One-Step Doping of P and S Elements to Fe-ZIF-8 Derivatives for Enhanced ROS Generation and Antibacterial Application.

Artificial enzymes is an emerging field of research owing to the remarkable advantages of enzyme mimics over their natural counterpart, including tunable catalytic efficiencies, lower cost, ease of preparation, and excellent tolerance to variations of the reaction system. Herein, we report an efficient peroxidase mimic based on a copper-modified covalent triazine framework (CCTF). Owing to its unique specific surface area, atomically dispersed active Cu sites, efficient electron transfer, and enhanced photo-assisted enzyme-like activity, the CCTF showed enhanced peroxidase-like enzyme activity. Therefore, copper modification represents an effective route to tailor the peroxidase-like activity of the covalent triazine frameworks. Furthermore, the mechanism of the enhanced peroxidase-like activity and stability of the CCTF were investigated. As a proof of concept, the CCTF was used for the colorimetric detection of H2 O2 and decomposition of organic pollutants. This work provides a new strategy for the design of enzyme mimics with a broad range of potential applications.

Simple Design of an Enzyme-Inspired Supported Catalyst Based on a Catalytic Triad

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

Oxygen-bridged Schottky junction in ZnO–Ni3ZnC0.7 promotes photocatalytic reduction of CO2 to CO: Steering charge flow and modulating electron density of active sites

We established four kinds of good dispersing systems of graphene and its derivatives with different structural characteristics to estimate their peroxidase-like activity. Besides graphene oxide (GO), it is demonstrated that defect-free graphene, low-oxygen graphene, and iron(III)-doped graphene oxide (GO-Fe) are all capable of H2O2 activation to oxidize peroxidase substrates. As for defect-free graphene, the dispersibility in reaction medium exerts great impact on its catalytic activity and our further judgements concerning the nature of active sites. Improved stability and further exfoliation of defect-free graphene in reaction medium are beneficial to the access of reactants to active sites on the basal planes and enhance its peroxidase-like activity, which is superior to that of low-oxygen graphene and much higher than that of GO. In addition, their peroxidase-like activity can be greatly inhibited by the addition of iron chelators. Interestingly, the introduction of trace ferric ions into GO does not lead to an apparent change except for remarkable increase of its peroxidase-like activity. Therefore, we propose that the observed iron impurities rather than the doped nonmetallic heteroatoms play an important role in the peroxidase-like activity of graphene and its derivatives. In this light, saturated iron(III) was immobilized onto the oxygen-donor coordination of GO to immensely promote its activity. The peroxidase-like activity of the prepared GO-Fe was systematically evaluated by using 3,3',5,5'-tetramethylbenzidine and pyrogallol as peroxidase substrates and was compared to that of horseradish peroxidase and hemin. As a result, GO-Fe shows excellent peroxidase-like catalytic activity, which is comparable to that of hemin. Furthermore, GO-Fe was used for the quantitative detection of H2O2 and glucose.

Ionic current rectification (ICR) is one of interesting characteristics displayed by nanochannels with asymmetric geometry, ionic concentration or charge distribution, which has been utilized for the development of chemical sensors and biosensors. Herein we report the ICR phenomenon observed with ultrathin silica isoporous membrane (SIM), which was prepared by laminating two layers of SIM with opposite charges and different pore diameters, designated as bipolar SIM (bp-SIM). The negatively charged layer, called as n-SIM, was 86 nm-thick and consisted of channels with a diameter of 2-3 nm. The positively charged layer with a thickness of 59 nm, termed as p-SIM, was comprised of channels of 4.5-5.5 nm in diameter. They were primarily grown on the solid surface using the Stöber-solution and biphasic-stratification growth approaches, respectively, and then exfoliated to obtain perforated structures by the polymer-protected chemical etching and transfer method. The negative charges of n-SIM and positive ones of p-SIM were generated by the deprotonation of pristine surface silanol and postmodified ammonium groups, respectively. Neither n-SIM nor p-SIM alone displays the ICR characteristic, because of their symmetric structure and uniform charge distribution. When laminating two of them, an apparent ICR characteristic was observed for the bp-SIM with a typical diode-like current-voltage response. This behavior was rationalized to arise from the asymmetric charge distribution on two layers by finite element simulations. Considering the facile preparation and diverse surface functionalities, as well as its uniform and highly porous structure, the bp-SIM provides an attractive platform for designing ICR-based sensors.

