Iron-doped cobalt oxide nanoarray for efficient electrocatalytic nitrate-to-ammonia conversion

Boosting electrocatalytic nitrate-to-ammonia of single Fe active sites via coordination engineering: From theory to experiments

Atomically dispersed iron-nitrogen-carbon (Fe-N4-C) catalysts show great promises for the electrocatalytic nitrate (NO3-) reduction to ammonia (NH3). Nevertheless, the microenvironmental engineering of the single Fe active sites for further optimizing the catalytic performance remains a challenge. Herein, we proposed to regulate the coordination environment of single Fe active sites to boost its intrinsic electrocatalytic activity for NO3- -to-NH3 conversion by the incorporation of new heteroatoms, including B, C, O, Si, P, and S. Our results revealed that most of the candidates possess low formation energies, showing great potential for experimental synthesis. Moreover, incorporating heteroatoms effectively modulates the charge redistribution and the d-band center of single Fe active sites, enabling the regulation of the binding strength of nitrogenous intermediates. As a result, the N and C coordinated Fe active site (Fe-N3C) exhibits superior catalytic performance for NO3- electroreduction with a relatively low limiting potential (-0.13 V) due to its optimal adsorption strength with nitrogenous intermediates induced by its moderate charge and d-band center. Importantly, our experimental measures confirmed such theoretical prediction: a maximum NH3 yield rate of 21.07 mg h-1 mgcat.-1 and 95.74 % Faradaic efficiency were achieved for NO3- electroreduction on Fe-N3C catalyst. These findings not only suggest a highly efficient catalyst for nitrate reduction but also provide insight into how to design and prepare electrocatalysts with enhanced catalytic performance.

Enhancing Efficiency of Nitrate Reduction to Ammonia by Fe and Co Nanoparticle-Based Bimetallic Electrocatalyst

The green and sustainable electrocatalytic conversion of nitrogen-containing compounds to ammonia is currently in high demand in order to replace the eco-unfriendly Haber-Bosch process. Model catalysts for the nitrate reduction reaction were obtained by electrodeposition of metal Co, Fe, and bimetallic Fe/Co nanoparticles from aqueous solutions onto a graphite substrate. The samples were characterized by the following methods: SEM, XRD, XPS, UV-vis spectroscopy, cyclic (and linear) voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. In addition, the determination of the electrochemically active surface was also performed for all electrocatalysts. The best electrocatalyst was a sample containing Fe-nanoparticles on the layer of Co-nanoparticles, which showed a Faradaic efficiency of 58.2% (E = -0.785 V vs. RHE) at an ammonia yield rate of 14.6 μmol h-1 cm-2 (at ambient condition). An opinion was expressed to elucidate the mechanism of coordinated electrocatalytic action of a bimetallic electrocatalyst. This work can serve primarily as a starting point for future investigations on electrocatalytic conversion reactions to ammonia using model catalysts of the proposed type.

Defect engineering on electrocatalysts for sustainable nitrate reduction to ammonia: Fundamentals and regulations

Electrocatalytic nitrate (NO3 -) reduction to ammonia (NH3) is a "two birds-one stone" method that targets remediation of NO3 --containing sewage and production of valuable NH3. The exploitation of advanced catalysts with high activity, selectivity, and durability is a key issue for the efficient catalytic performance. Among various strategies for catalyst design, defect engineering has gained increasing attention due to its ability to modulate the electronic properties of electrocatalysts and optimize the adsorption energy of reactive species, thereby enhancing the catalytic performance. Despite previous progress, there remains a lack of mechanistic insights into the regulation of catalyst defects for NO3 - reduction. Herein, this review presents insightful understanding of defect engineering for NO3 - reduction, covering its background, definition, classification, construction, and underlying mechanisms. Moreover, the relationships between regulation of catalyst defects and their catalytic activities are illustrated by investigating the properties of electrocatalysts through the analysis of electronic band structure, charge density distribution, and controllable adsorption energy. Furthermore, challenges and perspectives for future development of defects in NO3RR are also discussed, which can help researchers to better understand the defect engineering in catalysts, and also inspire scientists entering into this promising field.

