Density Of Aerogels Research Articles

Hydrothermal formation of graphene aerogel for oil sorption: the role of reducing agent, reaction time and temperature

Different reducing agents including vitamin C, ammonia and ethanediamine can significantly affect the density, strength, morphology and adsorption performance of graphene aerogels.

Platinum Nanoparticle Loading of Boron Nitride Aerogel and Its Use as a Novel Material for Low‐Power Catalytic Gas Sensing

A high‐surface‐area, highly crystalline boron nitride aerogel synthesized with nonhazardous reactants has been loaded with crystalline platinum nanoparticles to form a novel nanomaterial that exhibits many advantages for use in a catalytic gas sensing application. The platinum nanoparticle‐loaded boron nitride aerogel integrated onto a microheater platform allows for calorimetric propane detection. The boron nitride aerogel exhibits thermal stability up to 900 °C and supports disperse platinum nanoparticles, with no sintering observed after 24 h of high‐temperature testing. The high thermal conductivity and low density of the boron nitride aerogel result in an order of magnitude faster response and recovery times (<2 s) than reported on alumina support and allow for 10% duty cycling of the microheater with no loss in sensitivity. The resulting 1.5 mW sensor power consumption is two orders of magnitude less than commercially available catalytic gas sensors and unlocks the potential for wireless, battery‐powered catalytic gas sensing.

Polymer aerogels for efficient removal of airborne nanoparticles

Abstract This study evaluates the potential of polymer aerogel monoliths in removing airborne nanoparticles. Macroporous monolithic aerogels of δ-form syndiotactic polystyrene (sPS) are synthesized for this purpose via thermoreversible gelation of a solution of sPS in a good solvent followed by supercritical drying. The air permeability and airborne nanoparticle removal efficiency are determined as function of the bulk density of aerogels. The data reveal a power-law dependence of particle removal efficiency and air permeability on bulk density. The data also reveal that efficiency greater than 99.95% can be achieved if the bulk density is kept at 0.042 g/cm3 or higher. These materials show air permeability of the order of 10−10 m2. The gradient density aerogels produced via sequential injections of sPS solutions show improvements in filtration efficiency attributed to additional skin layers. This idea is exploited in designing gradient density aerogel filters that offer higher efficiency and higher air permeability at a much lower bulk density than the single density monoliths of the same thickness.

Preparation of Cellulose Nanocrystal Aerogel from Wastepaper through Freeze-Drying Technique

Cellulose nanomaterials processing for aerogel preparation has received considerable attention among the scientific community due to its fascinating properties. In this work, we report on the preparation of cellulose nanocrystals (CNCs) aerogel from wastepaper using a freeze-drying technique. Structural analysis of the cellulosic particles extracted was investigated by Fourier Transform Infrared Spectroscopy (FTIR). Morphological analysis of the extracted cellulose and CNCs were carried out by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) respectively. We achieved density of aerogel down to 0.012 g/cm3 which is comparable with typical values of cellulosic aerogels. The preparation of the CNCs aerogel might offers a wide range of aerogel applications through an environmentally friendly conversion of wastepaper material.

Changes in the structure of cellulose aerogels with depolymerization

To compare the cellulose aerogels from hydrolyzed and unhydrolyzed cotton linter, we prepared cellulose wet gels from cellulose solution dissolved in hydrated calcium thiocyanate at 110 °C and dried them by using the freeze-drying method. The initial root-mean-square (RMS) radius and the weight average molar mass of cotton linter decreased from 71 nm and 405 kg·mol −1, respectively, to 13 nm and 35 kg·mol −1 upon acid hydrolysis. The density of cellulose aerogels increased from 39 to 87 kg/m3 as the cellulose starting material was depolymerized. The microstructure of the cellulose aerogel was viewed with a scanning electron microscope (SEM), and the microstructure and the micro-sized pores were found to be destroyed by cellulose degradation. The degree of polymerization (DP) of the cellulose was found to affect the aerogel’s density and network structure.

Elastic silica aerogel using methyltrimethoxysilane precusor via ambient pressure drying

The use of N,N-dimethylformamide (DMF) as a drying control chemical additive was found to be effective in obtaining methyltrimethoxysilane (MTMS) based silica aerogels in terms of excellent monolithic property, hydrophobicity and elasticity. The aerogels were produced by hydrolysis and condensation of methanol diluted MTMS in presence of ammonia catalyst followed by ambient drying. The molar ratio of DMF/MTMS varies from 0 to 1. It has been observed that higher DMF/MTMS value leads to lower density (~0.15 g/cm3) and higher porosity of aerogels with excellent hydrophobicity. For DMF/MTMS (~0.6) values, monolithic and elastic aerogels which can recover to their original shapes after compression were obtained. Narrower and more uniform pore size distribution was observed for the DMF modified aerogels in our study.

