Nanodiamond-filled chitosan as an efficient adsorbent for anionic dye removal from aqueous solutions

A series of novel chitosan/nanodiamond (CTS/ND) composites containing NDs with variable surface carboxyl groups and various concentrations were prepared using solution casting method. Powdery CTS/ND composites were employed as the adsorbent of a model anionic dye (methyl orange, MO). Experimental results showed that the incorporation of NDs with high carboxylic content (ND-H) in to CTS increased substantially the maximum adsorption capacity of neat CTS from 167 mg/g to 454 mg/g. The remarkable adsorption capacity of dye on CTS/ND composites was associated to the oxygen-containing groups on the outer surface of NDs which would be beneficial to interact with the dye molecules through hydrogen bonding and electrostatic interactions. NDs with higher carboxylic content could improve the degree of dispersion in the CTS which in turn improved the accessible surface area of NDs and adsorption affinity of CTS/ND. The adsorption kinetics of CTS/ND adsorbent was well described by pseudo-second-order kinetics and Langmuir isotherm model showed very good fit with adsorption data.