Organic Sol-gel Research Articles

Ultramicroporous Tröger's Base Framework Membranes for pH-Neutral Aqueous Organic Redox Flow Batteries.

Processable polymers of intrinsic microporosity (PIMs) are emerging as promising candidates for next-generation ion exchange membranes (IEMs). However, especially with high ion exchange capacity (IEC), IEMs derived from PIMs suffer from severe swelling, thus, resulting in decreased selectivity. To solve this problem, we report ultramicroporous polymer framework membranes constructed with rigid Tröger's Base network chains, which are fabricated via an organic sol-gel process. These membranes demonstrate excellent antiswelling, with swelling ratios below 4.5% at a high IEC of 2.09 mmol g-1, outperforming currently reported PIM membranes. The rigid ultramicropore confinement and charged modification of pore channels endow membranes with both very high size-exclusion selectivity and competitive ion conductivity. The membranes thus enable the efficient and stable operation of pH-neutral aqueous organic redox flow batteries (AORFBs). This work presents the advantages of polymer framework materials as IEMs and calls for increasing attention to extending their varieties and utilization in other applications.

Quantitative morphometry of topological graphene-based aerogels and carbon foams by x-ray micro-computed tomography

In this work, we report quantitative morphometry of freeze-dried graphene-based aerogels (i.e., graphene aerogel-GA, nitrogenated GA-NGA, graphene-carbon nanotube hybrid-Gr-MWCNTs, carbon foam-CF, and CF-GA hybrid-CF-GA) and monoliths, prepared by hydrothermal and organic sol-gel methods, respectively. X-ray micro-computed tomography (XMCT) in combination with scanning and transmission electron microscopy allowed visualization of internal microstructures in three-dimensional space. Quantitative morphometry analysis through the reconstructed volume renderings from two-dimensional sliced images revealed hierarchical structures possessing interlaced thin sheets, honeycomb organization, and topological interconnected pore background domains. The influence of small-diameter functionalized multi-walled carbon nanotubes (MWCNTs) inclusions to graphene-like sheets and integration with CF is assessed through quantitative morphometry analysis in terms of volume-weighted pore size, wall thickness, and porosity levels. Hybrid composite porous solids elucidated cross-linking reinforced by a homogeneous distribution of CNTs into complex sheets of GA and CF matrices. A consistent trend impacting porosity and interconnectedness was found following NGA ≥ GA > CF > Gr-MWCNT2:1 > CF-GA > Gr-MWCNT3:1 > Gr-MWCNT5:1, from XMCT image processing and analyses in corroboration with physical properties and reliability. The experimental results provide insights and guide the design of characteristic porous carbonaceous and graphene-based functional nanomaterials for energy sciences, environmental engineering, and fundamental reactive transport of fluids.

Exploring the structural and electrochemical sensing of wide bandgap calcium phosphate/CuxFe3-xO4 core-shell nanoceramics for H2O2 detection

Calcium phosphate/Cu x- Fe 2-x O 4 core-shell nanoceramics have been synthesized using the organic sol-gel process and calcined at 600 o C. The nanoceramics were explored by X-ray powder diffractometry (XRD), transmission electron microscopy (TEM)), Fourier transforms infrared spectroscopy (FT-IR), UV–visible diffuse reflectance spectra (DRS), and electrochemical techniques including cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The FTIR results confirmed the presence of calcium phosphate (CP) and CP coated with Cu-ferrite (0-30 mol% Cu:Fe 3 O 4 ) core-shell nanoceramics. TEM analysis displayed nanospheres of calcium phosphate shielded with a porous spheres-like morphology with internal nanoparticles of about 33 nm. The reflectance spectra increase for all samples with increasing wavelength. Both direct and indirect gap transitions were detected with lower values of the direct case than the indirect type. The dielectric constant, refractive index, and optical electronegativity of all samples were calculated. When the ferricyanide was applied as the standard redox probe for the electrochemical characterization, CV and EIS results revealed a remarkable enhancement in the generated electrochemical signals. Moreover, modified screen-printed electrodes with the 20 Cu-CPF produced the highest redox current (0.198 mA) towards the direct oxidation of hydrogen peroxide. The obtained interesting features nominate the newly developed core-shell calcium phosphate/Cu x Fe 2-x O 4 nanoceramics as promising candidates for talented magneto-optical and peroxide sensor applications.

