RU2776582C1 - METHOD FOR OBTAINING PHOTOCATALYSTS ACTIVE IN THE VISIBLE RANGE OF THE SPECTRUM WITH NANOSCALE TITANIUM OXIDES WITH THE STRUCTURE OF ANATASE AND A MIXTURE OF ANATASE AND RUTILE DOPED WITH TRANSITION METALS (Ni, V, Ag, Cu, Mn) - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method for obtaining samples of nanoscale titanium dioxide with anatase structures or a mixture of anatase and rutile active in the visible range of the spectrum. The method consists in the fact that the reaction mixture is obtained by mixing and grinding powdered hydrated titanyl sulfate TiOSO₄×2H₂O, hydroperite (hydrogen peroxide clathrate with carbamide CO(NH₂)₂×H₂O₂) and salts of metal dopants V (VOSO₄×2H₂O), Ni (Ni(NO₃)₂×6H₂O, NiSO₄×7H₂O), Ag (AgNO₃), Cu (Cu(CH₃COO)₂), Mn (KMnO₄)), then the product is annealed at temperatures of 700-850°C for 1 h.

EFFECT: invention makes it possible to simplify the process of obtaining nanoscale titanium dioxide by reducing the number of stages and harmful reagents.

1 cl, 5 dwg, 6 ex

Description

The invention relates to a method for preparing nanoscale titanium dioxide with anatase structures or a mixture of anatase and rutile in different concentrations, doped with transition metals (Ni, V, Ag, Cu, Mn), used for photocatalytic purification of water contaminated with impurities of organic origin, under the action of visible radiation .

Of the three most well-known modifications of titanium dioxide (anatase, brookite, rutile), the most photocatalytically active under UV irradiation is nanosized anatase or a mixture of anatase and rutile [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; Hurum, DC, Agrios, AG, Gray, KA, Rajh, T. and Thurnauer, MC Explaining the Enhanced Photocatalytic Activity of Degussa P25 Mixed-Phase TiO ₂ Using EPR. The Journal of Physical Chemistry B. 2003. V. 107, Is. 19.PP. 4545-4549. doi:10.1021/jp0273934].

A method for producing a photocatalyst with a functional basis of nanoscale titanium dioxide with an anatase structure is described, which consists in preparing an aqueous solution of TiOSO ₄ with a concentration of 0.1-1.0 mol/l, followed by adding H ₂ SO ₄ to the solution to a final concentration of 0.15- 1 mol/l, hydrolysis of the reaction mixture under hydrothermal conditions at temperatures of 100-250°C for 0.5-24 h and drying the resulting suspension with titanium dioxide. The method allows to obtain a porous photocatalyst in the form of mesoporous particles with a high specific surface area, providing high photocatalytic properties [Zvereva I.A., Churagulov B.R., Ivanov V.K., Baranchikov A.E., Shaporev A.S., Missyul A.B. Method for producing a photocatalyst based on titanium dioxide. RF patent No. 2408427, 2009]. The obtained samples with mesoporous nanosized anatase exhibited photocatalytic activity (PCA) in UV light.

A known process for obtaining nanoscale anatase, including the stage of treatment of hydrated titanium dioxide TiO ₂ × n H ₂ O hydrogen peroxide in aqueous solution with the formation of Sol, which is then transferred to the gel at 50°C; the latter is dried at a temperature of about 100°C and the resulting xerogel is calcined at temperatures up to 1000°C [Etacheri V., Pillai S., Seery M., High temperature stable anatase phase titanium dioxide, Patent WO 2010/064225 A1]. The resulting nanosized anatase was characterized by crystallite sizes D = 50 nm (coherent scattering regions) and thermal stability up to 900°C. The disadvantage of this method is the need to preliminarily obtain TiO ₂ × n H ₂ O by hydrolysis of titanium tetrachloride TiCl ₄ , convert the resulting sol into a gel with further drying of the gel to obtain a xerogel.

