CZ2010348A3 - Nanotubes based on titanium white and process for producing tghereof - Google Patents

Abstract

Titanium dioxide-based nanotubes with high aspect ratio (> 50) have a crystal structure type characterized by three major electron diffraction maxima at diffraction vector values q = 1.75 A.sup.-1.n., 2.05 A.sup.- 1. at 3.35 A.sup.-1.on two other broad peaks q = 4.20 A.sup.-1.n., 5.25 A.sup.-1.n., where the diffraction vector q is defined by the equation q = 4.pi. • sin (?) /. lambda., and? is the diffraction angle α .lambda. is the wavelength of accelerated electrons.

Description

Technical field

The present invention relates to a novel crystalline modification of titanium dioxide in the form of nanotubes and to a process for the preparation of this form of titanium dioxide.

BACKGROUND OF THE INVENTION

Titanium dioxide nanotubes (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 end product showed anatase crystalline structure. Several years later, a series of works have shown that TiNT can be prepared not only from the anatase modification of TiOi [Seo D S, Lee J K and Kim H 2001 J. Cryst. Growth. 229 428; Wang Y Q, Hu G Q, Duan X F, Sun H L and Xue Q K 2002 Chem. Phys. Lett. 365 427; Wang W Z, Varghese O K, Paulose M, Grimes C A, Wang Q L and Dickey E C 2004 J. Mater. Res. 19, 417], but also from a rutile modification [Kasuga T, Hiramatsu M, Hoson A, Sekino T and Niihara K 1999 Adv. Mater. 11 1307; Thome A, Kruth A, Tunstall D, Irvine J T and Zhou W Z 2005 J. Phys. Chem. B 110 5439; Lan Y, Gao X P, Zhu Y, Zheng Z F, Yan T Y, Wu F, Ringer S P and Song D Y 2005 Adv. Funct. Mater. 15 1310], amorphous Ti O? [Kolenko Y V, Kovnir K A, Gavrilov A I, Garshev A V, Frantti J, Lebedev O I, Churagulov B R, Van Tendeloo O G and Yoshimura M 2006 J. Phys. Chem. Β 110 4030] and mixtures thereof [Tsai C and Teng H S 2006 Chem. Mater. 18 367; Tsai C and Teng H S 2004 Chem. Mater. 16 4352]. Some studies report that nanotubes are formed only in strongly alkaline environments [Yang J J, Jin Z S, Wang X D, Li W, Zhang, J W, Zhang S L, Guo X Y, and Zhang Z J 2003 Dalton Trans. 3898; Chen Q, Zhou W Z, Du G H and Peng L M 2002 Adv. Mater. 14 1208], others emphasize the importance of final treatment of the product with HCi [Kasuga T, Hiramatsu M, Hoson A, Sekino T and Niihara K 1999 Adv. Mater. 11 1307; Tsai C and Teng H S 2004 Chem. Mater. 16 4352; Kasuga T 2006 Thin Solid Films 496,141]. A number of researchers focused on the crystalline structure of TiNT. Some studies have already shown the anatase modification of TiO2 [Kasuga T, Hiramatsu M, Hoson A, Sekino T and Niihara K 1998 Langmuir 14 3160; Yao B D, Khan Y F, Zhang X Y, Zhang W F, Yang Z Y and Wang N 2003 Appl. Phys. Lett. 82 281; 7 Seo D S, Lee J K and Kim H 2001 J. Cryst. Growth. 229 428], others suggested less common structures such as H2Ti3O7 or NajTijCh [Chen Q,

Zhou WZ, Du GH, and Peng LM 2002 Adv. Mater. 14 1208; Yuan ZY and SuB L 2004 Colloid Surface A 241 173] H ₂ Ti ₂ O ₅ .H ₂ O or Na ₂ Ti ₂ O _with .H ₂ O [Yang JJ, Jin ZS, Wang XD, Li W, Zhang, JW, Zhang SL, Guo XY and Zhang ZJ 2003 Dalton Trans. 3898; Zhang M, Jin ZS, Zhang JW, Guo XY, Yang HJ, Li W, Wang XD, and Zhang ZJ 2004 J. Mol. Catal. A-Chem. 217203] H ₂ TÍ4Og H ₂ 0 [Nakahira A, Kato N, Tamai M, T and Isshiki Nishio K 2004 J. Mater. Sci. 39 4239] or lepidocrit titanates [Kubota Y, Chickens H and Isoda S 2006 Mol. Cryst Liq. Cryst. 445 107]. Finally, most authors agreed that TiNTs exhibited the structure of rolled-up layers of titanate octahedra [Wang WZ, Varghese OK, Paulose M, Grimes CA, Wang QL and Dickey EC 2004 J. Mater. Res. 19,417; Lan Y, Gao XP, Zhu HY, Zheng ZF, Yan TY, Wu F, Ringer SP and Song DY 2005 Funct. Mater. 15 1310].

