ORDERED CROSS-STACKED METAL OXIDE NANOWIRE ARRAY MATERIAL AND PREPARATION METHOD THEREOF

Abstract

A method for preparing an ordered cross-stacked metal oxide nanowire array is provided. The method includes the following steps: conducting synthesis by using an amphiphilic diblock copolymer as a structure directing agent, tetrahydrofuran (THF) as a solvent and polyoxometalates (POMs) as an inorganic precursor, where the diblock copolymer can interact with POMs via an electrostatic force to form a core-shell cylindrical micelle in the solvent, which self-assembles to form an ordered multilayer-crossed organic-inorganic composite nanostructure during an evaporation process; the template is removed by calcination in air, thereby obtaining ordered and crossed metal oxide nanowires with various elements doping. The nanowire array material has a high specific surface area, a high crystallinity, and realizes uniform doping of heteroatoms.

Claims

1. A method for preparing an ordered cross-stacked metal oxide nanowire array, wherein a core-shell cylindrical micelle is formed through an electrostatic force between a hydrophilic block of an amphiphilic diblock copolymer template with a hydrophobic block having an ultra-high molecular weight and a polyoxometalates (POMs) anion, wherein the amphiphilic diblock copolymer template consists of polystyrene-block-poly(ethylene oxide) (PEO-b-PS) the hydrophilic block is a PEO block and the hydrophobic block is a PS block; an ordered mesoscopic organic-inorganic composite structure is obtained by evaporation-induced self-assembly (EISA), and an ordered metal oxide semiconductor nanowire material with a high crystallinity is obtained by carrying out calcination-induced structural transformation to remove the amphiphilic diblock copolymer template, wherein the method specifically comprises: (1) dissolving the PEO-b-PS with a high molecular weight in a solvent, wherein the PEO-b-PS has a molecular weight M.sub.n of 15,000-35,000 g mol.sup.−1, and stirring thoroughly to obtain a first transparent solution, with a concentration of 1-5 wt %; adding a POMs hydrate to the solvent to obtain a second transparent solution, with a concentration of 5-10 wt %; mixing the first transparent solution, and the second transparent solution, and stirring thoroughly to obtain a transparent colloidal solution; (2) transferring the colloidal solution to a petri dish to volatilize at room temperature for 2-12 h; transferring the petri dish to an oven to curing at 70-100° C. for 12-48 h to obtain a transparent organic-inorganic composite film, scraping the transparent organic-inorganic composite film from the petri dish, and grinding to obtain powder; and (3) placing the powder in a tube furnace, and calcinating the powder in nitrogen for 1-2 h by heating up to 350-500° C. at a rate of 1-3° C./min to obtain a sample; calcinating the sample in air at 400-450° C. for 0.5-1 h, removing carbon therein to obtain a crystalline crossed metal oxide nanowire material.

2. The method according to claim 1, wherein in step (1), the solvent used is one or more selected from the group consisting of tetrahydrofuran (THF), toluene, chloroform and dimethylformamide; a molecular weight of the PEO block of the amphiphilic diblock copolymer is 2,000-5,000 g/mol, and a molecular weight of the PS block is 10,000-30,000 g/mol; the POMs used is one or more selected from the group consisting of silicotungstic acid, phosphotungstic acid, silicomolybdic acid and phosphomolybdic acid.

3. The method according to claim 2, wherein an array spacing and a nanowire diameter of the crystalline crossed metal oxide nanowire material are controlled by changing lengths of the PS block and the PEO block of the amphiphilic diblock copolymer, respectively.

4. The method according to claim 2, wherein metal oxide nanowire materials, composed of different elements, with a high crystallinity and a high specific surface area, or bimetal or multi-metal composite oxide materials are synthesized by using different oxometallate hydrates as inorganic precursors.