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.

Selective Reduction of Aqueous Nitrate to Ammonium with an Electropolymerized Chromium Molecular Catalyst

Nitrate (NO3-) is a common nitrogen-containing contaminant in agricultural, industrial, and low-level nuclear wastewater that causes significant environmental damage. In this work, we report a bioinspired Cr-based molecular catalyst incorporated into a redox polymer that selectively and efficiently reduces aqueous NO3- to ammonium (NH4+), a desirable value-added fertilizer component and industrial precursor, at rates of ∼0.36 mmol NH4+ mgcat-1 h-1 with >90% Faradaic efficiency for NH4+. The NO3- reduction reaction occurs through a cascade catalysis mechanism involving the stepwise reduction of NO3- to NH4+ via observed NO2- and NH2OH intermediates. To our knowledge, this is one of the first examples of a molecular catalyst, homogeneous or heterogenized, that is reported to reduce aqueous NO3- to NH4+ with rates and Faradaic efficiencies comparable to those of state-of-the-art solid-state electrocatalysts. This work highlights a promising and previously unexplored area of electrocatalyst research using polymer-catalyst composites containing complexes with oxophilic transition metal active sites for electrochemical nitrate remediation with nutrient recovery.

Size-induced d band center upshift of copper for efficient nitrate reduction to ammonia

Electrocatalytic nitrate reduction (NO3RR) technique has emerged as a hotspot in NH3 production, for its practicability, and a series of advanced electrocatalysts with high activity and robust stability needed to be constructed in today's era. In this work, size-tunable Cu nanoparticles on porous nitrogen-doped hexagonal carbon nanorods (Cu@NHC) were reasonably designed and served for catalyzing NO3RR in neutral media. Especially, Cu30%@NHC demonstrated a remarkable electroactivity for NH3 production as it showed a suitable grain size with massive catalytic centers and favorable d band structure with faster *NO3--to-*NO2- catalytic dynamics. As expected, Cu30%@NHC (3628.28 µg h-1 mgcat.-1) had a much higher NH3 yield than those for Cu20%@NHC (1268.42 µg h-1 mgcat.-1) and Cu40%@NHC (725.03 µg h-1 mgcat.-1). And those collected NH3 products indeed derived from NO3RR process revealed by 15N isotope-labeling and systemic control tests. Moreover, Cu30%@NHC was also durable for NO3RR bulk electrolysis with minor loss in activity. This work offered an effective modifying tactics to boost NO3RR catalysis and could guide the design of other advanced electrocatalysts via size-induced surface engineering.

Ammonia Synthesis via Electrocatalytic Nitrate Reduction Using NiCoO2 Nanoarrays on a Copper Foam

Ammonia (NH3) plays a vital role in industrial and agricultural development. The electrocatalytic nitrate reduction reaction (eNO3RR) is an effective method to produce NH3 under environmental conditions but also requires considerably active and selective electrocatalysts. Herein, a copper foam was used as a conductive substrate for the electrode materials. Specifically, a Co metal-organic framework (Co-MOF) was in situ grown on the copper foam, etched, and calcined to form NiCoO2@Cu nanosheets, which were used as cathode electrodes for the eNO3RR. In 0.1 M Na2SO4 with 0.1 M NaNO3 electrolyte, NiCoO2@Cu nanosheets realized an NH3 yield of 5940.73 μg h-1 cm-2 at -0.9 V vs reversible hydrogen electrode (RHE), with a Faradaic efficiency of 94.2% at -0.7 V vs RHE. After 33 h of the catalytic reaction, the selectivity of NH3-N increased to 99.7%. The excellent electrocatalytic performance of NiCoO2@Cu nanosheets was attributed to the apparent synergistic effect between the Ni atoms and the Co atoms of bimetallic materials. This study shows that the Ni doping of NiCoO2@Cu nanosheets effectively facilitated the adsorption of NO3- on NiCoO2@Cu, and it promoted the eNO3RR.

