Adsorption layer structure on the surface of carbon-silica composite in the presence of proteins of different internal stability and Cu(II) ions – The effect on solid aggregation

Abstract

The paper focused on the structure of adsorption layer formed on the surface of carbon-silica composite (C-SiO2) in the presence of proteins (ovalbumin (OVA), lysozyme (LSZ)) as well as its impact on the solid aggregation tendency. The composite was characterized using nitrogen adsorption/desorption isotherms method as well as FTIR analysis. In turn, adsorption and aggregation mechanisms were explained based on the results of measurements: zeta potential study, potentiometric titration, CPS analysis and adsorbed amount determination. The experiments were conducted without and with heavy metal ions – copper(II). It was observed that the C-SiO2 composite was a good sorbent relative to proteins, especially at protein isoelectric point (pI), i.e. at pH 5 for OVA and pH 11 for LSZ. For the protein initial concentration equal to 800 mg/L, the adsorbed amount of OVA was 150.6 mg/g (pH 5), whereas that of LSZ was 216.7 mg/g (pH 11). Cu(II) ions reduced the protein adsorption on the composite surface significantly. At pH 5 the adsorbed amount of proteins did not exceed 8.2 mg/g. The strongest aggregation of the C-SiO2 particles was noted in the simultaneous presence of ovalbumin and Cu(II) ions. Then the aggregate diameter equaled 0.152 μm. This phenomenon was enhanced by OVA denaturation caused by heavy metal ions.