Silica Gel Skeleton Research Articles

Preparation and Machine-Learning Methods of Nacre-like Composites from the Self-Assembly of Magnetic Colloids Exposed to Rotating Magnetic Fields.

Composite materials designed by nature, such as nacre, can display unique mechanical properties and have therefore been often mimicked by scientists. In this work, we prepared composite materials mimicking the nacre structure in two steps. First, we synthesized a silica gel skeleton with a layered structure using a bottom-up approach by modifying a sol-gel synthesis. Magnetic colloids were added to the sol solution, and a rotating magnetic field was applied during the sol-gel transition. When exposed to a rotating magnetic field, magnetic colloids organize in layers parallel to the plane of rotation of the field and template the growing silica phase, resulting in a layered anisotropic silica network mimicking the nacre's inorganic phase. Heat treatment has been applied to further harden the silica monoliths. The final nacre-inspired composite is created by filling the porous structure with a monomer, leading to a soft elastomer upon polymerization. Compression tests of the platelet-structured composite show that the mechanical properties of the nacre-like composite material far exceed those of nonstructured composite materials with an identical chemical composition. Increased toughness and a nearly 10-fold increase in Young's modulus were achieved. The natural brittleness and low elastic deformation of silica monoliths could be overcome by mimicking the natural architecture of nacre. Pattern recognition obtained with a classification of machine learning algorithms was applied to achieve a better understanding of the physical and chemical parameters that have the highest impact on the mechanical properties of the monoliths. Multivariate statistical analysis was performed to show that the structural control and the heat treatment have a very strong influence on the mechanical properties of the monoliths.

Robust Silica-Cellulose Composite Aerogels with a Nanoscale Interpenetrating Network Structure Prepared Using a Streamlined Process.

Silica aerogels can be strengthened by forming a nanoscale interpenetrating network (IPN) comprising a silica gel skeleton and a cellulose nanofiber network. Previous studies have demonstrated the effectiveness of this method for improving the mechanical properties and drying of aerogels. However, the preparation process is generally tedious and time-consuming. This study aims to streamline the preparation process of these composite aerogels. Silica alcosols were directly diffused into cellulose wet gels with loose, web-like microstructures, and an IPN structure was gradually formed by regulating the gelation rate. Supercritical CO2 drying followed to obtain composite aerogels. The mechanical properties were further enhanced by a simple secondary regulation process that increased the quantity of bacterial cellulose (BC) nanofibers per unit volume of the matrix. This led to the production of aerogels with excellent bendability and a high tensile strength. A maximum breaking stress and tensile modulus of 3.06 MPa and 46.07 MPa, respectively, were achieved. This method can be implemented to produce robust and bendable silica-based composite aerogels (CAs).

Fabrication of elastic silica-bacterial cellulose composite aerogels with nanoscale interpenetrating network by ultrafast evaporative drying

A nanoscale interpenetrating network (IPN) structure comprised of silica gel and bacterial cellulose gel is designed and surface-modified, to enable the fabrication of intact composite aerogels via direct heating to a relatively high temperature (110 °C). Compared to currently employed supercritical drying, freeze drying and ambient pressure drying, this process shortens the drying time of the aerogels from more than a few hours to less than 10 min. Although wet silica gels and bacterial cellulose gels seriously crack and shrink, respectively, when they exist individually, synergic effects between the fragile silica gel skeleton and soft bacterial cellulose gel skeleton ensure structural integrity of the composite gels during ultrafast evaporative drying. In particular, these synergic effects endow the composite aerogels with excellent elasticity so that they could recover their initial shapes even after undergoing 60% deformation. Hence, in addition to their low density (less than 0.12 g cm−3), high specific surface area (823 m2 g−1) and low thermal conductivity (0.032 W m−1 K−1) are well preserved, these synergic effects also aid to overcome some limitations with respect to practical applications of the fragile silica aerogels and soft bacterial cellulose aerogels, particularly when they are used as effective kinetic energy absorbers and recyclable oil absorbents.

