Ammonia Detection Methods in Photocatalytic and Electrocatalytic Experiments: How to Improve the Reliability of NH3 Production Rates?

Encapsulating bimetallic nanoparticles on Mn0.3Cd0.7S solid solution for boosted photocatalytic selective imines synthesis

The synergetic combination of hydrogen (H2) generation with benzylamine (BA) dehydrogenation shows promise in terms of avoiding sacrificial agents and emitting pollutants without using up unlimited solar energy. However, the rational design of the electron transfer bridge and active sites of photocatalysts remains constrained, reducing the effectiveness of the target selective photocatalytic BA dehydrogenation coupling (PBDC) system. Herein, a bimetallic CuCo nanoparticles used as an efficient cocatalyst is coated on the Mn0.3Cd0.7S (MCS) nanorods (CuCo/MCS) that endows an optimal electronic structure, a directional electron transport tunnel, and suitable reactive sites for the PBDC reaction. Theoretical and experimental studies reveal that the synergistic effect of Cu and Co nanoparticles lowers the overall energy barrier of BA, facilitating the N-benzylidenebenzylamine (NBBA) and H2 generation. The incorporation of CuCo nanoparticles as cocatalysts into MCS not only reduces the overpotential of proton reduction but also weakens the adsorption of imine, thus producing H2 at a rate of 14.10 mmol g-1 h-1, with a BA conversion of 94.43 % and selectivity of 99 %. This work will offer a profound understanding of bimetal-anchored photocatalysts in electron transfer for synergetic renewable fuels and valuable chemical production.

Low-dimensional materials for ammonia synthesis

Ammonia is an essential chemical due to its immense usage in agriculture, energy storage, and transportation. The synthesis of "green" ammonia via carbon-free routes and renewable energy sources is the need of the hour. In this context, photo- and/or electrocatalysis proves to be highly crucial. Low-dimensional materials (LDMs), owing to their unique properties, play a significant role in catalysis. This review presents a vast library of LDMs and broadly categorizes their catalytic performance according to their dimensionality, i.e., zero-, one-, and two-dimensional catalysts. The rational design of LDMs can significantly improve their catalytic performance, particularly in reducing small molecules like dinitrogen, nitrates, nitrites, and nitric oxides to synthesize ammonia via photo- and/or electrocatalysis. Additionally, converting nitrates and nitrites to ammonia can be beneficial in wastewater treatment and be coupled with CO2 co-reduction or oxidative reactions to produce urea and other valuable chemicals, which are also discussed in this review. This review collates the works published in recent years in this field and offers some fresh perspectives on ammonia synthesis. Through this review, we aim to provide a comprehensive insight into the catalytic properties of the LDMs, which are expected to enhance the efficiency of ammonia production and promote the synthesis of value-added products.

Allicin enhances urea-N conversion to microbial-N by inhibiting urease activity and modulating the rumen microbiome in cattle

BACKGROUND

Urea serves as a vital nonprotein nitrogen source in ruminant nutrition, but its efficient utilization is often hampered due to rapid urease activity in the rumen. This study explores the potential of allicin, a garlic-derived compound, as a urease inhibitor to improve urea nitrogen utilization. Enzyme inhibition kinetics and molecular docking were used to identify allicin's interaction sites on urease. Additionally, metagenomic and 15N-urea metabolic flux analyses were conducted to evaluate allicin's impact on microbial populations and urea-N metabolism.

RESULTS

Allicin was identified as an inhibitor of ruminal urease, with an IC50 of 126.77 ± 1.21 μM. Molecular docking studies have shown that allicin forms hydrogen bonds with key urease residues, leading to the preemption of the urease active site and thus impeding urea binding. In a simulated rumen environment, allicin significantly reduced urea hydrolysis and ammonia production. Furthermore, allicin modified the rumen microbial community by inhibiting Prevotella species while promoting the growth of Ruminobacter species and Denitrobacterium detoxificans. A 15N-urea metabolic flux analysis revealed that allicin facilitated the incorporation of urea-derived nitrogen into microbial amino acids and nucleotides.

CONCLUSION

Allicin effectively inhibits urease activity in the rumen, enhancing the conversion of urea-N into microbial biomass. These findings suggest that allicin has significant potential to optimize urea metabolism in the rumen, offering a novel strategy for improving ruminant nitrogen nutrition. Video Abstract.

Activity-Selectivity Trends in Electrochemical Urea Synthesis: Co-Reduction of CO2 and Nitrates Over Single-Site Catalysts

Electrochemical co-reduction of carbon dioxide and nitrates (CO2NO3RR) holds promise for sustainable urea production. However, the sluggish kinetics of the sixteen-electron transfer and unclear mechanistic understanding strongly impede its development. Here, combined experimental and computational approaches are employed to screen a series of metal phthalocyanine as model catalysts (MPcs, M = Zn, Co, Ni, Cu, and Fe) to uncover the activity-selectivity trends in electrochemical CO2NO3RR. The theoretical simulations reveal that the thermodynamics of urea synthesis is significantly influenced by key intermediates, where the enhanced adsorption of *HOOCNO, coupled with reduced adsorptions of *N and *COOH, and moderate adsorption of *H2O, can significantly promote the urea production. ΔG*HOOCNO-ΔG*N-ΔG*COOH+ΔG*H2O as a potential descriptor is proposed for predicting the efficiency of CO2NO3RR toward urea formation. The findings provide systematic guidance for the future design of high-efficiency catalysts for urea electrosynthesis, addressing a crucial need for sustainable nitrogen fixation.

Harnessing Lithium-Mediated Green Ammonia Synthesis with Water Electrolysis Boosted by Membrane Electrolyzer with Polyoxometalate Proton Shuttles

Integrating water electrolysis (WE) with lithium-mediated nitrogen reduction (Li-NRR) offers a sustainable route for green ammonia production by directly utilizing protons from water oxidation, eliminating reliance on grey or blue hydrogen. Here, polyoxometalates (POMs) function as electron-coupled proton buffers (ECPBs) to seamlessly link WE with Li-NRR in a three-compartment flow reactor comprising an aqueous anode, an organic cathode, and a gas feed chamber. POMs serve as proton shuttles while suppressing the competing hydrogen evolution reaction (HER), facilitating efficient ammonia synthesis. The addition of polymethyl methacrylate (PMMA) enhances catholyte hydrophobicity, mitigating water contamination. By optimizing ECPB concentration, a dynamic balance is achieved between lithium nitride intermediates (LiNxHy) formation and consumption, yielding ammonia at 573.7 ± 5.2 µg h⁻¹ cm⁻2 with a Faradaic efficiency of 54.2%. This design advances flow reactor technology by uniquely utilizing water oxidation as a direct proton source, bypassing conventional hydrogen oxidation methods. The use of POMs as proton shuttles establishes a new benchmark for green ammonia production, reinforcing its potential in sustainable chemistry.

Regulating Multifunctional Oxygen Vacancies for Plasma-Driven Air-to-Ammonia Conversion

Current ammonia (NH₃) synthesis is hindered by challenges including N₂ activation, NH₃ separation and process complexity. Here, we report a plasma-electrochemical process for the production of gaseous ammonia from air generated NOx, decoupled from processes employing liquid phase intermediaries such as NO₃⁻ and final product (NH4 +). Importantly, this process uses air for scalable ammonia production under ambient conditions and directly produces gaseous NH₃ which facilitates efficient product separation. For NOx reduction to NH₃, we propose a universal strategy combining plasma pretreatment and wet chemical calcination to introduce multifunctional oxygen vacancies. The resulting highly defective Fe₂O₃ nanoparticles on Cu achieves a significant ammonia production rate of 628 nmol·s⁻¹·cm⁻2, along with nearly 100% faradaic efficiency.

