RU2469788C1 - PHOTOCATALYST BASED ON NANOSIZED η-MODIFICATION OF TITANIUM DIOXIDE - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: described is titanium dioxide-based catalyst, characterised by application of nanosized metastable η-modification of titanium dioxide with area of specific surface 4.5-16 m²/g as titanium dioxide.

EFFECT: increased photocatalytic activity.

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Description

The invention relates to a phase composition and a method for preparing a titanium oxide catalyst used primarily for the photocatalytic treatment of water contaminated with molecular impurities of organic origin.

Photocatalysts based on rutile and anatase modifications of titanium dioxide are known [Kazuhito Hashimoto, Hiroshi Irie, and Akira Fujishima, TiO ₂ Photocatalysis: A Historical Overview and Future Prospects, AAPPS Bulletin December 2007, Vol.17, No.6, 12-29]. However, the rates of decomposition reactions of organic substances with their participation are not high enough.

The best results for the decomposition of methyl orange using the industrial catalyst Degussa P25 (contains anatase and rutile in a ratio of 3: 1) were achieved at pH 3, an initial dye concentration of not more than 50 mg / l, a catalyst content of 0.8 g / l; Under these conditions, complete dye decomposition was achieved in 5 hours [Guetta N. N., Ait Amar H. Photocatalytic oxidation of methyl orange in the presence of titanium dioxide in aqueous suspension. Pan 1: Parametric study. // Desalination. 2005. V.185 No. 1-3. PP.427-437]. In the case of methylene blue, a degree of decomposition of 92.3% was achieved in 160 minutes using nanosized (22.5 nm) anatase at pH 2, a dye concentration of 0.20 g / l and a catalyst content of 1.5 g / l [Jun Yao and ChaoxiaWang, Decolorization of Methylene Blue with TiO ₂ Sol via UV Irradiation Photocatalytic Degradation, International Journal of Photoenergy, 2010, Volume 2010, Article ID 643182, 6 pages].

The closest technical solution is a photocatalyst based on the anatase modification of titanium dioxide with a particle size of less than 20 nm, processed in a mixture with a dye using ultrasound for 10 minutes; with a dye concentration of 0.2 mmol / l and a catalyst content of 0.4 g / l, complete decomposition of methyl violet was achieved in 75 min, methylene blue in 105 min, methyl red, rhodamine B, sudan blue and methyl orange in 120 min [Azarmidokht Hosseinnia, Mansoor Keyanpour-Rad and Mohammad Pazouki, Photo-catalytic Degradation of Organic Dyes with Different Chromophores by Synthesized Nanosize TiO ₂ Particles, World Applied Sciences Journal 8 (11): 1327-1332. 2010].

In the patent [United States Patent Application Publication. US 2006/0171877) describes a titanium dioxide based photocatalyst in which nanoscale η-modification of titanium dioxide with a crystal size of 10 to 50 Ǻ, a specific surface area of 290-320 m ² / g, and a pore volume of 0.36-0.40 cm is used as titanium dioxide ² / g and a surface hydroxyl content of about 2.7 mmol / g. The results of any studies of photocatalytic activity are not given in this patent.

The technical result of the invention is to increase the photocatalytic activity of titanium dioxide.

The technical result is achieved by using as a photocatalyst decomposition of organic dyes in a wide range of pH values (1-8) at a dye concentration of 0.33-1.04 mmol / L and a catalyst content of 2.5-5 mmol / L of titanium dioxide of nanoscale η-modification, which differs from previously used metastability (Fig.7, 8), smaller particle size (8-14 nm), as well as greater hydration and hydroxylation of the surface, compared with the prototype (Fig.8, 9). The content of surface hydroxyl groups is more than 3 mmol / g (Fig. 8, 9).

Nanoscale η-modification of titanium dioxide (η-TiO ₂ ) was obtained by the method described in [United States Patent Application Publication. US 2006/0171877], in order to more fully precipitate titanium dioxide and improve its photocatalytic properties, powdered titanium (IV) oxysulfate solvated with water and sulfuric acid (TiOSO ₄ · xH ₂ SO ₄ · yH ₂ O) was mixed with water at mass the ratio of TiOSO ₄ · xH ₂ SO ₄ · yH ₂ O: H ₂ O = 1: (3.5-6.5), temperature 75-97 ° C, and a solution of potassium chloride with its content of 1.5 was used as a coagulant -4 mol / L in the final volume of the reaction mixture.

The phase composition and size of crystallites (regions of coherent scattering) in the obtained samples were monitored by the traditional X-ray diffraction method (Fig. 1, Table 1), the size of nanoparticles - by the small-angle X-ray scattering method, morphology - by scanning methods (Fig. 2) and transmission electron microscopy with electron diffraction (FIG. 3), microstructure characteristics — by the Brunauer-Emmett-Teller method, the content of surface groups —OH — by differential scanning calorimetry (FIGS. 8, 9).

