Preparation and use of hybrid organic–inorganic catalysts

Various approaches towards the immobilization of molecular homogeneous catalysts are introduced, focusing on catalysts where an organic molecule is attached to the surface of an inorganic support material via a covalent bond forming the so-called hybrid organic–inorganic catalysts. The application of this new class of catalysts in a wide variety of organic reactions is reviewed.     

Weatherability of hybrid organic–inorganic silica protective coatings on glass

Currently, there is a growing interest in the application of silicon-based technologies for the development of advanced hybrid organic–inorganic coatings with strong weatherability. In this study, the sol–gel process is used to prepare such coatings on glass and their resistance to weathering effects is assessed afterwards. Various sols were prepared by mixing a silica-based inorganic matrix (tetraethyl orthosilicate) with different quantities of silica alkoxides functionalised with various organic groups. Subsequently, the sols were dip-coated onto glass samples at low temperatures without any heat treatment. The coatings prepared were analysed before and after three model ageing tests simulating various weathering parameters. After ageing, the best performing coatings showed good overall homogeneity and transparency (optical microscopy, SEM), improved water repellency and adhesion to the glass substrate (static contact angle measurements, cross-cut tape tests) and no colour or chemical composition changes (UV–VIS, FTIR). Compared with commercial hybrid silica products, the alkyl- and methacryloxy-functionalised silica coatings particularly displayed improved homogeneity, elasticity and barrier properties. Thus, these low temperature coatings, easily applicable to thin films, appear to fulfil the main requirements for the protection of the glass exposed to weathering phenomena.     

An organic–inorganic hybrid nickel-substituted arsenotungstate consisting of three types of polyoxotungstate units

A new organic–inorganic hybrid nickel-substituted arsenotungstate [Na(H₂O)₃]₂[Ni(H₂O)₆]₂[Ni(H₂O)₅]{[Ni₃(dap)(H₂O)₂]₂(H₂W₄O₁₆)}{(α-H₂AsW₆O₂₆)[Ni₆(OH)₂(H₂O)(dap)₂](B-α-HAsW₉O₃₄)}₂·7H₂O (1) (dap = 1,2-diaminopropane) has been hydrothermally synthesized and structurally characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. Crystal data for 1: C₁₈H₁₄₄As₄N₁₂Na₂Ni₂₁O₁₇₆W₃₄, Mr = 11174.92, triclinic, space group P-1, a = 15.004(4) Å, b = 16.357(5) Å, c = 22.070(6) Å, α = 80.458(5)°, β = 79.291(5)°, γ = 72.074(5)°, V = 5030(3) Å³, Z = 1, GOOF = 1.007, R₁ = 0.0703, wR₂ = 0.1670. The skeleton of 1 is a centric nanoscale cluster and is composed of two asymmetric sandwich-type clusters {(α-H₂AsW₆O₂₆)[Ni₆(OH)₂(H₂O)(dap)₂](B-α-AsW₉O₃₄)}^7? linked by a symmetric cluster {[Ni₃(dap)(H₂O)₂]₂(H₂W₄O₁₆)}⁶⁺. Notably, 1 is an interesting polyoxometalate containing the trivacant Keggin [B-α-AsW₉O₃₄]^9?, hexavacant Keggin [α-AsW₆O₂₆]^11? and tetrameric [W₄O₁₆]^8? units. Magnetic measurements indicate that 1 shows the ferromagnetic interactions within Ni^II centers.     

UV-curable nano-silver containing polyurethane based organic–inorganic hybrid coatings

The preparation of nano-silver containing polyurethane based UV-curable organic–inorganic hybrid coatings that have antibacterial activity is presented in this paper. Trimethoxysilane end-capped bis[(4-β-hydroxyethoxy)phenyl] methyl phosphine oxide urethane was synthesized as a coupling agent and used to improve the compatibility between the organic and inorganic phases of the hybrid coating. Due to its strong antibacterial activity, silver nanoparticles were prepared and added to the nanocomposite formulations. The relationships between the amount of coupling agent and the final coating properties were investigated. The hybrid coatings presented good thermal stability. Tests for abrasion, hardness, gloss, and adhesion of the coatings were also performed. The morphological investigation was performed by SEM to determine the size of the silver nanoparticles. The nano-silver containing coatings exhibited good antibacterial activity against E. coli and S. aureus.     

