Metal (Mo, W, Ti) Carbide Catalysts: Synthesis and Application as Alternative Catalysts for Dry Reforming of Hydrocarbons-A Review.

Dry reforming of hydrocarbons (DRH) is a pro-environmental method for syngas production. It owes its pro-environmental character to the use of carbon dioxide, which is one of the main greenhouse gases. Currently used nickel catalysts on oxide supports suffer from rapid deactivation due to sintering of active metal particles or the deposition of carbon deposits blocking the flow of gases through the reaction tube. In this view, new alternative catalysts are highly sought after. Transition metal carbides (TMCs) can potentially replace traditional nickel catalysts due to their stability and activity in DR processes. The catalytic activity of carbides results from the synthesis-dependent structural properties of carbides. In this respect, this review presents the most important methods of titanium, molybdenum, and tungsten carbide synthesis and the influence of their properties on activity in catalyzing the reaction of methane with carbon dioxide.

Water-Assisted Concerted Proton-Electron Transfer at Co(II)-Aquo Sites in Polyoxotungstates With Photogenerated RuIII (bpy)33+ Oxidant.

The cobalt substituted polyoxotungstate [Co6 (H2 O)2 (α-B-PW9 O34 )2 (PW6 O26 )]17- (Co6) displays fast electron transfer (ET) kinetics to photogenerated RuIII (bpy)33+ , 4 to 5 orders of magnitude faster than the corresponding ET observed for cobalt oxide nanoparticles. Mechanistic evidence has been acquired indicating that: (i) the one-electron oxidation of Co6 involves Co(II) aquo or Co(II) hydroxo groups (abbreviated as Co6(II)-OH2 and Co6(II)-OH, respectively, whose speciation in aqueous solution is associated to a pKa of 7.6), and generates a Co(III)-OH moiety (Co6(III)-OH), as proven by transient absorption spectroscopy; (ii) at pH>pKa , the Co6(II)-OH→RuIII (bpy)33+ ET occurs via bimolecular kinetics, with a rate constant k close to the diffusion limit and dependent on the ionic strength of the medium, consistent with reaction between charged species; (iii) at pH

Synthesis, characterization and biological evaluation of octyltrimethylammonium tetrathiotungstate.

Octyltrimethylammonium tetrathiotungstate salt (ATT-C8) was synthesized and its ability to chelate copper was evaluated. The biological and toxic aspects were evaluated by in vitro and in vivo assays, using bovine aorta endothelial cells (BAEC) and zebrafish (Danio rerio) embryos. The obtained results suggest that ATT-C8 has better biocompatibility, showing a significantly lower lethal concentration 50 (LC50) value in comparison to ammonium tetrathiotungstate (ATT). Zebrafish embryos assay results indicate that both tetrathiotungstate salts at the studied concentrations increase the hatching time. Even more, an in vivo assay showed that synthesized materials behave as copper antagonists and have the ability to inhibit its toxicological effects. Also, both materials were found to be active for the in vitro 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The characterization of the materials was carried out using the following spectroscopic techniques: Ultraviolet-Visible (UV-Vis), Fourier Transform Infrared (FTIR) and proton nuclear magnetic resonance (1H-NRM).

Synthesis, Characterization, Electrochemistry, Photoluminescence and Magnetic Properties of a Dinuclear Erbium(III)-Containing Monolacunary Dawson-Type Tungstophosphate: [{Er(H2O)(CH3COO)(P2W17O61)}2]16.

Reaction of the trilacunary Wells-Dawson anion {α-P2W15O56}12- with ErIII ion in a 1 M LiOAc/HOAc buffer (pH 4.8) solution produces a dinuclear erbium(III) substituted sandwich-type structure [{Er(H2O)(CH3COO)(P2W17O61)}2]16- (1). The isolated compound was structurally characterized using single crystal and powder X-ray diffraction, FTIR spectroscopy, mass spectrometry and thermogravimetric analysis. The electrochemical, electrocatalytic, photoluminescence and magnetic properties of 1 were investigated.

Synthesis, characterization and in vitro antibacterial mechanism study of two Keggin-type polyoxometalates.