Fact or fiction: What is in your 15N2 and 15NH3 cylinders for sustainable ammonia and urea research?

Attaining reliable performance indicators via 15N-labeling is a daunting research endeavor for sustainable ammonia and urea synthesis processes, as currently obtained reaction rates and yields are often low. However, artifact and misinterpretation can be induced by ppm-level impurities in commercial 15N2 and 15NH3 cylinders, which are not well understood. Here, we report quantitative in-line gas chromatography-mass spectrometry (GC-MS) analysis of impurities in commercial 15N2 and 15NH3 cylinders at ppm level, in conjunction with 1H-NMR methods, exemplified by 808-16,252 ppm of 14N15N, 0-4,891 ppm 15NH3, 3-319 ppm 14NH3, 0-231 ppm of 14NO2, 0-176 ppm 15NO2, and 0-566 ppm 15N16O impurities, some of which were not reported in cylinder certification nor previous studies. The collected results have formed recommended protocols applicable to all future 15N labeling experiments intended to eliminate false positives.

Ni-Co bimetallic phosphide catalyst toward electrocatalytic ammonia synthesis under ambient conditions

Electrocatalytic nitrate reduction reaction (NitRR) under ambient conditions is a promising sustainable and eco-friendly method for ammonia (NH3) synthesis, which currently highly relies on the energy-consuming Haber-Bosch process with enormous CO2 emissions. In this work, we report the synthesis of a Ni-Co bimetallic phosphide catalyst (NiCoP) using the traditional hydrothermal combined high-temperature phosphorization method. Compared with monometallic phosphides such as Ni2P and CoP, the as-synthesized NiCoP catalyst with synergistic effects exhibits remarkable NitRR performance with the highest faradaic efficiency (FE) of 91.3 ± 4.4% at -1.2 V (vs. RHE) with the maximum NH3 yield rate of 5553.4 ± 400.8 μg h-1 cm-2 at -1.4 V (vs. RHE). Further in situ different electrochemical mass spectrometry (DEMS) analysis is employed to identify the intermediate produced during the electrocatalytic NitRR process, confirming NiCoP as a promising electrocatalyst for NH3 synthesis.

Electrocatalytic CN Coupling: Advances in Urea Synthesis and Opportunities for Alternative Products

Urea is an essential fertilizer produced through the industrial synthesis of ammonia (NH3) via the Haber-Bosch process, which contributes ≈1.2% of global annual CO2 emissions. Electrocatalytic urea synthesis under ambient conditions via CN coupling from CO2 and nitrogen species such as nitrate (NO3 -), nitrite (NO2 -), nitric oxide (NO), and nitrogen gas (N2) has gained interest as a more sustainable route. However, challenges remain due to the unclear reaction pathways for urea formation, competing reactions, and the complexity of the resulting product matrix. This review highlights recent advances in catalyst design, urea quantification, and intermediate identification in the CN coupling reaction for electrocatalytic urea synthesis. Furthermore, this review explores future prospects for industrial CN coupling, considering potential nitrogen and carbon sources and examining alternative CN coupling products, such as amides and amines.

Design Refinement of Catalytic System for Scale-Up Mild Nitrogen Photo-Fixation

Ammonia and nitric acid, versatile industrial feedstocks, and burgeoning clean energy vectors hold immense promise for sustainable development. However, Haber-Bosch and Ostwald processes, which generates carbon dioxide as massive by-product, contribute to greenhouse effects and pose environmental challenges. Thus, the pursuit of nitrogen fixation through carbon-neutral pathways under benign conditions is a frontier of scientific topics, with the harnessing of solar energy emerging as an enticing and viable option. This review delves into the refinement strategies for scale-up mild photocatalytic nitrogen fixation, fields ripe with potential for innovation. The narrative is centered on enhancing the intrinsic capabilities of catalysts to surmount current efficiency barriers. Key focus areas include the in-depth exploration of fundamental mechanisms underpinning photocatalytic procedures, rational element selection, and functional planning, state-of-the-art experimental protocols for understanding photo-fixation processes, valid photocatalytic activity evaluation, and the rational design of catalysts. Furthermore, the review offers a suite of forward-looking recommendations aimed at propelling the advancement of mild nitrogen photo-fixation. It scrutinizes the existing challenges and prospects within this burgeoning domain, aspiring to equip researchers with insightful perspectives that can catalyze the evolution of cutting-edge nitrogen fixation methodologies and steer the development of next-generation photocatalytic systems.

Layered Anion-Mixed Oxycompounds: Synthesis, Properties, and Applications

Layered anion-mixed oxycompounds have emerged as pivotal materials across diverse technological domains encompassing electronics, optics, sensing, catalysis, and energy applications. Capitalizing on the unique properties imparted by the additional anion, these compounds exhibit exceptional characteristics including ultra-large charge carrier mobility, giant second-harmonic generation, visible-light-driven photocatalysis, and outstanding thermoelectricity. This article aims to provide a comprehensive summary of layered anion-mixed oxychalcogenides, oxyhalides, oxynitrides, and oxypnictides. Organized by chemical composition and crystal structures, the classification of these oxycompounds precedes an in-depth exploration of various synthesis methodologies. Subsequently, their properties are elucidated in electronics, optics, magnetics, and ferroelectrics, contextualizing their utility in electronic, optical, and catalytic applications. The review culminates in a critical assessment of extant challenges and opportunities within this realm. Furthermore, insights are proffered into the future trajectory of research, underpinning the significance of advancing novel 2D multi-anion oxygenated compounds and their attendant applications.

Ultra-precise ruler for ammonia nitrogen quantification in electrochemical synthesis experiments

The field of electrochemical ammonia synthesis has made rapid advancements, attracting a large number of scientists to contribute to this area of research. Accurate detection of ammonia is crucial in this process for evaluating the efficiency and selectivity of electrocatalysts. In this study, we systematically investigate the indophenol blue method for ammonia detection, examining the effects of key factors such as solution pH, nitrate concentration, and metal ion concentration on measurement accuracy. Based on experimental optimization and mathematical algorithms, we propose an iterative refinement method supported by custom-developed code. This method automates the generation and adjustment of calibration curves, reduces measurement errors, and enhances detection precision, offering a valuable framework for the quantitative detection of ammonia and other small molecules in electrochemical synthesis.

Exfoliation of triazole-based C3N4.8, C3N6, and C3N7 nanosheets for efficient photocatalytic ammonia production

Atomically thin two-dimensional nanosheets of nitrogen-rich C3N4.8, C3N6, and C3N7 are synthesized by sonochemical process. Despite their high nitrogen content, their triazole-based crystal structures remain intact after exfoliation. Among the present materials, the nitrogen-richest C3N7 nanosheets display the highest photocatalytic activity for ammonia production, highlighting the synergetic effect of composition control and exfoliation.

