Inorganic Clusters Research Articles

From Solid-State Cluster Compounds to Functional PMMA-Based Composites with UV and NIR Blocking Properties, and Tuned Hues.

New nanocomposite materials with UV-NIR blocking properties and hues ranging from green to brown were prepared by integrating inorganic tantalum octahedral cluster building blocks prepared via solid-state chemistry in a PMMA matrix. After the synthesis by the solid-state chemical reaction of the K4[{Ta6Bri12}Bra6] ternary halide, built-up from [{Ta6Bri12}Bra6]4- anionic building blocks, and potassium cations, the potassium cations were replaced by functional organic cations (Kat+) bearing a methacrylate function. The resulting intermediate, (Kat)2[{Ta6Bri12}Bra6], was then incorporated homogeneously by copolymerization with MMA into transparent PMMA matrices to form a brown transparent hybrid composite Ta@PMMAbrown. The color of the composites was tuned by controlling the charge and consequently the oxidation state of the cluster building block. Ta@PMMAgreen was obtained through the two-electron reduction of the [{Ta6Bri12}Bra6]2- building blocks from Ta@PMMAbrown in solution. Indeed, the control of the oxidation state of the Ta6 cluster inorganic building blocks occurred inside the copolymer, which not only allowed the tuning of the optical properties of the composite in the visible region but also allowed the tuning of its UV and NIR blocking properties.

Hydrogen-Bonded Framework of a Polyanionic Cluster and Its Growth from 2D to 3D for Dual-Selective Adsorption and pH-Controlled Oxidation.

For fabricating a hydrogen-bonded framework with a stabilized hybrid structure for versatile functional properties, an inorganic polyanionic cluster that bears covalently grafted organic groups for hydrogen bond connection is synthesized. By modifying two guanine groups into a disklike polyoxometalate [Mn(OH)6Mo6O18]3- on both sides symmetrically, a polyanionic hybrid building block is obtained. With the cluster serving as a bridge and the grafted guanine unit serving as the binding sites, a polyoxometalate built-in hydrogen-bonded framework in the form of a square lattice shape within a two-dimensional plane has been fabricated as a single-layer assembly. In a further step, the counterion connection and hydrophilic/hydrophobic effect are used to drive the growth of layered framework assembly along the perpendicular direction. The resulting cluster-embedded framework possesses permanent porosity and inner-layer ionic characteristics after activation, which allows the framework to exhibit both high charge-/size-selective adsorption of organic cations and pH-controlled catalytic oxidation of methionine via the charged property.

Direct wiring of redox cofactors onto gold electrodes via inorganic iron-sulfur clusters enhances charge transport

Inorganic iron-sulfur clusters (Fe–S) have emerged as potential electrode anchors and electron shuttles for enzymatic biosensor systems involving nicotinamide adenine dinucleotide (NAD) cofactor. In this work, we report how other cofactors that include nicotinamide adenine dinucleotide phosphate (NADP), flavin adenine dinucleotide (FAD), pyrroloquinoline quinone (PQQ), and coenzyme-Q10 (CoQ10), electrochemically respond to iron-sulfur mediated gold electrodes. Here, select redox cofactors were tethered onto gold electrode supports via inorganic Fe–S (FeS, FeS2, Fe2S3, Fe3S4) and organic Fe–S (Ferredoxin), using the layer-by-layer self-assembly. A combination of docking simulations, secondary ion mass spectrometry, and Fourier-transform infrared spectroscopy revealed the formation of iron carbonyl bonds between FeS and NAD, leading to electrochemical interactions between Fe–S and the redox cofactors. Electrochemical studies confirmed both inorganic and organic iron-sulfur molecules can anchor cofactors onto the gold electrode supports. Up to a 300% increase in anodic peak currents was observed when the inorganic Fe–S replaced the organic counterpart, Ferredoxin, to wire the cofactors onto the gold electrodes. Electrode kinetic measurements revealed the reversible and quasi-reversible behavior of the inorganic and organic Fe–S electrodes, respectively. Reductive desorption studies indicated Fe3S4 closely followed by FeS, forming robust wiring associations with gold by displaying the highest surface coverage, desorption power, and the lowest resistance. Consequently, the inorganic iron-sulfur clusters facilitate an effective method for fabricating enzymatic biosensors for many analytes based on the enzyme-cofactor combination.