In this article, two Keggin-type polyoxometalates [Co(L)2]3[PMo12O40] (1) and [Co(L)2]3[PW12O40] (2) (HL = 2-acetylpyrazine thiosemicarbazone) were prepared and fully characterized. The compounds are stable in aqueous solution with different pH values and show superior antibacterial activity against Escherichia coli (E. coli: minimal inhibitory concentration (MIC) = 0.00375, 0.12 µg/mL), Agrobacterium tumefaciens (A. tumefaciens: MIC = 0.06, 0.12 µg/mL), Bacillus subtilis (B. subtilis: MIC = 0.015, 0.06 µg/mL) and especially for Staphylococcus aureus (S. aureus: MIC = 0.00048, 0.015 µg/mL) for 1 and 2, respectively. The time kill studies showed the entire killing of specific bacteria during 4 to 8 h. In addition, the possible antibacterial mechanism of compound 1 was explored systematically. The experimental results proved that cell wall/membrane damage, leakage of protein, inhibition of respiratory chain dehydrogenases activity, enhancement of intracellular reactive oxygen species (ROS) and depletion of glutathione (GSH) were the potential causes of bacteria death.

Effective inhibitory activity against MCF-7, A549 and HepG2 cancer cells by a phosphomolybdate based hybrid solid.

A novel Strandberg type polyoxomolybdate based organic-inorganic hybrid solid, [{4,4'-H2bpy}{4,4'-Hbpy}2{H2P2Mo5O23}]·5H2O (1) has been synthesized and structurally characterized by the single crystal X-ray diffraction technique. The structure consists of a discrete type phosphomolybdate cluster, [H2P2Mo5O23]4-, connected with three protonated 4,4'-bipyridine molecules by strong hydrogen bonding interactions. The In vitro anti-tumoral activity of compound (1) was tested against human breast cancer (MCF-7), human lung cancer (A549) and human liver cancer (HepG2) cells. The Strandberg type cluster was used against the MCF-7 and A549 cancer cells for the first time hitherto. It shows considerable inhibitory effect with IC50 values of 33.79 µmol L-1, 25.17 µmol L-1, and 32.11 µmol L-1 against HepG2, A549 and MCF-7 respectively. The anti-tumoral activity of 1 was also found to be comparable with that of a routinely used chemotherapeutic agent, methotrexate (MTX), with an IC50 value of 42.03 µmol L-1 for HepG2, 26.93 µmol L-1 for A549 and 49.79 µmol L-1 for MCF-7. The anti-proliferation activity is mediated by the arrest of the A549 and HepG2 cells in the S phase and MCF-7 in the G2/M phase of the cell cycle as suggested by flow cytometry. Results suggest that apoptosis and necrosis pathways ultimately lead to the death of the cancer cells.

Folin-Ciocalteu Assay Inspired Polyoxometalate Nanoclusters as a Renal Clearable Agent for Non-Inflammatory Photothermal Cancer Therapy.

Similar to translated thermal ablative techniques in clinic, the occurrence of cellular necrosis during tumor photothermal therapy (PTT) would induce inflammatory responses that are detrimental to therapeutic outcomes. Inspired by the well-known colorimetric Folin-Ciocalteu assay, monodispersed and renal-clearable tungsten (W)-based polyoxometalate nanoclusters (W-POM NCs, average diameter of around 2.0 nm) were successfully obtained here through a facile redox reaction with natural gallic acid in alkaline aqueous solution. Apart from excellent stability in the form of freeze-dried powder, the as-prepared W-POM NCs occupied considerable biocompatibility toward normal cells/tissues both in vitro and in vivo, since no obvious toxicities were observed by treating female Balb/c mice with concentrated W-POM NCs during the 30 day post-treatment period. More importantly, W-POM NCs exhibited not only considerable near-infrared (NIR) light absorption (coloration effect originated from the existence of electron-trapped W5+) for efficient PTT but also impressive anti-inflammatory ability (eliminating inflammation-related reactive oxygen species by the oxidation of W5+ into W6+ state) to achieve better therapeutic outcomes. Thus, our study pioneers the application of POMs for non-inflammatory PTT with expected safety and efficiency.

Towards Covalent Photosensitizer-Polyoxometalate Dyads-Bipyridyl-Functionalized Polyoxometalates and Their Transition Metal Complexes.

