Generation Of NH3 Research Articles

Band gap engineering of ADG/NiO nanocomposite and applications for photocatalytic reduction of nitrogen and photo-oxidation of dyes

The use of solar-driven semiconductor photocatalysis to solve energy and environmental issues is an intriguing and difficult subject. As a consequence, various types of photocatalysts have been developed subsequently to fulfill the requirements of photocatalysis.Since graphene was discovered, materials based on graphene have garnered considerable interest. The aloe-vera derived (ADG)/nickel oxide (NiO) nanocomposite is a notable example of a graphene derivative.The uniform structure of graphene fibre is altered by nickel oxide(NiO) which tunes its band gap and causes electronic arrangements within graphene that is requiste for photocatalysis. Herein, we have used a one-pot chemical approach to design aloe vera-derived graphene/nickel oxide nanocomposites (ADG/NiO), a novel photocatalyst that show high molar absorbance, suitable band gap of 2.68 eV, good photo-stability and reusability. Under solar light irradiation, the ADG/NiO nanocomposite exhibited remarkable photocatalytic activity. It effectively fixed nitrogen into ammonia with an apparent quantum efficiency(AQE) of 0.64% and efficiently photo-oxidized dyes. Specifically, it achieved a dye removal efficiency of 94.2% for methylene blue (MB) and 86.41% for Eosin-B, converting them into harmless inorganic species like CO2 and H2O within just 90 minutes. The cost-effective ADG/NiO nanocomposite shows significant potential as a photocatalyst activated by solar light for practical applications such as the selective generation of NH3 and the purification of industrial wastewater containing dyes.

Molybdenum carbide nanosheets with iron doping as electrocatalysts for highly efficient ammonia electrosynthesis

The electrochemical reduction of nitrogen to ammonia represents a greener alternative to the Haber-Bosch process, demanding a shift towards low-cost and high-efficiency electrocatalysts. Recent advances in research have demonstrated the potential of molybdenum carbide-based catalysts to have their unique electronic structure and physicochemical properties. This study introduces ultrathin iron-doped molybdenum carbide nanosheets (Fe-MoC) as a novel catalyst for ammonia electrosynthesis. Demonstrating a remarkable ammonia production rate of 16 µg h−1 mg−1 and a Faradaic efficiency (FE) of approximately 13 % at −0.2 V, our synthesized Fe-MoC nanosheets stand out for their superior catalytic activity and selectivity towards nitrogen activation. The indophenol technique was employed to identify the generation of NH3 in our experiments, followed by UV–vis spectrometry for quantitative analysis. Additionally, various characterization techniques, including XRD, Raman, and XPS, were used to analyze the material structure and surface properties. Through comprehensive characterization and electrochemical studies, we reveal the pivotal role of iron doping in enhancing the electrocatalytic performance for nitrogen reduction reaction (NRR), offering insights into the mechanistic pathways facilitated by Fe-MoC. The future development and perspective of Fe-MoC towards high performance are proposed.

A high-performance electrocatalyst for sustainable ammonia synthesis via single-atom Ru-embedded Fe2O3 nitrogen-DOPED carbon

Ammonia (NH3) is an important industrial chemical, but the production of NH3 by the conventional Haber-Bosch process consumes large amounts of energy and has a serious environmental impact. Electrochemical nitrogen reduction reaction (NRR) offers a promising green alternative, but challenges remain in developing efficient catalysts. Here, we report the synthesis of single-atom Ru-embedded metal–organic framework-derived Fe2O3 nitrogen-doped carbon (Ru/Fe2O3-NC) materials via plasma-enhanced chemical vapour deposition. Under ambient conditions, the Ru/Fe2O3-NC catalyst exhibited a high NH3 yield rate of 141.18 μg h−1 mgcat.−1 in 0.1 M K2SO4 with a Faraday efficiency (FE) of 48.89 %, which was superior to the pristine Fe2O3-NC catalyst. Online differential electrochemical mass spectrometry (DEMS) analysis confirmed the selective generation of NH3 and no by-product N2H4 was detected. The Ru/Fe2O3-NC catalyst also showed remarkable stability during prolonged electrolysis. This work demonstrates the synergistic effect of incorporating single-atomic Ru in the Fe2O3-NC framework and provides a new platform for the development of advanced catalysts for the efficient and sustainable electrochemical synthesis of NH3.

