Functional Group Analysis of Silica Gel Based on River Sand Magnetic Mineral as Heavy Metal Absorbance

Functional group analysis of silica gel synthesized from river sand magnetic minerals using the sol-gel method was conducted. River sand magnetic mineral samples were taken from Sompang River, Lombok. The synthesis method used is a sol-gel method with variation of HCl acid 10 M and NH4OH base 10 M. Morphological characterization using a Scanning Electron Microscope (SEM) and mineral content analysis using Energy Dispersive X-ray (EDX). The morphology of the resulting silica gel is granular, showing crystalline properties with a silica concentration of 77.99 ± 0.17 atomic percent. Silica functional groups before absorption showed three stretching vibrations, namely OH group stretching vibrations in Si-OH and H2O at an absorption wavelength of 3669.77 cm-1, Si-O stretching vibrations from siloxane (Si-O-Si) at an absorption wavelength of 2858.51 cm-1 and Si-O asymmetric stretching vibrations from silanol (Si-OH) at an absorption wavelength of 962.88 cm-1. While the results of the analysis of silica gel after absorption show that almost all samples have vibrational absorption in the range of 400-500 cm-1. Other vibrational absorptions in silica samples that have been used as water filters indicate that the bonding between nano-silica as an absorber and heavy metals is due to the magnetic properties of nano-silica.