Absorption of essential oils in Laponite: Stability enhancement and structural characteristics

Abstract

The suitability of Laponite (Lap) for essential oils (EO) capture is investigated in this work by directly mixing both components (Lap–EO samples). This simple and green approach avoids the use of solvents and heat, which would otherwise compromise the EO's physical-chemical properties. Lavender, tea tree, and rosemary oils were used for this purpose, and the samples were produced with an initial 1:2 mass ratio of Lap to EO. Thermal stability of EO and absorption efficiency of Lap–EO composites were determined using thermogravimetric analysis (TGA), revealing a rapid degradation of the pure EO which was significantly diminished when molecules were incorporated into the Lap matrix. The EO absorption was quantified, and the results showed that all the samples had absorptions greater than 240 mg∙g−1. X-ray diffraction (XRD), scanning electron microscopy (SEM), and small- and wide-angle X-ray scattering (SAXS/WAXS) experiments were carried out in order to study the structure formed by the Lap–EO composites. The results showed an increase in the Lap interlayer d-spacing, indicating that molecules were successfully intercalated, conserving Lap's structure integrity, and forming larger grain aggregates. Even further, SAXS/WAXS data allowed for the determination of the specific surface area and porosity, important parameters for characterizing porous materials. For Lap−EO samples, there was a 160% increase in surface area and a 120% increase in porosity; this information allowed for the development of a geometric model of the Lap layers, in good agreement with experimental data.