Bacterial cellulose–silica organic–inorganic hybrids

Bacterial cellulose (BC) hydrated membranes present nanometric reticulated structure that can be used as a template in the preparation of new organic–inorganic hybrids. BC–silica hybrids were prepared from BC membranes and tetraethoxysilane, (TEOS) at neutral pH conditions at room temperature. Macroscopically homogeneous membranes were obtained containing up to 66 wt.% of silica spheres, 20–30 nm diameter. Scanning electron micrographs clearly show the silica spheres attached to cellulose microfibrils. By removing the cellulose, the silica spheres can be easily recovered. The new hybrids are stable up to 300 °C and display a broad emission band under UV excitation assigned to oxygen-related defects at the silica particles surface. Emission color can be tuned by changing the excitation wavelength.     

Self-assembly of functionalized inorganic–organic hybrids

Recent advances on the synthesis and self-assembly of hybrid inorganic–organic materials have been reviewed in terms of the synthetic strategies and emerging techniques, including in-situ self-assembly, template-induced self-assembly, evaporation-induced self-assembly, and layer-by-layer assembly for assembling functional hybrids. The perspectives and outlook on this research topic are given.     

Two extended organic–inorganic hybrids based on sandwich tungstogermanates

Two inorganic–organic composite polyoxotungstates, [Cu(en)₂(H₂O)]₂[Cu(en)₂(H₂O)₂]-{[Cu(en)₂]₃[Cu₄(GeW₉O₃₄)₂]} · 10H₂O (1, en = ethylenediamine) and (H₂en){[Zn(en)₂]₄-[Zn₄(Hen)₂(GeW₉O₃₄)₂]} · 10H₂O (2), were hydrothermally synthesized and their structures determined by single-crystal X-ray diffraction. Compounds 1 and 2 consist of sandwich polyanions [Cu₄(B-α-GeW₉O₃₄)₂]^12? or [Zn₄(Hen)₂(GeW₉O₃₄)₂]^10? linked by [M(en)₂]²⁺ bridges to form 2-D networks, which are further packed into a 3-D supramolecular porous framework via extensive hydrogen bonding interactions. Their IR and UV spectra, thermal stabilities, and cyclic voltammograms were also investigated.     

Optical filters and resonant cavities based on di-ureasil organic–inorganic hybrids

Sol–gel derived poly(oxyethylene)/siloxane organic–inorganic di-ureasil hybrids containing different amounts (20–60% mol) of methacrylic acid (McOH) modified zirconium oxo-clusters (Zr-OMc) were processed as thin films and transparent and shape controlled monoliths. Laser direct writing was used to create channel waveguides, Bragg gratings, Fabry–Perot cavities and optical filters. The resulting Fabry–Perot optical cavity displays a free spectral range of 16.55 GHz and a fringe intensity contrast of 5.35 dB. Optical rejection values between 6.7 and 10.4 dB were obtained by varying the amount of the Zr-OMc oxo-clusters.     

Multi-component hybrid inorganic–organic–inorganic particles with various metal oxide outer shells

Non-agglomerated hybrid particles of 200 nm diameter with an outer metal oxide shell were prepared by reacting the COOH groups of poly((S)-N-dicarbazolyl-lysine)-covered silica particles with metal alkoxides, such as titanium, zirconium and aluminum alkoxides, followed by sol–gel processing. With tetraethoxysilane (Si(OEt)₄), the silica particle core was growing rather than forming an external metal oxide shell, as observed for the other tested metal alkoxides.     

Terbium(III)-containing organic–inorganic hybrids synthesized through hydrochloric acid catalysis

