Synthesis of functionalized silica and its application to water treatment

Abstract

The functionalized silica has been an effective material for the removal of heavy metal from aqueous solutions and the support of nanoparticles. Silica substrates are usually synthesized from expensive precursors i.e., tetraethoxysilane or tetramethoxysilane. Several works have reported on the preparation of functionalized silica from sodium silicate, a cheap silica precursor. However, almost processes used for the functionalization of sodium silicate-based silica are complicated and time consuming because they are conducted in organic solvents. Therefore, the objective of this work is to synthesize silica via a sol-gel process using sodium silicate and then to functionalize the silica with a facile and costeffective method. The obtained functionalized silica could be used for the water purification. In this dissertation, the synthesis and functionalization of precipitated silica were presented in chapter 2 and 3. The tunable properties of precipitated silica can be controlled by reaction parameters such as gelation time and temperature. Aminofunctionalization was prepared by simultaneously adding 3- aminopropyltriethoxysilane (APTES) and H2SO4 into the as-synthesized precipitated silica. The result indicated that the amino-functionalized silica is an effective supporting material for silver nanoparticles. The majority of the dissertation focused on the functionalization of silica gel for the support of silver nanoparticles and water treatment. Basically, silica gel was synthesized via a sol-gel method by using sodium silicate (Na2O·3.4 SiO2) and 40% H2SO4. The properties of silica can be controlled by washing, aging, and hydrothermal process. Amino-functionalized silica gel was prepared in water and organic solvent, while thiol-functionalized silica gel was prepared by a gentle method using a mixture of ethanol and water. A method so-called “dry method”proposed in the dissertation helps to significantly reduce time and cost of functionalization process. The thiol and amino functionalized silica gel proved as an effective supporting material for silver nanoparticles and as a promising absorbent for removal of heavy metal from water. Besides that, silver nanoparticle can be immobilized on functionalized-free silica gel by the manipulation of its pore size distribution. An effective method for water disinfection using silver nanoparticle-containing silica beads (Ag-NPBs) has been proposed. A filter containing Ag-NPBs did not require any extra external inputs such as electricity or high pressure. Such filter may be suitable for water treatment at the point-ofuse, in particular at natural disaster sites caused by flooding, tsunamis, and earthquakes. The present study proposes a facile method for the synthesis of cost effective functionalized silica, which may suitable for a large scale production. The amino and thiol functionalized silica can be used as absorbent to remove heavy metal from water and the Ag-NPBs are potential material for water disinfection.