A facile and efficient method for preparing La-doped Co3O4 by electrodeposition as an efficient air cathode in rechargeable zinc-air batteries: Role of oxygen vacancies

A rechargeable zinc-air battery (ZAB) is a promising candidate for simple and low-cost energy storage systems. However, preparing the air cathode material using a binder-free method and a bifunctional catalyst is still the major challenge in the field. Herein, we demonstrate the effect of different La contents doped into the Co3O4 spinel structure in the presence of oxygen vacancies prepared by a facile and efficient electrodeposition technique on the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and ZAB performance. Incorporating the La dopant into the Co3O4 improves the OER and ORR performances and thus enhances the specific capacity and energy density of ZAB. The optimal La-doping amount in the CoLa-1 catalyst demonstrates high feasibility for practical application with a capacity of 780 ± 24 mAh/g and an energy density of 901 ± 39 mW g-1, significantly outperforming the pristine Co3O4. The stability and cycling tests reveal good durability performance after 300 cycles and 100 h of testing without degradation, which is much more stable than the benchmark Pt/C + RuO2 electrode. The performance enhancement is attributed to the synergetic effect of high active surface area, low charge transfer resistance, and optimal oxygen vacancies. A kinetic micromechanism is proposed to illustrate the importance of the oxygen vacancy amount in trapping oxygen gas and maximizing the number of ORR and OER reactions.

Bifunctional bimetallic oxide nanowires for high-efficiency electrosynthesis of 2,5-furandicarboxylic acid and ammonia

It is an appealing avenue for electrosyntheis of high-valued chemicals at both anode and cathode by coupling 5-hydroxymethylfurfural (HMF) oxidation and nitrate reduction reactions simultaneously, while the development such bifunctional electrocatalysts is still in its infancy with dissatisfied selectivity and low yield rate. Here, we first report that Zn-doped Co3O4 nanowires array can be served as an efficient and robust dual-functional catalyst for HMF oxidation and nitrate reduction at ambient conditions. Specifically, the catalyst shows a faradaic efficiency of 91 % and a yield rate of 241.2 μmol h-1 cm-2 for 2,5-furandicarboxylic acid formation together with a high conversion of nearly 100 % at a potential of 1.40 V. It also displays good cycling stability. Besides, the catalyst is capable of catalyzing the reduction of nitrate to NH3, giving a maximal faradaic efficiency of 92 % and a peak NH3 yield rate of 4.65 mg h-1 cm-2 at a potential of -0.70 V. These results surpass those obtained using pristine Co3O4 and are comparable to those of state-of-the-art electrocatalysts. Moreover, the catalyst is further employed as the cathode catalyst to assemble a Zn-nitrate battery, giving a peak power density of 5.24 mW cm-2 and a high yield rate of 0.72 mg h-1 cm-2. Theoretical simulations further reveal that Zn-doping favors the adsorption and dissociation of nitrate and HMF species and reduces the energy barrier as well. Our work demonstrates the potential interest of Co3O4-based materials for the highly selective production of valuable feedstocks via ambient electrolysis.

Rod-Shaped Spinel Co3O4 and Carbon Nitride Heterostructure-Modified Fluorine-Doped Tin Oxide Electrode as an Electrochemical Transducer for Efficient Sensing of Hydrazine

Engineering low-cost and efficient materials for sensing hydrazine (HA) is critical given the adverse effects of high concentrations on humans. We report an efficient electrode made up of rod-shaped Co3O4/g-C3N4 (Co3O4/graphitic carbon nitride (GCN))-coated fluorine-doped tin oxide as a desirable electrode for the detection of HA. GCN is synthesized by the thermal decomposition of melamine, Co3O4, and the heterostructure is grown by a hydrothermal process. The as-prepared materials were characterized by using spectroscopic and microscopic techniques. The voltammetric studies showed that HA can be oxidized at a lower onset potential of 0.24 V vs reference Ag/AgCl, and the composite yielded a significantly enhanced oxidation peak current than the pure components because of the high electrocatalytic activity and the synergy between Co3O4 and GCN. By employing chronoamperometry, the proposed sensor can detect HA in a wide range with a high sensitivity of 819.52 μA mM-1 cm-2 and a detection limit of 3.14 μM. The high conductivity of Co3O4, enhanced electroactive surface area, the rich redox couples of Co2+/Co3+, and the additional catalytic sites from GCN are responsible for the high performance of the heterostructure.

