NN Bond Research Articles

D-band center modulation of B-mediated FeS2 to activate molecular nitrogen for electrocatalytic ammonia synthesis

Electrocatalytic nitrogen fixation is a promising approach for ambient ammonia synthesis. The key that limits the improvement of ammonia evolution performance is the NN bond cleavage of molecular nitrogen. One effective route to break this bottleneck is the d-band center modulation of catalysts. Herein, a nonmetal boron mediated FeS2 (B-FeS2) is developed for electrocatalytic nitrogen fixation. The B-mediation alters the spin-orbits of Fe site and upshifts the d-band center of FeS2, thus inducing a strong d-π* interaction between the Fe site and nitrogen to activate NN bond. Besides, the experimental and theoretical calculations indicate the B-mediation reduces the energy barrier for *NNH intermediate, thus significantly accelerating ammonia production. As a result, B-FeS2 displays high ammonia yield (1.56 mmol·g−1·h−1) with 12.6 % Faradaic efficiency. This strategy of d-band center tuning induced by the B-mediation provides a distinctive insight for the design of high-efficiency electrocatalysts.

In situ fabrication of N-doped Ti3C2Tx-MXene-modified BiOBr Schottky heterojunction with high photoelectron separation efficiency for enhanced photocatalytic ammonia synthesis

NH3 synthesis under ambient conditions remained great challenge owing to the strong NN bond energy, high ionization energy, and poor proton affinity of NH3. Herein, dopamine hydrochloride was selected as a N doping source to in-situ polymerization on the Ti3C2Tx MXenes surface forming a highly efficient co-catalyst, and then integrated into BiOBr to induce a super high photocatalysis for ammonia synthesis. As expected, BiOBr was evenly dispersed on the N-Ti3C2Tx MXene surface. The photocatalysis possessed a high degree of photocatalytic ammonia evolution (270.73 μmol/g·h and 3.27 times higher than that of BiOBr) and retained about 60 % of its ammonia evolution after five consecutive cycles. The photocatalyst mechanism is high dispersion and elevated conduction band potential of N-Ti3C2Tx MXene nanosheets facilitated charge transfer to the active sites of the nanosheets. This study proved the potential use of dopamine hydrochloride in MXene photocatalytic materials for solar energy utilization ammonia synthesis.

Design of novel transition metal doped pyrazine-modified graphyne as highly effective electrocatalysts for nitrogen fixation

The production of ammonia consumes plenty of energy every year, so it is crucial to develop efficient and sustainable methods of electrocatalytic ammonia synthesis. Although some materials have shown high catalytic activity for nitrogen reduction reaction (NRR), searching for catalytic materials with excellent electrical properties is still a promising topic. Graphyne and its family are well suited as catalysts due to their high electrical conductivity and carrier mobility. In this paper, we have systematically studied the catalytic properties of transition metal atoms anchored on pyrazine-modified graphyne (pyGY) for NRR by density functional theory calculations. Through a series of scanning procedures, Nb, Mo and W-pyGYs are found to be excellent catalysts for electrocatalytic NRR with limiting potentials of − 0.43 V, − 0.36 V, and − 0.46 V, respectively. Moreover, solvation effects are considered and the lowering effect of solvent on the limiting potential is revealed. In addition, the mechanism of superior catalytic activity is explored from an electronic perspective. Finally, two descriptors related to electronegativity and valence electron number are selected to clarify the trend of NRR activity. The volcano diagram trends of NN bond length, Gibbs free energy change in the first hydrogenation step and limiting potential are revealed. This work provides a reliable method for screening efficient electrocatalytic nitrogen fixation catalysts.

