Titanate (IV) nanosheets (TiNSs) have a 2D structure where TiO₆

octahedra In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ...

are edge-linked in a

lepidocrocite Lepidocrocite (γ-FeO(OH)), also called esmeraldite or hydrohematite, is an iron oxide-hydroxide mineral. Lepidocrocite has an orthorhombic crystal structure, a hardness of 5, specific gravity of 4, a submetallic luster and a yellow-brown strea ...

-type 2D lattice with chemical formula H_xTi₂—_x/4☐_x/4O₄ ⦁ H₂O (x~0.7; ☐, vacancy). Titanate nanosheets may be regarded as sheets with molecular thickness and infinite planar dimensions. TiNSs are typically formed via liquid-phase exfoliation of protonic titanate. In inorganic layered materials, individual layers are bound to each other by van der Waals interactions if they are neutral, and additional Coulomb interactions if they are composed of oppositely charged layers. Through liquid-phase exfoliation, these individual sheets of layered materials can be efficiently separated using an appropriate solvent, creating single-layer colloidal suspensions. Solvents must have an interaction energy with the layers that is greater than the interaction energy between two layers. ''In situ'' X-Ray diffraction data indicates that TiNSs can be treated as macromolecules with a sufficient amount of solvent in between layers so that they behave as individual sheets. Exfoliation of Inorganic Layered Materials

Exfoliation of Inorganic Layered Materials

Properties

Unilamellar TiNSs have a number of unique properties, and are said to combine those of conventional titanate and titania. Structurally, they are infinite ultrathin (~0.75 nm) 2D sheets with a high density of negative surface charges originating from the oxygen atoms at the corners of the adjoint octahedrons . TiNSs may balance this anionic charge by inserting a counterionic layer between the two sheets either via layering or in aqueous solution. This electric double layer gives the material flexible interlayer distances, high cation exchange capacity, and excellent dielectric capabilities. Typically,

titanium oxide Titanium oxide may refer to: * Titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), o ...

suffers from oxygen vacancies, which diminish its potential as capacitors due to vacancies acting as high-leakage paths and charge carrier traps, however, TiNSs possess Ti vacancies, which promote channels for electron transfer. When Ti vacancies are present, the effective charge felt by electrons on oxygen atoms reduces and allows less hindered electron motion.

Applications

TiNSs can act as highly efficient

adsorbents Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which ...

and

photocatalysts In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. In catalyzed photolysis, light is absorbed by an adsorbed substrate. In photogenerated catalysis, the photocatalytic activity depends on the abil ...

due to their two-dimensional geometry and structure. This phenomenon can be exploited for several applications, including the removal of metal ions and dyes from water systems. Further, TiNSs potential as an

electrocatalyst An electrocatalyst is a catalyst that participates in electrochemical reactions. Electrocatalysts are a specific form of catalysts that function at electrode surfaces or, most commonly, may be the electrode surface itself. An electrocatalyst c ...

may enhance fuel cell efficiency during fuel oxidation. Similarly, intercalated myoglobin is proven to be an efficient catalyst for H₂O₂. TiNSs may also be used for immobilizing

biomolecules A biomolecule or biological molecule is a loosely used term for molecules present in organisms that are essential to one or more typically biological processes, such as cell division, morphogenesis, or development. Biomolecules include larg ...

. When a monolayer of

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...

is intercalated into TiNSs, the electron transfer between the active sites of the protein and the electrodes is amplified, and electrocatalytic activity for O₂ reduction increases. In addition, heterostructured nanosheets of Fe₃O₄-Na₂Ti₃O₇ can be used for protein separation. When placed in the aqueous environment at pH 6, positively charged hemoglobin binds to the nanosheets, whereas negative

albumin Albumin is a family of globular proteins, the most common of which are the serum albumins. All the proteins of the albumin family are water-soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins ...

can be detected in the supernatant. Perhaps the most interesting application of TiNSs is in the development of a material dominated by electrostatically repulsive interactions. TiNSs exhibit maximum

electrostatic repulsion Electrostatics is a branch of physics that studies electric charges at rest (static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for amber ...

when they are aligned cofacially. To create the

hydrogel A hydrogel is a crosslinked hydrophilic polymer that does not dissolve in water. They are highly absorbent yet maintain well defined structures. These properties underpin several applications, especially in the biomedical area. Many hydrogels ar ...

based on this, a solution of TiNSs is placed in a strong magnetic field where repulsive forces induce a quasi-crystalline structure. Upon irradiation with UV-light, the solution polymerizes and creates cross-linked network, which is non-covalently attached to the TiNSs. This creates a composite that resists orthogonally applied compressive forces, but easily deforms due to shear forces. TiNSs solutions of this sort may be used as an anti-vibration or vibration-isolating material and in the design of

artificial cartilage Artificial cartilage is a synthetic material made of hydrogels or polymers that aims to mimic the functional properties of natural cartilage in the human body. Tissue engineering principles are used in order to create a non- degradable and bioc ...

. Titanate nanosheets can also be aligned within polymer, parallel to the surface of the substrate by simple drop casting. The

intercalation Intercalation may refer to: * Intercalation (chemistry), insertion of a molecule (or ion) into layered solids such as graphite *Intercalation (timekeeping), insertion of a leap day, week or month into some calendar years to make the calendar foll ...

of polymer and orientation of nanosheets were studied by

small-angle X-ray scattering Small-angle X-ray scattering (SAXS) is a small-angle scattering technique by which nanoscale density differences in a sample can be quantified. This means that it can determine nanoparticle size distributions, resolve the size and shape of (monodi ...

(SAXS) using in-plane and symmetrical scan. SAXS mapping indicated homogeneous alignment of titanate nanosheets within polymer. The mechanical reinforcement of polyamic acid using titanate nanosheets matched with Halpin-Tsai model, which is a composite model that assume the filler is in aligned position.

References

{{Reflist Two-dimensional nanomaterials Titanates