Formation Of Active Sites Research Articles

Mathematical Modeling of Alkaline Direct Glycerol Fuel Cells

Mathematical modeling and computer simulation are tools of great importance for the development of fuel cells. Thus, the objective of this work is to carry out the kinetic modeling of glycerol oxidation in a DGFC (direct glycerol fuel cell), considering two different approaches: (1) realistic phenomenological models for the partial oxidation of glycerol in Pt/C, considering its adsorbed intermediates; (2) models of artificial neural networks (ANN—artificial neural networks) for oxidation mainly of PtAg/C and PtAg/MnOx/C. The models were fitted to experimental data already available for validation and determination of their parameters, both using Matlab software, v. R2018a (MathWorks, Natick, MA, USA). Results for the phenomenological models developed showed excellent fits for the polarization curve, with an RMSE (root mean squared error) value on the order of 0.352 to 0.404 mA/cm2, in addition to coverage fractions consistent with the literature for the adsorbed species. The kinetic parameters with the greatest influence on the response of the models were those associated with the consumption of glyceric acid and the formation of tartronic acid and with the dissociative adsorption of water and the formation of Pt-Oads active sites. Regarding the neural models, excellent prediction fits were obtained for all of them, with RMSE values on the order of 0.008 to 0.014 mA/cm2, indicating the possibility of representing the functional interdependence between input variables and the density cell current for cases where it would be too complex to do so via mechanistic modeling (i.e., for PtAg/C and PtAg/MnOx/C oxidation).

Bromine Ion-Intercalated Layered Bi2WO6 as an Efficient Catalyst for Advanced Oxidation Processes in Tetracycline Pollutant Degradation Reaction.

The visible-light-driven photocatalytic degradation of pharmaceutical pollutants in aquatic environments is a promising strategy for addressing water pollution problems. This work highlights the use of bromine-ion-doped layered Aurivillius oxide, Bi2WO6, to synergistically optimize the morphology and increase the formation of active sites on the photocatalyst's surface. The layered Bi2WO6 nanoplates were synthesized by a facile hydrothermal reaction in which bromine (Br-) ions were introduced by adding cetyltrimethylammonium bromide (CTAB)/tetrabutylammonium bromide (TBAB)/potassium bromide (KBr). The as-synthesized Bi2WO6 nanoplates displayed higher photocatalytic tetracycline degradation activity (~83.5%) than the Bi2WO6 microspheres (~48.2%), which were obtained without the addition of Br precursors in the reaction medium. The presence of Br- was verified experimentally, and the newly formed Bi2WO6 developed as nanoplates where the adsorbed Br- ions restricted the multilayer stacking. Considering the significant morphology change, increased specific surface area, and enhanced photocatalytic performance, using a synthesis approach mediated by Br- ions to design layered photocatalysts is expected to be a promising system for advancing water remediation.

Enhanced degradation of Congo-red dye by Cr3+ doped α-Fe2O3 nano-particles under sunlight and industrial wastewater treatment

Considering the increasing amount of water pollution, nanocomposite advances for the effective elimination of hazardous pollutants are still needed. α-Fe2O3, Cr0·5Fe1·5O3 and CrFeO3 nanoparticles were synthesized via an eco-friendly material synthesis i. e hydrothermal route without using any precipitating agent and were studied to remove congo-red dye using photocatalytic properties. X-ray diffraction (XRD), Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FESEM), Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS) characterizations have been performed to know about the material structure and properties of synthesized samples. High efficiency (95.2%) of degradation was achieved under sunlight using a very low amount of CrFeO3 catalyst (0.2 g/L) at a 6-pH level of dye and was confirmed using UV spectroscopy, TOC (84%), LC-HRMS. Also, the potential to degrade the CR dye was concluded from the high rate of BOD5/COD. The results showed a significant enhancement in the degradation of α-Fe2O3 from 52.3% to 95.2% in a short duration of 15 min by introducing chromium as a dopant. The doping of chromium influenced the major factors responsible for the photocatalytic activity such as the increase in range of absorbance, increased e−-h+ pair separation, improvement in the charge transfer process and active site formation which significantly enhanced the process of degradation. We found that the Cr-doped α-Fe2O3 nanomaterial could effectively remove dyes, such as congo-red, from industrial water-waste.

