WO2013076321A1

WO2013076321A1 - Method for obtaining anatase-phase titanium-dioxide particles

Info

Publication number: WO2013076321A1
Application number: PCT/ES2011/070814
Authority: WO
Inventors: Daniel FERNANDEZ HEVIA
Original assignee: Inael Electrical Systems, S.A.
Priority date: 2011-11-24
Filing date: 2011-11-24
Publication date: 2013-05-30

Abstract

Method for the synthesis of anatase-phase titanium-dioxide particles with controlled morphology for fomenting the exposure of ultrareactive faces and/or obtaining self-assembled microspheres of high crystallinity via a non-hydrothermal route, at atmospheric pressure and low temperature (< 100°C), and in non-sealed, non-pressurized receptacles. The method is implemented at moderate temperatures below 100°C and at atmospheric pressure, allowing the rapid, efficient and safe industrial set-up thereof in return for moderate investment and making use of limited energy/natural resources and economic resources, without damaging the environment.

Description

PROCEDURE FOR OBTAINING TITANIUM DIOXIDE PARTICLES IN ANATASE PHASE

TECHNICAL FIELD OF THE INVENTION

The present invention belongs to the field of synthesis of titanium dioxide particles with controlled morpho logy ^¬ to promote exposure of ultra reactive faces or to obtain microspheres self assembled bladas high crystallinity.

Said invention relates to a sustainable method of synthesizing particles of titanium dioxide in anatase phase. The procedure is carried out by non-hydrothermal route, at atmospheric pressure and low temperatures (below 100 ° C), and allows its industrial implementation quickly, efficiently, and safely, through moderate economic investments, using raw materials abundant, economical, and environmentally acceptable, and exploiting natural and energy resources in an efficient, controlled and sustainable manner. The invention also relates to the particles obtained by the method of the invention and the use thereof in the generation of hydrogen from water.

BACKGROUND OF THE INVENTION

In general, the functional properties of semiconductor inorganic crystals critically depend on the physical and chemical properties of the surfaces (crystalline faces) exposed in the morphology of the crystal. The "custom" design and synthesis of inorganic crystals with highly energetic surfaces and very high reactivity has become one of the most active areas of scientific research during the last 2-3 years, due to the enormous importance and variety of its practical applications. Titanium dioxide is a common constituent of minerals found in igneous rocks such as iron-titanium oxide, perovskites, and replacing the iron in some species of silicates such as pyroxene and divi ^¬ us. It is a transition metal oxide that forms different polymorphs in nature: rutile (tetragonal), anatase (tetragonal centered on the faces) and brookite (orthorhombic) with the rutile phase being the thermodynamically more stable structure. Unfortunately, the surfaces of higher reacti vity ^¬ _A-TiO2 (titanium dioxide in anatase phase) are also higher surface energy and therefore are rapidly removed and disappear during which ^¬ WANT synthesis process. A-TIO ₂ crystals have existed, so far, in the form of octahedral bipyramids with the vast majority of their surface formed by thermodynamically favorable crystalline faces (faces {101}), which, in turn, are the more inert and less reactive and, therefore, less interesting from the point of view of any of the aforementioned applications.

The synthesis of crystals A-TiO ₂ controlled morphologies, such that expose a greater PERCENTAGE of the most reactive crystal faces (special ^¬ the {001}), is a technological breakthrough of enormous significance, only achieved over the past 2-3 years. Unfortunately, all the methods developed so far involve ^¬ two hydrothermal processes, at high pressures and temperatures, energy intensive, environmentally unsustainable and economically unprofitable. This lack of environmental sustainability and economic / commercial viability is aggravated by the frequent use of extraordinarily aggressive surfactants, such as hydrofluoric acid (HF), whose industrial use implies safety and health risks, and equipment and process costs which, in practice, make their industrial development and commercial promotion unfeasible.

