CN100503448C - Method for synthesizing anatase type crystallizing titanium dioxide nano nuclear-shell or shell structure material by water phase one-step method - Google Patents

Method for synthesizing anatase type crystallizing titanium dioxide nano nuclear-shell or shell structure material by water phase one-step method Download PDF

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CN100503448C
CN100503448C CNB200610011968XA CN200610011968A CN100503448C CN 100503448 C CN100503448 C CN 100503448C CN B200610011968X A CNB200610011968X A CN B200610011968XA CN 200610011968 A CN200610011968 A CN 200610011968A CN 100503448 C CN100503448 C CN 100503448C
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shell
polystyrene microsphere
titanium
titanium dioxide
polystyrene
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CNB200610011968XA
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CN101077792A (en
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只金芳
吴良专
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中国科学院理化技术研究所
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Abstract

The present invention relates to preparation process of core-shell material and hollow material, and is especially water phase one-step synthesis process for preparing nanometer crystallized anatase type titania material in core-shell and hollow structure. Water soluble titanium peroxide precursor is treated through a sol-gel process so as to coat a nanometer titania layer onto the surface of polystyrene, and the nanometer titania layer in the shell is crystallized directly at relatively low temperature to form nanometer anatase type titania without needing sintering. Furthermore, the precursor may be controlled properly, so that the polystyrene core serving as the template may be dissolved spontaneously after the shell is formed and crystallized and nanometer hollow titania may be obtained directly in water phase. The present invention is simple, easy to operate, low in cost and suitable for batch production, and may find wide application in different aspects.

