CN104549377A - Hydrothermal preparation method of iodine-doped TiO2 nanocatalyst and its use in catalytic conversion of trans-carotenoid configuration - Google Patents

Abstract

The invention relates to a hydrothermal preparation method of iodine-doped titanium dioxide nanometer non-photocatalyst and the use of heterogeneously catalyzing trans-carotenoid configuration conversion. The preparation method adopts hydrothermal precrystallization and vacuum calcination combined process to quickly prepare highly active iodine-doped titanium dioxide nano-catalysts, that is, firstly prepare titanium dioxide nanoparticles by hydrothermal method, and then obtain iodine-doped titanium dioxide nanoparticles by vacuum drying-vacuum roasting process. catalyst. Compared with the iodine-doped titanium dioxide nano-catalyst prepared by the conventional sol-gel method, the crystallization degree of the catalyst prepared by the invention is significantly improved, the thermal stability is greatly improved, the preparation process period is greatly shortened, and the amount of organic solvent used is greatly reduced. The catalyst has high activity for catalyzing the conversion of all-trans carotenoids into its cis-isomer, and has the advantages of short conversion time, high conversion efficiency, stable catalytic activity, reusability and the like.

Description

Hydrothermal preparation method of iodine-doped TiO2 nanocatalyst and its use in catalytic conversion of trans-carotenoid configuration

technical field

The present invention relates to a preparation method of a nanocatalyst and its use for heterogeneously catalyzing the configuration transformation of trans-carotenoids, in particular to a method for rapidly preparing high-activity iodine-doped titanium dioxide by using a hydrothermal precrystallization-vacuum roasting combined process A method of nanocatalysts for the conversion of trans-configured carotenoids to cis-configured carotenoids. The invention belongs to the technical field of inorganic nanometer catalytic material and health food production.

Background technique

Carotenoids are a class of compounds with special physiological and pharmacological functions, which play an important role in human health. Under the steric hindrance effect of methylation, the conjugated double bonds in carotenoid molecules cannot be rotated arbitrarily, so carotenoids have a much lower number of spatial isomers than the theoretical number. Common lycopene spatial isomers include all-trans, 5-cis, 7-cis, 9-cis, 13-cis and 15-cis, etc. Common β-carotene spatial isomers Including all-trans, 9-cis, 13-cis and 15-cis isomers, etc.

Natural carotenoids in food (such as tomato) mainly exist in the all-trans structure, while in human tissues and cells, the cis-configuration is the main form. Existing research results show that cis-configuration carotenoids such as cis-lycopene and cis-β-carotene usually have higher biological potency and stronger physiological activity than their all-trans isomers . In addition, the 5-cis isomer in cis-lycopene has the highest antioxidant activity and stability, and the 9-cis isomer in cis-β-carotene has the effect of inhibiting atherosclerosis and reducing the incidence of cancer. The most active. Therefore, increasing the proportion of cis-configuration in carotenoids, especially increasing the proportion of 5-cis-lycopene in lycopene or 9-cis-beta-carotene in β-carotene, will be expected Significantly improve the physiological activity of carotenoid products.

Common methods for preparing carotenoids with a high cis-configuration ratio through isomerization treatment using carotenoids as raw materials include thermal isomerization technology and photoisomerization technology.

Thermal isomerization technology refers to heating to reflux in the organic phase, or direct heating under certain conditions to promote the conversion of its configuration from the all-trans configuration to the cis configuration. Patents PCT/EP2007/006747, PCT/EP02/00708, US7126036, and CN101575256 respectively disclose a technology for preparing cis-lycopene by heating and refluxing in the organic phase, but these technologies generally have complex operations, long cycles, and 5-cis The disadvantage of low lycopene content.

Photoisomerization technology can be divided into direct photochemical isomerization technology and iodine-promoted photochemical isomerization technology. Direct photochemical isomerization technology, that is, under the conditions of a certain temperature and a certain wavelength range of light, taking oxygen avoidance measures to make the group at the double bond of the active ingredient undergo a cis-trans configuration conversion method. CN10131 4554 discloses a method for preparing cis-lycopene isomers using all-trans-lycopene as a raw material by direct photochemical isomerization. There are obvious deficiencies in photoisomerization technology, such as the need for a special reaction device; the scale of the reaction is difficult to expand; if elemental iodine is used as a catalyst, elemental iodine is easy to sublimate and lose, and secondly, it is difficult to remove after the reaction. Sex is not guaranteed, while inevitably increasing production costs.

