HIGH REFRACTIVE INDEX NANOPARTICLES

Abstract

Disclosed is a synthesis method for preparing tantalum pentoxide colloid including the steps of: a. Providing a transparent solution of amorphous tantalum pentoxide, b. Subjecting the solution to solvothermal conditions in order to form tantalum pentoxide nanocrystals, c. Dispersing the tantalum pentoxide nanocrystals in a solvent so as to form a tantalum pentoxide colloid.

Claims

1. Synthesis method for preparing tantalum pentoxide colloid comprising the steps of: a. Providing a transparent solution of amorphous tantalum pentoxide, b. Subjecting said solution to solvothermal conditions in order to form tantalum pentoxide nanocrystals, c. Dispersing said tantalum pentoxide nanocrystals in a solvent so as to form a tantalum pentoxide colloid.

2. Synthesis method according to claim 1, wherein the transparent solution of amorphous tantalum pentoxide is provided through adding an acidic aqueous solution to an amorphous tantalum pentoxide aqueous solution.

3. Synthesis method according to claim 1, wherein the transparent solution of amorphous tantalum pentoxide is provided through adding an acidic aqueous solution of boric acid and an aqueous solution of organic ammonium fluoride to an amorphous tantalum pentoxide aqueous solution.

4. Synthesis method according to claim 1, wherein step b includes heating the solution by an oven.

5. Synthesis method according to claim 1, wherein step b includes heating the solution through microwaves, preferably between 120 and 200 C.

6. Synthesis method according to claim 1, wherein step c is performed by ultrasonic dispersion.

7. Synthesis method according to claim 1, further comprising a solvent exchange step to obtain tantalum pentoxide colloid in a hydroalcoholic mixture.

8. Synthesis method according to claim 1, wherein the tantalum pentoxide colloid is a colloid dispersed in water.

9. Synthesis method according to claim 1, further comprising a step of concentrating the obtained tantalum pentoxide colloid.

10. Synthesis method according to claim 1, wherein the obtained concentrated tantalum pentoxide colloid has a dry content of at least 10% by weight.

11. Synthesis method according to claim 1, wherein the tantalum pentoxide colloid is a colloid dispersed in an alcohol.

12. Tantalum pentoxide colloid comprising at least 10% by weight of orthorhombic tantalum pentoxide crystals in alcohol.

13. Tantalum pentoxide according to claim 12, wherein the crystals present a rodlike shape.

14. An optical article, comprising a transparent polymer substrate and at least one coating prepared from a composition comprising a Tantalum pentoxide colloid according to claim 12.

15. Synthesis method according to claim 1, wherein the transparent solution of amorphous tantalum pentoxide is provided through adding an acidic aqueous solution to an amorphous tantalum pentoxide aqueous solution, wherein the acidic aqueous solution is selected from the group consisting of boric acid, organic acids and their mixtures.

16. Synthesis method according to claim 1, wherein step b includes heating the solution by an oven to between 120 and 220 C.

17. Synthesis method according to claim 1, wherein step b includes heating the solution through microwaves to between 120 and 200 C.

18. Synthesis method according to claim 1, further comprising a solvent exchange step to obtain tantalum pentoxide colloid in an alcohol.

19. Synthesis method according to claim 1, further comprising a solvent exchange step to obtain tantalum pentoxide colloid in methanol.

20. Synthesis method according to claim 1, further comprising a step of concentrating the obtained tantalum pentoxide colloid by ultrafiltration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention will be more fully understood from the following detailed description of the embodiments thereofto which the invention is not limited howevertaken together with the drawings in which:

[0042] FIG. 1 is a bloc diagram of an exemplary synthesis according to the invention,

[0043] FIG. 2 is an X-Ray Diffraction (XRD) pattern of a tantalum pentoxide colloid obtained through a synthesis according to the present invention,

[0044] FIG. 3 is an image obtained by high-resolution transmission electron microscopy (HRTEM) of the sample used to generate the XRD pattern of FIG. 2,

[0045] FIG. 4 is an XRD pattern of a tantalum pentoxide colloid obtained through another embodiment of the present invention,

[0046] FIG. 5 is an HRTEM image of the sample used to generate the XRD pattern of FIG. 4,

[0047] FIG. 6 is an XRD pattern of a tantalum pentoxide colloid obtained through another embodiment of the present invention, and

[0048] FIG. 7 is an HRTEM image of the sample used to generate the XRD pattern of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] In an exemplary embodiment of the present invention which corresponds to FIG. 1, a tantalum pentoxide colloid is synthetized.