Synthesis of some novel silicone-imide hybrid inorganic–organic polymer and their properties

Synthesis and properties of poly(imide-siloxane) hybrid polymers (PIS), having alternate diimide and disiloxane units, based on 1,3-bis(succinyl anhydride)1,1,3,3-tetraorganodisiloxane (I or II) have been described. Polymers have been synthesized by the precursor synthesis i.e., poly(amic acid), using siloxanes (I or II) and 4,4′-diaminodiphenylmethane (DDM) or 4,4′-diaminodiphenylsulphone (DDS) in N,N-dimethylacetamide (DMAc) followed by thermal imidization. FT-IR, thermal (TGA and TMA), solvent resistant and dielectric properties of the compounds have also been studied. The glass transition, thermal stability and char yields of these hybrid polymers increased appreciably. These materials also showed very good solvent resistant properties in protic and aprotic solvents.     

Micrometer and nanometer-scale parallel patterning of ceramic and organic–inorganic hybrid materials

This review gives an overview of the progress made in recent years in the development of low-cost parallel patterning techniques for ceramic materials, silica, and organic–inorganic silsesquioxane-based hybrids from wet-chemical solutions and suspensions on the micrometer and nanometer-scale. The emphasis of the discussion is placed on the application of soft-lithographic methods, but photolithography-aided patterning methods for oxide film growth are also discussed. In general, moulding-based patterning approaches and surface modification-based patterning approaches can be distinguished. Lateral resolutions well below 100 nm have been accomplished with some of these methods, but the fabrication of high-aspect ratio patterns remains a challenge.     

Warm white light-emitting diodes using organic–inorganic halide perovskite materials coated YAG:Ce3+ phosphors

This work reports warm white light-emitting diodes (WLEDs) using organic–inorganic halide perovskite materials coated YAG:Ce³⁺ phosphors by a liquid phase synthesis method. The perovskite MAPbBr_3?xI_x-coated YAG:Ce³⁺ phosphors have more red light contribution than YAG:Ce³⁺ phosphors without the perovskite coating. The chromaticity coordinate of white LED with YAG:Ce³⁺ remote phosphor is (x = 0.3134, y = 0.3497) 6359. However, those of MAPbBr_2.5I_0.5 and MAPbBr_2.0I_1.0-coated YAG:Ce³⁺ remote phosphor shift to (x = 0.4220, y = 0.3725) 2908 and (x = 0.4067, y = 0.4028) 3525, respectively. The colors of perovskite-coated samples are more red and warm. Therefore, the perovskite-coated YAG:Ce³⁺ method is useful for warm WLED.     

Polydimethylsiloxane (PDMS)-based antibacterial organic–inorganic hybrid coatings

UV-curable antibacterial organic–inorganic hybrid coatings were prepared by sol–gel method. Triethoxysilane-terminated poly(dimethylsiloxane) (TESi-PDMS) as a new coupling agent to improve the compatibility between organic and inorganic phases was synthesized. PDMS-based urethane methacrylate oligomer was obtained by reacting isophorone diisocyanate with hydroxyethyl methacrylate and hydroxyl-terminated PDMS. The formulations were applied onto polycarbonate panels and then cured by UV radiation. Physical properties of UV-cured free films such as gel content, stress–strain, and conversion of acrylate double bond were examined. In addition, the antibacterial effects of the coatings were investigated. Nanosilver-containing formulations exhibited high antibacterial effect against Escherichia coli and Staphylococcus aureus. Thermogravimetric analysis indicated that thermal stability of the hybrids was significantly higher than the organic polymer. Contact angle measurement showed that addition of silane precursor increased the contact angle from 95° to 110°.     

Robust multifunctional superhydrophobic organic–inorganic hybrid macroporous coatings and films

We demonstrate a facile and efficient method for fabricating multifunctional superhydrophobic organic–inorganic hybrid macroporous coatings and films with robust environmental stabilities involving the electrospinning of phenylsilsesquiazane (PhSSQZ) in the presence of polystyrene (PS). The resulting freestanding PhSSQZ/PS webs, which featured hierarchical fibrous structures with the unique chemical properties of PhSSQZ, provided a practical material with potential uses in many applications including structural coatings, oil–water separation membranes, and high-performance air filters. The materials maintained their fibrous structures and superhydrophobicity even after heat treatment at 600 °C under an ambient atmosphere, which is among the highest level reported up to date for solution-processed superhydrophobic surfaces with soft materials. The solvent resistance and mechanical strength of the PhSSQZ/PS webs were significantly enhanced through the structured siloxane network due to thermally induced hydrolysis of PhSSQZ and condensation of the resulting silanols. The properties of this novel material suggest that the present approach will advance our knowledge and capability to design and develop multifunctional smart materials with robust superhydrophobicity and macroporosity.     

