Search Results (89)

A binder-free Co₃O₄ nanoneedle electrode grown directly on nickel foam (Co₃O₄@NF) was fabricated by hydrothermal synthesis followed by calcination and evaluated for electrocatalytic nitrate reduction to ammonium. The integrated three-dimensional architecture combines the catalytic activity of Co₃O₄ with the high conductivity and open porosity of nickel foam, thus exposing abundant active sites, shortening electron-transfer pathways, and facilitating mass transport. Among the electrodes prepared at different calcination temperatures, Co₃O₄@NF calcined at 400 °C delivered the best performance. Under the optimal conditions of −1.4 V vs. Ag/AgCl, pH 7, and an initial NO₃⁻-N concentration of 50 mg L⁻¹, the electrode achieved 83.4% nitrate removal within 480 min together with 98.7% ammonium selectivity. Electrochemical measurements revealed a markedly enlarged electrochemically active surface area and reduced charge-transfer resistance after Co₃O₄ loading. Mechanistic analyses via TBA quenching experiments and DFT calculations revealed that both the direct pathway and the hydrogen-assisted indirect pathway were operative, with the indirect pathway being dominant due to its lower free energy barrier while maintaining negligible nitrite accumulation. The electrode also showed good cycling stability and retained high ammonium selectivity in real water matrices. These results demonstrate that binder-free Co₃O₄ nanoneedles supported on nickel foam constitute a promising cathode architecture for coupling nitrate removal with ammonia recovery. Full article

A novel ternary nanocomposite, comprising reduced graphene oxide/polyaniline/gadolinium oxide (RGO-PANI-Gd₂O₃), was successfully synthesized using the Hummers method, followed by in situ emulsion polymerization of polyaniline. The final composite was produced by hydrothermally adding gadolinium nitrate. The composite was subjected to a systematic analysis that included optical, microstructural, physical, and Raman spectroscopic analysis, as well as current-voltage (J-V) measurements. The morphology of this composite material was investigated using scanning electron microscopy (SEM). The addition of Gd₂O₃ nanoparticles decreases the band gap energy from 3.5 eV (PANI) to 2.7 eV (RGO-PANI-Gd₂O₃). The UV–Vis spectra revealed a redshift in the π-π* transition peak from 318 nm (PANI) to 346 nm, indicating increased conjugation length and synergistic effects. This eco-friendly material has excellent catalytic activity for triiodide reduction. The manufactured counter-electrode (CE) demonstrated remarkable transparency and conversion efficiency comparable to platinum, with a current density of 11.7 mA·cm⁻² versus 8.2 mA·cm⁻² for platinum. Under simulated solar light (AM 1.5 G, 100 mW·cm⁻²), the RGO-PANI-Gd₂O₃ based nanocomposite CE achieved an excellent 4.3% photo conversion efficiency. These findings indicate that RGO-PANI-Gd₂O₃ nanocomposites have potential as efficient, platinum-free counter electrodes in dye-sensitized solar cells (DSSCs). Full article

Nitrate pollution in groundwater poses severe threats to ecosystems and human health, making the electrochemical nitrate reduction reaction (NO₃RR) a promising remediation technology. Conductive metal–organic frameworks (cMOFs) with π-d conjugation, dispersed active sites, and tunable structures are ideal candidates for electrocatalysis. Herein, we synthesized a series of cMOFs (M₃(HHTP)₂, M = Fe, Zn, Cu, Co, Ni) via conjugated coordination between hexahydroxytriphenylene (HHTP) ligands and metal ions and systematically investigated their NO₃RR performance. Electrochemical tests revealed that Fe₃(HHTP)₂ exhibits superior catalytic performance for nitrate reduction, achieving a high NH₃ selectivity of 99.5% and a yield rate of 676.4 mg·g_cat⁻¹·h⁻¹ at −1.0 V vs. RHE (reversible hydrogen electrode), along with excellent cyclic and structural stability. In situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy identified key intermediates (*NO₂, *NH₂OH) and proposed the reaction pathway: NO₃⁻ → *NO₃ → *NO₂ → *NO → *NOH → *NH₂OH → *NH₂ → *NH₃. DFT calculations revealed that Fe center exhibited a lower energy barrier for NO₃RR compared to other metal ions (Zn, Cu, Co, Ni). This study demonstrates the significant potential of Fe₃(HHTP)₂ for efficient NO₃RR and provides new insights into the structure-function relationship of cMOF-based electrocatalysts. Full article

