Gel Templates Research Articles

Form-Stable phase change composites based on porous carbon derived from polyacrylonitrile hydrogel

Three-dimensional hierarchical porous carbon (3D-HPC) carriers were fabricated by pyrolyzing porous polyacrylonitrile hydrogels at high temperature, which were further applied to achieve simultaneous guarantee of the high energy storage density, thermal conductivity, shape stability and optical/electric-thermal energy conversion performance of PCMs. • Synthesis of PAN gels is green and facile; AMPS helps polymerization and pyrolysis. • Carbonization of PAN aerogel produces high-performance 3D-HPC carriers. • 3D-HPC can load PEG > 85 wt% with shape stability and thermal cycling stability. • 3D-HPC/PEG CPCMs present 10 times increase in thermal conductivity than PEG. • CPCMs possess optical/electric-thermal energy conversion capability. How to improve thermal conductivity as well as energy conversion efficiencies and to prevent melting leakage of solid–liquid phase change materials (PCMs) has been the essential challenges for the development of energy storage technology for storing a tremendous amount of waste heat and renewable and sustainable solar energy. Here, we reported the fabrication of high-performance form-stable composite PCMs (CPCMs) using the thermal conductive 3D-HPC carriers produced from the pyrolysis of porous polyacrylonitrile (PAN) copolymer hydrogels to confine the polyethylene glycol (PEG) PCMs. The porous 3D network PAN gel templates generate hierarchical cavities with micro/mesopores on the skeleton after pyrolysis which provides more space as well as the capillary adsorption and chemical interaction for the storage of PEG PCMs. The 3D-HPC/PEG CPCMs show high energy storage density (as high as 173.5 J g −1 ), high phase transformation efficiency and excellent thermal cycle stability. The carbon scaffold highly enhanced the thermal conductivity of CPCMs ∼ 10 times of the pure PEG and ensured its optical/electric-thermal energy conversion performance. This study demonstrates a facile, efficient and green way to fabricate hierarchical porous carbon with controllable porosity and degree of graphitization for improving the energy storage density, thermal conductivity, shape stability and energy conversion performance of PCMs.

In2S3‐Polymer Hybrid Gels Derived from In(III) Metal–Organic Gels for Dye Adsorption, Photodegradation, and Bacteria Removal

AbstractCurrently, the treatment of wastewater that contains organic dyes and bacteria attracts a considerable amount of attention, and the fabrication of photoinduced catalytic materials to address the problem is still a challenge. In this work, indium(III) sulfide hybrid gels are prepared by in situ polymerization and sulfurization using In(III) metal–organic gels as sacrificial templates. Two In(III) metal–organic gels are fabricated by the coordination interaction between multitopic pyridyl ligands and indium ions, where the assembled structure of the gel templates can be tuned by employing different multitopic ligands to obtain the networks of nanofibers and nanoparticles. After templated fabrication, the resulting In2S3‐polymer hybrid gels show improved mechanical strength, and can be used as novel photocatalysts for the photodegradation of organic dyes, such as rhodamine B and methylene blue, and efficient adsorbents for the adsorption of anionic dyes, such as Congo red. Experiments that involve pure and mixed bacteria demonstrate the bacteria‐removing activities of the hybrid gels due to their electrostatic adsorption and photoinduced sterilization of the bacteria. Therefore, this new kind of hybrid gel might have potential applications in the photoinduced purification of water by scavenging organic dyes and bacteria in the aqueous phase.

