Effect of Heat on the Adsorption Properties of Silica Gel

Abstract

Abstract-Adsorption properties of silica gel have been attributed to the surface hydroxyl groups of silica gel. Some hydroxyl groups are free standing and called free silanol groups. Some are hydrogen bonded to neighbouring silanol groups. Christy has shown that a high silanol number and a balanced concentration proportionality between these two different types of hydroxyl groups is necessary for effective adsorption of water molecules.Thermal treatment of silica gel samples alters the proportions of these groups and the above fact was investigated by using thermally treated silica gel samples. Two silica gel samples of varying surface areas and silanol numbers were dried under vacuum at 200 o C and their adsorption characteristics were followed by using NIR spectroscopy. Then the samples were subjected to heating at 350, 450, 600 degrees to cause changes in the concentrations of the surface silanol groups and their surface and adsorption characteristics were followed.The results clearly indicate that the heating process both remove free and hydrogen bonded silanol groups and alter the ratio between the two. Furthermore, the heating causes reduction in silanol umber and upsets the balance in the proportionality of the silanol groups for effective adsorption of water molecules.

Tackling elemental mercury removal from the wet-gas phase by enhancing the performance of redox-active copper-based adsorbents utilising an operando pre-heating system

“…47 Therefore, the CuCl 2 -silica adsorbent sample as the starting material presumably showed the presence of largely hydrated copper(II) species, of CuCl 2 . 47,[58][59][60] Silica is a known water adsorbent via its surface silanol functionality, 43,55 which correlated with the TGA analysis and showed an approximately 3 wt% H 2 O loss at around 150°C (see TGA results in ESI †). Based on the amount of water and CuCl 2 loaded onto silica, the mol ratio of H 2 O : Cu in the supported sample was estimated to be around 5 : 1, and this showed that this amount of water was sufficient to cause full hydration of the copper(II) metal centre.…”

“…This is due to the nature of the silica support, which is hydrophilic, and it is used as a desiccant due to its large capacity for water (∼40 wt%), 43 and the adsorption properties are due to the surface hydroxyl groups known as silanol groups. 55 This high affinity for water molecules is anticipated to lead to capillary condensation or pore blocking on silica, thereby resulting in immediate mercury breakthrough. The effect of water on silica is severe but the effect on activated carbon is milder and it is incorrect to say that carbon is hydrophobic since the sorption of water vapour on activated carbon follows an S-shaped curve on the adsorption isotherm.…”

Mild hydrothermal synthesis of pollucite from soil for immobilization of Cs in situ and its characterization

“…For the peak at 2220 nm (4505 cm -1 ) due to Si-O group and OH stretch combination vibration [30], however, the analcime peak was lower, which indicates that most of structure water existing in the To further verify the different state of the water molecular in the structure between pollucite and analcime, we also investigated the thermal decomposition behaviors for pollucite and analcime by TG and DTG (Fig. 11) for the first time.…”

Silica and its Peculiarities

“…Esse tipo de sílica encontra usos extensivos como dessecante, absorvente seletivo, suporte cromatográfico, substrato, catalisador e isolante (térmico e sonoro). [48][49][50] A sílica gel pode absorver mais de 40% do seu próprio peso de água e, quando tingida com sais de cobalto, é conhecida como dessecante auto-indicador: anidro, azul; hidratado, rosa, podendo ser regenerado rapidamente por aquecimento. É quimicamente inerte, não tóxico e dimensionalmente estável.…”