Adsorptive removal of crystal violet dye from aqueous solution onto coconut coir

Abstract

The untreated and sodium chlorite-treated coconut coir was implemented to remove crystal violet (CV) dye from an aqueous solution by batch adsorption experiments. The adsorption capacity, equilibrium time, and adsorption kinetics of CV on both adsorbents were regulated by the pH of the dye solution. High pH favors the comparative adsorption capacity for both adsorbents. In contrast, the untreated coconut coir (UT-CC) shows higher adsorption efficiency (9.61 mg g-1) than sodium chlorite-treated coconut coir (SCT-CC) at low pH. At lower pH (2.00), the equilibrium was established within 60 min by both adsorbents. However, the quick attainment of the equilibrium (30 min) was observed using both the adsorbents at higher pH (8.00). The isotherm data for both the adsorbents was found to have better agreement with the Freundlich than the Langmuir model at pH 8.00. The kinetic data was well-fitted with Ho’s pseudo-second-order model. Both adsorbents were characterized by FTIR and SEM to get evidence for the proposed adsorption mechanism. Density functional theory (DFT) also supports this result which illustrates the adsorption of CV on lignin of CC with the adsorption energy -51.16 kJ/mol at the B3LYP/6-31(d,p) level of theory.

Keywords

• coconut coir
• sodium chlorite
• crystal violet
• adsorption kinetics
• adsorption mechanism
• density functional theory