Pre-concentration of pesticides in water using isophorone diamine multiwalled carbon nanotubes-based solid-phase extraction technique and analysis by gas chromatography–mass spectrometry

The existence of pesticides in water at ultra-trace levels necessitates the use of a suitable pre-concentration method for their detection. The objective of this study was to develop an ultra-synthetic adsorbent to extract chlorpyrifos (CPF) and imazalil (IMA) pesticides in water. X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy confirm that both oxidised and isophorone diamine multiwalled carbon nanotubes (IPD-MWCNTs) were successfully prepared with an intact structure; which was further confirmed by transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). The Brunauer–Emmet–Teller (BET) showed a high surface area of both oxidised and IPD-MWCNTs, which is linked to the formation of additional active sites. TGA further showed that the nanocomposites were highly stable within the pesticides quantification operating temperature. CPF and IMA were recovered using a low dosage of IPD-MWCNTs adsorbent (0.030 g) and eluted by a combined solvent (ethanol and chloroform (50:50, v/v)). The adsorbent was reusable over seven repeated cycles, with an acceptable percentage relative standard deviation (%RSD) ranging from 3 to 8%. The IPD-MWCNTs adsorption sites are highly stable and cannot be easily fouled, as compared to that of oxidised MWCNTs. Lower limits of detection (LOD) and quantification (LOQ) for CPF (0.026 and 0.078 µg.L−1) and IMA (0.033 and 0.100 µg.L−1) were achieved. Better recoveries for both analytes at low and high concentrations (as well as in real water samples) were obtained by IPD-MWCNTs whereas a conventional adsorbent (i.e. polymeric reverse phase) can only achieve better recoveries at high concentrations.

Histidine modulates amyloid-like assembly of peptide nanomaterials and confers enzyme-like activity

Amyloid-like assembly is not only associated with pathological events, but also leads to the development of novel nanomaterials with unique properties. Herein, using Fmoc diphenylalanine peptide (Fmoc–F–F) as a minimalistic model, we found that histidine can modulate the assembly behavior of Fmoc–F–F and induce enzyme-like catalysis. Specifically, the presence of histidine rearranges the β structure of Fmoc–F–F to assemble nanofilaments, resulting in the formation of active site to mimic peroxidase-like activity that catalyzes ROS generation. A similar catalytic property is also observed in Aβ assembled filaments, which is correlated with the spatial proximity between intermolecular histidine and F-F. Notably, the assembled Aβ filaments are able to induce cellular ROS elevation and damage neuron cells, providing an insight into the pathological relationship between Aβ aggregation and Alzheimer’s disease. These findings highlight the potential of histidine as a modulator in amyloid-like assembly of peptide nanomaterials exerting enzyme-like catalysis.

Construction of Highly Active and Selective Molecular Imprinting Catalyst for Hydrogenation.

Surface molecular imprinting (MI) is one of the most efficient techniques to improve selectivity in a catalytic reaction. Heretofore, a prerequisite to fabricating selective catalysts by MI strategies is to sacrifice the number of surface-active sites, leading to a remarkable decrease of activity. Thus, it is highly desirable to design molecular imprinting catalysts (MICs) in which both the catalytic activity and selectivity are significantly enhanced. Herein, a series of MICs are prepared by sequentially adsorbing imprinting molecules (nitro compounds, N) and imprinting ligand (1,10-phenanthroline, L) over the copper surface of Cu/Al2O3. The resulting Cu/Al2O3-N-L MICs not only offer promoted catalytic selectivity but also enhance catalytic activity for nitro compounds hydrogenation by an creating imprinting cavity derived from the presorption of N and forming new active Cu-N sites at the interface of the copper sites and L. Characterizations by means of various experimental investigations and DFT calculations disclose that the molecular imprinting effect (promoted activity and selectivity) originates from the formation of new active Cu-N sites and precise imprinting cavities, endowing promoted catalytic selectivity and activity on the hydrogenation of nitro compounds.