An inorganic–organic hybrid zinc phosphite framework with unusual topology

Employing piperazine (= ppz) as a bridging ligand, a new three-dimensional (3D) inorganic–organic hybrid zinc phosphite framework [Zn₂(HPO₃)₂(ppz)]_n (1) has been synthesized hydrothermally and structurally characterized by single crystal X-ray diffraction. The structure of 1 features a pillared-layer framework with unusual (3,4)-connected dmc topology. The results demonstrate that it is possible to add organic ligands into an open zinc phosphite framework for the construction of hybrid materials.     

Preparation and characterization of photopolymerizable organic–inorganic hybrid materials by the sol-gel method

A series of UV-curable organic–inorganic hybrid materials were prepared by the sol-gel technique and coated onto Plexiglass^® substrate. The effects of the content of EGDMA and the content of the inorganic part on various properties of the coatings, such as tensile strength, hardness, gloss, and cross-cut adhesion, were investigated. It was found that the properties of the coating were improved by the addition of an inorganic part. The thermal properties of the hybrids were enhanced by incorporating silane sol into the organic part. Furthermore, it was found that the coating containing silica had a higher char content at 800 °C than the coating without silica. SEM studies indicated that nanosized (about 50 nm) silica particles were evenly dispersed throughout the organic matrix. A photo-DSC investigation showed that the organic coating polymerized more quickly than the hybrid coating.     

Corrosion protection of aluminum alloy substrate with nano-silica reinforced organic–inorganic hybrid coatings

Organic–inorganic hybrid (OIH) thin films derived from the sol–gel process have emerged as sustainable metal pretreatment alternatives to toxic heavy metal-based systems. In recent years, such OIH systems based on Si, Zr, and Ti have been successfully developed and commercialized for pretreatment of aluminum alloys, galvanized steel, cold-rolled steel, and many other metals and alloys, for improving adhesion and corrosion resistance performance. A variety of approaches are being used to further enhance performance of such OIH systems to match or surpass that obtained from chromate-based systems. In the present study, a novel bis-silane compound has been synthesized and used as a primary sol–gel precursor for OIH coatings. In order to further improve their mechanical and corrosion resistance performance, colloidal nanoparticles have been incorporated. The microstructure of the deposited films as a function of their composition and formation of Si–O–Si structural network has been studied by Confocal Raman spectroscopic technique. The chemical structure of the OIH films has been characterized by FTIR analysis. Electrochemical impedance spectroscopy, DC polarization measurements, and accelerated neutral salt-fog test (ASTM B117) have been used to evaluate corrosion resistance performance of coatings on industrial aluminum alloy AA 3003 H14. Nano-indentation tests of these OIH films have been performed to study the effect of colloidal nanoparticles on coating micro/nano structure and their mechanical properties. The study reveals that colloidal nanoparticles improve the corrosion resistance of OIH coatings by formation of a protective barrier to diffusion of corrosive species to the metal surface. The optimum content of colloidal nanoparticles that can provide best corrosion protection has been determined. Electrochemical study provides useful insight into the significance of interaction between the sol–gel hybrid and silica particles in the corrosion protection mechanism.     

Electrochemical behavior of an inorganic–organic hybrid based on isopolymolybdate anions and ethylenediamine

The one-dimensional inorganic–organic compound, (C₂H₁₀N₂)[Mo₃O₁₀], was synthesized hydrothermally, and characterized by single crystal X-ray diffraction. The compound was used as a bulk-modifier to fabricate a renewable three-dimensional chemically modified carbon paste electrode (Mo-CPE) by direct mixing. The electrochemical properties of (C₂H₁₀N₂)[Mo₃O₁₀]-modified Mo-CPE were investigated with respect to their pH-dependence, stability and electrocatalytic activity. The hybrid material bulk modified Mo-CPE not only displays good electrocatalytic activity toward the reduction of BrO₃ ⁻, IO₃ ⁻, NO₂ ⁻ and H₂O₂, but also exhibits good stability and multiple repeatability by simply polishing on the surface of a wet filter paper, a feature which is important for practical applications.     

