Study On Modification And Properties Of BiPO₄ Photocatalyst

BiP04 is a new type oxy-acid salt catalyst. It exhibits high photocatalytic activity because of its unique structure and has attracted more and more attention. Some articles have reported that BiPO4 showed higher photocatalytic activity than P25 in the degradation of pollutants. As BiPO4 is a wide band gap semiconductor, it does not show photocatalytic activity under visible light irradiation. This paper mainly researches the modification of BiPO4 by metal-doping and loaded on natural diatomite, its aim is to increase optical absorption performance and photocatalytic activity of BiPO4. Structures, properties and morphologies of samples are measured and analyzed by a variety of characterization methods, such as XRD, FTIR, SEM. Optimal preparation condition of BiPO4, effects of different metal ions with different concentration doping on structure and properties of BiPO4, effects of different preparation condition on structures and properties of BiPO4/diatomite are investigated in detail.(1) The synthetic method used to prepare BiPO4 is hydrothermal method. The effects of temperature, time on BiPO4 were researched. The result showed that the optimal condition:hydrothermal time was 24h and temperature was 180℃. Under this preparation condition, the crystal structure of the product is monazite-type structure and the morphology is mainly a rod shape. Put 0.1g BiPO4 synthesized under the optimal condition into the 100mL methyl orange solution with a concentration of 10mg/L and the suspension became colorless after 80min under UV light irradiation.(2) Three kinds of metal ions Cu, Fe, Sn were introduced into BiPO4 under the optimal condition with doping concentrations of 0.5%,1%,2%,5%. Cu doping and Sn doping caused a small red shift of optical absorption. Fe doping caused a shoulder peak in the absorption spectrum and the band edge of optical absorption expands to more than 400nm. But in the experiment of degrading methyl orange under UV light irradiation, the photocatalytic activity of doped BiPO4 was lower than that of undoped BiPO4. Besides, after doping Fe ion, the morphology changed from rod to irregular bulk and specific surface area increased. Specific surface area of 2%Fe-BiPO4 was 6.136m2/g.(3) BiPO4/diatomite was synthesized by hydrothermal method similarly and diatomite aerobic calcined at 600℃ was as carrier. By this way, only a small part of BiPO4 was loaded on the surface of diatomite. The result of absorption spectrum showed that the BiPO4/diatomite prepared under the condition that precursor pH was 0.7 and percentage of BiPO4 was 30 was better. In the experiment of degrading methyl orange, BiPO4/diatomite didn’t show photocatalytic activity no matter under UV light irradiation or visible light irradiation. Changing precursor pH and percentage of BiPO4 during BiPO4/diatomite preparation can’t increase the photocatalytic activity. Diatomite resulted in the catalyst deactivation.