Description

The method of water one-step synthesis Detitanium-ore-type crystallizing titanium dioxide nano nuclear-shell or ghost structural material
Technical field
The present invention relates to the preparation method of nucleocapsid-ghost structural material, particularly the method for water one-step synthesis Detitanium-ore-type crystallizing titanium dioxide nano nuclear-shell or ghost structural material.
Background technology
Nucleocapsid and hollow shell structure nano material be in catalysis, chromatography, and the bioactive agents protection, wastewater treatment, the great application prospect in fields such as macromole slow-releasing system, controlled preparation nucleocapsid and hollow shell structure nano material become the emphasis of people's research just day by day.Nano titanium oxide nucleocapsid and hollow shell structure make it in environmental purification owing to photocatalytic activity, catalysis, and coating, fields such as opto-electronic conversion are with a wide range of applications; Moreover, because titanium dioxide is in the low absorption of visible and near-infrared region and high specific refractory power, make nucleocapsid and hollow shell structure nano titanium dioxide ball become preparation photonic crystal ideal material, thereby make that also preparation nucleocapsid and hollow shell structure nano titanium dioxide ball become the focus in the synthetic field of present nanometer.By sol-gel method at first at the surperficial encasement layer material of mould material (being generally polymer microsphere), remove template by sintering or dissolving again and obtain hollow shell structure, obtained using widely (1.Imhof as a kind of synthetic nucleocapsid of routine and the method for ghost structural material, A., Preparation andcharacterization of titania-coated polystyrene spheres and hollow titania shells.Langmuir 2001,17, (12), 3579~3585.2.Caruso, R.A.; Susha, A.; Caruso, F., Multilayered titania, silica, and Laponite nanoparticle coatings on polystyrenecolloidal templates and resulting inorganic hollow spheres.Chemistry of Materials2001,13, (2), 400~409.3.Wang, D.B.; Song, C.X.; Lin, Y.S.; Hu, Z.S., Preparation and characterization of TiO2 hollow spheres.Materials Letters 2006,60, (1), 77~80.).The nucleocapsid and the hollow shell structure semiconductor material that are different from other are synthetic, because the strong polarity of titanium ion, make its hydrolysis of control difficult relatively, therefore, report by sol-gel method water synthesis of titanium dioxide nucleocapsid and hollow shell structure is less relatively, alcoholysis then is widely used the organic compound that utilizes titanium as an alternative as presoma, but the defective of these class methods is outstanding equally, in order to obtain the titanium dioxide hollow shell structure of crystallization, high temperature sintering step or special hydrothermal reaction condition is absolutely necessary.Have numerous superiority by water miscible titanium precursor body material preparation titanium compound as titanium organic compound class presoma alternative, at first, from the angle of environment, water is synthetic can effectively to be reduced environmentally hazardous substance and uses and discharge; Secondly, water-soluble precursor can effectively reduce synthetic cost; At last, can show reduction titanium dioxide shell crystallization temperature by water is synthetic.
Summary of the invention
The object of the present invention is to provide a kind of simple and easy to controlly, respond well, be suitable for the water one-step synthesis Detitanium-ore-type crystallizing titanium dioxide nano nuclear-shell of large-scale commercial production or the method for ghost structural material.
The present invention utilize first the water-soluble titanium peroxide precursor by sol-gel method at polystyrene surface clad nano titanium oxide layer, shell titanium oxide (80~100 ℃) water direct crystallization under low relatively temperature be anatase octahedrite nano titanium oxide and need not sintering.Moreover, by control, can make shell after formation and crystallization, thereby spontaneous dissolving directly obtain the nano titanium oxide hollow shell structure at water as the polystyrene core of template to presoma pH.
Preparation method of the present invention at first disperses to obtain lotus positive electricity polystyrene milk sap with polystyrene spheres by cats product, thereby the water-soluble titanium peroxide presoma secondly by different pH values reacts with it and obtains final product.
The method of water one-step synthesis Detitanium-ore-type crystallizing titanium dioxide nano nuclear-shell of the present invention or ghost structural material may further comprise the steps:
(1). the positive electrical treating of polystyrene microsphere surface lotus
Utilize cats product in pure water, to disperse to obtain surperficial lotus positive electricity polystyrene microsphere emulsion again the powder polystyrene microsphere; Wherein, the mass percent of powder polystyrene microsphere and cats product is 0.001~10% in the emulsion, and polystyrene microsphere and pure water mass percent are 0.001~30%; Described cats product is the derivative of organic amine;
(2). the preparation of water-soluble titanium presoma
Dissolve positive metatitanic acid with superoxol and obtain titanium peroxide solution, wherein, the molecule mole ratio of hydrogen peroxide and titanium ion is 50~1; The pH value of regulating titanium peroxide solution with ammoniacal liquor and hydrochloric acid is 0~10; Wherein, the mass percentage concentration of hydrogen peroxide is 1~30%, and the mass percentage concentration of ammoniacal liquor is 1~25%, and the mass percentage concentration of hydrochloric acid is 1~37.2%;
(3) nucleocapsid structure product preparation
The titanium peroxide solution of pH=5~10 that step (2) is prepared and the surperficial lotus positive electricity polystyrene microsphere emulsion that step (1) obtains are (wherein, titanium peroxide solution is that 10:1~1:1 mixes with polystyrene microsphere emulsion volume ratio, in temperature is 80~100 ℃ of following stirring reactions, the stirring reaction time is 0.1~12 hour, and obtaining with the crystallization anatase-type nanometer titanium dioxide is shell and polystyrene is the nucleocapsid structure product of nuclear; Or
The titanium peroxide solution of pH=0~5 that step (2) is prepared and the surperficial lotus positive electricity polystyrene microsphere emulsion that step (1) obtains are (wherein, titanium peroxide solution and the volume ratio of polystyrene microsphere emulsion are 10:1~1:1) mix, in temperature is 80~100 ℃ of following stirring reactions, the stirring reaction time is 0.1~12 hour, and obtaining with the crystallization anatase-type nanometer titanium dioxide is the hollow shell structure product of shell;
(4) purification of products