Refining the active phases of silver/nickle-based catalysts achieves a highly-selective reduction of nitrate to ammonium at low overpotential

The electrocatalytic conversion of NO3‾ to NH3 (NO3RR) with elevated activity and exceptional selectivity at low potential remains a formidable challenge. Herein, the A-Ag@Ni/Ni(OH)2 NWs with atomic-level Ag/Ni interfaces were synthesized via electrochemical activation of Ag@Ni/Ni(OH)2 NWs at −1.05 V vs. RHE for 1 hour, and subsequently employed for electrocatalytic NO3RR. Specially, Ag sites could afford active centers for the adsorption of NO3‾ and convert it to NO2‾. Furthermore, Ni/Ni(OH)2 sites as vibrant centers for electrocatalytic H2O splitting, generating atomic H on the catalyst surface (Hads), thereby facilitating the rapid conversion of NO2‾ to NH3 via the Hads-mediated pathway. DFT calculations further substantiate that the Hads-mediated pathway is thermodynamically more favorable than the electron reduction pathway, the former of which facilitates the generation of NH3 and is an energy-efficient process, thus, the A-Ag@Ni/Ni(OH)2 NWs show outstanding electrocatalytic activity and selectivity for NO3‾-to-NH3 transformation at low potential.

Use of solid thermolytic salts to facilitate microwave-induced in situ amorphization

Moisture was frequently used as dielectric heating source in classical microwave-able systems to facilitate microwave-induced in situ amorphization, however such systems may face the potential of drug hydrolysis. In this study, solid thermolytic salts were proposed to function as moisture substitutes and their feasibility and impacts on microwave-induced in situ amorphization were investigated. It was found that NH4HCO3 was a promising solid alkaline salt to facilitate both microwave-induced in situ amorphization and in situ salt formation of acidic indomethacin (IND). Moreover, it could improve the chemical stability of the drug and the dissolution performance of compacts relative to classical moisture-based compacts upon microwaving. Further mechanistic study suggested that the in situ amorphization occurred prior to the in situ salt formation, especially in formulations with low drug loadings and high solid salt mass ratios. For compacts with low polymer ratios, in situ salt formation took place subsequently, where the previously amorphized IND within compacts could interact with the NH3 gas produced in situ by the decomposition of NH4HCO3 and form the ammonium IND salt. Microwaving time showed great impacts on the decomposition of NH4HCO3 and the in situ generation of water and NH3, which indirectly affected the amorphization and salt formation of IND. In comparison to the moisture-based systems, the NH4HCO3-based system showed a number of advantages, including the reduced potential of IND hydrolysis due to the absence of absorbed moisture, a wider category of applicable polymeric carriers other than hygroscopic polymers, and an increase in drug loading up to 50% (w/w).

Simultaneous degradation of SMX for efficient nitrogen fixation to ammonia and hydrogen evolution using AgVO3@rGO-Ag3PO4 (110) heterojunction