Nitrate (NO₃⁻), as a stable nitrogen-containing compound, has caused serious harm to the ecological environment and human health. To reduce nitrate pollution, the catalytic reduction of nitrate (NO₃RR) to ammonia (NH₃) is a very promising solution. Recently, single-atom catalysts (SACs) have received extensive attention due to their excellent activity and stability. Here, we study the nitrate catalytic reduction properties of hexagonal-boron-nitride-(h-BN)-supported single-atom Cu systematically and theoretically and compare it with monolayer h-BN. We find that (1) due to the stronger electronegativity of the N atom, Cu atom is preferentially doped at the N top site, resulting in the significant electron rearrangement; (2) the doped Cu atom at the N top site for monolayer h-BN can provide extra 3d-orbital electrons at the Fermi level, which can significantly enhance the conductivity, reduce the bandgap width, and increase the reducibility; (3) the NO₃⁻ ion preferentially adsorbs at the hollow site of monolayer h-BN, while the NO₃⁻ ion is adsorbed more strongly at the Cu top site of h-BN-supported single-atom Cu due to the abundant d-electron supply from the Cu atom; (4) single-atom Cu can significantly reduce the energy barrier of the rate-determining step (RDS) and increase the probability of nitrate reduction. In conclusion, h-BN-supported single-atom Cu exhibits excellent catalytic performance of NO₃RR. Full article

Nitrate contamination of water resources poses significant ecological and public health risks. This study developed a cobalt-immobilized microplastic catalyst (Co–MP) capable of activating peroxymonosulfate (PMS) and facilitating formic-acid-assisted catalytic denitrification of nitrate. Characterization via Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Energy-Dispersive X-ray Spectroscopy (EDX), and X-ray diffractometry (XRD) confirmed successful Co deposition, with the surface cobalt content reaching 5.2%. The system’s performance was optimized using Response Surface Methodology (RSM), identifying catalyst dosage and Co(II) concentration as the most significant factors. Under the optimized conditions (pH 5.5, reaction time 120 min, catalyst dosage 1.5 g L⁻¹, and Co(II) concentration 60 mg L⁻¹), the system achieved a nitrate removal efficiency of 90.6%, in excellent agreement with the model prediction (90.93%), along with an 86.7% reduction in total nitrogen, confirming stepwise denitrification to gaseous nitrogen species (N₂). The Co(II)/Co(III) redox cycle, sustained by PMS-assisted regeneration and driven by formic acid as the electron donor, ensured stable performance with minimal cobalt leaching (0.05 mg L⁻¹). This coupled oxidative–reductive system offers a sustainable dual-remediation strategy that simultaneously achieves selective nitrate conversion and valorizes microplastic waste for catalytic environmental applications. Full article

Ammonia serves as a critical industrial feedstock and a potential carbon-free energy carrier. However, its conventional synthesis method (the Haber–Bosch process) suffers from high energy consumption and substantial carbon emissions. The electrochemical nitrate reduction reaction (eNO₃RR) has emerged as a promising alternative pathway, capable of converting nitrate pollutants in water into high-value ammonia under mild conditions, enabling green synthesis while offering dual benefits of environmental remediation and energy conversion. Single-atom catalysts (SACs), with their maximal atom utilization efficiency, well-defined active sites, and highly tunable electronic structures, have demonstrated exceptional catalytic performance and selectivity in eNO₃RR. This review systematically summarizes recent advances of SACs in eNO₃RR, with a focus on reaction mechanisms, advanced in situ characterization techniques, theoretical calculation, and the catalytic behavior and structure–activity relationships of various non-noble metal centers (e.g., Cu, Fe, Co). Key strategies for enhancing SACs performance are elaborated, alongside an analysis of microenvironmental influences such as electrolyte composition, pH, and potential. Finally, we outlines current challenges in material design, dynamic active site identification, and the industrial application of SACs, and propose future research directions aimed at facilitating the practical implementation of eNO₃RR technology and contributing to the establishment of a sustainable ammonia economy. Full article

