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.     

Cytotoxicity of a metal–organic framework: Drug delivery

A new Zn(II) metal–organic framework of [Zn₆(L)₃(DMA)₄]·5DMA (1) (H₄L = [1,1′:3′,1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid), was used as a drug carrier of 5-fluorouracil (5-FU) for drug delivery. Drug release behavior was also investigated under different pH condition. 5-FU is released in a highly controlled and progressive manner with 95.8% of the drug release after 96 h at acidic condition and with 91.6% after 96 h at PBS. Vitro cytotoxicity assays indicated that the 1 possesses no obvious cytotoxicity.     

The effect of rippled graphene sheet roughness on the adhesive characteristics of a collagen–graphene system

A great amount of effort has been made in order to reach a more precise understanding of the adhesion phenomenon that happens as a vital component of several biological systems. Therefore, a firm understanding of the important factors that influence this phenomenon is of special importance in triggering the adhesive characteristics of different biological, bio-inspired and synthetic materials in fields such as tissue engineering.In this study the adhesive characteristics of a multi-material system consisting of the frequently used synthetic material, graphene, in the form of armchair-configuration sheets, and an important biological filament which is type 1 Collagen consisting of 3 alpha helices, has been studied in detail. The main emphasis of this study is placed on understanding the effects of the roughness characteristics of the inorganic elements which are the graphene sheets on the overall adhesive features of the system which are quantified within the framework of two main criteria: adhesion energy and peeling force. At first, the methodology used in order to obtain graphene sheets with various roughness values is described in detail. The abovementioned criteria are then evaluated through Molecular Dynamics (MD) modeling of the system in the NAMD simulation software environment and various simulation scenarios are studied.     

Influence of vibrations on interface delamination in metal–polymer composites

The main objective of this work was the study of vibration effects on the viscoelastic coating protecting the steel layer in a metal–polymer composite, with simulated conditions of the transportation of food containers. Mechanical resonance tests in metal–polymer [electrolytic chromium-coated steel–poly(ethylene terephthalate) (PET)] sheets were performed to generate vibration conditions to induce structural modifications in the viscoelastic layer covering the surface of the plates. Consequently, schematic representations of the areas affected by these modifications were made. The modified structures were later analyzed by electron microscopy to detect and evaluate alterations in the morphology of the material. In addition, vibrational Raman spectroscopy analyses were performed to assess the chemical and structural changes on the protective PET at the metal–polymer interface level. The results of this study are expected to provide basic information on the mechanisms and nature of the delamination processes taking place in metal–polymer laminates employed in food-container applications. These damages have previously been detected in some food containers made of PET materials. The study of these damages can lead to the improvement of current composites or the development of higher quality materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Decoration of graphene network with metal–organic frameworks for enhanced electrochemical capacitive behavior

Well-intergrown nanocrystals of zeolitic imidazolate frameworks (ZIF-8) supported on three-dimensional (3D) graphene were prepared by a counter diffusion technique. The incorporation of ZIF-8 crystals greatly improves the surface areas of the graphene composites. The carbonized graphene–ZIF composites with hierarchical pore structures showed high electrochemical capacitance and good stability. This work provides an efficient method to synthesize porous carbon materials with high capacitance.     

Epoxidation of alkenes with molecular oxygen catalyzed by a manganese porphyrin-based metal–organic framework

The flexible nature of reticular assemblies and high specific surfaces of metal–organic frameworks (MOFs) offers new opportunities for the design of heterogeneous catalysts capable of industrially relevant reactions. We demonstrate the first instance of alkene epoxidation at mild conditions using molecular oxygen by a manganese porphyrin containing MOF, MOF-525-Mn [Zr₆O₄(OH)₄(MgC₄₈H₂₄O₈N₄Cl)₃]. This zirconium MOF with a manganese porphyrin catalyst shows minimal deactivation over long periods and maintains its structure and high activity after multiple catalytic cycles. Kinetic studies of styrene epoxidation are in agreement with theoretical and experimental studies of homogeneous reactions with the same porphyrin unit, suggesting that the heterogeneous catalyst operates according to a similar mechanism as its homogeneous counterpart.     

Observation of the semiconductor–metal transition behavior in monolayer graphene

We have observed that during temperature-dependent four-terminal resistance measurement of monolayer graphene, the resistance exhibits anomalous rising and falling behavior at different temperature regions. At lower temperature region (2–200 K) the resistance decreases gradually, but when the temperature rise further it turn to a sudden increase, and after 280 K it resumes gradual decrease. The rising and falling resistance behavior is characteristic of semiconductor or metal property. Consequently, the resistance transition follows a phase of semiconductor–metal–semiconductor. However, when a perpendicular magnetic field is applied, the resistance shows reverse transition behavior which follows a sequence of metal–semiconductor–metal. The novel transition property is attributed to the competition between the disorder of lattice defects as a short-range scattering in monolayer graphene and the Landau levels interaction. Magneto-transport measurement reveals that the excitonic gap induced by magnetic field in the monolayer graphene show an anomalous thermally activated property.     