The simultaneous degradation of organic pollutants and generation of value-added compounds like ammonia and hydrogen energy has recently gained considerable attention in photocatalysis. The present study deals with successful preparation of novel AgVO3 nanowire@rGO-tetrahedral Ag3PO4 (110) (AGA) heterojunction and utilized for enhanced generation of NH3 and H2 from N-containing antibiotic sulfamethoxazole (SMX) under visible light. The prepared catalyst was well characterized by XRD, SEM, TEM and XPS to confirm the formation of heterojunction. The results indicated that the composite exhibited 546.0 μmol g−1 of hydrogen evolution rate, which is approximately 3.6 (153.6 μmol g−1) and 5.1 (108.7 μmol g−1) times higher than the pure AgVO3 and Ag3PO4 respectively after 6 h. Similarly, 38.3 mg L−1g−1 of NH3 generation was observed during 6 h of SMX degradation, which is about 1.9 and 2.8 times higher than the pure AgVO3 (20.1 mg L−1g−1) and Ag3PO4 (13.7 mg L−1g−1) respectively. The formation of heterojunction between AgVO3 and Ag3PO4 not only promotes the transfer of electron but also prevents the recombination which eventually enhances the catalytic conversion of N-element to NH3 and for H2 generation during water splitting. Furthermore, the plausible degradation pathway in SMX was proposed and the results revealed that the SMX was mineralized by the composite further converted to NH3 and generates H2 during the degradation process. Thus, our study provides new insights into novel photocatalytic treatment methodologies for simultaneous degradation of SMX to produce NH3 and H2 as value-added compounds from antibiotic wastewaters during water treatment process.

Iron phthalocyanine hollow architecture enabled ammonia production via nitrate reduction to achieve 100 % Faradaic efficiency

Eight electron nitrate (NO3–) reduction to ammonia (NH3) offers a cost–effective and energy efficient route than the Haber–Bosch process. The state of art electrocatalysts for nitrate reduction shows potential activity, albeit suffering from poor Faradaic efficiency, kinetically sluggish multi electron–proton process, and competitive hydrogen evolution reaction. Herein, we present a hollow iron phthalocyanine (FePc) rectangular nanotube (RNTs) electrocatalyst with 100 % Faradaic efficiency and 35067.09 µg h–1 mgcat–1 ammonia yield, which is 3.5 times higher than that of FePc nanorods. One-of-a-kind hollow nanostructure has Fe-N4 active motif sites necessary for NO3– activation, dissociation, specific intermediate formation, and interaction, resulting in the energy-efficient generation of NH3, according to in-situ research combined with theoretical analysis of molecular scale reaction mechanism. These unique results, coupled with the monitoring of pH changes in real time during electrolysis, open up new possibilities for progressive ammonia production with reduced carbon footprint.

Kinetic roles of excited state species in the oxidation of n-pentane/air assisted by nanosecond-pulsed discharge

Despite the significant advancement in plasma assisted combustion recently, many of the underlying plasma/combustion interaction mechanisms remain unknown. Critical data such as cross sections for large hydrocarbons and reaction rate constants involving excited species are still limited. To address these issues, a detailed plasma chemistry mechanism governing the oxidation processes in a n-pentane/air combustion mixture was proposed and studied by including a complete set of e-n-pentane cross section and excited state chemistry of n-pentane. The concentrations of alkane (CH4, C2H6, C3H8), alkene (C2H4, C3H6), methanol, NO2 and NH3 were measured by GC and a small amount of liquid products are qualitatively characterized by GC-MS. The electron-scattering cross sections of n-pentane were obtained by the R-matrix method. The rate constants of excited species of n-pentane which involved the chemical reactions were calculated via Fridman α-model and MMVT method. A linear increase in reactants consumption with increased voltages was observed experimentally, suggesting that n-pentane excitation by plasma was decoupled from the low-temperature chemistry. The kinetic mechanism accurately predicted the generation of alkane and hydrogen and captured the overall trend. However, it underestimated the generation of NH3 and NO2, indicating certain reaction pathways in NH3 and NO2 generation were missed. The results showed that because of the introduction nitrogen in the system, the excited states of the oxidant molecules O(1D), O(1S), N2(B) and N2(C) reacted with n-pentane to form fuel radicals via H-atom abstraction reactions RH + X* → R + XH. The excited species of n-pentane reacted with O, H, OH to form n-pentane radicals via RH* + X → R + XH, accordingly enhancing the chain initial reactions. Importantly, ammonia was produced in a n-pentane/air mixture with plasma assistance through the pathway of N2 → N(2D) → NH → NH2 → NH3. These results highlight strong roles of excited species in a complex n-pentane/air plasma chemistry system.

Understanding the Thermal Degradation Mechanism of High-Temperature-Resistant Phthalonitrile Foam at Macroscopic and Molecular Levels.