Chitosan–silica composite aerogels: preparation, characterization and Congo red adsorption

A series of aerogels composed of chitosan and/or silica were fabricated by tuning their feeding ratios. They were characterized by FTIR, thermogravimetric analysis, and X-ray diffraction; pore structures were analyzed by Brunauer–Emmett–Teller (BET) nitrogen sorption and scanning electron microscopy (SEM); adsorption capacities to Congo red were explored as well. The incorporation of silica enhances the thermostabilization of chitosan in gels. And as silica content increases, bulk densities of aerogels decrease gradually, while porosities, pore volumes, and surface areas obtained via BET method increase consequently; as well, porous structure becomes more regular and pore size tends to be smaller that was observed by SEM. The adsorption capacities of chitosan-containing aerogels to Congo red reach as high as about 150 mg/g, much higher than that of pure silica (17 mg/g), demonstrating their potential as a class of novel adsorbent materials. A series of chitosan- and/or silica-based aerogels were fabricated, which were named as C5S0, C4S1, C1S1, C1S4, and C0S5, with different designed CS/SiO2 mass ratios of 100/0, 80/20, 50/50, 20/80, and 0/100, respectively. Their compositions and structures as well as adsorption properties to Congo red were analyzed and compared in detail.

The Optimum of Preparation and Characterization of Aerogels like Hydrophobic Titania by Ambient Pressure Drying

The influence of different factors in the alcogel preparation process and ambient pressure drying process on packing density of hydrophobic TiO2 aerogel synthesized by ambient pressure drying (APD) and the optimum preparation conditions were investigated by the orthogonal test with four-factor and three-level L9(34), respectively. The morphology and structural properties of hydrophobic TiO2 aerogels with different density were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetry (TG), N2 adsorption-desorption measurement and Scanning Electron Microscope (SEM). The results showed that the most important factors in the preparation process for TiO2 aerogels with low-density under ambient pressure are aging time, the volume ratio of C2H5OH to TBT, ethanol immersion time and hydrophobic modification time. The optimized preparation conditions are that aging time is 24 h, the volume ratio of C2H5OH to TBT is (7+7) : 5, the volume ratio of H2O to TBT is 1.7 : 5, the volume ratio of HAc to TBT is 1.7 : 5, ethanol immersion time is 24 h, hydrophobic modification time is 48 h, hexane solvent replacement time is 24 h and the drying temperature is 393 K. TiO2 aerogels with density of 460 kg/m3 was obtained at the optimized conditions. TiO2 aerogel with lower density displays higher specific surface area, porosity and pore volume as well as the larger pore size.

A Simple and Efficient Approach to Cellulose/Silica Composite Aerogel with High Silica Utilization Efficiency

Cellulose aerogel is a fascinating material with high porosity, low density and biocompatibility. However, cellulose aerogel lacks sufficient thermal stability. Recombination between cellulose aerogel with silica is efficacious for enhance the cellulose aerogel’s thermal stability. This work described a simple and efficient approach to the cellulose/silica composite aerogel via a dropwise manner, using tetraethoxysilane as silicon source and NaOH solution as cellulose solvent. The result showed that the thermal stability of cellulose aerogel was enhanced by introducing silica. And by this manner, the utilization efficiency of silica was up to 95%. The composite aerogel had a low density and a high porosity, which promised the material a good heat insulation performance, and the thermal conductivity of the composite aerogel was low to 0.0161W/(m·K). Moreover, by adjusting cellulose concentration and tetraethoxysilane amount, the density, porosity and thermal conductivity of the composite aerogel could be controlled. This work contributed to improving the utilization efficiency of silica for the composite aerogel with better performances.

Ultralow Density, Monolithic WS2, MoS2, and MoS2/Graphene Aerogels.

We describe the synthesis and characterization of monolithic, ultralow density WS2 and MoS2 aerogels, as well as a high surface area MoS2/graphene hybrid aerogel. The monolithic WS2 and MoS2 aerogels are prepared via thermal decomposition of freeze-dried ammonium thio-molybdate (ATM) and ammonium thio-tungstate (ATT) solutions, respectively. The densities of the pure dichalcogenide aerogels represent 0.4% and 0.5% of full density MoS2 and WS2, respectively, and can be tailored by simply changing the initial ATM or ATT concentrations. Similar processing in the presence of the graphene aerogel results in a hybrid structure with MoS2 sheets conformally coating the graphene scaffold. This layered motif produces a ∼50 wt % MoS2 aerogel with BET surface area of ∼700 m(2)/g and an electrical conductivity of 112 S/m. The MoS2/graphene aerogel shows promising results as a hydrogen evolution reaction catalyst with low onset potential (∼100 mV) and high current density (100 mA/cm(2) at 260 mV).

