Photocatalytic Properties of the MgHPO4•3H2O and MgKPO4•6H2O Phosphates

Magnesium double phosphates, MgHPO4 center dot 3H(2)O and MgKPO4 center dot 6H(2)O, isostructural with the minerals newberyite and struvite-K have been synthesized in powder form via coprecipitation. Ceramics with a relative density of similar to 76% have been prepared by cold pressing followed by firing. The highest sintering temperature was t(max) = 130 degrees C. Using optical diffuse reflectance spectroscopy of polycrystalline samples, we have determined their band gap and absorption energy. The absorption energy of MgKPO4 center dot 3H(2)O has been found to be 3.10 eV, and that of MgKPO4 center dot 6H(2)O, 3.13 eV, which corresponds to absorption in the 400- and 396-nm ranges, respectively. The specific surface area of the powder samples studied has been determined by static vacuum volumetry. The results are 7.35 and 17.082 m(2)/g for MgHPO4 center dot 3H(2)O and MgKPO4 center dot 6H(2)O, respectively. To assess the photocatalytic activity of the synthesized phosphates for the oxidation of aromatic hydrocarbons in the vapor phase, using toluene as an example, we used purpose-designed test chambers. In our tests, UV radiation and light in the visible spectral region were used. The results obtained on photocatalytic decomposition of toluene demonstrate high catalytic activity of the synthesized polycrystalline phosphates. In a 2-h experiment with the use of visible light and UV radiation, the concentration of the aromatic hydrocarbon decreased by 12.2 and 1.9% in the case of MgKPO4 center dot 3H(2)O and by 9.8 and 9.1% in the case of MgKPO4 center dot 6H(2)O. To assess the chemical stability of the phosphates, we have carried out hydrolytic tests of the pressed ceramics in distilled water at room temperature.