CN107983415B - Honeycomb TiO using microporous starch as template2Porous microspheres and method for preparing same - Google Patents
Honeycomb TiO using microporous starch as template2Porous microspheres and method for preparing same Download PDFInfo
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- GWEVSGVZZGPLCZ-UHFFFAOYSA-N titanium dioxide Inorganic materials O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims abstract description 62
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- B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
- B01J31/26—Catalysts comprising hydrides, coordination complexes or organic compounds containing in addition, inorganic metal compounds not provided for in groups B01J31/02 - B01J31/24
- B01J31/38—Catalysts comprising hydrides, coordination complexes or organic compounds containing in addition, inorganic metal compounds not provided for in groups B01J31/02 - B01J31/24 of titanium, zirconium or hafnium
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- B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
- B01J13/02—Making microcapsules or microballoons
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Abstract
The invention discloses a honeycomb TiO with microporous starch as a template2Porous microspheres and a preparation method thereof. The invention obtains microporous starch after hydrolyzing starch by biological enzyme; to nano TiO2Adding dispersant and adhesive to obtain nanometer TiO2An emulsion; mixing the microporous starch with nano TiO2Mixing the emulsions, centrifuging, drying and grinding the precipitate to obtain the honeycomb TiO2Porous microspheres. The invention directly mixes TiO2Loaded on microporous starch, preparing porous microspheres by virtue of adsorption property of the microporous starch, and preparing the prepared TiO2The porous microsphere has the advantages of high specific surface area, high specific pore volume and good adsorption performance, has the unique advantages of improving the light capturing efficiency and the photocatalytic performance, can be directly used as a photocatalyst without template removal treatment, and has the advantages of high catalytic efficiency, mild preparation process conditions, short production period, cheap and easily obtained raw materials, environmental friendliness and wide application prospect in the aspect of photocatalytic degradation of organic pollution.
Description
Technical Field
The invention belongs to the technical field of semiconductor photocatalytic materials. More particularly, relates to cellular TiO taking microporous starch as a template2Porous microspheres and a preparation method thereof.
Background
Nano TiO 22As an N-type semiconductor photocatalytic material, when irradiated by ultraviolet light, electrons in a valence band absorb photon energy and transition to a conduction band,forming photo-generated electron-hole pairs, electrons and TiO2The oxygen molecules adsorbed on the surface react to generate superoxide ion free radicals (
) While the holes will adsorb on the TiO2Of surfaces
Ion reaction to form very reactive hydroxyl radical(s) ((
）。
And
all are active free radicals with strong oxidizability, and can directly oxidize various organic matters into CO2，H2O and the like. In view of nano TiO2The composite material has strong oxidizing property, good photocatalysis property and photochemical stability, and has wide application prospect in the aspects of sewage treatment, air purification, disinfection and sterilization, surface coating and the like. In particular in the field of photocatalysis, nano TiO2In degrading organic pollutants in water, such as organic phosphorus compounds (pesticides, insecticides), halogen-containing compounds, surfactants, dyes, hydrocarbons, benzenes, oils, phenols, etc., and harmful gases in air (such as formaldehyde, SO)2) And the like, are widely researched and applied. But nano-sized TiO2The powder is easy to agglomerate, and the agglomerated TiO2The specific surface area is greatly reduced, so that the photocatalytic performance of the catalyst is reduced; second, nano TiO2The particle size is fine, and the separation, recovery and regeneration are very difficult, so that the photocatalyst loss is serious, and the cost is high. Thus, nano TiO2Is often limited in practical application.
To solve the above problems, people turn the center of gravity of research to synthesize TiO with different sizes and special structural appearances2In order to increase the specific surface area and improve the light-capturing efficiency.There has been considerable research devoted to obtaining photocatalysts of specific morphologies, such as nanowires, nanotubes, core-shell microspheres, hollow microspheres, and the like. In which TiO is used2Hollow microspheres are of most interest and are characterized by TiO2The hollow microsphere has the characteristics of low density, large specific surface area, good surface permeability, high light-capturing efficiency and the like. The hollow structure with high specific surface area can adsorb a large amount of reactant molecules, and a large amount of mesopores contained on the surface of the shell layer are favorable for inward diffusion of the reactant molecules; photo-generated electrons and holes generated by light excitation are easier to separate and migrate to different positions of the surface, so that the photo-generated electrons and holes have more surface reaction active points, and the quantum efficiency and the photocatalytic activity are improved.
