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Utilizing renewable energy such as offshore wind power to electrolyze seawater for hydrogen production offers a sustainable development pathway to address energy and climate change issues. In this study, by incorporating nitrogen-doped carbon quantum dots (N-CDs) into precursors, we successfully synthesized a nitrogen-doped carbon (NC)-layer-coated Co(OH)F/CoP2 catalyst NC@Co(OH)F/CoP2/NF loaded on nickel foam (NF). The introduction of N-CDs induced significant morphology change of the catalyst, facilitating the exposure of numerous active sites, ensuring the presence of catalytically active species CoP2 in nanoparticle form and avoiding agglomeration, which was advantageous to enhancing the overall hydrogen evolution reaction (HER) activity of the catalyst. The formation of Co–N bonds accelerated electron transfer, regulated the electronic structure, and optimized the catalyst's adsorption capacity for H* intermediates, which resulted in remarkably improved HER performance. In addition, Co(OH)F can also serve as a structural support, preventing the catalyst from collapsing during the HER catalytic process. NC@Co(OH)F/CoP2/NF exhibited excellent HER activity in alkaline freshwater and alkaline seawater, respectively requiring overpotentials of only 107 and 128 mV to achieve a current density of 100 mA cm−2. More importantly, it also demonstrated excellent HER activity at high current densities, with overpotentials of 189 and 237 mV at a current density of 1000 mA cm−2 in alkaline freshwater and alkaline seawater, respectively. This work provides new insights into the design and construction of highly efficient HER catalysts for applications in alkaline freshwater and seawater. [ABSTRACT FROM AUTHOR]

Electrochemical nitrate reduction to ammonia (ENO3RR) has attracted great attention owing to its characteristics of treating wastewater while producing high value-added ammonia. In this study, we successfully prepared a heterojunction electrocatalyst Fe2O3/ZnO consisting of Fe2O3 nanosheets and ZnO nanoparticles, where the construction of the Fe2O3/ZnO heterojunction not only increased the exposure of the active sites of the catalyst, accelerated the interfacial electron transfer, and improved the conductivity of the catalyst but also optimized its overall electronic structure. Thus, Fe2O3/ZnO demonstrated a high Faraday efficiency of 97.4% and an ammonia yield of 6327.2 μg h−1 cm−2 at −1.0 V (vs. RHE) in 0.1 M KNO3 and 0.1 M PBS. DFT calculations also confirmed that the constructed Fe2O3/ZnO heterojunction effectively decreased the reaction energy barrier of *NO → *NHO and accelerated the reaction kinetics, which is favourable for ENO3RR. This study provides a new and facile design strategy of catalysts for electrochemical nitrate reduction to ammonia. [ABSTRACT FROM AUTHOR]

The electrochemical nitrate reduction reaction (ENO3RR) is a green ammonia synthesis method under ambient conditions relative to the traditional Haber–Bosch technology, which does not require high-temperature or high-pressure conditions and can convert nitrate pollutants in the environment into value-added NH3, thus achieving a dual purpose. However, more electrocatalysts with a remarkable performance towards high-efficiency ENO3RR need to be developed. In this work, a Cu/NiO-NF composite electrocatalyst with a nanorod structure on nickel foam was successfully fabricated, which contains heterogeneous interfaces between Cu and NiO toward selective electrocatalytic nitrate reduction for ammonia synthesis. The steric nanorod morphology of the catalyst can significantly increase the surface area, expose more active sites, and improve the reaction activity. Moreover, the construction of the composite and the interface effectively boosts the synergistic effect of the active species Cu and NiO, which can regulate the electronic structure of the catalyst, expose more active sites, enhance the conductivity of the material, and accelerate the interfacial electron transfer, thereby further promoting the ENO3RR performance. This Cu/NiO-NF composite exhibits a high NH3 yield of 0.6 mmol h−1 cm−2 and up to 97.81% faradaic efficiency at the optimal applied potential of −1.0 V (vs. RHE) in a concentration of 0.1 M NO3−-containing 0.1 M PBS. Furthermore, it demonstrates excellent electrochemical cycle stability. This work provides insights into the rational design and fabrication of ENO3RR electrocatalysts for potential electrocatalytic applications. [ABSTRACT FROM AUTHOR]