Selective removal of lead ion from polluted seaport water using a highly porous functionalized monolithic silica sorbent prepared by agarose template

A simple and inexpensive method for the synthesis of silica-based highly porous monolithic sorbents using agarose gel templates was developed for selective and efficient removal of Pb2+ from polluted seaport water samples. By controlling the agarose gel concentration, sorbents with different porosities could be obtained. The agarose gel was shaped as discs, silanized with (3-aminopropyl) triethoxysilane, calcined in 700 °C and functionalized by (E)-2-hydroxy-5-(phenyldiazenyl) benzaldehyde. The synthesized monolithic sorbent was then characterized by Fourier transform infrared spectrometry, X-ray diffraction, scanning electron microscopy and nitrogen sorption measurements. The results confirmed the mesoporous structure of the sorbent. Using two agarose gel concentrations of 2.5 and 7%, silica sorbents with porosities of 32.2 and 33.8 m2 g−1 were obtained. Evidences of variations in the structures and particle sizes were observed for the two sorbents. The influence of four parameters on the removal of Pb2+ from aqueous samples were optimized using a multivariate central composite design method. Under the optimized conditions, i.e. using 100 mg of the adsorbent for a 9.1 mL water sample in pH 7.9 and stirring for 56 min, 96.8% removal efficiency was obtained with a relative standard deviation of 7.4% for 5 replicates. The sorbent could be easily regenerated by a 0.2 mol L−1 HCl solution to be also used for enrichment and sensitive determination of the target ion.

Ion Gel Dynamic Templates for Large Modulation of Morphology and Charge Transport Properties of Solution-Coated Conjugated Polymer Thin Films.

Dynamic surfaces play a critical role in templating highly ordered complex structures in living systems but are rarely employed for directing assembly of synthetic functional materials. We design ion gel templates with widely tunable dynamics ( Tg) to template solution-coated conjugated polymers. We hypothesize that the ion gel expedites polymer nucleation by reconfiguring its surface to facilitate cooperative multivalent interactions with the conjugated polymer, validated using both experimental and computational approaches. Varying ion gel dynamics enables large modulation of alignment, molecular orientation, and crystallinity in templated polymer thin films. At the optimal conditions, ion-gel-templated films exhibit 55 times higher dichroic ratio (grazing incidence X-ray diffraction) and 49% increase in the relative degree of crystallinity compared to those templated by the neat polymer matrix. As a result, the maximum hole mobilities increase by factors of 4 and 11 along the π-π stacking and the backbone directions. Intriguingly, we observe a synergistic effect between the gel matrix and the ionic liquid that produces markedly enhanced templating effect than either component alone. Molecular dynamics simulations suggest that complementary multivalent interactions facilitated by template reconfigurability underlie the observed synergy. We further demonstrate field-effect transistors both templated and gated by ion gels with average mobility exceeding 7 cm2 V-1 s-1.

Fabrication of 3D PDMS Microchannels of Adjustable Cross-Sections via Versatile Gel Templates.

Flexible gel fibers with high stretchability were synthesized from physically cross-linked agar and covalently cross-linked polyacrylamide networks. Such gel material can withstand the temperature required for thermal curing of polydimethylsiloxane (PDMS), when the water in the gel was partially replaced with ethylene glycol. This gel template supported thermal replica molding of PDMS to produce high quality microchannels. Microchannels with different cross sections and representative 3D structures, including bifurcating junction, helical and weave networks, were smoothly fabricated, based on the versatile manipulation of gel templates. This gel material was confirmed as a flexible and reliable template in fabricating 3D microfluidic channels for potential devices.

Alumina based doped templated carbons: A comparative study with zeolite and silica gel templates

Alumina based templates were used for preparation of nitrogen and platinum doped templated carbons and compared with silica gel and zeolite templated carbons. For alumina based templated carbons, 5–6 times higher surface area was obtained compared to corresponding templates while that for zeolite and silica gel templates, it was only 1–2 times higher. The surface area of surfactant modified alumina templated carbon was comparable with that of microporous zeolite templated carbon but pore size and volume was comparable to that of mesoporous silica templated carbon. Higher dispersion of the Pt metal was observed within the matrix of mesoporous templates with highest for surfactant modified alumina templated carbon. The morphology of surfactant modified alumina templated carbon was similar to that of silica gel templated carbon and co-doping with platinum resulted in noddle like structure. At 25 bar and −196 °C the hydrogen uptake was in the range of 4–3.4 wt% and decreased linearly with decrease in surface area. Both surface area and pore volume dropped for all Pt co–doped samples. However uptake capacity varied; for co–doped silica gel and zeolite templated carbons it was reduced, while that of co–doped alumina based templated carbons it increased. The highest hydrogen uptake of 4.1 wt% for surfactant modified alumina templated co–doped carbon was attributed to synergistic effect of significant surface area, highest pore volume and highly dispersed platinum. The study concludes that alumina based templates are equally good or better for synthesis of the templated carbons.

