Silicotungstic Acid Research Articles

A novel highly efficient co-catalyst for enhancement of photocatalytic hydrogen production activity and stability of Cd0.5Zn0.5S: Silicotungstic acid nanoparticles embedded with NiOx clusters

A novel highly efficient co-catalyst for enhancement of photocatalytic hydrogen production activity and stability of Cd0.5Zn0.5S: Silicotungstic acid nanoparticles embedded with NiOx clusters

Heteropolyacids combined with Y zeolite as superior solid acid catalysts to accelerate lactic acid esterification

AbstractBACKGROUNDEthyl lactate produced via esterification between lactic acid and ethanol can be used in plastics, polymers and food industries and renowned for its biodegradability and low toxicity. However, lactic acid self‐catalyzed esterification presents a slow reaction process, and acid catalysts are needed to improve the catalysis. Homogeneous acid catalysts like H2SO4 are corrosive, as well as being difficult to be seperated from the reaction media; therefore, advanced heterogeneous catalysts are more ideal. In this study, two kinds of heteropolyacid–zeolite catalysts, involving loading silicotungstic acid and phosphotungstic acid onto Y zeolite, were synthesized, characterized using X‐ray diffraction, NH3 temperature‐programmed desorption and scanning electron microscopy and analyzed for their catalytic efficiency in the catalytic esterfication.RESULTSResults showed that the Keggin structures of heteropolyacids were retained during the preparation process and strong acid sites of Y zeolite were enriched, which made the main contribution to the esterification of lactic acid and ethanol. Furthermore, the initial‐stage reaction rate of esterification was significantly enhanced. During the first hour of esterification, the conversion of lactic acid increased from 18% to 65%. Exp Dec1 index model was employed to determine the activation energies of 60HSiW‐Y and 60HPW‐Y, which exhibit values of 29.3 and 28.2 kJ mol−1, respectively.CONCLUSIONThis study indicates that Keggin structures of heteropolyacids play a key role in the esterification and heteropolyacid–zeolite catalysts can effectively catalyze the esterification. Meanwhile, the results of the kinetic experiments can be of reference significance for large‐scale industrial processes involving esterification. © 2024 Society of Chemical Industry (SCI).

Electrospun Pt-TiO2 nanofibers Doped with HPA for Catalytic Hydrodeoxygenation

Electrospinning is utilized to fabricate catalytic nanofiber scaffold for biocrude upgrading in hydrodeoxygenation (HDO) following computational studies suggesting the need for nano-catalysts for efficient HDO conversion and selectivity. Here, Pt-TiO2 nanofibers are fabricated through electrospinning, followed by wet impregnation with a heteropoly acid (HPA), tungstosilicic acid. Intensive heat treatments were incorporated during and after processes to obtain a HPA doped Pt-TiO2 nano-catalyst. Catalytic HDO was performed in a batch reactor with phenol as the raw biocrude dissolved in hexadecane. The HPA doped Pt-TiO2 catalyst demonstrated promising HDO performance of 37.2% conversion and a 78.9% selectivity to oxygen free benzene and the remainder 21.1% as diphenyl ester as a result of esterification by acidic components of the catalyst. Additionally, BET surface area characterization show a low surface area 16.9 m2 g−1 significantly lower than existing commercial catalysts and a mesoporous nature suitable for selectivity. The presence of HPA on the anatase nanofiber compensated for low platinum nanoparticles crystallinity on the nanofibers. This work might create needed alternatives for preparing HDO catalysts for efficient aromatics production.

Cross-linked proton exchange membrane covalently bonded with silicotungstic acid for enhanced proton conductivity

Proton exchange membranes with cross-linked structures often showed excellent mechanical and chemical stability, but their water absorption and proton conductivity were restricted. This study reported a convenient and efficient thermal cross-linking reaction of sulfonic acid groups and benzene rings using dimethyl sulfoxide and sulfolane mixed solvents to prepare the membrane. To further illustrate, phenoxyphenyl-attached silicotungstic acid (POP-SiWA) was incorporated in the sulfonated poly(ether ether ketone) membrane and covalently bonded with the polymer by thermal cross-linking reaction. The immobilization ratio for the membranes prepared with 10∼30 wt% POP-SiWA addition was 88.0–63.7%. The modified membranes exhibited high hydrophilicity and improved proton conductivity under hydrated or low relative humidity conditions due to the strong acidity and water-retaining properties of silicotungstic acid. Specifically, the proton conductivity of the modified membrane with 30 wt% POP-SiWA reached 212 mS/cm. It exhibited a fuel cell power density of 629 mW/cm2 at 80 °C and 100% relative humidity, which were 1.90 and 2.67 times higher than the pristine membrane.