Characteristics of samples with nanoscale η-modification of titanium dioxide:

Table 1 X-ray data d, Ǻ (interplanar distances) I,% (relative intensity): 18.86 60 3.526 one hundred 2.711 fifteen 2.365 10 1.877 thirty

Crystallite size (coherent scattering region): 3-6 nm

Nanoparticle Size: 8-14 nm

Microparticle Size: 200-300 nm

Specific surface: 4.5-16 m ² / g

Pore volume: 0.001-0.03 cm ³ / g

The content of surface groups-OH: 10-21 mmol / g

The examples show the results of photocatalytic decomposition using η-TiO _{2 of} such compounds as organic dyes methyl orange, methylene blue and xylenol orange under the influence of UV radiation (UV-B-4 irradiator, λ = 250-400 nm, E = 3.11-4.97 eV, the volume of the reaction mixture was 50 ml, the irradiation area was 0.09 m ² , and the reaction mixture was constantly mixed) (Table 2).

The complete decomposition of methyl orange occurs in 70-110 minutes, methylene blue - in 115-180 minutes without preliminary treatment of the reaction mixture and 60-95 minutes after sonication (figure 4). The reaction rate constant does not decrease when reusing η-TiO ₂ samples (FIG. 5). It was found that the photocatalytic activity of η-TiO ₂ samples increases sharply with increasing pH of the medium in the reaction mixture (Fig.6). In a wide pH range, the photocatalytic activity of η-TiO ₂ samples is significantly higher than the previously described photocatalysts (Table 2, Fig. 6).

Example 1

Powdered titanium dioxide η-modification is mixed with a 1.04 M solution of methyl orange indicator with a mass content of η-TiO ₂ equal to 0.4 g / l, and the pH of the reaction mixture is 2-3, stirred with a magnetic stirrer for 30 minutes, then, without stopping mixing, irradiated with a UV lamp for 60 min until the chromophore group is completely destroyed, determined by the disappearance of the absorption peak at a wavelength of 492-510 nm. The decomposition reaction rate constant is 0.077 min ^-1 .

Example 2

Powdered titanium dioxide of η modification is mixed with a 0.33 M solution of methylene blue indicator with a mass content of η-TiO ₂ equal to 0.4 g / l, and the pH of the reaction mixture is 2-3, it is dispersed with ultrasound for 3 min, then, with stirring, irradiated with UV -lamp for 85 min until the complete destruction of the chromophore group, established by the disappearance of the absorption peak at a wavelength of 620-650 nm. The decomposition reaction rate constant is 0.017 min ^-1 .

Example 3

Powdered titanium dioxide η-modification is mixed with a 0.33 M solution of methylene blue indicator with a mass content of η-TiO ₂ equal to 0.4 g / l, and the pH of the reaction mixture is 7-9, stirred with a magnetic stirrer for 30 minutes, then, without stopping stirring, irradiated with a UV lamp for 114 min until the chromophore group is completely destroyed, determined by the disappearance of the absorption peak at a wavelength of 620-650 nm. The decomposition reaction rate constant is 0.040 min ^-1 .

Example 4

Powdered titanium dioxide η-modification is mixed with a 0.66 M solution of methylene blue indicator with a mass content of η-TiO ₂ equal to 0.4 g / l, and the pH of the reaction mixture is 7-9, stirred with a magnetic stirrer for 30 minutes, then, without stopping stirring, irradiate with a UV lamp for 95 min until the chromophore group is completely destroyed, determined by the disappearance of the absorption peak at a wavelength of 620-650 nm. The decomposition reaction rate constant is 0.050 min ^-1 .

table 2 Photocatalytic activity of catalyst samples with η-TiO ₂ (k is the dye decomposition reaction constant: 1 - methyl orange, 2 - xylenol orange, 3 - methylene blue) Sample k, min ^-1 one 2 3 pH 2 pH 3.5 pH 5 pH 8 pH 3.5 pH 2 pH 3.5 pH 8 one 0.034 0.053 0 0.038 2 0.017 3 0.037 0.046 four 0.016 0 0.027 5 0.067 0.055 6 0.077 7 0.043 8 0.019 0.025 0 0.032 Degussa P25 (anatase: rutile ~ 3: 1) [1] 0.0142 0.0086 0.0026 0.0011 Hombikat UV-100 (anatase) [1] 0.0056 Anataz [2] 0.016 0.0014 Anataz [3] 0.0083 0.0095

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Claims (1)

A titanium dioxide-based photocatalyst, characterized in that nanoscale metastable η-modification of titanium dioxide with a specific surface area of 4.5-16 m ² / g is used as titanium dioxide.

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