Developing bifunctional electrocatalysts that simultaneously enable green hydrogen production and water purification is essential for advancing sustainable energy and environmental technologies. In this study, we present Cu@Pd core–shell nanostructures fabricated through template-assisted electrodeposition of Cu, followed by galvanic Pd modification on pyrolytic graphite electrodes (PGEs). The optimised catalyst exhibited superior hydrogen evolution reaction (HER) activity, with an onset potential of 70 mV, a low Tafel slope of 33 mV dec⁻¹ and excellent stability during prolonged HER operation. In addition to hydrogen evolution, Cu@Pd/PGE shows significantly enhanced nitrate reduction reaction (NRR) activity compared to Cu/PGE in both alkaline and neutral conditions. Under ideal conditions, the catalyst achieved 60% nitrate removal with high selectivity towards ammonia and minimal nitrite formation, emphasising its superior performance. This enhanced bifunctionality arises from the synergistic Cu–Pd interface, facilitating efficient nitrate adsorption and selective hydrogenation. Despite their high catalytic activity for both HER and NRR, the Cu@Pd nanostructures could often emerge as a versatile platform for integration into sustainable hydrogen production and an effective denitrification process. Full article

Introduction: 5-HMF is a molecule found in carbohydrate-rich foods that is associated not only with cancer and anaphylactic reactions, but also with anti-oxidant properties. Questions arose as to whether 5-HMF exhibited a catalytic effect in relation to lipid peroxidation and lipoprotein oxidation in presence of metals and/or radicals. Methods: Peroxynitrite (ONOO⁻)-induced chemiluminescence and ONOO⁻ nitration of tyrosine residues on BSA using anti-nitro-tyrosine-antibodies were used to measure the protection of 5-HMF against peroxides or nitration compared to vitamin C (VitC). The reductive potential of 5-HMF or VitC on Cu²⁺ or Fe³ was estimated using the bicinchoninic acid (BCA) or Fenton-complex method. Human plasma was used to measure the generation of malondialdehyde (MDA), 4-hydroxynonenal (HNE), and total thiols after Fe²⁺/H₂O₂ oxidation in the presence of different concentrations of 5-HMF or VitC. Finally, Cu²⁺ oxidation of LDL after 4 h was carried out with 5-HMF or VitC, measuring the concentration of MDA in LDL with the thiobarbituric assay (TBARS). Results: VitC was 4-fold more effective than 5-HMF in scavenging ONOO⁻ to nearly 91.5% at 4 mM, with the exception of 0.16 mM, where the reduction of ONOO⁻ by VitC was 3.3-fold weaker compared to 0.16 mM 5-HMF. VitC or 5-HMF at a concentration of 6 mM inhibited the nitration of tyrosine residues on BSA to nearly 90% with a similar course. While 5-HMF reduced free Fe³⁺ in presence of phenanthroline, forming Fe²⁺ (phenantroleine)₃ [Fe²⁺(phe)₃] or complexed Cu²⁺(BCA)₄ to Cu⁺(BCA)₄ weakly, VitC was 7- to 19-fold effective in doing so over all the used concentrations (0–25 mM). A Fe²⁺—H₂O₂ solution mixed with human plasma showed a 6–10 times higher optical density (OD) of MDA or HNE in the presence of 5-HMF compared to VitC. The level of thiols was significantly decreased in the presence of higher VitC levels (1 mM: 198.4 ± 7.7 µM; 2 mM: 160.0 ± 13.4 µM) compared to equal 5-HMF amounts (2562 ± 7.8 µM or 242.4 ± 2.5 µM), whereas the usage of lower levels at 0.25 µM 5-HMF resulted in a significant decrease in thiols (272.4 ± 4.0 µM) compared to VitC (312.3 ± 19.7 µM). Both VitC and 5-HMF accelerated copper-mediated oxidation of LDL equally: while the TBARS levels from 4 h oxidized LDL reached 137.7 ± 12.3 nmol/mg, it was 1.7-fold higher using 6 mM VitC (259.9 ± 10.4 nmol/mg) or 6 mM 5-HMF (239.3 ± 10.2 nmol/mg). Conclusions: 5-HMF appeared to have more pro-oxidative potential compared to VitC by causing lipid peroxidation as well as protein oxidation. Full article