Polymer foam, a special form of polymer, usually demonstrates some unexpected properties that rarely prevail in the bulky polymer. Studying the thermal degradation behavior of a specific polymer foam is important for its rational design, quick identification, objective evaluation, and industrial application. The present study aimed to discover the thermal degradation mechanism of high-temperature-resistant phthalonitrile (PN) foam under an inert gas atmosphere. The macroscopic thermal decomposition of PN foam was carried out at the cost of size/weight loss, resulting in an increasing number of open cells with pyrolyzation debris. Using the TGA/DTG/FTIR/MS technique, it was found that PN foam involves a three-stage thermal degradation mechanism: (I) releasing gases such as H2O, CO2, and NH3 generated from azo-containing intermediate decomposition and these trapped in the closed cells during the foaming process; (II) backbone decomposition from C-N, C-O, and C-C cleavage in the PN aliphatic chain with the generation of H2O, CO2, NH3, CO, CH4, RNH2, HCN, and aromatic gases; and (III) carbonization into a final N-hybrid graphite. The thermal degradation of PN foam was different from that of bulky PN resin. During the entire pyrolysis of PN foam, there was a gas superposition phenomenon since the release of the decomposition volatile was retarded by the closed cells in the PN foam. This research will contribute to the general understanding of the thermal degradation behavior of PN foam at the macroscopic and molecular levels and provide a reference for the identification, determination, and design of PN material.

Multifunctional metal (Ag, Bi)-organic frameworks: a versatile platform for photocatalytic degradation, CO2 and N2 reduction, and enhanced antibacterial applications

The facile synthesis of a bimetallic-organic framework is successfully established to portray an efficient catalyst in photocatalytic degradation and photoreduction of nitrogen (N2) and carbon dioxide (CO2) and with antibacterial properties. In the current study, a novel B-BTC (where B represents Ag and Bi) organic framework was successfully synthesized and opted for advanced characterizations. The high-resolution transmission electron microscopy and X-ray photon spectroscopy illustrate the heterostructure formation, whereas X-ray diffraction spectroscopy, zeta sizer, and zeta potential were used to reveal the crystallinity, polydispersity, and average size of the nanomaterial. The material was characterized for photoluminescence analysis to understand the recombination rate and has been compared with the Bi-organic framework. B-BTC was further opted to determine the photocatalytic efficacy, through photocatalytic degradation of amoxicillin (AMX), photocatalytic reduction of N2 to ammonia (NH3), photoreduction of CO2, and antibacterial disinfection. The catalyst showcased ∼90% degradation of AMX under light-emitting diode light irradiation for 60 min. Successful photoreduction of N2 and CO2 showcases a fair generation of NH3 and value-added hydrocarbons, respectively. For each photocatalytic application, a mechanism has been knitted for understanding the overall reactions concerning the proposed reactions. Interestingly, the catalyst also showcased excellent antibacterial activity toward Escherichia coli and Staphylococcus aureus, with a proposed mechanism.

Aloe vera-derived graphene-coupled phenosafranin photocatalyst for generation and regeneration of ammonia and NADH by mimicking natural photosynthetic route.

Aloe vera-derived graphene (ADG) coupled system photocatalyst, mimicking natural photosynthesis, is one of the most promising ways for converting solar energy into ammonia (NH3 ) and nicotinamide adenine dinucleotide (NADH) that have been widely used to make the numerous chemicals such as fertilizer and fuel. In this study, we report the synthesis of the aloe vera-derived graphene-coupled phenosafranin (ADGCP) acting as a highly efficient photocatalyst for the generation of NH3 and regeneration of NADH from nitrogen (N2 ) and oxidized form of nicotinamide adenine dinucleotide (NAD+ ). The results show a benchmark instance for mimicking natural photosynthesis activity as well as the practical applications for the solar-driven selective formation ofNH3 and the regeneration of NADH by using the newly designed photocatalyst.