[0050] All reagents used were of analytical grade purity. Tantalum pentachloride (TaCl.sub.5), tantalum pentaethanolate (C.sub.10H.sub.25O.sub.5Ta), tetrabutylammonium fluoride trihydrate (C.sub.16H.sub.36FN.3H.sub.2O), tetrapropyl Ammonium Fluoride (C.sub.12H.sub.28FN), tetraethyl ammonium fluoride dihydrate (CsH.sub.20FN.2H.sub.2O) and ammonium fluoride (NH.sub.4F) were provided from J&K Scientific Ltd. Ethanol (CH.sub.3CH.sub.2OH), methanol (CH.sub.3OH), ammonium hydroxide (NH.sub.3*H.sub.2O), hydrofluoric acid (HF), orthoboric acid (H.sub.3BO.sub.3), oxalic acid dihydrateacetyl (H.sub.2C.sub.2O.sub.4.2H.sub.2O), citric acid (C.sub.6H.sub.8O.sub.7), tartaric acid (C.sub.4H.sub.6O.sub.6), acetylacetone and catechol and trisodium citrate dihydrate (Na.sub.3C.sub.6H.sub.5O.sub.7.2H.sub.2O) were obtained from Sinopharm Chemical Reagent Co., Ltd.; deionized water was used in the experiment.

[0051] First, a tantalum precursor Ta.sup.5+, e.g. in the form of TaCl.sub.5 or tantalum pentaethanolate (C.sub.10H.sub.25O.sub.5Ta), ethanol and ammonia water are used to prepare amorphous tantalum pentoxide (Ta.sub.2O.sub.5). The pH is preferentially adjusted to a value of 8. The resulting slurry can advantageously be filtered and washed until the electroconductivity of the filtrate is below 100 s/cm.

[0052] Hydrofluoric acid (HF), alone or combined with organic ammonium fluoride, with a combination of water and alcohol as solvent, is then added to the amorphous tantalum pentoxide under mechanical stirring, preferably under strong mechanical stirring, until the amorphous tantalum pentoxide is completely dissolved.

[0053] The reactants mole ratio TaCl.sub.5:HF preferably ranges from 0.05:1 to 0.20:1, more preferably is of 0.1:1.

[0054] When an organic ammonium fluoride is used, it is preferably chosen among one of tetrabutylammonium fluoride trihydrate (C.sub.16H.sub.36FN.3H.sub.2O), tetrapropyl Ammonium Fluoride (C.sub.12H.sub.28FN), tetraethyl ammonium fluoride dihydrate (CsH.sub.20FN.2H.sub.2O) or ammonium fluoride (NH.sub.4F). The preferred reactants mole ratio NR.sub.4F:HF is from 0:1 to 2:1.

[0055] In order to obtain a transparent solution, an amount of boric acid (H.sub.3BO.sub.3) or of an organic acid, preferably an organic acid chosen among one of oxalic acid dihydrateacetyl (H.sub.2C.sub.2O.sub.4.2H.sub.2O), citric acid (C.sub.6H.sub.8O.sub.7) or tartaric acid (C.sub.4H.sub.6O.sub.6), more preferably oxalic acid dihydrateacetyl, is added to the solution.

[0056] In case of boric acid, the preferred reactants mole ratio TaCl.sub.5:H.sub.3BO.sub.3 is from 0.02:1 to 0.1:1, preferably 0.04:1.

[0057] In case of organic acid, the preferred reactants mole ratio TaCl.sub.5:organic acid is from 0.25:1 to 5:1, preferably 0.5:1.

[0058] The transparent solution is then transferred into a Teflon autoclave to be subjected to solvothermal conditions during a solvothermal time, and heated by oven or microwave (MASR: microwave assisted solvothermal reaction) so as to form tantalum pentoxide nanocrystals. The optimal solvent to perform this solvothermal step is a mixture of water and ethanol with a volumetric ratio of ethanol:water=2:8. The solvothermal temperature preferably ranges between 120-220 C., more preferably 180 C. In case of a regular oven, the solvothermal time preferably ranges from 6 h to 36 h, preferably about 24 h. In case of MASR, the MASR time ranges from 15 minutes to 3 hours, preferably around 1 hour.

[0059] After the system has been cooled to room temperature, the obtained tantalum pentoxide nanocrystals are added to a buffer solution, e.g. a Na.sub.3C.sub.6H.sub.5O.sub.7.2H.sub.2O solution, to bring the pH into neutral range, preferably between 6 and 7. The nanocrystals are then dispersed by an ultrasonic cell crasher such as XQ-1000D, Nanjing Xian'ou biological Technology Co., Ltd to form a tantalum pentoxide colloid in water. The obtained colloid is semi-transparent, a state which can also be referred to as translucent which means the colloidal solution diffuses the light of the visible spectrum without stopping it altogether.