Organic–inorganic hybrids incorporating Tb(acac)₃·3H₂O (where acac is acetylacetonate) were synthesized via conventional hydrolysis sol–gel reaction in the presence and absence of an acid catalyst (hydrochloric acid, HCl). The host framework of these materials, named di-ureasils, is formed by polyether-based chains grafted to both ends to a siliceous backbone through urea cross-linkages (–NHC(CO)NH–). Four different concentrations of HCl (0.5, 1.0, 1.5, and 2.0 mol L^?1) were used as catalyst for hydrolysis reactions. The gelation time of the resulting materials depends on the HCl concentration varying between 5 and 20 min. The hybrids were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ²⁹Si and ¹³C magic-angle spin nuclear magnetic resonance (NMR) and photoluminescence spectroscopy. The emission quantum yield for the undoped hybrids lies between 8.7 and 10.6%, much higher than those obtained for analogous samples prepared via conventional hydrolysis in the absence of catalyst. For the Tb³⁺-containing hybrids the lanthanide local environment was affected due to different synthetic conditions used. An increase in the ⁵D₄ lifetime values, relatively to that of the isolated Tb(acac)₃·3H₂O complex, is in good agreement with a smaller ⁵D₄ non-radiative transition probability in the hybrids suggesting the replacement of the Tb³⁺coordinated water molecules by the oxygen atom of the carbonyl group of the di-ureasil host.     

Hybrid UV-cured organic–inorganic IPNs

Hybrid organic–inorganic UV-cured coatings based on interpenetrating polymer networks (IPN) were prepared starting by an equimolar methacrylate-epoxy UV-curable mixture (bisphenol-A-diglycidyl dimethacrylate/bisphenol-A-diglycidyl ether, abbreviated as BisGMA/BADGE), in the presence of tetrafunctional silane monomer tetrakis(methacryloyloxy-ethoxy)silane (TetMESi) as inorganic precursor. The photocuring kinetics of the BisGMA/BADGE IPN monomer mixture were strongly affected by the order of the cure of the individual components. Addition of TetMESi resulted in higher degrees of reaction. DMTA of the BisGMA/BADGE IPN suggest a two phase structure. The rubbery modulus of the hydrolysed BisGMA/BADGE/TetMESi systems increased as the level of TetMESi was raised in the formulation due primarily to the significant reinforcing effect of the nano-silica particles. TGA of the BisGMA/BADGE IPN showed three degradation stages with no residual char but the hydrolysed BisGMA/BADGE/TetMESi systems formed a carbonaceous silica char which increased in mass as the level of TetMESi was raised. The two phase morphology of the BisGMA/BADGE IPN was confirmed by FE-SEM analysis. For IPNs prepared with TetMESi, SiO₂ particles are evident in the FE-SEM image and have diameters in the nanometric size range.     

Two new layered inorganic–organic hybrids: intercalation of 1,3,5-benzenetricarboxylate in lead bisphosphonate

Hydrothermal reactions of N-benzyl-iminobis(methylenephosphonic acid), C₆H₅CH₂N(CH₂PO₃H₂)₂ (H₄L), with lead(II) carbonate in the presence of butane diacid resulted in a new layered lead(II) amino-bisphosphonate, namely, Pb₃L(H₂L)·1.5H₂O 1. When 1,3,5-benzene-tricarboxylic acid (H₃BTC) was used instead of butane diacid, a new layered lead(II) amino-bisphosphonate containing noncoordinated H₃BTC molecules, Pb₃(HL)₂·2(H₃BTC)·2H₂O 2 was isolated. Compound 1 crystallizes in the monoclinic space group P2₁/c with cell dimensions of a=17.6776(14) Å, b=10.0111(8) Å, c=16.6017(13) Å, β=104.134(2)° and Z=4. Compound 2 crystallizes in triclinic space group P-1 with cell parameters of a=4.8797(4) Å, b=9.9736(7) Å, c=24.3631(17) Å, α=97.680(2)°, β=95.0000(10)°, γ=102.4340(10)° and Z=1. Both compounds feature a layered structure and have a same metal/ligand ratio of 3:2. Compound 1 contains two types of ligands with different charges, −2 and −4, respectively. The lead(II) ions are bridged by bisphosphonate ligands, resulting in a 〈100〉 layer. In compound 2, the interconnection of the lead(II) ions by bridging phosphonate groups resulted in a 〈001〉 layer, with the neutral H₃BTC ligand intercalated between two layers, forming hydrogen bonds with lattice water molecules, noncoordinated phosphonate or carboxylate groups. In both compounds, the phenyl groups of the ligands are orientated toward the interlayer space. TGA and IR spectra for both compounds have been also studied.     

