CZ20995U1 - Titanium dioxide based nanotubes - Google Patents

Description

Technical field

The technical solution concerns a new crystalline modification of titanium oxide in the form of nanotubes. Background Art

Titanium dioxide nanotubes (hereinafter TiNT) were first prepared in 1998 [Kasuga T, Hiramatsu M, Hoson A, Sekino T and Niihara K 1998 Langmuir 14 3160]. It was a hydrothermal synthesis, the starting and ending product exhibiting anatase crystalline structure. A few years later, a series of works followed that showed that TiNT can be prepared not only from the anatase modification TiO ₂ [Seo DS, Lee JK and Kim H 2001J. Cryst. Growth. 229 428; Wang YQ, Hu io GQ, Duan XF, Sun HL and Xue QK 2002 Chem. Phys, Lett. 365 427; Wang WZ, Varghese OK, Paulose M, CA Grimes, Wang QL and Dickey EC 2004 J. Mater. Res. 19 417], but also from the modification of rutile [Kasuga T, Hiramatsu M, Hoson A, Sekino T and Niihara K 1999 Adv. Mater, 11,1307; Thome A, Kruth A, Tunstall D, Irvine JTS and Zhou WZ 2005 J. Phys. Chem. B 109 5439; Lan Y, Gao XP, Zhu Y, Zheng ZF, Yan Y, Wu F, Ringer SP and Song DY 2005

Adv. Funct. Mater. 15 13 10], amorphous TiO ₂ [Kolenko YV, Kovnir KA, Gavrilov AI, Garshev A V, Frantti J, Lebedev O, Churagulov BR, Van Tendeloo OG and Yoshimura M 2006 J. Phys. Chem. B 110 4030] and mixtures thereof [Tsai CC and Teng HS 2006 Chem. Mater. 18 367; Tsai CC and Teng HS 2004 Chem. Mater. 16 4352]. Some studies suggest that nanotubes are formed only in a strongly alkaline environment [Yang JJ, Jin ZS, Wang XD, Li W, Zhang, JW,

Zhang SL, Guo XY and Zhang ZJ 2003 Dalton Trans, 3898; Chen Q, Zhou WZ, Du GH and Peng LM 2002 Adv. Mater. 14 1208], others emphasize the importance of final product treatment with HCl [Kasuga T, Hiramatsu M, Hoson A, Sekino T and Niihara K 1999 Adv. Mater. 11 1307; Tsai CC and Teng HS 2004 Chem. Mater. 16 4352; Kasuga T 2006 Thin Solid Films 496,141]. The Board of Researchers has investigated the crystalline structure of TiNT. Some studies have shown the already mentioned TiO ₂ anatase modification [Kasuga T, Hiramatsu M, Hoson A, Sekino T and Niihara K 1998 Langmuir 14 3160; Yao BD, Khan YF, Zhang XY, Zhang WF, Yang ZY and Wang N 2003 Appl, Phys. Lett. 82 281; 7 Seo DS, Lee JK and Kim H 2001 J. Cryst. Growth. 229 428], others suggested less common structures such as H ₂ Ti ₃ O ₇ or Na ₂ Ti ₃ O ₇ [Chen Q, Zhou WZ, Du GH and Peng LM 2002 Adv, Mater. 14 1208; Yuan ZY and Su BL 2004 Colloid Surface A

241 173] H ₂ Ti ₂ O ₅ .H ₂ O or Na ₂ Ti ₂ O ₅ .H ₂ O [Yang JJ, Jin ZS, Wang XD, Li W, Zhang. JW,

Zhang S L, Guo X Y and Zhang Z J Dalton Trans. 3898; Zhang M, Jin Z S, Zhang J W, Guo X Y, Yang H J, Li W, Wang X D and Zhang Z J 2004 J. Mol. Catal. A-Chem. 217 203], H2T4O9.H2O [Nakahira A, Kato W, Tamai M, Isshiki T and Nishio K 2004 J. Mater. Sci. 39 4239] or lepidocrit titanates [Kubota Y, Chickens H and Soda S 2006 Mol. Cryst. Liq.

Cryst. 445 107]. Finally, most authors agreed that TiNTs exhibited rolled titanate octahedral layers [Wang WZ, Varghese OK, Paulose M, CA Grimes, Wang QL and Dickey EC 2004 J. Mater. Res. 19 417; Lan Y, Gao XP, Zhu Y, Zheng ZF, Yan Y, Wu F, Ringer SP and Song DY 2005 Adv. Funct. Mater. 15 1310]. Based on the results of the diffraction measurements given in the cited sources, it can be stated that the TiNTs described so far have predominantly known crystalline modifications derived from TiO ₂ . Furthermore, the TiNTs described so far often exhibit starting TiO ₂ residues from which they have been prepared (anatase, rutile, etc.).

