Ambient Pressure Drying Process Research Articles

Effect of Drying Control Agent on Physicochemical and Thermal Properties of Silica Aerogel Derived via Ambient Pressure Drying Process

This paper presents the effect of drying control agents on the physicochemical and thermal properties of hydrophobic silica aerogels derived via the ambient pressure drying (APD) method by a surface silylation using a TMCS/n-hexane mixture. The structural and physicochemical properties of synthesized DMF-modified and unmodified hydrophobic silica aerogels were characterized using Brunauer–Emmett–Teller (BET) analysis, thermo-gravimetric analysis, FT-IR, and Raman spectroscopic techniques. Based on the obtained results, the differences in structure between samples before and after a surface silylation and the effect of drying control agents were documented. The structural measurements confirmed the efficient silylation process (TMCS/n-hexane), as well as the presence of DMF residues of hydrogen bonded with unreacted Si-OH silanol groups within the silica backbone after surface modification. Based on TG analysis, it was found that DMF addition improves thermal resistance (up to 320 °C) and hydrophobic character of prepared aerogel. Modification of the silica aerogel synthesis process by DMF also resulted in a significant increase in BET—the specific surface area, for the unmodified aerogel was ~828 m2/g, and for the DMF-modified aerogel more than 1200 m2/g—much higher than the value of silica aerogels available on the market.

Flexible, Strong, Multifunctional Graphene Oxide/Silica-Based Composite Aerogels via a Double-Cross-Linked Network Approach.

Multifunctional silica-based aerogels are an emerging material due to their unique properties and wide applications. However, their large-scale production and application are limited due to the high cost and cumbersome preparation process. Herein, we prepare graphene oxide (GO)/silica-based composite aerogels via a simple in situ sol-gel reaction. GO nanosheets (GOs) are functionalized with polyethylenimine (PEI) and 3-glycidyloxypropyltrimethoxysilane (GPTMS) successively. After a cohydrolysis and condensation of trimethoxymethylsilane (MTMS) and dimethoxydimethylsilane (DMDMS) in the presence of GOs and a convenient ambient-pressure drying process, the composite aerogels are obtained. In addition to the normal cross-linking of MTMS and DMDMS, the GOs also behave as cross-linking points to significantly enhance the mechanical properties and thermal stability of the network of the composite aerogels. The pore structure of the aerogels is tailored by varying the GO loads as well as its surface modification. The Young's modulus of a composite aerogel with a GO load of 0.5 wt % is about 5 times that for a neat polysiloxane aerogel, and the maximum degradation rate temperature is increased to over 90 °C. Compared with pure polysiloxane aerogel, the thermal insulation and flame resistance are also improved by a small addition of GOs. Moreover, GO/silica-based composite aerogels show stable piezo-resistive behavior. With the excellent mechanical properties, thermal stability, and multifunctionality, GO/silica-based composite aerogels show promising applications under some harsh and extreme conditions.

Preparation of Nanoporous Silica Aerogel from Wheat Husk Ash by Ambient Pressure Drying Process for the Adsorptive Removal of Lead from Aqueous Solution

Hydrophilic nonporous silica aerogels were synthesized from a low-cost wheat husk silica precursor via ambient pressure drying method for the first time. The prepared aerogels were characterized by using Fourier transform infrared spectra (FTIR), nitrogen adsorption/desorption measurement and scanning electron microscopy- energy dispersive X-ray (SEM -EDX) techniques. The aerogels were used in adsorption of lead (II) ions from aqueous solutions under various conditions such as pH, the adsorbent dosage, the initial lead (II) concentration and the contact time. The optimum adsorption efficiency (99%) was obtained in a pH of 5.5, adsorbent dosage of 4 g L-1, initial lead concentration of 50 mg mL-1 and contact time of 30 minutes. The adsorption data was well described by Langmuir isotherm and pseudo-second-order kinetic model. These results show that low-cost silica aerogel prepared from an agricultural waste can be used as an effective sorbent for lead (II) ions removal.

