Photodegradation comparison for methyl orange by TiO2, H2O2 and KIO4.

The photodegradation of methyl orange in water by the catalyst TiO2 or the oxidants (H2O2, KIO4) or their combination (TiO2 + H2O2, TiO2 + KIO4) under UV light illumination is studied. During the above process, as far as the photodiscoloration degree of methyl orange is concerned, the effect sequence is KIO4 + TiO2 >> KIO4 > TiO2 + H2O2 > TiO2 > H2O2; as far as the photomineralization degree of methyl orange is concerned, the effect sequence is TiO2 ≈ TiO2 + H2O2 > H2O2 > KIO4 + TiO2 >> KIO4; as for the catalysis of TiO2, h+ plays more important role than HO·, the inorganic ions ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]) are generated, especially for the amount of [Formula: see text]. Active HO· is generated, we can measure HO· by terephthalic acid (TA) indirectly: TA reacts with HO· to form highly fluorescent product, namely 2-hydroxyterephthalic acid (TAOH).

Photocatalytic degradation of methyl orange by PbXO4 (X=Mo, W).

PbMoO4 and PbWO4 are prepared by the simple precipitation method in this work, they show the photocatalytic activities for the degradation of methyl orange in water under the UV light illumination. In the above photocatalytic degradation processes, methyl orange concentration decreases quickly, the total organic carbon (TOC) decreases slowly; inorganic ions (SO4(2-), NO3(-), NO2(-), NH4(+)) can be formed and measured by the ion chromatograph; the pH value in the systems decreases gradually; a small quantity of HO˙(-)·can be generated and measured by the terephthalic acid (TA) indirectly. In order to estimate the roles of active species during the above photocatalytic degradation processes, isopropanol, (NH4)2C2O4, and 1,4-benzoquinone as the scavengers for HO˙, h(+), O2˙(-) are introduced into the systems, respectively. Isopropanol and (NH4)2C2O4 are effective scavengers for active species HO˙ and h(+) respectively, but 1,4-benzoquinone is not a satisfactory scavenger in all cases to capture O2˙(-), at least in this work. At last, PbMoO4 and PbWO4 are characterized by nitrogen sorption, DRS, SEM, TEM and XRD.