Nitrate Reduction by NiFe-LDH/CeO2: Understanding the Synergistic Effect between Dual-Metal Sites and Dual Adsorption.

Electrocatalytic nitrate reduction reaction (EC-NITRR) shows a significant advantage for green reuse of the nitrate (NO3-) pollutant. However, the slow diffusion reaction limits the reaction rate in practical EC-NITRR, causing an unsatisfactory ammonia (NH3) yield. In this work, a multifunctional NiFe-LDH/CeO2 with the dual adsorption effect (physisorption and chemisorption) and dual-metal sites (Ce3+ and Fe2+) was fabricated by the electrodeposition method. NiFe-LDH/CeO2 performed an expected ability of enrichment for NO3- through the pseudo-first-order and pseudo-second-order kinetic models, and the polymetallic structure provided abundant sites for effective reaction of NO3-. At-0.6 V vs RHE, the ammonia (NH3) yield of NiFe-LDH/CeO2 reached 335.3 µg h-1 cm-2 and the selectivity of NH3 was 24.2 times that of NO2-. The nitrogen source of NH3 was confirmed by 15NO3- isotopic labeling. Therefore, this work achieved the recycling of the NO3- pollutant by synergy of enrichment and catalysis, providing an alternative approach for the recovery of NO3- from wastewater.

Construction of Frustrated Lewis Pair Sites in CeO2-C/BiVO4 for Photoelectrochemical Nitrate Reduction.

Photoelectrochemical nitrate reduction reaction (PEC NIRR) could convert the harmful pollutant nitrate (NO3-) to high-value-added ammonia (NH3) under mild conditions. However, the catalysts are currently hindered by the low catalytic activity and slow kinetics. Here, we reported a heterostructure composed of CeO2 and BiVO4, and the "frustrated Lewis pairs (FLPs)" concept was introduced for understanding the role of Lewis acids and Lewis bases on PEC NIRR. The electron density difference maps indicated that FLPs were significantly active for the adsorption and activation of NO3-. Furthermore, carbon (C) improved the carrier transport ability and kinetics, contributing to the NH3 yield of 21.81 µg h-1 cm-2. The conversion process of NO3- to NH3 was tracked by 15NO3- and 14NO3- isotopic labeling. Therefore, this study demonstrated the potential of CeO2-C/BiVO4 for efficient PEC NIRR and provided a unique mechanism for the adsorption and activation of NO3- over FLPs.

Strengthening the Stability of the Reconstructed NiOOH Phase for 5-Hydroxymethylfurfural Oxidation.

Electrochemical oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) is a promising approach to produce high-value chemicals such as 2,5-furandicarboxylic acid (FDCA). However, the undesirable stability of catalysts commonly limits its potential application value. In this work, NiOOH derived from Ni(OH)2 was determined as the main catalytic site for HMF oxidation, but the collapse of Ni(OH)2 caused severe instability during the electrocatalytic process because of the crystal structure mismatch between NiOOH and Ni(OH)2. The implantation of Ce in Ni(OH)2 (Ce-Ni(OH)2) was successfully realized to address the stability issue of bare Ni(OH)2, since the larger ion radius of Ce could increase the Ni-O bond length and d-spacing. As a result, the activity of 14%Ce-Ni(OH)2 has not obviously decayed after the 50 cyclic voltammetry (CV)-cycle test. HMF conversion is close to 100%, and the Faraday efficiency (FE) reaches 86.6% at the potential of 0.45 V vs Ag/AgCl. This study provides a new strategy to design stable catalysts for the conversion of biomass derivatives.

CeO2/Ni-MOF with Synergistic Function of Enrichment and Activation: Efficient Reduction of 4-Nitrophenol Pollutant to 4-Aminophenol.