Structure and in vivo anticalcification properties of a polymeric calcium–sodium–phosphocitrate organic–inorganic hybrid

This paper describes the synthesis, characterization and crystal structure of an organic–inorganic polymeric hybrid composed of Ca, Na, and phosphocitrate (CaNaPC). CaNaPC is synthesized by reaction of CaCl₂·2H₂O and Na₄(HPC)·3H₂O in water, at pH 2. Its structure is polymeric with Ca(PC)₂(H₂O) “monomers” connected through Na⁺ bridges. The 9-coordinate Ca occupies the center of an irregular polyhedron defined by four phosphate, four carbonyl, and one H₂O oxygens. CaO(C) distances are in the 2.446(2)–2.586(2) Å range. There is a short distance of 2.477(1) Å between Ca and the ester O from C–O–PO₃H₂. All –COOH groups are protonated. There are three dissociated protons per two PC molecules, all coming from –PO₃H₂. Na ions are six-coordinate surrounded by –COOH’s. The anticalcification properties of CaNaPC on plaque growth were studied in vivo using rats as model systems. Na–phosphocitrate is an effective inhibitor, but its effectiveness diminishes when a lower dose is used (9.7 mg as H₅PC), resulting in only 30% plaque reduction. Superior inhibition activity becomes evident by following treatment with CaNaPC, at an equal dose (9.6 mg as H₅PC) giving nearly quantitative (95%) plaque inhibition.     

New high performance waterborne organic–inorganic hybrid materials from UV curing

The third generation glycerol based hyperbranched polyester (HBPE-3G) was synthesized by reacting glycerol and 2,2-bis(hydroxymethyl)propionic acid in a stoichiometric molar ratio. This polyester was used as preparation for waterborne hyperbranched UV cured polyurethane–silica hybrid coatings. The acrylic terminated waterborne coatings were prepared by modifying some of the hydroxyl groups HBPE-3G to acidic groups by reacting with maleic anhydride. The remaining hydroxyl groups were reacted with NCO terminated acrylate. Then the prepolymer was neutralized with triethyl amine and dispersed in water. The waterborne hybrid formulations were prepared by mixing 3, 5 and 10% of trimethoxysilylpropyl methacrylate (TMSPM) into the acrylic terminated waterborne coatings. The films were casted and cured under UV light. The various film properties were studied by XRD, AFM, TGA and DMTA instruments. TGA result suggests that the onset degradation temperature and final mass residue increase with increasing TMSPM concentration. DMTA results show that the storage modulus and glass transition temperature increase for the hybrid formulations with increasing TMSPM concentration. The structural characterization of the hybrid coatings was performed using FTIR spectroscopy. The tensile test demonstrated that the mechanical properties improve with the increasing TMSPM content. Surface morphology was studied by atomic force microscopy (AFM). AFM study revealed that TMSPM was crosslinked homogenously through the polymer matrix. The TGA and DMTA data suggest that higher thermal stability and glass transition temperature (T_g) for the TMSPM hybrid films compared to their pure counterparts were obtained with increasing the TMSPM content.     

Negatively charged organic–inorganic hybrid silica nanofiltration membranes for lithium extraction

Effective extraction of lithium from high Mg~(2+)/Li+ratio brine lakes is of great challenge. In this work, organic–inorganic hybrid silica nanofiltration(NF) membranes were prepared by dip-coating a 1,2-bis(triethoxysilyl)ethane(BTESE)-derived separation layer on tubular TiO_2 support, for efficient separation of LiC l and MgCl_2 salt solutions. We found that the membrane calcinated at 400 °C(M1–400) could exhibit a narrow pore size distribution(0.63–1.66 nm) owing to the dehydroxylation and the thermal degradation of the organic bridge groups. All as-prepared membranes exhibited higher rejections to LiCl than to MgCl_2, which was attributed to the negative charge of the membrane surfaces. The rejection for LiCl and MgCl_2 followed the order: LiCl N MgCl_2, revealing that Donnan exclusion effect dominated the salt rejection mechanism. In addition, the triplecoated membrane calcined at 400 °C(M3–400) exhibited a permeability of about 9.5 L·m~(-2)·h~(-1)·bar~(-1) for LiCl or MgCl_2 solutions, with rejections of 74.7% and 20.3% to LiCl and MgCl_2,respectively, under the transmembrane pressure at 6 bar. Compared with the previously reported performance of NF membranes for Mg~(2+)/Li+separation, the overall performance of M3–400 is highly competitive. Therefore, this work may provide new insight into designing robust silica-based ceramic NF membranes with negative charge for efficient lithium extraction from salt lakes.     

