Silica aerogels are ultra-porous materials with three-dimensional cage-like morphology that makes these materials ideal for separation applications. However, their hydrophilic behavior and shrinkage ...of the porous network during drying makes them impractical for such applications. Therefore, conducting a proper modification strategy is crucial both in imparting a hydrophobic behavior to aerogels and in preserving the porous network during drying. This study evaluated the performance of silica aerogels silylated with mono (TMCS), tri (MTMS, MTES), or organofunctional silanes (MEMO, GLYMO) as potential adsorbing materials for oil pollution remediation. Silica aerogels were prepared by the sol-gel method under ambient conditions and were characterized by conducting Si-NMR, BET, TGA, and contact angle measurements. Among the samples, silica aerogels modified with TMCS and MTMS exhibited good hydrophobicity (θ > 140°), well-constructed solid network with mesoporous structure, high porosity (94%, 89%), and low density (0.13 g/cm3 and 0.24 g/cm3). These samples also can selectively separate oil or organic solvents from water and the adsorption capacity can reach 12.5 g/g and 8.7 g/g for S-TMCS and S-MTMS, respectively. They displayed enduring adsorption property for organic solvents after 7 cycles, which shows that silica aerogels modified with TMCS and MTMS can be promising candidates for oil/organic solvent clean up practices.
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•Silica aerogels were synthesized in ambient pressure by two-step sol-gel method.•Silylation agents TMCS, MTMS, MTES, MEMO and GLYMO were selected for modification.•Si-NMR analysis supports hydrophobic characteristics of the samples S-TMCS, S-MTMS and S-MEMO.•Adsorption properties of the hydrophobic samples were investigated for various oils and organic solvent pollutants.•S-TMCS and S-MTMS has very high adsorption capacities especially for kerosene and diesel oil.
Surface modification, which is simply about the end-capping of the reactive silanol groups located in silica wet gel to satisfy hydrophobic behavior, has great importance in the production of silica ...aerogels in ambient conditions. In this study, silica aerogels were synthesized with a sol-gel method via ambient pressure drying. A two-step surface modification was performed on wet gels by using various silanes with different contents (6%, 10% or 20% by vol in n-hexane) to control the extent of irreversible shrinkage during drying. Mono-functional (TMCS) and three-functional silanes (MTMS, MTES and MEMO) were selected for this purpose. The impact of the type and amount of the silylating agents on the microstructure, pore characteristics and hygroscopic nature of resulting aerogels were identified by conducting FTIR, SEM and BET analyses and contact angle measurements. According to characterization results, MTES exhibits a competitive performance compared to classically used TMCS, as the silica aerogels modified with 10% of MTES was obtained in a well-developed with mesoporous structure with very high specific surface area (SBET = 964m2/g) and high hydrophobicity (Θ = 137°). On the other hand, organically functionalized silane MEMO and MTMS, also display noteworthy results (monolithical structure with highly developed porous network and high degree of hydrophobicity) at the low contents (at 6% and 10%). These outcomes are crucial as they may encourage the future attempts on introducing three-functional silanes during surface modification, as these silanes yield high silylation performance and causes the synthesis of well-qualified silica aerogel in ambient conditions.
In
this study ionic liquid mediated sol-gel silica adsorbents were prepared and characterized
to investigate the sorption of Cr (VI) ions from aqueous solutions. For this
purpose silica based ...adsorbents containing ionic liquids (ILs) were synthesized
by following the sol-gel method in ionic liquid media. Thus the high extracting
ability of ILs were combined with the surface properties of silica substances.
Commercial (Aliquat 336® and EMIMTf2N) and synthesized
(A336NO3) ionic liquids were incorporated directly by sol-gel process.
Silica based adsorbents were being initiated with silica precursor (TEOS),
water, alcohol and ionic liquid hydrolysis in the presence of an acid catalyst
then completed with a condensation reaction. Chemical and morphological
characterization of prepared adsorbents have been investigated by FTIR, SEM and
BET analysis. The materials exhibited average pore diameter of 2 nm, pore
volume of 0.3 cm3/g and BET surface area of 300–600 m2/g.