In addition to the above-mentioned thermal isomerization technology and photoisomerization technology, CN201410736320.3 discloses a method for using iodine-doped titanium dioxide nano-catalyst to heterogeneously catalyze the configuration conversion of trans-carotenoids. However, the preparation method of the iodine-doped titania nanocatalyst has disadvantages such as low crystallization degree of the product, poor thermal stability, high raw material cost, long preparation process cycle and environmental protection problems caused by difficult solvent recovery, which lead to the failure of the catalyst. The preparation not only has low production efficiency, pollutes the environment, but also wastes iodine resources, which also limits its industrial application.

The hydrothermal synthesis method has been applied in the field of catalysts because of its advantages of high purity, good dispersibility, and easy control of particle size. Patent CN103418334A discloses a hydrothermal preparation method of highly adsorbed N, I co-doped _TiO2 porous network structure powder, and carried out adsorption and removal experiments on cationic dye solution with the prepared porous powder. Patent CN103638953A discloses a method for preparing an iodine-doped titanium dioxide-graphene composite photocatalyst for degrading organic pollutants. So far, there has been no literature report on the preparation of highly active iodine-doped titania nanocatalysts by the combined process of hydrothermal precrystallization and vacuum calcination, and using it to catalyze the configuration transformation of trans-carotenoids.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art CN201410736320.3, and provide a rapid and environmentally friendly preparation method for the preparation of iodine-doped titanium dioxide nano-catalyst by hydrothermal precrystallization-vacuum roasting combination process, which can be used to catalyze lycopene Carotene and β-carotene are carotenoids with a high proportion of cis configuration, which are used as common food ingredients, functional food raw materials or dietary supplement raw materials.

Technical scheme of the present invention is as follows:

The preparation method of iodine-doped titania nano-catalyst, its concrete steps are as follows:

(1) Hydrothermal precrystallization

Add the iodine-containing compound and complexing agent to the aqueous solution and mix uniformly to obtain a mixture A; add the inhibitor to the titanate and mix uniformly to obtain a mixture B; slowly add the mixture B dropwise at room temperature and under vigorous stirring into the mixture A, after the dropwise addition, continue to stir for 2-6 hours to obtain a titanium dioxide sol solution; place the titanium dioxide sol solution in a container of a hydrothermal reaction kettle, and react under the conditions of a temperature of 80-160°C and a time of 12-36 hours. The liquid is separated to obtain pre-crystallized nano-scale titanium dioxide;

(2) Vacuum roasting treatment

Dry the titanium dioxide obtained in step (1) at 60-100°C and a vacuum of 0.1MPa for 12 hours, then grind it into titanium dioxide powder for the first time; roast it at a vacuum of 0.1MPa and a temperature of 160-220°C for 2.0 -4.0h, grind again to obtain iodine-doped titanium dioxide nano-catalyst.

Described iodine-containing compound is potassium iodide or sodium iodide;

The titanate is tetrabutyl titanate or tetraisopropyl titanate;

Described inhibitor is acetic acid or acetylacetone;

Described complexing agent is polyvinylpyrrolidone or polyethylene glycol.

The mass ratio of the iodine-containing compound to the titanate is 2:100-6:100;

The volume ratio of inhibitor to titanate is 1:20-1:1;

The mass ratio of the complexing agent to the iodine-containing compound is 1:50-1:20.

The use of iodine-doped titanium dioxide nanocatalyst heterogeneously catalyzing the configuration conversion of trans-carotenoids is to heat and reflux trans-lycopene or β-carotene, catalyst and ethyl acetate under dark conditions, and the reaction ends After the reaction solution is cooled and the catalyst is separated by centrifugation, the ethyl acetate is evaporated in a vacuum to obtain lycopene or β-carotene with a high cis ratio.

