Sepiolite-Hydrogels: Synthesis by Ultrasound Irradiation and Their Use for the Preparation of Functional Clay-Based Nanoarchitectured Materials

Abstract

Sepiolite and palygorskite fibrous clay minerals are 1D silicates featuring unique textural and structural characteristics useful in diverse applications, and in particular as rheological additives. Here we report on the ability of grinded sepiolite to generate highly viscous and stable hydrogels by sonomechanical irradiation (ultrasounds). Adequate drying of such hydrogels leads to low-density xerogels that show extensive fiber disaggregation compared to the starting sepiolite—whose fibers are agglomerated as bundles. Upon re-dispersion in water under high-speed shear, these xerogels show comparable rheological properties to commercially available defibrillated sepiolite products, resulting in high viscosity hydrogels that minimize syneresis. These colloidal systems are thus very interesting as they can be used to stabilize many diverse compounds as well as nano-/micro-particles, leading to the production of a large variety of composites and nano/micro-architectured solids. In this context, we report here various examples showing how colloidal routes based on sepiolite hydrogels can be used to obtain new heterostructured functional materials, based on their assembly to solids of diverse topology and composition such as 2D and 1D kaolinite and halloysite aluminosilicates, as well as to the 2D synthetic Mg,Al-layered double hydroxides (LDH).

Tailoring the properties of nanocellulose-sepiolite hybrid nanopapers by varying the nanocellulose type and clay content

“…Independently of the nanocellulose type and the sepiolite content, all the nanopapers showed an homogeneous assembly between the organic and inorganic component, probably thanks to the sequential high-shear dispersion and ultrasound treatment applied in the preparation of precursor NC-S suspensions (González del Campo et al 2018Campo et al , 2020Lisuzzo et al 2020;Ruiz-Hitzky et al 2021). As an example, FE-SEM images of the surface of nanopapers made with CNFs and different sepiolite content (0 %, 5 %, 10 % and 20 %) are shown in Supporting Information (Fig.…”

“…Its microporosity and high aspect ratio (length of 1-5 μm and diameter of 50-100 nm for sepiolite from deposits in Spain) give rise to an elevated specific surface area (ca. 300 m 2 g − 1 ) and singular adsorption and rheological properties of paramount importance for many applications (Ruiz-Hitzky 2001;Ruiz-Hitzky et al 2021). This fibrous clay presents non-accessible Mg-OH groups inside the structural blocks and silanol (Si-OH) groups on the external surface of the silicate.…”

Influence of Organic-Modified Inorganic Matrices on the Optical Properties of Palygorskite–Curcumin-Type Hybrid Materials

“…Most often, these are essential oils [23], dyes [24][25][26] or enzymes [27] loaded on the inorganic matrices, resulting in hybrid materials that preserve their original properties in different environments, in which factors, such as light, temperature, or pH, can degrade organic compounds. The processes of loading inorganic matrices with bioactive compounds take place through ion exchange processes, adsorption at microwaves or ultrasound-assisted processes [20,28,29]. Such hybrid materials usually have antioxidant or antimicrobial properties and are used in the food and pharmaceutical industry [30][31][32][33].…”

Impact of Increased Sonication-Induced Dispersion of Sepiolite on Its Interaction with Biological Macromolecules and Toxicity/Proliferation in Human Cells

“…These two types of active sites are central to the adsorption mechanisms that occur at the external surfaces of fibrous clay minerals. 26 Natural raw sepiolite appears at the electronic microscope as bundles resulting from the agglomeration of their silicate microfibers, which can be disaggregated in concentrated water dispersions by applying high-speed mechanical shearing or by ultrasonication. The resulting products at the industrial level are considered samples of "rheological grade" sepiolite products, which have been commercialized as thickening or suspending agents (e.g., Pangel S9).…”

“…Some mechanical irradiation (ultrasounds) has also been proposed as a procedure to efficiently defibrillate sepiolite to generate colloidal routes to obtain new heterostructured functional nanomaterials. 26 The individual particles of sepiolite (even those that have been previously defibrillated) can easily aggregate in water through hydrogen bonding and van der Waals interactions to form bundles and aggregates, limiting clay dispersion. 29 Of note, a recent study reports on the colloidal dispersion behavior of individual sepiolite fibers by analyzing the diffusive motion of some natural clays.…”