TiO2The preparation method of the hollow microsphere mainly comprises a template method and a non-template method. The non-template method has the advantages of simple synthesis process, high efficiency and the like, but the shape and the size of the product are difficult to control, and the method is often limited in the practical application process. The template method is mainly characterized in that composite solid microspheres with core/shell structures are formed by depositing or coating precursor species on the surface of a template by means of electrostatic attraction or sol-gel and the like, and then the template is removed by means of roasting or dissolving and the like to obtain the required hollow microspheres; the template mainly comprises hard template (such as polystyrene microsphere, carbon sphere, SiO)2Microspheres, etc.) and soft templates (e.g., vesicles, microemulsion micelles, surfactant micelles, etc.). Preparation of TiO by template method2The hollow microsphere can realize the regulation and control of the size of a cavity of a target product by changing the physical size of the template, and can also regulate and control the thickness of a shell layer of the hollow microsphere by changing the coating times, so that the template method has the advantages of high repetition rate, good predictability, controllable size, uniform shape, stable performance and the like. However, the existing TiO2The preparation method of the hollow microspheres mostly uses organic matters as templates, needs to use a large amount of organic solvents and needs to be subjected to template removal treatment, and releases a large amount of organic gases when the templates are removed by high-temperature calcination, so that the preparation method is not environment-friendly and has high cost. The search for low-cost, environmentally friendly preparation methods is therefore of great importance for their engineering applications.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide the cellular TiO which is low in cost, environment-friendly and free of harmful gas and takes microporous starch as the template2Porous microsphere and preparation method thereof, and prepared TiO2The porous microspheres can be directly used as a photocatalyst without template removal treatment, and have the advantages of large specific surface area, high specific pore volume, good adsorption performance and the like, and high catalytic efficiency.
The invention aims to provide cellular TiO taking microporous starch as a template2A preparation method of porous microspheres.
The invention also aims to provide cellular TiO prepared by the method and taking microporous starch as a template2Porous microspheres.
The above purpose of the invention is realized by the following technical scheme:
honeycomb TiO using microporous starch as template2The preparation method of the porous microspheres comprises the steps of hydrolyzing starch by biological enzyme to obtain microporous starch; to nano TiO2Adding dispersant and adhesive to obtain nanometer TiO2An emulsion; mixing the microporous starch with nano TiO2Mixing the emulsion to obtain nano TiO2Adsorbing and depositing on the surface of the microporous starch, centrifuging, drying and grinding the precipitate to obtain the starch.
Preferably, the starch is mixed with nano TiO2The mass ratio of the two raw materials is 25-250: 1 to 5.
Preferably, the starch is any one of corn starch, wheat starch, potato starch or sweet potato starch.
More preferably, the starch is corn starch. Experiments show that the pore-forming effect of the corn microporous starch is superior to that of other starch raw materials, and the corn microporous starch is more suitable for preparing TiO2Porous microspheres.
Preferably, the biological enzymes are α -amylase and glucoamylase.
The ratio of the α -amylase to the saccharifying enzyme is preferably 1-5: 1, more preferably 2-4: 1, and even more preferably 3.2: 1.
The total usage amount of the α -amylase and the saccharifying enzyme is preferably 1-5 g/L, and more preferably 4 g/L.
Preferably, the pH value of the biological enzyme hydrolysis is 4-6, the temperature is 40-60 ℃, and the time is 5-13 h.
More preferably, the pH of the biological enzyme hydrolysis is 4.4, the temperature is 55 ℃, and the time is 9 h.
Preferably, the mass of the microporous starch is 1-5 g; the nano TiO2In the nanometer TiO2The concentration of the emulsion is preferably 1 to 5 g/L, and more preferably 3 g/L.
Preferably, the binder is selected from any one of sodium carboxymethylcellulose, polyvinyl alcohol and dextrin, and the addition amount of the binder is preferably 0.05-1.5 g/L, and more preferably 1 g/L.
More preferably, the binder is sodium carboxymethyl cellulose, and the addition amount of the sodium carboxymethyl cellulose is 1 g/L.
