Photocatalysis Of Polyoxometalates For C.I.Reactive Orange 5 Solution Degradation

On the basis of review of the basic properties of polyoxometalates and the photocatalytic degradation progress of organic pollutants in water with polyoxometalates, the photocatalytic decomposition of C. I. Reactive orange 5 (abrreviated as KGN) with Keggin - type polyoxometalate of H3PW12O40 was investigated in a homogeneous solution with a 20W UV lamp and a 500W Xe arc lamp and natural sunlight. At the same time the kinetic effect factors on the reaction rate and the mechanism were studied in this paper. In addition, H4SiW12O40 and TiO2 were also employed as photocatalysts for the degradation of KGN. The difference of mineralization of KGN with these 3 photocatalysts was studied, too.The main results of experiment were as follows,The photocatalytic degradation reaction of KGN with H3PW12O40 in a homogenous solution can be described by Langmuir-Hinshelwood equation, the reaction was a pseudo-first-order at lower initial concentration( 30mg/L). And as the initial concentration went up, the order of the reaction was reduced from 1 to 0. The effects of all kinds of factors such as initial mass concentration, irradiation intensity, dosage of catalyst, initial pH value, H2O2, inorganic ions on the photocatalytic degradation KGN were investigated in details. Generally speaking the reaction manifested the first order with lower concentration and the zero order with higher concentration. For the different initial KGN concentration there was a diverse optimum amount of catalyst. When the pH value was smaller than 2 the rate of reaction was faster than that of pH>2. Under the given condition neither the system of H2O2/UV nor the system of H3PW12O40/UV were less efficenct than that of the system of (H2O2+ H3PW12O40)/UV for the photocatalytic degradation of KGN. The decolorization of KGN was diversly affecedt by the existence of inorganic ions(Mg2+, Ca2+, Mn2+, Al3+, Cu2+, Ba2+, NO3-, SO42-,PO43-, Cl-, CO32-). In respect of the efficiency of decolorization and mineralization of KGN, H3PW12O40 was comparable with TiO2 under the irradiationof UV lamp. Under the sunlight the KGN solution photocatalyzed withcould be biologically degraded although TiO2 was better than H3PW12O40 as thephotocatalyst. As for H4SiW12O40 the efficency of photocatalysis was the lowest.The photocatalysis degradation mechanism of KGN with H3PW12O40 was illustrated. It can be seen that there is synergistic effect between the oxidation of OH radicals and the direct photocatalysis of KGN with...