Based on the results of the diffraction measurements given in the cited sources, it can be concluded that the previously described TiNTs show predominantly known crystalline modifications derived from TiO ₂ . In addition, the TiNTs described so far often show residues of the starting TiO ₂ from which they were prepared (anatase, rutile, etc.).

In recent years, methods for the preparation of nanotubes with pure ir * anatase structure have been patented [Kasuga et al., Japanese Application No. 2-259182. US Patent 6,027,775 and US Patent 6,537,517], anatase-rutile nanotubes [CZ Patent 297 774] and perovskite nanotubes [Wong et al., US Patent 7 _x 147 _and 834J.

Japanese Patent Application No. 8-259182 and US Patent 6,027,775 relates to nanotubes having a diameter of 5 to 80 nm and a wall thickness of 2 to 10 nm with a crystalline modification of anatase, which are characterized by high light absorption in the UV region and are intended as photoactive catalysts oxidation reactions. The preparation of these nanotubes according to US Patent 6 _X 537 _X 517 is based on the action of 30¼ to 50% aqueous NaOH solution at elevated temperature and elevated pressure on crystalline TiO ₂ . The preparation of TiNTs according to the above-mentioned documents is aimed at achieving their maximum photoactivity and catalytic efficiency and thus indirectly at achieving the greatest possible surface area on which these properties depend. The aspect ratio (defined as the ratio of nanotube thickness to total nanotube length) of TiNT is not a major concern in these documents, but it can still be seen from the examples that the highest aspect ratios achieved are at most 50.

The nanotubes according to the invention of Wong and co-workers (US Patent 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 are mainly intended for ferroelectric applications.

Czech patent no. 297 774 relates to a photoactive modification of T102 in the form of nanofibres as a catalyst for oxidation reactions.

SUMMARY OF THE INVENTION

The present invention is based on titanium dioxide nanotubes which do not exhibit the defects of the prior art nanotubes and above all excel in the high aspect ratio, high structural purity of the material without traces of residual anatase, rutile or perovskite as the primary substances for their preparation. In addition, they exhibit a different crystalline structure, which is reflected, for example, in an electron diffraction pattern. The nanotubes of the invention exhibit uniform morphology. The method of preparation of the nanotubes according to the invention is characterized by the possibility of broadly controlling the aspect ratio of the nanotubes without having to carry out any of the steps of the inert atmosphere process.

The nanotubes according to the invention have a diameter (D) of between 8 and 40 nm at a length (L) of at least 1 to 20 pm, having an average aspect ratio (L / D) of at least 50 and at least 100 to 500. of the invention comprise at least 2 and at most 12 layers of planar crystalline modification of titanium dioxide which differs from the crystalline modification of the initial T10O2 and is characterized by characteristic peaks on the electron diffraction pattern at certain diffraction vector q values. The diffraction vector q is defined by the equation q = 4π · δϊη (θ) / λ, where Θ is the diffraction angle and λ is the wavelength of the accelerated electrons. The three most intense characteristic peaks in the diffraction pattern appear at q = 1.75 A ^-1 , 2.05 A ^-1 and 3.35 A ^-1, and two other broad peaks appear around q = 4.20 A * ¹ and 5.25 a ^first Depending on preparation conditions TiNT and electron diffraction measurement conditions, two major peaks, q = 1.75 Å ^-1 and 2.05 A ^'1 may overlap.

The process of preparing nanotubes according to the invention consists of three successive steps:

In the first step, the prepared slurry T1O2 in NaOH solution, the concentration of TiO ₂ in the slurry is at least 0.01 'g / 100 m | and less than 6 g / 100 ml and the concentration of NaOH is at least 2 m and up to 16 M.

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

In step 3, the nanotubes are isolated from the reaction mixture and dried, preferably by lyophilization. The NaOH solution, after isolation of the nanotubes, can be reused to prepare a T10O2 suspension in Step 1 of the repeat procedure. During the isolation, TiNT can be neutralized with HCl without affecting the quality of the resulting product.

