2019年4月22日星期一

How To Clean Up Herbicide Pollution by Strontium Tungstate

In recent years, photocatalytic degradation technology has been paid more and more attention to the treatment of environmental pollution.

Photocatalytic treatment of pesticide wastewater is considered to be an ideal method from energy consumption and effect. The tungstate photocatalyst is well received by people for its energy saving, high efficiency, easy operation, wide application range, thorough degradation of pollutants and no secondary pollution.

Herbicide pesticide is widely used, because of its rapid effect, easy to use, has played an important role in weed management, however, with the increasing mechanization of farming, excessive use of herbicides has also begun to remain in the arable land, causing environmental pollution. Studies have shown that herbicides can cause chronic damage to humans and animals through the food chain, showing potential carcinogenic and genetic mutations, which is by no means alarmist, and the harmless degradation of herbicide wastewater is imminent.

herbicide spraying image

According to the newspaper records, in order to solve the residual damage of the herbicide, people have used biochemical treatment method, wet oxidation, or activated carbon treatment. However, either the cost is too high, or the process is troublesome, moreover, the effect is low, it is really a big problem. In recent years, with the discovery of photocatalytic degradation technology, it is found that the phosphotungstic acid in the tungstate agent has a very good photocatalytic degradation effect, and the way is right, and the trouble will be swept away.

So, how can photocatalytic degradation of herbicides be done with strontium tungstate? Before using the herbicide, add a small amount of strontium phosphate to the herbicide, stir it, and then spray along with the herbicide. After the herbicide has reached the weeding effect, the residual agent in soil will soon degrade into harmless water molecules under the synergistic action of strontium and sunlight.

Some scholars have evaluated the effect of strontium tungstate as a herbicide, and a small amount of Fe3+ and natural zeolite have been added in the process. The results showed that the degradation efficiency of herbicide was highest by using strontium tungstate as photocatalyst, and almost 96.2% of the herbicide was achieved.

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Nano Tungstate Preparation by Sol-Gel Method

Sol-gel method is first used for glass and ceramic production, it refers to metal inorganic compounds, metal organic compounds or a mixture of the two under the action of surfactants.

The process of preparing tungstate by the process of sol-gel and drying, roasting and other heat treatment process. Modern sol-gel method is mainly used to prepare nano film coating, for example, in optical field, some kind of optical film (such as high reflectivity film, low reflectivity film and waveguide film) is often needed. Sol-gel method can prepare nano tungstate by controlling the temperature, colloid composition, particle size of precursor and pH value in liquid.

nano tungstate film image

The advantage of sol-gel method is that: 1. The chemical homogeneity is good. Because the sol is prepared by the solution in the process of sol-gel, the chemical composition between the colloidal particles and the colloidal particles is exactly the same. 2. High purity; 3. Particle size is less than 0.1 um. 4. This method can accommodate the insoluble fractions and pellet fractions, after gelation, insoluble components can be naturally fixed in the gel system.

In view of the above advantages, sol-gel method is widely used in industrial practice, and there are few manufacturers of tungstate using this method. For example, an enterprise using sol-gel method to prepare tungstate film, with six valence tungsten salt and other two valence metal salt as raw material, dissolved in solvents to form a homogeneous solution, the sol is formed by the hydrolysis reaction of solute and solvent, and then converted into gel by certain method. After drying, the dry gel is obtained, and then the nano tungstate powder is obtained by high temperature treatment. 

However, the solution-gel method also has some unavoidable defects such as the instability of the sintered spherical agglomerated granular material, the drying shrinkage, and so on. Therefore, no matter how many years the solution gel method has been applied, the scholars in China have been studying and improving it.

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Wastewater Nemesis -- Bismuth Tungstate

In recent years, photocatalytic degradation technology has been paid more and more attention to the treatment of environmental pollution.

Photocatalytic treatment of pesticide wastewater is considered to be an ideal method from energy consumption and effect. The tungstate photocatalyst is well received by people for its energy saving, high efficiency, easy operation, wide application range, thorough degradation of pollutants and no secondary pollution.

Bismuth tungstate is also a kind of tungstate. Since 1999, it has been reported that bismuth tungstate Bi2WO6 has photocatalytic activity after visible light radiation at wavelengths greater than 420 nm. Bi2WO6 can be excited by visible light and has a high catalytic activity under visible light due to its narrow bandgap width (about 2.7eV) and become a new addition to photocatalytic materials.

bismuth tungstate wastewater treatment image

Some scholars have found in the visible light response Bi2WO6 can effectively degrade harmful substances such as chloroform and acetaldehyde, it must known that chloroform and acetaldehyde are notorious toxic pollutants, which are stored in waste water. If they flow into rivers, lakes and seas, they can cause irreversible damage to the ecological environment. Fortunately, the study of Bi2WO6 photocatalytic materials opens up a new way for photocatalytic removal and degradation of organic pollutants such as chloroform and acetaldehyde, and has very important practical value in environmental purification.

In addition, bismuth tungstate is also used to degrade the trouble with methyl dye wastewater. Methyl orange, for example, is a complex dye compound of azo and quinone structures in acid and alkaline conditions, is hard to remove, but bismuth tungstate can neat and quick to cut the Gordian knot, the methyl orange degradation was obedient. It has been proved that under acidic pH value, Bi2WO6 is highly targeted to methyl dyes and can achieve almost 99% photocatalytic degradation efficiency.

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Zirconium Tungstate

Expansion and contraction is a common physical phenomenon.

However, there are some materials do not follow the routines, showing the opposite nature of the heat shrinkage, this phenomenon is called "negative thermal expansion", these materials are collectively referred to as negative thermal expansion materials.

In the industrial field, the traditional commonly used negative thermal expansion materials are aluminum, titanium, zirconium, synthetic resin, zirconium tungstate is ammonium paratungstate and zirconium oxychloride synthesis of products, it's a new kind of material with negative thermal expansion coefficients over conventional materials.

zirconium tungstate image

The study shows that zirconium tungstate ZrW2O8 is a kind of negative thermal expansion material with excellent properties, zirconium tungstate has cubic appearance at normal temperature. It has stable negative thermal expansion performance in the whole range of temperature range from 0.3 to 1050.0K, the negative thermal expansion coefficient can reach -9 x 10-6K-1 and is isotropic. This excellent property is the main reason why zirconium tungstate stands out from a variety of negative expansion materials.

Zirconium tungstate can be used either as heat shrinkable material or mixed with other materials to prepare composites with controllable thermal expansion coefficient or zero expansion, in industrial applications, it can reduce the mechanical fatigue, creep and microstructural changes caused by thermal stress and greatly improve the material properties. Therefore, it is widely used in microelectronic components, laser equipment, optical fiber communication, aerospace technology, engine components and precision machinery and other fields. In addition, zirconium tungstate has been added to the modified asphalt to solve the problem of low temperature cracking.

Preparation of zirconium tungstate is mainly based on ammonium paratungstate and zirconium oxychloride. The preparation methods include impregnation method, coprecipitation method, hydrothermal method, sol-gel method, hydrothermal method, all the methods have a common point, that is difficult to synthesize, high cost, which is currently restricting the development of zirconium tungstate material. When the problem can be satisfactorily resolved, the future will be limitless of zirconium tungstate.

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