In recent years, methods have been patented for the preparation of pure anatase structure nanotubes [Kasuga et al., Japanese application JP 8-259182, US 6,027,775 and US 6,537,517], nanotube with anatase-rutile mixture structure [CZ 297 774] and a perovskite nanotube [ Wong et al., US 7,147,834].

The original Japanese patent application JP 8-259182 and derived therefrom US 6,027,775 relates to nanotubes having a diameter of 5 to 80 nm with a wall thickness of 2 to 10 nm with crystalline anatase modification which are characterized by high UV absorption and are intended as photoactive catalysts oxidation reactions. The process for preparing these nanotubes according to US 6,537,517 is based on action

-1CZ 20995 Ul

30% to 50% aqueous NaOH at elevated temperature and elevated pressure to crystalline TiO ₂ . The method of preparing TiNT according to said documents is aimed at achieving the highest possible photoactivity and catalytic efficiency thereof, and thus indirectly at achieving the greatest specific surface on which these properties depend. The aspect ratio (defined as the ratio of thickness to 5 notrubby to the total length of the nanotube) of TiNT is not a major concern in these documents, but it can be seen from the examples that the highest attained maximum of 50.

The nanotubes according to the invention of Wong and co-workers (US 7,147,834), in contrast to the above, are characterized by a relatively long length and a high aspect ratio, according to their chemical composition, they are calcium, strontium and barium titanates and, for their electrical properties, are primarily intended for ferroelectric applications.

Czech patent CZ 297 774 relates to the invention of photoactive modification of TiO ₂ in the form of nanofibers as a catalyst of oxidation reactions.

The essence of the technical solution

The essence of the technical solution is titanium dioxide nanotubes, which do not exhibit defects of previously known nanotubes and above them excel above all by high aspect ratio, high structural purity of the material without traces of residual anatase, rutile or perovskite as primary substances for their preparation. In addition, they exhibit a different crystalline structure that manifests itself, for example, in an electron diffraction pattern. Nanotubes exhibit uniform morphology. The process for preparing nanotubes is characterized by the ability to control the aspect ratio of the nanotube 20 in a wide range without the need for any of the process steps in an inert atmosphere.

Nanotubes have a diameter (D) of between 8 and 40 nm with a length (L) of at least 1 to 20 µm, their average aspect ratio (L / D) always being more than 50 and reaching a value of at least 100 to 500. The nanotube walls are at least 2 and at most 12 layers of crystalline titanium dioxide crystalline modification that differs from the crystalline modification, the starting TiO _2, and is characterized by cha25 characteristic peaks on the electron diffraction pattern at certain values of the diffraction vector q. The diffraction vector q is defined by the equation q = 4n.sin (0) / X, where 0 is the diffraction angle and λ is the wavelength of the accelerated electrons. The three most intense characteristic peaks on the diffraction pattern appear at q = 1.75 A ¹ , 2.05 A ' ¹ and 3.35 A' ¹ and two other Wide peaks appear around q = 4.20 A ' ¹ and 5.25 A ' ¹ . Depending on the conditions for the preparation of TiNT and on the conditions of the electron diffraction measurement, the two closest peaks, q = 1.75 A ' ¹ and 2.05 A' ¹ , may partially overlap.

The process of preparing nanotubes consists of three consecutive steps:

In step 1, a suspension of TiO ₂ in NaOH solution is prepared, whereby the concentration of TiO ₂ in the suspension is at least 0.01 g / 100 ml and at most 6 g / 100 ml and the concentration of NaOH is at least 2 M and at most

16 M.

In step _{2, the} TiO ₂ suspension is tempered with stirring to at least 60 ° C and at most 160 ° C for at least 12 hours.

In step 3, nanotubes are isolated from the reaction mixture and dried preferably by lyophilization. The NaOH solution after isolation of the nanotubes can be used again to prepare the TiO ₂ suspension in Step 1 of the repeated procedure. During isolation, TiNT can be neutralized with HCl without affecting the quality of the final product.