Self-supported P-doped NiFe2O4 micro-sheet arrays for the efficient conversion of nitrite to ammonia

The nitrite reduction reaction (NO2-RR) is an important process for eliminating toxic nitrites from water while simultaneously producing high-value ammonia under ambient conditions. For the aim to improve the NO2-RR efficiency, we designed a new synthetic strategy to prepare a phosphorus-doped three-dimensional NiFe2O4 catalyst loaded onto a nickel foam in-situ and evaluated its performance for the reduction of NO2- to NH3. The catalyst achieved a high Faradaic efficiency (FE) of 95.39%, and an ammonia (NH3) yield rate of 34788.51 µg h-1 cm-2 at - 0.45 V vs. RHE. A high NH3 yield rate and FE were maintained after 16 cycles at - 0.35 V vs. RHE in an alkaline electrolyte. This study provides a new direction for the rational design of highly stable electrocatalysts for the conversion of NO2- to NH3.

Multi-metal electrocatalyst with crystalline/amorphous structure for enhanced alkaline water/seawater hydrogen evolution

The development of well-defined nanomaterials as non-noble metal electrocatalysts has broad application prospect for hydrogen generation technology. Recently, multi-metal electrocatalysts for hydrogen evolution reaction (HER) have attracted extensive attention due to their high catalytic performance arising from the synergistic effect of multi-metal interaction. However, most multi-metal catalysts suffer from the limited synergistic effect because of poor interfacial compatibility between different components. Here, a novel multi-metal catalyst (Ni/MoO2@CoFeOx) nanosheet with a crystalline/amorphous structure is demonstrated, which shows high HER activity. Ni/MoO2@CoFeOx exhibits an ultra-low overpotential of 18, 39, and 93 mV at 10 mA cm-2 in alkaline water, alkaline seawater and natural seawater, respectively, which outperformances most of the state-of-the-art non-noble metal compounds. In addition, the catalyst shows exceptional stability under 500 mA cm-2 in alkaline solution. In-situ Raman and other advanced structural characterization confirms the excellent catalytic activity is mainly contributed by: (1) the strong synergistic effect of multi-metal components provides multiple active sites in the catalytic process; (2) the crystalline/amorphous interface in Ni/MoO2@CoFeOx boosts the catalytically active sites and structure stability; (3) the crystalline phase enhances the intrinsic conductivity greatly; and (4) the amorphous phase provides abundant unsaturated sites for improved intrinsic catalytic activity. This work provides a feasible way to design electrocatalyst with high activity and stability for practical applications.

Cu doping in FeP enabling efficient electrochemical nitrate reduction to ammonia in neutral media

Electrochemical nitrate reduction to ammonia (NH3) not only provides a promising strategy for green NH3 synthesis, but also removes harmful nitrates from water. Herein, a Cu-doped FeP electrocatalyst was prepared for nitrate reduction, which achieved a high NH3 faradaic efficiency of 92.5% and a high NH3 yield of 0.787 mmol h-1 cm-2 in a neutral electrolyte, greatly surpassing its FeP counterpart.