[0060] A small amount of complexing agent such as acetylacetone or catechol can be added in order to improve the dispersity and stability of the tantalum pentoxide colloid. In that case, the preferred mass ratio of complexing agent acetylacetone or catechol and Ta.sub.2O.sub.5 is from 0:1 to 0.03:1.

[0061] Then, the semitransparent colloid is washed with methanol and concentrated by ultrafiltration until the conductivity is stabilized at the lowest point, below 5 s/cm and until the dry content reaches 20% in weight. The ultrafiltration is performed on membrane equipment Sartorius, 10,000 MWCO PES.

[0062] In the preparation process, the organic ammonium fluoride could be used to control the size of the tantalum pentoxide nanocrystals.

[0063] In order to characterize the tantalum pentoxide colloids, the as-prepared Ta.sub.2O.sub.5 colloid was deposited in a copper-coated carbon grid for investigation by field emission transmission electron microscopy and high-resolution transmission electron microscopy (HRTEM, JEOL JEM-2100F) with the microscope operated at an acceleration voltage of 200 kV. The zeta potential and size distribution of Ta.sub.2O.sub.5 colloid was measured on a Zetasizer 3000HS (Malvern InstrumentDynamic Light Scattering method). The powder samples were obtained after the sol was dried at 40 C., and then investigated by an X-ray diffraction (XRD) analysis with a Rigaku D/MAX-RB diffractometer using Cu Ku radiation.

[0064] The tantalum pentoxide particles grain size has been calculated by Scherrer's formula and is checked to be consistent with the result of HRTEM.

[0065] Using amorphous tantalum pentoxide, hydrofluoric acid (HF), tetrabutylammonium fluoride trihydrate (TBAFC.sub.16H.sub.36FN.3H.sub.2O), with a mole ratio TBAF:HF equal to 1 and boric acid as reactants, heated by oven at 180 C. for 24 hours, provided tantalum pentoxide nanocrystals with a very good dispersity in water and methanol. Nanocrystals have a zeta potential of 19.0 mV and mean size of 89 nm. The XRD and HRTEM analysis results shown in FIGS. 2 and 3 showed that the tantalum pentoxide particles were orthorhombic crystal with size of about 2 nm.

[0066] A 10.0% in weight tantalum pentoxide colloid in methanol remained stable for one week. When the solid content reached a value above 10.0% in weight, the solution became gel because of the small particle size.

[0067] Using the reaction system of amorphous tantalum pentoxide, hydrofluoric acid and oxalic acid dihydrateacetyl, heated by oven at 180 C. for 24 hours, the dispersity and stability of the tantalum pentoxide colloid is improved. The obtained tantalum pentoxide nanocrystals can be well dispersed in water and methanol. Nanocrystals have a zeta potential of 31.7 mV and mean size of 51 nm. The XRD and HRTEM analysis results, which correspond to FIGS. 4 and 5 confirmed that the tantalum pentoxide particles were orthorhombic crystal and had a rodlike shape with a long axis of 30-50 nm and a short axis of 3 to 5 nm. The obtained tantalum pentoxide colloids can be concentrated to 20% solid content in methanol and remain stable for at least one month.

[0068] FIGS. 6 and 7 correspond to the result of an experimental protocol in which the heating was performed through microwave instead of a regular oven. Microwave reaction has two effects. On the first hand, it causes a dramatic increase of the reaction rate, and on the other hand, it causes rapid volumetric heating. As such, the microwave-assistant heat leads to explosive nucleation, more nuclei and small size nanocrystals. Microwave-assistant solvothermal reaction (MASR), using amorphous tantalum pentoxide, hydrofluoric acid and oxalic acid dihydrateacetyl as reactant, heated by microwave at 180 C. for 1 hour, lead to tantalum pentoxide nanocrystals which can be well dispersed in water and methanol. Nanocrystals have a zeta potential of 59.5 mV and mean size of 60 nm. The XRD and HRTEM analysis results, which correspond to FIGS. 6 and 7, show that the tantalum pentoxide particles are orthorhombic crystals and have rodlike shape with a long axis of 15-25 nm and a short axis of 3-5 nm. The tantalum pentoxide colloids can be concentrated to 20 wt % solid content in methanol and remain stable for at least one month.

[0069] It is understood that the herein described embodiments do not limit the scope of the present invention and that it is possible to implement improvements without leaving the scope of the present invention.

[0070] Unless explicitly stated otherwise, the word or is equivalent to and/or. Similarly, the word one or a is equivalent to at least one, unless stated otherwise.