Visible-Light-Activated Multilayered Photocatalyst And The Method Of Its Preparation

Abstract

Visible-light-active and photostable, multilayered materials and their preparation method based on surface-modified titanium(IV) oxide have been invented.

Claims

1. Preparation method of a visible-light-activated multilayered photocatalyst characterized in that: a) modifies the surface of titanium(IV) oxide in the form of powder or coating by impregnation with a modifier solution, where the modifier is an aromatic organic compound with at least two OH or COOH groups or a hexachloroplatinate(IV) ion, b) the protective layer of titanium(IV) oxide is applied on the modified material, where the known ALD or spin-coating techniques are used.

2. Method according to claim 1, characterized in that it uses crystalline titanium(IV) oxide with a structure of anatase or being a mixture of anatase and rutile structure.

3. Method according to claim 1, characterized in that stage a) is carried out in water or alcohol solution of the modifier of the 10.sup.4 mol/dm.sup.3 minimal concentration and the product of the modification is dried.

4. Method according to claim 1, characterized in that the organic compound is preferably an organic compound from the group encompassing a compound with formula I: ##STR00024## where: R.sub.1-R.sub.4 denotes H, saturated or unsaturated substituents, NH.sub.2, NH.sub.3.sup.+or SO.sub.3M, in which M denotes H.sup.+, K.sup.+, Na.sup.+, Li.sup.+, NH.sub.4.sup.+, and R.sub.5 i R.sub.6 denotes OH or COOH, ascorbic acid, 2,5-dihydroxyterephthalic acid, hexachloroplatinic acid, hematoxylin and bromopyrogallol red.

5. Method according to claim 1, characterized in that the organic is a compound selected from the group consisting of phthalic acid, 4-sulfophthalic acid, 4-amino-2-hydroxybenzoic acid, 3-hydroxy-2-naphthoic acid, salicylic acid, 6-hydroxysalicylic acid, 5-hydroxysalicylic acid, 5-sulfosalicylic acid, 3,5-dinitrosalicylic acid, 2,5-dihydroxyterephthalic acid, aurintricarboxylic acid, disodium salt of 1,4-dihydroxy-1,3-benzenodisulfonic acid, gallic acid, pyrogallol, 2,3-naphthalenediol, 4-methylcatechol,3-5-di-tert-butyl-catechol, p-nitrocatechol, 3,4-dihydroxy-1-phenylalanine (DOPA), catechol (Table 2), rutin and ascorbic acid.

6. Method according to claim 1, characterized in that stage b) uses alcoholates, preferably titanium(IV) isopropylate, as precursors for the synthesis of the protective layer.

7. Method according to claim 1, characterized in that application temperature of the layers is not higher than 150 C.

8. Method according to claim 1, characterized in that the mean thickness d of the external TiO.sub.2 layer is within the range of 1-20 nm.

9. Photocatalyst characterized in that it contains two, in principle parallel surfaces consisting of titanium(IV) oxide and an appropriate binding layer between them consisting of an aromatic organic compound with minimum two OH or COOH groups or hexachloroplatinate(IV) ion, where, preferably, the organic compound is one of the group encompassing a compound with formula I: ##STR00025## where: R.sub.1-R.sub.4 denotes H, saturated or unsaturated substituents, NH.sub.2, NH.sub.3.sup.+or SO.sub.3M, in which M denotes H.sup.+, K.sup.+, Na.sup.+, Li.sup.+, NH.sub.4.sup.+, and R.sub.5 and R.sub.6 denote OH or COOH, ascorbic acid, 2,5-dihydroxyterephthalic acid, chloroplatinic acid, hematoxilin and bromopyrogallol red.

10. Photocatalyst according to claim 9, characterized in that the organic compound is selected from the group encompassing: phthalic acid, 4-sulfophthalic acid, 4-amino-2-hydroxybenzoic acid, 3-hydroxy-2-naphthyl acid, salicylic acid, 6-hydroxysalicylic acid, 5-hydroxysalicylic acid, 5-sulfosalicylic acid, 3,5-dinitrosalicylic acid, disodium salt of 1,4-dihydroxy-1,3-benzenodisulfonic acid, gallic acid, pyrogallol, 2,3-naphthalenediol, 4-methylcatechol, 3-5-di-tert-butyl-catechol, p-nitrocatechol, 3,4-dihydroxy-1-phenylalanine (DOPA), catechol, 2,5-dihydroxyterephthalic acid, rutin, and ascorbic acid.