Polyoxometalate-Enhanced 3D-Printed Supercapacitors.

The contemporary critical energy crisis demands the fast and cost-effective preparation of supercapacitors to replace old-fashioned batteries. 3D-printing has been established as a fast, cheap, and reliable new manufacturing technique that enables the preparation of such devices.. Unfortunately, carbon-based filaments used in 3D printing lack the necessary electrical properties to build supercapacitors by themselves and have to be combined with other materials to reach their full potential. In this study, carbon-based 3D-printed carbon electrodes (3D-PCE) have been combined with two polyoxometalates (that share the same redox cluster) by drop casting of the inorganic cluster mixed with a conducting slurry. The modified electrodes show higher capacitances than reference carbon electrodes showing the exceptional properties of the polyoxometalates. Moreover, the different nature of the polyoxometalate counter ions allows for their distinct deposition, giving rise to a different coverage of the surface of the 3D-PCE. The different coverage and the nature of the interaction of the counter ion with the electrolyte significantly modify the capacitance and resistance of the materials, playing a key role that should not be overlooked during their preparation.

Construction of dual sulfur sites in metal–organic framework for enhanced mercury(II) removal

Highly efficient removal of mercury ion (Hg2+) from aqueous solution is a serious concern. Herein, a novel metal–organic framework (MOF) containing dual sulfur sites was successfully constructed via an in-situ method. Different with previous reports, thiophene and thiol sites were simultaneously introduced via organic linker and inorganic cluster, resulting in high-density sulfur sites. The composition and porosity of the newly synthesized DUT-67-SH (DUT, Dresden University of Technology) were systematically characterized. Based on abundant sulfur sites and strong host–guest interaction, DUT-67-SH exhibits a high adsorption capacity (370.2 mg g−1) and rapid adsorption kinetics (∼3 min for equilibrium). Excellent separation selectivity, regenerability, and applicability under wide acidic pH range were further confirmed. Mechanism analysis suggests that the chemical bonding between sulfurs and Hg2+ is the main driven force. Thus, our work demonstrates that DUT-67-SH is a potential adsorbent for Hg2+, and more importantly, provides a new insight for introducing high-density sulfur sites in MOFs.

Multiscale Isomerization of Magic-Sized Inorganic Clusters Chemically Driven by Atomic-Bond Exchanges

Multiscale Isomerization of Magic-Sized Inorganic Clusters Chemically Driven by Atomic-Bond Exchanges

The Physicochemical Structure of Inorganics in PIM-1/Alox Hybrid Membranes Synthesized Via Vapor Phase Infiltration (VPI)

Polymers of intrinsic microporosity (PIMs) represent a unique class of polymer membranes defined by their inherent microporosity, leading to excellent separations ability. However, the poor solvent stability of these organic membranes limits their use for organic solvent separations. Vapor phase infiltration (VPI) is an emerging technique adapted from atomic layer deposition (ALD) processes that infiltrates inorganic clusters into polymeric materials, generating hybrid organic-inorganic materials with improved chemical stability. VPI treated polymer of intrinsic microporosity 1 (PIM-1) has shown dramatically improved resistance to solvent dissolution while maintaining its microporosity, making it a much more robust membrane. However, the lack of clarity around the structure of the inorganic clusters within VPI synthesized hybrid materials limits the ability to design these hybrid membranes to optimize potential trade-offs between chemical stability, permeance, and separation performance.Currently, most VPI literature refers to the inorganic components within the hybrid as “metal oxides” or “MOx”. This oversimplification does not fully describe the possible cluster structure or inorganic-to-organic bonding characteristics likely present in these hybrid structures. Moreover, the atomic-scale and long-range disorder of these inorganic clusters make them difficult to describe with traditional methods used for inorganic crystals or polymeric solids. Thus, a more sophisticated understanding of the inorganic structure is needed to inform both process and function design of these hybrid materials. This talk will discuss combined experimental and computational efforts to clarify the structure of inorganic clusters in VPI treated PIM-1/AlOx membranes. XPS and FTIR in conjunction with DFT calculations indicate that the final inorganic species is an oxyhydroxide species. Further, solid state NMR suggests the final inorganic cluster is a 6-coordinate species that is at least dimerized, with water molecules coordinating to the structure to fill out the coordination sphere. DFT calculations validate this claim as the lowest energy structure compared to the monomer form as well as other aluminum oxyhydroxide species. This interdisciplinary work explores the structural characteristics of PIM-1/AlOx hybrid membranes and its impact on the VPI treated material properties such as solvent stability.

