Preparation and characterization of a Pickering oil-in-water emulsion based on TiO2 coated with phytochemicals derived from the bark of a native Argentine tree

Abstract

Micron-sized Pickering oil-in-water emulsions (POWEs) were prepared by ultrasonically mixing olive oil (OO) as the dispersed organic phase, laponite XLG (LAP) as the emulsion stabilizer, and with TiO2 nanoparticles uncoated or coated with phytochemicals present in an aqueous extract of bark from the Argentine native tree Schinopsis lorentzii (TiO2@SL). Polyphenolic and tannic acids and flavonoids were identified as the major phytochemicals forming the TiO2@SL coating. The two types of POWEs with different compositions were prepared according to a full factorial design model with two factors and three levels, and the POWEs with the smallest droplet size and greater stability were selected for further characterization by several techniques. Despite their high hydrophilicity, confocal Raman and scanning electron microscopies confirmed that both types of nanoparticles were forming the interface of the emulsion. Viscosity, spreadability, and microdroplet size determinations show that both POWEs exhibit pseudoplastic fluid behavior with excellent spreading ability and long-term stability. In comparison to the emulsion formulated with uncoated TiO2, the TiO2@SL-based POWE did not demonstrate UV-induced photocatalytic degradation of organic dyes and exhibited an enhanced sun protection factor. These findings were attributed to the UV-filtering and antioxidant capabilities of the polyphenolic compounds that constitute the coating of the TiO2 nanoparticles. This study demonstrates the potential of utilizing residual forest resources to prepare valuable modified TiO2 nanocomposites, which may be suitable for the formulation of cosmetic products without the risk of phototoxicity.