Pd-Doped Co3 O4 Nanoarray for Efficient Eight-Electron Nitrate Electrocatalytic Reduction to Ammonia Synthesis

Ammonia (NH3 ) is an indispensable feedstock for fertilizer production and one of the most ideal green hydrogen rich fuel. Electrochemical nitrate (NO3 - ) reduction reaction (NO3 - RR) is being explored as a promising strategy for green to synthesize industrial-scale NH3 , which has nonetheless involved complex multi-reaction process. This work presents a Pd-doped Co3 O4 nanoarray on titanium mesh (Pd-Co3 O4 /TM) electrode for highly efficient and selective electrocatalytic NO3 - RR to NH3 at low onset potential. The well-designed Pd-Co3 O4 /TM delivers a large NH3 yield of 745.6 µmol h-1 cm-2 and an extremely high Faradaic efficiency (FE) of 98.7% at -0.3 V with strong stability. These calculations further indicate that the doping Co3 O4 with Pd improves the adsorption characteristic of Pd-Co3 O4 and optimizes the free energies for intermediates, thereby facilitating the kinetics of the reaction. Furthermore, assembling this catalyst in a Zn-NO3 - battery realizes a power density of 3.9 mW cm-2 and an excellent FE of 98.8% for NH3 .

Heterostructured Co/Co3O4 anchored on N-doped carbon nanotubes as a highly efficient electrocatalyst for nitrate reduction to ammonia

The electrochemical reduction of nitrate (NO₃^-) to ammonia (NH₃) has emerged as an attractive approach for selectively reducing NO₃^- to highly value-added NH₃ and removing NO₃^- pollutants simultaneously. In this work, a heterostructured Co/Co₃O₄ electrocatalyst anchored on N-doped carbon nanotubes was prepared and applied for the NO₃^- reduction towards NH₃ under alkaline conditions. The catalyst achieves outstanding performance with up to 67% NH₃ faradaic efficiency at -1.2 V vs. Hg/HgO and 8.319 mg h^-1 mg_cat^-1 yield at -1.7 V vs. Hg/HgO. In addition, it also exhibits good long-term stability. ¹⁵N isotopic labelling experiments prove that the yielded NH₃ is derived from NO₃^- species. In situ electrochemical Raman spectra revealed that the structure of the as-prepared catalyst showed outstanding stability and identified possible intermediates during the electrocatalytic NO₃^- reduction reaction (NO₃RR).

Improved Electrochemical Alkaline Seawater Oxidation over Cobalt Carbonate Hydroxide Nanowire Array by Iron Doping

Constructing efficient and low-cost oxygen evolution reaction (OER) catalysts operating in seawater is essential for green hydrogen production but remains a great challenge. In this study, we report an iron doped cobalt carbonate hydroxide nanowire array on nickel foam (Fe-CoCH/NF) as a high-efficiency OER electrocatalyst. In alkaline seawater, such Fe-CoCH/NF demands an overpotential of 387 mV to drive 500 mA cm^-2, superior to that of CoCH/NF (597 mV). Moreover, it achieves excellent electrochemical and structural stability in alkaline seawater.

Cr3C2 nanoparticles decorated carbon nanofibers for efficient nitrate reduction to ammonia at ambient conditions

Electrochemical nitrate (NO₃^-) reduction is a promising approach to relieve nitrate pollution and produce value-added ammonia (NH₃), but efficient and durable catalysts are required due to the large bond dissociation energy of nitrate and low selectivity. Herein, we propose chromium carbide (Cr₃C₂) nanoparticles loaded carbon nanofibers (Cr₃C₂@CNFs) as electrocatalysts to convert nitrate to ammonia. In phosphate buffer saline containing 0.1 mol L^-1 NaNO₃, such catalyst achieves a large NH₃ yield of 25.64 mg h^-1 mg^-1_cat. and a high faradaic efficiency of 90.08% at -1.1 V vs the reversible hydrogen electrode, which also shows excellent electrochemical durability and structural stability. Theoretical calculations reveal the adsorption energy for nitrate at Cr₃C₂ surfaces reaches -1.92 eV and the potential determining step (*NO→*N) for Cr₃C₂ hits a low energy increase of 0.38 eV.