A novel 3D Eu(III) metal–organic framework (Eu-MOF-1) formulated as [Eu(L)(H2O)(DMA)] (L = 2-(2-nitro-4-carboxylphenyl)terephthalic acid) has been successfully synthesized under solvothermal conditions and characterized by structural analyses. Eu-MOF-1 displays a new 3D framework containing EuIII ions, ligand L, and coordinated DMA molecules and water molecules. The fluorescence investigations indicate that Eu-MOF-1 emits bright red luminescence, and shows relatively high water stability and outstanding chemical stability under a relatively wide range of pH conditions. It is noteworthy that Eu-MOF-1 can quantitatively detect p-aminophenol (PAP) which is a metabolite of phenylamine in human urine. More significantly, Eu-MOF-1 is the first reported multi-responsive luminescent sensor for detecting the biomarker PAP, and MnVII and CrVI anions with high selectivity, sensitivity, recyclability and relatively low detection limits in aqueous solutions. Furthermore, the possible sensing mechanisms of Eu-MOF-1 for selective sensing have also been explored in detail. Eu-MOF-1 could be an ideal candidate as a multi-responsive luminescent sensor in biological and environmental areas. [ABSTRACT FROM AUTHOR]

Three novel Cd(II)/Zn(II) coordination polymers (CPs), namely [Cd(L)(BPDC)0.5H2O]·0.5H2O (1), [Zn2(L)2(BPDC)]·2H2O (2) and [Cd2(L)(BTC)H2O]·3H2O (3) (L = 4-(tetrazol-5-yl)phenyl-4,2′:6′,4′′-terpyridine, H2BPDC = 4,4′-biphenyldicarboxylic acid, and H3BTC = 1,3,5-benzenetricarboxylic acid), have been successfully synthesized and characterized. CP 1 and CP 2 display new two-dimensional double-layered honeycomb frameworks containing uncoordinated nitrogen atoms from pyridine and tetrazole rings, which can easily form hydrogen bonds with various analytes. CP 3 exhibits a 3D framework also with uncoordinated nitrogen atoms from pyridine and tetrazole rings. The fluorescence explorations indicate that CPs 1–3 exhibit strong blue luminescence and excellent chemical stability under a relatively wide range of pH conditions. It is worth noting that CPs 1–3 can quantitatively detect hippuric acid (HA), which is a metabolite of toluene in human urine, with high selectivity, sensitivity, fast response and relatively low detection limits. Moreover, the sensing mechanism of CPs 1–3 for HA can mainly be ascribed to fluorescence resonance energy transfer (FRET). CPs 1–3 could be ideal candidates as HA sensors in human urine samples for practical applications. Notably, to the best of our knowledge, we report for the first time Cd(II)/Zn(II)-based luminescent sensors for detecting HA in simulated urine. [ABSTRACT FROM AUTHOR]

Five new 3D isostructural lanthanide metal organic frameworks (Ln-MOFs), [Ln(HL)1.5(H2O)(DMF)]·2H2O (Ln = GdIII (1), SmIII (2), DyIII (3), EuIII (4) and TbIII (5), H3L = 5-(3′,5′-dicarboxylphenyl) nicotinic acid) were synthesized by solvothermal methods and studied by structural analyses, magnetic analyses and luminescence sensing. Crystallographic studies revealed that these compounds are 3D frameworks in which the LnIII-COO chains with alternating four and two carboxylate bridges are interlinked by the organic ligands L, and contain microporous channels with accessible Lewis-base sites, coordinated water molecules and uncoordinated carboxyl groups, which are easy to combine and recognise various analytes. Magnetic studies demonstrated that the carboxylate bridges transmit interchain dominant ferromagnetic interactions in Gd-MOF (1) and Dy-MOF (3), while the decrease of the χT value in Sm-MOF (2) is due to the thermal depopulation effect of the excited levels. Furthermore, Dy-MOF (3) also shows slow magnetic relaxation behaviour under a zero dc field. The luminescence selective sensing experiments showed that Eu-MOF (4) and Tb-MOF (5) can act as recyclable sensors towards Fe3+ ions in water and the simulated biological fluids, and towards ketones in a water system with high sensitivity, selectivity and relatively low detection limits. [ABSTRACT FROM AUTHOR]

