Chemical modification of cellulose with zwitterion moieties used in the uptake of red Congo dye from aqueous media

Two zwitterionic celluloses were prepared by grafting amphoteric precursors AS (APTES with 1,4 butane sultone) and TAS (Trimethoxysilylpropyldiethylenetriamine with 1,4 butane sultone) onto activated cellulose with NH4OH in a heterogeneous system. Information about the zwitterionic modification in celluloses was achieved by FT-IR and C-13/Si-29 NMR CP/MAS spectroscopy. These analyses demonstrated the chemical structure and level of grafting of the zwitterionic precursors onto cellulose. Moreover, grafting degree (GD) of Cel-AS (31.5%) and Cel-TAS (16.6%) was evaluated by Elemental analysis. The amount of free amino groups from the grafted residues in both samples was tested by ninhydrin method. Here, results demonstrated that around a sixth part of the grafting in Cel-AS remains as aminopropylsilane. In the case of Cel-TAS, the half of butane sultone was bonded to a secondary nitrogen resulting in three possible zwitterionic configurations. These zwitterionic materials were used as adsorbents of Congo red dye in aqueous solution at different concentrations. Uptake experimental data fit well with Langmuir model, with a maximum theoretical adsorption capacity of 541.8 mg g(-1) for Cel-TAS and 81.2 mg g(-1) in Cel-AS at pH 6. Kinetics results for these systems showed the limiting rate step driven by chemisorption process, since they followed a pseudo-second order model. Finally, zwitterionic modification of cellulose with TAS conferred an increase on more than eightfold of Congo red adsorption capacity in comparison with unmodified cellulose. [GRAPHICS] .