Purification and Value-Added Conversion of NOx under Ambient Conditions with Photo-/Electrocatalysis Technology

As primary air pollutants from fossil fuel combustion, the excess emission of nitric oxides (NOx) results in a series of atmospheric environmental issues. Although the selective catalytic reduction technology has been confirmed to be effective for NOx removal, green purification and value-added conversion of NOx under ambient conditions are still facing great challenges, especially for nitrogen resource recovery. To address that, photo-/electrocatalysis technology offers sustainable routes for efficient NOx purification and upcycling under ambient temperature and pressure, which has received considerable attention from scientific communities. In this review, recent advances in photo-/electrocatalysis technology for the purification and value-added conversion of NOx are critically summarized. The target products and reaction mechanisms for NOx conversion systems, together with the responsible active sites, are discussed, respectively. Then, the realistic environmental practicability is proposed, including strict performance evaluation criteria and application in realistic conditions for NOx purification and upcycling by the application of photo-/electrocatalysis. Finally, the current challenges and future opportunities are proposed in terms of catalyst design, NOx conversion enhancement, reaction mechanism understanding, practical application conditions, and product separation techniques.

Heteropoly blue-modified ultrathin bismuth oxychloride nanosheets with oxygen vacancies for efficient photocatalytic nitrogen fixation in pure water

Photocatalytic nitrogen reduction is a promising green technology for ammonia synthesis under mild conditions. However, the poor charge transfer efficiency and weak N2 adsorption/activation capability severely hamper the ammonia production efficiency. In this work, heteropoly blue (r-PW12) nanoparticles are loaded on the surface of ultrathin bismuth oxychloride nanosheets with oxygen vacancies (BiOCl-OVs) by electrostatic self-assembly method, and a series of xr-PW12/BiOCl-OVs heterojunction composites have been prepared. Acting as a robust support, ultrathin two-dimensional (2D) structure of BiOCl-OVs inhibits the aggregation of r-PW12 nanoparticles, enhancing the interfacial contact between r-PW12 and BiOCl. More importantly, the existence of oxygen vacancies (OVs) provides abundant active sites for efficient N2 adsorption and activation. In combination of the enhanced light absorption and promoted photogenerated carriers separation of xr-PW12/BiOCl-OVs heterojunction, under simulated solar light, the optimal 7r-PW12/BiOCl-OVs exhibits an excellent photocatalytic N2 fixation rate of 33.53 µmol g-1h-1 in pure water, without the need of sacrificial agents and co-catalysts. The reaction dynamics is also monitored by in situ FT-IR spectroscopy, and an associative distal pathway is identified. Our study demonstrates that construction of heteropoly blues-based heterojunction is a promising strategy for developing high-performance N2 reduction photocatalysts. It is anticipated that combining of different defects with heteropoly blues of different structures might provide more possibilities for designing highly efficient photocatalysis systems.

High-Throughput Screening for Enhanced Thermal Stability of Inherently Salt-Tolerant l-Glutaminase and Its Efficient Expression in Bacillus licheniformis

In addressing the challenges posed by extended fermentation cycles and high-salt conditions in high-salt liquid-state fermentation soy sauce (HLFSS) production, a high-throughput screening method was devised to identify thermally stable l-glutaminase mutants. This study yielded mutants A146D and A51D, exhibiting enhanced thermal stability. Computer-aided analysis revealed that these mutations introduced additional forces, compacting the protein structure and lowering the Gibbs free energy, thereby improving thermostability. Furthermore, the incorporation of aspartic acid augmented the negative surface charge, contributing to superior salt tolerance compared to the wild type (WT). Notably, in a 25% NaCl buffer, A146D and A51D demonstrated half-lives of 72.57 and 71.31 day, respectively, surpassing the WT's 59.08 day. In a 5 L bioreactor, the optimal mutant A146D achieved a remarkable enzymatic activity of 2800.78 ± 98.1 U/mL in recombinant Bacillus licheniformis fermentation broth, setting a new benchmark. This research offers valuable insights and a foundation for the modification and application of l-glutaminase in the food industry, particularly in HLFSS brewing.

Antagonistic Effect of Nitrate Conversion on Photocatalytic Reduction of Aqueous Pertechnetate and Perrhenate

Sustainable photocatalysis can effectively reduce the radioactive 99TcO4- to less soluble TcO2·nH2O(s), but the reduction efficiency is highly susceptible to coexisting nitrate (NO3-). Here, we quantitatively investigate photocatalytic remediation conditions for Tc-contaminated water stimulated by the analogue perrhenate (ReO4-) in the presence of NO3-, and we elucidate the influence mechanism of NO3- by in situ characterizations. The interfering NO3- can compete with Re(VII) for the carbonyl radical (·CO2-) produced by formic acid (HCOOH) oxidation to generate nitrogen-containing products such as NH4+, NO2-, and NOx, resulting in the decrease in the Re(VII) reduction ratio. Under the conditions of 4% (volume ratio) HCOOH and pH = 3, the yield of NOx is the lowest, and the selectivity of N2 reaches 93%, which makes the overall reaction more in line with the pollution-free concept. The X-ray absorption fine structure reveals that the redox product Re(IV) mainly exists in the form of ReO2·nH2O(s) and is accompanied by a decrease with the increase in NO3- concentration. Re(VII)/Tc(VII) reduction suffers from a serious interferential effect of NO3-, whereas the higher the concentration of NO3-, the more conducive to slowing down the reoxidation of the reduction products, which is advantageous for the subsequent sequestration or separation.

Photocatalytic applications of covalent organic frameworks: synthesis, characterization, and utility

Photocatalysis has emerged as an energy efficient and safe method to perform organic transformations, and many semiconductors have been studied for use as photocatalysts. Covalent organic frameworks (COFs) are an established class of crystalline, porous materials constructed from organic units that are easily tunable. COFs importantly display semiconductor properties and respectable photoelectric behaviour, making them a strong prospect as photocatalysts. In this review, we summarize the design, synthetic methods, and characterization techniques for COFs. Strategies to boost photocatalytic performance are also discussed. Then the applications of COFs as photocatalysts in a variety of reactions are detailed. Finally, a summary, challenges, and future opportunities for the development of COFs as efficient photocatalysts are entailed.

Amorphous Ni3B Promotes Electroreduction of Nitrate to Ammonia

The electrocatalytic nitrate reduction to ammonia (NRA) can address nitrogen cycle imbalance and high carbon emissions; however, the intense competition of hydrogen evolution reaction (HER) restricts the rate of NH3 production. Herein, amorphous Ni3B (a-Ni3B) is designed to balance the NRA and HER. The NH3 yield of a-Ni3B surpasses those of pure Ni and NiO, which is attributed to the preferential adsorption of NO3- on the B and Ni sites of a-Ni3B for the NRA reaction, greatly inhibiting the HER. Furthermore, the a-Ni3B possesses advantages in NRA performance compared to crystalline Ni3B (c-Ni3B) due to more active hydrogen (*H) generated during the catalytic process. The *H in the NRA process on a-Ni3B is verified by the electron spin resonance technique. The NRA mechanism is comprehensively discussed based on the results of in situ characterization and density functional theory calculations. The a-Ni3B can enhance NH3 production by inhibiting HER, which provides ideas for sustainable NH3 synthesis.