A New Approach for Synthesizing the Hybrid Silica Aerogels

Uniform Polyurethane/silica hybrid aerogels were achieved at ambient pressure via an approach in which an aqueous polyurethane dispersion was used and the hybridization step carried out before gelation step. The FT-IR spectra confirmed the incorporation of polymer chains into the silica network and hybrid network formation.As the H2O/TEOS molar ratio increased after hybridization in this method, the effect of H2O/TEOS molar ratio changes and PU content on the density of hybrid aerogels was investigated separately. The density of native silica aerogels decreases commonly with increasing the water content while increasing the aqueous PU dispersion content increases the density of hybrid aerogels. The density difference between the hybrid aerogel sample with a certain aqueous PU dispersion and the similar native silica aerogel with the same H2O/TEOS molar ratio demonstrated the intensive polyurethane chain effect on the aerogel density. The results showed that the simultaneous increase of H2O/TEOS molar ratio and PU content could be led to the uniform structure of hybrid aerogels. However, the effect of polyurethane on the aerogel density was more sensitive than H2O/TEOS molar ratio effect especially in high polyurethane content (≥10wt.%) that increased the density of hybrid aerogels.

Density controlled oil uptake and beyond: from carbon nanotubes to graphene nanoribbon aerogels

The relationship between oil adsorption capacity and aerogel parameters has been fabricated by delicately manipulating the density of carbon aerogels.

Silica-Aerogel Cotton Composites as Sound Absorber

AbstractIn the research reported in this paper, silica aerogel was synthesized in a cotton nonwoven mat (CNM) and then the composite was used as a sound absorber. The experimental data indicated that using aerogel as a coating on CNM significantly improved sound absorption up to 2,500 Hz. However for higher frequencies silica aerogel coating reduced sound absorption compared to neat CNM. The best sound absorption performance of the CNM coated aerogel happened between 250 and 2,500 Hz. The effects of different processing conditions were studied on the final properties of the silica aerogel and consequently on the sound absorption of the coated CNM. The pore size and surface area of the synthesized silica aerogel had no direct influence on the sound absorption properties of the composites; on the other hand, the density of the silica aerogel was the only critical factor that determined the sound absorption coefficients of the composites.

Hydrophobization of Silica Aerogels: Insights from Quantitative Solid-State NMR Spectroscopy

Silica aerogels have exceptional physical and chemical properties related to their nanoporous structure and high specific surface area. The hydrophobization of the silica surfaces, for example by modification with trimethylsilyl groups (TMS), is of central importance for silica aerogel production by ambient drying methods, particularly on an industrial scale. This study monitored the chemical modification of silica aerogels by quantitative and two-dimensional solid-state NMR spectroscopy. A series of two-step, acid/base-catalyzed silica alcogels were hydrophobized for different times in hexamethyldisiloxane (HMDSO) and subsequently dried at ambient pressure. Two-dimensional 1H–29Si heteronuclear correlation NMR spectroscopy confirms that both ethoxy and TMS groups are chemically bonded to the silica surfaces. For the single-pulse spectra, a procedure to calibrate the absolute 1H, 13C, and 29Si NMR signal intensities with external references was developed. The quantification procedure is validated by the internal consistency between the 1H, 13C, and 29Si results and the agreement between the measured sample mass and that predicted from the NMR data. The quantitative speciation data on the aerogel samples show that the silica surface is covered by a monolayer of ethoxy, TMS, and silanol groups. Silanol groups are progressively replaced by TMS groups with increasing modification time, and the TMS content has a strong effect on the density of the final aerogel.

The Influence of SiO<sub>2</sub> on Properties of Cellulose Aerogel

Cellulose hydrogel was prepared from cellulose/NaOH aqueous solutions. Silica was added into cellulose hydrogel by TEOS hydrolysis method. Finally aerogel was obtained by the freeze-drying technique. The influence of silica on the properties of cellulose aerogel was studied in detail. With cellulose content 3%, the water absorption of cellulose-SiO2composite aerogel was only about 50% of the water absorption of cellulose aerogel. The result showed that silica could effectively reduce the water absorption of cellulose aerogel significantly and reduce the extent of structural damage that resulted from highly water absorption of cellulose aerogel. At the same time, with the increase of cellulose content, density of cellulose aerogel increased, while porosity decreased. It led to the water absorption of aerogel decrease with the increasing of cellulose content.