5. An ordered cross-stacked metal oxide nanowire array material prepared by using the method according to claim 1.

6. The ordered cross-stacked metal oxide nanowire array material according to claim 5, wherein in step (1), the solvent used is one or more selected from the group consisting of tetrahydrofuran (THF), toluene, chloroform and dimethylformamide; a molecular weight of the PEO block of the amphiphilic diblock copolymer is 2,000-5,000 g/mol, and a molecular weight of the PS block is 10,000-30,000 g/mol; the POMs used is one or more selected from the group consisting of silicotungstic acid, phosphotungstic acid, silicomolybdic acid and phosphomolybdic acid.

7. The ordered cross-stacked metal oxide nanowire array material according to claim 6, wherein an array spacing and a nanowire diameter of the crystalline crossed metal oxide nanowire material are controlled by changing lengths of the PS block and the PEO block of the amphiphilic diblock copolymer, respectively.

8. The ordered cross-stacked metal oxide nanowire array material according to claim 6, wherein metal oxide nanowire materials, composed of different elements, with a high crystallinity and a high specific surface area, or bimetal or multi-metal composite oxide materials are synthesized by using different oxometallate hydrates as inorganic precursors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1A is a field emission scanning electron microscopy (FESEM) image of ordered cross-stacked metal oxide nanowire materials, where the metal oxide is Si—WO.sub.3;

[0017] FIG. 1B is a FESEM image of ordered cross-stacked metal oxide nanowire materials, where the metal oxide is P—WO.sub.3;

[0018] FIG. 1C is a FESEM image of ordered cross-stacked metal oxide nanowire materials, where the metal oxide is Si—MoO.sub.3;

[0019] FIG. 1D is a FESEM image of ordered cross-stacked metal oxide nanowire materials, where the metal oxide is P—MoO.sub.3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] Reagents

[0021] Polyethylene oxide monomethyl ether (PEO, molecular weight 5,000 g/mol), 2-bromoisobutyryl bromide, N,N,N′,N,′N″-pentamethyldiethylene triamine (PMDETA) were purchased from Acros. PEO5000 was dehydrated in a vacuum oven at 30° C. for 24 h, and stored in a desiccator for later use.

[0022] Silicotungstic acid hydrate (H.sub.4SiW.sub.12O.sub.40.xH.sub.2O), phosphotungstic acid hydrate (H.sub.3PW.sub.12O.sub.40.xH.sub.2O), and phosphomolybdic acid hydrate (H.sub.3PMO.sub.12O.sub.40.xH.sub.2O) were purchased from Aladdin. Silicomolybdic acid hydrate (H.sub.3PMO.sub.12O.sub.40.xH.sub.2O) was purchased from Sigma-Aldrich.

[0023] Styrene (St), pyridine, tetrahydrofuran (THF), anhydrous ether, petroleum ether (b. p. 60-90° C.), cuprous bromide (CuBr) and neutral alumina (200 mesh) were all analytically pure and purchased from Shanghai Chemical Reagent Limited company.

[0024] The neutral alumina was activated at 120° C. for 2 h, and placed in a desiccator to cool for later use. The St was filtered through a neutral alumina column to remove a polymerization inhibitor and stored at −15° C. for later use. After the CuBr was purified by glacial acetic acid, it was protected from light and stored for later use.

[0025] Preparation

EXAMPLE 1

Synthesis of Ordered Cross-Stacked Si—WO.SUB.3 .Nanowire Material

[0026] (1) 0.10 g of PEO-b-PS (M.sub.n=20,000 g.Math.mol.sup.−1) was dissolved in 5.0 mL of THF, and stirred to obtain a uniform solution A. 0.35 g of the silicotungstic acid hydrate (H.sub.4SiW.sub.12O.sub.40.xH.sub.2O) was dissolved in 2.0 mL of THF, and stirred to obtain a uniform solution B. Solution A and solution B were stirred together to obtain a pale blue transparent colloidal solution.

[0027] (2) The solution was transferred to a petri dish to volatilize at room temperature for 2 h. Then the petri dish was transferred to an oven at 100° C. to further evaporate the solvent and solidify for 24 h to obtain a transparent composite film. The composite film was scraped from the petri dish to obtain a yellow powder.

