Determination of halloysites in carbon nanotubes

UDC 552.578.2
DETERMİNATİON OF HALLOYSİTES İN CARBON NANOTUBES
N. V.Hasankhanova, F. J.Salahova
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In the modern trend of obtaining low molecular weight olefins, while maintaining the obtained high yield of ethylene and ensuring the obtaining of propylene with a greater yield, the problem of searching for new types of catalysts that allow the yield of both ethylene and propylene to be sufficiently high in a wide temperature range arises. From this point of view, natural halloysite nanotubes with the chemical formula Al₂Si₂O₅(ОН)₄*2H₂O attract attention, and their difference from kaolinite is that there is an additional monolayer of water between the adjacent layers. They are also called halloysites (10 Å) due to their structural periodicity – 10 Å. During heating, halloysite-(10 Å) can easily and irreversibly dehydrate to halloysite-(7 Å).
Keywords: low molecular olefins, halloysites, nanotubes, ionization
INTRODUCTION
Pure halloysite is a white mineral that can easily be ground into pomegranate powder. In addition to aluminum oxide, silicon and water hydrate, halloysite contains a small amount of other metal ions such as Fe+3, Cr+3, Ti+4.
Mixed oxide of iron is also found in the mineral halloysite (up to 3% by weight). Such a lot of iron oxide can be formed due to the presence of interconnected oxides in the mineral and also due to the isomorphous replacement of Fe+3 by Al+3 in the octahedral layer of aluminum oxide.
As a result of the influence of atmospheric conditions and geothermal processes, these layers are wrapped in the halloysite mineral and fall into the shape of a tube. In halloysite nanotubes, the silicon layer is on the outer surface of the tube, and the aluminum oxide is on the inner surface of the lumen.
The diversity of the chemical structure of the outer and inner side of the halloysite layer gives halloysite nanotubes unique properties that do not exist in other nanotubes. One of the characteristics of halloysite is the variety of chemical properties of its tubes and the surface and inner sides of the tubes. Dielectric and ionization properties of silicon and aluminum oxide are different, this was observed in the ξ-potential of colloidal water solutions of these oxides.

Fıgure .1 Halloysite nanotube -(7 Å)
The outer diameters of nanotubes vary from 40 to 100 nm, and the average value is 70 nm. The diameter of the internal lumen varies from 10 to 50 nm and is equal to 20 nm on average. Tubules range in length from 0.5 to 2.0 μm. Although kaolinites have the same chemical structure as halloysites, they have a layered structure. Bates et al. have shown in their research that 7 Å halloysite nanotubes can be formed in layers and ribbons during dehydration of 10 Å halloysite.
Depending on the deposit and its processing method, halloysite nanotubes have a high specific surface area ranging from 80 to 150 m2/g, so these minerals have a very high cation exchange property - from 0.02 to 0.68 mol/kg.
Hydrated halloysite nanotubes can adsorb salts, especially inorganic potassium, ammonium and cesium salts in the interlayer area. Carr et al. observed the interlayer adsorption of more than 50 salts on halloysites. The presented work also provides information on the accumulation of inorganic salts in the lumen. In addition to inorganic salts, halloysite formaldehyde, glycerin, ethanol, acetone, etc. also adsorbs organic compounds.
According to the X-ray diffraction study, the addition of salts and organic compounds to halloysite increases the distance between the nanotubes. Absorption of low molecular weight substances is estimated to occur mainly by adsorption of halloysite by interlaminar spacing. However, high-molecular substances with a molecular mass greater than 300 g/mol (molecules of polymers, proteins, etc.) are adsorbed mainly by accumulation in the inner lumen of the tube, and its application is of special interest in many fields of medicine and technology.
Halloysites with high specific surface area and long tubular shape can act as nanocontainers, and halloysite, which is environmentally friendly, can be widely used in industry, mainly in the field of ceramics. Unlike other nanotube materials (such as BN, silicon or carbon nanotubes [206]), halloysite is inexpensive, which makes it superior for many technological applications. Halloysite refers to clay materials and is used as additives in polymer composites such as kaolinite, montmorillonite, bentonite, etc. can replace
Especially in paper production, it has been proven that the modification of wood fibers with halloysite nanotubes increases the porosity and brightness of sheets. In the pottery industry, halloysite has been used as an additive in porcelain for dinnerware and in bone china. Halloysite has several effective applications in the field of nanotechnology. US, UK, and Chinese companies (such as Atlas Mining Co., Applied Minerals Inc., NanoDynamics, Aymeris, Naturalnano, etc.) produce halloysite materials .