The average aspect ratio of the resulting nanotubes can be controlled by the mean particle size of the starting TiCl _{2 by} modifying the starting TiO ₂ and the ratio of the starting TiO ₂ and NaOH concentrations in suspension in combination with the reaction temperature and time as well as the final product drying method. The specific preparation process consists mainly in combination of the concentrations of the reactants, the average particle size of the input TiO ₂ , the crystalline modification of the input TiO ₂ , the reaction temperature, the reaction time and the method of drying the product. Application of suitable reaction conditions then yields the resulting TiNT product with the characteristics described above. The interaction of the reactant concentration, the crystalline modification of the input TiO ₂ , the average particle size of the input TiO ₂ powder, the temperature and the reaction time can basically be described as follows:

1) the average aspect ratio of TiNT increases with decreasing TiO2 concentration,

2) the particle size and crystalline modification of the input TiO ₂ together influence the length and diameter of the TiNT, but the high aspect ratio is maintained,

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

The nanotubes of the invention are very well tolerated by living tissues, unlike others. This, in combination with their unique morphology, implies that the TiNTs of the invention are an ideal reinforcing component of both living tissues, especially bone and cartilage, and their synthetic substitutes based on TiNT-reinforced composites.

The advantage of the TiNTs according to the invention is that their high aspect ratio and extremely low agglomerates make it possible to adjust the mechanical properties of the composite implant material to a sufficiently wide extent so that the implants exhibit the same deformation behavior as the bone or cartilage parts to replace.

BRIEF DESCRIPTION OF THE DRAWINGS

Giant. 1: Table of the effect of crystalline modification and mean particle size of input TiO ₂ on morphology and aspect ratio of the resulting TiNTs; TiNTs were prepared at a TiO ₂ concentration of 0.1 g / 100 ml, a NaOH concentration of 10M, a temperature of 120 ° C for 20 hours.

Giant. 2: Table of the effect of concentration of input T1O2 on the aspect ratio of the resulting TiNTs; TiNTs were prepared at 10M NaOH, 120 ° C for 20 hours.

Giant. 3: Table of the effect of reaction conditions on the aspect ratio of the resulting TiNTs; TiNTs were prepared from anatase with a mean particle size of 1 µm and a T 10 O 2 concentration of 0.1 g / 100 ml.

Giant. 4: Measured electron dithractograms (dashed lines) and theoretically calculated X-ray diffractograms (solid lines) of TiNT (a), anatase (b) and rutile (c), which demonstrate that the crystal structure of TiNT is fundamentally different from conventional T1O2 modifications. The TiNT diffractogram corresponds to Example 1; in the other examples, the TiNT diffractogram is identical, only in the Examples 5 * 7, the residual anatase peaks (which correspond to the diffractogram (b)) also appear on the TiNT diffractogram.

Giant. 5: FESEM micrographs of TiNTs according to Example 3 illustrating an exceptionally high aspect ratio of prepared nanotubes (TiNTs are shown in FESEM as white fibers on a dark background). From the ratio of the measured average nanotube thickness (D) to nanotube length (Z), it can be estimated that the aspect ratio (D / L) is at least 500 here. This is a lower estimate since most nanotubes are so long that landscape image.

Giant. 6: HRTEM photomicrographs of TiNTs obtained according to Example 1, illustrating that the nanotube's walls are typically made up of three layers of planar-arranged T1O2 (TiNTs are shown in the HRTEM as black hollow tubes on a lighter background; types of periodicities in TiNT).

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Default TiO? in the form of anatase, ground to powder with the mean particle size of 1 micron was' suspended in ¹ * 10 M NaOH solution, the concentration of T1O2 in the suspension was 0.1 g / 100 * · 7 ml. The suspension was then tempered in a stirred autoclave at 120 ° C for 20 hours. The solid from the reaction mixture was then filtered, washed with water and freeze-dried. For dry product, diameter and length were determined using field emission gun scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) measurements, the crystalline structure of TiNT was determined using powder X-ray diffraction (PXRD) and selected area SAED (selected area) electron diffraction), chemical purity was verified by microscopic and spectroscopic methods EDX (energy dispersive analysis of X-rays) and RS (Raman Spectroscopy), the number of layers was determined by HRTEM (high resoiution transmission electron microscopy). It was found that the diameter of the nanotubes (D) was 20 nm and their mean length (L) was at least 2 gm, so that the average aspect ratio of prepared nanotubes (D / L), estimated from image analysis, was above 100. the walls of nanotubes consist mostly of 3 layers of planarly arranged TiO ₂ , the presence of residual anatase was not detected by SAED, PXRD or RS. On the electron diffractogram of the resulting nanotubes, the three most intense, characteristic peaks were found at the diffraction vector q = 1.75 A ^-1 , 2.05 A ^-1 and 3.35 A ^-1, and two other broad peaks around q = 4, 20 A ' ¹ , 5.25 A' ¹ .