Cyclonickelated complexes featuring a terminal or bridging triazole

Cyclometallated complexes can serve as models for studying the mechanistic details of CH functionalization processes. In this context, we have shown that the cyclonickelated complexes {κP,κC-(i-Pr)2PO-Ar}Ni(Br)(NCMe) can be isolated from CH nickelation of aryl phosphinites. Previous studies showed that treating these compounds with PhCH2Br or (i-Pr)2PCl allows CC and CP functionalized products, respectively, whereas reaction with hydroxylamines HO-N(CH2R)2 fails to promote the desired CN functionalization, giving instead the imine adducts {κP,κC-(i-Pr)2PO-Ar}Ni(Br)(κN-N(CH2R)CH = CHR) arising from net dehydration of the hydroxylamine substrate. The present report describes a study on the reactivities of the dimeric complexes [{κP,κC-(i-Pr)2P-OAr}Ni(μ-Br)]2 (Ar = C6H4, 1a;4-OMe-C6H3, 1b; 4-Cl-C6H3, 1c; 1-naphthyl, 1d; 4-OMe,1-naphthyl, 1e) with 4-Amino-4H-1,2,4-triazole featuring a potentially labile NN bond. As was observed previously with hydroxylamines, here too the hoped-for CN functionalization did not materialize, the reactions giving instead the mononuclear triazole adducts {κP,κC-(i-Pr)2P-OAr}Ni(Br)(κN-4-amino-4H-1,2,4-triazole) 2a and 2e and the triazole-bridged dinuclear adducts [{κP,κC-(i-Pr)2PO-Ar}Ni(Br)}2(μ,κN,κN’-4-amino-4H-1,2,4-triazole) 3b, 3c, and 3d. The solid-state structures of these new compounds reveal the following three features: (a) slightly distorted square planar geometries around the Ni center, (b) 50-65° angles between the plane of the triazole ligand and the coordination planes, and (c) significantly shorter Ni-N distances in the mononuclear adducts. Variable temperature NMR monitoring of the reactions between the Ni precursors and the triazole substrate pointed to a dynamic exchange process between the mono- and dinuclear triazole adducts.

In silico screening of potential Tumor necrosis factor alpha (TNF-α) inhibitors through molecular modeling, molecular docking, and pharmacokinetics evaluations

The multifunctional cytokine TNF-α serves as a key biological mediator for several important immune processes, such as inflammation, infection, and antitumor responses. It is crucial for both acute and chronic neuroinflammation, as well as several neurodegenerative diseases. For the treatment of inflammatory diseases, the synthetic antibodies etanercept, adalimumab, and the generic medication Diclophenac directly bind to TNF-α, preventing it from interacting with the tumor necrosis factor receptor (TNFR). These approved drugs have detrimental side effects. There is therefore a lot of interest in the scientific world to identify new small-molecule-based TNF-α inhibition therapies. In this study, a set of molecular modeling techniques have been applied including the QSAR model, docking, and pharmacokinetics prediction to identify and optimize novel TNF-α inhibitors. Based on the modeling techniques applied, the QSAR shows (R2= 0.9534, Q2 = 0.8707, Rpred2= 0.8599, cRr2= 0.8994, SEE = 0.1067). The results showed that the function of these discovered compounds was not connected to lipophilicity, whereas less lengthy NN bonds and long substituents might lead to quite bioactive molecules. The discovered hits indicate promising inhibition against TNF-α and lacked harmful effects. Most of the discovered molecules had higher TNF-binding affinity than the reference substance. Furthermore, comparing the reference drug grading (ds) of 0.38, molecule 74 with PubChem ID 2998055 exhibits superior properties with a drug grading (ds) of 0.76. As a whole, the discovered molecules have favorable pharmacokinetics, pharmacodynamics, and drug interaction properties that suggest promising TNF- inhibition and lacked toxicity, suggesting that they are potential drug candidates.

Dissociative recombination of N_2hbox {H}^+: a revisited study

Dissociative recombination of N_2H^+ is explored in a two-step theoretical study. In a first step, a diatomic (1D) rough model with a frozen NN bond and frozen angles is adopted, in the framework of the multichannel quantum defect theory (MQDT). The importance of the indirect mechanism and of the bending mode is revealed, in spite of the disagreement between our cross section and the experimental one. In the second step, we use our recently elaborated 3D approach based on the normal mode approximation combined with R-matrix theory and MQDT. This approach results in satisfactory agreement with storage-ring measurements, significantly better at very low energy than the former calculations.

