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

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 remedia- tion 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 (SiO 2 -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 (SiO 2 -SO 3 H). 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), rhoda- mine 6G (Rh 6G), and crystal violet (CV) with SiO 2 -SH and SiO 2 -SO 3 H 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 SiO 2 -SO 3 H results in an increased electrostatic interaction with the cationic dyes, which leads to better remediation characteristics for SiO 2 -SO 3 H as compared to SiO 2 -SH. The reusability of the developed adsorbents was also assessed by investigating adsorption/desorption of dyes. The simple fab- rication process provides a facile avenue to the adsorbents with efficient remediation towards cationic dyes.