Cellulose-Silica Composite Aerogels Prepared with Sodium Silicate by Freeze Drying Method

The cellulose-silica composite aerogels (CAs) were fabricated through a permeation sol-gel process in the regenerated cellulose hydrogels followed by freeze drying. The precursor Na2SiO3 instead of traditional organic precursor was diffused in the cellulose matrix followed by permeating the catalyst into the cellulose nanofibers network gradually to promote the in situ condensation of Na2SiO3 to form a SiO2 gel skeleton from outside to inside. The obtained CAs displayed the interpenetrating network (IPN) structure of the regenerated cellulose nanofibers network and the SiO2 gel skeleton in nanoscale. In the IPN structure, the flexible cellulose nanofibers network was supported by the hard inorganic network effectively to sustain the compression and the silica gel skeleton protect the cellulose nanofibers to avoid the remodeling of their shape in the process of solvent replacement before freeze drying. Due to the synergic effects of the different network, the IPN structure endows the CAs with high compression modulus (as high as 15.48 MPa), high specific surface area (as high as 621 m2 g-1) and low density (less than 0.182 g cm-3).

Preparation and proton conductivity evaluation of a silicate gel composite doped with a metal–Schiff-base–POM-MOF

A silica gel composite (denoted as 1–SG) doped with a proton-conductive metal–Schiff-base–POM-MOF, {[Cu3(L)2(H2O)4][Cu(DMF)4(SiW12O40)]·9H2O}n (1) (where L is N, N′-bis[1-(2-methoxyphenol-6-yl)-methylidene] hydrazine hydrate, DMF is dimethyl formamide, POM-MOF is polyoxometalates-based metal–organic framework), was prepared by sol–gel method. The structure of as-synthesized 1–SG was confirmed by infrared spectrometry and X-ray powder diffraction, and its proton conductivity was calculated based on electrochemical impedance spectroscopic measurement. It was found that the structural characteristics of complex 1 are retained successfully in the silica gel skeleton of as-prepared 1–SG. Besides, though 1–SG contains just 6.25 wt% complex 1, it exhibits good proton conductivities of as much as 1.51 × 10−3–1.26 × 10−2 S cm−1 in the temperature range of 25–100 °C under a relative humidity of 98 %; and in particular, it shows better proton conductivity than both complex 1 and silica gel at the same conditions, due to the presence of a large number of micropores and mesopores filled with “liquid”.

Flexible aerogels based on an interpenetrating network of bacterial cellulose and silica by a non-supercritical drying process

Flexible and crack-free bacterial cellulose (BC)–silica composite aerogels (CAs) are prepared through a sol–gel process followed by freeze drying, in which the BC matrix and silica gel skeleton form an interpenetrating network microstructure. The BC–silica CAs exhibit low density (0.02 g cm−3), high specific surface area (734.1 m2 g−1) and low thermal conductivity (0.031 W m−1 K−1), almost the same as pure silica aerogels. Due to the synergic effects of the BC matrix and silica gel skeleton, the obtained CAs show excellent robustness and flexibility which overcome the inherent fragility of traditional inorganic aerogels. Furthermore, the dried CAs can withstand a huge capillary force and keep their integrity and flexibility even upon being immersed in a liquid phase again. Hence, the CAs can be functionalized conveniently in a liquid phase to extend their applications. The hydrophobization modified CAs have potential to be used as adsorbents for water purification and show excellent oil absorption capability on the surface of water, and can be removed from water conveniently.

Macropore Formation of Silica Gel in the Presence of Sodium Dodecyl Sulfate by Inducing Phase Separation in Alcohol-free Aqueous Solution

Bimodal porous silica gel with both macropores and mesopores was prepared from water glass (WG) in the presence of low-molecular-weight surfactant, sodium dodecyl sulfate (SDS), by inducing phase separation during sol-gel reaction. The macroporous morphology was controlled by changing starting composition and gelation temperature: the change in the concentration of SDS was effective to control connectivity of macropores and silica gel skeleton in micrometer size, and the gelation temperature significantly affected macropore size. From the change in morphology with the concentration of SDS, it is considered that a homogeneous reacting solution separated into a phase of SDS and that of polymerized silica in contrast to other silica-surfactant systems, where phase separation proceeds between solvent and surfactant associated with silica gel surface. It is also suggested that SDS forms associated complex or micelle in aqueous acidic solution, and the formation of such structure plays an important role in the phase stability. We also controlled mesopore structures in the macroporous silica gel by aging as-geled samples under basic conditions.