Preferably, the dispersant is selected from any one of polyvinylpyrrolidone, sodium dodecyl sulfate, cetyl trimethyl ammonium bromide or sodium polyacrylate; the addition amount of the dispersing agent is nano TiO20.5 to 1.0 percent of the total weight of the composition.
More preferably, the dispersing agent is polyvinylpyrrolidone, and the addition amount of the polyvinylpyrrolidone is nano TiO20.75% of.
Particularly preferably, the cellular TiO takes microporous starch as a template2The preparation method of the porous microspheres comprises the following steps:
s1, weighing starch, adding a citric acid-sodium citrate buffer solution with the pH value of 4-6, stirring to prepare a starch suspension, adding biological enzyme, carrying out water bath stirring reaction at 40-60 ℃ for 5-13 h, carrying out suction filtration and washing on the reaction solution, drying the precipitate at 40-60 ℃, and crushing to obtain microporous starch;
s2 taking nano TiO2Dissolving the powder into distilled water, adding a dispersing agent, stirring for 20-40 min, and then performing ultrasonic dispersion for 20-40 min to obtain a dispersion emulsion; adding binder, stirring, and mixingDispersing the sound for 10-20 min to obtain the nano TiO2An emulsion;
s3, putting the microporous starch obtained in the step S1 into the nano TiO obtained in the step S22Magnetically stirring the mixture in the emulsion for 50-70 min, centrifuging the mixture for 5-15 min at 1000-5000 rpm/min, discarding the supernatant, drying the precipitate for 10-14 h at 40-60 ℃, and grinding the dried precipitate to obtain the honeycomb TiO2Porous microspheres.
The concentration of the starch suspension in the step S1 is preferably 50-250 g/L, and more preferably 150 g/L.
Preferably, the starch in step S1 is one of corn starch, wheat starch, potato starch or sweet potato starch; more preferably, the starch is corn starch.
Preferably, the biological enzyme in the step S1 is α -amylase and saccharifying enzyme, the ratio of α -amylase to saccharifying enzyme is preferably 1-5: 1, more preferably 2-4: 1, and further preferably 3.2: 1, and the usage amount of α -amylase and saccharifying enzyme is preferably 1-5 g/L, and more preferably 4 g/L.
Preferably, the pH of the biological enzyme hydrolysis in the step S1 is 4-6, the temperature is 40-60 ℃, and the time is 5-13 h; more preferably, the pH of the biological enzyme hydrolysis is 4.4, the temperature is 55 ℃, and the time is 9 h.
Preferably, the washing in step S1 is: washing 3 times with distilled water as solvent.
Preferably, the drying time in the step S1 is 12-24 h.
Preferably, the pulverization in step S1 is carried out at a high speed of 10000 to 40000 rpm (preferably 25000 rpm), and the pulverized material is passed through an 80-mesh sieve.
Preferably, the nano TiO in step S22The concentration of the solution is 1-5 g/L, and further preferably, the nano TiO is2The concentration of the solution was 3 g/L.
Preferably, the binder in step S2 is selected from any one of sodium carboxymethyl cellulose, polyvinyl alcohol and dextrin, and the addition amount of the binder is 0.05-1.5 g/L.
More preferably, the binder is carboxymethylSodium cellulose. Sodium carboxymethyl cellulose is used as adhesive to make nano TiO2Can be firmly adhered to the surface of microporous starch to form TiO2The porous microspheres have larger grain size, so that the porous microspheres are easier to separate and recover and more convenient to recycle, and overcome the defects of nano TiO2The powder is difficult to separate after being used, is easy to run off and the like.
More preferably, the addition amount of the sodium carboxymethylcellulose is 1 g/L.
Preferably, the dispersant in step S2 is any one of polyvinylpyrrolidone, sodium dodecylsulfate, cetyl trimethyl ammonium bromide or sodium polyacrylate, and the amount of the dispersant added is nano TiO20.5 to 1.0 percent of the powder. Adding proper amount of dispersant to make nanometer TiO2Fully dispersed in the emulsion and reduced agglomeration.
More preferably, the dispersant is polyvinylpyrrolidone.
Further preferably, the addition amount of the polyvinylpyrrolidone is nano TiO20.75% of the powder.