Rearranged Copolyurea Networks for Selective Carbon Dioxide Adsorption at Room Temperature.

Copolyurea networks (co-UNs) were synthesized via crosslinking polymerization of a mixture of tetrakis(4-aminophenyl)methane (TAPM) and melamine with hexamethylene diisocyanate (HDI) using the organic sol-gel polymerization method. The subsequent thermal treatment of between 200 and 400 °C induced the sintering of the powdery polyurea networks to form porous frameworks via urea bond rearrangement and the removal of volatile hexamethylene moieties. Incorporating melamine into the networks resulted in a higher nitrogen content and micropore ratio, whereas the overall porosity decreased with the melamine composition. The rearranged network composed of the tetraamine/melamine units in an 80:20 ratio showed the highest carbon dioxide adsorption quantity at room temperature. The results show that optimizing the chemical structure and porosity of polyurea-based networks can lead to carbon dioxide adsorbents working at elevated temperatures.

Preparation of high surface area nitrogen doped graphene for the assessment of morphologic properties and nitrogen content impacts on supercapacitors

Supercapacitors have been caught great attention owing to their high power density and fast charge/discharge ability with superior capacitance retention which originates from the formation of an electrical double layer on high surface area electrodes. In this study, Two-step organic sol-gel procedure is applied to graphene oxide to produce high surface area nitrogen doped graphene samples varying in surface area and nitrogen content. The higher impacts of specific surface area and porosity on capacitative performance of graphene than nitrogen content are observed in different electrolytes. All the samples give superior capacitative performance than those of graphene oxide and blank sample, but higher in acidic electrolyte than the alkaline yielding a volumetric specific capacitance of ~118 F·cm−3 with Coulombic efficiency of >99% and capacitance retention >80% after 10,000 successive cycle. Based on the weight of active material, the maximum gravimetric energy density is as high as 39 Wh·kg−1 in acidic electrolyte at 0.1 A·g−1, which is almost 2.6 times of graphene oxide used in this study.

Polyaniline nanotube/reduced graphene oxide aerogel as efficient counter electrode for quasi solid state dye sensitized solar cell

Polyaniline nanotube/reduced graphene oxide aerogel (PAniNT/rGOA) is studied as a potential counter electrode material for a quasi-solid-state dye-sensitized solar cell (DSSC) fabricated with poly(methyl methacrylate) based polymer gel electrolyte. The aerogel, prepared via an organic sol–gel route, having a high surface area of 294.73 m2 g−1 exhibits excellent electro-catalytic activity towards the reduction of triiodide ions in the electrolyte. The excellent catalytic activity of the aerogel based electrodes is manifested with cyclic voltammetry based analyses. Electrochemical impedance analyses and current density vs voltage plots are employed to gauze the photovoltaic performance of the DSSCs fabricated with PAniNT/rGOA counter electrode. The thickness of the counter electrode is a crucial factor that affects the performance of the DSSC: thicker films offer more surface area for electro-catalytic reduction reaction whilst increasing the charge and mass transport resistances simultaneously. At an optimum PAniNT/rGOA electrode film thickness of 8.68 µm, a power conversion efficiency of 5.47% is achieved. In addition, an improvement of open circuit voltage is observed due to the capacitance involved at the electrolyte/electrode interface.

