Carboxylic acid functionalized para-xylene based hypercrosslinked polymer as a novel and high performance adsorbent for heavy metal removal

Abstract

In this work, hypercrosslinked polymeric adsorbent (HCP) was synthesized from para-Xylene precursor through Friedel-Crafts reaction. Additionally, heavy metal adsorption experiments from a multi component system including lead, cadmium, nickel, and copper ions were conducted. To enhance lead uptake selectivity over other metallic ions, the resulting HCP sample was functionalized through carboxylic acid incorporation into the HCP adsorbent skeleton. The adsorption process modeling was carried out by using Central Composite Design- Response Surface Methodology technique. In addition, the adsorption capability dependency of the resulting samples to the operational condition including temperature from 25 °C to 65 °C, solution pH value from 4 to 10, and solution initial concentration from 20 mg/l to 100 mg/l was investigated. Additionally, process optimization was applied aim to maximize the lead uptake selectivity, the optimal condition including a temperature of 31.8 °C, pH of 5.0, and initial concentration of 82.50 mg/l were obtained for HCP sample, also the optimal condition namely a temperature of 30 °C, pH of 5.5, and initial concentration of 100 mg/l were obtained for modified HCP sample. As a result of isotherm modeling, the Hill model was obtained as the best model, additionally, thermodynamically investigation of the process resulted in spontaneously and physically adsorption of the metallic ions by HCP samples, with respect to Gibbs free energy (ΔG0 < 0) and adsorption process enthalpy (ΔH0 < 20 kJ/mol). Finally, adsorbents regeneration were evaluated and minor losses in the adsorption capacity of samples were yielded after ten cycles.

Keywords

• Heavy metal adsorption
• Carboxylic acid functionalization
• Selectivity
• Response Surface Methodology