclusion, the catalyst can be applied to the fuel cell system, overcoming the high cost, activity, and durability issues.

Insight into the activity of TiO2@nitrogen-doped hollow carbon spheres supported on g-C3N4 for robust photocatalytic performance

Designing an advance nanostructure semiconductor is an efficient strategy to promote the charge separation and thus improve the photocatalytic activity. Herein, a relatively high recombination rate of electron-hole pairs and low specific surface area of g-C3N4 (GCN) were subjected to the surface deposition of the core shell nanoparticles composed of nitrogen doped hollow carbon spheres (N-HCSs) as the supporting scaffold and TiO2 nanoparticles as the photoactive layer. The ternary composites with different TiO2@N-HCS content were prepared through a simplified nanocasting method followed by the two consecutive hydrothermal process. The effects of nitrogen doping in carbon framework, and nanoparticles amount were evaluated on the photocatalytic ability through the photodegradation of tetracycline (TC) molecules under the visible light irradiation. At the optimum content of core shell nanoparticles (7 wt%), the solar-driven TC photocatalytic degradation for ternary composite was approximately 85%, which was much better (about three times) than that of the pure GCN. More interestingly, the experimental results revealed that doping of nitrogen atoms has a positive role on the charge separation and the resulting photocatalytic efficiency. The employed hollow carbon spheres here play three important roles: (1) providing a substrate to uniformly dispersion of TiO2 nanoparticles without any aggregation; (2) reducing the combination of charge carriers and improving the separation of photoinduced carriers; (3) formation of larger surface area and more active sites on the photocatalyst surface. Furthermore, the underlying photocatalytic degradation mechanism was introduced by the controlled experiments using photoluminescent and radical scavenger tests.

Hierarchical Design of Functional, Fibrous, and Microporous Polymer Monoliths for the Molecular Recognition of Diethylstilbestrol.

This paper demonstrates the hierarchical design of functional, fibrous polymer monoliths. The monoliths are composed of conjugated microporous polymers that not only are embedded with heteroatoms but also feature fibrous yet compressible structures due to the in situ self-assembly process that occurs during the polymerization process. Therefore, the doped nitrogen atoms can allow the growth of zeolitic imidazolate framework (ZIF) nanocrystals, which causes the homogeneous encapsulation of individual fibers. The resulting hybrid monoliths exhibit enhanced physical properties as well as catalytic activity, allowing the formation of an additional coating layer via a thiol-epoxy reaction. The deliberate inclusion of template molecules during the reaction forms molecularly imprinted sites on the fibers to afford functional monoliths. As a proof of concept, the hierarchically designed materials are able to show effective recognition properties toward diethylstilbestrol, an endocrine disruptor, taking advantage of the binding sites that selectively capture the analyte molecules and the fibrous morphology that increases the accessibility of these binding sites. We envisage that the incorporation of various heteroatoms or nanocrystals will bring about the bespoke design of advanced monoliths with autonomous functions, leading to smart textile systems.

Theoretical insights for CoNxC4-x-graphene (x = 0–4) materials as high performance low-cost electrocatalysts for oxygen reduction reactions

Transition metal-doped two-dimension carbon matrices have attracted particular interest as oxygen reduction reaction (ORR) catalysts because of their low-cost, good conductivity of electricity, and promising applications in fuel cells and metal-air batteries. Herein, a density functional theory study is performed on the CoNxC4-x (x = 0–4) embedded graphene to investigate the effect of N atoms doping number and doping configurations. The calculated formation energy and average bond length of Co–C/N drop off with the increase in N atoms of the CoNxC4-x graphene system. The most stable adsorption configurations and the relevant adsorption free energies of key ORR intermediates on Co–N sites toward the CoNxC4-x graphene system are obtained, indicating that N doping levels and doping configurations have a regular influence on this system. On this basis, scaling relations can be obtained among the adsorption free energies of *OH, *OOH, and *O. The volcano plot of ORR theoretical overpotential (ηth) using ΔG*OH−ΔG*O as a descriptor was further established, which revealed that ηth is influenced by the adsorption mode and the free energy change in the active site. For all studied systems, the ORR substeps are all downhill at zero potential from the plotted free energy diagrams. The density of states is employed to further illustrate that the hybridization between the Co atom and the O atom is a deterring factor on electrocatalyst activity. These calculations reveal the influence of nitrogen atom doping in Co–N-graphene catalysts and afterward point a direction for designing high-performance non-precious metal ORR electrocatalysts.