Among the applications of A-T1O ₂ morphol controlled ^¬ ogy, those related to sis fotocatáli- have gained an extraordinary importance in recent years. Photocatalytic efficiency requires a high separation of electrical charge in the material, in order to avoid recombination between the photogenerated electron-hole pairs. There is a huge difference between the temporal scale of electron photogeneration processes (~ ^10-15 s) and the participation of these electrons in photochemical reactions on the surface of the material (~ 10 ^{~ 12} s). This makes the existence of charge storage mechanisms that allow the accumulation of the excess of photogenerated electrons in the hope of their efficient participation in oxidation / reduction reactions a characteristic of enormous value. To this end, it has been found very useful cons truction ^¬ microstructures hierarchical self - assembled from the agglomeration of nanoparticles, so that the micro between nanoparticles act as micro-capacitor charging accumulators ELECTRIC ^¬ ca. These microstructures must simultaneously have high crystallinity and have the additional advantage of avoiding the health and safety problems associated with direct handling of nanoparticles. Unfortunately, for the synthesis of these microstructures, there is no They have described economically viable and environmentally sustainable procedures essentially based on the "green chemistry" which require ments proce ^¬ atmospheric pressure, implementable in reci- tainers unpressurized, and occurring at low

temperatures and, therefore, with low energy consumption.

In US application number pu ^¬ cation US2011003684 a sol-gel method is described to prepare dioxide environment titanium anatase temperature from a titanium precursor and a solvent consisting of water, alcohol and an acid or base catalyst . However precipitates derived from sol-gel method are usually amorphous in nature and require a subsequent heat treatment for crystallization indu ^¬ cir thereof. The method does not seek morphological control aimed at the exposure of ultra-reactive surfaces, or the obtaining of self-assembled microspheres, therefore being radically different from the invention claimed herein.

In US application number US2011150753 pu ^¬ lication a method rar prepared titanium dioxide in anatase phase comprising the mixture of a titanium alkoxide and a salt of cetyl ammonium methyl described water, subjecting the mixture to about ^¬ Hydrothermal reservoir in pressurized vessel at high pressure and at a temperature between 60 ° C and 120 ° C. Hydrothermal treatments are applied to INCREM.ENCODER ^¬ tar crystallinity but requiring long aging for titanium dioxide cris ^¬ Talino low temperature. In addition, the hydro ^¬ thermal treatment makes it difficult to control the morphology of the particles, since the titanium cations that participate Breads in the reaction are susceptible to nucleophilic attack by water, resulting in too rapid hydrolysis and causing the particles to grow uncontrollably. In any case, again, the method does not seek a specific morphological control ^¬ cally aimed at exposing ultrareactivas surfaces, nor obtaining self - assembled microspheres high crystallinity is achieved, and is therefore radically different from the invention claimed in the present document.

As can be seen from the cited documents, although various processes for the synthesis of titanium dioxide have already been described, there is still a need for sustainable, simple and economical process for obtaining industrial scale dioxy ^¬ do titanium in anatase phase with controlled morphology, increasing the exposure of ultrareactive faces and / or obtaining self-assembled microstructures from nanoparticles, with the advantages that both materials provide and which have already been discussed above.

DESCRIPTION OF THE INVENTION The inventors have found a process pa ^¬ ra preparing particles of titanium dioxide with morpho ^¬ controlled logy, leading either to obtaining nanoparticles with increased exposure ultrareac faces ^¬ tions (001), or to obtain of self-assembled microspheres from agglomerates of nanoparticles. The process is non-hydrothermal, and comprises a solution of a titanium precursor at atmospheric pressure and at temperatures below 110 ° C thus avoiding extreme reaction conditions and the need to use high-cost sealed and pressurized reactors and high energy consumption.

The first aspect of the invention relates to a process for synthesizing titanium dioxide particles in the anatase phase, in unsealed or pressurized containers, which comprises the steps of:

a) dissolve an organic titanium precursor in a C2-C4 alcohol at atmospheric pressure and in a temperature range between 70 ° C and 100 ° C, for a reaction time between 10 hours and 30 hours;

b) cooling the solution resulting from step a);

c) evaporate to dryness.

The advantages of the process are among others that it is carried out under moderate conditions and with non-polluting reagents in the environment. Furthermore, with the process of the invention no additional steps are necessary to obtain the crystallinity of the particles. Finally, with the process of the invention the aging times are not high.

A second aspect of the invention relates to nanoparticles obtained by the method des ^¬ Crito above, where step a) is performed in the presence of a surfactant and in a temperature range which is between 70 ° C and 90 ° C and which also includes the stages of:

d) disposal of organic remains; e) ^¬ tion of an aqueous suspension of the nanoparticles obtained in step d); f) preparation of a solution of hexachloroplatinic acid IV, H ₂ PtCl ₆ in distilled water with a metal filler content between 0.5% and 0.95% by weight; g) mixing of the suspension aqueous of step e) with the platinum solution of step f) and with a C2-C4 alcohol; h) illumination of the mixture of step g) with a lamp in the region below 410 nm in the presence of a nitrogen purge; i) centrifugation and j) drying.

