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Chemical modification to obtain a zwitterionic cellulose and its performance in the uptake of Congo red dye
In this study was successfully synthesized a new adsorbent by the modification of cellulose with zwitterionic moieties as well as its removal efficiency of Congo red dye was evaluated. The chemical functionalization followed three steps: 1) synthesis of the zwitterionic precursor (TS) with N1-3-(trimethoxysilylpropyl)diethyelenetriamine and 1-4 butane sultone with equimolar moieties, 2) cellulose activation with NH4OH and 3) co-condensation reaction between available hydroxyl groups of cellulose with hydroxyl groups of the hydrolyzed precursor in heterogeneous media. The material was characterized by FT-IR, 13C/29Si NMR CP/MAS spectroscopy and ninhydrin method. These characterization tests demonstrated that chemical modification of cellulose was successfully carried out with a substitution degree up to 16.93%. Batch experiments were applied for evaluation of the uptake of Congo red in aqueous solutions. The isotherm equilibrium data fitted well with Langmuir model, with a maximum theorical adsorption capacity up to 541.8 mg g-1. The kinetics of sorption data for this system followed a pseudo-second order model. Almost complete removal was possible with 10 mg of the adsorbent from 6 mL of dye solution sample of 400 ppm in 1.3 h. Despite of the natural affinity of cellulose for Congo red dye, modified cellulose showed an improved uptake up to 8.6 times.