With the product centrifugation that step (3) prepares, centrifugation again after resulting precipitation is disperseed again with the pure water washing is also ultrasonic repeats above washing step three times; Then resulting precipitation is disperseed again with absolute ethanol washing is also ultrasonic, centrifugation, vacuum-drying obtain Detitanium-ore-type crystallizing titanium dioxide nano nuclear-shell or ghost structural material.
The used polystyrene microsphere of present method can be commercially available or utilize vinylbenzene to prepare for polymerizable raw material that particle diameter is 0.1~100 μ m.
The derivative of described organic amine is uncle's ammonium, secondary ammonium, tertiary amine, quaternary amines salt compound or their any mixture.
Described uncle's ammonium salt compounds has following structure R-NH 2HX; Described secondary ammonium salt compounds has following structure R-NHCH 3HX; Described tertiary amine salt compounds has following structure R-N (CH 3) 2HX; Described quaternary ammonium compound has following structure R-N (CH 3) 3X;
Wherein: R is C 5~C 16Alkyl chain, X is a halogen, as Br, Cl.
Present method can be regulated the radius of the nuclear of nucleocapsid structure by changing the polystyrene microsphere particle diameter.
The present invention compares with the traditional preparation process method, and method flow of the present invention is simple, and is workable, relative cost is cheap simultaneously, is applicable to batch preparations, possesses the possibility of suitability for industrialized production, in environmental purification, medicament transport, aspects such as photonic crystal are with a wide range of applications.
Description of drawings
Figure 1A. the Detitanium-ore-type crystallizing titanium dioxide nano nuclear-shell structure product transmission electron microscope picture that the embodiment of the invention 1 is prepared.
Figure 1B. the Detitanium-ore-type crystallizing titanium dioxide nano nuclear-shell structure product sem photograph that the embodiment of the invention 1 is prepared.
The Detitanium-ore-type crystallizing titanium dioxide nano hollow shell structure product transmission electron microscope picture that Fig. 2 A. embodiment of the invention 2 is prepared.
The Detitanium-ore-type crystallizing titanium dioxide nano hollow shell structure product sem photograph that Fig. 2 B. embodiment of the invention 2 is prepared.
The Detitanium-ore-type crystallizing titanium dioxide nano hollow shell structure product sem photograph that Fig. 2 C. embodiment of the invention 2 is prepared.
Fig. 3. the Detitanium-ore-type crystallizing titanium dioxide nano hollow shell structure product X RD spectrogram that the embodiment of the invention 1,2 is prepared.
Embodiment
Embodiment 1:
Get commercially available 5g particle diameter and be about 200nm polystyrene microsphere powder, add the 0.25g cetyl trimethylammonium bromide as the dispersion agent ultra-sonic dispersion in the 1000ml pure water; Titanic Acid precipitation mass percentage concentration be 30% aqueous hydrogen peroxide solution (with the ratio of titanium ion mole molecule number be 4) dissolving, with mass percentage concentration is the pH=7 that 2.5% ammoniacal liquor is reconciled solution, this solution of 200ml is added in the above-mentioned polystyrene emulsion, in temperature is under 80~100 ℃, intense mechanical stirring and refluxing reaction 1 hour, the centrifugal product that obtains of 2500rpm speed, resulting product with pure water washing three times and ultrasonic disperse again after centrifugation again, again with absolute ethanol washing and ultrasonic dispersion again, centrifugation, drying obtain the nucleocapsid structure product.
The products therefrom pattern utilizes transmission electron microscope (referring to Figure 1A) and scanning electron microscope (referring to Figure 1B) to characterize.The products therefrom crystal structure analysis adopts the X ray electron diffraction instrument to characterize, and the result is referring to Fig. 3.
Embodiment 2:
Get commercially available 5g particle diameter and be about 200nm polystyrene microsphere powder, add the 0.25g palmityl trimethyl ammonium chloride as the dispersion agent ultra-sonic dispersion in the 1000ml pure water; Titanic Acid precipitation mass percentage concentration be 30% aqueous hydrogen peroxide solution (with the ratio of titanium ion mole molecule number be 4) dissolving, with mass percentage concentration is the pH=3 that 2.5% ammoniacal liquor is reconciled solution, this solution of 200ml is added in the above-mentioned polystyrene emulsion, in temperature is under 80~100 ℃, intense mechanical stirring and refluxing reaction 1 hour, the centrifugal product that obtains of 2500rpm speed, resulting product with pure water washing three times and ultrasonic disperse again after centrifugation again, again with absolute ethanol washing and ultrasonic dispersion again, centrifugation, drying obtain the hollow shell structure product.
The products therefrom pattern utilizes transmission electron microscope (referring to Fig. 2 A) and scanning electron microscope (referring to Fig. 2 B, 2C) to characterize.The products therefrom crystal structure analysis adopts the X ray electron diffraction instrument to characterize, and the result is referring to Fig. 3.
Embodiment 3:
Get commercially available 5g particle diameter and be about 500nm polystyrene microsphere powder, add 0.15g Trimethyllaurylammonium bromide and 0.15g Dodecyl trimethyl ammonium chloride as the dispersion agent ultra-sonic dispersion in the 1000ml pure water; Titanic Acid precipitation mass percentage concentration be 30% aqueous hydrogen peroxide solution (with the ratio of titanium ion mole molecule number be 4) dissolving, with mass percentage concentration is the pH=7 that 2.5% ammoniacal liquor is reconciled solution, this solution of 200ml is added in the above-mentioned polystyrene emulsion, in temperature is under 80~100 ℃, intense mechanical stirring and refluxing reaction 1 hour, the centrifugal product that obtains of 2500rpm speed, resulting product with pure water washing three times and ultrasonic disperse again after centrifugation again, again with absolute ethanol washing and ultrasonic dispersion again, centrifugation, drying obtain the nucleocapsid structure product.
Embodiment 4:
Get commercially available 5g particle diameter and be about 1 μ m polystyrene microsphere powder, add 0.15g dodecyl dimethyl brometo de amonio and 0.15g dodecyl methyl ammonium chloride as the dispersion agent ultra-sonic dispersion in the 1000ml pure water; Titanic Acid precipitation mass percentage concentration be 30% aqueous hydrogen peroxide solution (with the ratio of titanium ion mole molecule number be 4) dissolving, with mass percentage concentration is the pH=3 that 2.5% ammoniacal liquor is reconciled solution, this solution of 200ml is added in the above-mentioned polystyrene emulsion, in temperature is under 80~100 ℃, intense mechanical stirring and refluxing reaction 1 hour, the centrifugal product that obtains of 2500rpm speed, resulting product with pure water washing three times and ultrasonic disperse again after centrifugation again, again with absolute ethanol washing and ultrasonic dispersion again, centrifugation, drying obtain the hollow shell structure product.