Programmable Reconfiguration of Supramolecular Bottlebrush Block Copolymers: From Solution Self-Assembly to Co-Crystallization-Assistant Self-Assembly.

Achieving structural reconfiguration of supramolecular bottlebrush block copolymers toward topological engineering is of particular interest but challenging. Here, we address the creation of supramolecular architectures to discover how assembled topology influences the structured aggregates, combining hydrogen-bonded (H-bonded) bottlebrush block copolymers and electrostatic interaction induced polymer/inorganic eutectics. We first design H-bonding linear-brush block copolymer P(NBDAP-co-NBC)-b-P(NBPEO), bearing linear block P(NBDAP-co-NBC) (poly(norbornene-terminated diaminopyridine-co-norbornene-terminated hexane)) with pendant H-bonding DAP (diaminopyridine) motifs, and PEO (poly(ethylene oxide)) densely grafted P(NBPEO) brush block. Thanks to H-bonding association between DAP and thymine (Thy), incorporation of Thy-functionalized polystyrene (Thy-PS65) enables solution self-assembly and formation of H-bonded bottlebrush block copolymers, generating augmented nanospheres with increasing Thy-PS65 amount. Noteworthy that integration of inorganic cluster silicotungstic acid (STA) to P(NBC-co-NBDAP)-b-P(NBPEO), endows the formation of PEO/STA eutectic core. Therefore, co-crystallization-assistant self-assembly at the interfaces of polymeric, inorganic and supramolecular chemistry is realized, reflecting multi-stage morphology transformation from hexagonal platelets, needle-like, curved rod-like micelles, finally to end-to-end closed rings, by gradually increasing Thy-PS65 while fixing STA content. Interestingly, such solution self-assembly to co-crystallization-assistant self-assembly strategy not only endows unique nanostructure transition, also induce in-to-out reconfiguration of PS domains. These findings clearly provide unique methodology towards programmable fabrication of geometrical objects promising in smart materials.

Redox kinetics of multi-electron transfer reactions of polyoxometalates (POMs) relevant to electrochemical devices

The formal equilibrium potential (E0′) and heterogeneous rate constant (k0) are characteristics of any electron-transfer reaction. The estimation of these characteristics for very fast multiple electron-transfer reactions of polyoxometalates (POMs) relevant to various applications including redox flow batteries, hydrogen storage materials, and electrocatalysis is highly challenging by the conventional electrochemical methods. Therefore, E0′and k0 (k0∼10–2 cm sec‑1) of such reactions (for e.g., that of tungstosilicic acid (SiW12) and phosphotungstic acid (PW12)) separated by small potential windows are estimated from the background current free higher harmonic response of large-amplitude AC voltammetry. For SiW12/PW12 redox species, the E0′ values of processes 1, 2, and 3 estimated from the minima of second harmonic response are -0.326/-0.127, -0.530/-0.380 and -0.691/-0.701 (V vs. Ag/AgCl), respectively. The k0 values of the first redox process (P1) of SiW12 (SiW12/ SiW12-,4.8 × 10–2 cm sec‑1) and PW12 (PW12/PW12-,5.2 × 10–2 cm sec‑1) estimated from the large-amplitude AC voltammetry are further validated through the impedance measurement (2.1 × 10–2 and 2.4 × 10–2 cm sec‑1). The uniqueness of large-amplitude AC voltammetry over conventional DC techniques and impedance spectroscopy is illustrated. The relevance of k0 values in the context of electrocatalytic processes and RFBs system is also presented.

Design, Synthesis, and Characterization of Polyoxotungstate-Decorated Ionic Liquid-Based Hybrid Material, [BmIm]4[SiW12O40] toward Rapid Adsorption of Dye and Antibacterial Activities.

