Surface-functionalized silica gel adsorbents for efficient remediation of cationic dyes

Abstract

The toxic and non-biodegradable nature of organic dyes necessitates the design and synthesis of novel adsorbents for their effective removal from the environment. This study reports an effective remediation behavior of surface-functionalized silica gel against water-soluble cationic dyes (up to 98 % removal). Thiol groups were functionalized at the surface of silica gel (SiO2-SH). The surface-tethered -SH groups were further oxidized to sulfonic acid groups to generate the negatively charged moieties at the surface of silica gel (SiO2-SO3H). The morphology of the developed adsorbents and the surface modifications were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Uptake study of three cationic dyes, namely, rhodamine B (Rh B), rhodamine 6G (Rh 6G), and crystal violet (CV) with SiO2-SH and SiO2-SO3H adsorbents was performed by varying the adsorbent amount, contact time, pH of solution, and temperature. The presence of negatively charged species at the surface of SiO2-SO3H results in an increased electrostatic interaction with the cationic dyes, which leads to better remediation characteristics for SiO2-SO3H as compared to SiO2-SH. The reusability of the developed adsorbents was also assessed by investigating adsorption/desorption of dyes. The simple fabrication process provides a facile avenue to the adsorbents with efficient remediation towards cationic dyes.