Nitrogen modified templated carbons for energy application: Effect of templates and nitrogen precursors

Nitrogen modified templated carbons were prepared by carbonization at 923 K with dwelling time of 3 h. The effects of nitrogen precursors and templates on the surface area, pore structure and nitrogen loading of modified carbons were studied. Acetonitrile and aniline were used as nitrogen precursors, while zeolite and silica gel as inorganic templates. The surface areas of nitrogen modified carbons were reduced as compared to that of unmodified carbons. The effect is more significant for aniline precursor and zeolite template. Irrespective of nitrogen precursors, zeolite and silica gel templates resulted in mainly microporous and mesoporous carbons respectively. The nitrogen modified templated carbons were tested for hydrogen uptake. The hydrogen uptake of silica gel templated carbons increased on incorporation of nitrogen in spite of decrease in surface area. The high uptake of silica gel templated modified carbon can be attributed to higher activation of hydrogen by nitrogen centers present in the carbon network. However, drop in hydrogen uptake for zeolite templated modified carbons may be attributed to significant decrease in surface area. The hydrogen desorption kinetics was observed to depend on porous structure. Presence of micropores offered higher diffusion resistance, making desorption of hydrogen slower.

Prediction of the formation of microporous aluminophosphates containing (6, 8)-rings using support vector machines

A support vector machine (SVM) method has been used on the database of aluminophosphate (AlPO) synthesis with ca. 1700 reaction data to predict the formation of AlPOs with (6, 8)-rings based on 20 synthetic parameters associated with the gel composition, solvent and templates. Furthermore, four zeotype structures with different channel systems, such as AEN, AWO, ERI and CHA have been computational classified in the family of (6, 8)-ring-containing AlPOs. Analysis results reveal that several synthetic parameters, particular the molar ratio of solvent/Al2O3 (F3), and the Van der Waals (VDW) volume (F14), the greatest length (F11), and the number of free rotated single bond (F20) of templates have significant effects in directing the formation of target structure. Using single or combinations of several parameters, a better classifier can be trained to distinguish the (6, 8)-ring-containing AlPOs with desired zeotype structure or not, and the classification accuracy is about 85%. This work demonstrates that the computational method together with database of AlPO synthesis provides a possibility to establish the relationship between the synthetic factors and the resulting structures, which is important in guiding the rational synthesis of microporous aluminophosphate materials.

Mesoporous alumina materials synthesized in different gel templates

Abstract In this study, mesoporous alumina materials were constructed by using GP-1/PG organogel or agarose hydrogel respectively as a template. The XRD, SEM and TEM characterizations were performed to determine the crystalline phase and microstructure of the alumina. Our results suggest that different mesostructures could be formed using different gel systems. The alumina synthesized in GP-1/propylene glycol organogel is γ -Al 2 O 3 with wormlike mesochannels whilst the alumina prepared in agarose hydrogel is η -Al 2 O 3 with parallel lath mesostructure. The gel system induces the formation of alumina crystalline phase and morphology, as a result, different mesoporous alumina materials can be formed in different gel templates.

The role of nanoscale architecture in supramolecular templating of biomimetic hydroxyapatite mineralization.