A multifunctional polyoxometalate-ionic liquid (POM-IL)-based hybrid material comprising silicotungstic acid, [BmIm]4[SiW12O40], has been synthesized and demonstrated its efficiency toward methylene blue removal and as an antibacterial agent. Single-crystal XRD analysis confirms that the material crystallizes in monoclinic symmetry (SG: Pn), with lattice parameters a = 13.1396(5) Å, b = 16.9655(8) Å, c = 14.3493(7) Å, and Z = 2. The structure comprises a single polyanionic [SiW12O40]4- moiety surrounded by four cationic [BmIm]+ units of two different conformations, which supported DFT and Hirshfeld surface analysis. The material shows excellent removal efficiency for methylene blue, with a maximum adsorption capacity of 92.47 mg/g and 83.05% reusability after five cycles. On the contrary, FTIR and ζ-potential analyses confirm that electrostatic interactions are the predominant factors governing the adsorption process. The material also acts as a superior antibacterial agent against the opportunistic pathogens Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli with a MIC of 500-700 μg/mL. However, a comparative assessment showed that the material was more effective against P. aeruginosa compared to the other two pathogens. PXRD analysis confirms the phase purity, and FESEM and TEM analyses exhibit block-shaped morphology with particle sizes ∼2-3 μm.

Direct application of tungstosilicic acid hydrate for the treatment of high free fatty acid in acidic crude palm oil and for biodiesel production

AbstractThis study explored the use of industrial acidic crude palm oil (ACPO) for biodiesel production, facing a significant obstacle due to its high free fatty acid (FFA) content, which complicates the biodiesel production process. Typically, esterification is employed to convert FFAs into fatty acid methyl ester (FAME). Herein, the effectiveness of tungstosilicic acid hydrate (TSAH) as an unsupported heteropoly acid (HPA) catalyst for FFA esterification in ACPO was investigated. The FFA content was reduced from 8.43% to 0.95% under optimum conditions (4 wt% catalyst dosage, a methanol to oil molar ratio of 10:1, 150 min and a temperature of 60°C). Noteworthy, the TSAH catalyst showed stability over 7 cycles. The kinetic analysis revealed that the FFA esterification process closely followed pseudo first‐order kinetics, with an R2 value of 0.94. Furthermore, the biodiesel produced from TSAH‐treated ACPO meets the standard specifications outlined by ASTM D6751 and EN 14214. This research highlights the effectiveness of TSAH in catalyzing FFA esterification without the need for additional support materials or modifications.

Effects of silico-tungstic acid on the pseudo capacitive properties of manganese oxide for electrochemical capacitors applications

In this work manganese oxide (MnO2) is modified with silico-tungstic acid (STA). Three samples are synthesized by the co-precipitation method. The powders obtained after elaboration are characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) imaging coupled to Electron Dispersive Spectroscopy (EDS) analysis and Brunauer-Emmet-Teller (BET) for their surface area determination. The effect of the modification of the manganese oxide with STA on its surface is determined. It is shown that MnO2 modified with STA exhibits better cumulative high specific surface areas and mesoporous volumes areas. For example, the sample fabricates with 10% STA (MnO2 – 10% STA) has a BET surface area of 153.6 ​m2 ​g−1 and volume area 0.92 ​cm3 ​g−1 whereas the sample without STA (MnO2 – 0% STA) has a surface area of 132.57 ​m2 ​g−1 and a mesoporous area of 0.26 ​cm3 ​g−1. The electrochemical performance analysis of the different working electrodes prepared for super-capacitors applications is carried out using cyclic voltammetry (CV)., using a solution of 0.5 M K2SO4 as an electrolyte in potential range of −0.4 and 0.9 ​V at a sweep speed of 10 ​mV/s. The CV results are correlated to those of the BET surface and mesoporous areas values Accordingly, it is shown that samples spiked with STA exhibit higher electrochemical double layer capacitance than those of none modified with STA. These measurements respectively give 38 ​F ​g−1, and 181 ​F ​g−1 for MnO2 without STA (MnO2 – 0% STA), and MnO2 modified with 10% STA (MnO2 – 5% STA).