The assembly of POM-induced inorganic–organic hybrids based on copper ions and mixed ligands

Three inorganic–organic hybrid materials based on Keggin-type polyoxometalates (POMs), [Cu^II₂(phen)₂(4,4′-bipy)(H4,4′-bipy)₂(H₂O)₂][PMo₁₂O₄₀]₂·2H₂O (1), [Cu^II(phen)₂(H4,4′bipy)][PW₁₂O₄₀]·H₂O (2), and [Cu^II₂(phen)₂(4,4′-bipy)(BW₁₂O₄₀)(H₂O)₂](H₂4,4′-bipy)_0.5·3H₂O (3) (phen = 1,10-phenanthroline, 4,4′-bipy = 4,4′-bipyridine), were synthesized using different POMs in the hydrothermal conditions. Compounds 1–3 were characterized by single-crystal X-ray diffraction, IR spectra, elemental analyses, powder X-ray diffraction analyses, and thermogravimetric analyses. Compound 1 presents a two-dimensional (2-D) network containing the Keggin-type [PMo₁₂O₄₀]^3? anion and dinuclear metal–organic units [Cu^II₂(phen)₂(4,4′-bipy)(H4,4′-bipy)₂(H₂O)₂]³⁺. Compound 2 is a 2-D architecture constructed from a [PW₁₂O₄₀]^3? and mononuclear metal–organic units [Cu^II(phen)₂(H4,4′-bipy)]³⁺. In 3, the [BW₁₂O₄₀]^5? anions link [Cu^II₂(phen)₂(4,4′-bipy)] units to form a one-dimensional (1-D) chain [Cu^II₂(phen)₂(4,4′-bipy)(BW₁₂O₄₀)(H₂O)₂]; the 1-D chain connects with protonated 4,4′-bipy ligands and lattice waters, yielding a 2-D layer. Fluorescence spectra, UV–vis spectra, and electrochemical properties of 1–3 have been investigated.     

Functionalization of mesostructured inorganic–organic and porous inorganic materials

The capability to functionalize the interior channels and/or high internal surface areas of mesostructured inorganic–organic or porous inorganic solids with specific organic or inorganic moieties has dramatically expanded the potential applications for these versatile materials in catalysis, separations, optical and opto-electronic devices, drug delivery, sensors, and energy conversion. Key to the widespread application of these materials are the various synthetic schemes that have been developed to provide control over the types of species incorporated and, more importantly, their distributions within the mesostructured hosts. Furthermore, multiple active species can often be independently incorporated and collectively optimized to yield multifunctional properties that widen application prospects. Several recent developments and examples in this rapidly growing field of materials chemistry and engineering are highlighted and discussed.     

Syntheses and characterization of inorganic–organic hybrids with 4-(isonicotinamido)phthalate and some divalent metal centers

Four new inorganic–organic hybrid frameworks [Mn(L)(H₂O)₂]_n (1), {[Co(L)(H₂O)₃]·2H₂O·CH₃OH}_n (2), {[Zn(L)(H₂O)]·H₂O}_n (3) and [Cd(HL)₂]_n (4) [H₂L = 4-(isonicotinamido)phthalic acid] have been synthesized and characterized by single-crystal X-ray diffraction analysis. Complex 1 has three-dimensional (3D) structure and topology related to SrAl₂ (sra) with Schläfli symbol of (4²·6³·8). And 2 displays (3,3)-connected two-dimensional (2D) network with (4,8²) topology, while 3 exhibits a uninodal (3,3)-connected (6,3) 2D network, which is further linked by N–H?O hydrogen bonding interactions to give 3D structure with hms topology and Schläfli symbol of (6³)(6⁹·8). Complex 4 with partial deprotonated HL⁻ ligands also has a 2D network structure. In addition, the magnetic property of 1, nonlinear optical property of 3 and photoluminescence of 3 and 4 were investigated.     

