At present, environmental pollution has become one of the most important concerns of mankind, especially organic pollutants.
Their damage to the environment such as water, atmosphere and soil will be damaged if they are not dealt with in time, and cause an irreversible loss. In recent years, photocatalytic degradation has become one of the most important methods for organic pollutants because of its high efficiency, environmental protection and easy operation.
As far as photocatalytic reaction is concerned, titanium dioxide TiO2 is one of the most studied semiconductors. This is due to its early application, cheapness, ease of handling, large specific surface area, and stability. Photocatalysis has attracted the most attention in the field of wastewater purification and treatment. But what can not be evaded is that TiO2 band gap is wider (about 3.2 e V), it can only be excited by ultraviolet light, the use of solar energy is limited, photoinduced electron recombination with hole is fast. it leads to low photon efficiency, which limits its practical application.
In recent years, phosphotungstic acid has been used as a kind of heteropoly acid type catalytic material, it has become a star because of its unique acidity, quasi - liquid behavior, multifunctional (acid, oxidation and photoelectric catalysis) and the strong absorption of polyoxometalates in the ultraviolet and visible regions. However, compared with TiO2, phosphotungstic acid has the disadvantage of being easily soluble in water, alcohol and acid liquid phase, so it is difficult to recover and reuse.
Titanium dioxide and phosphotungstic acid each has their own specialty, and each has its own characteristics. Try mixing the two together to see whether each of them brings advantages, therefore, some scholars will use sol-gel method to mix TiO2 and phosphotungstic acid. The mixing ratio is 1:0.05, and the process of mixing is as follows:
A certain amount of deionized water and 1/3 anhydrous ethanol were mixed into A solution, a certain amount of four butyl titanate, glacial acetic acid and phospho tungstic acid were added to the 2/3 anhydrous alcohol under a rapid stirring, and then B solution was prepared. Then A solution is slowly dripped into the B solution under rapid agitation, a uniform white solution is obtained. After the white gel is formed, the stirring is stopped, and the obtained colloid is dried for 12 hours at a constant temperature of 80°C. The ethanol on gel stone slowly evaporates, and white solid block is obtained. The white solid block turn into white powder after grinding, and put in the muffle furnace stone, the mixture powder of TiO2 and phosphotungstic acid was obtained at high temperature for a certain time.
What's the effect of mixing the two? Scholars use titanium dioxide and phosphotungstic acid mixed powder to degrade industrial dye wastewater methylene blue, it is concluded that TiO2 and phosphotungstic acid powder have photocatalytic adsorption effect on methylene blue, at the condition of 0.6g. L-1 catalyzer, and illumination time of 3.0, the decolorization rate of methylene blue reached 91.1%. After 4 times use, the photocatalyst still has high catalytic activity.
The test proved that TiO2 and phosphotungstic acid combines reached the expecting effect, the photocatalytic effect of titanium dioxide is enhanced, and the deficiency of the recovery and reuse of phosphotungstic acid is overcome. Another point can not be ignored, that is the price, the current market price is that phosphotungstic acid is 4.5 times the price of titanium dioxide, using phosphotungstic acid would be more luxury, combining the two not only reduces the cost, and also improves the photocatalytic performance, so it is a flexible and effective degradation of organic waste water price scheme.
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