We report here the successful use of a protozoan model organism P. caudatum to investigate the toxicity of clay nanoparticles (montmorillonite, halloysite, kaolin, and bentonite), silica nanospheres and graphene oxide nanoflakes.

A self-assembly of clay nanotubes in functional arrays for the production of organized organic/inorganic heterostructures is described. These 50-nm-diameter natural alumosilicate nanotubes are biocompatible. Halloysite allows for 10–20 wt % chemical/drug loading into the inner lumen, and it gives an extended release for days and months (anticorrosion, self-healing, flame-retardant, antifouling, and antibacterial composites). The structured surfaces of the oriented nanotube micropatterns enhance interactions with biological cells, improving their capture and inducing differentiation in stem cells. An encapsulation of the cells with halloysite enables control of their growth and proliferation. This approach was also developed for spill petroleum bioremediation as a synergistic process with Pickering oil emulsification. We produced 2–5-nm-diameter particles (Au, Ag, Pt, Co, Ru, Cu–Ni, Fe3O4, ZrO2, and CdS) selectively inside or outside the aluminosilicate clay nanotubes. The catalytic hydrogenation of benzene and phenol, hydrogen production, impacts of the metal core–shell architecture, the metal particle size, and the seeding density were optimized for high-efficiency processes, exceeding the competitive industrial formulations. These core–shell mesocatalysts are based on a safe and cheap natural clay nanomaterial and may be scaled up for industrial applications.

Here we overview the recent advances in the fabrication of sustainable composite nanomaterials with decontamination capacity towards inorganic and organic pollutants.

Complexation of biopolymers with halloysite nanotubes (HNTs) can greatly affect their applicability as materials building blocks. Here we have performed a systematic investigation of fabrication of halloysite nanotubes complexes with nucleotides and genomic DNA. The binding of DNA and various nucleotide species (polyAU, UMP Na2, ADP Na3, dATP Na, AMP, uridine, ATP Mg) by halloysite nanotubes was tested using UV-spectroscopy. The study revealed that binding of different nucleotides to the nanoclay varied but was low both in the presence and absence of MgCl2, while MgCl2 facilitated significantly the binding of longer molecules such as DNA and polyAU. Modification of the nanotubes with DNA and nucleotide species was further confirmed by measurements of ζ-potentials. DNA-Mg-modified nanotubes were characterized using transmission electron (TEM), atomic force (AFM) and hyperspectral microscopies. Thermogravimetric analysis corroborated the sorption of DNA by the nanotubes, and the presence of DNA on the nanotube surface was indicated by changes in the surface adhesion force measured by AFM. DNA bound by halloysite in the presence of MgCl2 could be partially released after addition of phosphate buffered saline. DNA binding and release from halloysite nanotubes was tested in the range of MgCl2 concentrations (10–100 mM). Even low MgCl2 concentrations significantly increased DNA sorption to halloysite, and the binding was leveled off at about 60 mM. DNA-Mg-modified halloysite nanotubes were used for obtaining a regular pattern on a glass surface by evaporation induced self-assembly process. The obtained spiral-like pattern was highly stable and resisted dissolution after water addition. Our results encompassing modification of non-toxic clay nanotubes with a natural polyanion DNA will find applications for construction of gene delivery vehicles and for halloysite self-assembly on various surfaces (such as skin or hair).

With increased interest in the practical use of graphene-based materials, concerns about the remediation of the environmental nanotoxicity of graphene and graphene-related materials have grown. In this study, we report that kaolin nanoclay significantly alleviates the toxicity of graphene oxide in aqueous environments. We employed the Paramecium caudatum protozoan to demonstrate the effects of equal concentrations of kaolin on the remediation of graphene oxide toxicity on survival and growth rates, chemotaxis, galvanotaxis, DNA complexation, and food vacuole formation. Importantly, the toxicity of graphene oxide coagulated with kaolin is reduced without the aggregated particles being removed from the environment.

The problem of purifying domestic and hospital wastewater from pharmaceutical compounds is becoming more and more urgent every year, because of the continuous accumulation of chemical pollutants in the environment and the limited availability of freshwater resources. Clay adsorbents have been repeatedly proposed as adsorbents for treatment purposes, but natural clays are hydrophilic and can be inefficient for catching hydrophobic pharmaceuticals. In this paper, a comparison of adsorption properties of pristine montmorillonite (MMT) and montmorillonite modified with stearyl trimethyl ammonium (hydrophobic MMT-STA) towards carbamazepine, ibuprofen, and paracetamol pharmaceuticals was performed. The efficiency of adsorption was investigated under varying solution pH, temperature, contact time, initial concentration of pharmaceuticals, and adsorbate/adsorbent mass ratio. MMT-STA was better than pristine MMT at removing all the pharmaceuticals studied. The adsorption capacity of hydrophobic montmorillonite to pharmaceuticals decreased in the following order: carbamazepine (97%) > ibuprofen (95%) > paracetamol (63–67%). Adsorption isotherms were best described by Freundlich model. Within the pharmaceutical concentration range of 10–50 µg/mL, the most optimal mass ratio of adsorbates to adsorbents was 1:300, pH 6, and a temperature of 25 °C. Thus, MMT-STA could be used as an efficient adsorbent for deconta×ating water of carbamazepine, ibuprofen, and paracetamol.

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Toxicity of graphene oxide to cells reduced by almost 20% after its incubation with kaolin, most likely because of its adhesion to the platy clay nanoparticles, which was detected by atomic force microscopy.