A triol-functionalized 2,2'-bipyridine (bpy) derivative has been synthesized and used for the tris-alkoxylation of polyoxometalate (POM) precursors. The resultant POM-bpy conjugates of the Wells-Dawson- and Anderson-type feature a C-C bond as a linkage between the POM and bpy fragments. This structural motif is expected to increase the hydrolytic stability of the compounds. This is of particular relevance with respect to the application of POM-bpy metal complexes, as photocatalysts, in the hydrogen-evolution reaction (HER) in an aqueous environment. Accordingly, Rh(III) and Ir(III) complexes of the POM-bpy ligands have been prepared and characterized. These catalyst-photosensitizer dyads have been analyzed with respect to their electrochemical and photophysical properties. Cyclic and square-wave voltammetry, as well as UV/vis absorption and emission spectroscopy, indicated a negligible electronic interaction of the POM and metal-complex subunits in the ground state. However, emission-quenching experiments suggested an efficient intramolecular electron-transfer process from the photo-excited metal centers to the POM units to account for the non-emissive nature of the dyads (thus, suggesting a strong interaction of the subunits in the excited state). In-depth photophysical investigations, as well as a functional characterization, i.e., the applicability in the HER reaction, are currently ongoing.

Synthesis, structural characterisation, and cytotoxicity studies of Bi, W, and Mo containing homo- and hetero-bimetallic polyoxometalates.

Three new and different homo- and hetero-bimetallic polyoxometalate (POM) species have been synthesised by simple one-pot synthetic methods utilising naturally occurring bismite (Bi2O3) (or Bi(NO3)3·5H2O) and aryl sulfonic acids. The POM species isolated are (NH4)14[Bi2W22O76]·14H2O (1·14H2O), (NH4)[Bi(DMSO)7][Mo8O26]·H2O (2·H2O) and [(NH4)4(Mo36O108(OH)4·16H2O)]·45H2O (3·45H2O). The compounds have been characterised by X-ray crystallography, energy dispersive X-ray spectroscopy (EDX), powdered X-ray diffraction (PXRD), mass spectrometry (ESI-MS), Raman spectroscopy, thermogravimetric (TGA) and ICP analyis. In vitro cytoxicity and proliferation studies conducted on 1 and 3, highlight the low toxicity of these species.

Synthesis, functionalization and properties of uniform europium-doped sodium lanthanum tungstate and molybdate (NaLa(XO4)2, X = Mo,W) probes for luminescent and X-ray computed tomography bioimaging.

A one-pot simple procedure for the synthesis of uniform, ellipsoidal Eu3+-doped sodium lanthanum tungstate and molybdate (NaLa(XO4)2, X  = W, Mo) nanophosphors, functionalized with carboxylate groups, is described. The method is based on a homogeneous precipitation process at 120 °C from appropriate Na+, Ln3+ and tungstate or molybdate precursors dissolved in ethylene glycol/water mixtures containing polyacrylic acid. A comparative study of the luminescent properties of both luminescent materials as a function of the Eu3+ doping level has been performed to find the optimum nanophosphor, whose efficiency as X-ray computed tomography contrast agent is also evaluated and compared with that of a commercial probe. Finally, the cell viability and colloidal stability in physiological pH medium of the optimum samples have also been studied to assess their suitability for biomedical applications.

Cobalt- and Nickel-Containing Germanotungstates Based on Open Wells-Dawson Structure: Synthesis and Characterization of Tetrameric Anion.

Two transition-metal-substituted compounds K10H10{[Co(H2O)2]2[Co(H2O)3]2(Ge4W36O130)}·32H2O (1Co) and K10H10{[Ni(H2O)2]2[Ni(H2O)3]2(Ge4W36O130)}·32H2O (2Ni), have been successfully synthesized, both of which consist of the S-shaped tetrameric structure {Ge4W36} constructed from trivacant Keggin-type germanotungstate precursor K8Na2[ A-α-GeW9O34]·25H2O. These compounds were characterized by single crystal X-ray diffraction crystallography, X-ray powder diffraction (XRD), Raman spectra, thermogravimetric analysis (TGA), electrochemistry, and IR spectra. In addition, the UV spectra and the electrospray-ionization mass spectra (ESI-MS) were employed to investigated the stable pH value range of 1Co and 2Ni in aqueous solution.

A novel method to construct a 3D FeWO4 microsphere-array electrode as a non-enzymatic glucose sensor.

As the special sensor for glucose detection, a non-noble-metal nanoarray architecture is extremely attractive due to its easy accessibility to target molecules and more exposed surface area. In this communication, we report the first synthesis of FeWO4 microsphere-array on the three-dimensional (3D) Ni foam (FeWO4 microspheres/NF) as the mimetic electrode for efficient catalytic oxidation of glucose in an alkaline medium. When used as an artificial analog glucose sensor, the result of the present sensing system can also be calculated with a sensitivity of 2810 µA mM cm-2, a linear range from 0.04 mM to 2 mM and a detection limit up to 1.4 µM (S/N = 3). This glucose sensor with satisfactory stability and reproducibility can also be applied to the detection of glucose in human serum. As a promising sensing platform, this proposed 3D FeWO4 microspheres/NF may open a new strategy for pursuing electrochemical detection of biomolecules.

