Effect of high energy ball milling on organic pollutant adsorption properties of chitosan.

In the present work, chitosan physicochemical transformations that occur during high energy ball milling are investigated and correlated with adsorption capacity of organic pollutants (using azo-dye reactive red 2 as molecular probe). Experimental results reveal that chitosan ball milled for 1 h shows a 70% increase of adsorption capacity, compared to unmilled one, while longer milling time causes a sensible reduction of such capacity. This trend correlates with specific surface area evolution under milling, thus suggesting the primary role of particle comminution in augmenting chitosan adsorption properties. Amorphization of particle surface was found to be marginally relevant for adsorption capacity enhancement. Maximum adsorption capacity (estimated by isothermal equilibrium study) and adsorption rate are augmented by ball milling, with an optimal value found at 1 h milling. Finally, the milled materials were tested to adsorb perfluorooctane sulfonate, obtaining 1.54 mmol g uptake with 1 h milled chitosan. This suggests that chitosan could be used as a cheap expendable material to remove those pollutants, like perfluorooctane sulfonate and the other perfluoroalkyl substances, that deserves destruction and cannot be removed by conventional degradation technologies.