Furan-functionalised melamine-formaldehyde particles performing Diels-Alder reactions

Functionalised particles are highly requested in materials research, as they can be used as vital components in many advanced applications such as smart materials, functional coatings, drug carrier systems or adsorption materials. In this study, furan-functionalised melamine-formaldehyde (MF) particles were successfully prepared for the first time using an organic sol-gel process. Commercially available 2-Aminomethylfuran (AMF) and 2-Aminomethyl-5-methylfuran (AMMF) were used as modifying agents. In the isolated polymer particles, a melamine (M) to modifying agent ratio of M:AMF mol/mol 2.04:1 and M:AMMF ratio of mol/mol 1.25:1 was used. The obtained particles were isolated in various centrifugation and re-dispersion cycles and analysed using ATR-FT-IR, Raman and solid state 13C NMR spectroscopy, TGA, SEM and DSC measurements. Upon functionalisation the size of the MF particles increased (MF 1.59 µm, 27% CV (coefficient of variation); MF-AMF 2.56 µm, 25% CV; MF-AMMF 2.20 µm, 35% CV). DSC measurements showed that another type of exothermic residual reactivity besides condensation-based curing takes place with the furan-modified particles that is not related to the liberation of volatile compounds. The newly obtained particles are able to undergo Diels-Alder reactions with maleimide groups. The characteristic IR and Raman absorbance bands of the reaction products after the particles were reacted with 4,4′-Diphenylmethanebismaleimide reagent confirm the formation of a Diels-Alder adduct.

Preparation and characterization of melamine-formaldehyde/Ag composite microspheres with surface-enhanced Raman scattering and antibacterial activities

A facile and environmentally friendly approach was proposed to decorate Ag nanoparticles on melamine-formaldehyde (MF) colloidal particles (MF/Ag composite microspheres). In this approach, monodisperse MF colloidal particles were prepared via a two-step organic sol-gel process and served as the active templates for the decoration of Ag nanoparticles. Then, the [Ag(NH3)2]+ ions as the Ag precursors can be adsorbed onto the surfaces of the MF colloidal particles and were in situ reduced into metallic Ag nanoparticles, forming MF/Ag composite microspheres. During this synthesis, neither presurface activation nor extra reductants were necessary. These MF/Ag composite microspheres can be used as the surface-enhanced Raman scattering (SERS) active substrates for the trace detection of organic compounds, e.g., 4-aminobenzenethiol (4-ABT) and penicillin G sodium. Furthermore, these MF/Ag composite microspheres also showed excellent antibacterial activities against both Escherichia coli (E. coli, gram-negative bacteria) and Staphylococcus aureus (S. aureus, gram-positive bacteria).

Compare the phase transition properties of VO2 films from infrared to terahertz range

ABSTRACTVO2 with reversible semiconductor–metal phase transition properties is particularly available for the application in smart opto-electrical devices. However, there are rare reports on comparing its phase transition properties at different ranges. In this study, the VO2 films are designed with the similar crystalline structure and stoichiometry, but different morphologies by inorganic and organic sol-gel methods, and their phase transition characteristics are compared both at infrared and terahertz range. The results indicate that the VO2 film prepared by inorganic sol-gel method shows more compact nanostructure. It results in larger resistivity change, infrared and terahertz switching ratio in the VO2 film. Moreover, it presents that the phase transition intensity of VO2 film in terahertz range is more sensitive to its microstructure. This work is helpful for understanding the susceptibility of terahertz switching properties of VO2 to its microstructure. And it can provide insights for the applications of VO2 in terahertz smart devices.

Sol gel-derived hydroxyapatite films over porous calcium polyphosphate substrates for improved tissue engineering of osteochondral-like constructs.

Articular cartilage interfaces with bone through a zone of calcified cartilage. This study describes a method to generate an "osteochondral-like" implant that mimics this organization using isolated deep zone cartilage cells and a sol-gel hydroxyapatite coated bone substitute material composed of calcium polyphosphate (CPP). Developing a layer of calcified cartilage at the interface should contribute to enhancing the success of this "osteochondral-like" construct following implantation to repair cartilage defects.

Carbon nanocasting in ion-track etched polycarbonate membranes

We replicate the unique pore structure of ion-track etched polymers with carbon using an organic sol-gel precursor strategy. First, phenol resin is cross-linked in the membrane pores, followed by selective dissolution of the template matrix and carbonization at a temperature of 550°C. The potential to create nanomaterials of novel morphology is demonstrated by synthesizing free-standing, interconnected networks composed of aligned carbon nanowires of defined or modulated diameter.