NiMoO4 nanorods with oxygen vacancies self-supported on Ni foam towards high-efficiency electrocatalytic conversion of nitrite to ammonia

As an eco-friendly and sustainable strategy, the electrochemical reduction of nitrite (NO2–) can simultaneous generation of NH3 and treatment of NO2– contamination in the environment. Herein, monoclinic NiMoO4 nanorods with abundant oxygen vacancies self-supported on Ni foam (NiMoO4/NF) are considered high-performance electrocatalysts for ambient NH3 synthesis by reduction of NO2−, which can deliver an outstanding yield of 18089.39 ± 227.98 μg h−1 cm−2 and a preferable FE of 94.49 ± 0.42% at −0.8 V. Additionally, its performance remains relatively stable during long-term operation as well as cycling tests. Furthermore, density functional theory calculations unveil the vital role of oxygen vacancies in promoting nitrite adsorption and activation, ensuring efficient NO2–RR towards NH3. A Zn-NO2– battery with NiMoO4/NF as the cathode shows high battery performance as well.

High‐Resolution Mass Spectroscopy for Revealing the Charge Storage Mechanism in Batteries: Oxamide Materials as an Example

The pursuit of high‐performance electrode materials is highly desired to meet the demand of batteries with high energy and power density. However, a deep understanding of the charge storage mechanism is always challenging, which limits the development of advanced electrode materials. Herein, high‐resolution mass spectroscopy (HR‐MS) is employed to detect the evolution of organic electrode materials during the redox process and reveal the charge storage mechanism, by using small molecular oxamides as an example, which have ortho‐carbonyls and are therefore potential electrochemical active materials for batteries. The HR‐MS results adequately proved that the oxamides could reversibly store lithium ions in the voltage window of 1.5–3.8 V. Upon deeper reduction, the oxamides would decompose due to the cleavage of the C–N bonds in oxamide structures, which could be proved by the fragments detected by HR‐MS, 1H NMR, and the generation of NH3 after the reduction of oxamide by Li. This work provides a strategy to deeply understand the charge storage mechanism of organic electrode materials and will stimulate the further development of characterization techniques to reveal the charge storage mechanism for developing high‐performance electrode materials.

Responses of Swine Carcasses Continuously Exposed to 43°C Inside a Small-Scale Finishing Room

Highlights Carcass and room temperatures, as well as CO, CO2, O2, and NH3, were continuously monitored. NH3 release was approximately half when carcass leachate was removed from the shallow pit. Gompertz and logistic models fit data well for daily carcass mass reduction and leachate production. Abstract. A catastrophic mortality event for swine would present numerous challenges with the management and disposal of infected carcasses. This study explored a new strategy for biosecure in-barn processing of swine carcasses as an alternative to traditional management and disposal approaches. A small-scale, mobile laboratory with two discovery rooms (DRs), replicating a swine finishing facility, was constructed to execute tests of in-barn disposal methods. Carcasses were desiccated by subjection to heat at a room air temperature of 43°C (110°F) for 16 days. Three carcasses (average = 82 kg, SE=1.27 kg) were elevated over individual leachate collection systems in DRA, thereby removing leachate from the room. Three carcasses in DRB were placed on concrete slats with cumulative leachate collection in the pit below. Environmental data were collected for DR, outdoor, and slat temperatures; and CO2, CO, O2, and NH3 gas concentrations. Carcasses were characterized by rectal and shoulder temperature monitoring and daily weighing of carcasses and leachate in DRA. The air exchange rate for this unventilated system was quantified based on wind and thermal-driven infiltration. Room environments were compared for thermal performance and gas levels. Carcass temperatures were compared, and data suggested no significant impact of flooring material on internal carcass temperature. Gompertz and logistic models were fit to leachate production data and carcass mass reduction data. Ammonia generation rates were found to have a peak production rate of 96.5 g AU-1 day-1 (15.8 g animal-1 day-1) in DRA and 120 g AU-1 day-1 (19.7 g animal-1 day-1) in DRB. Over the study, the generation of NH3 in DRB (360 g) was nearly twice that of DRA (182 g) due to leachate removal. Further quantification and qualification of in-barn management strategies will better define biosecure disposal approaches in the event of a catastrophic mortality event. Keywords: Ammonia, Catastrophic event, Disposal, Foreign animal disease, Mortality management, Pig.