Optimizing Aluminum Oxyhydroxide Vapor Phase Infiltration for the Vapor Phase Mordanting of Natural Dyes to Polyester Fabrics

Industrial textile dyeing and finishing processes are a significant environmental concern producing large quantities of wastewater that require significant treatment to remove unused synthetic chemicals. Polyester fabrics in particular utilize high temperatures and chemical carrier agents in their dyeing processes. In this work, we present a method for attaching natural dye materials derived from madder root to polyethylene terephthalate fabrics via the introduction of aluminum oxyhydroxides through vapor phase infiltration. Vapor phase infiltration (VPI) is an emerging polymer modification technique that exposes a polymer to metalorganic precursors that diffuse into the polymer and become entrapped as inorganic clusters. The resulting hybrids have unique properties of both organic and inorganic materials. The VPI process has found significant use in modifying the properties of textile materials including their mechanical and optical properties. Here, without VPI treatment, the PET fabric cannot be dyed with this natural dye. This talk will discuss how controlling the inorganic loading of hybrid AlOx-PET fabrics infiltrated with trimethylaluminum (TMA) and co-reacted with water vapor at 80 ˚C and 140 ˚C can optimize fabrics for dyeability while minimizing impact on key fabric mechanical properties. At low temperatures (80 ˚C) the resulting hybrid contains inorganic clusters not strongly bound to the polymer chain while at high temperatures (140 ˚C) the inorganic is chemically bound via the carbonyl group. Inorganic loading was controlled by varying the dose pressure of TMA (moles of TMA) and fabric mass (moles of carbonyl functional group) during VPI and quantified using thermogravimetric analysis (TGA). The resulting hybrid AlOx-PET fabrics had various inorganic loadings from one weight percent aluminum oxyhydroxide to above twenty weight percent. The hybrid fabrics were then dyed with Alizarin (derived from madder root) and the dye absorbance was quantified with UV-Vis spectroscopy. At low inorganic loadings for both temperatures, the strength of color varied with inorganic content, but a steady-state absorbance was reached at around 1.8 percent inorganic loading. At these low inorganic loadings, the hybrid fabrics maintain key mechanical behaviors such as stiffness (as measured by drape) which is seen to increase significantly with additional inorganic loading. In addition to optimizing strength of color and fabric stiffness, the time to dye saturation was also explored by varying dye times and quantifying with UV-Vis. By exploring dye saturation curves for different inorganic loadings and infiltration temperatures, kinetic information was gathered to further optimize this dyeing process for industrialization. Overall, using VPI as a vapor phase mordanting process to fix natural dyes to PET fabrics illustrates the impact that even small quantities of the vapor deposited inorganic can create enough of a base for dye to adhere to, highlighting the practical use of these fabrics in the field of textile sustainability.