Ammonia Synthesis with Visible Light and Quantum Dots

Light-assisted synthesis of ammonia from nitrate and nitrite sources is a sustainable approach to reduce the burden of the energy-intensive Haber-Bosch process. However, poor selectivity and the need for UV-active photocatalysts are the current bottlenecks in the synthesis of ammonia from nitrate and nitrite sources. Herein, we introduce selective visible-light-driven ammonia production from nitrate and nitrite ions with indium phosphide quantum dots (InP QDs) as the photocatalyst. The presence of catalytic indium sites and microenvironment modulation through an interplay of catalyst-reactant interactions resulted in efficient and selective ammonia formation under visible light. Ammonia was produced in an attractive yield of ∼94% in both aqueous and gaseous phases within 2 h of visible-light irradiation at room temperature. A decent formation of ammonia was observed under sunlight as well, strengthening the translational prospects of InP QD photocatalysts. Mechanistic investigations ascertained a negligible role of competing hydrogen evolution in direct nitrate reduction, confirming the active participation of photoexcited charge carriers from InP QDs in the ammonia synthesis. Kinetic studies revealed the energetically challenging nitrate-to-nitrite conversion as the rate-determining step, with subsequent reactions proceeding with ∼100% conversion to yield ammonia. A series of experiments concluded that water is the proton source in the InP QD-photocatalyzed synthesis of ammonia. Our study shows the impact of the rationally designed core and surface of InP QD-based photocatalysts in developing sustainable routes to produce ammonia beyond the Haber-Bosch process.

Light-driven nitrogen fixation routes for green ammonia production

The global goal for decarbonization of the energy sector and the chemical industry could become a reality by a massive increase in renewable-based technologies. For this clean energy transition, the versatile green ammonia may play a key role in the future as a fossil-free fertilizer, long-term energy storage medium, chemical feedstock, and clean burning fuel for transportation and decentralized power generation. The high energy-intensive industrial ammonia production has triggered researchers to look for a step change in new synthetic approaches powered by renewable energies. This review provides a comprehensive comparison of light-mediated N2 fixation technologies for green ammonia production, including photocatalytic, photoelectrocatalytic, PV-electrocatalytic and photothermocatalytic routes. Since these approaches are still at laboratory scale, we examine the most recent developments and discuss the open challenges for future improvements. Last, we offer a technoeconomic comparison of current and emerging ammonia production technologies, highlighting costs, barriers, recommendations, and potential opportunities for the real development of the next generation of green ammonia solutions.

Fe3O4 nanostructure films as solar-thermal conversion materials for ammonia synthesis

Here, we report that black photothermal materials elevate solar heating temperatures across high solar absorption and low infrared radiation. Fe3O4 nanostructure films can be heated to 350 °C under light irradiation, and this system shows effective visible-light-driven ammonia synthesis production of 3677 μg g-1 h-1 under gas-solid phase catalysis without noble metals.

Bi2Ti2O7 Quantum Dots for Efficient Photocatalytic Fixation of Nitrogen to Ammonia: Impacts of Shallow Energy Levels

Photocatalytic fixation of nitrogen to ammonia represents an attractive alternative to the Haber-Bosch process under ambient conditions, and the performance can be enhanced by defect engineering of the photocatalysts, in particular, formation of shallow energy levels due to oxygen vacancies that can significantly facilitate the adsorption and activation of nitrogen. This calls for deliberate size engineering of the photocatalysts. In the present study, pyrochlore Bi2Ti2O7 quantum dots and (bulk-like) nanosheets are prepared hydrothermally by using bismuth nitrate and titanium sulfate as the precursors. Despite a similar oxygen vacancy concentration, the quantum dots exhibit a drastically enhanced photocatalytic performance toward nitrogen fixation, at a rate of 332.03 µmol g-1 h-1, which is 77 times higher than that of the nanosheet counterpart. Spectroscopic and computational studies based on density functional theory calculations show that the shallow levels arising from oxygen vacancies in the Bi2Ti2O7 quantum dots, in conjunction with the moderately constrained quantum confinement effect, facilitate the chemical adsorption and activation of nitrogen.

Electrocatalytic Synthesis of Urea: An In-depth Investigation from Material Modification to Mechanism Analysis

Industrial urea synthesis production uses NH3 from the Haber-Bosch method, followed by the reaction of NH3 with CO2, which is an energy-consuming technique. More thorough evaluations of the electrocatalytic C-N coupling reaction are needed for the urea synthesis development process, catalyst design, and the underlying reaction mechanisms. However, challenges of adsorption and activation of reactant and suppression of side reactions still hinder its development, making the systematic review necessary. This review meticulously outlines the progress in electrochemical urea synthesis by utilizing different nitrogen (NO3 -, N2, NO2 -, and N2O) and carbon (CO2 and CO) sources. Additionally, it delves into advanced methods in materials design, such as doping, facet engineering, alloying, and vacancy introduction. Furthermore, the existing classes of urea synthesis catalysts are clearly defined, which include 2D nanomaterials, materials with Mott-Schottky structure, materials with artificially frustrated Lewis pairs, single-atom catalysts (SACs), and heteronuclear dual-atom catalysts (HDACs). A comprehensive analysis of the benefits, drawbacks, and latest developments in modern urea detection techniques is discussed. It is aspired that this review will serve as a valuable reference for subsequent designs of highly efficient electrocatalysts and the development of strategies to enhance the performance of electrochemical urea synthesis.

The vertical partitioning between denitrification and dissimilatory nitrate reduction to ammonium of coastal mangrove sediment microbiomes

Mangrove aquatic ecosystems receive substantial nitrogen (N) inputs from both land and sea, playing critical roles in modulating coastal N fluxes. The microbially-mediated competition between denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in mangrove sediments significantly impacts the N fate and transformation processes. Despite their recognized role in N loss or retention in surface sediments, how these two processes vary with sediment depths and their influential factors remain elusive. Here, we employed a comprehensive approach combining 15N isotope tracer, quantitative PCR (qPCR) and metagenomics to verify the vertical dynamics of denitrification and DNRA across five 100-cm mangrove sediment cores. Our results revealed a clear vertical partitioning, with denitrification dominated in 0-30 cm sediments, while DNRA played a greater role with increasing depths. Quantification of denitrification and DNRA functional genes further explained this phenomenon. Taxonomic analysis identified Pseudomonadota as the primary denitrification group, while Planctomycetota and Pseudomonadota exhibited high proportion in DNRA group. Furthermore, genome-resolved metagenomics revealed multiple salt-tolerance strategies and aromatic compound utilization potential in denitrification assemblages. This allowed denitrification to dominate in oxygen-fluctuating and higher-salinity surface sediments. However, the elevated C/N in anaerobic deep sediments favored DNRA, tending to generate biologically available NH4+. Together, our results uncover the depth-related variations in the microbially-mediated competition between denitrification and DNRA, regulating N dynamics in mangrove ecosystems.

Reactive capture of CO2 via amino acid

Reactive capture of carbon dioxide (CO2) offers an electrified pathway to produce renewable carbon monoxide (CO), which can then be upgraded into long-chain hydrocarbons and fuels. Previous reactive capture systems relied on hydroxide- or amine-based capture solutions. However, selectivity for CO remains low (<50%) for hydroxide-based systems and conventional amines are prone to oxygen (O2) degradation. Here, we develop a reactive capture strategy using potassium glycinate (K-GLY), an amino acid salt (AAS) capture solution applicable to O2-rich CO2-lean conditions. By employing a single-atom catalyst, engineering the capture solution, and elevating the operating temperature and pressure, we increase the availability of dissolved in-situ CO2 and achieve CO production with 64% Faradaic efficiency (FE) at 50 mA cm-2. We report a measured CO energy efficiency (EE) of 31% and an energy intensity of 40 GJ tCO-1, exceeding the best hydroxide- and amine-based reactive capture reports. The feasibility of the full reactive capture process is demonstrated with both simulated flue gas and direct air input.