Preparation of a new nano-layered materials and organic–inorganic nano-hybrid materials, Zn–Si LDH

Layered double hydroxides are nano-ordered layered compounds. Layered double hydroxide (LDH) well known for its ability to intercalate anionic compounds has been prepared conventionally only with divalent and trivalent cations. In this study, Zn–Si LDH consisting of divalent and tetravalent cations was prepared, and reacted with organic acids and formed nano-hybrid materials. X-Ray diffraction patterns of the prepared LDH (Zn–Si–CO₃) showed that interlayer spacing of the LDH was 0.67 nm and increased to be 4.2 nm in the case of stearate anion as the guest. The spacing 0.67 nm was small compared to the usual LDH (Zn–Al–CO₃) of 0.76 nm in the case of carbonate anion as the guest. Also, DTA, TG and DTG analyses indicated that the electrostatic force between the layers and carbonate anions increased where the carbonate anions in Zn–Si LDH decomposed at 259 °C while those in Zn–Al–CO₃ decomposed at 230–240 °C.     

An update on the mechanism of the graphene–NO reaction

Cognizant of the key experimental facts from studies of carbonaceous solids ranging from soot to graphite, we performed a quantum chemistry study of the interaction of NO monomer or dimer with one or more zigzag sites. Thermodynamic and kinetic results were used to examine two alternative mechanisms proposed in the literature, and to compare them with the graphene–O₂ reaction mechanism. The chemisorption stoichiometry similarities are striking; but the differences, especially regarding the intermediate role of N₂O, have important practical implications. Monomer chemisorption on an isolated site is a dead-end and temporarily inhibiting process, similar to that of formation of a stable C–O surface complex in the graphene–O₂ reaction. When two sites are available, successive monomer adsorption eventually leads to N₂O formation subsequent to parallel reorientation of the first NO molecule. If three contiguous sites are available, N₂ and CO are the principal products. Chemisorption of the dimer provides a straightforward path to N₂ and CO₂ when one site is available and to N₂ and CO when two sites are available. The formation of N₂O is also feasible in this case, both during adsorption and desorption; in the adsorption phase it is very sensitive to the details of the electron pairing processes.     

High photonic effect of organic dye degradation by CdSe–graphene–TiO2 particles

Photocatalytic activity of CdSe (cadmium selenide) decorated graphene composites coupled with TiO₂ (titanium oxide) was investigated with organic dye solutions. The characterizations of composites were studied by X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscope (SEM), and with transmission electron microscope (TEM). The degradation of methyl orange (MO) and rhodamine B (RhB) was observed by measuring the decrease in the concentration by UV spectrophotometer. The synergistic effect of graphene on CdSe and TiO₂ was demonstrated by comparative study. The composites were tested for recyclability, investigating the stability of CdSe–graphene/TiO₂ composites.     

Enhanced corrosion-resistant performance of the PEO coatings on AA7075 alloy by a sol–gel-derived silica layer

The paper aimed to increase the corrosion-resistant performance of AA7075 alloy by the incorporation of sol–gel with plasma electrolytic oxidation (PEO) technologies. The AA7075 alloy substrate was first coated by an oxide ceramic layer with the help of the PEO process and then covered by a sol–gel-derived SiO₂ layer. The results from an X-ray diffraction and scanning electron microscope clearly show that a layer of sol–gel-derived SiO₂ uniformly covered and sealed the surface microporous structure of PEO coatings on AA7075 alloy, effectively enhancing the corrosion-resistant performance of PEO-coated AA7075 alloy in an aqueous solution containing 3.5-wt.% NaCl. The lower current density of 2.09 × 10⁻⁷ A/cm² and the larger polarization resistance of 5.35 × 10⁴ Ω cm² were found for sol–gel/PEO-coated AA7075 alloy as compared with 3.68 × 10⁻⁶ A/cm² and 9.81 × 10³ Ω cm² for individual PEO-coated AA7075 alloy. Thus, it is an effective strategy to improve the corrosion-resistant performance of the AA7075 alloy by combining the PEO and sol–gel techniques.     

Study on a new cyclodextrin based metal–organic framework with chiral helices

Staring from β-cyclodextrins and Na salts, a new metal–organic framework with chiral helices, (C₄₂O₃₅H₇₀)₂(NaOH)₄·H₂O (CD-MOF-1), has been successfully synthesized. X-ray diffraction analysis reveals that CD-MOF-1 exhibits a 3D framework with left-handed helical channels running through the structure created by the ligation of Na ions to the primary and secondary faces of the β-cyclodextrins rings. Additionally, inclusion properties of CD-MOF-1 were also studied, and the result shows that the inclusion rate using CD-MOF-1 as inclusion materials is higher than that of β-cyclodextrins, which is expected to become a new type of green crystal material from edible natural products.     