Beneficial effects of the present invention

Compared with the existing reported process, the innovation of the present invention to prepare iodine-doped titania nano-catalyst is:

(1) After mixing the titanate and the inhibitor, directly react with the aqueous solution containing the complexing agent to prepare the sol. This step does not require the action of ethanol, thus greatly reducing the solvent usage cost compared with the prior art;

(2) The sol in (1) above is subjected to a hydrothermal reaction instead of the sol-gel method of the prior art. The advantages of this improvement are as follows: firstly, the pre-crystallized nano-scale titanium dioxide can be separated from the reacted mixed solution only by centrifugation, which is also convenient for the recovery and reuse of organic solvents, thus reducing the production cost of the catalyst. In the aging process of the prior art process, the solvent is difficult to be recycled and reused, so the present invention also solves the environmental protection problems existing in the prior art; secondly, the time required for this step is only 100% of that of the aging step of the prior art. About 1/8, thus greatly improving the efficiency of catalyst preparation;

(3) Compared with the existing iodine-doped titanium dioxide nano-catalyst, the catalyst obtained by the present invention not only improves the activity of its catalytic all-trans carotenoid isomerization, but also has high crystallinity, good thermal stability and higher catalytic activity. The advantages of stability.

The catalyst obtained in the present application shows high activity for catalyzing the isomerization of trans-configuration carotenoids into cis-isomers, and when used for isomerization of lycopene, the proportion of total cis-lycopene in the product reaches more than 75%. When used to catalyze the isomerization of β-carotene, the total cis-β-carotene in the product accounts for more than 50%, and can obtain a higher content of 5-cis-lycopene and 9-cis-β-carotene white. The preparation time of the catalyst is only about 1/4 of the existing sol-gel method. The catalyst has the characteristics of simple preparation process, high efficiency, economy, repeated utilization and environmental friendliness. The cis-carotenoids catalyzed by the catalyst help to improve the functionality of health food, thereby broadening the application field of carotenoids.

Description of drawings

Fig. 1. The catalyst obtained in Example 5 of the present invention according to the catalyst activity evaluation method in the summary of the invention, catalyzes isomerization of all-trans lycopene (purity 90%) after 2h of reaction HPLC spectrogram. It can be seen from Figure 1 that the relative percentage of total cis-lycopene is 83.75, and the relative percentage of 5-cis-lycopene is 19.91.

Fig. 2. The catalyst obtained in Example 5 of the present invention according to the catalyst activity evaluation method in the summary of the invention, catalyzes isomerization of all-trans β-carotene (purity 90%) after 2h of reaction HPLC spectrogram. It can be seen from Fig. 2 that the relative percentage content of total cis-β-carotene is 55.62, and the relative percentage content of 9-cis-β-carotene is 22.78.

Fig. 3. The catalyst obtained in Example 5 of the present invention, the image diagram obtained through transmission electron microscopy (TEM) detection, as can be seen from Fig. 3, the catalyst is a nanoscale particle.

Fig. 4. the catalyst that obtains with comparative example 1 in the embodiment of the present invention 5, detects the spectrogram that obtains through X-ray diffraction (XRD), as can be seen from Fig. 4, the obtained catalyst of the present invention is a single anatase phase, and its crystallinity better than existing sol-gel techniques.

Fig. 5. the catalyst that obtains in the embodiment 5 of the present invention, the N that detects through the specific surface area measuring instrument _- desorption curve and the corresponding pore size distribution figure, according to the BET equation and the BJH method, the specific surface area of the sample is ^189.851m /g, the average pore diameter is It can be seen from Fig. 5 that the detection of the catalyst sample shows an obvious hysteresis loop, and the adsorption isotherm is a typical type IV, which has a mesoporous structure.

Fig. 6 and Fig. 7. the catalyst before the vacuum roasting that obtains in the embodiment of the present invention 5 and comparative example 1, detect the spectrogram that obtains through thermogravimetric analyzer (TG), as can be known from Fig. 6 and Fig. 7, in 50～200 In the range of °C, the weight loss of the catalyst obtained in Example 5 is only 1.465%, which is far lower than 10.76% in Comparative Example 1, which shows that the catalyst obtained in the present invention has good thermal stability.