A method for obtaining nanosized TiO ₂ with an anatase structure with high photocatalytic activity upon UV irradiation by hydrolysis of TiOSO ₄ is described in [Savinkina EV, Kuzmicheva GM, Obolenskaya LN, Efficient synthesis and properties of η-titania, Proceedings of the 2nd European Conference of Chemical Engineering, Puerto De La Cruz, Spain, December 10-12, 2011, 93-96].

The disadvantages of all methods for obtaining nanosized titanium dioxide with the anatase structure or a mixture of anatase and rutile from solution include the leaching of Ti ^VI ions into the solution and, as a result, a decrease in the yield of the finished product. Also, the disadvantage of the above and similar methods for producing titanium dioxide is the activity of the finished product only in UV irradiation, which requires the creation of additional sources of UV radiation.

The closest analogue of the claimed invention is a method for producing nanoscale titanium dioxide [Obolenskaya L.N. Savinkina E.V., Kuzmicheva G.M., Kopylova E.V. Method for producing nanosized titanium dioxide. RU Patent 2565193 C1] (anatase, rutile or a mixture of anatase with rutile), which consists of mixing dry reagents (titanyl sulfate dihydrate with carbamide adduct with hydrogen peroxide (hydroperite)) followed by annealing at a temperature of 600-1000°C for 1-60 min. Under these conditions, titanium dioxide is formed in the form of anatase, in some cases with an admixture of rutile. The highest PCA was achieved on samples obtained at an annealing temperature of 700–900°C for 1 hour, containing a mixture of ~97% anatase and 3% rutile. However, all obtained samples showed PKA (methylene orange, fungicide - propiconazole) only in the UV region of the spectrum.

For the preparation of photocatalysts based on titanium dioxide, active under visible light (including sunlight), metal doping is mainly used [Banerjee AN The design, fabrication, and photocatalytic utility of nanostructured semiconductors: focus on TiO ₂ -based nanostructures, Nanotechnology, Science and Applications 2011, 4, 35-65]. Usually, water-soluble salts of the corresponding doping ion (for example, Fe ^III , V ^IV , V ^V , Cr ^III , Ni ^II , Ag ^I ) introduced during the synthesis of titanium dioxide from titanium-containing precursors in aqueous or organic solvents are usually used as doping agents [P. Kokila, V. Senthilkumar, K. Prem Nazeer. Preparation and photocatalytic activity of Fe ³⁺ -doped TiO ₂ nanoparticles. Scholars Research Library, Archives of Physics Research 2011, 2, 246-253; M. Pelaez et. al. A Review on the Visible Light Active Titanium Dioxide Photocatalysts for Environmental Applications. Applied Catalysis B:Environmental . 2012. V. 125, pp. 331-349].

A known method of obtaining a photocatalyst based on titanium dioxide with an anatase structure doped with non-metals (C, N, S) [Police Anil Kumar Reddy, Pulagurla Venkata Laxma Reddy, Vutukuri Maitrey Sharma, Basavaraju Srinivas, Valluri Durga Kumari, Machiraju Subrahmanyam. Photocatalytic Degradation of Isoproturon Pesticide on C, N and S Doped TiO ₂ . J. Water Resource and Protection, 2010, 2, 235-244] by introducing into the reaction mixture during the hydrolysis of titanium isopropoxide thiourea in an amount of 5 wt% of the amount of titanium. When irradiated with sunlight (λ > 420 nm, 450 W), the decomposition of the isoproturonic herbicide is completed after 150 min (the volume of the reaction mixture is 50 ml).

The disadvantage of these methods is the need to remove by-products by washing with water, and, consequently, the subsequent separation of titanium dioxide from the liquid.

The technical result of the invention is to obtain photocatalysts based on nanoscale modifications of titanium dioxide with structures of anatase or a mixture of rutile anatase doped with metals (Ni, V, Ag, Cu, Mn), active when irradiated with visible light, including repeated use; simplifying the process of obtaining and reducing the amount of reagents used, reducing the stages and costs.