Boosting the performance of enzyme-free biosensing system with Ni–Co bimetallic nanorod anchored on macroporous carbon composites for glucose monitoring

In this study, a nickel–cobalt bimetallic nanorod-codoped macroporous carbon nanocomposite (NiCo NR/MPC) was prepared and used for glucose detection. NiCo NR was uniformly embedded into MPC scaffolds. The synergistic effect between the excellent electrocatalytic activity of NiCo NR and the remarkable conductivity of MPC carriers increased the electron transfer and the formation of numerous usable active sites. For glucose detection, the NiCo NR/MPC-glassy carbon electrode (GCE) exhibited a good linear range (0.1–831.7 μM) and a low limit of detection (0.063 μM) (S/N = 3), with a high corresponding sensitivity of 206.8 μA mM−1 cm−2. Additionally, the GCE sensor was used to detect glucose under the same test conditions; the relative standard deviation (RSD) of the sensor was 4% after 10 repeated measurements. This indicated the reproducibility of the constructed NiCo NR/MPC-GCE sensor. Therefore, the constructed NiCo NR/MPC glucose electrochemical sensor has good application prospects.

Modulating the Reaction Configuration by Breaking the Structural Symmetry of Active Sites for Efficient Photocatalytic Reduction of Low-concentration CO2.

Photocatalytic conversion of low-concentration CO2 is considered as a promising way to simultaneously mitigate the environmental and energy issues. However, the weak CO2 adsorption and tough CO2 activation process seriously compromise the CO production, due to the chemical inertness of CO2 molecule and the formed fragile metal-C/O bond. Herein, we designed and fabricated oxygen vacancy contained Co3O4 hollow nanoparticles on ordered macroporous N-doped carbon framework (Vo-HCo3O4/OMNC) towards photoreduction of low-concentration CO2. In-situ spectra and ab initio molecular dynamics simulations reveal that the constructed oxygen vacancy is able to break the local structural symmetry of Co-O-Co sites. The formation of asymmetric active site switches the CO2 configuration from a single-site linear model to a multiple-sites bending one with a highly stable configuration, enhancing the binding and structural polarization of CO2 molecules. As a result, Vo-HCo3O4/OMNC shows unprecedent activity in the photocatalytic conversion of low-concentration CO2 (10% CO2/Ar) under laboratory light source or even natural sunlight, affording a syngas yield of 337.8 or 95.2 mmol g-1 h-1, respectively, with an apparent quantum yield up to 4.2%.

Modulating the Reaction Configuration by Breaking the Structural Symmetry of Active Sites for Efficient Photocatalytic Reduction of Low‐concentration CO2

AbstractPhotocatalytic conversion of low‐concentration CO2 is considered as a promising way to simultaneously mitigate the environmental and energy issues. However, the weak CO2 adsorption and tough CO2 activation process seriously compromise the CO production, due to the chemical inertness of CO2 molecule and the formed fragile metal‐C/O bond. Herein, we designed and fabricated oxygen vacancy contained Co3O4 hollow nanoparticles on ordered macroporous N‐doped carbon framework (Vo−HCo3O4/OMNC) towards photoreduction of low‐concentration CO2. In situ spectra and ab initio molecular dynamics simulations reveal that the constructed oxygen vacancy is able to break the local structural symmetry of Co−O−Co sites. The formation of asymmetric active site switches the CO2 configuration from a single‐site linear model to a multiple‐sites bending one with a highly stable configuration, enhancing the binding and structural polarization of CO2 molecules. As a result, Vo−HCo3O4/OMNC shows unprecedent activity in the photocatalytic conversion of low‐concentration CO2 (10 % CO2/Ar) under laboratory light source or even natural sunlight, affording a syngas yield of 337.8 or 95.2 mmol g−1 h−1, respectively, with an apparent quantum yield up to 4.2 %.

