Highly Efficient Removal of Acid Red 18 from Aqueous Solution by Magnetically Retrievable Chitosan/Carbon Nanotube: Batch Study, Isotherms, Kinetics, and Thermodynamics

A new strategy to retrieve chitosan-decorated carbon nanotube (CS/CNT) from aqueous dispersion was proposed. The CS/CNT, prepared via a “surface deposition–crosslinking” method, exhibited an aggregation microstructure with plentiful interstitial spaces. By introducing magnetic nanoparticle (MNP) into CS/CNT dispersion solution, MNP was embedded in the CS/CNT aggregates, which endowed the CS/CNT with magnetic retrievability. Using this strategy, a simple and convenient operation for the removal of anionic azo dye (acid red 18 (AR18)) was achieved by directly adding CS/CNT and MNP into the dye solution, where CS/CNT acted as an adsorbent and MNP enabled all CS/CNT aggregates to be magnetically retrievable. Effects of pH, ionic strength, contact time, temperature, and initial AR18 concentration on adsorption efficiency were investigated. Results showed that AR18 adsorption could achieve equilibrium quickly and the maximum adsorption capacity could be up to 809.9 mg·g–1 at 323.15 K. Full kinetic and thermodynamic investigations as well as isotherm analysis were also undertaken. Moreover, the reusability of magnetically retrievable CS/CNT was evaluated, and the result showed that the removal of AR18 was kept relatively constant (99.11 % to 99.76 %) in 10 consecutive cycles. The study suggests that the magnetically retrievable CS/CNT is a promising adsorbent for removal of anionic azo dyes from aqueous solution.