Stability of Metal Hydroxide Organic Frameworks for Oxygen Evolution

The oxygen evolution reaction (OER) is central to storing electrical energy via chemical bonds in energy carriers and fuels through reactions such as electrochemical water splitting to produce hydrogen, CO2 reduction for CO and liquid hydrocarbons, and nitrogen to ammonia. While there has been considerable work towards the engineering of inexpensive yet highly active OER catalysts, current state-of-the-art materials are still at least an order of magnitude less active than oxygen evolving complexes found in biological systems that intricately combine inorganic metal-oxo clusters with organic ligands.1 As a result, metal organic frameworks (MOFs) have drawn considerable attention as hybrid organic-inorganic systems that can potentially mimic the unique structure of biological oxygen evolving complexes. Recently, metal hydroxide organic frameworks (MHOFs),2 a new class of MOFs that combine layered hydroxides with aromatic carboxylate linkers that stabilize the structure via π-π interactions, have been shown to display three times the tunability of layered hydroxides, offering extensive opportunities for further engineering of its electrochemical properties for numerous applications. However, the long-term stability of these material during OER is still unclear, which would be paramount to understand for further rational design of this class of material.In this study, we investigated Ni-based MHOFs with carboxylate linkers of varying π-π interaction strengths to understand how these differences affect the electrochemical stability of these materials during OER. We observed that the MHOFs all undergo activation during OER leading to two orders of magnitude increase in OER activity, where the MHOFs with weaker π-π interaction strengths tend to transform at a faster rate than the MHOFs with stronger π-π interaction strengths. We further characterized the MHOFs using a wide range of analytical techniques, including scanning transmission electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and hard x-ray absorption spectroscopy, before and after extended OER cycling and galvanostatic tests to understand the transformed phase, which suggested that while the bulk structure largely remains unchanged, the surface undergoes significant restructuring into a Ni(OH)2-like phase during OER. Using operando UV-vis and Raman spectroscopy measurements on the MHOFs during OER to understand the factors that induce the transformation process, we found that there was a clear link between the Ni2+/3+, 4+ redox couple observed around 1.4 VRHE and a loss in the carboxylate organic linkers for the linkers with weak π-π interactions. However, for the MHOFs synthesized with linkers exhibiting strong π-π interaction strengths, there were smaller changes to the overall material during OER, suggesting that the bulk stability of these materials is largely dictated by the linker interaction strength and activation are primarily only surface transformations. These results directly demonstrate that linker selection also plays a key role in the stability MOFs under electrochemical conditions and are pertinent for rational design and understanding of the stability and activity of hybrid organic-inorganic materials as electrocatalysts.

Investigating the Thermo-Oxidative Degradation and Operational Limits for Hybrid AlOX–PET Fabrics Created Via Vapor Phase Infiltration (VPI)

In vapor phase infiltration (VPI), vapor phase metalorganic precursors are diffused into polymers and further reacted with water vapor to form hybrid organic-inorganic materials. Hybrid materials created through VPI have shown utility in industrially relevant applications including membranes for chemical separation, photovoltaics, and catalysis. VPI can be conducted at different temperatures, with each processing temperature resulting in different chemical states that alter the properties of the hybrid material. In this project, polyethylene terephthalate (PET) fabrics are infiltrated with a trimethylaluminum (TMA) precursor and co-reacted with water vapor at a range of infiltration temperatures (60-140 ˚C) to create hybrid AlOX - PET fabrics. The purpose of this project is to develop a set of thermal operational limits for these hybrid organic-inorganic materials and translate techniques for thermal characterization from the textile community to the VPI community. Thermo-oxidative degradation for the hybrid fabrics was quantified through changes in degradation temperature and activation energies. Thermogravimetric analysis (TGA) was employed to quantify inorganic loadings (~20 weight percent inorganic), degradation temperatures, and the activation energy for degradation using the Flynn/Wall/Ozawa (FWO) method for decomposition kinetics. Most hybrid fabrics demonstrated lower degradation temperatures than neat PET, except for the fabric infiltrated at 140˚C which had increased degradation temperatures. Activation energies for the first thermal-oxidative degradation event for the 80˚C, 100˚C, and 140˚C fabrics decreased by a range of 62˚C to 84˚C compared to neat PET, while the 120˚C fabric’s activation energy slightly increased by 10˚C. Additionally, a new degradation event occurred for fabrics infiltrated at low temperatures which was explored through FTIR characterization and attributed to structural rearrangements of the inorganic component. Overall, this work demonstrates how VPI process conditions alter both the organic-to-inorganic chemical binding as well as the inorganic cluster structure in these hybrids and how these structural features affect thermophysical operational limits of the material.