Understanding and mimicking the hierarchical structure of mineralized tissue is a challenge in the field of biomineralization and is important for the development of scaffolds to guide bone regeneration. Bone is a remarkable tissue with an organic matrix comprised of aligned collagen bundles embedded with nanometer-sized inorganic hydroxyapatite (HAP) crystals that exhibit orientation on the macroscale. Hybrid organic-inorganic structures mimic the composition of mineralized tissue for functional bone scaffolds, but the relationship between morphology of the organic matrix and orientation of mineral is poorly understood. Herein the mineralization of supramolecular peptide amphiphile templates, that are designed to vary in nanoscale morphology by altering the amino acid sequence, is reported. It is found that 1D cylindrical nanostructures direct the growth of oriented HAP crystals, while flatter nanostructures fail to guide the orientation found in biological systems. The geometric constraints associated with the morphology of the nanostructures may effectively control HAP nucleation and growth. Additionally, the mineralization of macroscopically aligned bundles of the nanoscale assemblies to create hierarchically ordered scaffolds is explored. Again, it is found that only aligned gel templates of cylindrical nanostructures lead to hierarchical control over hydroxyapatite orientation across multiple length scales as found in bone.

Strong Silica Monoliths with Large Mesopores Prepared Using Agarose Gel Templates

Mesoporous silica pellets with controllable shape and pore size were prepared using agarose gel templates. Robust (compressive strength of 3.3-25.1 MPa), crack-free silica monoliths have been produced with large mesopores (14-23 nm), high surface areas (410-540 m(2) g(-1)), and large pore volumes (1.1-1.2 cm(3) g(-1)). The synthesis was achieved by infusing preformed agarose gels with tetraethyl orthosilicate and the nonpolar condensation catalyst tetrabutyl ammonium fluoride. The infiltrated gels were transferred to water to initiate hydrolysis and condensation of the silica precursor. Fluoride catalyzed the gelation of silica in a matter of minutes; hence, the oxide maintained the shape of the agarose pellet. The mesopore size could be modified by altering the weight percent of agarose gel used. The method employed here is simple and reproducible. As these materials have such large mesopore dimensions, they could be used as hard templates or could be specifically functionalized for use in environmental remediation, as environmentally responsive materials, biocatalysts, or catalysts.

α-Rhamnosidase and β-glucosidase expressed by naringinase immobilized on new ionic liquid sol–gel matrices: Activity and stability studies

Novel ionic liquid (IL) sol–gel materials development, for enzyme immobilization, was the goal of this work. The deglycosylation of natural glycosides were performed with α- l-rhamnosidase and β- d-glucosidase activities expressed by naringinase. To attain that goal ILs with different structures were incorporated in TMOS/Glycerol sol–gel matrices and used on naringinase immobilization. The most striking feature of ILs incorporation on TMOS/Glycerol matrices was the positive impact on the enzyme activity and stability, which were evaluated in fifty consecutive runs. The efficiency of α-rhamnosidase expressed by naringinase TMOS/Glycerol@ILs matrices increased with cation hydrophobicity as follows: [OMIM] > [BMIM] > [EMIM] > [C 2OHMIM] > [BIM] and [OMIM] ≈ [E 2-MPy] ≫ [E 3-MPy]. Regarding the imidazolium family, the hydrophobic nature of the cation resulted in higher α-rhamnosidase efficiencies: [BMIM]BF 4 ≫ [C 2OHMIM]BF 4 ≫ [BIM]BF 4. Small differences in the IL cation structure resulted in important differences in the enzyme activity and stability, namely [E 3-MPy] and [E 2-MPy] allowed an impressive difference in the α-rhamnosidase activity and stability of almost 150%. The hydrophobic nature of the anion influenced positively α-rhamnosidase activity and stability. In the BMIM series the more hydrophobic anions (PF 6 −, BF 4 − and Tf 2N −) led to higher activities than TFA. SEM analysis showed that the matrices are shaped lens with a film structure which varies within the lens, depending on the presence and the nature of the IL. The kinetics parameters, using naringin and prunin as substrates, were evaluated with free and naringinase encapsulated, respectively on TMOS/Glycerol@[OMIM][Tf 2N] and TMOS/Glycerol@[C 2OHMIM][PF 6] and on TMOS/Glycerol. An improved stability and efficiency of α- l-rhamnosidase and β-glucosidase expressed by encapsulated naringinase on TMOS/Glycerol@[OMIM][Tf 2N] and TMOS/Glycerol@[C 2OHMIM][PF 6] were achieved. In addition to these advantageous, with ILs as sol–gel templates, environmental friendly processes can be implemented.