In one preferred embodiment, the nano TiO described in step S22The powder is selected from P25 powder (commercial nanometer TiO manufactured by Degussa, Germany)2) The nano TiO is added2Dissolving the powder in distilled water, adding 0.75% polyvinylpyrrolidone, stirring for 30 min, performing ultrasonic dispersion for 30 min to obtain dispersed emulsion, adding 1 g/L sodium carboxymethylcellulose, stirring, performing ultrasonic dispersion for 15min to obtain 3 g/L nanometer TiO2And (3) solution.
Preferably, step S3 is: putting the microporous starch obtained in the step S1 into the nano TiO obtained in the step S22Magnetically stirring in emulsion for 60 min, centrifuging at 3000 rpm/min for 10 min, discarding supernatant, drying the precipitate at 50 deg.C for 12 hr, and grinding to obtain cellular TiO2Porous microspheres.
Preferably, the mass of the microporous starch in the step S3 is 1-5 g.
More preferably, in the step S3, the microporous starch is dissolved in distilled water to prepare microporous starch with the concentration of 1-5 g/LAfter suspending, the suspension is mixed with the nano TiO obtained in the step S22And (4) mixing the emulsions.
In addition, the cellular TiO prepared by any one of the preparation methods and using the microporous starch as the template2The porous microspheres and the application thereof in serving as or preparing a photocatalytic material are also within the protection scope of the invention.
The preparation of the porous microspheres is influenced by many factors, and the formation of the porous microspheres is influenced by different types of templates, the addition amount of the templates, the reaction temperature, the enzymolysis time, the addition amount of enzymes, the drying conditions and the like. The invention directly mixes TiO2Loading on microporous starch, preparing porous microsphere by means of the adsorption property of microporous starch, and regulating the formation of microporous starch pores by controlling the starch type, starch addition amount, enzymolysis condition, binder addition amount, etc., to obtain TiO2The porous microsphere has high specific surface area, high specific pore volume and good adsorption performance, can be directly used as a photocatalyst, improves the catalytic performance, has simple preparation method and easily obtained raw materials, and can be widely applied to the fields of sewage treatment, air purification, disinfection, surface coating and the like.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention adopts cellular microporous starch with porous structure as a template, utilizes hydroxyl groups on the surface of the template and excellent adsorption performance to lead nano TiO to be self-assembled2Adsorbing and depositing on the surface of microporous starch to form TiO with special cellular structure2The porous microspheres can be directly used as a photocatalyst without template removal treatment, and the catalytic efficiency is high.
2. Honeycomb TiO prepared by the invention2The porous microsphere structure has high specific surface area and high specific pore volume, has good adsorption and enrichment effects on photocatalytic degradation products (liquid or gas), has the unique advantages of improving the light capturing efficiency and the photocatalytic performance, and has good application prospect in the aspect of photocatalytic degradation of organic pollution.
3. The invention adds proper amount of dispersant and binder in turn, firstly makes the mixture firstNano TiO 22Fully dispersed in the emulsion, reduces the agglomeration phenomenon and promotes the nano TiO2Firmly loading nano TiO on the surface of microporous starch granules to reduce free state2Formed TiO2The porous microspheres have larger grain size, so that the subsequent separation and recovery are easier, the recycling is more convenient, and the defects of nano TiO are overcome2The powder is difficult to separate after being used, is easy to run off and the like.
4. The preparation method has the advantages of mild preparation process conditions, short production period, cheap and easily-obtained raw materials, environmental friendliness and obvious advantages compared with the traditional preparation method.
5. Honeycomb TiO prepared by the invention2The porous microspheres have high catalytic efficiency, the degradation rate of methylene blue after ultraviolet irradiation for 150 min is more than 82%, and the method is suitable for industrial production.
Drawings
FIG. 1 is a honeycomb TiO of example 12Scanning electron micrographs of porous microspheres.
FIG. 2 is a honeycomb TiO of example 22Scanning electron micrographs of porous microspheres.
FIG. 3 is a honeycomb TiO of example 32Scanning electron micrographs of porous microspheres.
FIG. 4 shows a honeycomb TiO of example 42Scanning electron micrographs of porous microspheres.
FIG. 5 shows a honeycomb TiO of example 52Scanning electron micrographs of porous microspheres.
FIG. 6 is a scanning electron micrograph of different types of starch after treatment.