The conversion of organic pollutants to value-added chemicals has been considered as a sustainable approach to solve environmental problems. However, it is still a challenge to construct a suitable heterogeneous catalyst that can synchronously achieve the enrichment and activation of organic pollutants (such as 4-nitrophenol, 4-NP). Here, an organic-inorganic hybrid catalyst (CeO2/Ni-MOF) was successfully fabricated for efficiently reducing 4-NP to 4-aminophenol (4-AP) with water as the hydrogen source. Based on the synergistic effect of Ni-MOF (adsorption action) and CeO2 (active sites), CeO2/Ni-MOF could achieve a reaction rate of 1.102 µmol min-1 mg-1 with an ultrahigh Faraday efficiency (FE) (99.9%) and conversion (97.6%). In addition, the catalytic mechanism of 4-NP reduction over CeO2/Ni-MOF was elaborated in depth. This work presents a new avenue for the effective reduction of pollutants and provides a new strategy for designing high-performance catalysts for rare-earth metals.

In Situ Electrochemical Reconstitution of CF-CuO/CeO2 for Efficient Active Species Generation.

Achievement of the intrinsic activity by in situ electrochemical reconstruction has been becoming a great challenge for designing a catalyst. Herein, an effective electrochemical strategy is proposed to reconstruct the surface of the CF-CuO/CeO2 precursor. Under the stimulation of oxidative/reductive potential, abundant active sites were successfully generated on the surface of CF-CuO/CeO2. Remarkably, the implantation of oxygen vacancy-rich CeO2 synergistically optimizes the chemical composition and electronic structure of CF-CuO/CeO2, greatly promoting the generation of active species. Systematic electrochemical experiments indicate that the superior catalytic performance of reconstructed CF-CuO/CeO2 could be attributed to CuOOH/CeO2 and Cu2O/Ce2O3 active species, respectively. The oxidative-/reductive-activated CF-CuO/CeO2 was further employed in a paired cell for the synergistic catalysis of hydroxymethylfurfural oxidation with 4-nitrophenol hydrogenation. As a result, nearly 100% Faraday efficiency for furandicarboxylic acid/4-aminophenol production was achieved in the paired system (-0.9 V vs Ag/AgCl, 1.5 h). Therefore, the electrochemical reconstruction via oxidative/reductive activation has been confirmed as a feasible approach to significantly excite the intrinsic activity of a catalyst.

Stable iridium dinuclear heterogeneous catalysts supported on metal-oxide substrate for solar water oxidation.

Atomically dispersed catalysts refer to substrate-supported heterogeneous catalysts featuring one or a few active metal atoms that are separated from one another. They represent an important class of materials ranging from single-atom catalysts (SACs) and nanoparticles (NPs). While SACs and NPs have been extensively reported, catalysts featuring a few atoms with well-defined structures are poorly studied. The difficulty in synthesizing such structures has been a critical challenge. Here we report a facile photochemical method that produces catalytic centers consisting of two Ir metal cations, bridged by O and stably bound to a support. Direct evidence unambiguously supporting the dinuclear nature of the catalysts anchored on α-Fe2O3 is obtained by aberration-corrected scanning transmission electron microscopy (AC-STEM). Experimental and computational results further reveal that the threefold hollow binding sites on the OH-terminated surface of α-Fe2O3 anchor the catalysts to provide outstanding stability against detachment or aggregation. The resulting catalysts exhibit high activities toward H2O photooxidation.

Boosted Photoelectrochemical N2 Reduction over Mo2C In Situ Coated with Graphitized Carbon.

Photoelectrochemical N2 reduction reaction (PEC NRR) is a promising method to solve the problems of environmental protection and energy sustainability. However, the strong chemical stability of the N≡N bond and competitive hydrogen evolution reaction (HER) cause the nonideal efficiency of N2 → NH3 conversion in actual operation. For the first time, a Mo2C/C heterostructure was fabricated as a PEC cathode for N2 reduction under environmental conditions. The Mo2C/C heterostructure could effectively decrease the coverage of hydrogen spillover and inhibit the competitive HER, resulting in a desirable selectivity for N2 activation. Meanwhile, the decoration of the C shell further promoted the stability and conductivity of Mo2C. Mo sites of Mo2C were considered as activation centers, which played a dominant role in the final PEC performance. An optimal NH3 yield rate of up to 6.6 µg h-1 mg-1 was achieved with the Mo2C/C heterostructure, which was almost 3 times that with pristine C. The faradic efficiency (FE) of the Mo2C/C heterostructure was 37.2% at 0.2 V (vs Ag/AgCl). This work not only provides an insight into the interplay between the Mo2C/C heterostructure and N2 activation, but also reveals its great potential in NH3 synthesis by a green route.