Objective(S): Natural and artificial enzymes have shown important roles in biotechnological processes. Recently, design and synthesis of artificial enzymes especially peroxidase mimics has been interested by many researchers. Due to disadvantages of natural peroxidases, there is a desirable reason of current research interest in artificial peroxidase mimics. Methods: In this study, magnetic multiwall carbon nanotubes with a structure of Fe3O4/MWCNTs as enzyme mimetic were fabricated using in situ co-precipitation method. The structure, composition, and morphology of Fe3O4/MWCNTs nanocomposite were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The magnetic properties were investigated by the vibrating sample magnetometer (VSM). Peroxidase-like catalytic activity of nanocomposite was investigated using colorimetric and electrochemical tests with 3,3ʹ,5,5ʹ-tetramethylbenzidine (TMB) substrate. Results: The obtained data proved the synthesis of Fe3O4/MWCNTs nanocomposite. The average crystallite size of nanostructures was estimated about 12 nm by Debye–Scherer equation. It was found that Fe3O4/MWCNTs nanocomposite exhibit peroxidase-like activity. Colorimetric and electrochemical data demonstrated that prepared nanocomplex has higher catalytic activity toward H2O2 than pure MWCNT nanocatalyst. From electrochemical tests concluded that the Fe3O4/MWCNTs electrode exhibited the better redox response to H2O2, which is ~ 2 times larger than that of the MWCNTs. Conclusions: The synthesis of Fe3O4nanoparticles on MWCNTs was successfully performed by in situ co-precipitation process. Fe3O4/MWCNTs nanocatalyst exhibited a good peroxidase-like activity. These biomimetic catalysts have some advantages such as simplicity, stability and cost effectiveness that can be used in the design of enzyme-based devices for various applied fields.

Nanoarchitectured biomass-waste derived activated charcoal nanozymes and its application in visual analysis of nitrite in pickled food.

Caspase-2, the most evolutionarily conserved member in the human caspase family, may play important roles in stress-induced apoptosis, cell cycle regulation, and tumor suppression. In biochemical assays, caspase-2 uniquely prefers a pentapeptide (such as VDVAD) rather than a tetrapeptide, as required for efficient cleavage by other caspases. We investigated the molecular basis for pentapeptide specificity using peptide analog inhibitors and substrates that vary at the P5 position. We determined the crystal structures of apo caspase-2, caspase-2 in complex with peptide inhibitors VDVAD-CHO, ADVAD-CHO, and DVAD-CHO, and a T380A mutant of caspase-2 in complex with VDVAD-CHO. Two residues, Thr-380 and Tyr-420, are identified to be critical for the P5 residue recognition; mutation of the two residues reduces the catalytic efficiency by about 4- and 40-fold, respectively. The structures also provide a series of snapshots of caspase-2 in different catalytic states, shedding light on the mechanism of capase-2 activation, substrate binding, and catalysis. By comparing the apo and inhibited caspase-2 structures, we propose that the disruption of a non-conserved salt bridge between Glu-217 and the invariant Arg-378 is important for the activation of caspase-2. These findings broaden our understanding of caspase-2 substrate specificity and catalysis.

Coordination Number Regulation of Molybdenum Single-Atom Nanozyme Peroxidase-like Specificity

Oxygen deficiency (O-vacancy) contributes to the photoefficiency of TiO2 semiconductors by generating electron rich active sites. In this paper, the dispersion of O-vacancies in both bulk and surface of anatase and rutile phases was computationally investigated. The results showed that the O-vacancies dispersed in single- and double-cluster forms in the anatase and rutile phases, respectively, in both bulk and surface. The distribution of the O-vacancies was (roughly) homogeneous in anatase, and heterogenous in rutile bulk. The O-vacancy formation energy, width of defect band, and charge distribution indicated the overlap of the defect states in the rutile phase and thus eased the formation of clusters. Removal of the first and the second oxygen atoms from the rutile surface took less energy than the anatase one, which resulted in a higher deficiency concentration on the rutile surface. However, these deficiencies formed one active site per unit cell of rutile. On the other hand, the first O-vacancy formed on the surface and the second one formed in the subsurface of anatase (per unit cell). Supported by previous studies, we argue that this distribution of O-vacancies in anatase (surface and subsurface) could potentially create more active sites on its surface.