Example 2

The starting TiO ₂ in the form of anatase ground to a powder with an average particle size of 200 nm was suspended in a 10 M NaOH solution, the TiO ₂ concentration in the suspension being 0.1 g / 100 ml. TiNTs were prepared from this suspension under the reaction conditions described in Example I. Properties of TiNT were evaluated as described in Example 1 and it was found that the nanotube diameter was 15 nm and their mean length was less than 2 gm, so that the average aspect ratio of the prepared nanotubes is at least 130. The average number of layers arranged planate TiO _2, observed in HRTEM In the electron diffractogram of the resulting nanotubes, characteristic peaks were again found: the three most intense peaks at the diffraction vector q-values of 1.75 A ¹ , 2.05 A ^-1 and 3.35 A * ^1. and two additional broad peaks around ^q-1 4.20 a 5.25 a ^'l.

Example 3

The starting TiO ₂ in the form of rutile ground to a powder with a mean particle size of 1 gm was

Λ suspended in a 10 M NaOH solution, the concentration of TiO ₂ in the suspension being 0.1 g / 100 ml. TiNTs 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 nanotubes were found to have a diameter of 40 nm and a mean length of at least 20 gm. so the average aspect ratio of the prepared nanotubes was greater than 500. Typical number of layers of flameproof TiO ₂ observed in HRTEM photomicrographs was 6. The characteristic peaks were again found on the electron diffractogram of the resulting nanotubes:

the three most intense peaks at diffraction vector values q = 1.75 A ^'1, A ¹ 2.05 3.35 A' ¹ and two additional broad peaks around q - 4.20 ^A-1, 5.25 A ' ¹ .

Example 4

The starting TiO ₂ in the form of rutile ground to a 50 nm mean particle size powder was suspended in 10 µM NaOH solution, the TiO ₂ concentration in the suspension being 0.1 g / 100 ml. TiNTs 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 nanotubes were found to have a diameter of 8 nm and a mean length of at least 1 µm, so that the average aspect ratio of the prepared nanotubes was greater than 125. : the three most intense peaks at the values of the diffraction vector q - 1.75 A ^-1 , 2.05 A * ¹ and 3.35 A ^-1 and two other broad peaks around q = 4.20 A ^-1 , 5.25 A ' ¹ .

Example 5

The starting TiO ₂ in the form of anatase ground to a powder of mean particle size of 1 µm was suspended in 10 µM NaOH solution, the TiO ₂ concentration in the suspension being 1.0 g / 100 ml. TiNTs 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 it was found that isomeric anatase particles and aggregates of glued nanotubes were rarely present in the mixture, so that the average aspect ratio of the prepared nanotubes decreased by about 20%. In addition to the characteristic diffraction of the nanotubes (three major peaks at q = 1.75 A ^-1 , 2.05 A ^-1 and 3.35 A ^-1, and two other broad peaks around q = 4.20 A ¹ 5.25 a ¹⁾ also diffractions due to anatase (most intense peaks at Q = 1.80 ^a-1, 2.55 a ^'1 and 3.30 a' ^1).

Example 6

The starting TiO ₂ in the form of anatase ground to a powder with a mean particle size of 1 µm was suspended in a 10 mM NaOH solution, the TiO ₂ concentration in the suspension being 6.0 g / 100 ml. TiNTs 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 it was found that isometric anatase particles and nanotube aggregates were present in the mixture, thereby reducing the average aspect ratio of the prepared nanotubes by approximately 40%. In addition to the characteristic diffraction of the nanotubes (three main peaks at q = 1.75 A ^-1 , 2.05 A ⁴ and 3.35 A -1 ⁾ and two other broad peaks around q = 4.20 A ⁴ , 5.25 A ⁴ ) also anatase-related diffraction (most intense peaks at q - 1.80 A ⁴ , 2.55 A ⁴ and 3.30 A ⁴ ).

Example 7

TiNTs were prepared under the same reaction conditions as in Example 1, except for a shorter reaction time of 8 h (instead of 20 h). Similar end product to Examples 5 and 6: the unique presence of isometric anatase nanoparticles and nanotube aggregates reduced the average aspect ratio of nanotubes by about 20% (so that it was approximately 80 instead of 100).

AND

AND

Example 8 I

TiNTs were prepared under the same reaction conditions as in Example 1, except for a longer reaction time of 60 h (instead of 20 h). The same end product as in Example 1, including an average aspect ratio of more than 100.

Example 9

TiNT were prepared under the same reaction conditions as in Example 1, to a lower temperature which was 60 ° C (instead of 120 C ^Q). Similar end product to Examples 5 and 6: presence of isometric anatase nanoparticles and nanotube aggregates reduced average aspect

In the ratio of nanotubes by about 40% (so instead of 100 it was about 60).

