Optimization of Nickel(II) adsorption by sodium tripolyphosphate crosslinked chitosan using response surface methodology (RSM)

Abstract

This study aimed to synthesize chitosan crosslinked by sodium tripolyphosphate with different concentrations and optimize it for Ni(II) adsorption in a batch adsorption system. The BET analysis and the solubility/swelling test showed that as the crosslinking degree increased, the surface area and total pore volume decreased while the physicochemical properties improved. The effect of the initial pH and temperature on the adsorption of Ni(II) was studied in a batch adsorption system, and thermodynamic parameters were calculated. In order to enhance the adsorption capacity of crosslinked chitosan, Response Surface Methodology (RSM) was employed to establish a correlation between two independent experimental factors, namely pH and crosslinking degree, and the Ni(II) adsorption capacity. By changing these factors, the aim was to optimize the adsorption capacity of crosslinked chitosan. The constructed model was well-aligned with the experimental data with an R2 = 96.05%. According to the model, an adsorption capacity of 31.94 mg/g could be achieved at a pH of 7.21 and a crosslinking degree of 2.93% (w/v). Among isotherm models investigated, the Langmuir model was found to be more appropriate for studying Ni(II) adsorption with maximum adsorption capacity in the order of chitosan beads> crosslinked chitosan beads. The mechanism of adsorption and crosslinking reaction was also investigated using FT-IR and SEM-EDS techniques, implying that the amine groups were the primary sites for metal ions uptake as well as crosslinking reaction. A mixture of NaCl and H2SO4 could release the sorbed Ni(II) ions from STPP-CB5% with a recovery of 83% after one sorption-desorption cycle.

Keywords

• Batch adsorption study
• Heavy metals
• Statistical analysis
• Ni(II)
• Mechanism study