The technical result is achieved by mixing powdered reagents, hydrated titanyl sulfate TiOSO ₄ × 2H ₂ O with hydroperite (hydrogen peroxide clathrate with carbamide CO(NH ₂ ) ₂ × H ₂ O ₂ ) and with nitrates or acetates of metal dopants (Ni, V, Ag , Mn, Cu) followed by annealing at a temperature t _anneal =700-850°C (1 h).

Samples of nanosized titanium dioxide were obtained by mixing powdered titanyl sulfate dihydrate, metal nitrates or acetates (Ni, V, Ag, Cu, Mn) with carbamide clathrate with hydrogen peroxide, followed by annealing at a temperature of 700–850°C for 60 minutes. Under these conditions, predominantly nanocrystalline anatase or a mixture of nanocrystalline anatase and rutile is formed in different ratios depending on the nature of the dopant metal.

The phase composition of the samples was controlled by the traditional X-ray diffraction method (Figs. 1, 2). The samples were shown to contain anatase (2θ~25.3°, 37.8°, 48°; JCPDS No. 89-4921) or a mixture of anatase and rutile (JCPDS No. 89-8304) in various ratios, and X-ray amorphous hydrated titanium dioxide (HD) at 2θ ~11-13°. The variable composition of HD is reflected by the formula TiO _2-x (OH) _2x × y H ₂ O ( y ~1), which can be represented as hydrated Ti(OH) ₄ , acidic H ₂ TiO ₃ , H ₄ TiO ₄ , or anionic mixed ( TiO)(HSO ₄ ) _x (OH) _y phases [I. Vasilyeva, G. Kuz'micheva, A. Pochtar, A. Gainanova, O. Timaeva, A. Dorokhov, V. Podbel'skiy, New J. Chem , 2016, 40, 151-161]. To determine the average sizes of coherent scattering regions (D, nm), the Scherrer formula was used: D=Kλ/βcosΘ: λ is the wavelength, 2Θ~25° (for anatase) and 2Θ~27.5° (for rutile) β is the integral peak width, the empirical coefficient K was taken equal to 0.9. Standard deviation ±5%.

To control the amount of reactive oxygen species (ROS) formed on the surface of titanium dioxide nanoparticles (anatase, rutile), the chemiluminescence method was used (Fig. 3, 4) (Lum-5773 chemiluminometer) [SP Mulakov, PM Gotovtsev, AA Gainanova, GV Kravchenko , GM Kuz'micheva and VV Podbel'skii, J. Photochemistry & Photobiology A: Chemistry, 2020, 393, 1], using luminol (an indicator of ROS - ^• OH, ^• O ₂ ^- and H ₂ O ₂ ) under the action of visible radiation from a fluorescent lamp with a power of 45 watts. Chemiluminescence spectra were processed using a computer program [GM Kuzmicheva, VV Podbelsky and SP Mulakov, Certificate of state registration of a computer program no. 201866661169, 2018].

The photocatalytic activity of samples with nanosized titanium dioxide was controlled by the rate of photodecomposition in their presence of the systemic fungicide difenoconazole (C ₁₉ H ₁₇ Cl ₂ N ₃ O ₃ , [cis,trans-3-chloro-4[4-methyl-2-(1Н-1 ,2,4-triazol-1-yl-methyl)-1,3-dioxolan-2-yl-]phenyl-4-chlorophenylether]), used in agriculture as a seed dressing, against a wide range of phytopathogens. The initial concentration of the fungicide is 0.06 mmol/l, the concentration of nanosized titanium dioxide is 1 g/l. Photocatalytic reactions were carried out in a double-walled cylindrical glass reactor (to maintain a constant temperature of the photocatalytic reaction, 25°C, water was passed between the walls of the reactor). The photoreaction mixture was stirred on a magnetic stirrer at a constant rotation speed. A Camelion 26W mercury lamp (wavelength range 260–400 nm) was used as a source of UV radiation, and a Camelion 45W fluorescent lamp (>450 nm) was used as a source of visible radiation. The lamps were located 5 cm from the reactor. Prior to irradiation, the reaction mixtures were stirred in the dark for 1 hour. The concentration of organic pollutants in water was measured every 30 min on an Akvilon SF200 spectrometer.

