Materials Chemistry and Physics 131 (2011) 507–511 Contents lists available at SciVerse ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Investigations on the effect of experimental parameters on the porosity features of silica aerogels synthesized at ambient drying conditions S. Smitha a,b , P. Shajesh a , K.G.K. Warrier a,∗ a Materials and Minerals Division, National Institute for Interdisciplinary Science and Technology (CSIR), Pappanamcode, Trivandrum, Kerala – 19, India b Magnetics Laboratory, Department of Physics Cochin University of Science and Technology, Cochin, Kerala – 22, India article info Article history: Received 15 November 2010 Received in revised form 19 May 2011 Accepted 8 October 2011 Keywords: Sol–gel growth Amorphous materials Microporous materials Adsorption abstract Silica aerogels were synthesized through an ambient pressure drying technique, and the porosities of the aerogels were tailored over a wide range, by varying the experimental parameters such as hydrol- ysis temperature, gelation pH, aging pH and aging solvent. Pore size, pore volume and surface area could tailor between 6.2–18 nm, 0.99–2.04 cc g -1 and 452–635 m 2 g -1 respectively by changing the hydrolysis–condensation conditions. By varying the aging pH from 3 to 11, pore size and pore volume was tailored in between 5.8–13.4 nm and 0.88–1.45 cc g -1 respectively. The investigation will be highly beneficial for the synthesis of tailor made silica aerogels at ambient conditions. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Silica aerogels are a fascinating class of nanoporous materials derived by sol–gel technique and has shown great potential for a range of applications in the areas including thermal insulation, catalysis, gas storage, nuclear waste confinement, optics and elec- tronics [1–10]. The high interest in aerogel arises from its unique properties such as ultra low density, high porosity, large inner sur- face area, small index of refraction, low sound velocity, low thermal conductivity and low dielectric constant [1]. Major challenges dur- ing the synthesis of low-density, high-surface-area materials at ambient pressures are the large capillary pressure that develops during drying (a result of the small pore sizes) and low stiffness of the gel (a result of the low-density) [11]. Drying at supercritical conditions of the solvent removes the drying stress [12]. However, the high temperature and pressure required to achieve the super- critical conditions of common solvents used in aerogel synthesis renders the technique expensive and hazardous [13–15]. The vol- ume of the autoclave also imposes restriction on the sample sizes. In addition, the supercritical drying results in fragile aerogels which are extremely difficult to handle [16]. The ambient pressure drying technique which involves aging and solvent exchange has evolved as an effective technique for the ∗ Corresponding author at: Materials & Minerals Division, National Institute for Interdisciplinary Science and Technology (Formerly Regional Research Laboratory), Industrial Estate, Pappanamcode, Trivandrum – 695019, India. Tel.: +91 471 2515280, fax: +91 471 2491712. E-mail address: wwarrierkgk@yahoo.co.in (K.G.K. Warrier). synthesis of silica aerogels [17–21]. Numerous studies and reviews are available in the literature on the effect of processing parame- ters on the properties of resultant silica aerogels [22,23]. Haereid et al. has shown that aging TEOS-based alcogels in solutions of TEOS/ethanol can favourably increase the strength and stiffness and reduce the shrinkage during drying at ambient pressures. Low- density silica xerogels ( = 0.24 g cm -3 ) were obtained by changing aging parameters such as time and temperature [17,20,24]. Titu- laer et al. found that the pore structure development of spherical silica gel bodies on aging is influenced by temperature, pH and the silica to water ratio which affects the rate of silica transport [25]. Chou et al. studied the effect of aging solvent on silica gels [26]. They related the surface area to the polarity parameter of the aging solvent. Hdach et al. investigated the influence of aging and pH on the modulus of aerogels [27]. Davis et al. reported that aging at higher pH yield lower surface area, larger pore volume and a nar- row pore size distribution [28]. Lee et al. studied the effect of pH on the physicochemical properties of silica aerogels prepared by an ambient pressure drying [29]. Rao et al. investigated the effect of precursors, methylation agents and solvents on the properties of resultant silica aerogels, and they prepared low density aerogels (0.14–0.3 g cm -3 ) using TMOS and sodium silicate as precursors and TMCS or HMDS as surface modifiers [30]. Kumar et al. reported the synthesis of high surface area silica by solvent exchange in alkoxy derived silica aerogel under subcritical conditions [31]. They found that solvents of low vapour pressure and high molecular weight favour the formation of gels with high pore volume. We had recently reported on an ambient pressure drying technique which involves washing and silane aging steps to obtain aerogels. A comprehensive study on the effect of various parameters like 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.10.012