Claims (5)

1. the method for water one-step synthesis Detitanium-ore-type crystallizing titanium dioxide nano nuclear-shell or ghost structural material is characterized in that this method may further comprise the steps:
(1). the positive electrical treating of polystyrene microsphere surface lotus
Utilize cats product in pure water, to disperse to obtain surperficial lotus positive electricity polystyrene microsphere emulsion again the powder polystyrene microsphere; Wherein, the mass percent of powder polystyrene microsphere and cats product is 0.001~10% in the emulsion, and polystyrene microsphere and pure water mass percent are 0.001~30%;
Described cats product is the derivative of organic amine;
(2). the preparation of water-soluble titanium presoma
Dissolve positive metatitanic acid with superoxol and obtain titanium peroxide solution, wherein, the molecule mole ratio of hydrogen peroxide and titanium ion is 50~1; The pH value of regulating titanium peroxide solution with ammoniacal liquor and hydrochloric acid is 0~10;
(3) nucleocapsid structure product preparation
The titanium peroxide solution of pH=5~10 that step (2) is prepared mixes with the surperficial lotus positive electricity polystyrene microsphere emulsion that step (1) obtains, and wherein, the volume ratio of titanium peroxide solution and polystyrene microsphere emulsion is 10:1~1:1; In temperature is 80~100 ℃ of following stirring reactions, and obtaining with the crystallization anatase-type nanometer titanium dioxide is shell and polystyrene is the nucleocapsid structure product of nuclear; Or
The titanium peroxide solution of pH=0~5 that step (2) is prepared mixes with the surperficial lotus positive electricity polystyrene microsphere emulsion that step (1) obtains, and wherein, the volume ratio of titanium peroxide solution and polystyrene microsphere emulsion is 10:1~1:1; In temperature is 80~100 ℃ of following stirring reactions, and obtaining with the crystallization anatase-type nanometer titanium dioxide is the hollow shell structure product of shell;
(4) purification of products
With the product centrifugation that step (3) prepares, washing, vacuum-drying obtains Detitanium-ore-type crystallizing titanium dioxide nano nuclear-shell or ghost structural material;
The derivative of described organic amine is uncle's ammonium, secondary ammonium, tertiary amine, quarternary ammonium salt compound or their any mixture.
2. method according to claim 1 is characterized in that: the mass percentage concentration of hydrogen peroxide is 1~30% in the described step (2), and the mass percentage concentration of ammoniacal liquor is 1~25%, and the mass percentage concentration of hydrochloric acid is 1~37.2%.
3. method according to claim 1 is characterized in that: the stirring reaction time described in the step (3) is 0.1~12 hour.
4. method according to claim 1 is characterized in that: the particle diameter of described polystyrene microsphere is 0.1~100 μ m.
5. method according to claim 1 is characterized in that: described uncle's ammonium salt compound has following structure R-NH 2HX; Described secondary ammonium salt compound has following structure R-NHCH 3HX; Described tertiary amine salt compound has following structure R-N (CH 3) 2HX; Described quarternary ammonium salt compound has following structure R-N (CH 3) 3X;
Wherein: R is C 5~C 16Alkyl chain, X are Br or Cl.
CNB200610011968XA 2006-05-23 2006-05-23 Method for synthesizing anatase type crystallizing titanium dioxide nano nuclear-shell or shell structure material by water phase one-step method CN100503448C (en)

