Copper ion removal from dilute solutions using ultrasonically synthesised BSA- and EWP-coated air bubbles

The aim of this study was to remove copper ions from dilute copper solution using an innovative material known as air-filled emulsion (AFE). AFE is composed of microscopic bubbles enclosed by a thin film of cysteine-rich protein distributed through the aqueous solution. The method using AFE as an extractant is combination of air-assisted solvent extraction (AASX) and biosorption techniques. The data obtained from X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) clearly showed the thiol, amino and carboxylic groups of bovine serum albumin (BSA) and egg white protein (EWP)-coated bubbles being responsible for copper adsorption. Moreover, it was also observed that manipulation of experimental conditions such as solution pH, temperature, biosorbent and copper concentration had a significant impact on copper ion uptake. Higher solution pH led to a greater metal uptake for both egg white protein emulsion (EWPEM) and bovine serum albumin emulsion (BSAEM). At lower pH, copper removal diminished and no copper removal was obtained at pH 2 due to the high concentration of hydrogen ions. The increase of copper uptake with temperature rise was due to both the exposure of more functional groups that were initially buried in the interior of the protein structure and an increase in reaction kinetics.