FIG. 7 is a graph showing the effect of different enzymatic hydrolysis temperatures on microporous materials.
FIG. 8 is a graph of the effect of different enzyme addition levels on microporous materials.
FIG. 9 is a graph showing the effect of different enzyme ratios on microporous materials.
FIG. 10 is a graph showing the effect of different enzymatic hydrolysis times on microporous materials.
FIG. 11 shows different nano-TiO2Influence of the amount added on the catalytic efficiency.
FIG. 12 is a graph of the effect of different binder addition levels on catalytic efficiency.
FIG. 13 is a graph showing the effect of catalytic materials on the degradation of methylene blue at different calcination temperatures.
Detailed Description
The invention is further described with reference to the drawings and the following detailed description, which are not intended to limit the invention in any way. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.
Unless otherwise indicated, reagents and materials used in the following examples are commercially available.
Example 1 cellular TiO templated by microporous starch2Porous microspheres
1. Preparation method
(1) Weighing 75 g of corn starch, adding a citric acid-sodium citrate buffer solution with the pH value of 4.5, and continuously stirring by using a magnetic stirrer to prepare a corn starch suspension with the concentration of 150 g/L;
(2) adding 4 g/L of α -amylase and saccharifying enzyme (α -amylase: saccharifying enzyme = 3.2: 1) into the corn starch suspension in the step (1), placing the mixture into a water bath kettle at the temperature of 55 ℃, stirring and reacting for 9 hours, carrying out suction filtration and distilled water washing on the reaction solution for 3 times, placing the precipitate into an oven at the temperature of 50 ℃, drying the precipitate, crushing the precipitate, and sieving the crushed precipitate with a 80-mesh sieve to obtain microporous starch;
(3) 1.5g of P25 powder (commercial nano TiO available from Degussa, Germany) was weighed2) Dissolving in 500 m L distilled water, adding 0.75% polyvinylpyrrolidone (calculated by P25 mass%) as dispersant, magnetically stirring for 30 min, and ultrasonically dispersing for 30 min to obtain nanometer TiO2Dispersing the emulsion;
(4) 0.5 g of sodium carboxymethylcellulose is weighed and put into the nano TiO in the step (3)2Dispersing in emulsion, stirring thoroughly, and ultrasonic dispersing for 20 min;
(5) weighing 2.5 g of microporous starch obtained in the step (2), putting the microporous starch into the emulsion obtained in the step (4), magnetically stirring for 60 min, centrifuging at 3000 rpm/min for 10 min, discarding the supernatant, drying the precipitate in an oven at 50 ℃ for 12 h, and grinding to obtain the honeycomb TiO2Porous microspheres.
2. Product characteristics and physicochemical properties
Honeycomb TiO obtained in this example2The porous microspheres are shown in figure 1, and when the microspheres are irradiated under ultraviolet light for 150 min, the degradation rate of the microspheres on methylene blue is 89.8%.
Example 2 cellular TiO Using microporous starch as template2Porous microspheres
1. Preparation method
(1) Weighing 50 g of corn starch, adding a citric acid-sodium citrate buffer solution with the pH value of 4.5, and continuously stirring by using a magnetic stirrer to prepare a corn starch suspension with the concentration of 100 g/L;
(2) adding 3 g/L of α -amylase and saccharifying enzyme (α -amylase: saccharifying enzyme = 2: 1) into the corn starch suspension liquid in the step (1), placing the mixture into a water bath kettle at the temperature of 50 ℃, stirring and reacting for 9 hours, carrying out suction filtration and washing of a reaction solution for 3 times by distilled water, placing a precipitate into an oven at the temperature of 50 ℃, drying the precipitate, crushing the precipitate, and sieving the crushed precipitate by a 80-mesh sieve to obtain microporous starch;
(3) weighing 1.5g of P25 powder, dissolving in 500 m L of distilled water, adding 0.5% of polyvinylpyrrolidone (calculated by P25 mass percent) as a dispersing agent, magnetically stirring for 30 min, and ultrasonically dispersing for 30 min to obtain the nano TiO2Dispersing the emulsion;
(4) 0.4 g of sodium carboxymethylcellulose is weighed and put into the nano TiO in the step (3)2Dispersing in emulsion, stirring thoroughly, and ultrasonic dispersing for 20 min;
(5) weighing 2.5 g of microporous starch obtained in the step (2), putting the microporous starch into the emulsion obtained in the step (4), magnetically stirring for 60 min, centrifuging at 3000 rpm/min for 10 min, discarding the supernatant, drying the precipitate in an oven at 50 ℃ for 12 h, and grinding to obtain the honeycomb TiO2Porous microspheres.