Fig. 8. The catalyst obtained in Example 5 of the present invention and the catalyst of Comparative Example 1, according to the catalyst activity evaluation method in the summary of the invention, the histogram of the effect on the isomerization of lycopene with the increase in the number of reuse times, from Fig. 7, it can be seen that the catalyst catalyst obtained in Example 5 catalyzed the reaction 1 to 5 times, and the relative percentage content of total cis-lycopene dropped from 83.75 to 71.4, while its relative percentage content dropped from 79.41 to 71.4 in the catalytic reaction of Comparative Example 1. 60.03. The reasons for the decrease in the relative percentage of total cis-lycopene with the increase in the number of catalyst reuses are as follows: firstly, the catalyst mass loss is inevitable with the increase in the catalyst reuse times; This shows that the stability of the catalyst obtained in the present application is higher than that of the existing sol-gel method technology.

Detailed ways

For a better understanding of the present invention, the present invention will be further described in detail below in conjunction with examples, but the scope of protection claimed by the present invention is not limited to the scope limited by the examples.

The reagents used in the following examples of the present invention were all purchased from Sinopharm Chemical Reagent Co., Ltd., and were of analytical grade unless otherwise specified, among which tetrabutyl titanate (relative density: 0.996) and tetraisopropyl titanate were chemically pure.

In order to more clearly express the hydrothermal precrystallization-vacuum heat treatment process operation steps in the embodiment of the present invention, so as to compare with the prior art (CN201410736320.3), the preparation method of the catalyst obtained in the present invention is divided into the following 6 steps in detail, wherein the steps (1)-(4) are hydrothermal pre-crystallization technology, (5) and (6) are vacuum roasting treatment technology.

Example 1

(1) At normal temperature, 200mg Kl and 4mg polyvinylpyrrolidone were added to 20mL deionized pure water, and mixed uniformly to obtain mixture A;

(2) Add 0.5 mL of acetic acid to 10 mL of tetrabutyl titanate (10 g in total), and mix well to obtain mixture B;

(3) Slowly add the mixture B to the mixture A under the conditions of room temperature and vigorous stirring, and continue to stir for 2 hours after the addition is completed;

(4) Place the reaction solution in step (3) in a container of a hydrothermal reaction kettle, react at a temperature of 80° C. and a time of 12 hours, and centrifuge the reaction solution to obtain titanium dioxide precipitation;

(5) After drying the titanium dioxide precipitate obtained in step (4) at 60° C. and a vacuum degree of 0.1 MPa for 12 hours, grind it into titanium dioxide powder for the first time;

(6) Calcining the titanium dioxide powder obtained in the step (5) at a vacuum degree of 0.1 MPa and a temperature of 160° C. for 2 h, and grinding again to obtain an iodine-doped titanium dioxide nanocatalyst.

Evaluation of catalytic activity: In a 25mL round bottom flask, add 20mg of lycopene or β-carotene with a purity of 90%, 10mg of catalyst and 20mL of ethyl acetate; connect the round bottom flask to a condensing device and nitrogen exhaust After installation, place in a water bath at 77°C to avoid light for 2 hours, cool in an ice-water bath, centrifuge at 10,000 r/min for 10 minutes, take 100 μL of the reaction solution, dilute it to 5 mL with ethyl acetate, and filter it with a 0.22 μm filter membrane. Use liquid chromatography to detect lycopene at 472nm and the relative percentage content of each isomer in β-carotene at 450nm by area normalization method. Chromatographic column: YMC C30 column (5μm, 250mm×4.6mm); mobile phase: phase A: methanol: acetonitrile = 25:75, phase B: 100% methyl tert-butyl ether; gradient conditions: 0 ~ 20min, phase A Decrease from 100% to 50%, 20-40min, keep phase A at 50%; sample solvent: ethyl acetate; flow rate: 1mL/min; column temperature: 30°C; injection volume: 20μL. The relative percentage content of total cis-lycopene was 60.26, and the relative percentage content of total cis-β-carotene was 35.38.