Preparation and conductivity of solid high-proton conductor silica gel containing 80 wt.% decatungstodivanadogermanic acid

The silica gel containing decatungstodivanadogermanic heteropoly acid was prepared by means of the sol-gel method. Infrared spectrum and XRD pattern revealed that the Keggin structure characteristic of GeW 10V 2O 40 6− anion was present in the silica gel skeleton. The regularity of the change of the characteristic peaks in the infrared spectrum was investigated. The silica gel exhibited considerably high-proton conductivity. The proton conductivity of the gel containing 80 wt.% decatungstodivanadogermanic acid is 5.37 × 10 − 2 S cm − 1 at room temperature (18 °C).

Silica‐Gel‐Confined Ionic Liquids: A New Attempt for the Development of Supported Nanoliquid Catalysis

A new concept of designing and synthesizing highly dispersed ionic-liquid catalysts was developed through physical confinement or encapsulation of ionic liquids (with or without metal complex) in a silica-gel matrix through a sol-gel process. We studied ionic liquids such as EMImBF4, BuMImBF4, DMImBF4, CMImBF4, BuMImPF6, either with or without [Pd(PPh3)2Cl2] and [Rh(PPh3)3Cl], in a silica-gel matrix (E = ethyl, Bu = butyl M = methyl, D = decyl, C = cetyl and Im = imidazolium). The contents of ionic liquids and loadings of Pd or Rh were 8-53 wt % and 0.1 approximately 0.15 wt %, respectively. Analyses of FT-Raman spectra showed that abnormal Raman spectra of the confined ionic liquids were observed in comparison with the bulk and pure ionic liquids. EMImBF4 and BuMImBF4 ionic liquids could be completely washed out from the silica-gel matrix under vigorous reflux conditions, but ionic liquids with larger molecular size, for example, DMImBF4 or CMImBF4, could be confined into the silica-gel nanopores relatively firmly. These results suggested that the ionic liquids were physically confined or encapsulated into the silica gel. The N2 adsorption measurements indicated that the silica-gel skeleton was mesoporous with 50-110 A pore size after the BuMImBF4 ionic liquid was removed completely. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis showed that the silica-gel matrix was amorphous and non-uniformly mesoporous. Carbonylation of aniline and nitrobenzene for synthesis of diphenyl urea, carbonylation of aniline for synthesis of carbamates, and oxime transformation between cyclohexanone oxime and acetone were used as test reactions for these catalysts. Catalytic activities were remarkably enhanced with much lower amounts of ionic liquids needed with respect to bulk ionic-liquid catalysts or silica-supported ionic-liquid catalysts prepared with simple impregnation, in which the ionic liquid may be deposited as a thin layer on the support. Such unusual enhancement in catalytic activities may be attributed to the formation of nanoscale and high-concentration ionic liquids due to the confinement of the ionic liquid in silica gel; this results in unusual changes in the symmetry and coordination geometry of the ionic liquids.

Preparation of photochromic sol–gel composite films containing dodecaphosphotungstic acid

A novel photochromic gel film was prepared through entrapping 12-phosphotungstic acid (PWA) into a kind of inorganic–organic matrix co-hydrolyzed from tetraethylorthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES). Infrared (IR) spectra revealed that the Keggin structure characteristic of PW12O403− anions was present in the amine-functionalized silica gel skeleton and PWA interacted with R-NH3+ cations strongly. The amorphous state of the gel film was proved by X-ray diffraction (XRD) pattern. The gel film exhibited reversible photochromicity. Irradiated with ultraviolet light, the transparent film changes from colorless to blue. Then, bleaching occurs when the film is in contact with air or O2 in the dark.