Mo2N as a high-efficiency catalyst for transfer hydrogenation of nitrobenzene using stoichiometric hydrazine hydrate

A straightforward and commonly-used approach of direct pyrolysis for the preparation of molybdenum nitride (Mo2N) is conducted via reduction of MoO3 under ammonia atmosphere. The as-synthesized Mo2N catalyst demonstrated high activity for transfer hydrogenation of nitrobenzene, giving a 99% aniline yield at near-room temperature of 30 °C within only 50 min. More significantly, the amount of the hydrogen donor hydrazine monohydrate (N2H4·H2O) can be limited to stoichiometric molar ratio (-NO2: N2H4·H2O = 1: 1.5), preventing the possible generation of hazardous NH3, which is seldom reported in previous protocols. Through various characterizations and control experiments, conclusively, the remarkable catalytic performance of Mo2N catalyst should be credited to the large quantity of Lewis-acidic Mo sites. This research might provide a practical approach to aromatic amines production.

Application of experiments and density function theory on the formation mechanism of NH3 during O2/Ar and O2/H2O combustion process of demineralized coals

Understanding the formation mechanism of NH3 during the pulverized coal combustion process is a feasible approach to reducing NOx emissions. In this study, the emission characteristics of NH3 during the O2/Ar and O2/H2O combustion processes were investigated by the isothermal combustion experiments and the Density Functional Theory (DFT) method. The experimental results demonstrated that H2O accelerated the conversion of HCN to NH3, and the positive effects of H2O were applied to all kinds of coal-based fuels. The DFT calculations deeply revealed the formation mechanism of NH3 through the homogeneous conversion of HCN and the heterogeneous hydrogenation of coal-N. The hydrogenation of coal-N is the primary source of NH3 emissions during O2/Ar combustion. During O2/H2O combustion process, the heterogeneous generation of NH3 was modified by the synergetic effects of O2 and H2O, and the additional H2O strengthened the proportion of the homogeneous reaction. The homogeneous conversion of HCN was the main NH3 formation pathway. This study is prone to coupling the experiments and quantum chemistry to deeply reveal the formation mechanisms of NH3 during O2/Ar and O2/H2O combustion processes, providing a relatively complete pathway for the emissions of NH3.

An Experimental Investigation on the Effects of Limestone Fines in Manufactured Sands on the Performance of Magnesia Ammonium Phosphate Mortar

Magnesium ammonium phosphate cement (MAPC) prepared with ammonium dihydrogen phosphate (NH4H2PO4, ADP) and dead-burned Magnesium oxide (MgO) is a new type of rapid patch repair material for concrete structures. In order to reduce the material costs of MAPC mortar, manufactured limestone sands, being a more widely-available resource with lower cost, was investigated in this study as an alternative to quartz sands for the preparation of MAPC mortar. The limestone fines in manufactured sands were found to be the key factor that influences properties of MAPC mortar by causing bubbling and volume expansion before hardening. As a result, the mechanical strength of MAPC mortar decreased with the increasing content of limestone fines due to increased porosity. According to microstructure analysis, the mechanism of these negative effects can be inferred as the reaction between limestone fines and ADP with the gas generation of CO2 and NH3. This reaction mainly occurred during a short period before setting while most limestone fines remained unreactive in the hardened MAPC mortar. Based on the above detailed experimental findings on the effects of limestone fines in manufactured sand on the properties of MAPC mortar, this paper pointed out that effective defoaming methods for inhibiting bubbling was the key to the utilization of manufactured sands in preparation of high performance MAPC mortar.