Open AccessCCS ChemistryRESEARCH ARTICLE25 May 2022Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne Yuxin Liu, Yang Gao, Feng He, Yurui Xue and Yuliang Li Yuxin Liu Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 University of Chinese Academy of Sciences, Beijing 100049 , Yang Gao Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 University of Chinese Academy of Sciences, Beijing 100049 , Feng He Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 University of Chinese Academy of Sciences, Beijing 100049 , Yurui Xue *Corresponding authors: E-mail Address: [email protected]; E-mail Address: [email protected] Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 Science Center for Material Creation and Energy Conversion, School of Chemistry and Chemical Engineering, Institute of Frontier and Interdisciplinary Science, Shandong University, Jinan 250100 and Yuliang Li *Corresponding authors: E-mail Address: [email protected]; E-mail Address: [email protected] Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 University of Chinese Academy of Sciences, Beijing 100049 https://doi.org/10.31635/ccschem.022.202202005 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Here we report an in situ assembly growth method that controls the growth of NiTCNQ on the surface of graphdiyne (GDY). The catalytic system of donor–acceptor–donor (GDY/TCNQ/Ni) structure with multiple charge transfer (CT) was achieved by controlling the growth of NiTCNQ on the surface of GDY. Significantly, a controlled double layer interface of GDY/TCNQ/Ni was formed. This system implemented simultaneously the two elements we expected (1) an incomplete CT, and (2) the infinite distribution of active sites originating from highly asymmetric surface charge distribution. The high conductivity and typical semiconductor characteristics of the catalyst endows it with high catalytic activity. We found that an electrolytic cell consisting of the CT salt as a catalyst provided a 1.40 V ultra-small cell voltage up to 10 mA cm−2 and the outer GDY film effectively prevented the corrosion of the catalyst. Our study is the first to introduce CT complexes to a novel catalytic material platform for high selectivity of catalysts, and undoubtedly demonstrates the high selectivity, stability, and activity of such catalytic systems, which provides a new space for the development of novel conceptual catalysts. Download figure Download PowerPoint Introduction The sustainable hydrogen (H2) production through electrocatalytic overall water splitting (OWS) provides a promising method to overcome the global energy crisis and environmental problems, which is of great significance for industrial and scientific progress.1,2 In terms of hydrogen conversion, precious metal-based materials (e.g., Ru or Ir-based materials for the oxygen evolution reaction (OER); Pt-based materials for the hydrogen evolution reaction (HER)) remain the benchmark catalysts with high catalytic performances, but they are not suitable for large-scale commercialization due to their high cost, low abundance, and insufficient stability. At present, the high cost of precious metals has seriously restricted the development of this field. Transition metal-based materials, such as metal hydroxides, oxides, nitrides, phosphides, carbides, and sulfides, have been extensively studied for anodic OER and cathodic HER.3–6 However, the low catalytic activity of these systems results in sluggish kinetics of OER and HER. In addition, there is no stability advantage of these catalysts. Furthermore, to meet the requirement of industrial alkaline water splitting for hydrogen production, the catalysts should produce large current densities at low cell voltages (e.g., ∼200–400 mA cm−2 at 1.8–2.4 V) and be synthesized from earth-abundant elements to minimize the H2 production cost.7–10 Therefore, to develop catalysts with excellent comprehensive performance, we need to find a new way to produce electrocatalysts with low cost, high activity, and high stability. The unique and excellent structures and properties of graphdiyne (GDY) has triggered extensive investigations on its fundamental properties and potential applications in various research fields, such as catalysis, energy conversion and storage, optical and electrical devices, and so on.11–26 As a new sp- and sp2-cohybridized two-dimensional carbon material, GDY shows large porous structure, high intrinsic activity, excellent electron transfer ability, high electronic conductivity, and high stability.27–29 GDY is an ideal carbon material for synthesizing high-performance catalysts with determined structures and abundant active sites, and provides the opportunities for clearly understanding the relationship of structure and performance. GDY can be grown on arbitrary substrates at low temperatures and ambient pressures, which protects the parent structure and the active site structure from destruction and generates new active sites. 7,7,8,8-Tetracyanoquinodimethane (TCNQ) is a well-known electron acceptor with high electron affinity, which easily reacts with metal atoms to form charge transfer (CT) complexes with high conductivity, high carrier density, and special electron transport properties.30 Metal-TCNQs show excellent electrical and optical properties, and unique and adjustable electron and high CT ability. CT complexes where the CT amount is not an integer is called incomplete CT; it is different from traditional inorganic complexes with an integer CT. Because of their high conductivity and semiconductor characteristics, they have attracted more and more interest in many research fields.31–34 However, until now, research on CT complexes mainly focused on controlled growth, photoelectric devices. and semiconductor properties, while basic and applied research in the field of catalysis remain silent. Recently, we took NiTCNQ–GDY as an example and explored the basis and application of NiTCNQ–GDY as an emerging catalyst in hydrogen energy conversion. In addition, we deeply understand the GDY plays the key role in the generation of efficient catalysts, and find its introduction overcomes important issues such as solvent corrosion, structural instability caused by