11. Photocatalyst, characterized in that it was prepared by the method according to claim 1.

Description

[0029] In order to aid understanding the essence of the invention as defined above, below examples are given and figures are attached.

[0030] FIG. 1 presents the structure of photocatalytic materials of TiO.sub.2 modified with surface protective layer.

[0031] FIG. 2 presents decrease in absorbance at =400 nm (absorption band of TiO.sub.2 surface complex with organic modifier) during irradiation (XBO-150, >435 nm) of materials in the powder form with or without TiO.sub.2 protective layer. A) K-9@P25, B) K-4@P25. Test details are described in example 4.

[0032] FIG. 3 presents increase in hydroxyterephthalic acid concentration during irradiation of terephthalic acid solution in the presence of materials in the powder form with or without the external protective layer A) K-9@N100, B) K-4@N100, C) K-9@P25, D) K-4@P25. Test details are described in example 5.

[0033] FIG. 4 presents changes in 4-chlorophenol concentration during irradiation in the presence of material in the powder form with or without the external protective layer. Test details are described in example 5.

EXAMPLE 1

Preparation of a Powder Form Visible-Light-Activated Photocatalyst With Protective Layer Deposited Using the ALD Technique

[0034] The starting substrates for the synthesis of materials are: [0035] not modified titanium(IV) oxide commercially available [0036] organic surface modifiers [0037] titanium isopropylate, deionized water

[0038] 0.2 g of commercially available TiO.sub.2 material was weighted (Evonik P25 or Hombikat N100). Than 1 ml of organic modifier solution from the group S (S-2, S-3, Table 1) or the group K (K-4, K-9, Table 2) prepared in 1 mmol/dm.sup.3 concentration of methanol was added into titanium(IV) oxide.

[0039] The substances were thoroughly stirred and then left to sediment for 24 h. After this time the supernatant liquid was collected from sediment and the sediment was flushed with water three times. Materials collected in the form of powders were air-dried. After drying, the powders were grinded using a mortar.

[0040] Every such prepared material was put into a crystallizer, which then was put into the reaction chamber of the ALD reactor (Picosun R-150).

[0041] The synthesis of the protective layer was performed using titanium(IV) isopropylate and deionized water as precursors. The precursors were administered in impulses every 0.2 second, sparging the system with nitrogen after each impulse for 3 seconds. The synthesis was finished after 300 cycles. The synthesis was carried out in the temperature of 150 C. The ready materials were air-dried.

EXAMPLE 2

Preparation of a Coating Form Visible-Light-Activated Photocatalyst on Glass Plate With Protective Layer Deposited Using the ALD Technique

[0042] The starting substrates for the synthesis of materials are: [0043] glass plates (basic microscope slides) [0044] not-modified nanocrystalline titanium(IV) oxide (anatase structure) in the form of colloidal water solution of particles smaller than 100 nm and surface modifiers.

[0045] The synthesis of coating on glass plates was carried out using the spin-coating technique from 5% w/w colloidal solution of titanium(IV) oxide. Application on a plate was performed at the speed of rotation of the plate of 8000 cycles/min. The plate was rotated for 30 seconds and, meanwhile, three times 200 ml of the colloidal solution were put into the reactor.

[0046] The plate was left to dry and then it was immersed in the solution of organic modifier of the S group (S-2,S-3, Table 1) or the K group (K-4,K-9, Table 2) prepared in the 1 mmol/dm.sup.3 concentration of methanol for 10 seconds. The plates were air-dried. Such prepared plates were put into the reaction chamber of the ALD (Picosun R-150) reactor. The synthesis of the protective layer was performed using titanium(IV) isopropylate and deionized water as precursors. The precursors were administered in impulses of 0.2 seconds, sparging the system with nitrogen after each impulse. The synthesis was finished after 300 such cycles. The synthesis was carried out in the temperature of 150 C. The ready materials were air-dried.

EXAMPLE 3

Preparation of a Coating Form of Visible-Light-Activated Photocatalyst on Glass Plate With the Protective Layer Deposited Using the Spin-Coating Technique

[0047] The starting substrates for the synthesis of materials are: [0048] glass plates (basic microscope slides) [0049] not-modified nanocrystalline titanium(IV) oxide (anatase structure), in the form of colloidal water solution of particles smaller than 100 nm and surface modifiers.