Au Nanowires Decorated Ultrathin Co3 O4 Nanosheets toward Light-Enhanced Nitrate Electroreduction

Nitrate is a reasonable alternative instead of nitrogen for ammonia production due to the low bond energy, large water-solubility, and high chemical polarity for good absorption. Nitrate electroreduction reaction (NO₃ RR) is an effective and green strategy for both nitrate treatment and ammonia production. As an electrochemical reaction, the NO₃ RR requires an efficient electrocatalyst for achieving high activity and selectivity. Inspired by the enhancement effect of heterostructure on electrocatalysis, Au nanowires decorated ultrathin Co₃ O₄ nanosheets (Co₃ O₄ -NS/Au-NWs) nanohybrids are proposed for improving the efficiency of nitrate-to-ammonia electroreduction. Theoretical calculation reveals that Au heteroatoms can effectively adjust the electron structure of Co active centers and reduce the energy barrier of the determining step (*NO → *NOH) during NO₃ RR. As the result, the Co₃ O₄ -NS/Au-NWs nanohybrids achieve an outstanding catalytic performance with high yield rate (2.661 mg h^-1 mg_cat ^-1 ) toward nitrate-to-ammonia. Importantly, the Co₃ O₄ -NS/Au-NWs nanohybrids show an obviously plasmon-promoted activity for NO₃ RR due to the localized surface plasmon resonance (LSPR) property of Au-NWs, which can achieve an enhanced NH₃ yield rate of 4.045 mg h^-1 mg_cat ^-1 . This study reveals the structure-activity relationship of heterostructure and LSPR-promotion effect toward NO₃ RR, which provide an efficient nitrate-to-ammonia reduction with high efficiency.

Advances in iron-based electrocatalysts for nitrate reduction

Excessive nitrate has been a critical issue in the water environment, originating from the burning of fossil fuels, inefficient use of nitrogen fertilizers, and discharge of domestic and industrial wastewater. Among the effective treatments for nitrate reduction, electrocatalysis has become an advanced technique because it uses electrons as green reducing agents and can achieve high selectivity through cathode potential control. The effectiveness of electrocatalytic nitrate reduction (NO₃RR) mainly lies in the electrocatalyst. Iron-based catalysts have the advantages of high activity and low cost, which are well-used in the field of electrocatalytic nitrates. A comprehensive overview of the electrocatalytic mechanism and the iron-based materials for NO₃RR are given in terms of monometallic iron-based materials as well as bimetallic and oxide iron-based materials. A detailed introduction to NO₃RR on zero valent iron, single-atom iron catalysts, and Cu/Fe-based bimetallic electrocatalysts are provided, as they are essential for the improvement of NO₃RR performance. Finally, the advantages of iron-based materials for NO₃RR and the problems in current applications are summarized, and the development prospects of efficient iron-based catalysts are proposed.

Cu-Doped Iron Oxide for the Efficient Electrocatalytic Nitrate Reduction Reaction

The electrochemical nitrate reduction reaction (NO₃RR) is a promising alternative synthetic route for sustainable ammonia (NH₃) production, because it not only eliminates nitrate (NO₃^-) from water but also produces NH₃ under mild operating conditions. However, owing to the complicated eight-electron reaction and the competition from the hydrogen evolution reaction, developing catalysts with high activities and Faradaic efficiencies (FEs) is highly imperative to improve the reaction performance. In this study, Cu-doped Fe₃O₄ flakes are fabricated and demonstrated to be excellent catalysts for electrochemical conversion of NO₃^- to NH₃, with a maximum FE of ∼100% and an NH₃ yield of 179.55 ± 16.37 mg h^-1 mg_cat^-1 at -0.6 V vs RHE. Theoretical calculations reveal that doping the catalyst surface with Cu results in a more thermodynamically facile reaction. These results highlight the feasibility of promoting the NO₃RR activity using heteroatom doping strategies.