Stepwise synthesis of two inorganic–organic hybrids based on the manganese monosubstituted Keggin polyanion chains

Two new hybrid compounds based on the manganese monosubstituted Keggin polyanion chains, [H₂bpy][Ag(bpy)]₂[HPMnMo₁₁O₃₉] (1) and [H₂bpy]₂[Hbpy][PMnMo₁₁O₃₉]·H₂O (2), (bpy = 4,4′-bipyridine) have been stepwise synthesized under hydrothermal condition and characterized by elemental analyses, IR spectra, thermogravimetry, and single-crystal X-ray diffraction technique. Structural characterization reveals that although both 1 and 2 contain manganese monosubstituted Keggin polyanion chains, the polyanion chains are not in the full consistent way. In 1, the neighboring manganese monosubstituted Keggin clusters are connected via sharing the para position oxygen atoms of the clusters to form a linear polyanion chain in which the monosubstituted Keggin clusters are further grafted by silver coordination polymer chains forming a 2D network. Whereas the polyanion chain in 2 exhibits a zigzag structure, which is formed by sharing the metaposition terminal oxygen atoms of the clusters, rather than para position terminal oxygen atoms as that in 1. Each zigzag chain contacts with four adjacent chains along four directions through short interspecies contacts, forming a 3D supramolecular framework. The protonated Hbipy⁺ and H₂bipy²⁺ molecules as the counter cations exist in voids of the supramolecular framework in 2. Furthermore, photocatalytic experiments indicate that 1 has good activities for photocatalytic degradation of RhB under UV irradiation.     

Responsive microstructures on organic–inorganic hybrid films

Micro-periodic structures exhibiting shape memory have been fabricated on organic–inorganic hybrid films. The microscale structures are obtained by forming wrinkles via buckling of the stiff surface layer. The surface-modified layers are obtained by surface photopolymerization or by oxidation of the hybrid films. The microscale structures are spontaneously formed by the shrinkage of the underlayer via gelation. The surface microstructures on titania- or silica-based films with hydrophilic swellable polymers exhibit a humidity response, i.e., a shape memory effect. This is observed when the surface microstructure disappears and is subsequently recovered with cyclic variation of the surrounding humidity. Micro-rolls are also fabricated by the selective swelling of surface-modified layers.     

Elastic organic–inorganic hybrid aerogels and xerogels

Novel aerogels and xerogels with methylsilsesquioxane (MSQ, CH₃SiO_1.5) networks have been prepared by a modified sol–gel process using surfactant and urea as a phase-separation inhibitor and as an accelerator for the condensation reaction, respectively. Optimized aerogels dried under a supercritical condition not only showed the similar properties as conventional pure silica aerogels such as high transparency and porosity etc, but also demonstrated outstanding mechanical strength against compression; the aerogel drastically shrank upon loading and then recovered when unloaded, which is called a “spring-back” behavior. On ambient pressure drying, the wet gel also exhibited the similar response against compression stress originated from the capillary pressure, and thus xerogels with the comparative structure and properties to those of corresponding aerogels have also been obtained. This unusual mechanical behavior is attributed to the trifunctional flexible networks of MSQ, low silanol concentration which prevents the irreversible shrinkage, and high concentration of a hydrophobic methyl group directly attached to every silicon atom which helps re-expansion after the temporal shrinkage.     

Preferred-handed helical conformation in organic–inorganic hybrid block copolymers with well-controlled stereoregularity

A novel block copolymer containing polyhedral oligomeric silsesquioxanes (POSS) features a well-controlled stereoregularity, that is, isotactic polymethacrylate-functionalized POSS-b-polymethyl methacrylate (it-PMAPOSS-b-PMMA), was prepared via controlled-anionic polymerization. The stereoregularity of each segment in the it-PMAPOSS-b-PMMA is evaluated using nuclear magnetic resonance (NMR) spectroscopy, which reveals an isotactic configuration in both the PMAPOSS and PMMA segments. The secondary structure of it-PMAPOSS-b-PMMA in a mixture with a small chiral dopant is clarified with electronic circular dichroism and vibrational circular dichroism measurements. By adding a chiral dopant, a controlled preferential helical conformation of the unilateral segment in achiral it-PMAPOSS-b-PMMA is achieved.     