Triethylenediamine cobalt complex encapsulated in a metal–organic framework cage to prepare a cobalt single-atom catalyst with a high Co-N4 density for an efficient oxygen reduction reaction

Transition metal single atom catalysts (TM SACs) are the most promising oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs) and metal-air batteries. However, the low density of M-Nx active sites seriously hinders further improvement of the ORR electrocatalytic activity. Here, a strategy for encapsulating nitrogen-rich guest molecules (triethylenediamine cobalt complex, [Co(en)3]3+) was proposed to construct a high-performance cobalt single-atom catalyst (Co-encapsulated SAC/NC). With this strategy, the guest molecules are encapsulated into metal–organic framework (MOF) cages as an additional cobalt source to boost cobalt loading, while abundant nitrogen from guest molecules contributes to the formation of Co-N4 active sites. Remarkably, the resulting Co-encapsulated SAC/NC has a high cobalt loading amount of 4.03 wt%, and spherical aberration-corrected transmission electron microscopy (AC-TEM) has confirmed that most cobalt exists in a single-atom state. As a result, the Co-encapsulated SAC/NC exhibits excellent ORR catalytic performance with a half-wave potential of 0.88 V. Furthermore, Zn-air batteries employing Co-encapsulated SAC/NC as air cathode show high peak power density and excellent cycling stability. Density functional theory (DFT) calculations reveal that adjacent active sites have different rate-determining steps and lower reaction energy barriers than a single active site.

Mechanistic study of heterogeneous propene metathesis on WOx/SiO2 catalysts

Silica-supported tungsten oxides are widely used industrial catalysts for olefin metathesis due to their low cost and robustness, yet the mechanisms for heterogeneously catalyzed metathesis reactions remain comparatively less understood. In this work, density-functional theory (DFT) calculations were used to study the model reactions of propene metathesis. Our calculations confirm that the metathesis reactions catalyzed by WOx/SiO2 largely follow the Chauvin cycle, with an overall energetic barrier of 142 kJ/mol. To understand how the initial alkylidene active sites are generated, three mechanisms were examined: The pseudo-Wittig mechanism was found to be most favorable and proceeds with a metallacycle intermediate, while the allylic and vinylic CH activations are much more difficult and require the reduction of surface sites to W(+4). Relative to the adsorbed reactant state, the overall intrinsic barriers for three mechanisms were computed to be 193, 261, and 355 kJ/mol, respectively. The higher barriers for active-site formation than for the metathesis cycle are consistent with the difficult, high-temperature pretreatment required in experiments to activate WOx/SiO2 catalysts.

Complexation of Bromelain, Ficin, and Papain with the Graft Copolymer of Carboxymethyl Cellulose Sodium Salt and N-Vinylimidazole Enhances Enzyme Proteolytic Activity.

This study investigates the features of interactions between cysteine proteases (bromelain, ficin, and papain) and a graft copolymer of carboxymethyl cellulose sodium salt with N-vinylimidazole. The objective is to understand the influence of this interactions on the proteolytic activity and stability of the enzymes. The enzymes were immobilized through complexation with the carrier. The interaction mechanism was examined using Fourier-transform infrared spectroscopy and flexible molecular docking simulations. The findings reveal that the enzymes interact with the functional groups of the carrier via amino acid residues, resulting in the formation of secondary structure elements and enzyme's active sites. These interactions induce modulation of active site of the enzymes, leading to an enhancement in their proteolytic activity. Furthermore, the immobilized enzymes demonstrate superior stability compared to their native counterparts. Notably, during a 21-day incubation period, no protein release from the conjugates was observed. These results suggest that the complexation of the enzymes with the graft copolymer has the potential to improve their performance as biocatalysts, with applications in various fields such as biomedicine, pharmaceutics, and biotechnology.

