Titanate nano-layer

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Structure of a titanate nano-layer

Titanate (IV) nanosheets (TINS) have a 2D structure, wherein TiO 6 - octahedron in a 2D lattice from lepidocrocite type having the chemical formula H x Ti 2 - x / 4 ☐ x / 4 O 4 ⦁ H 2 O (x ~ 0.7; ☐, gap) are edge-bound. Titanate nanosheets can be thought of as plates of molecular thickness and infinite planar dimensions.

Manufacturing

Exfoliation of inorganic layer materials . In the case of the protonated titanate, an inorganic starting material, which consists of alternating layers of charged material, consists of the cationic layer of protons, while the anionic layer consists of edge-bound TiO6 octahedra. A solvent is chosen so that it has a greater interaction energy with the leaves than they do with each other. This interaction replaces the bonds that hold the leaves together, creating colloidal suspensions of 2D nanosheets.

TiNs are typically formed by the liquid phase exfoliation of protonic titanate . In inorganic layered materials, individual layers are connected to one another by van der Waals interactions if they are neutral and additionally by Coulomb interactions if they consist of oppositely charged layers. Liquid phase peeling can efficiently separate these individual layers of layer materials with a suitable solvent, creating single-layer colloidal suspensions. The solvents must have an energy of interaction with the layers that is greater than the energy of interaction between two layers. In-situ - Röntgenbeugung- data show that Tins can be treated as macromolecules with a sufficient amount of solvent between the layers, so that they behave as single sheets.

properties

Unilamellar TiNSs have a number of unique properties and are said to combine the properties of conventional titanate and titanium dioxide . Structurally, they are infinite ultra-thin (~ 0.75 nm) 2D plates with a high density of negative surface charges that come from the oxygen atoms at the corners of the neighboring octahedra. TiNs can balance this anionic charge by inserting a counterionic layer between the two layers, either by layering them or in aqueous solution. This electrical double layer gives the material flexible spacing between the layers, high cation exchange capacity and excellent dielectric properties.

Usually titanium oxide suffers from oxygen vacancies, which reduce the potential as capacitors, since these vacancies act as large leaks and charge carrier traps, however, TiNS has titanium vacancies that promote channels for electron transfer. If there are titanium vacancies, the effective charge of the electrons on the oxygen atoms decreases and the movement of the electrons is hindered.

Applications

Due to their two-dimensional geometry and structure, TiNs can act as highly efficient adsorbents and photocatalysts . This phenomenon can be exploited for a variety of applications including the removal of metal ions and dyes from water systems. Furthermore, the potential of TiNS as an electrocatalyst can improve the efficiency of the fuel cell during fuel oxidation . Similarly, intercalated myoglobin has been shown to be an efficient catalyst for hydrogen peroxide .

TiNs can also be used to immobilize biomolecules . When a monolayer of hemoglobin is incorporated into TiNs, electron transfer between the active sites of the protein and the electrodes is increased and the electrocatalytic activity for O 2 reduction increases. In addition, heterostructured nanosheets made of Fe 3 O 4 -Na 2 Ti 3 O 7 can be used for protein separation. Positively charged hemoglobin is bound to the nanosheets at a pH value of 6 in an aqueous environment, while negative albumin can be detected in the solution.

Perhaps the most interesting application of TiNs is in the development of a material that is dominated by electrostatically repulsive interactions. TiNS show maximum electrostatic repulsion when they are cofacially aligned. In order to produce the hydrogel based on it , a solution of TiNs is placed in a strong magnetic field in which repulsive forces induce a quasi-crystalline structure. When exposed to UV light, the solution polymerizes and forms a cross-linked network that is not covalently bound to the TiNs. This creates a composite material that withstands orthogonally applied compressive forces, but is easily deformed due to shear forces. TiNS solutions of this type can be used as vibration damping or vibration isolating material and in the design of artificial cartilage .

Co-facial alignment of TiNs . The cofacial orientation of the anionically charged titanate maximizes the repulsion between cofacial layers and occurs under a magnetic field.

Titanate nanosheets can also be aligned parallel to the surface of the substrate within the polymer by simply drop casting. The intercalation of the polymer and the orientation of nanosheets were examined by small angle X-ray scattering (SAXS) using an in-plane scanner and a symmetrical scan. The SAXS mapping showed a homogeneous alignment of the titanate nanosheets within the polymer. The mechanical reinforcement of polyamic acid using titanate nano-sheets agreed with the Halpin-Tsai model, a composite model in which the filler is disposed in an aligned position.

