Bismuth Tungstate-Expanded Graphite Lamellar Nanocomposites and Their Preparation

Bismuth tungstate (Bi₂WO₆) is a layered structure with dielectric, luminescent and ionized conductors. Bismuth tungstate has photocatalytic properties under visible light. Bismuth tungstate can photolysis water and photodegradation organic pollutants under visible light. Therefore, Bismuth tungstate has good application prospects in many related fields.

Expanded graphite sheet has strong adsorption capacity, good thermal stability, acid and alkali resistance, rheological property, filling property, and good ion exchange, salt resistance, gelation resistance, pulping and high temperature phase transformation functions. It is a promising carrier material. Bismuth tungstate loaded on expanded graphite sheet is also a good choice for composite materials. But at present, the application of expanded graphite sheet in China is still at a low level.

To solve the existing technical problems, some scholars have proposed a preparation method of bismuth tungstate-expanded graphite sheet nanocomposites. The specific process is as follows:

1.Samples were taken according to the mass ratio of scale graphite, concentrated sulfuric acid, hydrogen peroxide and potassium dichromate at 10:30:5:1. The samples were oxidized in a constant temperature water bath at 40 ~C for 12 hours, then nitric acid was added in the amount of 1:0.9 HNO₃ of scale graphite, and the second layer was intercalated. The expanded graphite was obtained by continuous reaction for 30 minutes, washing, drying and instantaneous expansion in a muffle furnace at 900 ~C.

2.Measure 0.17g bismuth nitrate dissolved in 50 ml deionized water and stir for 30 minutes to get white solution; then add 0.047g sodium tungstate to white solution, mix for 30 minutes to get white mixture solution, add 0.2g expanded graphite to the solution and stir for 10 minutes to get black turbid solution; put the above solution into 100 ml PTFE reactor. After the reaction, the lower layer of black precipitation was obtained, and the upper layer of clarified solution was obtained. The black precipitation was washed with deionized water and anhydrous ethanol, then dried at 80 C, and grinded to obtain bismuth tungstate/expanded graphite lamellar nanostructure composite.

It was found that the porous structure and strong adsorption properties of expanded graphite could transfer the conductivity of graphite to avoid the recombination of photogenerated carriers, thus improving the photocatalytic activity of bismuth tungstate-expanded graphite lamellar nanocomposites, thus maintaining the high photocatalytic efficiency of bismuth tungstate suspension system. Moreover, using expanded graphite as carrier not only can promote the effective dispersion of bismuth tungstate, but also can effectively reduce the particle size of a single bismuth tungstate particle. Compared with pure bismuth tungstate, the catalytic activity of the composite is greatly improved.

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