Preparation and proton-conductibility of silica gel containing 64 wt.% undecatungstocobaltoaluminic heteropoly acid

Silica gel containing 64 wt.% undecatungstocobaltoaluminic acid was prepared by means of sol–gel method. Scanning electron microscope (SEM) and infrared (IR) spectrum revealed that the Keggin structure characteristic of [Al(H 2O)CoW 11O 39] 7− anion was present in the silica gel skeleton. The change of the characteristic peaks in the infrared spectrum was investigated. Thermogravimetry (TG) curve shows that there are three steps of weight loss. Differential thermal analysis (DTA) curve shows that the thermal stability of the gel is lower than that of pure undecatungstocobaltoaluminic acid. The silica gel exhibits considerably high proton conductivity of 1.30×10 −3 S cm −1 at room temperature (14 °C).

Preparation and conductibility of silica gels composited with undecatungstochromoferrous heteropoly acid

Silica gels composited with undecatungstochromoferrous acid have been prepared by the sol–gel method. FT-IR spectra and SEM declared that the Keggin structure characteristic of the Fe(H 2O)CrW 11O 39 6− anion was found in the silica gel skeleton. The change of characteristic peaks in IR spectra was analyzed. XRD pattern showed that the gel was amorphous. The gel exhibited considerably high-proton conductivity, which increased from 1.88×10 −3 to 1.11×10 −2 S cm −1 with the increase of the content of undecatungstochromoferrous acid at 20 °C.

Electrophoretic Deposition (EPD) Coatings of Sol-Gel Solutions and Suspensions

question, ∼300 m 2 /g, is made available by the mesopores. Because the total porosity of the monolithic silica matrix is higher than 80%, the user is able to perform his chromatography using a much lower back pressure than with conventional particles that have a total porosity of only app. 65%. By optimising the ratio of throughpores to total porosity and the silica gel skeleton thickness, separations become possible at higher flow rates. This is due to accelerated adsorption and desorption of the substances to be separated by the silica gel surface. Due to better mass transfer properties of a monolithic skeleton over distinct particles, highspeed separation is possible without noticeable impact on resolution. For example, five β-blockers were separated at high α values (α = k‘Substance2/k‘Substance1) and with excellent peak symmetry. At a flow rate of 1 ml/min, the 5 substances were separated within 5 minutes. Under these conditions, the total system backpressure was 13 bar. At a flow rate of 9 ml/min., the 5 β-blockers can be baseline separated within

Three-Dimensional Structure of a Sintered Macroporous Silica Gel

Three-dimensional (3D) macroporous morphology of a silica gel, formed as a result of the phase separation parallel to the sol−gel transition, was observed in real space by laser scanning confocal microscopy. The 3D image of the silica gel skeleton that was sintered into full dense pure silica glasses clearly demonstrated that the gel skeleton is continuous and interconnected in 3D space. The interface between the gel skeleton and the macropore was characterized in terms of interfacial curvatures. It was found that a large portion of the interface is hyperbolic, which is also found in a phase-separated structure of a binary polymer mixture developed during the spinodal decomposition (SD). Comparison was made in terms of the probability densities of the interfacial curvatures between the silica gel and a polymer mixture having an identical phase volume fraction to one of the phases. Although the probability density distribution of the mean curvature, H, representing geometrical characteristics of the interf...

Preparation, characterization and proton-conductivity of silica gel containing 71 wt.% 12-tungstogermanic heteropoly acid

Silica gel containing 71 wt.% 12-tungstogermanic acid was prepared by means of sol–gel method. Infrared (IR) spectrum and X-ray powder diffraction (XRD) pattern revealed that the Keggin structure characteristic of GeW 12O 40 4− anion was present in the silica gel skeleton. The change of the characteristic peaks in the IR spectra was investigated. Thermogravimetry (TG) curve shows that there are three steps of weight loss. Differential thermal analysis (DTA) curve shows that the thermal stability of gel is lower than that of pure 12-tungstogermanic acid. The silica gel exhibited considerably high proton conductivity. It is 4.00 × 10 −3 S cm −1 at room temperature (16°C).

