Rational modification of chitosan biopolymer for remediation of Cr(VI) from water

Abstract

Chitosan, a well-known bioadsorbent used for water treatment. It is treated with ammonium thiocyanate and subjected to microwave irradiation to obtain thiolated chitosan which makes the chitosan more stable and effective for metal adsorption through electrostatic interaction. The thiolated chitosan(TCH) has been thoroughly characterized to ensure the structural changes in the native chitosan. TCH has been efficaciously used for the detoxification of Cr(VI) from water. Batch adsorption methodology has been used to optimize all the parameters for the adsorption process. The Langmuir maximum adsorption capacity for Cr(VI)at 298 K and pH 3.0 was 340.1 mg/g. Adsorption kinetics and thermodynamic were studied for suitable rate model and spontaneity of the adsorption behavior. The adsorption of Cr(VI) onto TC H favors pseudo-second-order rate model. Uptake of Cr(VI) by thiolated chitosan was spontaneous and adsorption was enthalpy driven as obtained through the thermodynamic experimental results. The value of ΔH, ΔG and ΔS were found to be -94.26 kJ/mol, -12.92 kJ/mol and 0.272 kJ/mol.K, respectively. The breakthrough volume and exhaustion volume were found to be 1400 mL and 2100 Ml, respectively during fixed bed adsorption (column studies) of 200 mg/L of Cr(VI) with 1 g of the material proven its applicability for larger volumes of Cr(VI). TCH has greener perspective as it can be easily regenerated 5% (w/v) sodium hydroxide solution.