[0028] (3) The newly obtained sample was placed in a tube furnace to calcinate in nitrogen at 500° C. for 1 h by heating up at a rate of 1.0° C./min. The sample was calcinated in air at 450° C. for 1 h to obtain yellow green Si-W03 nanowire material.

EXAMPLE 2

Synthesis of Ordered Cross-Stacked P—WO.SUB.3 .Nanowire Material

[0029] (1) 0.10 g of PEO-b-PS (M.sub.n=21,000 g.Math.mol.sup.−1) was dissolved in 5.0 mL of THF, and stirred to obtain a uniform solution A. 0.30 g of the phosphotungstic acid hydrate (H.sub.3PW.sub.12O.sub.40.xH.sub.2O) was dissolved in 2.0 mL of THF, and stirred to obtain a uniform solution B. Solution A and solution B were stirred together to obtain a pale blue transparent colloidal solution.

[0030] (2) The solution was transferred to a petri dish to volatilize at room temperature for 2 h. Then the petri dish was transferred to an oven at 100° C. to further evaporate the solvent and solidify for 48 h to obtain a transparent composite film. The composite film was scraped from the petri dish to obtain a yellow powder.

[0031] (3) The newly obtained sample was placed in a tube furnace to calcinate in nitrogen at 450° C. for 1 h by heating up at a rate of 1.0° C./min. The sample was calcinated in air at 450° C. for 30 min to obtain a yellow green P—WO.sub.3 nanowire material.

EXAMPLE 3

Synthesis of Ordered Cross-Stacked Si—MoO.SUB.3 .Nanowire Material

[0032] (1) 0.10 g of PEO-b-PS (M.sub.n=18,000 g.Math.mol.sup.−1) was dissolved in 5.0 mL of THF, and stirred to obtain a uniform solution A. 0.25 g of the siliconiolybdic acid hydrate (H.sub.4SiW.sub.12O.sub.40.xH.sub.2O) was dissolved in 2.0 mL of THF, and stirred to obtain a uniform solution B. Solution A and solution B were stirred together to obtain a yellow transparent colloidal solution.

[0033] (2) The solution was transferred to a petri dish to volatilize at room temperature for 1 h. Then the petri dish was transferred to an oven at 100° C. to further evaporate the solvent and solidify for 24 h to obtain a transparent composite film. The composite film was scraped from the petri dish to obtain a blue powder.

[0034] (3) The newly obtained sample was placed in a tube furnace to calcinate in nitrogen at 350° C. for 2 h by heating up at a rate of 1.0° C./min. The sample was calcinated in air at 400° C. for 30 min to obtain a blue green Si—MoO.sub.3 nanowire material.

EXAMPLE 4

Synthesis of Ordered and Crossed P—MoO.SUB.3 .Nanowire Material

[0035] (1) 0.10 g of PEO-b-PS (M.sub.n19,000 g.mol.sup.−1) was dissolved in 5.0 mL of THF, and stirred to obtain a uniform solution A. 0.20 g of the phosphoomolybdic acid hydrate (H.sub.3PMO.sub.12O.sub.40.xH.sub.2O) was dissolved in 2.0 mL of THE, and stirred to obtain a uniform solution B, Solution A and solution B were stirred together to obtain a yellow transparent colloidal solution.

[0036] (2) The solution was transferred to a petri dish to volatilize at room temperature for 1 h. Then the petri dish was transferred to an oven at 100° C. to further evaporate the solvent and solidify for 48 h to obtain a transparent composite film. The composite film was scraped from the petri dish to obtain a blue powder.

[0037] (3) The newly obtained sample was placed in a tube furnace to calcinate in nitrogen at 350° C. for 2 h by heating up at a rate of 1.0° C./min. The sample was calcinated in air at 400° C. for 30 min to obtain a blue green P—MoO.sub.3 nanowire material.