A facile method for preparation of porous nitrogen-doped Ti3C2Tx MXene for highly responsive acetone detection at high temperature

Porous nitrogen-doped Ti3C2T[Formula: see text] MXene (N-TCT) with a three-dimensional network structure is synthesized via a simple sacrifice template method and then utilized as an acetone gas sensor. By introducing nitrogen atoms as heteroatoms into Ti3C2T[Formula: see text] nanosheets, some defects generate around the doped nitrogen atoms, which can greatly improve the surface hydrophilicity and adsorption capacity of Ti3C2T[Formula: see text] Mxene nanosheets. It resulted in the enhanced gas sensitivity, achieving a response value of about 36 ([Formula: see text]/[Formula: see text] × 100%) and excellent recovery time (9s) at 150[Formula: see text]C. Compared with the pure Ti3C2T[Formula: see text]-based gas sensor (381/92s), the response and recovery time are both obviously improved, and the response value increased by 3.5 times. The gas-sensing mechanism of the porous N-TCT is also discussed in detail. Based on the excellent gas sensitivity of porous N-TCT for highly responsive acetone detection at high temperatures, the strategy of nitrogen-doped two-dimensional nanomaterials can be extended to other nanomaterials to realize their potential applications.

Mechanism of Nitrogen-Doped Ti3C2 Quantum Dots for Free-Radical Scavenging and the Ultrasensitive H2O2 Detection Performance.

MXene quantum dots feature favorable biological compatibility and superior optical properties, offering great potential for biomedical applications such as reactive oxygen species (ROS) scavenging and fluorescence sensing. However, the ROS scavenging mechanism is still unclear and the MXene-based materials for ROS sensing are still scarce. Here, we report a nitrogen-doped titanium carbide quantum dot (N-Ti3C2 QD) antioxidant with effective ROS scavenging ability. The doped nitrogen atoms promote the electrochemical interaction between N-Ti3C2 QDs and free radicals and thus enhance their antioxidant performance. Density functional theory (DFT) simulations reveal the hydroxyl radical quenching process and confirm that the doped N element promotes the free-radical absorption ability, especially for -F and -O functional groups in N-Ti3C2 QDs. Furthermore, N-Ti3C2 QDs show rapid, accurate, and remarkable sensitivity to hydrogen peroxide in the range of 5 nM-5.5 μM with a limit of detection of 1.2 nM within 15 s, which is the lowest detection limit of the existing fluorescent probes up to now. Our results provide a new category of antioxidant materials, a real-time hydrogen peroxide sensing probe, promoting the research and development of MXene in bioscience and biotechnology.

Brønsted acid functionalized carbon catalyst for synthesis of biologically active coumarin-substituted bis(indolyl)methanes

A novel carbon based catalyst has been prepared for the synthesis of potential anticancer compounds with low toxicity by an ionic liquid assisted doping process. Sulphonic acid functionalized nitrogen sulphur co-doped graphite (SO3H-NSG) based catalyst was prepared by coating the carbon surface with the sulphonic acid bearing ionic liquid and annealing the resulting compound. X-ray photoelectron spectroscopy revealed the successful doping of nitrogen and sulphur atoms in the graphitic matrix and the functionalization of the surface with sulphonic acidic sites. The catalyst was used for the synthesis of biologically active coumarin-substituted bis(indolyl)methanes that were finally evaluated for their toxicity and anticancer properties. The cytotoxicity results unveiled that the iodo derivative of the coumarin-substituted bis(indolyl)methanes showed best anti-cancer activity among the four derivatives synthesized.

Synergistic effect of Cu decoration and N doping in divacancy defected graphene nanoribbons on hydrogen gas sensing properties: DFT study

Density functional theory (DFT) calculations have been employed to analyze the molecular hydrogen interaction on Cu decorated nitrogen doped divacancy defected graphene nanoribbons (GNRs). In this study, 5-8-5 double vacancy has been specified as a functional defect in order to study their effect on the electronic properties of GNRs. Divacancies are considered to be thermodynamically more favorable than monovacancies because of low formation energy. Moreover, the introduction of nitrogen defects had a massive influence on adsorption properties. The adsorption capability of the complex systems improved as the concentration of nitrogen atoms increased, but when four nitrogen atoms were doped, the efficiency decreased significantly. Aside from adsorption energy, other parameters such as bonding distance, charge transfer; electronic properties were examined and found to be consistent with the previous findings. Our results suggested that simultaneous doping of nitrogen atoms and Cu decorated defected GNR could be a potential material for hydrogen sensing and could be utilized for future applications. Hence, it is worth noting that adding appropriate dopants and defects to the graphene-based gas sensors could greatly improve their sensitivity.