Synthesis and characterization of hybrid organic–inorganic materials based on sulphonated polyamideimide and silica

The preparation of hybrid organic–inorganic membrane materials based on a sulphonated polyamideimide resin and silica filler has been studied. The method allows the sol–gel process to proceed in the presence of a high molecular weight polyamideimide, resulting in well dispersed silica nanoparticles (<50 nm) within the polymer matrix with chemical bonding between the organic and inorganic phases. Tetraethoxysilane (TEOS) was used as the silica precursor and the organosilicate networks were bonded to the polymer matrix via a coupling agent aminopropyltriethoxysilane (APTrEOS). The structure and properties of these hybrid materials were characterized via a range of techniques including FTIR, TGA, DSC, SEM and contact angle analysis. It was found that the compatibility between organic and inorganic phases has been greatly enhanced by the incorporation of APTrEOS. The thermal stability and hydrophilic properties of hybrid materials have also been significantly improved.     

Synthesis,characterization, and ionic conductivity of electrospun organic–inorganic hybrid gel electrolytes

In this work, we described the synthesis of organic–inorganic hybrid gel electrolytes combining electrospinning, sol–gel, and ultraviolet (UV) curing techniques in order to investigate their ionic conductivity properties. First, 3-glycidyloxypropyl trimethoxysilane modified polyamic acid and alkoxysilane functional poly(dimethyl siloxane) were electrospun together. Then, the following thermal imidization, the obtained fiber was cured in the UV curable gel formulation. To improve the interaction between fiber and gel matrix, 3-(trimethoxysilyl)propyl methacrylate was partly hydrolyzed and then used as a bifunctional crosslinker. Finally, the membrane was soaked into 0.5 M LiFP₆ salt solution to obtain organic–inorganic hybrid gel electrolytes. The chemical structure, ionic conductivity, and range of electrochemical stability window of the photocured nanocomposite electrolytes were investigated by using FTIR, thermogravimetric analysis, differential scanning calorimetry, electrochemical impedance spectroscopy, linear sweep voltammetry, and SEM analysis. The acquired results from experiments indicate that a convenient nanocomposite electrolyte for lithium-ion batteries with high electrolyte (Li salt) uptake, adequate conductivity (1.02 × 10⁻³ S cm⁻¹) at ambient temperature and electrochemically stable between 1 and 6 V had been prepared. POLYM. ENG. SCI., 60:619–629, 2020. © 2019 Society of Plastics Engineers     

Hydrothermal syntheses,crystal structures and photocatalytic properties of three POM-templated organic–inorganic hybrid compounds

Three new POM-templated organic–inorganic compounds, Cu₂(3,5-bptp)₂[H₂SiW₁₂O₄₀]·4H₂O (1), Ag₂(3,5-bptp)₂[HPW₁₂O₄₀]·4H₂O (2), [Cu₄(OH)₃Cl(H₂O)₃(4-bpo)₃](SiW₁₂O₄₀)·5H₂O (3) (3,5-bptp = 3,5-bis(3-(pyrid-4-yl)-1,2,4-triazolyl)-pyridine, 4-bpo = 2,5-bis(4-pyridyl)-1,3,4-oxadiazole) were hydrothermally synthesized and characterized by elemental analysis and single crystal X-ray diffraction. Crystal structural analysis indicates that compounds 1 and 2 are isostructural and show one dimensional zigzag chains with [H₂SiW₁₂O₄₀]^2 − as guest molecules. Compound 3 is two dimensional sheets constructed from [Cu₄(OH)₃Cl(H₂O)₃] clusters and 4-bpo ligands with [SiW₁₂O₄₀]^4 − as guest molecules. Furthermore, the photocatalytic degradation of methyl orange (MO) with 3 was studied under visible light irradiation, indicating excellent photocatalytic activity.     

Polymerizable inorganic–organic hybrid: Syntheses and structures of mono-lacunary Dawson polyoxometalate-based olefin-containing organosilyl derivatives

Three olefin-containing organosilyl derivatives supported on the mono-lacunary Dawson polyoxometalate (POM), [α₂-P₂W₁₇O₆₁{(RSi)₂O}]⁶⁻ (R = {CH₂C(CH₃)COO(CH₂)₃}, {CH₂CHCOO(CH₂)₃} and {CH₂CH}), as Me₂NH₂ salts, which can act as precursors for the immobilization of the POMs in polymer networks, were obtained by the 2:1 molar ratio reaction of the organosilyl precursor RSi(OCH₃)₃ with K₁₀[α₂-P₂W₁₇O₆₁] · 19H₂O in acidic MeOH/H₂O mixed solutions. X-ray crystallography revealed that the two organic chains connected through an –Si–O–Si– bond were grafted onto the mono-lacunary site of the POM. The four-coordination of each Si atom was attained with the bridging oxygen atom, the terminal organic group R in the organosilyl group, and 2 of the 4 oxygen atoms in the mono-lacunary site of the POM.