Bioinspired Cobalt Oxide Nanoball Synthesis, Characterization, and Their Potential as Metal Stress Absorbants

Massive accumulation of heavy metals in agricultural land as a result of enhanced levels of toxicity in the soil is an emerging global concern. Among various metals, zinc contamination has severe effects on plant and human health through the food chain. To remove such toxicity, a nanotechnological neutralizer, cobalt oxide nanoballs (Co₃O₄ Nbs) were synthesized by using the extract of Cordia myxa. The Co₃O₄ Nbs were well characterized via UV-vis spectrophotometry, scanning electron microscopy, and X-ray diffraction techniques. Green-synthesized Co₃O₄ Nbs were exposed over Acacia jacquemontii and Acacia nilotica at different concentrations (25, 50, 75, and 100 ppm). Highly significant results were observed for plant growth by the application of Co₃O₄ Nbs at 100 ppm, thereby increasing the root length (35%), shoot length (48%), fresh weight (44%), and dry weight (40%) of the Acacia species with respect to the control. Furthermore, physiological parameters including chlorophyll contents, relative water contents, and osmolyte contents like proline and sugar showed a prominent increase. The antioxidant activity and atomic absorption supported and justified the positive response to using Co₃O₄ Nbs that mitigated the heavy-metal zinc stress by improving the plant growth. Hence, the biocompatible Co₃O₄ Nbs counteract the zinc toxicity for governing and maintaining plant growth. Such nanotechnological tools can therefore step up the cropping system and overcome toxicity to meet the productivity demand along with the development of agricultural management strategies.

Cu nanoparticles decorated juncus-derived carbon for efficient electrocatalytic nitrite-to-ammonia conversion

Electrocatalytic nitrite reduction to value-added NH₃ can simultaneously achieve sustainable ammonia production and N-contaminant removal in natural environments, which has attracted widespread attention but still lacks efficient catalysts. In this work, Cu nanoparticles decorated juncus-derived carbon can be proposed as a high-active electrocatalyst for NO₂^--to-NH₃ conversion, obtaining a high Faradaic efficiency of 93.2% and a satisfactory NH₃ yield of 523.5 μmol h^-1 mg_cat.^-1. Density functional theory calculations were applied to uncover insightful understanding of internal catalytic mechanism.

Magnetic nanocomposites for biomedical applications

Tissue engineering and regenerative medicine have solved numerous problems related to the repair and regeneration of damaged organs and tissues arising from aging, illnesses, and injuries. Nanotechnology has further aided tissue regeneration science and has provided outstanding opportunities to help disease diagnosis as well as treat damaged tissues. Based on the most recent findings, magnetic nanostructures (MNSs), in particular, have emerged as promising materials for detecting, directing, and supporting tissue regeneration. There have been many reports concerning the role of these nano-building blocks in the regeneration of both soft and hard tissues, but the subject has not been extensively reviewed. Here, we review, classify, and discuss various synthesis strategies for novel MNSs used in medicine. Advanced applications of magnetic nanocomposites (MG-NCs), specifically magnetic nanostructures, are further systematically reviewed. In addition, the scientific and technical aspects of MG-NC used in medicine are discussed considering the requirements for the field. In summary, this review highlights the numerous opportunities and challenges associated with the use of MG-NCs as smart nanocomposites (NCs) in tissue engineering and regenerative medicine.

Heterogeneous Activation of Peroxymonosulfate by a Spinel CoAl2O4 Catalyst for the Degradation of Organic Pollutants

Bimetallic catalysts have significantly contributed to the chemical community, especially in environmental science. In this work, a CoAl2O4 spinel bimetal oxide was synthesized by a facile co-precipitation method and used for the degradation of organic pollutants through peroxymonosulfate (PMS) activation. Compared with Co3O4, the as-prepared CoAl2O4 possesses a higher specific surface area and a larger pore volume, which contributes to its becoming increasingly conducive to the degradation of organic pollutants. Under optimal conditions (calcination temperature: 500 °C, catalyst: 0.1 g/L, and PMS: 0.1 g/L), the as-prepared CoAl2O4 catalyst could degrade over 99% of rhodamine B (RhB) at a degradation rate of 0.048 min−1, which is 2.18 times faster than Co3O4 (0.022 min−1). The presence of Cl− could enhance RhB degradation in the CoAl2O4/PMS system, while HCO3− and CO32− inhibit RhB degradation. Furthermore, the considerable reusability and universality of CoAl2O4 were testified. Through quenching tests, 1O2 and SO4•− were identified as the primary reactive species in RhB degradation. The toxicity evaluation verified that the degraded solution exhibited lower biological toxicity than the initial RhB solution. This study provides new prospects in the design of cost-effective and stable cobalt-based catalysts and promotes the application of PMS-based advanced oxidation processes for refractory wastewater treatment.