The sorption behaviors of adsorbents have been investigated by using a series
of batch sorption studies. Cr(VI) sorption percentages of the adsorbents were
enhanced by containing ILs up to 99% with the adsorption capacity of 31.74
mg/g. It can be concluded that sorption of Cr(VI) ions from aqueous solution by
sol-gel silica based adsorbents containing Aliquat 336 takes place favorably
and these type of adsorbents are promising agents in the adsorption processes.
Son yıllarda, başta CO2 olmak üzere sera gazları olarak bilinen CH4, N2O, O3, CFC türü gazlar; yanma, endüstriyel emisyon veya anaeorobik bozunma gibi faaliyetlerle atmosfere salınmakta, yüksek ısı ...tutma kapasiteleri nedeniyle de yeryüzü sıcaklığının artmasına ve küresel iklim değişikliklerine neden olmaktadırlar. Dünya ülkelerinin CO2 salınımının azaltılması konularını öncelikli hedefleri olarak belirlemesiyle birlikte, bu konudaki gerek politik gerekse bilimsel çalışmalar büyük bir hız kazanmıştır Küresel karbon salınımlarının azaltılması için geliştirilen yöntemler; karbon yakalama ve depolama (carbon capture and storage) CCS teknolojileri olarak anılmaktadır. Bu yöntemler; yakma öncesi, yakma sonrası ve yakıtı oksitlendirme olmak üzere üç ana başlık altında toplanabilir. Adsorpsiyon, fiziksel ve/veya kimyasal absorpsiyon, membran ve kriyojenik (cryogenic) ayırma yöntemleri en yaygın kullanılan yanma sonrası CCS yaklaşımlarının başında gelmektedir. Gözenekli malzemeler de yanma sonrası akımlardan CO2’in fiziksel adsorpsiyon ile tutulmasında kullanılmaktadır. Ancak bu sistemlerin gerek seçimlilik gerekse döngüsel kullanım açısından zafiyetleri olduğu da bilinmektedir. Bu nedenle gözenekli malzemelerin CO2 ilgisi yüksek aminli gruplar ile modifiye edilmesi son yıllarda üzerinde çalışılan bir konu olmuştur. Hazırlanan bu derleme ile silika aerojellerin karbon tutma uygulamalarına yönelik güncel bilimsel çalışmalar taranmıştır. Derleme, silika arojellerin hazırlanması ve modifiye edilmesi, CO2 tutma başarımlarına yönelik yapılmış literatür çalışmaları ve gelecek uygulamaları olmak üzere başlıca üç kısımdan oluşmuştur. Sonuç olarak amin modifiye silika aerojellerin sahip oldukları üstün özelliklerle yanma sonrası süreçleri için ümit vaat eden malzemeler olduğu sonucuna varılmıştır.
Comprehensive investigations to achieve monolithic silica xerogels in crack-free form under ambient conditions were carried out. Seven silica xerogels (SXs) were synthesized by following two ...different production pathways (one-step, two-step) by changing the type of the sol components. Morphological and chemical characteristics of the silica xerogels were revealed with the aid of the FTIR, EDX, Contact Angle, SEM, TGA and BET analyses. Imidazolium based ionic liquids (ILs) were incorporated into the xerogel structure to serve as drying control chemical, as well as to promote spring-back effect during the solvent evaporation. Amine based silica source 3-aminopropyltriethoxysilane (APTES) was also included as a silica co-precursor to improve the silica network.
Surface modifications of final product were conducted by using 3-Methacryloxypropyltrimethoxysilane (MEMO) in order to transform the sample into hydrophobic characteristics. Visual observations were used as an instructive step to examine the monolithicity of the final product. As a result, volumetric ratio of the sol components (TEOS: APTES: IL: Ethanol: HCI) to achieve desired crack-free monolithic form with superior characteristics was determined as 1: 0.47: 0.1: 6.3: 7.4 × 10−5, respectively.