Example 1 . Titanium precursor in the amount of 1.8 g TiOSO ₄ × 2H ₂ O (chemically pure, Sigma Aldrich, Germany) and 0.3 g Ni-containing precursor Ni(NO ₃ ) ₂ × 6H ₂ O (Ni ²⁺ content in the finished TiO ₂ equal to 11 mol%) was ground with 1 g of hydroperite (NH ₂ ) ₂ CO×H ₂ O ₂ (chemically pure, Sigma Aldrich, Germany) in a porcelain mortar for 4 minutes. The reaction mixture was annealed in air for 1 h at 850°C ( Ni-TiO ₂ -1 ). X-ray examination of the Ni-TiO ₂ -1 sample (Fig. 1) shows that it contains a mixture of nanosized rutile (~90%) with average crystallite sizes D=38.4(3) nm and anatase (~10%) with D= 26.5(2) nm with a small admixture of X-ray amorphous hydrated HD titanium dioxide. The reaction rate constant of the photocatalytic decomposition of difenoconazole in the presence of a sample of Ni-TiO ₂ -1 under UV and visible radiation, respectively, is equal to k=0.0063 min ^-1 and k=0.0086 min ^-1 (Fig. 5).

Example 2 . Titanium precursor in the amount of 1.8 g TiOSO ₄ × 2H ₂ O (chemically pure, Sigma Aldrich, Germany) and 0.2 g of the V-containing precursor VOSO ₄ × 2H ₂ O (the content of V ⁴⁺ in the composition of the finished TiO ₂ is 11 mol % ) was ground with 1 g of hydroperite (NH ₂ ) ₂ CO×H ₂ O ₂ (chemically pure, Sigma Aldrich, Germany) in a porcelain mortar for 4 minutes. The reaction mixture was annealed in air for 1 h at 700°C ( V-TiO ₂ ). X-ray examination of the V-TiO ₂ sample (Fig. 1) shows that it contains predominantly nanocrystalline rutile (99%) with an average crystallite size of D=52.1(1) nm with a trace amount of anatase (~1%) and X-ray amorphous HD. The V-TiO ₂ sample is inert in the reaction of photocatalytic oxidation of difenoconazole under UV and visible radiation (Fig. 5).

Example 3 . The titanium precursor in an amount _of 1.8 g TiOSO ₄ × 2H ₂ O (chemically pure, Sigma Aldrich, Germany) and 0.17 g ^AgNO ₃ ( _the Ag ) ₂ CO×H ₂ O ₂ (chemically pure, Sigma Aldrich, Germany) in a porcelain mortar for 4 minutes. The reaction mixture was annealed in air for 1 h at 700°C ( Ag-TiO ₂ ). X-ray examination of the Ag-TiO ₂ sample (Fig. 1) shows that it contains a mixture of nanocrystalline anatase with average crystallite sizes D=25.8(3) nm and ~8% Ag ₂ O (2θ~28, 47, 68; JCPDS 42-0874) with a small admixture of X-ray amorphous HD. The reaction rate constant of the photocatalytic decomposition of difenoconazole in the presence of a sample of Ag-TiO ₂ under the action of visible radiation was k=0.0046 min ^-1 (Fig. 5).

Example 4 . The titanium precursor in an amount of 1.8 g TiOSO ₄ × 2H ₂ O (chemically pure, Sigma Aldrich, Germany) and 0.16 g KMnO ₄ (the content of Mn ⁷⁺ in the composition of the finished TiO ₂ is 11 mol%) was triturated with 1 g of hydroperite (NH ₂ ) ₂ CO×H ₂ O ₂ (chemically pure, Sigma Aldrich, Germany) in a porcelain mortar for 4 minutes. The reaction mixture was annealed in air for 1 h at 700°C ( Mn-TiO ₂ ). X-ray examination of the Mn-TiO ₂ sample (Fig. 2) shows that it contains a mixture of nanocrystalline anatase with average crystallites D=26.4(3) nm and ~12% MnO ₂ (2θ~28°, 35°; PDF 44- 0141) with a small admixture of X-ray amorphous HD. The reaction rate constant of the photocatalytic decomposition of difenoconazole in the presence of a sample of Mn-TiO ₂ under the action of visible radiation was k=0.0071 min ^-1 (Fig. 5).