The co-electrolysis of nitrate and CO₂ can contribute to urea production with low carbon-oxide emission rate and at the same time reduce NO₃⁻ to extremely low permissible concentrations. It was found that Ag and Fe particles, as thin catalytic layers, can potentially be used for the joint reduction of NO₃⁻ and CO₂ under benign ambient conditions. The linear voltammetry, chronoamperometry, electrochemical impedance spectroscopy, and electron scanning microscopy were used. The Fe/C electrocatalyst exhibits superior current density stability at −1.2 V vs. Ag/AgCl, whereas Ag/C electrocatalyst shows noticeable degradation over time. This reaction is necessary both for the removal of nitrates from wastewater and for the capture of carbon dioxide, which makes it one of the important applications of sustainable chemistry. Full article

The nitrogen cycle (N-cycle) is a cornerstone of global biogeochemistry, regulating nitrogen availability and affecting atmospheric chemistry, agricultural productivity, and ecological balance. Central to this cycle is the reversible interplay between nitrate (NO₃⁻) and nitrite (NO₂⁻), mediated by molybdenum-dependent enzymes—Nitrate reductases (NARs) and Nitrite oxidoreductases (NXRs). Despite catalyzing opposite reactions, these enzymes exhibit remarkable structural and mechanistic similarities. This review aims to elucidate the molecular underpinnings of nitrate reduction and nitrite oxidation by dissecting their enzymatic architectures, redox mechanisms, and evolutionary relationships. By focusing on recent structural, spectroscopic, and thermodynamic data, we explore how these two enzyme families represent “two sides of the same coin” in microbial nitrogen metabolism. Special emphasis is placed on the role of oxygen atom transfer (OAT) as a unifying mechanistic principle, the influence of environmental redox conditions, and the emerging evidence of bidirectional catalytic potential. Understanding this dynamic enzymatic interconversion provides insight into the flexibility and resilience of nitrogen-transforming pathways, with implications for environmental management, biotechnology, and synthetic biology. Full article

The electrochemical reduction of nitrate to ammonia offers a promising solution for both alleviating nitrate pollution in wastewater and providing a sustainable ammonia source for agriculture use. This review focuses on the role of carbon-based catalysts in electrochemical nitrate reduction to ammonia, emphasizing their potential in addressing environmental pollution and supporting sustainable ammonia production. Carbon materials, known for their abundance, affordability, and eco-friendly properties, are central to this process. The review highlights key strategies for enhancing catalytic performance, including heteroatom doping, the development of porous structures, and the integration of metal/metal oxide nanoparticles. Additionally, it addresses significant challenges such as weak nitrate adsorption, slow reaction kinetics, and competition with the hydrogen evolution reaction. Through the integration of advanced material design, mechanistic insights, and innovative engineering strategies, this review provides valuable guidance for the future design of carbon-based catalysts, paving the way for significant advancements in both nitrate removal and sustainable ammonia synthesis. Full article

The selective catalytic reduction of NO_x with CH₄ (CH₄-SCR) holds the potential to simultaneously abate harmful NO_x and CH₄ greenhouse gases. In this study, a series of bimetallic M-In/H-SSZ-39 catalysts (where M represents Cr, Co, Ce, and Fe) were prepared via an ion exchange method and subsequently evaluated for their CH₄-SCR activity. The influences of the preparation parameters, including the metal ion concentration and calcination temperature, as well as the operating conditions, such as the CH₄/NO ratio, O₂ concentration, water vapor content, and gas hourly space velocity (GHSV), on the catalytic activity of the optimal Cr-In/H-SSZ-39 catalyst were meticulously examined. The results revealed that the Cr-In/H-SSZ-39 catalyst exhibited peak CH₄-SCR catalytic performance when the Cr(NO₃)₃ concentration was 0.0075 M, the In(NO₃)₃ concentration was 0.066 M, and the calcination temperature was 500 °C. Under optimal operating conditions, namely GHSV of 10,000 h⁻¹, 400 ppm NO, 800 ppm CH₄, 15 vol% O₂, and 6 vol% H₂O, the NO_x conversion rate reached 93.4%. To shed light on the excellent performance of Cr-In/H-SSZ-39 under humid conditions, a comparative analysis of the crystalline phase, chemical composition, pore structure, surface chemical state, surface acidity, and redox properties of Cr-In/H-SSZ-39 and In/H-SSZ-39 was conducted. The characterization results indicated that the incorporation of Cr into In/H-SSZ-39 enhanced its acidity and also facilitated the generation of InO⁺ active species, which promoted the oxidation of NO and the activation of CH₄, respectively. A synergistic effect was observed between Cr and In species, which significantly improved the redox properties of the catalyst. Consequently, the activated CH₄ could further interact with InO⁺ to produce carbon-containing intermediates such as HCOO⁻, which ultimately reacted with nitrate-based intermediates to yield N₂, CO₂, and H₂O. Full article