Effect of the coordination environment on the ability of iron to bind/activate N2: A theoretical study with relevance to the nitrogenase mechanism

Activation of molecular dinitrogen to ammonia (and an accompanying metal-hydride formation) occurs in nitrogenases at an iron-sulfur active site. Iron-sulfur centers normally feature Fe(II) and/or Fe(III) oxidation states, which in general are not known to bind N2 or H+. Two peculiarities of the nitrogenase active site may be responsible for their unusual reactivity: an unusually reduced Mo(III) center in some of the nitrogenases (possibly suggesting an ability to also generate super-reduced Fe), and the presence of a central carbide anion, inverse-coordinated by 6 Fe centers within the iron-sulfur cluster. To try and deconvolute the factors that may allow the nitrogenase Fe to bind molecular nitrogen, we report here a density functional theory (DFT) study on the ability of a series of mononuclear Fe complexes to bind and activate N2. Structures of the type Fe(H2O)nR(N2) were examined, with the formal oxidation state of the iron varied from 0 to + 3, with octahedral or tetrahedral geometry, where R = H2O, HO–, CH3–, CH22–, H2S, H−. Iron-dinitrogen complexes only appear straightforward with lower oxidation states (0, +1), and the carbanion ligands appear distinctly better than oxygen or sulfur at facilitating N2 binding as well as activation/weakening of the NN bond. For Fe(II), higher spin states and carbanion ligation may in fact allow N2 binding as well – thus raising the question whether in nitrogenases (where sulfur and carbanion-ligated high-spin Fe(II) is present) do require Fe(I) in the catalytic cycle – at least from the point of view of initial N2 ligation.

Single-dislocation ultraviolet light emission

Micro-nano ultraviolet light sources have recently attracted great attention due to their promising applications in future quantum display, photoelectric detection sensors, biomedical devices, and so on. Design of ultraviolet light sources with smaller size, stronger emission intensity, and higher integration, are the key aspects for the development of high-performance micro-nano ultraviolet devices. Here, we demonstrate that unidirectional threading dislocation arrays in an AlN thin film can emit ultraviolet light with wavelength of ∼ 317 nm. The density of AlN dislocations is ∼ 4 × 1010 cm−2, and the light emission intensity of AlN dislocations is comparable to the intrinsic emission of the AlN thin film. By combining aberration-corrected transmission electron microscopy, atomic-resolution valence electron energy-loss spectroscopy, and first-principles calculations, the atomic and electronic structures and the band gaps of the AlN threading dislocations are determined. It is found that the AlN threading dislocations are comprised of edge, screw, and mixed dislocations. All the AlN dislocations exhibit smaller band gaps compared to the AlN bulk due to the increase of the Al-N bond length at the dislocation cores. The dangling bonds of Al and N at the edge dislocations, Al-Al and NN bonds at the screw dislocations cause the defect states in the band gaps. This study not only has clarified the atomic origin of dislocation nano-optics, but also will encourage the development of microelectronics and optoelectronic devices based on dislocation ultraviolet light emission.

Enhancing interfacial electric field in WO3-C3N4 through fermi level modulation for electrocatalytic nitrogen reduction

The electrocatalytic nitrogen reduction reaction (ENRR) has been identified as a promising method for environmentally friendly NH3 production under ambient conditions. The interfacial electric field has been found to hold significant potential for enhancing ENRR performance. The as-prepared WO3-C3N4-R catalyst exhibited a promising NH3 yield of 43.5 µg h−1 mgcat−1 and a high FE of 11.2 % in 0.1 M Li2SO4. DFT calculations indicate that the enlarged Fermi level can induce more electrons transfer from WO3 to C3N4 to form a strong interfacial electric field. In situ Raman and FTIR spectra demonstrate that the engineered intensified interfacial electric field in WO3-C3N4-R can enhance the adsorption of N2 molecules by forming strong W-N bonds and the polarization of NN bond through an "acceptance-donation" mechanism, resulting in a promoted ENRR kinetics. This work demonstrates a novel strategy to design NERR catalysts and provides insights into the effects of interfacial electric field on NERR.

