Removal of heavy metal ions from aqueous solution by anionic polyacrylamide-based monolith: equilibrium, kinetic and thermodynamic studies

In the present study, a macroporous polyacrylamide-based monolith bearing negatively charged sulfonic acid groups was synthesized as a new adsorbent for the removal of heavy metals ions (Pb2+, Cd2+, and Cr3+) from aqueous solutions. Vinylsulfonic acid was selected as an anionic monomer to introduce a negative charge on the surface of the resulting monolith that forms a complex with investigated metal ions. The influences of solution pH, contact time, monolith dosage, initial concentration, and temperature on Pb2+, Cd2+, and Cr3+ removal were determined using the batch equilibrium technique. Adsorption data were modeled with Langmuir, Freundlich, and Dubinin?Raduskevich isotherm models. The experimental equilibrium data for Pb2+, Cd2+, and Cr3+ using the synthesized monolith showed a good correlation with the Langmuir isotherm model. Based on the Langmuir model, the maximum monolayer adsorption capacities of the monolith were 22.8 mg g?1 for Cd2+, 33.3 mg g?1 for Pb2+, and 66.7 mg g?1 for Cr3+ at 25?C. Kinetic studies revealed that the adsorption of the metal ions onto the monolith followed pseudo-second-order kinetics. The negative and positive values of free energy (?G?) and enthalpy (?H?) revealed that the adsorption of the metal ions onto the monolith was spontaneous and endothermic, respectively.