CZ20012718A3 - Photocatalytically active composite and process for producing thereof - Google Patents

Abstract

The present invention relates to a photocatalytically active composite formed by magnetite coated on its surface with a layer of photocatalytically active titanium dioxide. The invented composite is prepared by hydrolysis of titanyl sulfate TiOSOi4 in water suspension of magnetite with urea at a temperature ranging from 80 to 100 degC and the obtained product is then dried at a temperature up to 120 degC. The composite makes it possible to easy separate the photocatalytically active titanium dioxide from the given medium by the action of magnetic field, for example when removing some organic compounds from water..

Description

Technical field

The present invention relates to a photocatalitically active titanium dioxide composite and to a process for its preparation.

BACKGROUND OF THE INVENTION

Both modifications of titanium dioxide (TiO ₂ ), anatase and rutile, consisting of small particles with a large specific surface area (of the order of hundreds of m ² g ^-1 ) show photocatalytic properties. Anatas at wavelengths below 385 nm and rutile below 410 nm. At these wavelengths, the respective titanium dioxide modifications are capable of cleaving organic bonds after adsorption of the light quantum. This brings new possibilities for their use eg in water purification. A technical problem is their difficult availability and also separation after use. These problems are solved by the present invention.

SUMMARY OF THE INVENTION

The object of the invention is a photocatalytically active composite, which according to the invention consists of a magnetite coated on the surface with a layer of photocatalytically active titanium dioxide. The composite is prepared by hydrolyzing titanyl sulphate (TiOSO ₄ ) in urea at 80-100 ° C in an aqueous magnetite suspension and drying the product to 120 ° C. The resulting product is preferably annealed up to 500 ° C. The magnetite-titanium dioxide composite thus prepared consists of agglomerates of primary magnetite particles coated with an anatase modification layer of titanium dioxide with a specific surface area of approximately 300 m ² g ^-1 , with a rising annealing temperature the specific surface area decreases (only 600 m ² is above 600 ° C ^{) 1} ) and the agglomerates are recrystallized. As the temperature rises, the anatase modification gradually becomes rutile. Using electron microscopy coupled to the EDAX analyzer using the element-based method. Mapping has been shown that TiO ₂ forms a layer on the surface of magnetite particles. The composite thus prepared allows easy separation of photocatalitically active titanium dioxide from the environment by a magnetic field, for example in the purification of water from certain organic compounds.

DETAILED DESCRIPTION OF THE INVENTION

The invention is further illustrated by the following examples.

Example 1

5g of 0.25 μκι magnetite in a 150 ml beaker was suspended in water by 25 kHz ultrasonic waves and added to a 51 beaker with four liters of distilled water, acidified with sulfuric acid, in which 30 g of titanyl sulphate (TiOSO ₄ ) was introduced. and 200 g urea. The solution was boiled under stirring and kept at this temperature until basic. The product was then decanted with water, filtered and washed again with water and dried at 120 ° C. The product obtained is a dark gray to black, very fine, fluffy powder with a specific surface area of 232 m ² g ^-1 and, according to X-ray powder diffraction, is an anatase modification of titanium dioxide with magnetite. According to SEM results, these are clusters of particles with EDAX analysis: 37.3% Ti and 17.8% Fe and 44.9% O.

Example 2

To a beaker of 51 liters with four liters of distilled water, acidified with sulfuric acid, and 30 g of titanyl sulfate and 200 g of urea, was added 1 g of magnetite treated as in Example 1. The solution was boiled under stirring and kept alkaline at this temperature. The product was then decanted with water, filtered and washed again with water and dried at 120 ° C. The product obtained is a light gray, very fine, fluffy powder with a specific surface area of 304 m ² g ^_1 and, according to X-ray powder diffraction, is an anatase modification of the oxide • * · · ~ ········· - J “··· Titanium dioxide with magnetite. According to the SEM results, these are clusters of rod-shaped particles with EDAX analysis: 38.7% Ti and 6.2% Fe and 55.1% 0.

Example 3

A beaker of 51 with four liters of distilled water, acidified with concentrated sulfuric acid, was charged with 3.45 g of ferric sulfate and 10 g of urea. The solution was kept at boiling point while stirring until the reaction was basic, and then 2.40g of ferrous sulfate and 10g of urea were added. After the solution was brought back to boiling, an aqueous ammonia solution was added until a black precipitate began. The reaction mixture was boiled under stirring for 30 minutes. Then the precipitated magnetite was washed by decanting and the volume of water was adjusted to four liters. Furthermore, 30 g of titanyl sulfate (TiOSO ₄ ) and 200 g of urea were added to the reaction mixture. The solution was brought to reflux with stirring and kept at this temperature again to the basic reaction. The product was then decanted with water, filtered and washed again with water on the filter and dried at 120 ° C. The product obtained is a light gray, very fine, fluffy powder with a specific surface of 307 m ² g -1 and according to X-ray powder diffraction, it is an anatase modification of titanium dioxide with magnetite. According to SEM results, these are clusters of spherical and rod-like particles with EDAX analysis: 49.5% Ti and 13% Fe and 37.5% O.

Industrial applicability

The photocatalitically active composite of the invention can be used, for example, in water purification.

Claims (3)

PATENT CLAIMS CLAIMS 1. A photocatalytically active composite comprising magnetite coated on a surface with a layer of photocatalytically active titanium dioxide. A process for the preparation of a photocatalitically active composite according to claim 1, characterized in that titanyl sulphate TiOSO _{4 is} hydrolyzed in urea at 80-100 ° C in an aqueous magnetite suspension and the product obtained is dried at a temperature of up to 120 ° C. The method of claim 2 wherein the dried product is annealed to a temperature of 500 ° C.