2. Product characteristics and physicochemical properties
Honeycomb TiO obtained in this example2The porous microspheres are shown in fig. 2, and when the microspheres are irradiated under ultraviolet light for 150 min, the degradation rate of methylene blue is 87.2%.
Example 3A Honeycomb Using microporous starch as templateTiO like2Porous microspheres
1. Preparation method
(1) Weighing 25 g of corn starch, adding a citric acid-sodium citrate buffer solution with the pH value of 4, and continuously stirring by using a magnetic stirrer to prepare a corn starch suspension with the concentration of 100 g/L;
(2) adding 1 g/L of α -amylase and saccharifying enzyme (α -amylase: saccharifying enzyme = 1: 1) into the corn starch suspension liquid in the step (1), placing the mixture into a water bath kettle at the temperature of 50 ℃, stirring and reacting for 6 hours, carrying out suction filtration and washing 3 times on a reaction solution by distilled water, placing a precipitate into an oven at the temperature of 50 ℃, drying the precipitate, crushing the precipitate, and sieving the crushed precipitate by a 80-mesh sieve to obtain microporous starch;
(3) weighing 1 g of P25 powder, dissolving in 500 m L of distilled water, adding 0.5% of polyvinylpyrrolidone (calculated by P25 mass percent) as a dispersing agent, magnetically stirring for 30 min, and ultrasonically dispersing for 30 min to obtain the nano TiO2Dispersing the emulsion;
(4) 0.25 g of sodium carboxymethylcellulose is weighed and put into the nano TiO in the step (3)2Dispersing in emulsion, stirring thoroughly, and ultrasonic dispersing for 20 min;
(5) weighing 2.5 g of microporous starch obtained in the step (2), putting the microporous starch into the emulsion obtained in the step (4), magnetically stirring for 60 min, centrifuging at 3000 rpm/min for 10 min, discarding the supernatant, drying the precipitate in an oven at 50 ℃ for 12 h, and grinding to obtain the honeycomb TiO2Porous microspheres.
2. Product characteristics and physicochemical properties
Honeycomb TiO obtained in this example2The porous microspheres are shown in fig. 3, and when the microspheres are irradiated under ultraviolet light for 150 min, the degradation rate of the microspheres on methylene blue is 84.5%.
Example 4 cellular TiO using microporous starch as template2Porous microspheres
1. Preparation method
(1) Weighing 125 g of corn starch, adding a citric acid-sodium citrate buffer solution with the pH value of 6, and continuously stirring by using a magnetic stirrer to prepare a corn starch suspension with the concentration of 250 g/L;
(2) adding 5 g/L of α -amylase and saccharifying enzyme (α -amylase: saccharifying enzyme = 5: 1) into the corn starch suspension in the step (1), placing the mixture into a water bath kettle at the temperature of 50 ℃, stirring and reacting for 11 hours, carrying out suction filtration and washing 3 times on a reaction solution by distilled water, placing a precipitate into an oven at the temperature of 50 ℃, drying the precipitate, crushing the precipitate, and sieving the crushed precipitate by a 80-mesh sieve to obtain microporous starch;
(3) weighing 2.5 g of P25 powder, dissolving in 500 m L of distilled water, adding 1% of polyvinylpyrrolidone (calculated by P25 mass percent) as a dispersing agent, magnetically stirring for 30 min, and ultrasonically dispersing for 30 min to obtain nano TiO2Dispersing the emulsion;
(4) 0.75 g of sodium carboxymethylcellulose is weighed and put into the nano TiO in the step (3)2Dispersing in emulsion, stirring thoroughly, and ultrasonic dispersing for 20 min;
(5) weighing 2.5 g of microporous starch obtained in the step (2), putting the microporous starch into the emulsion obtained in the step (4), magnetically stirring for 60 min, centrifuging at 3000 rpm/min for 10 min, discarding the supernatant, drying the precipitate in an oven at 50 ℃ for 12 h, and grinding to obtain the honeycomb TiO2Porous microspheres.