Fabrication of MgFe2O4/MoS2 Heterostructure Nanowires for Photoelectrochemical Catalysis.

A novel one-dimensional MgFe2O4/MoS2 heterostructure has been successfully designed and fabricated. The bare MgFe2O4 was obtained as uniform nanowires through electrospinning, and MoS2 thin film appeared on the surface of MgFe2O4 after further chemical vapor deposition. The structure of the MgFe2O4/MoS2 heterostructure was systematic investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometry (XPS), and Raman spectra. According to electrochemical impedance spectroscopy (EIS) results, the MgFe2O4/MoS2 heterostructure showed a lower charge-transfer resistance compared with bare MgFe2O4, which indicated that the MoS2 played an important role in the enhancement of electron/hole mobility. MgFe2O4/MoS2 heterostructure can efficiently degrade tetracycline (TC), since the superoxide free-radical can be produced by sample under illumination due to the active species trapping and electron spin resonance (ESR) measurement, and the optimal photoelectrochemical degradation rate of TC can be achieved up to 92% (radiation intensity: 47 mW/cm(2), 2 h). Taking account of its unique semiconductor band gap structure, MgFe2O4/MoS2 can also be used as an photoelectrochemical anode for hydrogen production by water splitting, and the hydrogen production rate of MgFe2O4/MoS2 was 5.8 mmol/h·m(2) (radiation intensity: 47 mW/cm(2)), which is about 1.7 times that of MgFe2O4.

Controllable evolution of NiOOH/Au3+ active species for the oxidation of 5-hydroxymethylfurfural.

To induce the generation of active species at the metal-carrier interface, a new synthetic strategy was successfully developed to reconstruct the Ni MOF-Au via electrochemical activation. This unique configuration not only obtained high-valence NiOOH-Au3+ species, but also stably anchored the Au nanoparticles on the surface of the catalyst. As a result, nearly 99.8% FDCA yield and 100% Faraday efficiency of FDCA were achieved at the optimal potential of 1.57 V vs. RHE. Therefore, this electrochemical reconstruction provides new insights for the development of efficient catalysts in other heterogeneous catalytic reactions.

Understanding the cascade heterojunction of CuPc/Bi-MOF for photoelectrochemical nitrate reduction.

Herein, a CuPc/Bi-MOF cascade heterojunction is synthesized exhibiting an excellent NH3 yield (7.13 µg h-1 cm-2) and stability. Characterization studies show that the cascade heterostructure with a unique morphology and oxygen vacancies offers new insights into future photoelectrocatalytic material design.

Electrocatalytic reduction of 4-nitrophenol over Ni-MOF/NF: understanding the self-enrichment effect of H-bonds.

The chemical adsorption and active sites play a key role in electrocatalysis, so Ni-MOF/nickel foam was fabricated for efficiently reducing 4-nitrophenol (4-NP) without any sacrificial agents. The coordinated water molecules induced the formation of hydrogen bonds (H-bonds) with the nitro group, contributing to the self-enrichment of 4-NP. The reaction rate reached 0.351 µmol min-1 mg-1. Therefore, this work provides a new insight into the H-bond effect in the field of electrocatalysis.

Ag/Ni-MOF heterostructure with synergistic enrichment and activation properties for electrocatalytic reduction of 4-nitrophenol.

The synchronous optimization of adsorption and activity dominates the practical performance in electrocatalysis, so Ag/Ni-MOF/Ni foam was synthesized for expediting 4-nitrophenol (4-NP) reduction under mild and green conditions. The synergistic combination of selective adsorption (Ni-MOF) and sites (Ag) contributed to the excellent performance of 4-NP reduction. The 4-NP (25 mM) conversion and Faraday efficiency have been achieved up to 98.4% and 99.8%, respectively. Therefore, this work provides a feasible approach for synergistic enrichment and activation to convert pollutants.