Active sites-induced decoration of nickel hydroxide nanosheets on copper oxide nanocubes as electroactive material of battery supercapacitor hybrids

Battery supercapacitor hybrids (BSH) comprising battery and supercapacitor-type electrodes can attain high energy/power densities and long cycle life. Copper oxide is regarded as a promising battery-type active material, due to low-cost, high chemical stability and good electrochemical properties. However, poor electrical conductivity and insufficient active sites should be improved to attain high energy storage ability. In this work, a novel battery-type material composed of Ni(OH)2 nanosheets decorated on Cu2O cages is synthesized via a facile solution process for the first time. Less deposition of Ni(OH)2 leads to sparse distribution on Cu2O cages, and full coverage of Ni(OH)2 is achieved via depositing four Ni(OH)2 layers on Cu2O cages. The largest specific capacitance (CF) of 389.1 F/g is achieved at 20 mV/s for the optimized Ni(OH)2 and Cu2O (Ni(OH)2@Cu2O) composite, while the Cu2O electrode shows a smaller CF value of 79.7 F/g. Coating Ni(OH)2 on Cu2O can induce active site formation and enhance electrical conductivity. The Ni(OH)2@Cu2O positive electrode and the active carbon negative electrode are used to assemble a BSH, which presents a maximum energy density of 4.09 Wh/kg at 500 W/kg and excellent cycling ability with CF retention of 70% and Coulombic efficiency higher than 97% after 10,000 charge/discharge cycles.

Computational Study of Single Metal Atom Anchored on Black Phosphorus for Methane Oxidation to Methanol by Nitrous Oxide.

Direct conversion of methane to high-value-added transportable methanol is a great challenge, which requires high energy input to break the strong C-H bond. Developing efficient catalysts for methane oxidation to methanol under mild conditions is of vital importance. In this work, single transition metal atoms (TM=Fe, Co, Ni, Cu) anchored on black phosphorus (TM@BP) were studied as catalysts to assist the methane oxidation to methanol by means of first-principles calculations. The results indicate that Cu@BP exhibits an outstanding catalytic activity through the radical reaction pathways and the formation of the Cu-O active site is rate-determining with an energy barrier of 0.48 eV. Meanwhile, electronic structure calculations and dynamic simulations show that Cu@BP offers excellent thermal stability. Our calculations provide a new approach for the rational design of single atom catalysts for methane oxidation to methanol.

Boosting photocatalytic nitrogen reduction reaction by Jahn-Teller effect

Compared with traditional the Haber-Bosch process, photocatalytic ammonia production has attracted a considerable attention due to its advantages of low energy consumption and sustainability. In this work, we mainly study the photocatalytic nitrogen reduction reaction (NRR) on MoO3·0.55H2O and α-MoO3. Structure analysis shows that compared to α-MoO6, the [MoO6] octahedrons in MoO3·0.55H2O obviously distort (Jahn-Teller distortion), leading to the formation of Lewis acid active sites that favors the adsorption and activation of N2. X-ray photoelectron spectroscopy (XPS) further confirms the formation of more Mo5+ as Lewis acid active sites in MoO3·0.55H2O. Transient photocurrent, photoluminescence and electrochemical impedance spectra (EIS) confirmed that MoO3·0.55H2O has a higher charge separation and transfer efficiency than α-MoO3. Density functional theory (DFT) calculation further confirmed that the N2 adsorption on MoO3·0.55H2O is more favorable thermodynamically than that on α-MoO3. As a result, under visible light irradiation (λ ≥ 400 nm) for 60 min, an ammonia production rate of 88.6 μmol·gcat-1 was achieved on MoO3·0.55H2O, which is about 4.6 times higher than that on α-MoO3. In comparison to other photocatalysts, MoO3·0.55H2O exhibits an excellent photocatalytic NRR activity under visible light irradiation without using sacrificial agent. This work offers a new fundamental understanding to photocatalytic NRR from the viewpoint of crystal fine structure, which benefits designing efficient photocatalysts.

High capacitance performance of hierarchically SiO2 self-doped porous activated carbon derived from palm empty fruit bunches