Enhanced photocatalytic activity of methylene blue using heterojunction Ag@TiO2 nanocomposite: Mechanistic and optimization study

The objective in this study is to investigate the adsorption-degradation of the methylene blue (MB) dye using a fabricated heterojunction Ag@TiO2 nanocomposite. The batch factors used in photo catalytic reactions were pH, UV-irradiation time, temperature, catalytic dosage, and concentration of MB. The results showed that 0.2 × 103 g·ml−1) of the catalytic dose caused the Ag@TiO2 adsorption to degrade by 96.67% with darks and UV exposure. Using the Langmuir-Hinshelwood model to determine the kinetic, the Ag@TiO2 displays a greater kinetic rate than TiO2 and silver nanoparticle (AgNPs). The photocatalytic degradation of MB, which is an endothermic reaction involving all catalysts, is shown by the thermodynamic parameter to have the positive value of enthalpy (ΔH°). The enthalpies observed were Ag@TiO2 (126.80 kJ·mol−1) < AgNPs (354.47 kJ·mol−1) < TiO2 (430.04 kJ·mol−1). Ascorbic acid (OH scavenger), 2-propanol (O2 scavenger), and ammonium oxalate (AO) (hole h+ scavenger) were employed to conduct the scavenger effects. The Ag@TiO2 demonstrated a reduction in MB degradation when combined with 2-propanol, and this clearly demonstrated that, in contrast to hydroxyl radicals (OH) and hole (h+) scavengers, superoxide radical anion (O2 scavenger) plays a significant role in MB degradation. Utilizing density functional theory (DFT) to elucidate the mechanism and B3LYP/6-311+G(d,p) level optimization, the degradation-adsorption process was explained. When the NN, CN or CC bonds were severed, the Fukui faction was demonstrated for nucleophilic, electrophilic, and radical attack.

The microscopic structure deformation and vibration spectra resolving of β-HMX under high temperature:A theoretical study based on AIMD simulation

The phase transition mechanism is always the challenge in energetic material fields, but it is crucial for understanding the microscopic ignition and detonation reaction performance. Here, we investigate the phase transition process of β-HMX under high temperature, using ab initio molecular dynamics simulation. The microscopic structure deformation and corresponding spectral characteristic is systematically studied. The corresponding relationship between microscopic structure and spectral signal is established through the partial spectra calculation. The results show that the equatorial CN bonds and axial NN bonds of HMX molecule have the most obvious shrinkage. It is the fundamental origination for the deformation of molecular ring and N-NO2 group, which would further induce the initial phase transition. The axial N-NO2 group plays the major role both in the β → α and β → δ phase transitions, while the deformation of equatorial NO2 group also closely affects the β → δ phase transition.

Co doping regulating electronic structure of Bi2MoO6 to construct dual active sites for photocatalytic nitrogen fixation

Although photocatalytic nitrogen reduction reaction (PNRR) is a green ammonia synthesis technology, it still encounters low adsorption/activation efficiency of N2 and lack of reaction active sites. Element doping is an efficient strategy to regulate electronic structure of catalyst. Nevertheless, the mechanism of the effect of doping elements on the N2 adsorption/activation, reaction active site and energy barriers is not well unraveled. Taking Co doped Bi2MoO6 (Co-Bi2MoO6) as a model photocatalyst, density functional theory (DFT) and experiment study were used to investigate the mechanism of Co doping on the PNRR performance over Bi2MoO6. DFT results reveal that Co doping regulates the electronic structure, activates Bi sites of Co-Bi2MoO6 and provides new Co active sites, thus constructing dual active sites for PNRR. Benefited from dual active sites for effectively adsorption/activation N2, the as-fabricated 3% Co-Bi2MoO6 exhibit the maximum NH3 generation rate of 95.5 μmol·g−1·h−1 without sacrificial agents, which is 7.2 times that of Bi2MoO6. Furthermore, the detail mechanism of NN bond adsorption/activation and hydrogenation reaction on Co-Bi2MoO6 was also proposed according to in-situ FTIR and DFT results. This study provides a promising strategy to design catalysts with dual active sites for PNRR, which is of great significance to the popularization of other material systems.