Low-cost fabrication of poly(methyl methacrylate) microchips using disposable gelatin gel templates

A simple method based on disposable gelatin gel templates has been developed for the low-cost fabrication of poly(methyl methacrylate) (PMMA) microfluidic chips. Gelatin was dissolved in glycerol aqueous solution under heat to prepare a thermally reversible impression material. The molten gel was then sandwiched between a glass plate and a SU-8 template bearing negative relief of microstructure. After cooling, the negative SU-8 template could be easily separated from the solidified gelatin gel and a layer of gelatin template bearing positive relief of the microstructure was left on the glass plate. Subsequently, prepolymerized methyl methacrylate molding solution containing a UV-initiator was sandwiched between the gel template and a PMMA plate and was allowed to polymerize under UV light to fabricate PMMA channel plate at room temperature. Complete microchips could be obtained by bonding the channel plates with covers using plasticizer-assisted thermal bonding at 90 degrees C. Gelatin gel template can be mass-produced and will find application in the mass production of PMMA microchips at low cost. The prepared microfluidic microchips have been successfully employed in the capillary electrophoresis analysis of several ions in connection with contactless conductivity detection.

Microsphere optical ion sensors based on doped silica gel templates

A simple method for doping ion-sensing ingredients into silanized silica particles (∼3.5 μm) was developed to fabricate carrier-based ion-selective microsphere optical ion sensors. These ion sensors operate according to established bulk optode principles. Na +-selective microsphere optical sensors were prepared with the ionophore tert-butylcalix[4]arene tetraacetic acid tetraethylester, the H +-chromoionophore 9-(diethylamino)-5-octadecanoylimino-5 H-benzo[a]phenoxazine (ETH 5294), the ion exchanger sodium tetrakis[3,5-bis(tri-fluoromethyl)phenyl]borate (NaTFPB), PVC and the plasticizer bis(2-ethylhexyl)sebacate (DOS). For Ca 2+ sensing, the grafted Ca 2+ ionophore AU-1 in poly( n-BA) was applied with ETH 5294, NaTFPB and DOS. Fluorescence microscopy and flow cytometry were used for characterization. The resulting microsphere optical ion sensors were found to obey bulk optode theory with reliable response, high selectivities, dynamic ranges suitable for physiological measurements and a shelf time of over 6 months. The measuring ranges (logarithmic molar concentrations) at pH 7.4 were −3.5 to −1.5 for the fabricated Na +-selective optical-sensing microspheres, and −4.5 to −1.5 for Ca 2+-selective optical-sensing microspheres. Corresponding thin optode films and regular PVC/DOS-based microspheres were prepared for comparison and showed similar response characteristics. The fabricated microsphere optical ion sensors were also deposited on an optical fiber bundle, and reproducible fluorescence signals were observed.

Spongelike Macroporous TiO2 Monoliths Prepared from Starch Gel Template

TiO2 materials with a hierarchical meso/macropore organization were fabricated by using titanium dioxide nanoparticles and starch gel templates. Starch sponges with high internal macroporosities were prepared by freezing and thawing of starch gels and were then infiltrated with colloidal suspensions of titania nanoparticles and air-dried to produce TiO2-starch foams with pores up to 200 μ m across depending on the starch concentration and the TiO2 loading. The TiO2 nanoparticles were deposited as coherent layers on the thin walls of the starch framework, which was removed by calcination without significant disruption of the TiO2 framework. The three dimensional macroporous structures of TiO2-starch sponge composite and TiO2 sponge induced extremely high photocatalytic activity.