Porous activated carbon derived from empty fruit bunch (EFB) has garnered significant attention as an electrode material for supercapacitors due to its low cost, abundance, and sustainability in real energy storage applications. However, there is still room for improvement in their performance compared to other renewable biomass resources. In our study, we successfully converted EFB biomass into porous activated carbon with outstanding performance, achieving a remarkably high specific capacitance of 459.28 F/g at 0.5 A/g, along with a moderate specific surface area (SSA) of 1215.38 m2/g. Furthermore, the quasi-solid-state supercapacitor assembled from the AC700 sample demonstrated excellent energy density, reaching 15.39 Wh/kg at a power density of 50 W/kg. Additionally, it exhibited remarkable cycling stability, with a capacitance retention of 93 % after 10,000 cycles. These exceptional results were achieved by simply adjusting the activation temperature. We utilized KOH as the activating agent and carbonized it at temperatures of 600 °C, 700 °C, and 800 °C for 2 h under an N2 atmosphere. The superior capacitive performance of the AC700 sample can be attributed to the combined effects of its high SSA, surface functional groups, and optimal pore size distribution. The optimum activation temperature of 700 °C resulted in the formation of porous activated carbon with the most structural defects, as well as an appropriate distribution of micropores (63.41 %) and mesopores (31.70 %), facilitating ion diffusion and providing multiple sites for charge storage. Additionally, the AC700 sample exhibited the highest SiO2 content, measuring at 34.33 %, and the lowest contact angle of 75°. The presence of SiO2 in the carbon framework promotes the formation of more hydrophilic active sites, thereby enhancing the pseudocapacitance performance and facilitating sufficient wetting between the electrolyte and electrode interface.

Active Site Descriptors from 95Mo NMR Signatures of Silica-Supported Mo-Based Olefin Metathesis Catalysts.

The olefin metathesis activity of silica-supported molybdenum oxides depends strongly on metal loading and preparation conditions, indicating that the nature and/or amounts of the active sites vary across compositionally similar catalysts. This is illustrated by comparing Mo-based (pre)catalysts prepared by impregnation (2.5-15.6 wt % Mo) and a model material (2.3 wt % Mo) synthesized via surface organometallic chemistry (SOMC). Analyses of FTIR, UV-vis, and Mo K-edge X-ray absorption spectra show that these (pre)catalysts are composed predominantly of similar isolated Mo dioxo sites. However, they exhibit different reaction properties in both liquid and gas-phase olefin metathesis with the SOMC-derived catalyst outperforming a classical catalyst of a similar Mo loading by ×1.5-2.0. Notably, solid-state 95Mo NMR analyses leveraging state-of-the-art high-field (28.2 T) measurement conditions resolve four distinct surface Mo dioxo sites with distributions that depend on the (pre)catalyst preparation methods. The intensity of a specific deshielded 95Mo NMR signal, which is most prominent in the SOMC-derived catalyst, is linked to reducibility and catalytic activity. First-principles calculations show that 95Mo NMR parameters directly manifest the local strain and coordination environment: acute (SiO-Mo(O)2-OSi) angles and low coordination numbers at Mo lead to highly deshielded 95Mo chemical shifts and small quadrupolar coupling constants, respectively. Natural chemical shift analyses relate the 95Mo NMR signature of strained species to low LUMO energies, which is consistent with their high reducibility and corresponding reactivity. The 95Mo chemical shifts of supported Mo dioxo sites are thus linked to their specific electronic structures, providing a powerful descriptor for their propensity toward reduction and formation of active sites.

Ultra-fast electrochemical preparation of Ni-Cu-Fe nano-micro dendrite as a highly active and stable electrocatalyst for overall water splitting

The development of highly active, durable, and low-cost electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) to advance the commercial applications of overall water electrolysis is regarded as a crucial matter. We describe an ultra-fast synthesis of multi-metal Ni-Cu-Fe micro-nano dendritic electrocatalysts were synthesized on nickel foam using a simple one-step constant current electrodeposition method. According to DFT simulations, Fe incorporation causes a downshift movement in the d-band center and the formation of additional catalytic active sites. Ni-Cu-Fe nano-micro dendrites have potential applications as bifunctional catalysts for electrochemical water splitting. Also, the increased electrical conductivity of the Ni-Cu-Fe electrode is due to the placement of more electronic states near the Fermi level and creating an optimal and porous dendritic structure that causes better electrolyte penetration in the pores. Experiments show that in the 1.0 M KOH electrolyte, Ni-Cu-Fe catalysts need an ultra-low overpotentials of 42 mV and 300 mV to supply a current density of −10 mA cm−2 for the HER and 50 mA cm−2 for the OER. Also, when Ni-Cu-Fe electrocatalyst is used as a bifunctional electrode in the overall water splitting system, it displays a low cell voltage of 1.54 V in a current density of 10 mA cm−2 can maintain this activity for more than 100 h.