Dinitrogen Functionalization with Carbon Dioxide and Carbon Disulfide Giving Symmetric and Unsymmetric Hydrazido Complexes

AbstractHere we show that a tridentate bis(aryloxide)anilide‐ligated titanium/potassium scaffold promotes functionalization of coordinated N2 with CO2 and CS2 through formation of N−C bonds. Treatment of a naphthalene complex with N2 gave an end‐on bridging dinitrogen complex featuring a [Ti2K2N2] core. The dinitrogen complex underwent insertion of CO2 into each Ti−NN bond to afford an N,N′‐dicarboxylated hydrazido complex. Stepwise nitrogen‐carbon bond formation at coordinated N2 proceeded to afford an unsymmetric hydrazido complex upon sequentially treating the dinitrogen complex with CS2 and CO2. Addition of Me3SiCl to the dicarboxylated hydrazido complex resulted in partial silylation of the carboxylate groups but did not lead to removal of the functionalized N2 unit from the metal centers. However, reduction of the dicarboxylated hydrazido complex with potassium naphthalenide afforded an oxo‐bridged dinuclear complex along with release of free potassium cyanate.

Electro-Elastic Modeling of Multi-Step Transitions in Two Elastically Coupled and Sterically Frustrated 1D Spin Crossover Chains

One-dimensional spin crossover (SCO) solids that convert between the low spin (LS) and the high spin (HS) states are widely studied in the literature due to their diverse thermal and optical characteristics which allow obtaining many original behaviors, such as large thermal hysteresis, incomplete spin transitions, as multi-step spin transitions with self-organized states. In the present work, we investigate the thermal behaviors of a system of two elastically coupled 1D mononuclear chains, using the electro-elastic model, by including an elastic frustration in the nearest neighbors (nn) bond length distances of each chain. The chains are made of SCO sites that are coupled elastically through springs with their nn and next-nearest neighbors. The elastic interchain coupling includes diagonal springs, while the nn inter-chain distance is fixed to that of the high spin state. The model is solved using MC simulations, performed on the spin states and the lattice distortions. When we only frustrate the first chain, we found a strong effect on the thermal dependence of the HS fraction of the second chain, which displays an incomplete spin transition with a significantly lowered transition temperature. In the second step, we frustrate both chains by imposing different frustration rates. Here, we demonstrate that for high frustration values, the thermal dependence of the total HS fraction exhibits multi-step spin transitions. The careful examination of the spin state structures in the plateau regions showed the coexistence of special dimerized ferro–antiferro patterns of type LL-HH-LL-HH along the first chain and HH-LL-HH-LL (H=HS and L=LS) along the second one, revealing that the two chains are antiferro-elastically coupled. This type of spatial modulation of the spin state and bond length distances is very attractive because it anticipates the possible existence of periodic structures in 2D lattices, made of alternate 1D SCO strings with HLHLHL structures, coupled in the ferro-like fashion along the interchain direction.

Spectroscopic, X-ray, mechanistic and DFT studies on formation of novel benzoimidazole-4-ones from cyclohexenyl carbothioamides