Boosting Blue Emission of Organic Cations in a Sn(IV)-Based Perovskite by Constructing Intermolecular Interactions.

Improving the photoluminescence (PL) efficiency of organic luminescent molecules is still a great challenge. Herein, a novel zero-dimensional Sn(IV)-based halide (C9H8N)2SnCl6 is prepared by assembling inactive quinoline cations and stable [SnCl6]2- polyhedra. Experimental characterizations and theoretical calculations show that the blue emission of (C9H8N)2SnCl6 centered at 433 nm is derived from the organic cations. Surprisingly, the PL efficiency of the as-prepared halide is nearly 50 times higher than that of the organic precursor and exhibits ultrahigh stability. Structural analysis shows that the introduction of inorganic clusters regulates the stacking mode of organic components and forms hydrogen bonds. This strong intermolecular interaction enhances the structural rigidity of (C9H8N)2SnCl6, inhibits concentration quenching and vibrational dissipation, and thus significantly improves the PL efficiency and stability of the organic cations. This work provides an important way to improve the PL performance and stability of organic species by constructing efficient intermolecular interactions.

A 1D helical eco-friendly Mn(II) halide coordination polymer: Luminescent properties involving resonant energy transfer and magnetic characterization

In the present work, we discuss the synthesis of nontoxic Mn(II) halide coordination polymer and explore the potential light emission properties for solar-cell devises through experimental and computational studies. The crystal structure was unveiled through Single Crystal Diffraction, whereas physical properties were investigated by means of thermal, spectroscopic, magnetic, optical and photoluminescence measurements. The observed left-right handed helical structure is built up from an infinite 1-D chains of Mn(II) octahedra. The polymeric network is stabilized through inter-molecular hydrogen bonding interactions and π···π face-to-face interactions. Furthermore, ferro-antiferromagnetic ordering has been proven through magnetic measurements. A deep investigation of the photoluminescence study reveals the presence of a bright bluish light emission with corresponding CIE color coordinates of (0.27, 0.35), CCT value of 8092 K and a very high CRI value of 96. The origin of this intense light emission is mainly attributed to the occurrence of the resonant energy and charge transfer processes between Triazolate ligand and inorganic Mn–Cl sub-lattices. Such behavior leads to the conversion of Frenkel excitons localized within the organic part to Mott-Wannier excitons localized in inorganic clusters. Based on these results, we strongly believe that the elaborated material can be a promising candidate for eco-friendly electronic applications.

Increased CO2 Affinity and Adsorption Selectivity in MOF-801 Fluorinated Analogues.

The novel ZrIV-based perfluorinated metal–organic framework (PF-MOF) [Zr6O4(OH)4(TFS)6] (ZrTFS) was prepared under solvent-free conditions using the commercially available tetrafluorosuccinic acid (H2TFS) as a bridging ditopic linker. Since H2TFS can be seen as the fully aliphatic and perfluorinated C4 analogue of fumaric acid, ZrTFS was found to be isoreticular to zirconium fumarate (MOF-801). The structure of ZrTFS was solved and refined from X-ray powder diffraction data. Despite this analogy, the gas adsorption capacity of ZrTFS is much lower than that of MOF-801; in the former, the presence of bulky fluorine atoms causes a considerable window size reduction. To have PF-MOFs with more accessible porosity, postsynthetic exchange (PSE) reactions on (defective) MOF-801 suspended in H2TFS aqueous solutions were carried out. Despite the different H2TFS concentrations used in the PSE process, the exchanges yielded two mixed-linker materials of similar minimal formulae [Zr6O4(μ3-OH)4(μ1-OH)2.08(H2O)2.08(FUM)4.04(HTFS)1.84] (PF-MOF1) and [Zr6O4(μ3-OH)4(μ1-OH)1.83(H2O)1.83(FUM)4.04(HTFS)2.09] (PF-MOF2) (FUM2– = fumarate), where the perfluorinated linker was found to fully replace the capping acetate in the defective sites of pristine MOF-801. CO2 and N2 adsorption isotherms collected on all samples reveal that both CO2 thermodynamic affinity (isosteric heat of adsorption at zero coverage, Qst) and CO2/N2 adsorption selectivity increase with the amount of incorporated TFS2–, reaching the maximum values of 30 kJ mol–1 and 41 (IAST), respectively, in PF-MOF2. This confirms the beneficial effect coming from the introduction of fluorinated linkers in MOFs on their CO2 adsorption ability. Finally, solid-state density functional theory calculations were carried out to cast light on the structural features and on the thermodynamics of CO2 adsorption in MOF-801 and ZrTFS. Due to the difficulties in modeling a defective MOF, an intermediate structure containing both linkers in the framework was also designed. In this structure, the preferential CO2 adsorption site is the tetrahedral pore in the “UiO-66-like” structure. The extra energy stabilization stems from a hydrogen bond interaction between CO2 and a hydroxyl group on the inorganic cluster.