Elucidation of Active Sites and Mechanistic Pathways of a Heteropolyacid/Cu-Metal–Organic Framework Catalyst for Selective Oxidation of 5-Hydroxymethylfurfural via Ex Situ X-ray Absorption Spectroscopy and In Situ Attenuated Total Reflection-Infrared Studies

Chemoselective oxidation of 5-hydroxymethylfurfural (HMF) over non-noble metals to produce a bioplastic monomer, 2,5-furandicarboxylic acid (FDCA), under alkaline-free conditions is challenging and worthy of investigation. HMF oxidation into FDCA involves the concurrent oxidation of primary alcohol and an aldehyde functional group into carboxylic groups, which therefore demand a bifunctional catalyst containing dual active sites and chemoselective oxidation of HMF. The present work demonstrated the formation of new selective active sites in a composite porous material (Cu-BTC_PMA) that consists of Cu-BTC (metal–organic framework (MOF)) and polyoxometalate (POM). The porous framework provides (Cu-BTC_PMA) the desired chemoselectivity, while a selective Cu metal center in Cu-BTC (MOF) and Cu–O–Mo sites functions as active sites for the concurrent oxidation of HMF into FDCA. This catalyst exhibited a HMF conversion of 89% and an FDCA selectivity of 92.3% under base-free and mild reaction conditions. In detail, X-ray absorption spectroscopy analysis demonstrated the chemical bond tuning, as well as electronic structural modulations of MOF and POM at the molecular level, which directs the formation of new synergistic interfacial active sites and charge transfer states. This phenomenon causes the generation of the unique redox environment of copper and the multiple oxidation states along with the oxygen vacancy in the Cu-BTC_PMA catalyst, which most likely behaves as active sites for base-free oxidation. A kinetics study of this reaction was followed using in situ attenuated total reflection-infrared spectroscopy, demonstrating the stabilization of the specific intermediates that lead to the formation of FDCA. Moreover, we made comparative density functional theory and quantum theory of atoms in molecules investigations on the surface interaction between the reactant (HMF) and two catalyst models of Cu-BTC and Cu-BTC_PMA to interpret quantitatively the higher catalytic activity of the Cu-BTC_PMA catalyst. The kinetics study also evaluates the rate-determining step and activation energy for the multistep oxidation reactions.

Nitrogen-Doped Carbon Coated Na3V2(PO4)2F3 Derived from Polyvinylpyrrolidone as a High-Performance Cathode for Sodium-Ion Batteries

Na super ionic conductor (NASICON)-type Na3V2(PO4)2F3 (NVPF) has been regarded as a prospective candidate of cathode materials for sodium-ion batteries due to its excellent structural stability, relatively high capacity and working voltage. However, the poor cyclability and rate capability, resulting from its low intrinsic electronic conductivity, have become a serious obstacle to their practical large-scale application. In this work, N-doped carbon coated NVPF composites (NVPF@NC) were successfully synthesized via a simple sol–gel method, in which low-cost polyvinylpyrrolidone was introduced as a nitrogen source. After high-temperature pyrolysis, a highly conductive N-doped carbon layer was in-situ constructed on the particle surface to enhance the sodium storage performance of NVPF. The optimized NVPF@NC cathode delivered high reversible capacity, excellent rate capability and long-term cycle life compared to pristine NVPF@C. The remarkable electrochemical performance of NVPF@NC cathode benefits from the modification strategy of introducing a heteroatom-doped carbon layer, triggering the formation of extrinsic defects and active sites in the N-doped amorphous carbon layer, which greatly enhances the electrical conductivity and the diffusion rate of sodium ions. This work provides a facile and effective approach for the preparation of N-doped carbon coated NVPF with remarkable sodium storage properties, which could be extended to other electrode materials electrochemical for energy storage.