In recent years, greenhouse gases known as, CH4, N2O, O3, CFC and especially CO2 are released into the atmosphere through activities such as combustion, industrial emission or anaerobic decomposition ...and they cause an increase in surface temperature and global climate changes due to their high heat absorption capacities. Both political and scientific studies gained momentum as the countries of the world set the priority for the reduction of CO2 emissions. Developing methods for reducing global carbon emissions; are known as carbon capture and storage are known as (CCS) technologies. They are mainly classified as pre-combustion, post- combustion and oxyfuel combustion processes. Adsorption, physical and/or chemical absorption, membrane and cryogenic process can be considered as the most common CCS technologies. Porous solid sorbents can be also used for the physical adsorption of carbon dioxide from flue gases, as well. However, these processes are also known to have weaknesses in terms of both selectivity and cyclic operation. More recently, modification of mesaporous materials with amine groups have been shown to be efficient solid adsorbents for CO2 capture. With this review, current scientific studies on the recent advances in carbon sorption applications of silica aerogels has been investigated. The review consists of three main sections: preparation and modification of silica aerogels, literature studies on CO2 sorption performances and future perspectives. As a result, it has been concluded that amine-modified silica aerogels are promising materials for the carbon capture for the post combustion processes with their superior properties.
The present research aims to investigate the chemical and morphological properties of the methylated silica xerogels produced via the co-gelation approach combined with surface silylation. In the ...sol−gel synthesis, methyltrimethoxysilane (MTMS) and tetraethylorthosilicate (TEOS) were utilized as silica precursors and trimethylchlorosilane (TMCS) served as a silylating agent. Structural changes were observed depending on the MTMS/TEOS molar ratio and on the post-synthesis-performed surface silylation of the xerogels. Post-synthesis silylation plays a critical role in the exchanging of the surface silanols with methyl groups, preserving the monolithic form. The morphological and structural changes were followed by SEM, 29Si-MAS-NMR, FTIR spectroscopy, nitrogen porosimetry, and contact angle measurements. The results have shown significant structural variations depending especially on the MTMS content. With an increasing MTMS content, the morphology of the samples has changed from a micro/mesoporous texture to a meso/macroporous texture. A higher degree of methyl substitution has been achieved for the silylated samples both confirmed by the FTIR and 29Si-NMR results. On the other hand, only the samples with a high MTMS content could preserve their structural integrity after evaporative drying, and all have exhibited a high degree of hydrophobicity with θ > 140°.
In this study, the effect of ionic liquid embedded silica aerogels on the mechanical properties of epoxy composites was investigated. The study consisted of two parts. In the first part, silica ...aerogels were synthesized by one-step sol–gel method and dried by supercritical drying. Two different silica aerogel powders with/without ionic liquid were prepared to investigate the effect of ionic liquid both on the physicochemical characteristics and the dispersion behavior of the silica aerogel. Various analyses such as FTIR, SEM/EDX, TGA, PSD and Zeta Potential analysis were conducted in order to investigate the effect of the contribution of ionic liquid on the physicochemical and textural structures of these powders and to identify the surface charge characteristics of the aerogels. According to characterization results, silica aerogels prepared by including ionic liquid, resulted in superior characteristics with lower density (0.16 g/cm
3
), higher porosity (93%), higher thermal stability (up to 400 °C), higher zeta potential value (28 mV) and smaller average particle diameter (40 nm). In the second part, silica aerogel-epoxy nanocomposites were produced by changing silica aerogel content and mechanical analyses of the composites were conducted. To examine the mechanical properties of nanocomposites, tensile and three-point bending tests were performed. The results have shown that the composites containing 1 wt% ionic liquid in silica aerogel had superior modulus of elasticity (4156.27 MPa) and tensile strength (51.96 MPa) compared to that of neat epoxy which had the elasticity modulus of 3538.08 MPa and tensile strength of 47.98 MPa.
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