Improvement of photocatalytic ammonia production of cobalt ferrite nanoparticles utilizing microporous ZSM-5 type ferrisilicate zeolite

The development of decarbonized synthesis approaches is a critical step in the fabrication of ammonia, an indispensable chemical and a potential carbon-neutral energy carrier. In this regard, the photocatalytic production technology has gained ample attention as a sustainable alternative to energy-intensive and environmentally detrimental Haber-Bosch process. Here, we present cobalt ferrite nanoparticles supported on microporous ZSM-5 type ferrisilicate zeolite as a desirable novel photocatalyst for the ammonia generation. The zeolite introduced as a microporous support increasing the catalytically active sites. A straightforward one-pot sol-gel method was used to synthesize cobalt ferrite (CoFe2O4) and CoFe2O4/ferrisilicate (CF/FS) nanocomposites with various weight percentages (10, 25 and 50%) of CoFe2O4. The photocatalytic performances of the samples in the production of ammonia were investigated under visible light irradiation. The highest rate of NH4+ production (484.74 µmol L-1 h-1) was achieved using the CF50%/FS photocatalyst. The distribution of < 50 nm-sized CoFe2O4 nanoparticles on the surface of the zeolite, as demonstrated by TEM images, and extensive BET surface areas are presented as convincing evidences for the improved photocatalytic activity paticularly in CF50%/FS photocatalyst.

A hydrogen radical pathway for efficacious electrochemical nitrate reduction to ammonia over an Fe-polyoxometalate/Cu electrocatalyst

Electrochemical nitrate (NO3-) reduction to ammonia (NH3), which is a high value-added chemical or high-energy density carrier in many applications, could become a key process overcoming the disadvantages of the Haber-Bosch process; however, current electrocatalysts have severe drawbacks in terms of activity, selectivity, and stability. Here, we report the hydrogen radical (H*) pathway as a solution to overcome this challenge, as demonstrated by efficacious electrochemical NO3- reduction to NH3 over the Fe-polyoxometalate (Fe-POM)/Cu hybrid electrocatalyst. Fe-POM, composed of Preyssler anions ([NaP5W30O110]14-) and Fe cations, facilitates efficient H* generation via H2O + e- → H* + OH-, and H* transfer to the Cu sites of the Fe-POM/Cu catalyst enables selective NO3- reduction to NH3. Operando spectroelectrochemical spectra substantiate the occurrence of the H* pathway through direct observation of Fe redox related to H* generation and Cu redox related to NO3- binding. With the H* pathway, the Fe-POM/Cu electrodes exhibit high activity for NO3- reduction to NH3 with 1.44 mg cm-2 h-1 in a 500 ppm NO3-/1 M KOH solution at -0.2 V vs. RHE, which is about 36-fold higher than that of the pristine Cu electrocatalyst. Additionally, it attains high selectivity with a faradaic efficiency of up to 97.09% at -0.2 V vs. RHE while exhibiting high catalytic stability over cycles.

Engineering Single-Atom Sites with the Irving-Williams Series for the Simultaneous Co-photocatalytic CO2 Reduction and CH3CHO Oxidation

The bonding effects between 3d transition-metal single sites and supports originate from crystal field stabilization energy (CFSE). The 3d transition-metal atoms of the spontaneous geometrical distortions, that is the Jahn-Teller effect, can alter CFSE, thereby leading to the Irving-Williams series. However, engineering single-atom sites (SASs) using the Irving-Williams series as an ideal guideline has not been reported to date. Herein, alkynyl-linked covalent phenanthroline frameworks (CPFs) with phenanthroline units are developed to anchor the desired 3d single metal ions from d5 to d10 (Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+). The Irving-Williams series was employed to accurately predict the bonding effects between 3d transition-metal atoms and phenanthroline units. To verify this, theoretical calculations and experimental results reveal that Cu-SASs/CPFs exhibits higher stability and faster charge-transfer efficiency, far surpassing other metal-SASs/CPFs. As expected, Cu-SASs/CPFs demonstrates a high photoreduction of CO2-to-CO activity (~30.3 μmol ⋅ g-1 ⋅ h-1) and an exceptional photooxidation of CH3CHO-to-CH3COOH activity (~24.7 μmol ⋅ g-1 ⋅ h-1). Interestingly, the generated *O2 - is derived from the process of CO2 reduction, thereby triggering a CH3CHO oxidation reaction. This work provides a novel design concept for designing SASs by the Irving-Williams to regulate the catalytic performances.

Fast and Sensitive Detection of Ammonia from Electrochemical Nitrogen Reduction Reactions by 1H NMR with Radiation Damping

A facile NMR method is reported for analysis of ammonia from the electrochemical reduction of nitrogen, which compares a calibrated colorimetric method, a calibrated 1H NMR method and two 1H NMR direct measurements using external reference materials. Unlike spectrophotometric methods, 1H NMR requires less bench time and does not require separation of ammonia from the electrolyte. A novel approach to the problem of radiation damping in NMR measurements considered the specific role of hardware tuning. Radiation damping is suppressed improving signal-to-noise ratio and detection limit (1.5 µg L-1). The method is demonstrated to be effective for the analysis of ammonia from direct electrochemical nitrogen reduction in KOH, and from lithium-mediated nitrogen reduction in a non-aqueous solution. An uncertainty budget is prepared for the measurement of ammonia.

Comparison of anaerobic co-digestion of vacuum toilet blackwater and kitchen waste under mesophilic and thermophilic conditions: Reactor performance, microbial response and metabolic pathway

Co-digestion of kitchen waste (KW) and black water (BW) can be considered as an attractive method to efficiently achieve the clean energy from waste. To find the optimal operation parameters for the co-digestion, the effects of different temperatures (35 and 55 °C) and BW:KW ratios on the reactor performances, microbial communities and metabolic pathways were studied. The results showed that the optimum BW:KW ratio was 1:3.6 and 1:4.5 for mesophilic and thermophilic optimal reactors, with methane production of 449.04 mL/g VS and 411.90 mL/g VS, respectively. Microbial communities showed significant differences between the reactors under different temperatures. For bacteria, increasing BW:KW ratio significantly promoted Defluviitoga enrichment (1.1%-9.5%) under thermophilic condition. For Archaea, the increase in BW:KW ratio promoted the enrichment of Methanosaeta (8.6%-56.4%) in the mesophilic reactor and Methanothermobacter (62.0%-89.2%) in the thermophilic reactor. The analysis of the key enzymes showed that, acetoclastic methanogenic pathway performed as the dominant under mesophilic condition, with high abundance of Acetate-CoA ligase (EC:6.2.1.1) and Pyruvate synthase (EC:1.2.7.1). Hydrogenotrophic methanogenic pathway was the main pathway in the thermophilic reactors, with high abundance of Formylmethanofuran dehydrogenase (EC:1.2.99.5).

