Sol-Gel-Derived Porous Silica: Economic Synthesis and Characterization

Abstract

Porous silica was synthesized via the sol-gel process using clay obtained locally from Ijero-Ekiti in Ekiti State, Nigeria and compared with silica synthesized under similar conditions from sodium metasilicate (Na 2 SiO 3 ) obtained comercially. The clay was initially refluxed with sodium hydroxide (NaOH) for 2 hours to extract SiO 2 to form Na 2 SiO 3 , which was subsequently hydrolyzed to form a gel. The gel obtained was washed with deionized water to get rid of impurities, dried and calcined at 800˚C for 3 hours. The obtained silica powders were characterized using atomic absorption spectrophotometer, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results showed that the vibrational modes and diffraction patterns of the silica derived from commercial Na 2 SiO 3 and that prepared from clay were similar containing pure amorphous SiO 2 . The morphology of the commercially obtained silica showed better arrangement of particles and exhibited slightly lesser porosity (62.4%) compared to that derived from clay which had a porosity of 65.5%. The result indicates that clay has a potential for use as an environmentally safe and economic starting material for preparing porous silica instead of high quality precursors.

Catalytic Activity of Sulfated and Phosphated Catalysts towards the Synthesis of Substituted Coumarin

“…The synthesis of coumarin molecules has been established using different approaches such as Pechmann condensation [22][23][24][25], Perkin reaction [26][27][28], Witting reaction [29][30][31], Claisen rearrangement [32], Reformatsky reaction [33], Knoevenagel condensation [34][35][36][37], and flash vacuum pyrolysis [38]. Among the mentioned methods, the Pechmann reaction remains one of the most successful techniques to synthesize coumarin compounds.…”

Sol-gel bioceramic material from bentonite clay

“…Bentonite clay of the type (OH) 4 Si 8 Al 4 O 20 ·nH 2 O shown in Figure 2(a) was reacted in strong basic medium to initially afford sodium metasilicate (reaction equation is shown elsewhere [26]) after evaporating the alkaline filtrate slowly to dryness at 120˚C. The waterglass obtained, Figure 2(b), from this reaction is hydrolysed under acidic conditions to silicic acid which undergoes condensation to disilicic acid and further reaction to a polycondensed hydrogel [26,27].…”

“…According to the extraction procedure reported by Essien et al [26], a mixture of bentonite clay (13.33 g) in 1 M NaOH (250.00 ml) was heated at 120˚C for 2 hours under reflux in a round bottom flask. The filtrate obtained was slowly evaporated to dryness at 130˚C to obtain sodium metasilicate (Na 2 SiO 3 ).…”

“…Clay has a wide origin and is particularly cheap and widely available in Nigeria [26]. The silicon oxide layer can be extracted using alkali at elevated temperature to give the corresponding alkali silicate as possible precursor for glass synthesis.…”

Bioactivity of quaternary glass prepared from bentonite clay

“…To prepare the bioactive glass with composition 46.99 mol% SiO 2 , 24.36 mol% Na 2 O, 25.50 mol% CaO, and 3.15 mol% P 2 O 5 , sodium metasilicate (Na 2 SiO 3 ) was first extracted from bentonite clay as described previously [15]. In a typical sol-gel procedure, appropriate amount of the obtained Na 2 SiO 3 was dissolved in deionized water to give a solution that was then added slowly to 1 M HNO 3 in a beaker furnished with a magnetic stirrer under ambient temperature for 1 h to facilitate complete hydrolysis.…”