Example 10

The TiNTs were prepared under the same reaction conditions as in Example 1, except for a higher temperature of 160 ° C (instead of 120 ° C). The same end product as in Example 1, including an average aspect ratio of more than 100.

Example 11

TiNTs were prepared under the same reaction conditions as in Example 1, except for a lower NaOH concentration of 5M (instead of 10M). A similar end product as in Examples 5 and 6, except that the average aspect ratio of the nanotubes decreased by about 30% (so that it was approximately 70 instead of 100).

Example 12

TiNTs were prepared under the same reaction conditions as in Example 1, except for a higher NaOH concentration of 16 M (instead of 10 M). The same end product as in Example 1, including an average aspect ratio of more than 100.

Example 13

The TiNTs were prepared under the same reaction conditions as in Example 1 except for the drying method: Example 1 was freeze-drying, while here the nanotubes were dried under vacuum at 60 ° C or in air at room temperature 25 ° C. The same results were obtained as in Example 1 except that the nanotubes tended to join into aggregates and clusters, thereby increasing their average thickness and the aspect ratio dropping to approximately 60.

Example 14

TiNTs were prepared under the same reaction conditions as in Example 1 and the resulting product was washed with distilled water and neutralized with a few drops of conc. HCl from alkaline to neutral, natural for biological applications. Then the resulting product was washed with distilled water. The result was the same end product as in Example 1 including an average aspect ratio of more than 100.

Industrial applicability

The titanium dioxide nanotubes according to the invention are useful as a reinforcing component of polymer composites, in particular composites intended for the manufacture of skeletal dentures and implants in medicine, as a component of augmentation materials for medical applications, and as a material for the manufacture of special filters.

Claims (17)

PATENT CLAIMS Titanium dioxide nanotubes having a mean diameter (Z>) of 8 to 40 nm and a mean length (L) of 1 to 20 µm and an aspect ratio (LID) of greater than 50, wherein the walls of the nanotubes are 2 to 12 plan layers of titanium oxide crystal modification characterized by three main diffraction maxima in electron diffraction vector values q - 1.75 a 2.05 a ^'1 and a ¹ of 3.35 and two additional broad peaks at g = 4.20 and' ^1, 5, 25 A ¹ (the diffraction vector q is defined by the equation iq = 4K-sin (0) / X, where 0 is the diffraction angle and λ is the wavelength of the accelerated electrons). 2. Titanium dioxide nanotubes according to claim 1, characterized in that the nanotubes are based on titanium dioxide the 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. 4. The titanium dioxide nanotubes of claim 2 having a mean diameter of 15 nm, a mean length of at least 2 µm, and an aspect ratio of at least 130. 5. Titanium dioxide nanotubes according to claim 2, characterized in that their the diameter is 40 nm, the mean length is at least 20 µm and the aspect ratio is at least 500. Titanium dioxide nanotubes according to claim 2, characterized in that their average diameter is 8 nm, the mean length is at least 1 µm and the aspect ratio is at least 125. 7. A process for the preparation of nanotubes according to claim 1, characterized in that a concentration of 0.01 g / 100- is prepared from TiO3 having an average particle size of 0.01 ' m ^ to 6 g / 100 ml, which is stirred at 60 to 160 ° C for at least 8 hours with stirring, and the resulting solid product is washed and dried after isolation from the solution. A process for preparing nanotubes according to claim 7, characterized in that the NaOH solution has a concentration of 10 wet. Method for preparing nanotubes according to claim 7 or 8, characterized in that the tempering time is 20 hours. Process for the preparation of nanotubes according to claims 7 or 8 or 9, characterized in that the suspension is tempered to 120 ° C. Process for preparing nanotubes according to claims 7 or 8 or 9 or 10, characterized in that the suspension has a concentration of 0.1 g / 100 ml. A process for the preparation of nanotubes according to claims 8, 9, 10 and 11, characterized in that the average particle size of TiO ₂ in the form of anatase is 1 µm. A process for preparing nanotubes according to claims 8, 9, 10 and 11 ₍ characterized in that the average particle size of T 10 O 2 in the form of anatase is 0.2 µm. A process for preparing nanotubes according to claims 8, 9, 10 and 11, characterized in that the average particle size of T102 in the form of rutile is 1 µm. A process for the preparation of nanotubes according to claims 48, 9, 10 and 11, characterized in that the average particle size of T102 in the form of rutile is 0.05 .mu.m. A process for the preparation of nanotubes according to claims II to 15, characterized in that the product is neutralized. A method for preparing nanotubes according to claims 11 to 16, characterized in that the product is freeze-dried.