light or electricity, and poor conductivity.35,36 In this work, we report the successful synthesis of a donor–acceptor–donor (GDY/TCNQ/–Ni) structure with multiple CT by in situ growing GDY layers on the surface of NiTCNQ nanowires (GDY–NiTCNQ). Experimental results demonstrated the incomplete CT and the infinite distribution of active sites originating from highly asymmetric surface charge distribution endow the catalyst with high conductivity, typical semiconductor characteristics, high catalytic activity, and excellent intrinsic properties. These unique and fascinating properties endow GDY–NiTCNQ with excellent catalytic activities toward OER, HER, and OWS. For instance, GDY–NiTCNQ exhibited small overpotentials of 218 and 61 mV at 10 mA cm−2 for OER and HER in 1.0 M KOH. When used as an electrolytic cell, it can drive 10 mA cm−2 at a low cell voltage of 1.40 V. This work provides a new direction toward the development of cost-effective and high-performance electrocatalysts. Experimental Methods Material TCNQ was purchased from Tokyo Chemical Industry (TCI, Shanghai, China). Acetonitrile and methanol were obtained from Concord Technology (Tianjin) Co., Ltd. Nickel foams (NFs) were treated with dilute hydrochloric acid, rinsed with deionized water, and dried with N2 flow before use. Deionized water was purified with a Millipore system. All chemicals were analytical grade and used without further purification unless otherwise specified. Preparation of NiTCNQ in acetonitrile A piece of freshly pretreated nickel film (3 cm × 1.5 cm) was immersed in 10 mM TCNQ acetonitrile solution for 10 min followed by the addition of 3% deionized water at room temperature. After reaction for 6 h, the material was removed from the solution, washed carefully with acetonitrile and water, and dried under the protection of N2. Preparation of GDY on NiTCNQ (GDY–NiTCNQ) A piece of NiTCNQ was immersed in 50 mL acetone solution of hexaethynylbenzene (HEB) at 50 °C under Ar atmosphere protected from light. After reaction for 12 h, the resulting GDY–NiTCNQ was washed with acetone, deionized water, and acetone, followed by drying at 50 °C in a vacuum oven. Characterization The morphology of the material was characterized by scanning electron microscopy (SEM; Hitachi, S 4800; Institute of Chemistry, Chinese Academy of Sciences), transmission electron microscopy (TEM, a JEOL JEM-2100F field-emission high-resolution transmission electron microscope at an accelerating voltage of 200 kV; Institute of Chemistry, Chinese Academy of Sciences), and high-resolution TEM (HRTEM). The energy-dispersive spectroscopy (EDS) mapping analysis was also obtained to characterize the elemental composition of the samples. X-ray diffraction (XRD) measurements were carried out on a PANalytical high-resolution XRD system (EMPYREAN) using Cu Kα radiation (λ = 1.540598 mm). X-ray photoelectron spectroscopy (XPS) was performed on a Thermo Scientific ECSALab 250Xi instrument with monochromatic Al Kα X-ray radiation (Institute of Chemistry, Chinese Academy of Sciences). Electrochemical measurements All electrochemical tests were carried out using an electrochemical workstation (CHI 760E) through a typical three-electrode system, in which the as-prepared samples, graphite rods, and saturated calomel electrode were used as the working electrode, the counter electrode, and the reference electrode, respectively. All the electrolytes used in the experiments were bubbled with Ar for 2 h before use. Linear sweep voltammetry (LSV) measurements were carried out at a scan rate of 2 mV s−1 in 1.0 M KOH solution. Cyclic voltammetry (CV) measurements were carried out at a scan rate of 100 mV s−1. Electrochemical impedance spectroscopy (EIS) was obtained at the frequency range of 100 KHz to 0.1 Hz with a sampling rate of 12 points per decade, and the data obtained was fitted. All potentials were converted to the reversible hydrogen electrode (RHE) according to ERHE = ESCE + E0SCE + 0.059 × pH. X-ray absorption fine structure measurements The X-ray absorption fine structure (XAFS) spectra (Ni K-edge) were collected at 1W1B station in Beijing Synchrotron Radiation Facility (BSRF). The storage rings of BSRF were operated at 2.5 GeV with an average current of 250 mA. Using a Si(111) double-crystal monochromator, the data collection was carried out in transmission/fluorescence mode using an ionization chamber. All spectra were collected in ambient conditions. XAFS analysis and results The acquired extended XAFS (EXAFS) data were processed according to the standard procedures using the ATHENA module implemented in the IFEFFIT software packages. The k3-weighted EXAFS spectra were obtained by subtracting the post-edge background from the overall absorption and then normalizing with respect to the edge-jump step. Subsequently, k3-weighted χ(k) data of Ni K-edge were Fourier transformed to real (R) space using a Hanning windows (dk = 1.0 Å−1) to separate the EXAFS contributions from different coordination shells. To obtain the quantitative structural parameters around central atoms, least–squares curve parameter fitting was performed using the ARTEMIS module of the IFEFFIT software packages. Results and Discussion As shown in Figures 1a and 1b, a two-step in situ growth strategy was used to selectively synthesize the GDY–NiTCNQ catalysts with D–A–D (GDY/TCNQ/Ni) structure, including the first in situ growth of NiTCNQ nanorods and the subsequent growth of the GDY film on the outer layer of the NiTCNQ nanorods that leads to the formation of GDY–NiTCNQ nanowires. Typically, with the dropwise addition of water into the acetonitrile solution of TCNQ, the Ni ions released from the substrate and then interacted with TCNQ forming the A–D (TCNQ–Ni) structure. The NiTCNQ assembled into highly ordered NiTCNQ-nanorods array on the surface of NF.37 The NiTCNQ was then immersed into the acetone solution, after which the HEB precursor was added to grow GDY films on the NiTCNQ surface with the morphology gradually changing from nanorod to nanowire. During this process, the D–A–D (GDY/TCNQ/Ni) structure was formed. Figure 1 | Schematic representation of the controlled synthesis route to the catalytic system of