Sedimentation analysis of organic–inorganic hybrid colloids

Hybrid organic–inorganic latex particles are synthesized to combine the beneficial properties of the constituents which thus lead to synergistic improvement in the properties. The properties of hybrid particles are dependent on the successful hybridization process, thus controlling or tuning of such processes by effective characterization is immensely important. Analytical ultracentrifugation provides these characterization possibilities owing to its high statistical capability and ability to characterize multiple parameters. The use of different detection methodologies can help in generating valuable information on the overall size and density distributions of the particles. Apart from that, it is also possible to quantify the presence of any free polymer and inorganic particles in the hybrid latex which would affect the properties of hybrid latexes. By following the densities of the pure and hybrid particles, it is also possible to quantify the amounts of the constituent phases in the hybrid particles. The density gradients generated in preparative ultracentrifugation also provide additional possibilities for the characterization of the hybrid particles which have densities higher than the measurable range in the analytical ultracentrifuge. Evolution of hybrid particles can also be studied as a function of time. It also provides advantage of separation of the various fractions for further characterization.     

Cotton fabrics treated with hybrid organic–inorganic coatings obtained through dual-cure processes

Cotton fabrics were treated with a hybrid organic–inorganic coating obtained through a dual-cure process, i.e. a photopolymerization reaction followed by a thermal treatment for promoting the formation of silica phases through a sol–gel process. To this aim, different amounts of a silica precursor were added to an acrylic UV-curable formulation in the presence of a suitable coupling agent. The thermo-mechanical properties of the treated fabrics were investigated and correlated to the composition and morphology of the hybrid organic–inorganic system. Furthermore, their flame retardancy and combustion behavior were evaluated by flammability tests and cone calorimetry and compared with the performances of pure cotton.     

Two inorganic–organic hybrids based on a polyoxometalate: Structures,characterizations, and epoxidation of olefins

Two new inorganic–organic hybrids, [Co₃(bpdo)₆(H₂O)₄Cl₂][SiW₁₂O₄₀]·H₂O (Co-SiW) and [Ni₃(bpdo)₆(H₂O)₄Cl₂][SiW₁₂O₄₀]·H₂O (Ni-SiW) (bpdo = 4,4′-bis(pyridine-N-oxide)), were synthesized from the Keggin-type [SiW₁₂O₄₀] anion and Co(II) and Ni(II) under hydrothermal conditions, respectively, and characterized by elemental analyses, powder XRD, IR spectra, and single-crystal X-ray diffraction. The structural analysis indicates that the 1D chain is constructed from a POM-based half-cage as a secondary building block linked by bridging bpdo ligands. The zigzag chains further stack into a three-dimensional body with channels. The 3D network structure with amphiphilic cavities is shaped by electrostatic interactions through the planes, which has potential to allow molecules such as styrene and H₂O₂ ingress and egress. Both of the hybrids demonstrated catalytic activity for epoxidation of olefins, which was examined using styrene and aqueous hydrogen peroxide (30%) as oxidant in acetonitrile, along with Co-SiW and Ni-SiW in a heterogeneous manner at 60 °C. Moreover, the conversion of epoxidation reaction in a heterogeneous manner is close to that of homogeneous catalysis, while being conveniently recovered and steadily reused without change of catalyst structure after epoxidation reactions.     

Hybrid organic–inorganic sol–gel coatings with interpenetrating network for corrosion protection of tinplate

Novel hybrid organic–inorganic coatings with interpenetrating network were synthesized by the acid-catalyzed hydrolytic co-polycondensation of tetraethoxysilane and 3-metacryloxypropyltrimethoxysilane, followed by radical polymerization with methyl methacrylate and triallyl isocyanurate (TAIC). The hybrid coatings were characterized by Fourier transformed infrared spectroscopy, thermogravimetric analysis and scanning electron microscope, and their anti-corrosion behaviors were evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy and salt spray test. The results indicated that the hybrid coatings exhibited excellent anti-corrosion ability by forming a physical barrier between metal and its external environment. Thermal stability of the hybrid coatings was increased after the addition of TAIC. Furthermore, hydrophobic properties of the hybrid coatings were examined by measuring the contact angles, and the change in wetting characteristics of the hybrid coatings was not obvious.