[0050] The synthesis of coating on glass plates was carried out using the spin-coating technique from 5% w/w colloidal solution of titanium(IV) oxide. Application on a plate was performed at the plate rotation speed of 8000 cycles/min. The plate was rotated for 30 seconds and, meanwhile, three times 200 ml of the colloidal solution were put into the reactor. The plate was left to dry and then it was immersed in the solution of organic modifier of the S group (S-2,S-3, Table 1) or the K group (K-4,K-9, Table 2) or the solution of hexachloroplatinic acid prepared in the 1 mmol/dm3 concentration of methanol for approx. 10 seconds. After drying, another layer of TiO.sub.2 was applied in an analogous manner, resulting in a modified TiO.sub.2 layer with a protective coating.

EXAMPLE 4

Photostability Tests of Powder Form of Materials With Protective Layer

[0051] Measurements of the photostability of powder materials modified by organic compounds from the K group (K-4, K-9, Table 2) with an additional protective layer deposited using the ALD technique were performed. An analogous test was performed for the same materials without the protective layer.

[0052] 20 mg of the tested material was added into 2 g of analytically pure BaSO.sub.4. The substances were thoroughly mixed and the resulting mixture was formed into a tablet.

[0053] Such a prepared tablet was put into a special holder designed for the analysis of diffuse-reflectance spectra and then irradiated for 30 min, recording diffuse-reflectance spectra of the sample every 5 min. Irradiation system consisted of a xenon illuminator XBO-150, a water filter with solution of copper(II) sulfate (cutting off radiation from the near infrared, >700 nm) and an upper flow filter tolerant for the irradiation in the range of >435 nm.

[0054] The sample was placed in the distance of 40 cm from the light source.

[0055] FIG. 2 presents changes in absorbance at =400 nm (absorption band of TiO.sub.2 surface complex with organic modifier) for samples of modified TiO.sub.2 with the protective layer and an analogous sample without it.

[0056] Samples protected with an additional TiO.sub.2 coating are characterized by a better photostability (lower degradation of the sensibilizer) than the analogous samples without it.

[0057] Results obtained are summarized in FIG. 2.

EXAMPLE 5

Photocatalytic Activity Tests of Powder Materials With Protective Coating

Variant 1. Photooxidation of Terephthalic Acid

[0058] Measurements of the photocatalytic activity of powder materials modified by organic compounds from the K group (K-4, K-9, Table 2) with an additional protective layer deposited using the ALD technique were performed. An analogous test was performed for the same materials without the protective layer.

[0059] Suspension of the material was prepared (1 g/dm.sup.3) in water solution of terephthalic acid (C=310.sup.3 mol dm.sup.3 TA, 0.02 mol dm.sup.3 NaOH).The suspension was put into a cylindrical cuvette of 5 cm diameter, capacity of 18 ml and with 1 cm optical path length. Such a prepared suspension was irradiated for 30 min (irradiation conditions as in example 4) collecting 1.5 ml of the sample every 5 minutes. The samples were filtered using a CME syringe filter with pores of 0.22 m in diameter. Hydroxyterephthalic acid results in the reaction of terephthalic acid with photogenerated hydroxyl radicals. The hydroxyterephthalic exhibits good emission properties.

[0060] The progress of reaction (increase in the product concentration) was monitored by recording the emission spectra of the collected solutions in the range of 320-600 nm (.sub.exc315 nm). Results were summarized in FIG. 3. Materials with the protective layer consisting TiO.sub.2 are characterized by a higher activity than materials without it.

Variant 2

Photodegradation of 4-Chlorophenol

[0061] Measurements were taken to assess the photoactivity of powder material modified by an organic compound from the S group (S-3, Table 1) and containing an additional protective layer deposited by the ALD technique.

[0062] An analogous test was performed for the same material without a protective layer.

[0063] Suspension of the material (1 g/dm.sup.3) in water solution of 4-chlorophenol (C=2.510.sup.4 mol/dm.sup.3) was prepared. The suspension was put into a cylindrical cuvette, 5 cm in diameter, capacity of 18 ml and with 1 cm optical path length.

[0064] Such a prepared suspension was irradiated for 30 minutes (irradiation conditions as in example 4), collecting 1.5 ml of the sample every 5 minutes. The samples were filtered using a CME syringe filter with pores of 0.22 m in diameter. The reaction progress was monitored with the use of a spectrophotometer by registering the disappearance of absorbance at a wavelength of =280 nm.

[0065] Results are summarized in FIG. 4. Materials with the protective layer consisting TiO.sub.2 are characterized by a higher activity than materials without it.