Homogeneous Ni(I)tetra Sulfonated Phthalocyanine Electrocatalyst Generated at Low Overpotential Clubbed with a Wet‐Scrubbing Column for High Efficiency NO Reduction to NH3

AbstractAlthough the degradation of NO gas to a less toxic form is a promising strategy to help solve atmospheric health and ozone depletion problems, conversion to a useful gas is a recent strategy. The generation of NH3 from NO with high efficiency per catalyst area or weight is in the early stages. In this investigation, a tetra sulfonated phthalocyanine with a Ni(II) (Ni(II)TSPc) complex was used to produce a low valent homogenous electrocatalyst Ni(I)TSPc in an alkaline medium at a lower overpotential. Ni(I)TSPc formation at a lower overpotential was demonstrated by the initial change in oxidation/reduction potential from 25 mV to −360 mV during electrolysis, peak potential change in cyclic voltammetry, and UV‐Vis spectral analysis. A potentiometric titration method used to quantify the electrogenerated Ni(I)TSPc revealed 90 % efficiency in 1 h. The decrease of Ni(I)TSPc concentration when contacting NO gas at the wet scrubber column showed that the NO removal process followed a Ni(I)TSPc (Ni(I)) mediation or mediated electrocatalytic reduction (MER) process. The NO removal efficiency reached almost 100 % at a 0.2 L/min gas flow rate of 20 ppm. The selective formation of NH3 with a maximum of 1492 μmol/g Ni(I) was achieved for the first time in the homogeneous electrocatalytic reduction process. The developed process generated NH3 from NO gas and has the potential for scale‐up.

Porous SiC–Si3N4 composite ceramics with excellent EMW absorption property prepared by gelcasting using DMAA

The porous SiC–Si3N4 composite ceramics with good EMW absorption properties were prepared by combination of gelcasting and carbothermal reduction. The pre-oxidation of Si3N4 powders significantly improved the rheological properties of slurries (0.06 Pa s at 103.92 s−1) and also suppressed the generation of NH3 and N2 from Si3N4 hydrolysis and reaction between Si3N4 and initiator APS, thereby reducing the pore defects in green bodies and enhancing mechanical properties with a maximum value of 42.88 MPa. With the extension of oxidation time from 0 h to 10 h, the porosity and pore size of porous SiC–Si3N4 composite ceramics increased from approximately 41.86% and 1.0–1.5 μm to 46.33% and ~200 μm due to the production of CO, N2 and gaseous SiO, while the sintering shrinkage decreased from 16.24% to 10.50%. With oxidation time of 2 h, the Si2N2O fibers formed in situ by the reaction of Si3N4 and amorphous SiO2 effectively enhanced the mechanical properties, achieving the highest flexural strength of 129.37 MPa and fracture toughness of 4.25 MPa m1/2. Compared with monolithic Si3N4 ceramics, the electrical conductivity, relative permittivity and dielectric loss were significantly improved by the in-situ introduced PyC from the pyrolysis of three-dimensional network DMAA-MBAM gel in green bodies and the SiC from the carbothermal reduction reaction between PyC and SiO2 and Si3N4. The porous SiC–Si3N4 composite ceramics prepared by the unoxidized Si3N4 powders demonstrated the optimal EMW absorption properties with reflection loss of −22.35 dB at 8.37 GHz and 2 mm thickness, corresponding to the effective bandwidth of 8.20–9.29 GHz, displaying great application potential in EMW absorption fields.

Atomic-level insights into the activation of nitrogen via hydrogen-bond interaction toward nitrogen photofixation

Summary As the activation of N2 molecules is generally regarded as the bottleneck in N2 reduction, it is of significant importance to develop promising strategies to efficiently activate N2 molecules. Herein, we discovered an innovative approach to activate N2 molecules via hydrogen-bond interaction in N2 photofixation. Porous Cu with surface modification of S atoms (3%-S/Cu) exhibited remarkable catalytic activity and stability in N2 photofixation. Further mechanistic studies revealed that surface S atoms directly participated in the catalytic process by accepting and donating H atoms. In addition, the forming S–H bond significantly promoted the activation of N2 molecules via hydrogen-bond interaction, contributing to the enhanced catalytic activity.