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GB0617480D0 (en) * 2006-09-06 2006-10-18 Univ Sheffield Novel nanoparticles
CN101497067B (en) * 2009-01-16 2011-11-09 北京航空航天大学 Preparation method for assembling large-area ordered microsphere template by liquid level swirl method
CN101629031B (en) * 2009-08-17 2012-07-04 湖北大学 Photocatalytic functional coating and preparation method thereof
CN101659773B (en) * 2009-09-28 2011-08-31 浙江理工大学 Nano TiO2-polystyrene microsphere compound and preparation method and application thereof
CN102100926A (en) * 2010-06-21 2011-06-22 浙江工业大学 Medical titanium or titanium alloy surface activation modifying method
CN101927164B (en) * 2010-07-12 2012-12-19 北京航空航天大学 Metallic ion-doping modification microsphere TiO2 photocatalyst and method for preparing same
CN101879441B (en) * 2010-07-12 2013-04-03 北京航空航天大学 Microsphere TiO2 photocatalyst and preparation method thereof
EP2752239A4 (en) 2011-08-31 2015-08-12 Shanghai World Prospect Chemtech Co Ltd Inorganic non-metal mineral composite material carrying titanium dioxide layer, and preparation process and use thereof
CN102989515A (en) * 2012-12-17 2013-03-27 江南大学 Preparation method of titanium dioxide/heteropolyacid compound photo-catalyst
CN104860348B (en) * 2015-04-22 2016-08-24 武汉理工大学 Titanium dioxide of core-shell structure that a kind of nanometer sheet is constructed and preparation method and application
US10039705B1 (en) 2017-04-28 2018-08-07 National Tsing Hua University Sun protection material and sun protection composition containing the same

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002074431A1 (en) * 2001-03-21 2002-09-26 Max-Planck-Gesellschaft Zur Förderung Der Wissenschaften Hollow spheres from layered precursor deposition on sacrificial colloidal core particles
CN1473791A (en) * 2003-07-31 2004-02-11 中国石油化工股份有限公司 Core-shell structure nano titanium serial composition and its preparing method
CN1762903A (en) * 2004-10-21 2006-04-26 华楙生化科技股份有限公司 Core-shell structured powder production method

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002074431A1 (en) * 2001-03-21 2002-09-26 Max-Planck-Gesellschaft Zur Förderung Der Wissenschaften Hollow spheres from layered precursor deposition on sacrificial colloidal core particles
CN1473791A (en) * 2003-07-31 2004-02-11 中国石油化工股份有限公司 Core-shell structure nano titanium serial composition and its preparing method
CN1762903A (en) * 2004-10-21 2006-04-26 华楙生化科技股份有限公司 Core-shell structured powder production method

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