In this work, porous silica gel-solid beads have been made from economically affordable water-glass precursors via sol-gel nano casting technique. A stable nanometric silica sol was prepared first from water glass and studied for surface potential and sol to gel transition. A free-flow, injectable gel was obtained upon aging the sol which was then assembled into spherical silica beads in a chemical bath. A surface area of 304.7 m 2 g -1 was obtained for water glass derived silica gel beads. These gel beads were impregnated with 3-aminopropyltrimethoxysilane (APTMS) and polyethylenimine (PEI) active functional groups at different percentages for turning the gel beads as sorbents for CO 2 gas adsorption. The effect of amine loading on the thermal stability, morphology as well as porosity was studied and was correlated with CO 2 adsorption values. Depending upon the amount of amine loaded in the gel support CO 2 uptake was found varied. These amine modified silica gel porous adsorbents showed CO 2 adsorption capacity at temperatures as low as 100 o C; samples modified with 15 wt% PEI had CO 2 adsorption capacity of 1.16 mmol g -1 at 50 o C.

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In this work, a lightweight inorganic–organic hybrid foam adsorbent is processed out of economically cheap “double-silicate” precursors employing natural bentonite and water glass through a facile cross-linking and polymerization technique. Poly­(vinyl alcohol) was used to provide structural strength to the three-dimensional framework. The foam adsorbent possessed an apparent density of 0.083 g cm–3, indicating its internetworks and exposed surface area for the uptake of dyes. The foam was systematically studied for the treatment of textile dye effluent. Multivariate optimization process was carried out using response surface methodology. The Box–Behnken model was used for the design of experiments and to study the interplay between the variables. Batch adsorption and continuous column adsorption studies were carried out at respective levels of initial concentration (200–1000 μM), adsorbent dose (1–10 g L–1), and contact time (0–120 min). The results revealed that the hybrid silicate foam exhibits adsorption capacity as high as 99.9, 98.9, and 98.2% for 200, 600, and 1000 μM concentrations of methylene blue in 120 min, respectively, and 100% adsorption for 200, 600, and 1000 μM concentrations of crystal violet in 120 min for 10 g L–1 of adsorbent. Adsorption equilibrium data fitted well to Langmuir isotherm, and the kinetics followed second-order kinetic model. Synthetic industrial effluent with 1000 μM dye concentration was also prepared and studied with continuous column for determining the working capacity of the adsorbent, and the results are presented. The silicate hybrid foam is a cheap adsorbent that does not produce any secondary waste and can be repeatedly used making it attractive for dye industries.