Ni/SiO2 catalyst with hierarchical pore structure prepared by phase separation in sol–gel process

Silica-supported nickel catalysts with both macropores and mesopores were prepared in an alkoxide-derived sol–gel process in the presence of poly(ethylene oxide) (PEO) with an average molecular weight of 100000. In this process, the interconnected macroporous morphology is formed when transitional structures of spinodal decomposition are frozen by the sol–gel transition of silica. The addition of nickel into a silica–PEO system has negligible effect on the morphology formation suggesting that phase separation in the nickel-containing system proceeds by repulsive interaction between the solvent and PEO adsorbed on the silica, as observed in the system without nickel. In gel formation, it was found that the Ni was distributed selectively in mesopores in the silica gel skeleton as fine particles rather than aggregated in macropores. It is considered that PEO interacts with both silica and nickel cations. The interaction between PEO and Ni makes nickel distribute in the silica phase and keeps Ni from aggregation during drying, resulting in a high dispersion of Ni.

Preparation and conductivity of solid high-proton conductor silica gels containing 12-tungstogermanic heteropoly acid

Silica gels containing 12-tungstogermanic acid were prepared by means of sol-gel method. Infrared spectra and XRD patterns revealed that the Keggin structure characteristic of GeW 12O 40 4− anion was present in the silica gel skeleton. The regularity of the change of the characteristic peaks in the infrared spectra was investigated. The silica gels exhibited considerably high-proton conductivity, and the conductivity increased with increasing 12-tungstogermanic acid content. The proton conductivity of gel containing 71 wt% 12-tungstogermanic acid is 4.00×10 −3 s cm −1 at room temperature (16°C).

Preparation and Performance of High-Proton Conductive Silica Gels Containing Molybdotungstovanadogermanic Heteropoly Acid

The silica gel containing molybdotungstovanadogermanic acid was prepared by means of the sol–gel method. SEM and infrared spectra revealed that the Keggin structure characteristic of the GeW9Mo2VO5−40 anion was presented in the silica gel skeleton. The regularity of the change of characteristic peaks in the infrared spectra was investigated. The XRD pattern of the gel was amorphous. The TG curve showed three steps of weight loss. The DTA curve showed that the thermal stability of the gel is lower than that of the pure molybdotungstovanadogermanic acid. The gel exhibited considerably high proton conductivity, which increased with the increase of the molybdotungstovanadogermanic acid content. The proton conductivity of the gel containing 71 wt% molybdotungstovanadogermanic acid is 1.86×10−3 S cm−1 at 18°C.

Preparation and proton-conduction of silica gels containing heteropoly acids

Bulk silica gels containing dodecatungstophosphoric acid, H 3PW 12O 40·29H 2O (WPA) or dodecamolybdophosphoric acid, H 3PMo 12O 40·29H 2O (MPA), were prepared by the sol-gel method using tetraethoxysilane and each heteropoly acid. Infrared spectra of the gels revealed that the Keggin structure characteristic of heteropoly anions was present in the silica gel skeleton. WPA- or MPA-doped silica gels exhibited higher conductivities by more tan two orders of magnitude than the pure silica gel. Remarkable coloration was observed in the electrochromic cell using the WPA-doped silica gel as a solid electrolyte; the reversibility and response of the coloring and bleaching were comparable to the case using a typical liquid electrolyte of H 2SO 4.

Effect of hydrothermal treatment in the presence of salts on the chromatographic properties of silica gel

The effects of hydrothermal treatment of silica gel in the presence of some inorganic salts on the chromatographic properties of the product have been studied. In addition to the specific surface area and the mean pore diameter, the selectivity and retention properties of the treated silica gel as well as some hydrodynamic properties are also changed. The extent of these changes depended both on the duration of the hydrothermal treatment and on the nature of the salt added. The treatment with phosphate ion solution produced a decrease in the specific pore volume and in the apparent specific weight of the silica gel skeleton, along with significant changes in its selectivity.