Embodiment 2 to the raw material that each step of embodiment 6 adopts and processing condition are shown in table 1:

Table 1

Comparative example 1 is that sol-gel method prepares iodine-doped nano-catalyst, according to this case catalyst activity evaluation method, it compares with the embodiment 5 of hydrothermal method, the raw material that each step adopts and processing condition are as shown in table 2:

Table 2

From the comparative example 1 of table 2 and the catalytic result of the gained catalyst of embodiment 5, the present invention has improved the activity of catalyst, and hydrothermal method does not need ethanol effect in step (1) and (2), thereby greatly reduces catalyst preparation cost. In step 3, the hydrothermal method only needs 12h, while the time required in the sol-gel method is as long as 96h. The hydrothermal process not only greatly improves the preparation efficiency of the catalyst, but also only needs centrifugation to separate and recover the solvent, thereby solving the problem of The problem of environmental protection and catalyst preparation cost increase caused by solvent volatilization in the sol-gel method. In summary, the preparation of iodine-doped nanocatalysts by hydrothermal method is more suitable for industrial production.

The above specific embodiments do not limit the technical solutions of the present invention in any form, and all technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the scope of protection of the present invention.

Claims (6)

1. The hydrothermal preparation method of iodine-doped titanium dioxide nanometer non-catalyst is characterized in that it adopts hydrothermal precrystallization-vacuum roasting combination process, and the preparation speed is fast, and its steps are as follows: (1) Hydrothermal precrystallization Add the iodine-containing compound and complexing agent to the aqueous solution and mix uniformly to obtain a mixture A; add the inhibitor to the titanate and mix uniformly to obtain a mixture B; slowly add the mixture B dropwise at room temperature and under vigorous stirring into the mixture A, after the dropwise addition, continue to stir for 2-6 hours to obtain a titanium dioxide sol solution; place the titanium dioxide sol solution in a container of a hydrothermal reaction kettle, and react under the conditions of a temperature of 80-160°C and a time of 12-36 hours. The liquid is separated to obtain pre-crystallized nano-scale titanium dioxide. (2) Vacuum roasting treatment Dry the titanium dioxide obtained in step (1) at 60-100°C and a vacuum of 0.1MPa for 12 hours, then grind it into titanium dioxide powder for the first time; roast it at a vacuum of 0.1MPa and a temperature of 160-220°C for 2.0-4.0 h, grinding again to obtain iodine-doped titania nanocatalyst. 2. the preparation method of iodine-doped titanium dioxide nano-catalyst according to claim 1 is characterized in that described iodine-containing compound is potassium iodide or sodium iodide; Described titanate is tetrabutyl titanate or titanic acid Tetraisopropyl ester; the inhibitor is acetic acid or acetylacetone; the complexing agent is polyvinylpyrrolidone or polyethylene glycol. 3. the preparation method of iodine-doped titanium dioxide nano-catalyst according to claim 1 is characterized in that the mass ratio of described iodine-containing compound and titanate is 2: 100-6: 100; Inhibitor and titanate The volume ratio of the compound is 1:20-1:1; the mass ratio of the complexing agent to the iodine-containing compound is 1:50-1:20. 4. the iodine-doped titanium dioxide nano-catalyst product prepared based on the process described in claim 1. It is characterized by a single anatase phase of TiO ₂ . 5. The iodine-doped titanium dioxide nano-catalyst product according to claim 4, which has the purposes of heterogeneously catalyzed trans-carotenoid configuration conversion, is characterized in that it is combined with trans-lycopene or β-carotene respectively The element, catalyst and ethyl acetate are heated and refluxed under the condition of avoiding light. After the reaction is completed, the reaction solution is cooled and centrifuged to separate the catalyst, and then the ethyl acetate is evaporated in a vacuum to obtain a cis configuration with a proportion of more than 75%. The lycopene or the β-carotene whose cis configuration accounts for more than 50%. 6. the purposes of heterogeneously catalyzed trans-carotenoid configuration conversion of iodine-doped titanium dioxide nano-catalyst according to claim 5, it is characterized in that when being respectively used for catalyzing lycopene, beta-carotene isomerization, Lycopene with 5-cis lycopene accounting for 19.91% and β-carotene with 9-cis β-carotene accounting for 22.78% can be quickly obtained.