Novel amino-ethyl Chitosan hydrogel for methyl orange removal from waste water: Kinetics, isotherms, and thermodynamics studies

The Methyl orange (MO) azo dye has been removed from dyes-contaminated wastewater for the first time using a novel amino-ethyl Chitosan crosslinked hydrogel (CS-ENH2). The induced amine groups served as positive charge centers to bind MO azo-dye anions. The MO adsorbents' capabilities in comparison to native Chitosan (CS) are directly correlated positively with the amination phase which a very rapid initial adsorption was seen in the first 60 min, then began to slow until it leveled off after 120 min and 180 min for CS and CS-ENH2. The adsorption temperature has a positive effect, particularly at low temperatures, between 25 °C and 30 °C, where the adsorption capacity of the CS-ENH2 is double that of the CS, while at higher temperatures that effect diminished. The kinetics, isotherms, and thermodynamics characteristics of the MO adsorption process were followed. The obtained results showed that the MO adsorption process adhered to the pseudo-second-order kinetic model, the Langmuir isotherm model, and had an endothermic and spontaneous character with a maximum adsorption Langmuir monolayer of 3.66 and 10.53 mg/g for CS and CS-ENH2. In conclusion, the CS-ENH2 adsorbent removed up to 2.86 folds of MO amount of that removed using Chitosan under the same operating conditions, which reflected in the reduction of the used adsorbent amount, adsorption time, and finally proved the cost-effective of the developed CS-ENH2 adsorbent.