Investigation of the Remazol Turquoise GN dye adsorption using silane-modified silica prepared from agricultural waste

In this study, silica sorbents obtained from paddy waste ash were functionalized with (3-Aminopropyl) trimethoxysilane (APTMS) and 3-Glycidyloxypropyl) trimethoxysilane (GPTMS), and used in the adsorption of Remazol Turquoise GN (RTGN) dye in a batch system. The effects of pH (2–8) and the concentration of dye (20–100 mg/L) on the dye removal were investigated. To explain the adsorption mechanism, Langmuir, Freundlich, Temkin and Henry adsorption isotherm models were used. The Langmuir model for Si-APTMS and the Henry model for Si-GPTMS were found to be in agreement with the experimental data. Pseudo first and second-order kinetic models were used for the investigating the adsorption kinetics. It was seen that the adsorption process with Si-APTMS and Si-GPTMS was expressed by Pseudo second-order kinetic model. The dye removal capacities of these sorbents were obtained as 273.87 and 27.51 mg/g, respectively. The dye adsorption behavior of the modified silica sorbents was confirmed by Thermogravimetric (TG), Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyzes. The higher dye removal ability of Si-APTMS sorbent was correlated with the amine functionality of this sorbent. According to the analysis results and proposed adsorption mechanism, it was determined that the electrostatic interaction between the charged -NH₃⁺ in the sorbent surface and the -SO₃⁻ groups in anionic dye molecule was mainly responsible for the adsorption process.