2. Product characteristics and physicochemical properties
Honeycomb TiO obtained in this example2The porous microspheres are shown in FIG. 4, and when the microspheres are irradiated under ultraviolet light for 150 min, the degradation rate of methylene blue is 82.7%.
Example 5 cellular TiO templated by microporous starch2Porous microspheres
1. Preparation method
(1) Weighing 100 g of corn starch, adding a citric acid-sodium citrate buffer solution with the pH value of 5, and continuously stirring by using a magnetic stirrer to prepare a corn starch suspension with the concentration of 200 g/L;
(2) adding 2 g/L of α -amylase and saccharifying enzyme (α -amylase: saccharifying enzyme = 4: 1) into the corn starch suspension liquid in the step (1), placing the mixture into a water bath kettle at the temperature of 50 ℃, stirring and reacting for 13 hours, carrying out suction filtration and washing 3 times on a reaction solution by distilled water, placing a precipitate into an oven at the temperature of 50 ℃, drying the precipitate, crushing the precipitate, and sieving the crushed precipitate by a 80-mesh sieve to obtain microporous starch;
(3) weighing 2 g of P25 powder, dissolving in 500 m L of distilled water, adding 0.6 percent of polyvinylpyrrolidone (calculated by the mass percentage of P25) as a dispersing agent, magnetically stirring for 30 min, and ultrasonically dispersing for 30 min to obtain the nano TiO2Dispersing the emulsion;
(4) 0.6 g of sodium carboxymethylcellulose is weighed and put into the nano TiO in the step (3)2Dispersing in emulsion, stirring thoroughly, and ultrasonic dispersing for 20 min;
(5) weighing 2.5 g of microporous starch obtained in the step (2), putting the microporous starch into the emulsion obtained in the step (4), magnetically stirring for 60 min, centrifuging at 3000 rpm/min for 10 min, discarding the supernatant, drying the precipitate in an oven at 50 ℃ for 12 h, and grinding to obtain the honeycomb TiO2Porous microspheres.
2. Product characteristics and physicochemical properties
Honeycomb TiO obtained in this example2The porous microspheres are shown in fig. 5, and when the microspheres are irradiated under ultraviolet light for 150 min, the degradation rate of methylene blue is 85.4%.
Example 6 preparation Process optimization
1. Selection of starch raw materials
(1) Selecting cheap and easily-purchased common starch for preparing the microporous starch, preparing the microporous starch under the same conditions, and observing the morphology of the microporous starch by a scanning electron microscope.
(2) FIG. 6 is a scanning electron micrograph of different types of starch after treatment. From starch morphology analysis: the sweet potato starch has uneven particle size (figure 6 a), smaller particles have better pore-forming property, and large starch particles have smooth surfaces and are not obviously enzymolyzed; the potato starch (figure 6 b) has larger particles and is elliptical, and the surface of the starch after enzymolysis is not provided with small holes and is smooth; the wheat starch (fig. 6 c) particles are flat and smooth in surface, which indicates that the enzymolysis effect is not obvious; the corn starch (fig. 6 d) has uniform particle size, regular shape, and the best pore-forming property after enzymolysis.
2. Effect of different enzymolysis temperatures on microporous materials
As shown in FIG. 7, when the temperature is 55 ℃, the starch has better pore-forming property, and the formed micropores are deeper and are distributed more uniformly. When the temperature is 50 ℃, the micropores formed on the surface of the starch granules are shallower, and the micropores are not formed on the surface of part of the granules (see figure 7 b); when the temperature is too high and reaches 60 ℃, the starch granules are disintegrated, so that the formed micropores are destroyed, and the microporous starch with complete granule structure is difficult to obtain (see figure 7 d).
3. Effect of enzyme addition on microporous Material
As shown in FIG. 8, when the enzyme was added in an amount of 3 mg/m L, the microporous starch showed the highest adsorption rate and the pore-forming effect was good (FIG. 8 a), and when the enzyme was added in an amount of 5 mg/m L, the microporous structure of part of the granules was destroyed and a small number of the granules were disintegrated (FIG. 8 b).
