Optimization of hydrolysis of polyacrylonitrile-kapok fiber composite for the adsorption of lead ions in aqueous solution

Abstract The adsorptive uptake of polyacrylonitrile-kapok fiber composite (PAN-KpF) for Pb(II) ions was improved by employing hydrolysis using sodium hydroxide (NaOH). The hydrolysis conditions, namely, reaction temperature, NaOH concentration, and reaction time, were optimized by response surface methodology (RSM) combined with three-level three-factorial Box-Behnken design (BBD) based on the adsorption capacity for Pb(II) uptake. Statistical analysis results suggest that the optimum reaction temperature, NaOH concentration, and reaction time for the hydrolysis of PAN-KpF are 55.28 °C, 3.96 w/w%, and 52.04 min, respectively. In addition, the predicted adsorption capacities calculated from the second-order polynomial regression were in relatively good agreement with the experimental results. The data points fit closely into a linear correlation with an R2 value of 0.9317. The effects of initial solution pH, adsorbent dosage, initial solution concentration, and contact time for the adsorption of Pb(II) onto the hydrolyzed PAN-KpF were investigated. Isotherm studies indicate that the adsorption was described well by the Langmuir isotherm model, wherein the maximum monolayer adsorption capacity for Pb(II) is 74.07 mg/g. This is 80 % higher than the adsorption capacity for unhydrolyzed PAN-KpF. Lastly, kinetic studies reveal that Pb(II) uptake is predicted by the pseudo-second-order kinetic model.