Unraveling the Self-Assembly of Heterocluster Janus Dumbbells into Hybrid Cubosomes with Internal Double-Diamond Structure.

Cubosomes are bicontinuous cubic-phase particles generated by amphiphile self-assembly with bicontinuous cubic phases, which creates an intricate network of interconnected nanochannels that endow these materials with special functions for advanced applications. On the other hand, clusters are an attractive class of molecules that exhibit intriguing functions and properties that differ from those of atoms and nanoparticles. Inspired by lipid self-assembly and attracted to the new functionalities of clusters, we prepared special heterocluster Janus dumbbells (HCJDs) composed of dissimilar nanoclusters: namely, a polyoxometalate and a polyhedral oligomeric silsesquioxane. HCJDs resemble conventional amphiphiles and, as such, they self-assemble in solution into faceted hybrid cubosomes via the transformation of vesicles into spongelike aggregates. Multiple mechanisms that lead to equilibrium, including molecular self-assembly, vesicle accumulation, membrane fusion, inner-structure reorganization, and cubic crystal growth, contributed to the overall process. On the basis of these results, we proposed a strategy for self-assembly-from basic molecular design that goes beyond traditional amphiphiles to the construction of micro- or nanomaterials with hierarchical structures and advanced functions.

Substitution Effect on the Charge Transfer Processes in Organo-Imido Lindqvist-Polyoxomolybdate.

Two new aromatic organo-imido polyoxometalates with an electron donor triazole group ([n-Bu4N]2[Mo6O18NC6H4N3C2H2]) (1) and a highly conjugated fluorene ([n-Bu4N]2[Mo6O18NC13H9]) (2) have been obtained. The electrochemical and spectroscopic properties of several organo-imido systems were studied. These properties were analysed by the theoretical study of the redox potentials and by means of the excitation analysis, in order to understand the effect on the substitution of the organo-imido fragment and the effect of the interaction to a metal centre. Our results show a bathochromic shift related to the charge transfer processes induced by the increase of the conjugated character of the organic fragment. The cathodic shift obtained from the electrochemical studies reflects that the electronic communication and conjugation between the organic and inorganic fragments is the main reason of this phenomenon.

Polyoxometalates as promising enzyme mimics for the sensitive detection of hydrogen peroxide by fluorometric method.

Polyoxometalates (POMs) have been proven to possess intrinsic peroxidase-like activity. However, by far, most of POMs with intrinsic peroxidase-like activity are stable at acid aqueous. Herein, we firstly utilized Na10[α-SiW9O34] with the peroxidase-like property in basic pH condition to build a CdTe quantum dots (QDs)-based fluorometric method for detection of hydrogen peroxide. In the CdTe QDs stable pH value, Na10[α-SiW9O34] can catalyze the decomposition of H2O2 into·OH radicals that could efficiently quench the fluorescence of CdTe QDs. The limit of detection in this system were 3.8 nmol/L. The RSD of detection were range from 0.88% to 2.78%. And the linear range of H2O2 is from 7.8 × 10-9 to 2.5 × 10-7 mol/L. The rate of recovery of sample addition was between 93.99% and 110.02%. The results not only built a simple, sensitive and easy handing assay but also enlarge the POMs' analytic application field.

A novel 3D heteropoly blue type photo-Fenton-like catalyst and its ability to remove dye pollution.

A environment-friendly 3D inorganic heteropoly blue (HPB) Ba2Na2 [HPWV4WVI8O40]·26H2O was directly synthesized by hydrothermal method and characterized by means of ICP, IR, XPS, X-ray single crystal and X-ray powder diffraction. It was an efficient heterogeneous photo-Fenton-like catalyst to degrade anionic dye methyl orange under visible light irradiation. It removed cationic dyes methylene blue in neutral environment and rhodamine B in acidic condition via flocculation. The removal efficiency of methylene blue and rhodamine B by flocculation was more than 95%. Moreover, it could degrade methyl orange and flocculate rhodamine B at the same time. For MO and MO-RhB solutions, the degradation rates of MO in 60 min were 85.5% and 49.1%, respectively. Furthermore, the possible pathways for the production of active species in the MO degradation reaction were discussed. This is the first HPB constructed with 4e-reduced phosphotungstate, Ba and Na ions, having the properties of photo-Fenton-like catalyst and flocculant.