4. Effect of enzyme dosage on microporous Material
As shown in fig. 9, when the enzyme ratio is 1: 1, the microporous starch has low adsorption rate, poor enzymolysis effect and slightly poor pore-forming property (fig. 9 a), and the saccharifying enzyme: the ratio of the alpha-amylase to the enzyme is 3: 1, the adsorption rate was high and the pore-forming property was good (FIG. 9 b).
5. Effect of enzymolysis time on microporous Material
As shown in fig. 10, when the enzymolysis time is 9 hours, more micropores are formed on the surface of the particles, the pore diameter is larger, and the pore depth is increased (fig. 10 a); when the enzymolysis time reaches 13h, the microporous structure of the starch granules is destroyed due to excessive enzymolysis, the starch granules collapse and even aggregate (fig. 10 b), and the granules are decomposed into fine granules until being completely hydrolyzed into oligosaccharide and glucose.
6. Nano TiO 22Influence of addition amount on catalytic efficiency
As shown in FIG. 11, with nano TiO2When the addition amount of the titanium dioxide is 3 mg/m L, the starch-supported nano TiO is loaded2The degradation rate of the catalytic material to methylene blue reaches 89.81 percent.
7. Effect of Binder addition on catalytic efficiency
As shown in FIG. 12, the catalytic performance of the recovered sample of the P25 porous microspheres added with the binder is higher than that of the sample without the binder, and the degradation rate is as high as 89.03% when the addition amount of the binder is 1 mg/m L, although the catalytic performance is not greatly improved, the loading effect is stable.
Example 7 high temperature calcination de-templating treatment cellular TiO templated with microporous starch2Effect of porous microspheres on catalytic Properties
Methylene blue degradation experiments were performed with porous microspheres calcined at different temperatures (subjected to high temperature calcination to remove the template) according to the method described in the above examples. FIG. 13 shows the effect of the catalytic material (i.e., P25 porous microspheres) calcined at different temperatures for template removal on the degradation of methylene blue. As can be seen from fig. 13, with the increase of temperature, the degradation rate of methylene blue first increases and then decreases, and the degradation rate of the calcined sample to methylene blue is maximum 85.3% at around 460 ℃, but the degradation rate of the calcined de-templated P25 porous microspheres to methylene blue is lower than that of the uncalcined sample.
Claims (2)
1. Honeycomb TiO using microporous starch as template2The preparation method of the porous microspheres is characterized by comprising the following steps of:
s1, weighing starch, adding a citric acid-sodium citrate buffer solution with the pH value of 4-6, stirring to prepare a starch suspension, adding biological enzyme, carrying out water bath stirring reaction at 40-60 ℃ for 5-13 h, carrying out suction filtration and washing on a reaction solution, drying a precipitate at 40-60 ℃, and crushing to obtain microporous starch;
s2, taking nano TiO2Dissolving the powder into distilled water, adding a dispersing agent, stirring for 20-40 min, and then performing ultrasonic dispersion for 20-40 min to obtain a dispersion emulsion; adding a binder, fully stirring, and then performing ultrasonic dispersion for 10-20 min to obtain nano TiO2An emulsion;
s3, putting the microporous starch obtained in the step S1 into the nano TiO obtained in the step S22Magnetically stirring the mixture in the emulsion for 50-70 min, centrifuging the mixture for 5-15 min at 1000-5000 rpm, discarding supernatant, drying the precipitate for 10-14 h at 40-60 ℃, and grinding the dried precipitate to obtain honeycomb TiO2Porous microspheres;
the starch and the nano TiO2The mass ratio of the two raw materials is 25-250: 1-5;
the starch is any one of corn starch, wheat starch, potato starch or sweet potato starch;
the biological enzyme is α -amylase and saccharifying enzyme in a mass ratio of 1-5: 1, wherein the total usage amount of α -amylase and saccharifying enzyme is 1-5 g/L;
the binder is selected from any one of sodium carboxymethylcellulose, polyvinyl alcohol or dextrin, and the addition amount of the binder is 0.05-1.5 g/L;
the dispersing agent is selected from any one of polyvinylpyrrolidone, sodium dodecyl sulfate, cetyl trimethyl ammonium bromide or sodium polyacrylate; the addition amount of the dispersing agent is nano TiO20.5 to 1.0 percent of the mass.
2. Cellular TiO templated by microporous starch prepared by the method of claim 12Porous microspheres.
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