Effects of processing parameters on the pore structure of mesoporous carbon membranes

Mesoporous carbon membranes have been prepared by means of an organic sol–gel method. The sol formed by resorcinol and formaldehyde was layered on the outer surface of a fly-ash-based microfiltration ceramic membrane, and was then subjected to gelling, drying, and carbonization to form a mesoporous carbon layer. Several surfactants were used to allow the carbon membranes to dry under ambient pressure. The pore properties of the carbon membranes have been examined by physical adsorption of nitrogen and subsequent pore structure analysis. The surface area, mesopore volume, and average pore diameter have been controlled by changing the surfactant species and concentration, the resorcinol/formaldehyde concentration, and the sol synthesis time. The as-prepared carbon membranes showed high performance with low transport resistance. The pore size/distribution can be tailored for a specific separation process by adjusting the preparation conditions. These carbon membranes can be applied in ultrafiltration separation processes.

Reaction mechanism and optimal conditions for preparation of high-quality vanadium oxide films by organic sol–gel for optoelectronic applications

Although vanadium oxides (VOx) are important functional materials for academic research and industrial applications, the reaction mechanism of VOx prepared by organic sol–gel remains unclear. In order to investigate this mechanism, VOx organic sols were reacted at different temperatures, by which various VOx thin films were prepared. The products were systematically characterized by infrared spectroscopy, Raman spectroscopy, UV–vis spectroscopy, thermogravimetric analysis, scanning electron microscopy, x-ray diffraction, and a high resistance meter. Results reveal that vanadium alkoxides are created through an alcoholysis reaction of V2O5 powder and isobutyl alcohol, and then a condensation reaction of the vanadium alkoxides leads to the formation of VOx networks. The as-prepared sols are strongly temperature-dependent, causing different chemical structures and physical properties for the resulting VOx films. Particularly, a moderate temperature of 110 °C prompts both alcoholysis and condensation reactions, and thus the VOx films that are produced by the sol reacted at 110 °C possess a low resistivity of 23 Ω cm, a high temperature coefficient resistance (TCR) of −3.2% K−1, and a low average transmittance of 54% in 580–1100 nm, compared with those prepared by the sols reacted at lower or higher temperatures. Therefore, 110 °C is a desirable sol temperature for producing VOx films serving as high-quality bolometric materials for uncooled infrared detectors. This work discloses not only the reaction mechanism of VOx films prepared by organic sol–gel, but also the route to yield desirable VOx films for optoelectronic applications.

On the synthesis and structure of resorcinol-formaldehyde polymeric networks – Precursors to 3D-carbon macroassemblies

With the new impetus towards the development of hierarchical graphene and CNT macro-assemblies for application in fields such as advanced energy storage, catalysis and electronics; there is much renewed interest in organic carbon-based sol–gel processes as a synthetically convenient and versatile means of forming three dimensional, covalently bonded organic/inorganic networks. Such matrices can act as highly effective precursors, scaffolds or molecular ‘glues’ for the assembly of a wide variety of functional carbon macro-assemblies. However, despite the utility and broad use of organic sol–gel processes – such as the ubiquitous resorcinol-formaldehyde (RF) reaction, there are details of the reaction chemistries of these important sol–gel processes that remain poorly understood at present. It is therefore both timely and necessary to examine these reactions in more detail using modern analytical techniques in order to gain a more rigorous understanding of the mechanisms by which these organic networks form. The goal of such studies is to obtain improved and rational control over the organic network structure, in order to better direct and tailor the architecture of the final inorganic carbon matrix. In this study we have investigated in detail, the mechanism of the organic sol–gel network forming reaction of resorcinol and formaldehyde from a structural and kinetic standpoint, by using a combination of real-time high field solution state nuclear magnetic resonance (NMR), low field NMR relaxometry and differential scanning calorimetry (DSC). These investigations have allowed us to track the network formation processes in real-time, gain both detailed structural information on the mechanisms of the RF sol–gel process and a quantitative assessment of the kinetics of the global network formation process. It has been shown that the mechanism, by which the RF organic network forms, proceeds via an initial exothermic step correlated to the formation of a free aromatic aldehyde. The network growth reaction then proceeds in a statistical manner following a first order Arrhenius type kinetic relationship – characteristic of a typical thermoset network poly-condensation process. And despite the relative complexity and ill-defined nature of the formaldehyde staring material, the final network structure is to a large extent, governed by the substitution pattern of the resorcinol molecule.

