Natural polymers as stability modifiers of suspensions containing carbonaceous materials obtained by microwave-assisted chemical activation of waste cornelian cherry stones

Abstract

The cornelian cherry (Cornus mas L.) stones were used as a precursor for the preparation of activated biocarbons for cosmetic applications. The microwave-assisted chemical activation with the use of phosphoric acid and potassium carbonate was applied. The resulting carbonaceous materials (CS_P and CS_K) are characterized by a well-developed specific surface area (600 – 800 m2/g) and micro/mesoporous structure with a mean pore diameter of about 2 nm. Their adsorption properties towards hydrolyzed collagen and phytokeratin were checked within the pH range 3–10, and the stability of protein-containing and protein-free suspensions was determined spectrophotometrically. To explain the adsorption and stability mechanisms in the examined systems the solid surface charge and electrokinetic measurements were additionally performed. The surface and electrokinetic properties of both carbon adsorbents were found to be quite similar, e.g. pHpzc points of 6.4 and 8.2, and the pHiep values of 3.5 and 3.6, for samples CS_P and CS_K, respectively. It was shown that the greatest amounts of both proteins were adsorbed in the case of H3PO4-activated biocarbon (587 mg/g at pH 6 for collagen and 585 mg/g at pH 3 for phytokeratin, so very close to their pI values of 5.4 and 3.5, respectively). These systems also exhibit the highest stability among all tested suspensions, as indicated by the smallest aggregate sizes of 23.8 and 21.4 μm, respectively. Such behaviour is highly desirable for cosmetic formulations containing activated biocarbon with adsorbed layers of proteins acting as active agents.