Ambient-pressure drying synthesis of large resorcinol–formaldehyde-reinforced silica aerogels with enhanced mechanical strength and superhydrophobicity

Silica aerogels generally exhibit poor mechanical properties, which seriously restrict their commercial use and makes it necessary to reinforce their structures to obtain materials strong enough to withstand mechanical stresses. The incorporation of polymers into silica aerogels is a promising approach due to the enhancement in mechanical strength afforded and the possibility of imparting the hydrophobicity of the polymers to the resulting aerogels. However, the processes typically employed to prepare polymer-reinforced silica aerogels are complex, arduous and costly, requiring multiple washing and soaking steps for the infiltration of the polymer precursors after gelation and supercritical drying. Additionally, diffusion problems can result in heterogeneity in aerogel monoliths due to the use of various cross-linked polymers and the autoclave-limited dimensions of aerogels. In this study, a facile sol–gel route was developed to fabricate a large (500 cm3) polymer–silica aerogel monolith that was stable under atmospheric conditions and suitable for machining. The synthesis of the polymer–silica aerogels began with a facile one-pot reaction involving resorcinol (R), formaldehyde (F), methyltrimethoxysilane (MTMS), and N-(β-aminoethyl)-γ-aminopropyl-trimethoxysilane (AEAPTES), followed by an ambient-pressure drying process. The resulting aerogels were characterised by nitrogen adsorption–desorption, scanning electron microscopy (SEM), contact angle, and thermal conductivity measurements, and the aerogel mechanical properties were evaluated by a unidirectional compression test. The Young's modulus of compression of the aerogels was observed to increase from 3.95 to 34.88 MPa with an increase in the density of the aerogels from 0.14 to 0.26 g cm−3. Simultaneously, the aerogels were observed to be superhydrophobic, with a contact angle as high as 168°, and exhibited low thermal conductivity (0.038 W m−1 K−1) and good absorption for organic liquids, which are critical characteristics for the practical application of aerogels, especially in energy-saving and oil-/chemical-cleanup practices.

Preparation and Characterization of SiO2-WO3 Composite Aerogel by Ambient Pressure Drying Process

Using sodium tungsten and industrial water glass as raw materials, SiO2-WO3composite aerogels were prepared by ambient pressure drying process. The hexamethyldisilazane(HMDSZ)/hexamethyldisiloxane(HMDSO)/hexane mixing solution was used to modify the sol-gel-derived SiO2-WO3wet gel. The microstructure, morphology and pore characteristics of the obtained SiO2-WO3composite aerogels were investigated by XRD, SEM, FTIR and BET N2 adsorption-desorption analysis. The adsorption/photocatalytic degradation for Rhodamine B of SiO2-WO3composite aerogel was investigated. The results indicate that mesoporous SiO2-WO3composite aerogel with specific surface area 660.8 m2/g and pore volume 1.94 cm3/g could be prepared by using HMDSZ/HMDSO/hexane mixing solution to modify the wet gel. The obtained SiO2-WO3composite aerogels have good adsorption/photocatalytic degradation for Rhodamine B than that of pure WO3aerogel.

Preparation of Silica Aerogel by Ambient Pressure Drying Process using Rice Husk Ash as Raw Material

Silica aerogel was prepared from rice husk ash by sol-gel process followed by ambient pressure drying. Silica was extracted from ash as sodium silicate by boiling it in sodium hydroxide solution. Sodium silicate was neutralized with nitric acid to form silica gel. To prepare aerogel, first the pore water of the gel was exchanged by ethanol and then surface modification was done by aging alcogel in tetraethylorthosilicate (TEOS)/ethanol solution. Before drying, TEOS/ethanol solvent was exchanged with n-heptane. Capillary stress and shrinkages were greatly reduced due to the low surface tension of n-heptane. The prepaid aerogel was a light and crack-free solid, with bulk de nsity cf 0.67 g.cm−3, porosity of about 80%, total pore volume of 3.1 cm3.g−1 and specific surface area of about 273 m2.g−1. The nature of surface modification and thermal stability of the aerogel was studied by FTIR and DSC/TG respectively.