A third aspect of the invention relates to the use of nanoparticles as described above ^¬ mers catalyzes the synthesis of hydrogen from water.

The use of the particles makes hydrogen synthesis more efficient than with the use of other known catalysts, with higher yields in a wide range of pH conditions, reagent concentration and irradiation. The synthesis of hydrogen in the presence of the particles of the invention is cheaper and less polluting than the already known processes of hydrogen synthesis from water.

BRIEF DESCRIPTION OF THE FIGURES

Herein, with a set of drawings, illustrative example prefe ^¬ ent, and never limiting the invention it is complemented.

1 shows an electronic microscopy by scanning field emission (MECEB) of the departed ^¬ particles obtained in Example 1 of the present inven ^¬.

Figure 2 shows an X-ray diffractogram of titanium dioxide synthesized at I) 60 ° C, for 4 hours; II) at 76 ° C for 4 hours and III) at 76 ° C for 4 hours plus calcination at 300 ° C for 2 hours. 3 shows an electronic microscopy by scanning field emission (MECEB) of the particles obtained ^¬ departed 76 ° C for 4 hours calcination at 300 ° C for 2 hours.

Figure 4 shows a MECEB of the titanium dioxide particles obtained in example 2 of the invention. DETAILED DESCRIPTION OF THE INVENTION

All terms used here, unless otherwise indicated, must be understood in the ordinary meaning in the state of the art. The more specific definitions for certain terms used in the present application, such as those indicated below, apply uniformly throughout the description and claims. The term "titanium precursor" as used herein refers to an organic titanium molecule that participates in the reaction to generate another titanium molecule. Examples of these titanium precursors are titanium halides such as titanium tetrachloride, titanium alkoxide such as titanium butoxide and tetradimethyl amino titanium. Preferably the titanium precursor is titanium butoxide.

The term "C2-C4 alcohol , " as used herein refers to straight chain alcohols or branched ^¬ gives having from 2 to 4 carbon atoms. Examples of these alcohols include, but are not limited to, ethanol, butanol or isopropanol. Preferably the alcohols are ethanol and butanol. The term "surfactant" as used herein refers to both anionic surfactants such as fatty acid salts of 5 to 30 carbon atoms, for example sodium lauryl sulfate and other fatty acid sulfate salts, oleic acid and cationic surfactants such as alkylamines of 8 to 22 carbon atoms, for example oleylamine and mixtures thereof.

Preferably it is a mixture of oleic acid and oleila ^¬ mine.

The term "nanoparticle" as used herein refers to particles with at least one of the dimensions of a size smaller than 10 m.

As already mentioned, the first aspect of the invention relates to a method of synthesizing particles of titanium dioxide in anatase phase, in unsealed or pressurized containers which comprise ^¬ of the steps of:

b) cooling the solution resulting from step a);

c) evaporate to dryness.

In a preferred embodiment, the reaction time is between 6 hours and 10 hours.

In the procedure mentioned above, microspheres of size greater than 1 μιη in diameter are obtained, approximately between 2 μιη and 4 μιη in diameter. The spheres are very homogeneous. Depending on the time and temperature, spherical particles or densi ^¬ fies or consist of aggregates of nanocrystals of titanium dioxide with a spherical macrostructure. The crystallinity of the particles obtained by the process according to the first aspect of the invention can be improved by removing the remains cos ^¬ Organi. Therefore, in a embodiment of the first aspect of the invention, the process further comprises a step of eliminating the organic residues.

Preferably the removal of organic residues is carried out by a calcination step at a temperature between 300 ° C and 400 ° C for a time between 2 hours and 4 hours. In another preferred materialization, waste disposal is done by sonication. In a more preferred materialization it is carried out by irradiation of ultraviolet rays.

In the process according to the first aspect of the invention, if step a) is carried out in the presence of a surfactant, and in a temperature range between 70 ° C and 90 ° C, nanoparticles of carbon dioxide are obtained. truncated anatase titanium phase at its ends. The use of surfactants has been designed so that they are economical, naturally abundant, simple to process, and environmentally benign.

