Biofilm of cross-linked Chitosan-Ethylene Glycol Diglycidyl Ether for removal of Reactive Red 120 and Methyl Orange: Adsorption and mechanism studies

In this study, a biofilm of cross-linked Chitosan-Ethylene Glycol Diglycidyl Ether (Chi-EGDE) was prepared and coated onto glass plate to act as a biosorbent for two structurally different Reactive Red 120 (RR120) and Methyl Orange (MO) dyes by applying non-conventional adsorption system without separation and filtration processes. The characterizations reveal that the Chi-EGDE biofilm has a low swelling index, good mechanical strength on glass plate, relatively high content (64.4%)of free amine (-NH2)groups, and pH(pzc) of similar to 6.8 indicating a positive surface charge occurs below pH(pzc). The adsorption data of RR120 and MO by the cross-linked Chi-EGDE biofilm were in agreement with Langmuir isotherm at 303 K, with maximum adsorption capacities of 165.3 mg/g and 131.2 mg/g, respectively. The kinetic data were well described by pseudo-second-order kinetic model. The adsorption process was spontaneous and endothermic in nature at cross-linked Chi-EGDE biofilm thickness of 4.24 mu m. The mechanism of adsorption included mainly hydrogen bonding interaction, electrostatic attractions, and n-pi stacking interaction. This study reveals that the cross-linked Chi-EGDE biofilm as a good candidate for adsorption of two structurally different reactive and acid dyes as it does not require any filtration process and adsorbents recovery during and post-adsorption process.