Example 5 . A titanium precursor in an amount of 1.8 g TiOSO ₄ × 2H ₂ O (chemically pure, Sigma Aldrich, Germany) and 0.18 g Cu(CH ₃ COO) ₂ (the content of Cu ²⁺ in the composition of the finished TiO ₂ is 11 mol%) was ground with 1 g of hydroperite (NH ₂ ) ₂ CO×H ₂ O ₂ (chemically pure, Sigma Aldrich, Germany) in a porcelain mortar for 4 minutes. The reaction mixture was annealed in air for 1 h at 700°C ( Cu-TiO ₂ ). X-ray examination of the Cu-TiO ₂ sample (Fig. 2) shows that it contains a mixture of nanocrystalline anatase with an average crystallite size of D=25.8(2) nm and ~5% rutile with a small admixture of X-ray amorphous HD. The reaction rate constant of the photocatalytic decomposition of difenoconazole in the presence of a Cu-TiO ₂ sample under the action of visible radiation was k=0.0090 min ^-1 (Fig. 5).

Example 6 . Titanium precursor in the amount of 1.8 g TiOSO ₄ × 2H ₂ O (chemically pure, Sigma Aldrich, Germany) and 0.28 g Ni-containing precursor NiSO ₄ × 7H ₂ O (the content of Ni ²⁺ in the finished TiO ₂ is 11 mol % ) was ground with 1 g of hydroperite (NH ₂ ) ₂ CO×H ₂ O ₂ (chemically pure, Sigma Aldrich, Germany) in a porcelain mortar for 4 minutes. The reaction mixture was annealed in air for 1 h at 700°C ( Ni-TiO ₂ -2 ). X-ray examination of the Ni-TiO ₂ -2 sample (Fig. 2) shows that it contains nanocrystalline anatase with D=20.0(2) nm with a small admixture of X-ray amorphous HD. The reaction rate constant of the photocatalytic decomposition of difenoconazole in the presence of a sample of Ni-TiO ₂ -2 under UV and visible radiation, respectively, is equal to k=0.0068 min ^-1 and k=0.0078 min ^-1 (figure 5).

Comparison of the chemiluminescence spectra with luminol, taken on the samples obtained in examples 1-3 (Fig. 3) and 4-6 (Fig. 4), indicates that the samples are active in the visible region of the spectrum and the amount of ROS (proportional to the area of the integrand in Fig. 3 and 4) decreases in the series of samples Ni-TiO ₂ -2 (example 6) → Ni-TiO ₂ -1 (example 1) → Ag-TiO ₂ (example 3) → Mn-TiO ₂ (example 4) → CuTiO ₂ (example 5) → V-TiO ₂ (example 2).

Claims (1)

A method for obtaining samples of nanosized titanium dioxide with anatase structures or a mixture of anatase and rutile active in the visible region of the spectrum, which consists in the fact that the reaction mixture is obtained by mixing and grinding powdered hydrated titanyl sulfate TiOSO ₄ × 2H ₂ O, hydroperite (hydrogen peroxide clathrate with carbamide CO(NH ₂ ) ₂ × H ₂ O ₂ ) and dopant metal salts V (VOSO ₄ × 2H ₂ O), Ni (Ni(NO ₃ ) ₂ × 6H ₂ O, NiSO ₄ × 7H ₂ O), Ag ( AgNO ₃ ), Cu (Cu(CH ₃ COO) ₂ ), Mn (KMnO ₄ )), then the product is annealed at temperatures of 700-850°C for 1 hour.

Images