Programmable Reconfiguration of Supramolecular Bottlebrush Block Copolymers: From Solution Self‐Assembly to Co‐Crystallization‐Assistant Self‐Assembly

Achieving structural reconfiguration of supramolecular bottlebrush block copolymers toward topological engineering is of particular interest but challenging. Here, we address the creation of supramolecular architectures to discover how assembled topology influences the structured aggregates, combining hydrogen‐bonded (H‐bonded) bottlebrush block copolymers and electrostatic interaction induced polymer/inorganic eutectics. We first design H‐bonding linear‐brush block copolymer P(NBDAP‐co‐NBC)‐b‐P(NBPEO), bearing linear block P(NBDAP‐co‐NBC) (poly(norbornene‐terminated diaminopyridine‐co‐norbornene‐terminated hexane)) with pendant H‐bonding DAP (diaminopyridine) motifs, and PEO (poly(ethylene oxide)) densely grafted P(NBPEO) brush block. Thanks to H‐bonding association between DAP and thymine (Thy), incorporation of Thy‐functionalized polystyrene (Thy‐PS) enables solution self‐assembly and formation of H‐bonded bottlebrush block copolymers, generating augmented nanospheres with increasing Thy‐PS amount. Noteworthy that integration of inorganic cluster silicotungstic acid (STA) to P(NBC‐co‐NBDAP)‐b‐P(NBPEO), endows the formation of PEO/STA eutectic core. Therefore, co‐crystallization‐assistant self‐assembly at the interfaces of polymeric, inorganic and supramolecular chemistry is realized, reflecting multi‐stage morphology transformation from hexagonal platelets, needle‐like, curved rod‐like micelles, finally to end‐to‐end closed rings, by gradually increasing Thy‐PS while fixing STA content. Interestingly, such solution self‐assembly to co‐crystallization‐assistant self‐assembly strategy not only endows unique nanostructure transition, also induce in‐to‐out switch of PS domains. These findings clearly provide unique methodology towards programmable fabrication of geometrical objects promising in smart materials.

Efficient conversion of chitin to HMF under the co-catalytic system of formic acid and silicotungstic acid

Efficient conversion of chitin to HMF under the co-catalytic system of formic acid and silicotungstic acid

Solvent‐Free Efficient Hydrogenation of Levulinic Acid over Silicotungstic Acid Promoting the Activity of CuNiAl Catalysts: A Synergistic Effect

AbstractMulti‐metallic catalysts rely on the synergistic effect between metals to perform better catalytic effect in biomass hydrogenation experiments compared with mono‐metallic catalysts. A series of CuNiAl composite metal oxide catalysts promoted by silicotungstic acid (HSiW), which were prepared by co‐precipitation and impregnation methods, were characterized by powder X‐ray diffraction (XRD), N2‐physisorption, scanning electron microscope (SEM) and NH3 program temperature desorption (NH3‐TPD) and pyridine infrared adsorption (Py‐FTIR). Their catalytic performance was evaluated in the hydrogenation of levulinic acid (LA) to prepare γ‐valerolactone (GVL). The results showed that the addition of Cu could improve the hydrogenation activity of Ni, and the addition of HSiW could further increase the amount of acid sites in the catalysts. Both of them could enhance the conversion of LA to some extent. CuNiAl‐5SiW, the par excellence catalyst, relied on the synergistic interactions between metals as well as the Brønsted and Lewis acid active sites to show efficient hydrogenation performance. The CuNiAl‐5SiW catalyst demonstrated 96.9 % conversion of LA and more than 99 % selectivity to GVL under 2 hours of reaction time, 180 °C of reaction temperature, 3.0 MPa of initial hydrogen pressure and solvent‐free conditions.

Optimizing acidic site control for selective conversion of biomass-based sugar to furfural and levulinic acid through HSiW/MCM-41 catalyst

Furfural and levulinic acid are valuable platform compounds that can be produced by acid catalyzed conversion of sugars. Modified MCM-41 with different contents of silicotungstic acid (20 wt%-50 wt%) was successfully prepared via a wet impregnation method in order to regulate the ratio of Brønsted acid to Lewis acid. Among these catalysts, 40 wt% HSiW/MCM-41 with superior acid site density (Brønsted acid 59.35 μmol/g, Lewis acid 33.69 μmol/g) showed excellent catalytic activity as it exposed the most acidic sites and the ratio of Brønsted acid to Lewis acid reached 1.76. The conversion of biomass-based sugar was as high as 99.01 %, the maximum yield of furfural could reach 56.75 %, and the yield of levulinic acid could reach 18.88 % catalyzed by 40 wt% HSiW/MCM-41. This study provided new insights into the development of efficient and sustainable catalytic systems for the production of biomass-derived compounds.