The average aspect ratio of the resulting nanotubes can be controlled by the process described above to control the mean particle size of the starting TiO ₂ , the modification of the starting TiO ₂ and the ratio of the starting TiO ₂ and NaOH concentrations in the slurry in combination with the reaction temperature and time as well as the final product drying method. . The specific process of preparation consists mainly in the combination of reactant concentrations, average TiO ₂ particle size, crystalline TiO ₂ modification, reaction temperature, reaction time and product drying method. Application of the appropriate reaction conditions results in the resulting TiNT product having the above-described characteristics of the properties described above. Mutual coupling reactant concentration of crystal modification input TiO _2, average particle size of the powder inlet TiO _2, temperature and reaction time can basically be described as follows:

1) with the decreasing TiO ₂ concentration, the average aspect ratio of TiNT increases,

2) Particle size and crystalline modification of TiO ₂ input together affect length and diameter

TiNT, but the high aspect ratio remains,

3) with increasing reaction time, temperature and NaOH concentration up to a certain value, the average aspect ratio of TiNT increases.

Nanotubes, unlike others, are very well tolerated by living tissues. From this fact, in combination with their unique morphology, it follows that TiNT according to the described technical solution is an ideal hardening component of both living tissues, especially bone tissue and cartilage, as well as their synthetic replacements based on TiNT hardened composites. The advantage of TiNT is that their high aspect ratio and extremely low agglomerate content allow the mechanical properties of the implant composite material to be adjusted to a sufficiently wide range so that im15 plantations exhibit the same deformation behavior as bone parts or cartilage to replace in specific applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Table of influence of crystalline modification and mean particle size of TiO ₂ on morphology and aspect ratio of resulting TiNT; TiNT were prepared at TiO ₂ concentration

0.1 g / 100 ml, NaOH concentration 10 M, 120 ° C for 20 hours.

FIG. 2: Table of the influence of TiO ₂ concentration on the aspect ratio of the resulting TiNT; TiNTs were prepared at a NaOH concentration of 10 M at 120 ° C for 20 hours.

FIG. 3: Table of the effect of reaction conditions on the aspect ratio of the resulting TiNT; TiNTs were prepared from anatase with a mean particle size of 1 µm and a TiO ₂ concentration of 0.1 g / 100 ml.

FIG. 4: Measured electron diffraction patterns (dashed lines) and theoretically calculated X-ray diffraction patterns (solid lines) of TiNT (a), anatase (b), and rutile (c), demonstrating that the TiNT crystal structure differs fundamentally from conventional TiO ₂ modifications. The TiNT diffractogram corresponds to Example 1; in the other examples, the TiNT diffractogram is identical.

FIG. 5: FESEM photomicrographs of TiNT according to Example 3 illustrating an exceptionally high aspect ratio of prepared nanotubes (TiNTs are shown in FESEM as white fibers on a dark support). From the ratio of the measured average nanotube thickness (D) to the lengths of the nanotubes (I), it can be estimated that the aspect ratio (D / L) is at least 500. This is the lower estimate since most nanotubes are so long that at a given magnification exceeds the real image width.

FIG. Figure 6: HRTEM photomicrographs of TiNTs obtained according to Example 1, which illustrates that the walls of the 35 notch tubes are generally composed of three layers of planar TiO ₂ (TiNTs are shown in the HRTEM as black hollow tubes on a lighter background; two main types of periodicity in TiNT).

Examples of technical solutions

Přikladl

The starting TiO ₂ , anatase powder ground to a particle size of 1 µm, was suspended in a 10 M NaOH solution with a TiO ₂ concentration of 0.1 g / 100 ml. The suspension was subsequently tempered in a stirred autoldate at 120 ° C for 20 hours. The solid was then filtered, washed with water and freeze-dried. For the dry product, the diameter and length were determined using FESEM measurements (field emission gun scanning electron microscopy) and TEM (transmission electron microscopy) photomicrographs, crystalline

-3CZ 20995 Ul structure of TiNT was determined by means of the PXRD (powder X-ray diffraction) and SAED (selected area electron diffraction) diffraction methods, the chemical purity was verified by means of microscopic and spectroscopic methods EDX (energy dispersive analysis of X-rays) and RS ( Raman Spectroscopy), the number of layers was determined by HRTEM (high resolution transmission electron microscopy). The diameter of the nanotubes (D) was found to be 20 nm and their mean length (L) was at least 2 μιη, so the average aspect ratio of the prepared nanotubes (D / L) estimated from the image analysis was above 100. The walls of nanotubes are most often composed of 3 layers of the TiO ₂ -flyed planet, the presence of residual anatase was not detected by SAED, PXRD, or RS. Three most intense, characteristic peaks at diffraction vector values q = 1.75 A * ¹ , 2.05 A ' ¹ and 3.35 A * ¹ and two other broad peaks around q = 4 were found on the electron diffractogram of the resulting nanotrucobes. , 20 A ¹ , 5.25 A ¹ .