Study of a New Sol-Gel Spin-Coating Technology and Thermal-Resistance Properties for Vanadium Oxide Thin Films

A new organic sol-gel spin-coating method was adopted to prepare the vanadium oxide (VOx) thin films. In this method, the sol-gel adopted was formed from the dispersion consisted of different proportions of V2O5 powder, benzyl alcohol and iso-butanol. Spin-coating technology and thermal-resistance properties of the VOx thin films were systematically investigated. In this method, V5+ in the solution was reduced to form the V4+ isobutanol complex. Compared with conventional inorganic sol-gel process, little hydrolysis happened and little precipitation was produced, and temperature for the post-heating treatment is relatively low. Compared with conventional organic sol-gel process, the raw materials used in this method have relatively low prices.

Incorporating fluorescent dyes into monodisperse melamine-formaldehyde resin microspheres via an organic sol-gel process: a pre-polymer doping strategy.

An organic sol-gel process was developed to incorporate fluorescent dyes into monodisperse melamine-formaldehyde (MF) resin microspheres. Various organic fluorescent dyes have been successfully incorporated by this process, and monodisperse fluorescent MF microspheres were prepared. Fluorescence-encoded microsphere arrays with dozens of sets were obtained by quantitatively incorporating several dyes at different doping concentrations. The characteristics and incorporating mechanism of these microspheres and their dyes were investigated by scanning electron microscopy, Malvern particle analysis, fluorescence spectroscopy, laser scanning confocal microscopy (LSCM), and flow cytometric analyses. Resonance energy transfer (RET) interactions of the doped dyes were investigated by steady-state and time-resolved fluorescence spectroscopy. The dye-incorporated microspheres were stable, and no leakage or deformation was found. With the occurrence of the RET effect among multi-doped dyes, prepared microspheres exhibited single excited, doping ratio-related emission signatures. The prepared dye-doped microspheres were coated with silica shells, which provided favorable surface properties for bioconjugate applications. This process of incorporating organic dyes could also be used to coat particles with dye-doped fluorescent MF shells. Multi-shell structured composite microspheres with fluorescent shells were also prepared by alternately repeating silica and MF coatings.

Manganese Oxide/Graphene Aerogel Composites as an Outstanding Supercapacitor Electrode Material

Graphene aerogels (GA), prepared with an organic sol-gel process, possessing a high specific surface area of 793 m(2) g(-1) , a high pore volume of 3 cm(3) g(-1) , and a large average pore size of 17 nm, were applied as a support for manganese oxide for supercapacitor applications. The manganese oxide was electrochemically deposited into the highly porous GA to form MnO2 /GA composites. The composites, at a high manganese oxide loading of 61 wt. %, exhibited a high specific capacitance of 410 F g(-1) at 2 mV s(-1) . More importantly, the high rate specific capacitances measured at 1000 mV s(-1) for these composites were two-fold higher than those obtained with samples prepared in the absence of the GA support. The specific capacitance retention ratio, based on the specific capacitance obtained at 25 mV s(-1) , was maintained high, at 85 %, even at the high scan rate of 1000 mV s(-1) , in contrast with the significantly lower value of 67 % for the plain manganese oxide sample. For the cycling stability, the specific capacitance of the composite electrode decayed by only 5 % after 50,000 cycles at 1000 mV s(-1) . The success of this MnO2 /GA composite may be attributed to the structural advantages of high specific surface areas, high pore volumes, large pore sizes, and three-dimensionally well-connected network of the GA support. These structural advantages made possible the high mass loading of the active material, manganese oxide, large amounts of electroactive surfaces for the superficial redox events, fast mass-transfer within the porous structure, and well-connected conductive paths for the involved charge transport.