Ethyl Cyanoacetate Reactions

Ethyl cyanoacetate is a chemical intermediate that has been frequently used. The esterification of cyanoacetic acid and absolute ethanol with a mixed catalyst yielded ethyl cyanoacetate (the same proportion of silicotungstic and p-toluene sulfonic acid as catalyst). The influence factors of the amount of catalyst, n (cyanoacetic acid): n (absolute ethanol), reaction time and reaction temperature on the esterification rate was investigated by orthogonal experiment of four factors and three levels. The product was analyzed by gas chromatography to determine the optimum reaction conditions

Unveiling zirconium phytate-heteropolyacids-ionic liquids membranes for PEM fuel cells applications up to 150 °C

In the context of escalating energy demands and the pressing issues of climate change, fuel cells emerge as a pivotal, economically feasible, and environmentally sound renewable energy alternative. This study highlights the importance of fuel cells, specifically focusing on high-temperature and Nafion-free membranes. Membranes composed of zirconium phytate, silicotungstic acid, polyethylene glycol, and ionic liquids employing porous polytetrafluoroethylene polymer for support are reported. Investigating varying ratios of silicotungstic acid, polyethylene glycol, and ionic liquids, electrochemical spectroscopy revealed heightened proton conductivity upon ionic liquids integration. Initially, the unmodified zirconium phytate membrane demonstrated a conductivity of 6.65 × 10−4 S/cm, escalating tenfold (2.23 × 10−3 S/cm) with silicotungstic acid addition. Further enhancements, such as incorporating polyethylene glycol, led to an increase in the conductivity to 3.81 × 10−2 S/cm. The maximum conductivity value obtained in this work (0.1 S/cm), comparable to Nafion, was achieved with 5.86 wt% of the 1-Hexyl-3-methylimidazolium tricyanomethanide. Testing at elevated temperatures up to 150 °C revealed a drop in conductivity by two orders of magnitude (10−3 S/cm), highlighting their remarkable conductive properties. Additionally, water uptake analysis demonstrated the membranes' ability to retain more than 60 wt% water molecules within their matrix. Furthermore, thermogravimetric analysis revealed the thermal stability of membranes at high temperatures up to 600 °C. These findings strongly indicate that these synthesized membranes possess considerable potential for high temperature proton exchange membrane fuel cell applications.

Unprecedented stepwise electron transfer and photocatalysis in supramolecular assembly derived hybrid single-layer two-dimensional nanosheets in water

Herein, a simple and effective outer-surface interactions assisted supramolecular hierarchical assembly has been first exploited to uniformly distribute tungstosilicic acid (TSA) inside the porous structure of cucurbit[10]uril-based single-layer 2D supramolecular-organic-frameworks (Q[10]-SOFs) in water. Importantly, the 2D Q[10]-SOFs can further serve as light harvesting antenna, achieving fast energy transfer to the embedded redox-active TSA upon photoexcitation, resulting in efficient visible light-driven selective oxidation of benzyl alcohols into the corresponding aldehydes in high yield at room temperature. Further studies revealed that the integrated of 2D Q[10]-SOFs and TSA played a key role in the catalytic process, due to the presence of a novel stepwise electron transfer route in the single-layer hybrid 2D structures.

Detailed Study on the Interfacial Interaction between Different Polyoxometalates and Tetronic Block Copolymers Exploring the Langmuir-Blodgett Technique.