Individual evidence

  1. ↑ a b c d Minoru Osada, Takayoshi Sasaki: Two-Dimensional Dielectric Nanosheets: Novel Nanoelectronics From Nanocrystal Building Blocks . In: Advanced Materials . tape 24 , no. 2 , January 10, 2012, p. 210-228 , doi : 10.1002 / adma.201103241 .
  2. ↑ a b Takayoshi Sasaki, Mamoru Watanabe, Hideo Hashizume, Hirohisa Yamada, Hiromoto Nakazawa: Macromolecule-like Aspects for a Colloidal Suspension of an Exfoliated Titanate. Pairwise Association of Nanosheets and Dynamic Reassembling Process Initiated from It . In: Journal of the American Chemical Society . tape 118 , no. 35 , 1996, pp. 8329-8335 , doi : 10.1021 / ja960073b .
  3. ^ A b J. N. Coleman, M. Lotya, A. O'Neill, SD Bergin, PJ King: Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials . In: Science . tape 331 , no. 6017 , February 4, 2011, p. 568-571 , doi : 10.1126 / science.1194975 .
  4. ↑ a b c Mingjie Liu, Yasuhiro Ishida, Yasuo Ebina, Takayoshi Sasaki, Takaaki Hikima: An anisotropic hydrogel with electrostatic repulsion between cofacially aligned nanosheets . In: Nature . tape 517 , no. 7532 , 2015, p. 68-72 , doi : 10.1038 / nature14060 .
  5. ↑ a b c Jiquan Huang, Yongge Cao, Zhonghua Deng, Hao Tong: Formation of titanate nanostructures under different NaOH concentration and their application in wastewater treatment . In: Journal of Solid State Chemistry . tape 184 , no. 3 , 2011, p. 712-719 , doi : 10.1016 / j.jssc.2011.01.023 .
  6. ↑ Megumi Ohwada, Koji Kimoto, Teruyasu Mizoguchi, Yasuo Ebina, Takayoshi Sasaki: Atomic structure of titania nanosheet with vacancies . In: Scientific Reports . tape 3 , no. 1 , December 2013, doi : 10.1038 / srep02801 , PMID 24077611 .
  7. ↑ Dmitry V. Bavykin, Frank C. Walsh: Elongated Titanate Nanostructures and Their Applications . In: European Journal of Inorganic Chemistry . tape 2009 , no. 8 , 2009, p. 977-997 , doi : 10.1002 / ejic.200801122 .
  8. ↑ L. Zhang, Q. Zhang, J. Li: Layered Titanate Nanosheets Intercalated with Myoglobin for Direct Electrochemistry . In: Advanced Functional Materials . tape 17 , no. 12 , August 13, 2007, p. 1958–1965 , doi : 10.1002 / adfm.200600991 .
  9. ^ Haisheng Tao, Jingjing Wang, Yang Ou, Wei Zhu, Huanchang Ling: Construction and Direct Electrochemistry of Hemoglobin-Intercalated Titanate Nanosheets . In: Nanoscience and Nanotechnology Letters . tape 6 , no. 2 , February 1, 2014, p. 99-105 , doi : 10.1166 / nnl.2014.1735 .
  10. ↑ Qinhua Zhou, Zhufeng Lu, Xuebo Cao: Heterostructured magnetite-titanate nanosheets for prompt charge selective binding and magnetic separation of mixed proteins . In: Journal of Colloid and Interface Science . tape 415 , 2014, p. 48-56 , doi : 10.1016 / j.jcis.2013.10.012 .
  11. ↑ Mingjie Liu, Yasuhiro Ishida, Yasuo Ebina, Takayoshi Sasaki, Takaaki Hikima: An anisotropic hydrogel with electrostatic repulsion between cofacially aligned nanosheets . In: Nature . tape 517 , no. 7532 , 2015, p. 68-72 , doi : 10.1038 / nature14060 .
  12. ^ Anne Ladegaard Skov: Like cartilage, but simpler: Materials science . In: Nature . tape 517 , no. 7532 , 2015, p. 25-26 , doi : 10.1038 / 517025a .
  13. ↑ Christian Harito, Dmitry V. Bavykin, Mark E. Light, Frank C. Walsh: Titanate nanotubes and nanosheets as a mechanical reinforcement of water-soluble polyamic acid: Experimental and theoretical studies . In: Composites Part B: Engineering . tape 124 , 2017, p. 54–63 , doi : 10.1016 / j.compositesb.2017.05.051 .