Supramolecular Copolymerization of Short Peptides and Polyoxometalates: toward the Fabrication of Underwater Adhesives.

Peptide assembly has reached exquisite levels of efficiency in the creation of bioactive materials. However, we have not yet been able to take what we have learned from peptide assembly to develop a general strategy for the fabrication of biomimetic underwater adhesives, which retain significant advantages as medical glue for clinical treatment. Herein we report a simple approach to prepare peptide-based adhesives through the supramolecular polymerization of cationic peptides drove by polyoxometalates (PMs). Mass spectra, Fourier-transform infrared spectra and 183W NMR spectra confirmed the structural integrity of peptides and PMs during the coassembly process. Scanning electron microscopy demonstrated that the multivalent interactions between peptides and polyoxometaltes led to the formation of robust 3D network structures. The rheological study revealed that the peptide/PM assemblies exhibited mechanically rigid gel-like behavior and self-healing property. Interestingly, the assemblies showed the capacity to adhere various wet solid materials under waterline. The shear strength of the peptide-based adhesives are stronger than that of the commercially available fibrin glue. This finding is exciting and serves to expand our capability of the fabrication of peptide-based materials.

Bottom-up synthesis of WS2 nanosheets with synchronous surface modification for imaging guided tumor regression.

Two-dimensional transition metal dichalcogenides (TMDs) have been receiving great attention as NIR photothermal transducing agent in tumor photothermal therapy. Keeping in mind the low efficiency of the conventional top-down exfoliated 2D TMDs and the complexity of their surface modifications, we herein proposed a bottom-up strategy for the one-pot hydrothermal and controlled synthesis of surface polyvinyl pyrrolidone (PVP) modified WS2 nanosheets. The material design was based on the chelating-coordinating effect between the lone pair electrons of oxygen of PVP carbonyl group and the unoccupied orbital (5d orbitals) of tungsten. The WS2 nanosheets with synchronous surface PVP grafting showed an excellent photothermal conversion performance, while the surface anchored PVP guaranteed its colloidal stability. Moreover, the strong X-ray attenuation ability and near-infrared (NIR) absorbance of WS2-PVP360kDa enabled the sensitive in vitro and in vivo computed tomography and photoacoustic imaging. The WS2-PVP360kDa nanosheets were biocompatible and exhibited promising in vitro and in vivo anti-cancer efficacy. Findings in this report may greatly promote the design of colloidal stable and biocompatible 2D TMDs and their future clinical translations. STATEMENT OF SIGNIFICANCE: A bottom-up strategy for the one-pot and controlled synthesis of surface polyvinyl pyrrolidone (PVP) modified WS2 nanosheets was proposed for the first time. By hydrothermally treating the mixture solution of tetrathiotungstate and PVP, Owing to the chelating-coordinating effect between the lone pair electrons of oxygen of PVP carbonyl group and the unoccupied orbital (5d orbitals) of tungsten, PVP was synchronously graphed on WS2-PVP nanosheets surface. The formed WS2-PVP nanosheets were colloidal stable, biocompatible, and exhibited promising computed tomography, photoacoustic imaging and tumor photothermal therapy efficacy both in vitro and in vivo.

Wet and Functional Adhesives from One-Step Aqueous Self-Assembly of Natural Amino Acids and Polyoxometalates.

Sessile organisms have undergone long-term evolution to develop the unique ability by positioning themselves on wet solid surface through secreting adhesive proteins. The present study reveals that natural amino acid monomers can also exhibit similar adhesion capacity. This kind of biomimetic adhesives were created by the one-step aqueous assembly of basic amino acids with assistance of anionic polyoxometalates. The polyoxometalates not only serve as multivalent scaffold to initiate the supramolecular cross-linking of amino acid molecules, but also function as a redox component, bestowing the wet adhesives with electrochromic features.

Synthesis and evaluation of pyridinium polyoxometalates as anti-HIV-1 agents.

The unique properties of polyoxometalates, such as molecular polarity, redox potential, surface charge distribution, shape and acidity, influence their response of recognition to targeted biological macromolecules. By using PM-19 (K7PTi2W10O40) as a lead-compound, a series of novel pyridinium polyoxometalates (A7PTi2W10O40), which hadn't been reported in literatures, were designed and synthesized. The evaluation was conducted using the single-cycle pseudovirus infection assay (TZM-bl assay), CCK-8 method was used for determining the cytotoxicity. The results indicated that the designed pyridinium polyoxometalates had a lower toxicity to TZM-bl cells, and showed higher inhibitory activity against HIV-1 virus.