Polyurea networks via organic sol–gel crosslinking polymerization of tetrafunctional amines and diisocyanates and their selective adsorption and filtration of carbon dioxide

Organic molecular networks were synthesized via organic sol–gel polymerization of tetrakis(4-aminophenyl)methane with various alkyl diisocyanates. Colloidal dispersions of nanoparticulate molecular networks were obtained by controlling monomer combinations and concentrations, which enabled liquid phase processing of the covalent networks into desired forms of materials. Pouring the sols into a non-solvent yielded nanoparticulate networks that showed highly selective adsorption for CO2 over N2 or CH4. Free-standing films of the network material were prepared by evaporation of the sols. The membranes exhibited unusual reverse-selective transport characteristics with lower permeability to CO2 than to N2. This is the first example of gas separation membranes directly prepared from the liquid phase of covalent molecular networks. The organic sol–gel chemistry of covalent molecular networks is promising for the development of new functional adsorbents and membranes because it will enable exploitation of intrinsic microporosity of molecular networks.

Effect of Tetraethoxysilane (hybrid sol) on chemical and abrasion resistance, and dyeability of nano polyamide mat

This work deals with the application of inorganic–organic sol–gel layer on polyamide nanofabrics to protect nanofibres against chemical and mechanical damages. To this aim, fabric specimens with different silica concentration (1, 5, 10, 20 and 40 %) have been prepared. Layers were deposited on polyamide nanofabrics by pad-dry-cure technique. Permeability was defined as the rate of airflow perpendicular to a test sample under specified conditions for the test area, pressure gradient, and time according to DIN EN ISO 9237. Abrasion resistance testing was performed for determining the weight loss of samples before and after sol–gel treatment. For chemical resistant measurement, Formic Acid was used. Infrared spectroscopy was also used for investigation of the chemical structure of the treated polyamide nano mats. The morphology of the fabrics was observed using a Scanning Electron Microscope. Also both untreated and sol–gel treated samples were dyed using cationic dyestuff and dyeability of polyamide nanomats after treating by hybrid sol were compared with untreated one. The results indicate that the K/S value of CI. Basic Red 46 are enhanced by increasing the concentration of Tetraethoxysilane based sol, respectively. Also by increasing the concentration of sol–gel to 50 %, the greatest resistance to formic acid was achieved.

Organic sol–gel synthesis of microporous molecular networks containing spirobifluorene and tetraphenylmethane nodes

AbstractThe microporous molecular networks based on rigid tetrafunctional units are synthesized via organic sol–gel polymerization of 2,2′,7,7′‐tetraamino‐9,9′‐spirobifluorene (TASBF) and/or tetrakis(4‐aminophenyl)methane (TAPM) with a diisocyanate, hexamethylene diisocyanate (HDI), or p‐phenylene diisocyanate. This study is performed as an extension of our previous report on the first organic sol–gel method, which enabled the synthesis of microporous molecular networks via a two‐stage mechanism involving the formation of colloidal dispersions of the nanoparticulate molecular networks and their subsequent growth to monolithic networks on solvent evaporation. The sol–gel‐synthesized molecular networks obtained by incorporating TASBF as a network former show improved porosity, processability, and thermal stability than the TAPM‐based system. The improved porosity of TASBF‐based networks is attributed to higher rigidity of the spirobifluorene compared with the tetraphenylmethane units. We also demonstrate the synthesis of mixed organic molecular networks by sol–gel copolymerization of the two network formers, TASBF and TAPM, and a diisocyanate monomer. The sol–gel transformation of TASBF/TAPM/HDI occurred at longer reaction times with increasing the amount of TASBF in the TASBF/TAPM/HDI mixture. The results indicate that the organic sol–gel method can be further optimized by adjusting various synthesis parameters to create new functional organic molecular network materials. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013