Geraldo José da Silva

The incorporation of essential oils (EOs) into layered charged matrices is a commonly pursued method for encapsulation and controlled-release applications. However, the interfacial mechanism governing their colloidal interactions in water-based dispersions and the resulting colloidal microstructure remains poorly understood. Here, the impact of chemically distinct EOs in the intermolecular interactions, hierarchical organization, and aging structural evolution of an aqueous synthetic Laponite (Lap) dispersion is investigated. With a combination of dynamic light scattering, electrophoretic measurements, ultra-small-angle X-ray scattering, and gas chromatography coupled with mass spectrometry, a correlation of how EOs molecular composition influences the colloidal interactions and Lap multi-level structural organization is established across a wide range of Lap and EOs concentrations. The results demonstrate that the presence of EO molecules significantly changes the electric double layer around Lap discs, with EOs adsorption leading to the transition from dispersed nanodiscs to complex, stable, hierarchically organized clusters with both mass- and surface-fractal morphologies, spanning from nano- to micro-scale. Moreover, aging restructures the large-scale cluster backbone, progressively going to an arrested colloidal network, evidencing structural changes related to face-to-face and face-to-edge interactions that are amplified by the presence of the EOs. These findings establish fundamental relationships between EOs chemistry, interfacial electrostatics, and hierarchical assembly in synthetic smectite Lap dispersions, providing mechanistic principles for using charged layered materials as colloidal EOs encapsulation systems.

A good material for CO₂ capture should possess some specific properties: (i) a large effective surface area with good adsorption capacity, (ii) selectivity for CO₂, (iii) regeneration capacity with minimum energy input, allowing reutilization of the material for CO₂ adsorption and (iv) low cost and high environmental friendliness. Smectite clays are layered nanoporous materials that may be good candidates in this context. Here we report experiments which show that gaseous CO₂ intercalates into the interlayer nano-space of smectite clay (synthetic fluorohectorite) at conditions close to ambient. The rate of intercalation, as well as the retention ability of CO₂ was found to be strongly dependent on the type of the interlayer cation, which in the present case is Li⁺, Na⁺ or Ni²⁺. Interestingly, we observe that the smectite Li-fluorohectorite is able to retain CO₂ up to a temperature of 35°C at ambient pressure and that the captured CO₂ can be released by heating above this temperature. Our estimates indicate that smectite clays, even with the standard cations analyzed here, can capture an amount of CO₂ comparable to other materials studied in this context.