Anatase phase titanium dioxide nanoparticles exhibit high exposure of reactive faces {001}. These faces were considered far as unstable and impossible to synthesize in significant quantities, although its nature ultra-reactive to highly desirable, both from a scientific point of view, as a technology for numerous applica ^¬ tions.

The fundamental problem in the synthesis of faceted titanium dioxide with highly reactive faces is due to the fact that the number of these faces decreases rapidly during the crystallization process due to the minimization of surface energy. In the particular case of titanium dioxide in the anatase phase, the crystals obtained under normal conditions are mostly formed by faces {101} that are thermodynamically more stable than {001} and {100}.

As in the case of the proce ^¬ lie microspheres may include a step of removing organic waste.

Particularly, in the process of obtaining nanoparticles, the titanium precursor is titanium butoxide, and the surfactant is a solution of oleic acid and oleylamine in absolute or pure ethanol with a stoichiometry l: x: y where 4≤ x ≤7 and 3 ≤ y ≤6, where x refers to oleic acid and oleylamine.

In a preferred embodiment the method of synthesis of nanoparticles, in particular step a) is performed in concentric vessels covered airtight ^¬ where precur is ^¬ sor titanium into the inner chamber, the surfactant and alcohol C ₂ -C ₄ , and in the outer vessel is a C ₂ -C ₄ alcohol with a purity between 90% and 98%. The outer cup alcohol diffuses very lentamen ^¬ dishing mix inner vessel so that the reaction control and the morphology of the synthesized nanoparticles is allowed.

The variables with which the morphology of the particles can also be controlled are the temperature of the C ₂ -C ₄ alcohol and the titanium precursor.

In a preferred embodiment the reaction temperature is between 70 ° C-81 ° C.

In another more preferred materialization the temperature is between 70 ° C and 85 ° C and alcohol is ethanol. Finally, in another materialization the temperature is between 85 ° C and 90 ° C and the alcohol is butanol.

The nanoparticles of the invention can be cu ^¬ O pen platinum so that they can be used as catalysts in the process of producing hydrogen from water.

Therefore, in an embodiment of the proce ^¬ ment of the first aspect of the invention wherein step a) is carried out in the presence of surfactants and includes a step of removing organic residues and further comprising the steps of: d) forming a aqueous suspension of the particles obtained in the organic waste removal stage;

e) preparation of a solution of hexachloplatinic acid IV, H ₂ PtCl ₆ in distilled water with a metal filler content between 0.5% and 0.95% by weight;

f) mixing the aqueous suspension of step d) with the platinum solution of step e) and with a C ₂ -C ₄ alcohol;

g) illumination of the mixture of stage f) with a lamp in the region below 410nm

h) centrifugation and

i) drying. Example 1: Synthesis Procedure

anatase phase titanium dioxide microspheres

A solution of titanium butoxide in absolute ethanol was prepared. It was then heated for 8 hours, at a constant temperature of 76 ° C. The

resulting solution was allowed to cool and evaporate to dryness at room temperature. The product obtained was washed with absolute ethanol. The X-ray diffractogram confirms that it is titanium dioxide with

Anatase type structure. Figure 1 shows the

formation of very homogeneous spherical particles, approximately 2-4 microns in diameter.

Crystallinity can be improved by

calcinations in conventional tubular ovens at temperatures. In Figure 3 compare the crystallinity of synthesized titanium dioxide at 60 ° C, at 76 ° C for 4 hours and at 76 ° C for 4 hours and then a calcination at a temperature of 300 ° C, for 2 hours.

The best crystallinity is that of the sample

calcined as shown in Figure 2. As shown in Figure 3 the size and morphology of the particles of the sample that was subjected to calcination was maintained. Example 2: Synthesis Procedure

anatase phase titanium dioxide nanoparticles

A solution of Ti (ButO) ₄ (titanium butoxide), oleic acid, and oleylamine in absolute EtOH is prepared. The stoichiometry was 1: 5: 5. It is introduced into a Teflon glass which is in turn introduced into a container containing 96% EtOH. The system is maintained at atmospheric pressure and at temperatures of 76 ° C. After 24 hours, crystals of approximately 12nm size were obtained. Post iormente the organic residue was removed me ^¬ Diante ultraviolet illumination. Figure 4 shows the MECEB Micrograph of T1O2 1: 5: 5 synthesized at 24 to 76 ° C and atmospheric pressure: with the organic residue removed by ultraviolet illumination.

