The Science Behind Bismuth Vanadate: Properties and Applications

Bismuth vanadate is a bright yellow inorganic chemical, it does not contain heavy metal elements that are harmful to human body, it is an environmentally friendly low carbon metal oxidation substance. Bismuth vanadate has a variety of crystalline phases, different crystalline phases of bismuth vanadate have different properties and applications.

Development of bismuth vanadate

Yellow is a very eye-catching color, according to information, people are only the most sensitive to 400~700nm wavelength of light, and at the wavelength of 555nm, the human eye has the highest perception, and its hue is in the yellow-green zone. Therefore, where people need to be highly visible, such as traffic signs, cabs, telephone booths, lifting machinery, postal facilities, etc., are generally painted in a striking, single yellow color. And although lead chromium yellow occupies an unshakable position in the inorganic yellow pigment, it has never been widely promoted and applied because it is a pigment containing lead. In addition, in 1992, the EU legislation stipulated that all lead compounds and compounds containing not less than 0.5% lead are classified as hazardous, so the tendency of lead-free pigments for industrial paints is increasing. At the same time, the color of iron oxide yellow is not bright enough, and the price of organic yellow pigment with superior performance is too expensive or the performance of covering power and weathering resistance is not strong, people hope to develop a new yellow pigment with bright color, good performance, no lead and non-toxic. Bismuth yellow was developed in this context.

Low carbon properties of bismuth vanadate

In addition to its properties as a colorant, bismuth vanadate also has photocatalytic properties. When exposed to light from the sun and fluorescent lamps, bismuth vanadate can promote chemical reactions that can kill E. coli, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, viruses, etc. In addition, bismuth vanadate is also used in office or home environment to decompose organic compounds and toxic substances in the air, such as benzene, formaldehyde, ammonia, TVOC, etc., to play a role in air purification. Bismuth vanadate can not only accelerate the chemical reaction, but also can use the natural process, which does not cause waste of resources and additional pollution formation, which is in line with the development of low-carbon economy.

Crystal structure of bismuth vanadate

There are four known lattice structures of bismuth vanadate, which have different applications depending on the lattice results:

1. tetragonal crystals, which are scheelite type crystals and can be used as yellow pigment;

2. tetragonal crystals, which are zirconium silicate type crystals and are very light yellow in color;

3. orthocrystals, which are vanadate crystals, and the bismuth vanadate present in nature is brown;

4. monoclinic crystal, can be used as yellow pigment.

Application of bismuth vanadate

I. All kinds of yellow traffic signs.

II. Applicable to paint, ink additive

III. Used in automobile top coat, rubber products and plastic products coloring and other occasions with high performance requirements

IV. Because of its high environmental protection, non-toxic performance, bismuth vanadate can also be widely used in food, toys and other fields.

V. bismuth vanadate also has a broad application prospect in the field of photocatalysis.

Pigment properties of bismuth vanadate

Bismuth vanadate is one of the new pigments entering the field of pigments. The pigment is made of bismuth vanadate (BiVO4) as the basic coloring component, the color is a bright yellow with high saturation and greenish tone, the reflectivity of 580nm wavelength light is as high as that of cadmium yellow and chrome yellow, so it can replace cadmium yellow and chrome yellow directly without collocating organic pigments, which fundamentally solves the toxicity in the production and use of pigments. This will not only protect people's health, but also expand the scope of pigment use. The pigment has good light resistance, and is resistant to acid, alkali, various solvents and sulfur dioxide, and its heat resistance reaches over 200 degrees.

Photocatalytic properties of bismuth vanadate

BiVO4 is a non-TiO2-based visible-light semiconductor photocatalyst. biVO4 has three crystal structures, monoclinic scheelite, tetragonal zircon and tetragonal scheelite, among which, when tetragonal zircon can be converted to monoclinic scheelite structure under heating conditions (when heated to 670~670 K), monoclinic scheelite and tetragonal scheelite types can also be converted to each other (528 K). The tetragonal monoclinic phase BiVO4 has the highest visible light activity. BiVO4 with scheelite structure (monoclinic crystal system) exhibits excellent catalytic activity under visible light irradiation and has higher oxygen production activity than typical photocatalyst WO3 (forbidden band 2.8 eV), and the quantum efficiency at 450 nm can reach 9%. This has led to the increasing attention of BiVO4 research in the field of visible light catalysis.

Bismuth vanadate (BiVO4) as a new visible-light active catalyst can provide a large surface area and pore size, which facilitates the contact between the substrate and the active site of the catalyst. Therefore, bismuth vanadate (BiVO4) exhibits excellent photocatalytic performance. However, the poor adsorption properties of pure bismuth vanadate (BiVO4) and the difficulty in migration of photogenerated electron-hole pairs lead to its low photocatalytic efficiency, which limits its application. To overcome these obstacles, loaded metals or metal oxides can always enhance the photocatalytic activity of catalysts by separating photogenerated electrons from holes.

Preparation of bismuth vanadate

1. Aqueous solution precipitation method: Bi3+ and V5+ salt high purity solution will be generated under certain conditions Bi-V oxide-hydroxide colloid. Increase the temperature for crystallization to form precipitated crude pigment. Available phosphate or oxide coating to improve the performance.

2. Calcination method: a certain proportion of oxide with a small amount of accelerator. The dry colloid obtained above can be used instead of the parent, and the pigment crystals are formed by calcination above 600℃. Wash the soluble components with alkali.

Summary

As a new type of inorganic pigment, bismuth vanadate (BiVO4) is chemically inert and stable to ultraviolet light. No color bleeding and no migration. Its better durability and hiding power are usually used in applications with light and weather aging requirements.

As a new type of visible semiconductor material, bismuth vanadate (BiVO4) is able to absorb visible light. The development and research of BiVO4-based composite photocatalytic materials with efficient visible light activity is of great significance for improving solar energy utilization.