Isolation of bacteria with plant growth-promoting properties from microalgae-bacterial flocs produced in high-rate oxidation ponds

Exploring plant growth-promoting (PGP) bacterial activity of microbial components aggregated by wastewater treatment can reduce dependence on fossil fuel-derived fertilisers. This study describes the isolation and identification of bacteria from microalgae-bacteria flocs (MaB-flocs) generated in high-rate algal oxidation ponds (HRAOP) of an integrated algal pond system (IAPS) remediating municipal wastewater. Amplified 16S rRNA gene sequence analysis determined the molecular identity of the individual strains. Genetic relatedness to known PGP rhizobacteria in the NCBI GenBank database was by metagenomics. Isolated strains were screened for the production of indoles (measured as indole-3-acetic acid; IAA) and an ability to mineralise NH 4 + , PO 4 3 - , and K + . Of the twelve bacterial strains isolated from HRAOP MaB-flocs, four produced indoles, nine mineralised NH 4 + , seven solubilised P, and one K. Potential of isolated strains for PGP activity according to one-way ANOVA on ranks was: ECCN 7b > ECCN 4b > ECCN 6b > ECCN 3b = ECCN 10b > ECCN 1b = ECCN 5b > ECCN 8b > ECCN 2b > ECCN 12b > ECCN 9b = ECCN 11b. Further study revealed that cell-free filtrate from indole-producing cultures of Aeromonas strain ECCN 4b, Enterobacter strain ECCN 7b, and Arthrobacter strain ECCN 6b promoted mung bean adventitious root formation suggestive of the presence of auxin-like biological activity.

Advancements in Electrocatalytic Nitrogen Reduction: A Comprehensive Review of Single-Atom Catalysts for Sustainable Ammonia Synthesis

Electrocatalytic nitrogen reduction technology seamlessly aligns with the principles of environmentally friendly chemical production. In this paper, a comprehensive review of recent advancements in electrocatalytic NH3 synthesis utilizing single-atom catalysts (SACs) is offered. Into the research and applications of three categories of SACs: noble metals (Ru, Au, Rh, Ag), transition metals (Fe, Mo, Cr, Co, Sn, Y, Nb), and nonmetallic catalysts (B) in the context of electrocatalytic ammonia synthesis is delved. In-depth insights into the material preparation methods, single-atom coordination patterns, and the characteristics of the nitrogen reduction reaction (NRR) are provided. The systematic comparison of the nitrogen reduction capabilities of various SAC types offers a comprehensive research framework for their integration into electrocatalytic NRR. Additionally, the challenges, potential solutions, and future prospects of incorporating SACs into electrocatalytic nitrogen reduction endeavors are discussed.

Gradient-concentration RuCo electrocatalyst for efficient and stable electroreduction of nitrate into ammonia

Electrocatalytic nitrate reduction to ammonia holds great promise for developing green technologies for electrochemical ammonia energy conversion and storage. Considering that real nitrate resources often exhibit low concentrations, it is challenging to achieve high activity in low-concentration nitrate solutions due to the competing reaction of the hydrogen evolution reaction, let alone considering the catalyst lifetime. Herein, we present a high nitrate reduction performance electrocatalyst based on a Co nanosheet structure with a gradient dispersion of Ru, which yields a high NH3 Faraday efficiency of over 93% at an industrially relevant NH3 current density of 1.0 A/cm2 in 2000 ppm NO3- electrolyte, while maintaining good stability for 720 h under -300 mA/cm2. The electrocatalyst maintains high activity even in 62 ppm NO3- electrolyte. Electrochemical studies, density functional theory, electrochemical in situ Raman, and Fourier-transformed infrared spectroscopy confirm that the gradient concentration design of the catalyst reduces the reaction energy barrier to improve its activity and suppresses the catalyst evolution caused by the expansion of the Co lattice to enhance its stability. The gradient-driven design in this work provides a direction for improving the performance of electrocatalytic nitrate reduction to ammonia.

Construction of hierarchical In2O3/In2S3-ZnCdS ternary microsphere heterostructures for efficient photocatalytic nitrogen fixation

Photocatalytic ammonia production holds immense promise as an environmentally sustainable approach to nitrogen fixation. In this study, In2O3/In2S3-ZnCdS ternary heterostructures were successfully constructed through an innovative in situ anion exchange process, coupled with a low-temperature hydrothermal method for ZnCdS (ZCS) incorporation. The resulting In2O3/In2S3-ZCS photocatalyst was proved to be highly efficient in converting N2 to NH3 under mild conditions, eliminating the need for sacrificial agents or precious metal catalysts. Notably, the NH4+ yield of In2O3/In2S3-0.5ZCS reached a significant level of 71.2 μmol g-1 h-1, which was 10.47 times higher than that of In2O3 (6.8 μmol g-1 h-1) and 3.22 times higher than that of In2O3/In2S3 (22.1 μmol g-1 h-1). This outstanding performance can be attributed to the ternary heterojunction configuration, which significantly extends the lifetime of photogenerated carriers and enhances the spatial separation of electrons and holes. The synergistic interplay between CdZnS, In2S3, and In2O3 in the heterojunction facilitates electron transport, thereby boosting the rate of the photocatalytic nitrogen fixation reaction. Our study not only validates the efficacy of ternary heterojunctions in photocatalytic nitrogen fixation but also offers valuable insights for the design and construction of such catalysts for future applications.

Electron repulsion tuned electronic structure of TiO2 by fluorination for efficient and selective photocatalytic ammonia generation

The photocatalytic conversion of nitrogen into high-value ammonia products holds tremendous potential in the global nitrogen cycle. However, the activation of N2 and competition of hydrogen evolution limit the improvement of nitrogen fixation performance. In this study, we developed a fluorinated TiO2 (F-TiO2) using a hydrothermal-annealing method. The incorporation of F dopants not only enhances the adsorption and activation of N2 through electronic structure regulation, but also facilitates an in situ increase in active sites via the electron repulsion effect between F and Ti atoms. In addition, the presence of F on the surface effectively improved the nitrogen supply problem and optimized the nitrogen fixation selectivity for its hydrophobic modulation. The NH3 yield of the F-TiO2 photocatalyst reached 63.8 μmol h-1 g-1, which was 8.5 times higher than that of pure TiO2. And the selectivity experiment showed that the electronic ratio of NH3 to H2 production reached 0.890. This research offers valuable insights for the design of highly efficient and selective nitrogen-fixing photocatalysts.

Electrocatalysts for Inorganic and Organic Waste Nitrogen Conversion

Anthropogenic activities have disrupted the natural nitrogen cycle, increasing the level of nitrogen contaminants in water. Nitrogen contaminants are harmful to humans and the environment. This motivates research on advanced and decarbonized treatment technologies that are capable of removing or valorizing nitrogen waste found in water. In this context, the electrocatalytic conversion of inorganic- and organic-based nitrogen compounds has emerged as an important approach that is capable of upconverting waste nitrogen into valuable compounds. This approach differs from state-of-the-art wastewater treatment, which primarily converts inorganic nitrogen to dinitrogen, and organic nitrogen is sent to landfills. Here, we review recent efforts related to electrocatalytic conversion of inorganic- and organic-based nitrogen waste. Specifically, we detail the role that electrocatalyst design (alloys, defects, morphology, and faceting) plays in the promotion of high-activity and high-selectivity electrocatalysts. We also discuss the impact of wastewater constituents. Finally, we discuss the critical product analyses required to ensure that the reported performance is accurate.