Understanding the Z-scheme heterojunction of BiVO4/PANI for photoelectrochemical nitrogen reduction.

Based on the idea that a heterojunction can significantly promote photoelectrochemical (PEC) efficiency, BiVO4/PANI (polyaniline), as a Z-scheme heterojunction, was designed in this work. BiVO4/PANI achieved a desirable NH3 yield rate (rNH3 = 0.93 µg h-1 cm-2) and faradaic efficiency (FE = 26.43%). This study presents novel insight into PEC NRR research, and it could be extended to the modification of other catalysts for boosting PEC N2 reduction reaction performance.

Biothiol-Functionalized Cuprous Oxide Sensor for Dual-Mode Sensitive Hg2+ Detection.

Hg2+ ions are one of the highly poisonous heavy metal ions in the environment, so it is urgent to develop rapid and sensitive detection platforms for detecting Hg2+ ions. In this work, a novel electrochemical and photoelectrochemical dual-mode sensor (l-Cys-Cu2O) was successfully fabricated, and the sensor exhibits a satisfactory detection limit (0.2 and 0.01 nM) for the detection of Hg2+, which is far below the dangerous limit of the U.S. Environmental Protection Agency. The linear ranges of dual-mode Hg2+ detections were 0.33-3.3 and 0.17-1.33 µM, respectively. Moreover, the sensor shows desirable stability, selectivity, and reproducibility for detecting Hg2+ ions. For river water samples, the recoveries of 96.6-101.4% (electrochemical data) and 93.0-105.6% (photoelectrochemical data) were obtained, indicating that the sensor could be successfully applied in the determination of Hg2+ ions in environmental water. Therefore, the designed sensor has a potential in the trace-level detection of Hg2+ ions.

Charge-transfer dynamics at a Ag/Ni-MOF/Cu2O heterostructure in photoelectrochemical NH3 production.

Ag-decorated ultrathin Ni-MOF on Cu2O was fabricated for the first time. The charge-transfer dynamics at the heterostructure was studied by ultrafast transient absorption spectroscopy in depth. An NH3 yield rate of 4.63 µg h-1 cm-2 with a faradaic efficiency of 24.3% has been achieved. DFT calculations further supported to further comprehend the nitrogen reduction reaction mechanism.

Ag-Pi/BiVO4 heterojunction with efficient interface carrier transport for photoelectrochemical water splitting.

The limitation of pristine BiVO4 photoanode severely causes the high carrier recombination efficiency and low energy conversion efficiency in the photoelectrochemical (PEC) system. In this work, the Ag-Pi/BiVO4n-n heterojunction has been rationally designed and fabricated for efficient PEC water splitting, through successive ionic layer adsorption reaction method. The built-in field of Ag-Pi/BiVO4 significantly promotes the separation efficiency of photogenerated carriers, benefiting for the participation of abundant holes in water oxidation. The photocurrent density of 40-Ag-Pi/BiVO4 has been enhanced to 2.32 mA/cm2, which is 4.5 times than that of the pristine BiVO4. Compared with the pristine BiVO4 (6.5%), the IPCE value of 40-Ag-Pi/BiVO4 achieves 22% (410 nm, 1.23VRHE). In addition, the charge injection efficiency (ηinjection) and charge separation efficiency (ηseparation) of 40-Ag-Pi/BiVO4 have been achieved to 74.36% (1.23 VRHE) and 31.57% (1.23 VRHE), respectively, revealing the excellent carriers' transfer behavior in the both bulk and interface. The desirable stability endows Ag-Pi/BiVO4 system with a great potential in the practical application in PEC water splitting, and the corresponding mechanism for in-depth understanding the process of carriers' transfer in Ag-Pi/BiVO4 structure has been also proposed. Therefore, the construction of Ag-Pi/BiVO4 heterojunction will provide a new insight for the configuration of efficient PEC system.

Amorphous MnCO3/C Double Layers Decorated on BiVO4 Photoelectrodes to Boost Nitrogen Reduction.

