Thin film composite membranes consisting of hyperbranched polyethylenimine (HPEI)-cysteamine layer for cadmium removal in water

The membrane composite of polyethersulfone (PES) integrated with (HPEI), trimesoyl chloride (TMC) and cysteamine (-SH) was prepared through interfacial polymerisation method for the removal of cadmium (II) ions from water. The prepared composite membranes were characterised for chemical composition, surface charge and morphology of the polyamide thin layer. The modified composite membranes known as polyethersulfone hyperbranched polyethyleneimine cysteamine (PES/HPEI-SH) showed improved hydrophilicity and water intake capacity as compared to the unmodified PES membrane. The batch experiments quantification analysis revealed that there was 22%, 53% and 99% Cd²⁺ removal for PES, PES/HPEI and PES/HPEI-SH respectively after 20 min of analyte adsorption. PES/HPEI-SH membrane displayed the highest adsorption efficiency, which was due to the adsorption properties of -SH that is based on the hard-soft acid and base theory. Thiol has high affinity to form a strong covalent bond with heavy metal ions (soft lewis acid), subsequently forming co-ordination [2R-S-Cd²⁺→R-S-Cd-2H⁺] complexes. Hence the PES/HPEI-SH membrane had the highest adsorption capacity of 135.59 mg cm⁻². Kinetics revealed that the adsorption reactions followed pseudo second order kinetic model meaning that chemisorption reaction took place.