The nanoparticles obtained in example 2 were platinized. Hexachloroplatinic acid solution different (IV) (H ₂ PtCl ₆₎ were prepared in distilled water ^¬ gives, corresponding to total filler contents metal 0.5 to 0.95% by weight. The solution is mixed with an aqueous suspension of the nanoparticles of example 2 of the present invention. The concentration of nanoparticles must be in the range of l-2g Ti0 _2/1. Isopropanol was added as a sacrificial agent with donor functions, with a final concentration in the range 0.2-0.4M. Photodeposition was carried out by lighting between 4h and 8h with a mercury lamp (300-500W) and a photon flow 2-3 ^χ 10 ^{~ 7} Einstein s ^_1 L ^_1 in the region below 410 nm. A constant nitrogen purge is maintained throughout the process and, finally, mind, the product is recovered by centrifugation and dried at 283K for 8-12h.

Once the nanoparticles have been synthesized

Platinized, hydrogen synthesis was performed in a reactor where the hydrogen that was produced was evacuated by supplying a controlled flow of nitrogen to the reactor. Inert gas is supplied to prevent oxygen from accepting photogenerated electrons and competing with hydrogen precursor hydrogen ions.

The reaction was carried out by illuminating with controlled UV radiation a liquid mixture containing, 2g of the platinized nanoparticles synthesized per liter of emulsion, 25% sacrificial agent, in this example methanol. The pH was maintained between 4.5 to 7.5. After the moment of lighting the lamps, the first injection was made to the gas chromatograph by means of a gas valve. Chromatograms were taken every 30 minutes. The experiment is maintained for 8 hours.

The results of the production of 2mmol per hour per gram of platinized nanoparticle demonstrate the good yields of the reaction.

Claims

1. -Procedure synthesis yield particles ^¬ oxide titanium anatase phase in containers or pressurized unsealed, comprising the steps of:

a) dissolve an organic titanium precursor in a C2-C4 alcohol at atmospheric pressure and in a temperature range between 70 ° C and 100 ° C, for a reaction time between 10 hours and 30 hours

b) cooling the solution resulting from step a)

c) evaporate to dryness.

2. -Procedure according to claim 1, charac ^¬ curly further comprising a step of removing the organic remains.

3. -Procedure according to claims 1-2, c ^¬ racterizado that step a) dissolution occurs in the presence of a surfactant and a range of tempera tures ^¬ that is between 70 ° C and 90 ° C.

4. -Procedure according to claim 3, charac ^¬ curly that the surfactant is a mixture of oleic acid and oleylamine.

5. Method according to claim 3-4, characterized in that step a) of the process is carried out in tightly sealed concentric vessels, where the titanium precursor, the surfactant and a C2-C4 alcohol are located in the inner vessel, and In the outer vessel is a C2-C4 alcohol with a purity of between 90% and 98%.

6. -Procedure according to claims 1-5, c ^¬ racterizado because the temperature range is buy ^¬ dido between 70 ° C and 81 ° C.

7. -Procedure according claims 1-5, c ^¬ racterizado because the temperature range is buy ^¬ dido between 70 ° C and 85 ° C and alcohol , C ₂ -C ₄ is ethanol.

8. -Procedure according to claim 1, charac ^¬ ripple because the temperature range is between 85 ° C and 90 ° C and alcohol , C ₂ -C ₄ is butanol.

9. -Procedure according to claims 1-8, c ^¬ racterizado because the reaction time is I understood ^¬ do between 6 hours and 10 hours.

10. -Procedure according claim 1-9, charac terized ^¬ because titanium precursor is titanium butoxide.

11. -Procedure according to claims 2-10, c ^¬ racterizado because the removal of organic residues is carried out by UV irradiation.

12. -Procedure according to claims 2-10, c ^¬ racterizado for removing organic waste is performed by sonication.

13. -Procedure according to claims 3-12, c ^¬ racterizado further comprising the steps of:

d) formation of an aqueous suspension of the particles obtained in the stage of elimination of organic residues;

e) preparation of a solution of hexaclo-acid roplatínico IV, H ₂ PtCl ₆ in distilled water with conteni do ^¬ metal loading between 0.5% and 0.95% by weight;

h) centrifugation and

i) drying.

14. THE PROCEDURE particles obtained by ^¬ to claim 13.

15. Use of the particles according to claim 14 in the synthesis of hydrogen from water.