Polyoxometalates (POMs) interact with various biologically relevant entities. A basic understanding of this interaction is very important for various applications in the biological field. In this work, the focus is on the study of the interaction between tetronics and Keggin POMs. T701 and T90R4 are the two tetronics considered here; they have different solubilities in water due to different PPO/PEO ratios. The arrangement of PPO and PEO is also different with respect to the central ethylenediamine groups. Three different Keggin-type POMs, phosphomolybdic acid (PMA), phosphotungstic acid (PTA), and silicotungstic acid (STA), with different charge densities are chosen for an elaborate investigation using Langmuir-Blodgett technique. The observation is analyzed thoroughly, which shows both electrostatic interaction and adsorption of POMs on the PPO blocks of the tetronics due to the chaotropic effect, which is responsible for the binding of POMs (in subphase) with the tetronic monolayer. This interaction results in an expanded yet rigid monolayer for POM-tetronic association on the surface. Surface pressure vs mean molecular area isotherm is the key characterization to reach the conclusion. UV-vis spectroscopy, NMR, ITC, ellipsometric studies, FTIR, and SEM also serve as supportive characterization techniques.

Electrostatic interactions mediated defibrillation of β-lactoglobulin fibrils using Keggin Polyoxometalates

The whey protein β-lactoglobulin (βLG) forms fibrils similar to the amyloid fibrils in the neurodegenerative diseases due to its higher predisposition of β-sheets. This study shed light on the understanding different inorganic Keggin polyoxometalates (POMs) interaction with the protein βLG fibrils. POMs such as Phosphomolybdic acid (PMA), silicomolybdic acid (SMA), tungstosilicic acid (TSA), and phosphotungstic acid (PTA) were used due to their inherent higher anionic charges. The interaction studies were monitored with fluorescence spectra and Thioflavin T assay for both the βLG monomers and the fibrils initially to elucidate the binding ability of the POMs. The binding of POMs and βLG is also demonstrated by molecular docking studies. Zeta potential studies showed the electrostatic mediated higher interactions of the POMs with the protein fibrils. Isothermal titration calorimetry (ITC) studies showed that the molybdenum containing POMs have higher affinity to the protein fibrils than the tungsten. This study could help understanding formation of food grade protein fibrils which have profound importance in food industries.

Heteropolyacid promoted lignin-MOF derived spherical catalyst for catalytic hydrogen transfer of 5-hydroxymethylfurfural

Catalytic conversion of biomass-derived value-added chemicals was of great significance for the utilization of renewable biomass resources to instead of fossil chemicals. Biomass-derived lignin was regarded as an important support and 5-hydroxymethylfurfural (HMF) was a vital platform chemical derived from cellulose. Herein, a series of lignin-MOF hybrid catalysts were prepared and modified with different heteropolyacids (HPAs), which were then successfully introduced into the selective conversion of HMF to 5-hydroxymethylfurfuryl alcohol (MFA). The effect of different HPA, calcination temperature, etc. were all studied, and all catalysts were well characterized. It was confirmed that silicotungstic acid modified catalyst (Ni3Co-MOF-LS@HSiW) exhibited the best catalytic performance, while the highest conversion of HMF was up to 100%, with the best MFA yield of 86.5%. The finding in this study could provide novel insights for the utilization of lignin and preparation of value-added biomass-derived chemicals.

Injectable hydrogel harnessing foreskin mesenchymal stem cell-derived extracellular vesicles for treatment of chronic diabetic skin wounds

Chronic skin wounds are a serious complication of diabetes with a high incidence rate, which can lead to disability or even death. Previous studies have shown that mesenchymal stem cells derived extracellular vesicles (EVs) have beneficial effects on wound healing. However, the human foreskin mesenchymal stem cell (FSMSCs)-derived extracellular vesicle (FM-EV) has not yet been isolated and characterized. Furthermore, the limited supply and short lifespan of EVs also hinder their practical use. In this study, we developed an injectable dual-physical cross-linking hydrogel (PSiW) with self-healing, adhesive, and antibacterial properties, using polyvinylpyrrolidone and silicotungstic acid to load FM-EV. The EVs were evenly distributed in the hydrogel and continuously released. In vivo and vitro tests demonstrated that the synergistic effect of EVs and hydrogel could significantly promote the repair of diabetic wounds by regulating macrophage polarization, promoting angiogenesis, and improving the microenvironment. Overall, the obtained EVs-loaded hydrogels developed in this work exhibited promising applicability for the repair of chronic skin wounds in diabetes patients.