donor–acceptor–donor (GDY/TCNQ/Ni) structures through in situ growth of (a) NiTCNQ nanorods and (b) GDY–NiTCNQ. Download figure Download PowerPoint Figure 2a shows that the color of the samples changed from gray for NF to dark green for NiTCNQ and black for GDY–NiTCNQ during the synthetic process. SEM images clearly show that the smooth surface of 3D NF (Figures 2b–2d) was covered by a film of NiTCNQ nanorods (average diameter, ∼210 nm; Figures 2e–2h). As shown in Supporting Information Figure S1, the NiTCNQ has a flat surface and a fringe lattice spacing of 0.254 nm. The electrostatic potential (ESP) of NiTCNQ (Figure 2h) confirms the interactions between Ni ions and TCNQ with evident CT from Ni to TCNQ, which also demonstrates the formation of the A–D structure. With the growing of GDY on the NiTCNQ surface, the morphology of the nanorods of NiTCNQ changed to nanowires for GDY–NiTCNQ (Figures 2i–2l). As revealed by HRTEM images (Figures 2l and 2m), an obvious shell layer was observed outside of the NiTCNQ core, confirming the successful growth of GDY on the surface of NiTCNQ (Figure 2m). GDY–NiTCNQ exhibits a rough and porous surface, which is beneficial for enlarging the active surface area and the number of active sites. The lattice spacing of the core structure of GDY–NiTCNQ is 0.254 nm ( Supporting Information Figure S2), in accordance with the NiTCNQ, indicating the structure of NiTCNQ was well maintained during the GDY growth process. Scanning TEM (STEM) and EDS mapping images (Figures 2n–2q and Supporting Information Table S1) confirm the presence of carbon, nitrogen, and nickel elements in the GDY–NiTCNQ sample without any impurities. Ni and N are densely distributed in the inner space and sparsely distributed in the edge, and C is evenly distributed throughout the whole material. These results demonstrated the formation of the double layer interface of GDY/TCNQ/Ni, and the GDY film on the outer layer can effectively prevent the catalyst corrosion, which guarantees the long-term stability of the catalyst. Figure 2 | Morphological characterizations of GDY–NiTCNQ and NiTCNQ. (a) Photographs of (i) NF, (ii) NiTCNQ, and (iii) GDY–NiTCNQ. SEM images of (b–d) NF, (e–g) NiTCNQ, and (i–k) GDY–NiTCNQ samples. (h) Electrostatic potential of NiTCNQ. TEM images of (l and m) GDY–NiTCNQ. Elemental mapping images (n–p) of C, Ni, and N atoms in the GDY–NiTCNQ. Download figure Download PowerPoint XRD and XPS measurements were performed to characterize the compositions and structures of the samples. As shown in Figure 3a, the intensity of the peaks for GDY–NiTCNQ decreased as compared with that of NiTCNQ, which might be due to the growth of GDY on NiTCNQ. The XPS survey spectra confirm the presence of Ni, C, and N elements in accordance with the EDS result ( Supporting Information Figures S3 and S4). Compared with pure NiTCNQ (Figure 3b), the C 1s XPS spectra of GDY–NiTCNQ shifted to higher binding energies (BE) by 0.75 eV, revealing the CT from GDY to NiTCNQ. The appearance of an sp-C peak in the C 1s spectra of GDY–NiTCNQ (Figure 3c) indicates the successful growth of GDY on NiTCNQ. Moreover, an independent new peak at 291.96 eV originating from the π–π* shakeup satellite implies the interactions between NiTCNQ and GDY.7 In the Ni 2p region (Figure 3d), the peaks for GDY–NiTCNQ decreased by 1.23 eV as compared with that of NiTCNQ ( Supporting Information Figure S5), revealing the remarkable CT between NiTCNQ and GDY. For GDY–NiTCNQ, the peaks for Ni2+ 2p3/2 and Ni2+ 2p1/2 appear at 856.39 and 873.72 eV, and Ni3+ 2p3/2 and Ni3+ 2p1/2 appear at 858.30 and 875.58 eV, respectively, indicating the presence of the mixed valence states of nickel species. The N 1s (Figure 3e) and O 1s (Figure 3f) peaks of GDY–NiTCNQ located at higher BE than those of pristine NiTCNQ further reveal the presence of electron-transfer in the GDY–NiTCNQ sample.38,39 The Raman ( Supporting Information Figure S6) and Fourier transform infrared (FTIR) ( Supporting Information Figure S7) measurements of the GDY layer were conducted. As shown in Supporting Information Figure S6, pure NiTCNQ spectra features several sharp characteristic peaks. GDY–NiTCNQ exhibits characteristic peaks corresponding to the D-band, G-band, and the vibration of conjugated diine links (2189.8 and 1926.2 cm−1), while the characteristic peaks of NiTCNQ diminished. Moreover, as shown in Supporting Information Figure S7, the FTIR shows the characteristic peak corresponding to GDY, as compared with that of pure NiTCNQ. These results demonstrated the successful growth of GDY on the surface of NiTCNQ. Figure 3 | Structural characterization of GDY–NiTCNQ. (a) XRD spectra of NiTCNQ and GDY-NiTCNQ. XPS spectra for GDY–NiTCNQ and NiTCNQ of (b and c) C 1s, (d) Ni 2p, (e) N 1s, and (f) O 1s. The inset figure in (b) represents the deformation charge density of NiTCNQ. (g) The normalized Co K-edge XANES spectra and (h) the first derivative XANES of GDY–NiTCNQ along with the references. (i) EXAFS spectra of GDY–NiTCNQ at the Co K-edge. Download figure Download PowerPoint Ni K-edge X-ray absorption near-edge structure (XANES) for the samples was performed. Figure 3g shows that the GDY–NiTCNQ exhibits the higher edge energy position than those of NiCl2 and NiO, suggesting the average valence state of nickel in GDY–NiTCNQ is larger than Ni2+. This also implies the mixed valence state of nickel in GDY–NiTCNQ (Figure 3h). The Fourier transforms of the Ni K-edge EXAFS spectrum of GDY–NiTCNQ exhibited a dominant peak at 1.6 Å, which could be assigned to the nearest shell coordination of the Ni–N bond (Figure 3i). The weak peak at 2.5 Å might be attributed to the aggregation of a small number of nickel atoms. The fitted Ni–N coordination number for GDY–NiTCNQ was 4.9 with an average Ni–N bond distance of 2.05 Å ( Supporting Information Table S2), smaller than that of hexa-coordinated NiTCNQ,40 which might be ascribed to the strong interactions between the GDY and NiTCNQ species. The obviously enhanced CT ability at the double layer interfaces of GDY/TCNQ/Ni was expected to endow the catalyst with incomplete CT and the infinite distribution of active sites originating from highly asymmetric surface charge