Biological Effects of EGCG@MOF Zn(BTC)4 System Improves Wound Healing in Diabetes.

Tea contains high levels of the compound epigallocatechin gallate (EGCG). It is considered an important functional component in tea and has anti-cancer, antioxidant, and anti-inflammatory effects. The eight phenolic hydroxyl groups in EGCG’s chemical structure are the basis for EGCG’s multiple biological effects. At the same time, it also leads to poor chemical stability, rendering EGCG prone to oxidation and isomerization reactions that change its original structure and biological activity. Learning how to maintain the activity of EGCG has become an important goal in understanding the biological activity of EGCG and the research and development of tea-related products. Metal–organic frameworks (MOFs) are porous materials with a three-dimensional network structure that are composed of inorganic metals or metal clusters together with organic complexes. MOFs exploit the porous nature of the material itself. When a drug is an appropriate size, it can be wrapped into the pores by physical or chemical methods; this allows the drug to be released slowly, and MOFs can also reduce drug toxicity. In this study, we used MOF Zn(BTC)4 materials to load EGCG and investigated the sustained release effect of EGCG@MOF Zn(BTC)4 and the biological effects on wound healing in a diabetic mouse model.

Inorganic doped libethenite nanoparticle clusters show high catalytic activity in hydrogen evolution reaction

A noble metal-free Na Al Si doped libethenite nanoparticle clusters were obtained by applying the method of hydrothermal synthesis. The Linear Sweep Voltammetry (LSV) curve of this nanoparticle cluster electrode shows that there is no noble metal in the hydrogen evolution reaction (HER), and it still exhibits good catalytic activity. The catalytic activity of the libethenite nanoparticle cluster is further enhanced after reduction by the amperometric i-t curve method (A i-t C). The electrochemical performance and catalytic mechanism were investigated by the cyclic voltammetry (CV) method. The characterization analysis by XRD, SEM, TEM, EDS, and XPS found that the catalyst was isomorphous with the natural mineral libethenite, but different from the minerals with Cu and P as the main components in nature when the crystal synthesized under hydrothermal conditions was doped. The heterogenous libethenite nanoparticle cluster framework is replaced by more additional Na, Al, and Si elements. Cu and P elements in the libethenite nanoparticle cluster structure are connected through the mineral framework and uniformly distributed in the crystal structure. This structure increases the electrochemical activity of its HER. Due to the interaction of Cu and P, the catalyst exhibits good catalytic performance for HER under acidic conditions. The reduction by the electrochemical i-t curve reduces the consumption of Cu and enhances the stability of the mineral framework.

Spin-Gated Selectivity of the Water Oxidation Reaction Mediated by Free Pentameric CaxMn5-xO5+ Clusters.

