Glutaraldehyde-cross-linked chitosan-alginate composite for organic dyes removal from aqueous solutions

We present an approach for synthesis of a micro-porous composite of two well-known biopolymers, namely chitosan and alginate, using glutaraldehyde as the cross-linking agent. Alginate and chitosan were pre-treated before being mixed, and the two biopolymers' proportions were also monitored. Chitosan was modified using aniline with the help of formaldehyde crosslinker and then the twizer was further crosslinked with alginate using glutaraldehyde. The synthesized composite, glutaraldehyde cross-linked chitosan-alginate composite [(Cs-F-An)-G-Al] was characterized using spectral techniques and employed as a potential adsorbent for three dyes namely Brilliant green, Methyl orange and Patent Blue V. The pH_PZC of the material was 7.5 and the maximum monolayer adsorption capacity (Q_max) was found to be 235.82, 198.09 and 117.34 mg g^-1 for BG (at pH 8.0), MO (at pH 6.0) and PBV (at pH 3.0) respectively. It was found that the adsorption process follows a Freundlich adsorption isotherm and pseudo second order kinetics. A thermodynamic study revealed that the process of adsorption was enthalpy-driven and spontaneous in nature. Interestingly, the values of the adsorption capacity obtained in column adsorption method are in close agreement with those obtained in batch adsorption experiments, which shows the potential of the synthesized composite for uptake of dyes.