distribution. The significantly increased number of active sites would further accelerate CT and lower energy barriers of the reaction. These are all beneficial to improve the catalytic activity of the catalysts. The OER catalytic performances of the samples were studied using a three-electrode system by testing LSV in O2-saturated 1.0 M KOH solution at the scan rate of 2 mV s−1. All polarization curves were corrected by the iR-compensation. NiTCNQ, NF, and RuO2 were also tested in the same conditions for reference. As shown in Figure 4a, the anodic peak appearing in the range of 1.3–1.4 V versus RHE referred to the nickel oxidation from Ni(II) to Ni(III), and the following peak represented the OER catalytic activity. GDY–NiTCNQ showed the best OER activity with the smallest overpotential of 218 mV at 10 mA cm−2 compared with pure NiTCNQ (343 mV) and commercial RuO2 (282 mV). Moreover, GDY–NiTCNQ exhibited a lower of mV than NiTCNQ mV NF mV and RuO2 mV indicating it the reaction kinetics for OER evolution (Figure For further of the OER activity, the frequency was At the overpotential of GDY–NiTCNQ a higher of s−1 than NiTCNQ NF and of the electrocatalysts ( Supporting Information Table Figure | OER and HER (a) curves of NiTCNQ, NF and RuO2 for OER at the scan rate of 2 mV s−1. (b) of the samples for curves of GDY–NiTCNQ obtained before and after OER (d) O 1s XPS spectra of GDY–NiTCNQ after OER (e) Ni 2p XPS spectra and (f) the of Ni2+ of GDY–NiTCNQ obtained after OER (g) curves of NiTCNQ, NF, and for HER at the scan rate of 2 mV s−1. (h) of the materials for HER. (i) curves of GDY–NiTCNQ obtained before and after HER O 1s XPS Ni 2p XPS and the of Ni2+ in GDY–NiTCNQ samples. Download figure Download PowerPoint stability of the catalyst is of great significance for As shown in Supporting Information Figure GDY–NiTCNQ maintained its catalytic activity for h under at mA revealing its long-term stability ( Supporting Information Figure GDY–NiTCNQ also a in catalytic activity during the tests for (Figure The of the GDY–NiTCNQ catalysts after the stability characterized by SEM ( Supporting Information Figure and TEM ( Supporting Information Figure showed no and the nanorod morphology was well the high stability of the as-prepared catalysts. situ XPS tests were on GDY–NiTCNQ to the structural evolution during the The O 1s XPS spectra showed two new peaks at and eV lattice oxygen in metal after the tests (Figure was also found that the position of the Ni 2p peak shifted to lower BE and the of the Ni2+ increased gradually during the catalysis (Figures and the of Ni2+ at these results confirm the generation of the was with the of Ni2+ in OER which a key role in the oxygen The HER catalytic activity of GDY–NiTCNQ was further tested in 1.0 M KOH solution. Figure shows the LSV curves of GDY–NiTCNQ exhibited a small overpotential of 61 mV at 10 mA which was smaller than NiTCNQ mV) and NF and to the catalyst mV). The corresponding of GDY–NiTCNQ, NiTCNQ, NF, and were and mV (Figure The for GDY–NiTCNQ, NiTCNQ, and NF were and respectively, at the overpotential of 100 All results the obvious of HER activity. Moreover, there was a in current density after indicating the high stability (Figure The of the GDY–NiTCNQ catalysts after the HER tests ( Supporting Information Figure for Supporting Information Figure for were well the high stability of the as-prepared catalysts. To reveal the of the catalytic activity, the in situ XPS measurements were conducted. As shown in Figure new peaks corresponding to the were observed at eV in the O 1s XPS spectra as compared with the as-prepared catalysts. The of Ni2+ decreased as the HER (Figures and the of state of nickel which might be the of of HER activity. For the further of the activity of GDY–NiTCNQ, were to the CT The parameters obtained were fitted with solution CT and absorption to the (Figure GDY–NiTCNQ exhibited the of and compared with NiTCNQ = = and NF = = which the conductivity and transfer process. The electrochemical active surface area was also through layer under various scan of (Figure and Supporting Information Figure GDY–NiTCNQ showed a larger of cm−2 than NiTCNQ and NF indicating the larger surface area and higher surface assigned to the introduction of GDY. on OER and HER performance, GDY–NiTCNQ was used as and in a for OWS. The catalytic system exhibited high with a low cell voltage of 1.40 V to 10 mA lower compared with those V) (Figure and the catalysts, including [email protected] V at 10 mA [email V at 10 mA V at 10 mA and so on (Figure and Supporting Information Table S4). During the of H2 and were from the and (Figure The catalytic in in basic demonstrates the promising in applications of GDY–NiTCNQ. Figure | Electrochemical properties and performance. (a) of samples in 1.0 M KOH solution. for and the fitting is (b) The at V of scan for samples. of the (d) activities of GDY–NiTCNQ and electrocatalysts. (e) The water in a working Download figure Download PowerPoint We report an in situ assembly growth method that controls the growth of NiTCNQ on the surface of GDY, to the formation of a unique D–A–D (GDY/TCNQ/Ni) structure with multiple CT. In such catalytic systems, the amount of CT between and acceptor is that incomplete CT between and surface charge distribution the number of active sites and intrinsic activity of the catalytic system, a new for the activity of the catalytic system through incomplete CT between the The results show that the by incomplete CT demonstrates excellent electrical conductivity and typical semiconductor characteristics, to the high catalytic activity of such a catalytic system in OER, HER, and OWS. We found that an electrolytic cell consisting of the CT salt as a catalyst provided a 1.40 V ultra-small cell voltage up to 10 mA is that the outer GDY film effectively prevented the corrosion of the which is to its long-term stability. This work provides a new way to selectively novel catalysts with high selectivity, activity, and stability. Supporting Information Supporting Information is the for the of Figure and Table of is no of interest to Information This research was by a from the and of the Science of and and the of the Chinese Academy of