NH3 is mainly obtained by the Haber-Bosch method in the process of industrial production, which is not only accompanied by huge energy consumption but also environmental pollution. The reduction of N2 to NH3 under mild conditions is an important breakthrough to solve the current energy and environmental problems, so the preparation of catalysts that can effectively promote the reduction of N2 is a crucial step. In this work, BiVO4 decorated with amorphous MnCO3/C double layers has been successfully synthesized by a one-step method for the first time. The C and MnCO3 have been formed as ultrathin film, which enables the establishment of a uniform and tight interface with BiVO4. The temperature-programmed desorption of N2 (N2-TPD) spectra confirmed that the MnCO3/C could endow BiVO4 with a drastic enhancement of the chemical absorption ability of a N2 molecule compared with the pristine BiVO4. Meanwhile, the method of isotope labeling proved that the catalyst exhibited excellent selectivity for the photocatalytic nitrogen reduction reaction (NRR). The production rate of NH3 up to 2.426 mmol m-2 h-1 has been achieved over the BiVO4/MnCO3/C, which is almost 8 times that of pristine BiVO4. The promoted production rate of NH3 over BiVO4/MnCO3/C could be mainly attributed to the cooperative process between MnCO3 and C amorphous layers. Therefore, this work could provide an alternative insight to understand the NRR process based on the model of a hierarchical amorphous structure.

1,8,16,23-Tetra-kis(2-cyano-benz-yl)bis-p-xylylbis-m-xylyldiamine.

The title compound {systematic name: 2,2',2'',2'''-[3,7,11,15-tetra-aza-1(1,4),5(1,3),9(1,4),13(1,3)-tetra-benzena-cyclo-hexadeca-phane-3,7,11,15-tetra-yltetra-methyl-ene]tetra-benzonitrile}, C(64)H(56)N(8), is a centrosymmetric macrocycle that is consolidated into the crystal structure by C-H⋯π inter-actions.

N,N'-Bis(2-hydroxy-ethyl)-N,N'-[ethyl-ene-dioxy-bis(o-phenyl-enemethyl-ene)]-diammonium fumarate tetra-hydrate.

The reaction of 1,2-bis-{2-[(2-hydroxy-ethyl)amino-methyl]-phen-oxy}ethane and fumaric acid in a mixed solution in ethanol-water (1:1 v/v) yields the title compound, C(20)H(30)N(2)O(4) (2+)·C(4)H(2)O(4) (2-)·4H(2)O. In the crystal structure, the anions, cations and water mol-ecules are connected via O-H⋯O and N-H⋯O hydrogen bonds into a three-dimensional network. The fumarate anion and the N,N'-bis-(2-hydroxy-ethyl)-N,N'-[ethyl-enedioxy-bis(o-phenyl-enemethylene)]diammonium cation are located on centers of inversion, whereas the two crystallographically independent water mol-ecules occupy general positions.

Core-shell structured ZnCo2O4@ZnWO4 nanowire arrays on nickel foam for advanced asymmetric supercapacitors.

One of the most effective tactics to promote the electrochemical performance of supercapacitors is to design and synthesize hybrid binder-free electrodes with core-shell structures. In this work, hierarchical ZnCo2O4@ZnWO4 core-shell nanowire arrays grown on nickel foam are successfully fabricated via a facile two-step hydrothermal route and subsequent thermal treatment. The ZnCo2O4 nanowire arrays supported on nickel foam serve as the backbone for anchoring ZnWO4 nanosheets. When tested as binder-free electrodes for supercapacitors, the as-prepared ZnCo2O4@ZnWO4 hybrid electrode exhibits an ultrahigh specific areal capacitance of 13.4 F cm-2 at a current density of 4 mA cm-2 and superb cycling stability (98.5% retention after 5000 continuous cycles at a current density of 100 mA cm-2). Furthermore, an asymmetric supercapacitor based on ZnCo2O4@ZnWO4//active carbon is successfully designed. The as-designed asymmetric supercapacitor can achieve a maximum energy density of 24 Wh kg-1 at a power density of 400 W kg-1. Moreover, two as-prepared asymmetric supercapacitor devices in a series connection are able to light up a white light-emitting diode over 30 min. The outstanding electrochemical properties of the hybrid electrode demonstrate that it holds great potential for next generation energy storage applications.