Example 2

The starting TiO ₂ as anatase ground to a powder having a mean particle size of 200 nm was suspended in a 10 M NaOH solution with a TiO ₂ concentration of 0.1 g / 100 ml in the suspension. TiNT were prepared from this suspension under the reaction conditions described in Example 1. Properties of TiNT were evaluated as described in Example 1 and it was found that the diameter of the nanotubes was 15 nm and their mean length was less than 2 μπι, so that the average aspect ratio of the prepared nanotubes is at least 130, average number of layers planate arranged TiO _2, observed in HRTEM Microphotographs were 3 as in Example 1. Again, characteristic peaks were found on the electron diffraction pattern of the resulting nanotubes: the three most intense peaks at the diffraction vector values q = 1.75 A ¹ , 2.05 A ¹ and 3.35 A ¹ and two others broad peaks around q = 4.20 A ¹ , 5.25 A ¹ .

Example 3

The starting TiO ₂ in the form of rutile ground to a medium particle size of 1 μπι was suspended in a 10 M NaOH solution with a TiO ₂ concentration of 0.1 g / 100 ml. TiNT were prepared from this suspension under the reaction conditions described in Example 1. The properties of the resulting TiNT were evaluated as described in Example 1 and the nanotube diameter was found to be 40 nm and their mean length was at least 20 µm, so the average aspect ratio of the prepared nanotubes was greater than 500.

TiO ₂ , observed on HRTEM microphotographs, increased to 6. Again, characteristic peaks were found on the electron diffractogram of the resulting nanotubes: the three most intense peaks at the diffraction vector values q = 1.75 A ' ¹ , 2.05 A' ¹ and 3.35 A ' ¹ and two other broad peaks nearby? = 4.20 ^A-1, 5.25 A ^'first

Example 4

The starting TiO ₂ in the form of rutile ground to a medium particle size 50 nm powder was suspended in a 10 M NaOH solution with a TiO ₂ concentration of 0.1 g / 100 ml in the suspension. TiNT were prepared from this suspension under the reaction conditions described in Example 1. The properties of the resulting TiNTs were evaluated as described in Example 1 and the nanotube diameter was found to be 8 nm and their mean length was approximately at least 1 μ, so the average aspect ratio of the prepared nanotubes was at least 125. Characteristic peaks were found again on the electron diffractogram of the resulting nanotubes : the three most intense peaks at the diffraction vector values q = 1.75 ^{1 1} , 2.05 a ¹ and 3.35 ' ¹ and two other broad peaks in the neighborhood q = 4.20''', 5.25 Å ' ¹ .

Industrial usability

Titanium dioxide nanotubes according to the described technical solution are useful as a reinforcing component of polymer composites, especially composites intended for the production of skeletal compositions-4CZ 20995 UL replacements and implants in medicine, as a component of augmentation materials for medical applications and as a material for the production of special filters.

Claims (3)

PROTECTION REQUIREMENTS 1. Titanium dioxide nanotubes having a mean diameter (D) of 8 to 40 nm and a mean length (Z) of 1 to 20 μιη and an aspect ratio (L / D) of greater than 50, wherein the walls of the nanotubes is between 2 and 12 layers of plains of crystalline modification of titanium dioxide characterized by three main diffraction maxima in electron diffraction vector values q - 1.75 ^a-1, 2.05 Å ^-1 and 3.35 a ^'1 and two additional broad peaks q - 4 , 20 A * ¹ , 5,25 A ' ¹ (the diffraction vector q is defined by the equation: q = 4π.8ίη (θ) / λ, where Θ is the diffraction angle and λ is the wavelength of the accelerated electrons). Titanium dioxide nanotubes according to claim 1, characterized in that their aspect ratio is at least 100 to 500. Titanium dioxide nanotubes according to claim 2, characterized in that their average diameter is 20 nm, the mean length is at least 2 µm and the aspect ratio is at least 100. 15 Dec Titanium dioxide nanotubes according to claim 2, characterized in that their mean diameter is 15 nm, the mean length is at least 2 µm and the aspect ratio is at least 130. Titanium dioxide nanotubes according to claim 2, characterized in that their mean diameter is 40 nm, the mean length is at least 20 µm and the aspect ratio is at least 500. 20. The titanium dioxide nanotubes of claim 2, wherein their average diameter is 8 nm, the mean length is at least 1 μπι, and the aspect ratio is at least 125. 3 drawings