Removal of chromium() from polluted wastewater by chemical modification of silica gel with 4-acetyl-3-hydroxyaniline

In the current study, a new adsorbent that is insoluble in water and many acid solutions and has a high adsorption capacity for Cr( vi ) metal ions was synthesized. In the synthesis process, 3-chloropropyl-trimethoxysilane (CPTS) was first modified on a silica gel (Si) surface. Secondly, 4-acetyl-3-hydroxyaniline (AHAP) was immobilized on the modified silica gel compound (Si-CPTS). As a result of the immobilization process, a new adsorbent compound named Si-CPTS-AHAP (silica gel-3-chloropropyltrimethoxy silane 4-acetyl-3-hydroxyaniline) was obtained, which was used to separate Cr( vi ) ions from aqueous solution (K 2 Cr 2 O 7 ) and industrial wastewater. The material was characterized using scanning electron microscopy and Fourier-transform infrared spectroscopy. The amount of chromium adsorbed was detected by ultraviolet-visible spectroscopy. The adsorption was evaluated using batch methods. The effects of temperature, pH, concentration, adsorbent amount and interaction time on the adsorption of Si-CPTS-AHAP were also investigated. The adsorption of Cr( vi ) ions on Si-CPTS-AHAP was investigated via adsorption kinetics, isotherm and thermodynamic studies. The value of the isotherm parameters and the highest adsorption yields were calculated from the Dubinin-Radushkevich, Freundlich and Langmuir isotherm equations. Thermodynamic features such as entropy (Δ S ), enthalpy (Δ H ) and free energy (Δ G ) were also calculated from the experimental results. The experimental results showed that the best recoveries of Cr( vi ) metal ions are under the conditions of 180 min (interaction time), 0.05 g (adsorbent amount) and 323.15 K (temperature) at pH 2. Si-CPTS-AHAP can be used for the removal of poisonous pollutants in wastewater. Use of a newly synthesized Si-CPTS-AHAP adsorbent in the removal of Cr( vi ) ions in wastewater treatment systems may potentially lead to low cost and highly efficient heavy metal removal.