Atom-dispersed copper and nano-palladium in the boron-carbon-nitrogen matric cooperate to realize the efficient purification of nitrate wastewater and the electrochemical synthesis of ammonia

Electrochemical nitrate reduction reaction (NIRR) driven by sustainable energy is not only expected to realize the green production of ammonia under ambient conditions, but also a promising way to purify nitrate wastewater. The ammonia yield rate and Faradaic efficiency of NIRR catalyzed by Pd10Cu/BCN constructed with structural constraints and pre-embedded reducing agent strategies were as high as 102,153 μg h^-1 mg_cat.^-1 and 91.47%, respectively. Pd10Cu/BCN can remove nearly 100% of 50 mg L^-1 NO₃^- without NO₂^- residue within 10 h, and the realization of this effect does not require the participation of any chloride. Control experiments and DFT calculations explain the efficient operation mechanism of NIRR on Pd10Cu/BCN, where the Pd and CuN4 sites play the role of synergistic catalysis. Compared with the reported literature, Pd10Cu/BCN with good biocompatibility has become an outstanding representative of NIRR catalyst, which provides an alternative way for the green production of ammonia and the purification of nitrate wastewater.

Boosted nitrate electroreduction to ammonia on Fe-doped SnS2 nanosheet arrays rich in S-vacancies

The electrochemical nitrate reduction reaction (NO₃RR) not only holds great potential for the removal of NO₃^- contaminants from the environment, but also potentially provides a renewable-energy-driven NH₃ synthesis method to replace the Haber-Bosch process. Herein, we report that Fe-doped SnS₂ nanosheets enriched with S-vacancies can be used as an efficient NO₃RR catalyst, showing a high NH₃ yield of 7.2 mg h^-1 cm^-2 (at -0.8 V) and a faradaic efficiency of 85.6% (at -0.7 V). Density functional theory (DFT) calculations revealed that S-vacancies on Fe-SnS₂ serve as the main active sites for the NO₃RR and the Fe-doping can further regulate the electronic structure of S-vacancies to optimize the binding energies of NO₃RR intermediates, resulting in reduced energy barriers and enhanced NO₃RR activity.

Nitrite reduction over Ag nanoarray electrocatalyst for ammonia synthesis

Electrochemical reduction of nitrite to ammonia can simultaneously achieve ammonia synthesis and N-contaminant removal under mild conditions, which has attracted widespread attention but still lacks efficient catalysts. In this work, Ag nanoarray using NiO nanosheets array on carbon cloth as support is reported as an efficient electrocatalyst to selectively reduce nitrite to ammonia. In 0.1 M NaOH with 0.1 M NO₂^-, such catalyst exhibits a maximum ammonia yield of 5,751 μg h^-1 cm^-2 (57,510 μg h^-1 mg_Ag^-1) and high Faradaic efficiency up to 97.7 %. Density functional theory calculations applied to uncover the catalytic mechanism of NO₂^- reduction reaction on Ag.

Direct eight-electron NO3−-to-NH3 conversion: using a Co-doped TiO2 nanoribbon array as a high-efficiency electrocatalyst

A Co-TiO2 nanoribbon array supported on a Ti plate is a high-efficiency catalyst for electrochemical NO3–-to-NH3 conversion, capable of attaining a large NH3 yield of 1127 μmol h−1 cm−2 and high Faradaic efficiency of 98.2%.

A colorimetric detection strategy and micromotor-assisted photo-Fenton like degradation for hydroquinone based on the peroxidase-like activity of Co3O4–CeO2 nanocages

Co3O4–CeO2 micromotors were fabricated and the colorimetric detection and micromotor-assisted photodegradation capability were studied.