Preparation Method of A Bentonite-Silver Phosphotungstate Catalyst

At present, with the rapid development of industrial technology, the water resources on which humans depend for survival are polluted to varying degrees. Water pollution has become an urgent problem for all countries in the world. The presence of pollutants in water, especially toxic organic pollutants, not only causes environmental pollution, ecological damage, but also seriously endangers human health. These organic pollutants include polycyclic aromatic hydrocarbons, polychlorinated biphenyls, pesticides, environmental interferons, dyes, and the like.

Silver phosphotungstate has attracted much attention due to its advantages of absorption of visible light, high catalytic activity, low cost, and non-toxicity. Further, silver phosphotungstate has a particularly high stability due to a Keggin structure having a heteropoly acid. However, low conversion efficiency limits its large-scale environmental applications.

The factors affecting the photocatalytic efficiency of silver phosphotungstate mainly include the utilization efficiency of light, the utilization efficiency of photogenerated electron-holes, stability, etc., and these factors are greatly dependent on the properties of silver phosphotungstate itself, such as crystal structure, Specific surface area, morphology and so on. It is believed that the synthesis of hollow structure silver phosphotungstate with large specific surface area, high crystallinity and high stability will be beneficial to improve the photocatalytic efficiency, which requires the addition of another substance.

Bentonite is a kind of clay rock with montmorillonite as the main mineral. It is a common catalyst carrier, but its general loading mechanism is to exchange catalytically active substances between bentonite layers through cation exchange. Silver phosphate is a solid salt, which is difficult to directly Implanted between layers of bentonite.

In order to achieve this goal, some scholars have provided a preparation method of a bentonite- silver phosphotungstate catalyst, and the method includes:

1) Weigh 2 to 2.4 mmol of silver nitrate, arrange it into a solution of 10 to 15 mmol/L, add dropwise dilute ammonia water to the solution, and shake while adding dropwise until the initial precipitate is completely dissolved, and a silver ammonia solution is obtained. ;

2) Weigh 20g bentonite, add to deionized water 80 ~ 100mL soak for 10 ~ 12h, add the silver ammonia solution to the soaked bentonite suspension, stir while adding dropwise, continue to stir after the addition is completed 3 ~ 4h, after the end of stirring, aging in water bath 80 ~ 85  C for 24h, after washing is finished 4 to 5 times, drying at 80 ~ 100 ° C, to obtain silver oxide pillared bentonite;

3) The obtained silver oxide pillared bentonite is added to 100-140 mL of absolute ethanol, and 1 to 1.5 mmol of phosphotungstic acid is added during stirring. After the phosphotungstic acid is dissolved, stirring is continued for 4 to 6 hours, and aging is 6 to 8 hours. After the aging, the mixture was washed with anhydrous ethanol for several times at 60 to 75 °C to obtain a bentonite-supported silver phosphotungstate catalyst.

The above method disperses the silver sulfide pillared bentonite in anhydrous ethanol, dissolves the phosphotungstic acid sufficiently, and restricts the movement of the silver ions. The phosphotungstic acid and the silver oxide react to form silver phosphotungstate, which is fixed between the bentonite layers to form The water is miscible with ethanol and does not remain between the layers of bentonite. Finally, the layer structure of bentonite is expanded by the Keggin structure of silver phosphotungstate, which expands the specific surface area, so that the inner surface area of  bentonite can adsorb more pollutants and improve the catalytic efficiency.

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