Constructing two new crystalline metal–organic frameworks based on a mixed-donor ligand

The self-assembly of a prominent ligand, 5-(4-(1H-tetrazolyl)phen)isophthalic acid (H₃TZPI), with Zn^2 +/Cu^2 + centres generates two new MOFs, [Zn₂(TZPI)(μ₃-OH)(H₂O)₂]·2H₂O (JUC-161) and [Cu(HTZPI)(μ₂-H₂O)_0.5(H₂O)_1.5]·5(H₂O) (JUC-162). JUC-161 exhibits fascinating three-dimensional structures containing rectangular channels with dimensions of 6.5 × 3.0 Å², and JUC-162 displays 3D supramolecular structures with 12.5 × 14.6 Å² hexagonal channels. The observed structural diversity in these frameworks is due to the two distinct coordinating moieties of the H₃TZPI ligand. The photoluminescence of JUC-161 and the magnetic properties of JUC-162 are also measured at room temperature. Photoluminescence investigations reveal that JUC-161 displays a strong main emission spectrum peak at 388 nm. JUC-162 is found to exhibit an antiferromagnetic interaction between Cu^2 + ions.     

Influence of hydrogen functionalization on the fracture strength of graphene and the interfacial properties of graphene–polymer nanocomposite

Using molecular dynamics and classical continuum concepts, we investigated the effects of hydrogen functionalization on the fracture strength of graphene and also on the interfacial properties of graphene–polymer nanocomposite. Moreover, we developed an atomistic model to assess the temperature and strain rate dependent fracture strength of functionalized graphene along various chiral directions. Results indicate that hydrogen functionalization at elevated temperatures highly degrade the fracture strength of graphene. The functionalization also deteriorates the interfacial strength of graphene–polymer nanocomposite. Near-crack-tip stress distribution depicted by continuum mechanics can be successfully used to investigate the impact of hydrogen passivation of dangling carbon bonds on the strength of graphene. We further derived a continuum-based model to characterize the non-bonded interaction of graphene–polymer nanocomposite. These results indicate that classical continuum concepts are accurate even at a scale of several nanometers. Our work provides a remarkable insight into the fracture strength of graphene and graphene–polymer nanocomposites, which are critical in designing experimental and instrumental applications.     

First-principles calculations of the effects of the interface microstructure on the wettability of a Cu–Ti/AlN system

The active element Ti is always added to Cu-, Ag-, or Sn-based fillers used to join ceramics, because it promotes the wetting of the fillers on ceramics. However, different mechanisms have been proposed on the mode of action of the active element Ti in promoting the wetting of the filler alloy. In this study, in order to gain a better understanding of the two controversial wetting mechanisms, which are based on adsorption and interfacial reaction, density functional theory (DFT) calculations were performed to investigate the role of the active element on the interfacial properties of the Cu–Ti/AlN wetting system. The following three typical wetting interface models were constructed: (1) the original interface of Cu/AlN, (2) adsorption interface of Cu/AlN(Ti), and (3) reaction interface of Cu/TiN. First, according to the convergence of the surface energy, a four-atom-layer Cu (111) slab, an eight-atom-layer AlN (001) slab, and a five-atom-layer TiN (001) slab were used to represent the Cu bulk, AlN bulk, and TiN bulk, respectively. Then, interface models were constructed and the work of adhesion, Bader charges, differential charge density, and density of states were analyzed, and the theoretical contact angles were calculated. The results indicate that both the adsorption of Ti at the interface and its reaction with AlN to form a TiN layer remarkably improve the wetting of Cu on AlN, and the contact angle decreased from 173° to 74° and then to 119°. This study constitutes a modest step toward clarifying the wetting mechanism of Ti-added active fillers on ceramics.     

Evaluation of the shear characteristics of steel–asphalt interface by a direct shear test method

Shear characteristics of steel–asphalt interface under the influences of temperature, normal stress level and tack coat material were investigated. The direct shear tests were conducted on composite specimens with epoxy asphalt (EA) and polymer modified asphalt (PMA) tack coat materials at temperatures of 25 and 60 °C and normal stress levels of 0, 0.2, 0.4, and 0.7 MPa for each temperature. Results show that the failure modes include adhesive failure at the primer-tack coat interface and material failure of asphalt concrete. Steel–asphalt interface shows strain softening behavior until it reaches the sliding state. The shear strength and the shear reaction modulus increase with decreasing temperature and increasing normal stress levels. The specimens with EA tack coat provides much higher interface shear strengths than those with PMA tack coat at 25 and 60 °C. In addition, the failure envelopes of the shear strength and residual shear strength were obtained for combinations of tack coat materials and temperature conditions based on the Coulomb failure law.     

Aluminum metal–organic framework as a new host for preparation of encapsulated metal complex catalysts

A facile strategy for encapsulation of metal complex guests into MOFs was proposed. This strategy involves pre-adsorbing metal salt on MOF, and then coordinating the metal ions with the organic ligand, as exemplified by encapsulation of tris(1,10-phenanthroline) Cu(II) complexes (CuPhen) in MIL-100(Al) (denoted as CuPhen/MIL). CuPhen encapsulated in MIL-100(Al) showed higher catalytic activity than the neat CuPhen and CuPhen encapsulated in zeolite-Y. The prepared CuPhen/MIL catalyst was stable and could be reused at least three times without significant loss in activity. This work is beneficial for the host–guest chemistry study and the development of new heterogeneous catalysts.