Enhanced biomass production and harvesting efficiency of Chlamydomonas reinhardtii under high-ammonium conditions by powdered oyster shell

Chlamydomonas reinhardtii prefers ammonium (NH4+) as a nitrogen source, but its late-stage growth under high-NH4+ concentrations (0.5 ∼ 1 g/L) is retarded due to medium acidification. In this study, oyster shell powders were shown to increase the tolerance of C. reinhardtii to NH4+ supplementation at 0.7 g/L in TAP medium in 1-L bubble-column bioreactors, resulting in a 22.9 % increase in biomass production, 62.1 % rise in unsaturated fatty acid accumulation, and 19.2 % improvement in harvesting efficiency. Powdered oyster shell mitigated medium acidification (pH 7.2-7.8) and provided dissolved inorganic carbon up to 8.02 × 103 μmol/L, facilitating a 76.3 % NH4+ consumption, release of up to 189 mg/L of Ca2+, a 42.1 % reduction in ζ-potential and 27.7 % increase in flocculation activity of microalgae cells. This study highlights a promising approach to utilize powdered oyster shell as a liming agent, supplement carbon source, and bio-flocculant for enhancing biomass production and microalgae harvesting in NH4+-rich environments.

A Solar to Chemical Strategy: Green Hydrogen as a Means, Not an End

Green hydrogen is the key to the chemical industry achieving net zero emissions. The chemical industry is responsible for almost 2% of all CO2 emissions, with half of it coming from the production of simple commodity chemicals, such as NH3, H2O2, methanol, and aniline. Despite electrolysis driven by renewable power sources emerging as the most promising way to supply all the green hydrogen required in the production chain of these chemicals, in this review, it is worth noting that the photocatalytic route may be underestimated and can hold a bright future for this topic. In fact, the production of H2 by photocatalysis still faces important challenges in terms of activity, engineering, and economic feasibility. However, photocatalytic systems can be tailored to directly convert sunlight and water (or other renewable proton sources) directly into chemicals, enabling a solar-to-chemical strategy. Here, a series of recent examples are presented, demonstrating that photocatalysis can be successfully employed to produce the most important commodity chemicals, especially on NH3, H2O2, and chemicals produced by reduction reactions. The replacement of fossil-derived H2 in the synthesis of these chemicals can be disruptive, essentially safeguarding the transition of the chemical industry to a low-carbon economy.

Photocatalytic Nitrogen Fixation Coupled with the Generation of Value-Added Chemicals from N2 and Cellulose over MoO3 Nanosheets

Photocatalytic nitrogen fixation from N2 provides an alternative strategy for ammonia (NH3) production, but it was limited by the consumption of a sacrificial electron donor for the currently reported half-reaction system. Here, we use naturally abundant and renewable cellulose as the sacrificial reagent for photocatalytic nitrogen fixation over oxygen-vacancy-modified MoO3 nanosheets as the photocatalyst. In this smartly designed photocatalytic system, the photooxidation of cellulose not only generates value-added chemicals but also provides electrons for the N2 reduction reaction and results in the production of NH3 with a maximum rate of 68 μmol·h-1·g-1. Also, the oxygen vacancies provide efficient active sites for both cellulose oxygenolysis and nitrogen fixation reactions. This work represents useful inspiration for realizing nitrogen fixation coupled with the generation of value-added chemicals from N2 and cellulose through a photocatalysis strategy.

Synergistic Integration of Amorphous Cobalt Phosphide with a Conductive Channel for Highly Efficient Electrocatalytic Nitrate Reduction to Ammonia

Electrocatalytic nitrate reduction to ammonia (NO3RR) is regarded as a viable alternative reaction to "Haber Bosch" process. Nevertheless, it remains a major challenge to explore economical and efficient electrocatalysts that deliver high NH3 yield rates and Faraday efficiencies (FE). Here, it demonstrates the fabrication of a 3D core-shell structured Co-carbon nanofibers (CNF)/ZIF-CoP for NO3RR application. Benefitting from the distinct electron transport property of Co-CNF and desirable mass transfer ability from amorphous CoP framework, the as-prepared Co-CNF/ZIF-CoP exhibits large NH3 FE (96.8 ± 3.4% at -0.1 V vs reversible hydrogen electrode (RHE)) and high yield rate (38.44 ± 0.65 mg cm-2 h-1 at -0.6 V vs RHE), which are better than Co-CNF/ZIF-crystal CoP. Density functional theory (DFT) calculations further reveal that amorphous CoP presents a lower energy barrier in the rate determination step of the protonation of *NO to produce *NOH intermediates compared with crystal CoP, resulting in a superior NO3RR performance. Eventually, an aqueous galvanic Zn-NO3 - battery is assembled by using Co-CNF/ZIF-CoP as cathode material to achieve efficient production of NH3 whilst simultaneously supplying electrical power. This work offers a reliable strategy to construct amorphous metal phosphide framework on conducting CNF as efficient electrocatalyst and enriches its promising application for NO3RR.

Two-dimensional Cu Plates with Steady Fluid Fields for High-rate Nitrate Electroreduction to Ammonia and Efficient Zn-Nitrate Batteries

Nitrate electroreduction reaction (eNO3 -RR) to ammonia (NH3) provides a promising strategy for nitrogen utilization, while achieving high selectivity and durability at an industrial scale has remained challenging. Herein, we demonstrated that the performance of eNO3 -RR could be significantly boosted by introducing two-dimensional Cu plates as electrocatalysts and eliminating the general carrier gas to construct a steady fluid field. The developed eNO3 -RR setup provided superior NH3 Faradaic efficiency (FE) of 99 %, exceptional long-term electrolysis for 120 h at 200 mA cm-2, and a record-high yield rate of 3.14 mmol cm-2 h-1. Furthermore, the proposed strategy was successfully extended to the Zn-nitrate battery system, providing a power density of 12.09 mW cm-2 and NH3 FE of 85.4 %, outperforming the state-of-the-art eNO3 -RR catalysts. Coupled with the COMSOL multiphysics simulations and in situ infrared spectroscopy, the main contributor for the high-efficiency NH3 production could be the steady fluid field to timely rejuvenate the electrocatalyst surface during the electrocatalysis.

Unveiling Cutting-Edge Developments in Electrocatalytic Nitrate-to-Ammonia Conversion

The excessive enrichment of nitrate in the environment can be converted into ammonia (NH3) through electrochemical processes, offering significant implications for modern agriculture and the potential to reduce the burden of the Haber-Bosch (HB) process while achieving environmentally friendly NH3 production. Emerging research on electrocatalytic nitrate reduction (eNitRR) to NH3 has gained considerable momentum in recent years for efficient NH3 synthesis. However, existing reviews on nitrate reduction have primarily focused on limited aspects, often lacking a comprehensive summary of catalysts, reaction systems, reaction mechanisms, and detection methods employed in nitrate reduction. This review aims to provide a timely and comprehensive analysis of the eNitRR field by integrating existing research progress and identifying current challenges. This review offers a comprehensive overview of the research progress achieved using various materials in electrochemical nitrate reduction, elucidates the underlying theoretical mechanism behind eNitRR, and discusses effective strategies based on numerous case studies to enhance the electrochemical reduction from NO3 - to NH3. Finally, this review discusses challenges and development prospects in the eNitRR field with an aim to guide design and development of large-scale sustainable nitrate reduction electrocatalysts.