Artificial enzymes based on the modification of a protein structure for the creation of new active catalytic sites have experienced a great boom in recent years. Multidisciplinary strategies of genetic engineering, chemical or chemical biological tools have been successfully described to synthetize them. However, a challenge has been focused on the creating of artificial enzymes with more than one active site. This could represent a new direction in the application of enzymatic tools in sustainable chemistry. Actually, only a few technologies have been described for designing artificial enzymes with two or multiple active sites. This review article underlines these most significant advances.

Artificial enzymes are widely investigated to mimic the active center and the recognition center of natural enzymes. The active center is responsible for the catalytic activity of enzymes, and the recognition center provides enzymes with specificity. Most of the previous studies on artificial enzymes preferred to solve the problem of activity rather than specificity due to the complexity of the enzyme structures related to substrate recognition. Inspired by the multilevel structures of enzymes and the unique net-structures of hydrogels, hemin-micelles immobilized in alginate hydrogels (HM-AH) were constructed by multistep self-assembly. The hemin-micelle was the active center and mimicked the microenvironment of the catalytic site in horseradish peroxidase (HRP). The alginate hydrogel further enhanced the catalytic activity and stability of hemin-micelles and endowed the artificial enzymes with a catalytic capability in harsh water conditions and non-polar organic solvents. The hydrogel also served as the recognition center, which exhibited substrate selectivity owing to the diffusivity differentiations of substrates in hydrogel fibers. It is the first example of constructing a micelle-hydrogel complex system as an artificial enzyme with both catalytic activity and substrate selectivity by the method of multistep self-assembly.