Spectroscopic studies of cyclohexenyl carbothioamides 2, obtained from condensation of 1,3-cyclohexandione with aryl isothiocyanates, predicted the proton transfer behaviour in solid, solution and gaseous phases. DFT studies in gaseous and solution phase shows good congruence with the experimental findings. Condensation of cyclohexenyl carbothioamide 2a with hydrazine hydrate unexpectedly embellished novel 2-(4-chlorophenyl)amino)-2,5,6,7-tetrahydro-4H-benzo[d]imidazol-4-one 4a and 2-(bis((4-chlorophenyl)amino)methylene)cyclohexane-1,3-dione 3a instead of the presumable 2H and 1H-indazole derivatives 5a and 6a, respectively. The proposed mechanism of formation of unconventional products 3a and 4a supported by experimental results is described. Spectroscopic investigations such as FT-IR, Mass and NMR (1H, 13C, DEPT-135, HSQC, COSY, NOESY) along with X-ray crystallographic results established the structure of two derived novel products 3a and 4a. The interesting feature of this study is NN bond cleavage of strained transit diazetidine ring and formation of CN bond leading to generation of novel benzoimidazol-4-one derivative 4a. Hirshfeld surface analysis of entitled compounds is reported.

Single Selenium Atomic Vacancy Enabled Efficient Visible-Light-Response Photocatalytic NO Reduction to NH3 on Janus WSSe Monolayer

The NO reduction reaction (NORR) toward NH3 is simultaneously emerging for both detrimental NO elimination and valuable NH3 synthesis. An efficient NORR generally requires a high degree of activation of the NO gas molecule from the catalyst, which calls for a powerful chemisorption. In this work, by means of first-principles calculations, we discovered that the NO gas molecule over the Janus WSSe monolayer might undergo a physical-to-chemical adsorption transition when Se vacancy is introduced. If the Se vacancy is able to work as the optimum adsorption site, then the interface's transferred electron amounts are considerably increased, resulting in a clear electronic orbital hybridization between the adsorbate and substrate, promising excellent activity and selectivity for NORR. Additionally, the NN bond coupling and *N diffusion of NO molecules can be effectively suppressed by the confined space of Se vacancy defects, which enables the active site to have the superior NORR selectivity in the NH3 synthesis. Moreover, the photocatalytic NO-to-NH3 reaction is able to occur spontaneously under the potentials solely supplied by the photo-generated electrons. Our findings uncover a promising approach to derive high-efficiency photocatalysts for NO-to-NH3 conversion.

Molybdenum based 2D conductive Metal–Organic frameworks as efficient single-atom electrocatalysts for N2 reduction: A density functional theory study

Electrocatalytic nitrogen reduction reaction (NRR) is a sustainable and eco-friendly process to generate ammonia (NH3). However, there are significant challenges including low catalytic performance, instability, and poor selectivity, which hinder its rapid development. Herein, a series of two-dimensional (2D) conductive metal-organic frameworks (i.e., TM3(HHTT)2, TM = Sc, Ti, V, Cr, Mo, W, Mn, Fe, Co, Ni, Cu and Zn) are investigated as single-atom catalysts (SACs) for NRR process by the density functional theory (DFT). The obtained results of Gibbs free energies of adsorption for N2, ∗NNH, ∗NH3, which are commonly used as activity descriptors to screen the effectiveness of catalysts, show that the Mo3(HHTT)2 monolayer (among all the TM3(HHTT)2 ones) can activate NN bonds, stabilize the adsorbed ∗NNH, and achieve the desorption of NH3. The Mo3(HHTT)2 monolayer also exhibits an excellent structural stability (with values of Ef = −2.96 eV and Udiss = 1.28 V). N2 can be effectively reduced into NH3 on the Mo3(HHTT)2 monolayer with a low limiting potential of −0.60 V along the distal pathway. Furthermore, the σ-donation and π∗ back-donation of N2 adsorbed onto the Mo3(HHTT)2 monolayer indicates an excellent electrical conductivity of Mo3(HHTT)2, which is beneficial for the effective electron transfer during the NRR process. Furthermore, the Mo3(HHTT)2 monolayer exhibits considerable selectivity for the NRR process over the hydrogen evolution reaction. Our study proved that this 2D c-MOFs carrying TM of the Mo3(HHTT)2 monolayer can be used as a promising catalyst for nitrogen fixation.