We report on the first preparation of isolated ligand-free CaMn4O5+ gas-phase clusters, as well as other pentameric CaxMn5-xO5+ (x = 0-4) clusters with varying Ca contents, which serve as molecular models of the natural CaMn4O5 inorganic cluster in photosystem II. Ion trap reactivity studies with D2O and H218O reveal a pronounced cluster composition-dependent ability to mediate the oxidation of water to hydrogen peroxide. First-principles density functional theory simulations elucidate the mechanism of water oxidation, proceeding via formation of a terminal oxyl radical followed by oxyl/hydroxy (O/OH) coupling. The critical coupling reaction step entails a single electron transfer from the oxyl radical to the accommodating cluster core with a concurrent O/OH coupling forming an adsorbed OOH intermediate group. The spin-conserving electron transfer step takes place when the spin of the transferred electron is aligned with the spins of the d-electrons of the Mn atoms in the cuboidal high-spin cluster isomer. The d-electrons provide a ferromagnetically ordered environment that facilitates the spin-gated selective electron transfer process, resulting in parallel-spin-exchange stabilization and a lowered transition state barrier for the coupling reaction involving the frontier orbitals of the oxyl and hydroxy reactant intermediates.

Effects of trimethylaluminum vapor pressure and exposure time on inorganic loading in vapor phase infiltrated PIM-1 polymer membranes

Vapor phase infiltration (VPI) is a post-polymerization modification method for infusing inorganic clusters into a polymer to create organic-inorganic hybrid materials with properties that are unique from the parent polymer. The properties of these hybrid materials can vary with the amount of VPI generated inorganic loading. However, the relationship between VPI processing conditions and inorganic loading is still not fully understood. In this paper, the effects of VPI dose pressure and exposure time on inorganic loading are explored using the technologically relevant membrane material known as “polymer of intrinsic microporosity 1” (PIM-1). At sufficiently low dose pressures and infiltration times (i.e., before saturation), inorganic loading can be controlled with both vapor pressure and exposure time. However, inorganic loading appears to saturate for this system when the polymer's functional groups become fully populated with bound VPI precursors. These experimental results can be understood with the use of a recently developed reaction-diffusion model for VPI. Critical to applying this model to these post-deposition measurements is re-normalizing the mass loading to the total number of functional groups in the polymer.

The Preyssler-Type Polyoxotungstate Exhibits Anti-Quorum Sensing, Antibiofilm, and Antiviral Activities.

Simple SummaryBesides showing the antibacterial activity of the Preyssler-type polyoxotungstate (POT) P5W30 with the ability to affect MRSA cells, we demonstrated that P5W30 also displays other proprieties, such as anti-quorum sensing and antibiofilm. These are biological activities that are reported for a POT for the first time. Quorum sensing and biofilm facilitate the bacterial colonization, antibiotic resistance and persistence in both the environment and host, and its impairment by POTs can greatly contribute to the control of bacterial infections, such as those caused by multiresistant bacteria. Moreover, antiviral activity was also observed using the enterovirus Qβ. NMR stability studies of P5W30 demonstrate that it remains intact, suggesting its responsibility in the described biological activities. Taken together, our results emphasize the potential biomedical use of POTs, particularly the Preyssler-type POT, to fight antibiotic-resistant MRSA strains and their ability to form biofilm, besides being a promising antiviral agent.The increase in bacterial resistance to antibiotics has led researchers to find new compounds or find combinations between different compounds with potential antibacterial action and with the ability to prevent the development of antibiotic resistance. Polyoxotungstates (POTs) are inorganic clusters that may fulfill that need, either individually or in combination with antibiotics. Herein, we report the ability of the polyoxotungstates (POTs) with Wells-Dawson P2W18, P2W17, P2W15, and Preyssler P5W30 type structures to differently affect Gram-negative and Gram-positive microorganisms, either susceptible or resistant to antibiotics. The compound P5W30 showed the highest activity against the majority of the tested bacterial strains in comparison with the other tested POTs (P2W15, P2W17 and P2W18) that did not show inhibition zones for the Gram-negative bacteria, A. baumanii I73775, E. coli DSM 1077, E. coli I73194, K. pneumoniae I7092374, and P. aeruginosa C46281). Generally, the results evidenced that Gram-positive bacteria are more susceptible to the POTs tested. The compound P5W30 was the one most active against S. aureus ATCC 6538 and MRSA16, reaching <0.83 mg·mL−1 (100 μM) and 4.96 mg·mL−1 (600 μM), respectively. Moreover, it was verified by NMR spectroscopy that the most promising POT, P5W30, remains intact under all the experimental conditions, after 24 h at 37 °C. This prompted us to further evaluate the anti-quorum sensing activity of P5W30 using the biosensor Chromobacterium violaceum CV026, as well as its antibiofilm activity both individually and in combination with the antibiotic cefoxitin against the methicillin-resistant Staphylococcus aureus 16 (MRSA16). P5W30 showed a synergistic antibacterial effect with the antibiotic cefoxitin and chloramphenicol against MRSA16. Moreover, the antibiofilm activity of P5W30 was more pronounced when used individually, in comparison with the combination with the antibiotic cefoxitin. Finally, the antiviral activity of P5W30 was tested using the coliphage Qβ, showing a dose-dependent response. The maximum inactivation was observed at 750 μM (6.23 mg·mL−1). In sum, P5W30 shows anti-quorum sensing and antibiofilm activities besides being a potent antibacterial agent against S. aureus and to exhibit antiviral activities against enteric viruses.

