Removal of Malachite Green dye from aqueous solution with Hydroxyapatite/Chitosan Nanocomposite

Chitosan (CS) has marked potential in environmental adsorption applications, but typically suffers from low specific gravity and sensitivity to pH. In this work, a hydroxyapatite-CS (HAp-CS) composite was developed via embedding of HAp into CS and used for removal of Malachite Green (MG) dye from aqueous solution. Effects of different weight contents of CS in HAp-CS composite, adsorbent dosage, initial pH, contact time and the initial dye concentration on MG removal were studied in detail using batch adsorption at room temperature. The kinetic data were best described by the pseudo-second-order model (R2 0.9999), while thermodynamic investigation of MG adsorption by HAp-CS composite confirmed a spontaneous adsorption. Further investigations demonstrated that the adsorption pattern fitted well with Langmuir model (R2 0.97) but less-satisfied with Freundlich model (R2 0.94). FT-IR and X-ray photoelectron spectroscopy studies showed that possible pathways for MG adsorption may include surface complexation, ion exchange and hydrogen bonding. HAp-CS composite containing 50 wt% of CS exhibited adsorption capacity of 781 mg g1 for MG (Langmuir model), which is much higher than that of pure CS, HA and other previously reported adsorbents.