Five Mn(ii) coordination polymers containing azide and carboxylate as simultaneous bridges have been derived from different imidazolium-carboxylate zwitterionic ligands: 1-methyl-3-(carboxylatomethyl)imidazolium (L1), 1,3-bis(carboxylatomethyl)imidazolium (L2), (S,S)-, (R,R)-, and (R,S)-1,3-bis(1-carboxylatoethyl)imidazolium (S,S-L3, R,R-L3 and R,S-L3). The compounds are formulated as [Mn(L1)(N3)2] (1), [Mn(L2)(N3)] (2), [Mn(R,R-L3)(N3)]·0.5CH3OH (3-R), [Mn(S,S-L3)(N3)]·0.5CH3OH (3-S), [Mn(R,S-L3)(N3)] (4). In compound 1, the neutral monocarboxylate zwitterion ligand (L1) leads to uniform chains with bis(azide)(carboxylate) bridges. For compounds 2–4, the anionic dicarboxylate zwitterions L2 and L3 lead to (azide)bis(carboxylate) bridges, but the overall coordination networks are different. In 2 and 3-S (or 3-R), chains with the (azide)bis(carboxylate) bridges are connected by L2 and S,S-L3 (or R,R-L3), respectively, to give achiral and chiral 2D coordination networks with different connecting topologies. In compounds 4, which is derived from the mesomeric ligand R,S-L3, linear trinuclear units with the (azide)bis(carboxylate) bridges are linked by μ-1,3 azides to give 2D layers, and the layers are pillared into a 3D framework by the 1,3-dimethyleneimidazolium tethers. Magnetic analyses suggested that compounds 1–3 behave as 1D antiferromagnetic systems, while 4 shows canted antiferromagnetism with weak ferromagnetic ordering below TC = 12.4 K. [ABSTRACT FROM AUTHOR]

The reactions of manganese(ii) acetate or perchlorate, sodium azide or sodium cyanate, and the zwitterionic dicarboxylate ligand 1,4-bis(4-carboxylatopyridinium-1-methylene)benzene (L) under different conditions yielded three different Mn(ii) coordination polymers with mixed carboxylate and azide (or cyanate) bridges: {[Mn (L1)0.5(N3)(OAc)]·3H2O}n(1), {[Mn4(L1)(N3)8(H2O)4(CH3OH)2]·[L1]}n(2), and {[Mn3(L1)(NCO)6(H2O)4]·[L1]·[H2O]2}n(3). The compounds exhibit diverse structures and magnetic properties. In 1, the 1D uniform anionic [Mn(N3)(COO)2]nchains with the (μ-EO-N3)(μ-COO)2triple bridges (EO = end-on) are interlinked by the dipyridinium L ligands into highly undulated 2D layers. Magnetic studies on 1reveal that the mixed triple bridges induce antiferromagnetic coupling between Mn(ii) ions. Compounds 2and 3consist of 1D neutral polymeric chains and co-crystallized zwitterions, and the chains are formed by the L ligands interlinking linear polynuclear units. The polynuclear unit in 2is tetranuclear with (μ-EO-N3)2as central bridges and (μ-EO-N3)2(μ-COO) as peripheral bridges, while that in 3is trinuclear with (μ-NCO)2(μ-COO) bridges. Magnetic studies demonstrate that the magnetic coupling through the mixed azide/isocyanate and carboxylate bridges in 2and 3is antiferromagnetic. An expression of magnetic susceptibility based on a 2-Jmodel for linear tetranuclear systems of classical spins has been deduced and applied to 2. [ABSTRACT FROM AUTHOR]

Two isomorphous 3D Mn(II) and Co(II) coordination polymers with a dicarboxylate inner salt and cyanate as coligands were synthesized and structurally characterized, and their magnetic properties have been studied. In the compounds, [M(L)(NCO)]n·nH2O (M = Mn, Co, L = 1-carboxymethylpyridinium-4-carboxylate), neighboring metal ions are linked by the 3-fold bridges of an end-on cyanate and two syn–syncarboxylate bridges to give an anionic chain of [M(µ-NCO)(µ–COO)2]n, and each chain is interlinked to four other chains by the cationic 1-methylpyridinium spacers to generate a 3D structure with the 42· 63· 8 net topology. They are the first compounds with mixed cyanate and carboxylate bridges. Magnetic studies reveal that the 3-fold mixed bridge propagates antiferromagnetic coupling in the Mn(II) compound but ferromagnetic coupling in the Co(II) compound. The rather complex magnetic behaviors of the Co(II) compound are analyzed taking into account the first-order spin-orbital coupling and the intrachain ferromagnetic interactions. [ABSTRACT FROM AUTHOR]