The Effect of Different Ratio in Carbon Aerogel on Pore Structure in Ambient Dry

Organic aerogels were prepared by sol-gel polycondensation of resorcinol and formaldehyde using sodium carbonate as a catalyst and dried under ambient pressure. Carbon aerogels were obtained by the dried organic aerogels carbonized under nitrogen atmosphere at high temperature. The pore structures and surface characteristic of the carbon aerogels obtained were investigated by N2 adsorption isotherms, scanning electron microscope (SEM). Through controlling the concentrations of the main ingredients (resorcinol and formaldehyde), catalyst concentration, we can find out the best concentration which the specific surface area can reach the highest. In this experiment the highest specific surface area was 1645m2/g. In addition, the results show that catalyst for the cross link effect between colloidal microspheres is greater than the growth of the colloid itself, and the effect of water solvent plays an important role in the density of carbon aerogel.

ICF流体力学不稳定性实验用柱状激波管的研制

In inertial confinement fusion (ICF) experiments, the surface (interface) roughness and defect of target capsule can lead to hydrodynamic instability when the target capsule is irradiated by high-intensity laser facility. Controlling and understanding the growth of hydrodynamic instability can strongly increase the feasibility of ignition experiment and is of the main importance for achieving ignition and high gain. A new cylindrical shock wave tube was designed and fabricated after consulting relevant references and the parameters of Shenguang Ⅱ laser facility. The cylindrical shock wave tube consisted of rippled polystyrene (CH) film, cylindrical carbonized-resorcinol-formaldehyde (CRF) aerogel and cylindrical CH tube. The cylindrical shock wave tube was obtained by assembling the rippled CH film and cylindrical CRF aerogel into the cylindrical CH tube. The target design and fabrication processes were described while the target parameters were measured. The results indicate that the length, diameter and density of cylindrical CRF aerogel are 1000 m, 730 m and 250 mgcm-3, respectively, the diameter and thickness of the rippled CH film are 15 m and 730 m, while the perturbation period and amplitude on its surface are 100 m and 4.3 m, the maximum axial assembly deviation of the cylindrical shock wave tube is 2 m, while its maximum diameter assembly deviation is 3 m.

Preparation of Silica Aerogel and Its Adsorption Performance to Organic Molecule

Hydrophobic and lipophilic silica aerogel was prepared from water-glass by gelling, aging, silylation, and drying under atmospheric pressure and characterized by FT-IR and SEM. The effect of preparation process on aerogel density and the aerogel density on contact angle of water on it were investigated in detail. pH 6 is most beneficial to shorten gelling time and to obtain the lowest density of silica aerogel. Increasing TEOS concentration of aging solution to 25 v% could decrease aerogel density to 0.093 g/cm3. The silica aerogel exhibits good hydrophobicity even though its density is 0.30 g/cm3. There are few changes in their adsorption capacities after 3 cycles of adsorption-desorption. The adsorption performance of the silica aerogel to organic solvent in water is different from in pure solvents. The critical surface tension (γC) of the silica aerogel prepared here is about 30.8 mN/m. If the surface tension of aqueous solvent solution (γ) is greater thanγC, it will wet the aerogel surface partially. Ifγ ≤ γC, the solution will wet all aerogel surface and be adsorbed well. This work delivers us a method to adsorb solvents from their waste water by adjusting the surface tension of the waste water to lower thanγCof the adsorbent.

The Preparation and Characterization of Spherical Cellulose Aerogels with Core-Shell Structure

The spherical cellulose aerogels with core-shell structure were prepared through hanging drop method in a regenerated non-polar solution. The procedures of these aerogels' preparation include solidification in the acetic acid solution to form a hydrogel, solvent exchange with t-butyl alcohol and freeze drying. The spherical cellulose aerogels were obtained with different cellulose solution concentration, and characterized with BET analysis and electron microscopy. Their density and porosity varied linearly with different cellulose content in the initial solution. And the gel shrinkage upon drying was limited to, on average, 7.3%. The density of spherical cellulose aerogel could be reached down to 0.14 g·cm-3 with high specific surface areas up to 210 m2·g-1. The mesopores' diameter of spherical cellulose aerogel at the highest peak in the size distribution curve is focus on 15nm.

Preparation of carbon aerogels at room temperature using acetonitrile as solvent

Carbon aerogels were synthesized at room temperature by a sol–gel polymerization route using resorcinol and formaldehyde as precursors, acetonitrile as solvent and hydrochloric acid as catalyst, followed by CO 2 supercritical drying and carbonization. FT-IR, SEM, XRD and nitrogen adsorption were used to characterize the microstructure of the aerogels. Results showed that the carbon aerogels are graphite-like amorphous materials with nano-skeleton networks formed by nanoparticles around 40–70 nm in diameter, whose specific surface area is up to 1300 m 2 g −1 and lowest density about 0.050 g/cm 3 . The heat of condensation and the catalytic action of hydrochloric acid made it possible to form gels at room temperature. The high surface area and low density of the as-prepared carbon aerogels were ascribed to a strong interaction between acetonitrile and –OH groups by hydrogen bonding. [New Carbon Materials 2012, 27(6): 462–468]