Preparation of the Precursor of Porous Alumina Particles using Immobilized Urease in Alginate Gel Templates

This paper describes a new method to precipitate the precursor of porous alumina particles by using a porous organic matrix as the template and an enzyme as the precipitant supplier. In this work, the precursor of aluminawas precipitated in urease-containing alginate gel spheres dispersed in aqueous solutions containing urea and Al 3 + ion. Urease was used to hydrolyze urea so that the precursor of alumina, basic aluminum sulfate, may be precipitated selectively within the gel spheres. By burning off the gel matrices after the precipitation of the precursor, porous alumina particles were obtained. The resultant alumina particles about 1 to 2 mm in diameter had sharp pore size distribution profiles around 0.1 to 0.01 μm. The inside of the alumina particles was able to be made either hollow or filled, depending on the aging time after the precipitation of the precursor.

Preparation of nanoporous MgO using gel as structure-direct template

MgO with various nanoscaled pore diameters were formed from magnesium nitrate adsorbed into the gel templates that are synthesized from hydroxyl ethyl methacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA) where the EGDMA worked as the cross-linker. The effects of molar ratio [HEMA]/[EGDMA] in the gel template on the porous structure of MgO formed in the template were investigated. The results indicated that the pore diameter of MgO could be varied by the [HEMA]/[EGDMA] molar ratio which directly affects the templating structure of gel. The smaller pore size and distribution were obtained with the increased molar ratio. The mechanism of the reaction was simply speculated.

Opal gel templated synthesis of oblate titania opal materials.

Ordered arrays of oblate titania bodies were template synthesized using opal gel templates under uniaxial compression at ambient temperature during the favorable titania sol/gel process. The aspect ratio was controllable by the compression degree.

Systematic Molecular Control of Interfacial Structure in Nanoporous Carbons

ABSTRACTThe present paper describes a new concept of synthesizing nanoporous carbons that allows control not only of the pore structure, but also of the molecular structure of the internal surfaces. Interfacial molecular control is achieved through the use of discotic liquid crystalline precursors whose molecular orientation on the substrate material is known or can be determined by simple measurements on flat substrate test samples. Here a suite of nanoporous (mesoporous) carbons are synthesized from various porous glass and silica gel templates, and a model is developed to predict the carbon properties from template properties thus allowing systematic template selection.

Starch Gel Templating of Spongelike Macroporous Silicalite Monoliths and Mesoporous Films

Silicalite nanoparticles and starch gel templates have been used to fabricate zeolite materials with a hierarchical micro/meso/macropore organization. Two methods were investigated. First, macroporous monoliths consisting of a continuous mesoporous framework of microporous silicalite were prepared by incorporating 50-nm-sized zeolite nanoparticles into freshly prepared viscous starch gels, followed by air-drying and calcination. Macropore sizes between 0.5 and 50 μm were achieved by varying the amount of starch and the starch/silicalite weight ratio. Mesoporous thin films of microporous silicalite, 2−15 μm in thickness, were also prepared by using gels containing low concentrations (2 wt %) of starch. Second, starch sponges with high internal macroporosities were prepared by freezing and thawing of starch gels and were then infiltrated with colloidal suspensions of silicalite nanoparticles and air-dried to produce silicalite−starch foams with pores up to 100 μm across depending on the starch concentration and the silicalite loading. The zeolite nanoparticles were deposited as coherent layers on the thin walls of the starch framework, which could be removed by calcination without significant disruption of the silicalite framework. In general, the methods described are facile, low in cost, and environmentally benign and can be readily extended to other inorganic materials with macroporous architectures, provided that suitable nanoparticle building blocks are available.