Experimental support for a new NOx formation route via an HNNO intermediate

Achieving minimal levels of nitrogen oxides (NOx) during combustion is a major constraint in the design of advanced high-efficiency engines. NOx can be formed during combustion of any fuel—including those without fuel-bound nitrogen—in air, where radicals can attack molecular nitrogen (N2) present in air to break the strong NN bond to ultimately form NOx. Paramount to the goal of minimizing NOx formation is knowledge of the fundamental routes by which the strong NN bond in N2 can be broken. Historically, there have been four known routes for breaking the strong NN bond in N2 to ultimately form NOx. We have recently posited that another route—mediated by an HNNO intermediate—may also play a role, particularly at the high pressures and low peak temperatures relevant to high-efficiency, low-NOx engines. Our previous theoretical and modeling studies show HNNO to be a major product of the N2O + H reaction at high pressures and low temperatures; once formed, HNNO is likely to react with radicals in barrierless reactions that would occur quickly and with high NOx yields. In the present paper, we report measurements of H2, O2, H2O, N2O, NO, NOx, and NH3 in jet-stirred reactor experiments for an H2/O2/N2O/NO/N2/Ar mixture that specifically target HNNO pathways. Importantly, we observe significant formation of NO and NH3—both of which provide signatures of the HNNO mechanism that are not predicted by previous models without it. Flame simulations using a new sub-model describing pressure-dependent formation and consumption of HNNO show these pathways to be among the most prominent formation routes at high pressures and low peak temperatures. However, exact quantification of the role of HNNO in NOx formation and quantitative predictions of NOx in general require more accurate rate constants for both HNNO pathways and mixture rules for pressure-dependent reactions.

Hole scavenger-free nitrogen photofixation in pure water with non-metal B-doped carbon nitride: Implicative importance of B species for N2 activation

Being the energy glutton and top ranker of greenhouse gas emission, Haber-Bosch is undoubtedly a grand challenge to reaching sustainability and carbon neutrality. Solar-driven nitrogen (N2) fixation under mild conditions is highly attractive and promising for sustainable ammonia (NH3) production. However, low conversion efficiency remains as a serious problem yet to be solved due to the difficult activation of strongly non-polar NN bond. In this study, defective and atomically thin g-C3N4 with boron sites was synthesized via a facile decomposition-thermal polymerization technique. The optimum photocatalyst displayed an NH3 yield of 213.59 μmol gcat−1 h−1 under visible light irradiation (λ > 400 nm) without any hole scavenger, bestowing high suitability for N2 fixation in pure water. The impressive performance is largely ascribed to the introduction of B species, which could act as the active sites for N2 adsorption, activation and reduction. Additionally, the atomically thin layer (∼3.25 nm) shortens charge carrier transport pathway while the B atoms and defects suppress quantum size effect as well as extends photo-response through bandgap reduction. These attributes synergistically lead to suppressed electron-hole recombination, efficacious charge transport, enhanced light utilization and enriched catalytic sites for N2 fixation. As a whole, this work presents an easy strategy to realize efficient N2 photofixation over a metal-free, low-cost and non-toxic photocatalyst in pure water as a continuous effort in advancing the burgeoning field of photocatalytic N2 fixation.

Newly designed photocatalyst of Fe4 single clusters on g-C6N6 for nitrogen reduction reaction

The current industrial synthesis of ammonia proceeds through Haber–Bosch process, in which the adsorbed N2 are directly dissociated, and the reaction is limited by Brønsted–Evans–Polanyi (BEP) relation. In this work, the catalytic properties of Fe4 clusters fixed on g-C6N6 for nitrogen reduction reaction (NRR) are explored by first-principle calculations. The studies on the structural stability, adsorption capacity for N2 and the change of Gibbs free energy proves that Fe4 cluster catalyst exhibits excellent catalytic activity and high selectivity for NRR. The “acceptance-donation” interaction between Fe4@g-C6N6 and N atoms presented by PDOS and Bader charge analysis will facilitate the breaking of NN bonds. The 100 % Faraday efficiency further proves the high NRR selectivity. The results provide an effective strategy for designing high-performance electrochemical NRR catalysts.