Metal-organic frameworks: A new generation potential material for aqueous environmental remediation

• Metal ion contamination is a major cause of water pollution. • MOFs displayed excellent adsorption performance towards metal ion decontamination. • Brief discussion on types, synthesis and characterisation of MOF materials. • Review of MOF-based nanoadsorbents for metal ion removal from aqueous medium. • Engineering advances and future perspective were highlighted. With the rapid increase in the human population, freshwater availability is decreasing at an alarming rate. A large amount of wastewater is generated every year due to rapid industrialization and agricultural development. Among the various organic and inorganic pollutants, metal ion contamination is a significant contributor to water pollution, which requires immediate and substantial remediation due to its high toxicity and detrimental effect on the environment and human health. Adsorption techniqueshave shown promising scope and are commonly used for water remediation and removal of metal ion pollutants. Recently, metal–organic framework (MOF), a novel three-dimensional porous and crystalline organic–inorganic cluster complex, has attracted increased attention for the adsorption of metal ion contaminants from an aqueous solution. These materials show unique properties such as high specific surface area (SSA), high and tunable porosity, flexible topology, and chemical functionality. This article compiles and reviews the recent progress in MOF-based materials as superior adsorbent materials for metal ion removal. A brief discussion of the various synthesis methods, characterization techniques, and a comparative study of the different MOF-based adsorbents and nanoadsorbents (NAs) for metal ion removal from water bodies are summarized. The effect of pH on the adsorption performance of the various MOFs and their selectivity towards specific metal ions in the presence of other metal ions in water has been discussed. The adsorption properties of the MOF-based materials are compared with those of other commonly used adsorbent materials. Finally, the review gives insight into the research gap and limitations of these MOF adsorbents in practical applications and the possible remediation techniques that can be employed for future research opportunities for advanced designing and development of cost-effective and efficient MOF for metal ion remediation.

Reinforced catalytic oxidation of polyoxometalate@charge transfer complex by on-site heating from photothermal conversion

Near infrared (NIR) absorption at low energy region has been demonstrated to devoted to photothermal conversion efficiently. This process provides a possibility for valuable extension in emerging photothermal catalysis following a specific approach of molecular composition. To exploit novel photothermal materials in increasing the catalytic activity of comment catalysts, a typical yet unnoticed charge transfer (CT) complex of 3,3′,5,5′-tetramethylbenzidine (TMBCT) is used here as an on-site heater. Through the electrostatic complexation of cationic CT complex bearing strong NIR absorption with series polyanionic clusters, composite catalysts are prepared. These nano-assembled catalysts in size of 5–10 nm display integrated NIR photothermal effect and highly enhanced catalysis for the mild oxidation of toluene and its derivatives into corresponding alcohols with high conversion and selection. While NIR photothermal stability of TMBCT is maintained, the catalytic activity of inorganic clusters is largely improved. The increments in conversion unattainable under external heating condition are realized and the extension to the mild oxidation of thioethers and olefins into sulfoxides and epoxides with acceptable catalytic recyclability and structural stability are demonstrated. All results from the detailed characterizations figure out the applicability of the NIR photothermal conversion to the catalytic reactions with similar catalytic centers.