**1. Introduction**

Essential oils (EOs) are secondary metabolites of diverse aromatic plants biosynthesized in different plant organs [1] that can be extracted from leaves, flowers, and fruits by hydrodistillation, solvent-solvent extraction, and liquid CO2 extraction [2, 3]. The EOs' chemical composition is too complex. It is a mixture of natural volatile compounds, such as terpenes, phenols, ketones, aldehydes, alcohols, carotenoids, flavonoids, esters, and phenylpropanoid [4]. Thank to these variable

bioactive molecules, EOs find uses as gastronomic, nutritional, organoleptic, antiulcer, antiaging, anticancer, antidepressant, antitussive, antipyretic, analgesic, larvicidal, insecticidal, etc. [5, 6]. Owing to their versatile biological properties and the increasing demand, by the consumers, for biobased products, EOs are amply used in pharmaceutics industry, cosmetics, food industry, food packaging, nutraceuticals, and even as agrochemicals [4, 7]. Nonetheless, their practice is constantly facing several barriers comprising the high volatility and high risk of degradation upon direct exposure to heat, humidity, light, and oxygen, intense odor and taste, dosedependent toxicity, and hydrophobicity [1, 4, 8]. The nanoencapsulation technology has been recommended as an innovative approach to overcome the limitations of the EOs use, by enhancing their bioavailability and bioefficiency and protecting them from extreme conditions [9]. Currently, liposomes, polymeric nanoparticles, metal nanoparticles, and carbon nanotubes are some of the broadly used nanomaterials. Yet, they present some impediments of use, as they are sometimes extremely toxic and/or carcinogenic in nature even in low concentrations, very expensive to acquire, and need very complex preparation processes [10].

Clay nanoparticles represent a promising alternative to nanomaterials mentioned above. In soil science, the term "clay" is related to a material class with a particle size <2 μm in equivalent spherical diameter. "Nanoclays" are included in the clay fraction with particle size <100 nm in diameter. Soil nanoclays are commonly predominated by phyllosilicates and often include metal hydroxides and organic matter. Ultrasonication, ultracentrifugation, and energetic stirring may be used to isolate them from the clay fraction [11]. Their structure may be lamellar, fibrous, or tubular nature with a hydrophilic character. Since ancient time, clay minerals have been widely investigated by humans in many fields including medicine, pharmacy, ceramic, plastic, cracking catalyst industries, food and beverage, coatings industry, agrochemicals. They are also helpful in environmental protection and remediation. All this interest for nanoclay exploitation in various fields is mainly due to their abundance, low cost, ecofriendly nature, nontoxicity as well as their unique and specific structural physicochemical and thermal properties, including large surface area, surface electric charges, immense porosity, low density, inertness, thermal and chemical stability, ion exchange capacity, and high adsorption capacity [12–15].

In this context, this chapter is dedicated to the illustration and update of clay/EOs nanosystems application in diverse fields. Firstly, the main clays used for EOs encapsulation are highlighted. Then, EOs' chemical composition and properties are briefly described. Finally, data concerning clay/EOs nanosystems development and valorization in various applications are provided, while emphasizing the benefits associated with nanoencapsulation, namely bioactivity, stability against aggressive conditions, and controlled release.

### **2. Clay minerals**

Clays are natural earth materials resulting from chemical weathering operations on the earth's crust [16]. These are minerals with very fine grain size smaller than two micrometers [17].

A clay deposit generally comprises of impurities, namely feldspar, quartz, volcanic dust, fossil fragments, heavy minerals, carbonates minerals, etc. [18].