Platinum was supported on ZSM5 at loadings from 0.1 to 1 wt% and tested for the Selective Catalytic Reduction of NO with H₂ under excess O₂ in a fixed bed reactor to address the issue of NO_x emission abatement from H₂-fueled internal combustion engines avoiding the additional devices for urea storage and injection. To reduce the undesired NO oxidation to NO₂, which is activated by platinum at T > 200 °C, the 0.1%Pt/ZSM5 catalyst was further promoted with sodium. 5 wt% loading of Na strongly inhibited the NO oxidation while giving only a limited impact on the H₂-SCR activity. Unpromoted and Na-promoted catalysts were characterized by XRD, SEM/EDX, N₂ physisorption, and NH₃-TPD to investigate the morphological, structural, and acid properties; H₂ pulse chemisorption and DRIFTS of CO chemisorption were used to investigate the nature of Pt active species. Steady-state and transient operando DRIFTS experiments under NO+H₂+O₂ flow were employed to identify the adsorbed NO_x species interacting with H₂, and reaction intermediates as a function of the reaction conditions. The formation of ammonium intermediates via the reduction of surface nitrate species, playing a key role in H₂-SCR catalyzed by 0.1Pt/ZSM5, was preserved at low Na load whilst NO₂ formation was largely inhibited. Full article

Electrocatalytic nitrate reduction to ammonia (ENRA) presents a promising strategy for simultaneous environmental remediation and sustainable ammonia synthesis. In this work, a Cu–Co bimetallic catalyst supported on functionalized reduced graphene oxide (RGO) was systematically designed to achieve efficient and selective ammonia production. Surface oxygen functional groups on graphene oxide (GO) were optimized through alkaline hydrothermal treatments, enhancing the anchoring capacity for metal active sites. Characterization indicated the successful formation of uniform Cu–Co bimetallic heterointerfaces comprising metallic and oxide phases, which significantly improved catalyst stability and performance. Among the studied compositions, Cu₆Co₄/RGO exhibited superior catalytic activity, achieving a remarkable ammonia selectivity of 99.86% and a Faradaic efficiency of 96.54% at −0.6 V (vs. RHE). Long-term electrocatalysis demonstrated excellent durability, with over 90% Faradaic efficiency maintained for ammonia production after 20 h of operation. In situ FTIR analysis revealed that introducing Co effectively promoted water dissociation, facilitating hydrogen generation (*H) and accelerating the transformation of nitrate intermediates. This work offers valuable mechanistic insights and paves the way for the design of highly efficient bimetallic electrocatalysts for nitrate reduction and ammonia electrosynthesis. Full article

The electrochemical reduction of toxic nitrate wastewater to green fuel ammonia under mild conditions has become a goal that researchers have relentlessly pursued. Existing designed electrocatalysts can effectively promote the nitrate reduction reaction (NO₃RR), but the study of the catalytic mechanism is not extensive enough, resulting in no breakthroughs in performance. In this study, a novel mechanism of hydrogenation-facilitated spontaneous N-O cleavage was explored based on density functional theory calculations. Furthermore, the E_ad−*OH (adsorption energy of the adsorbed *OH) was used as a key descriptor for predicting the occurrence of spontaneous N-O bond cleavage. We found that E_ad−*OH < −0.20 eV results into spontaneous N-O bond cleavage. However, excessively strong adsorption of OH* hinders the formation of water. To address this challenge, we designed the eligible Fe₂B₂ MBene, which shows excellent catalytic activity with an ultra-low limiting potential for NO₃RR of −0.22  V under this novel reaction mechanism. Additionally, electron-deficient Fe active sites could inhibit competing hydrogen evolution reactions (HERs), which provides high selectivity. This work may offer valuable insights for the rational design of advanced electrocatalysts with enhanced performance. Full article