Synthesis of Efficient S-Scheme Heterostructures Composed of BiPO4 and KNbO3 for Photocatalytic N2 Fixation and Water Purification

The preparation of catalysts with heterojunction structures is a strategy to achieve efficient charge separation and high photocatalytic activity of photocatalysts. In this work, BiPO4/KNbO3 heterostructure photocatalysts were fabricated by a combination of hydrothermal and precipitation methods and subsequently employed in catalyzing N2-to-NH3 conversion and RhB degradation under light illumination. Morphological analysis revealed the effective dispersion of BiPO4 on KNbO3 nanocubes. Band structure analysis suggests that KNbO3 and BiPO4 exhibit suitable band potentials to form an S-scheme heterojunction. Under the joint action of the built-in electric field at the interface, energy band bending, and Coulomb attraction force, photogenerated electrons and holes with low redox performance are consumed, while those with high redox performance are effectively spatially separated. Consequently, the BiPO4/KNbO3 shows enhanced photocatalytic activity. The NH3 production rate of the optimal sample is 2.6 and 5.8 times higher than that of KNbO3 and BiPO4, respectively. The enhanced photoactivity of BiPO4/KNbO3 is also observed in the photocatalytic degradation of RhB. This study offers valuable insights for the design and preparation of S-scheme heterojunction photocatalysts.

Customizing Wettability of Defect-Rich CeO2/TiO2 Nanotube Arrays for Humidity-Resistant, Ultrafast, and Sensitive Ammonia Response

In all their applications, gas sensors should satisfy several requirements, including low cost, reduced energy consumption, fast response/recovery, high sensitivity, and reliability in a broad humidity range. Unfortunately, the fast response/recovery and sensing reliability under high humidity conditions are often still missing, especially those working at room temperature. In this study, a humidity-resistant gas sensor with an ultrafast response/recovery rate was designed by integrating a defect-rich semiconducting sensing interface and a self-assembled monolayer (SAM) with controllable wettability. As a proof-of-concept application, ammonia (NH3), one of the atmospheric and indoor pollutants, was selected as the target gas. The decoration of interconnected defective CeO2 nanowires on spaced TiO2 nanotube arrays (NTAs) provided superior NH3 sensing performances. Moreover, we showed that manipulating the functional end group of SAMs is an efficient and simple method to adjust the wettability, by which 86% sensitivity retention with an ultrafast response (within 5 s) and a low limit of detection (45 ppb) were achieved even at 75% relative humidity and room temperature. This work provides a new route toward the comprehensive design and application of metal oxide semiconductors for trace gas monitoring under harsh conditions, such as those of agricultural, environmental, and industrial fields.

Solar-Driven Ammonia Production through Engineering of the Electronic Structure of a Zr-Based MOF

As a hydrogen carrier and a vital component in fertilizer production, ammonia (NH3) is set to play a crucial role in the planet's future. While its industrial production feeds half of the global population, it uses fossil fuels and emits greenhouse gases. To tackle this issue, photocatalytic nitrogen fixation using visible light is emerging as an effective alternative method. This strategy avoids carbon dioxide (CO2) emissions and harnesses the largest share of sunlight. In this work, we successfully incorporated a 5-nitro isophthalic acid linker into MOF-808 to introduce structural defects and open metal sites. This has allowed modulation of the electronic structure of the MOF and effectively reduced the band gap energy from 3.8 to 2.6 eV. Combination with g-C3N4 enhanced further NH3 production, as these two materials possess similar band gap energies, and g-C3N4 has shown excellent performance for this reaction. The nitro groups serve as acceptors, and their integration into the MOF structure allowed effective interaction with the free electron pairs on N-(C)3 in the g-C3N4 network nodes. Based on DFT calculations, it was concluded that the adsorption of N2 molecules on open metal sites caused a decrease in their triple bond energy. The modified MOF-808 showed superior performance compared with the other MOFs studied in terms of N2 photoreduction under visible light. This design concept offers valuable information about how to engineer band gap energy in MOF structures and their combination with appropriate semiconductors for solar-powered photocatalytic reactions, such as N2 or CO2 photoreduction.

Hollow mesoporous carbon supported Co-modified Cu/Cu2O electrocatalyst for nitrate reduction reaction

The electroreduction of nitrate (NO3-) pollutants to ammonia (NH3) provides a sustainable approach for both wastewater treatment and NH3 synthesis. However, electroreduction of nitrate requires multi-step electron and proton transfer, resulting in a sluggish reaction rate. Herein, we synthesized a Co-modified Cu/Cu2O catalyst supported on hollow mesoporous carbon substrates (Co/Cu/Cu2O-MesoC) by a one-step microwave-assisted reduction method. At -0.25 V vs. reversible hydrogen electrode (RHE), Co/Cu/Cu2O-MesoC shows a Faradaic efficiency (FE) of 100 ± 1% in 0.1 M NO3-. Notably, the maximum NH3 yield rate (YieldNH3) reaches 6.416 ± 0.78 mmol mgcat-1h-1 at -0.45 V vs. RHE, which is much better than most of the previous reports. Electrochemical evaluation and in-situ Fourier transform infrared (FTIR) spectroscopy reveal that the addition of Co could promote water electrolysis, and the generated H* is involved in the following hydrogenation of intermediates, ultimately leading to faster kinetics and energetics during electrocatalytic conversion of NO3- to NH3. This synergetic electrocatalysis strategy opens a new avenue for the development of high-activity, selectivity, and stability catalysts.

Recent Developments of Dual Single-Atom Catalysts for Nitrogen Reduction Reaction

Ammonia is vital for fertilizer production, hydrogen storage, and alternative fuels. The conventional Haber-Bosch process for ammonia production is energy-intensive and environmentally harmful. Designing environmentally friendly and low-energy consumption strategies for electrocatalytic N2 reduction reaction (ENRR) in mild conditions is meaningful. Single-atom catalysts (SACs) have been studied extensively for NRR due to their high atomic utilization and unique electronic structure but are limited by their poor faradic efficiency and low ammonia formation yield. Dual single-atom catalysts (DSACs) have recently emerged as a promising solution for the effective activation of molecular N2 , providing diverse active sites and synergistic interactions between adjacent atoms. In this review, we summarize the latest advances in metal DSACs for electrochemical ENRR based on both theoretical calculations and experimental studies, including aspects such as their variety, coordination, support, N2 adsorption and activity mechanisms, the characterization of NRR and electrochemical cell Configuration. We also address challenges and prospects in this rapidly evolving field, providing a comprehensive overview of DSACs for ENRR.

Review of Carbon Support Coordination Environments for Single Metal Atom Electrocatalysts (SACS)

This topical review focuses on the distinct role of carbon support coordination environment of single-atom catalysts (SACs) for electrocatalysis. The article begins with an overview of atomic coordination configurations in SACs, including a discussion of the advanced characterization techniques and simulation used for understanding the active sites. A summary of key electrocatalysis applications is then provided. These processes are oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CO2 RR). The review then shifts to modulation of the metal atom-carbon coordination environments, focusing on nitrogen and other non-metal coordination through modulation at the first coordination shell and modulation in the second and higher coordination shells. Representative case studies are provided, starting with the classic four-nitrogen-coordinated single metal atom (MN4 ) based SACs. Bimetallic coordination models including homo-paired and hetero-paired active sites are also discussed, being categorized as emerging approaches. The theme of the discussions is the correlation between synthesis methods for selective doping, the carbon structure-electron configuration changes associated with the doping, the analytical techniques used to ascertain these changes, and the resultant electrocatalysis performance. Critical unanswered questions as well as promising underexplored research directions are identified.