Transition metal-based materials have gained substantial interest for their role in enhancing the oxygen evolution reaction (OER) for green hydrogen production. Nickel boride (NixB) is a promising electrocatalyst owing to its electron-rich active sites and high efficiency in alkaline medium. However its practical application is hindered by particle agglomeration, which reduces site accessibility and can compromise long term stability. To overcome this challenge, we present a novel composite of mixed phase cobalt oxide/hydroxide Co3O4/Co(OH)2 combined in-situ with amorphous nickel boride NixB, with efficient activity toward OER in alkaline medium. The composite is constructed on flexible carbon cloth substrate and integrates a 0D/1D/2D architecture of Co3O4 nanorods, Co(OH)2 sheets and NixB particles. The hybrid structure combines the catalytic activity and stability of the cobalt oxides with the electron transfer efficiency of amorphous NixB.Structural characterisation via SEM, XRD and XPS confirm formation of this mixed phase material and its uniform distribution across the substrate. Electrochemical testing reveals that the composite demonstrates improved OER performance, with an overpotential of 336 mV at 10 mA cm2 and good stability with minimal current loss after chronoamperometry for 18 hours. There is a significant increase in electrochemical active surface area (ECSA) which is validated through EIS and capacitance measurements.The findings suggest that the mixed phase Co3O4/Co(OH)2/NixB composite may offer an efficient alternative to noble-based electrocatalysts and highlights the role of incorporating amorphous NixB with a support to minimize agglomeration, a key limitation of when using NixB. Future research will focus on optimizing the synthesis and exploring applications beyond OER.