•Photocatalysts PbMoO4 and PbWO4 are prepared by the precipitation method.•Inorganic ions (SO42−, NO3−, NO2−, NH4+) are measured by ion chromatograph.•HO− can be detected by terephthalic acid indirectly which is generated in the above process.•1,4-Benzoquinone is not a satisfactory scavenger in all cases to capture O2−.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 (SO42−, 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.

This work presents the preparation and photocatalytic activity of BiOX (X = Cl, Br), it is feasible to prepare BiOX by the hydrolysis of BiX3 (X = Cl, Br). Both BiOCl and BiOBr show photocatalytic activity for the photodegradation of azo dyes (methyl orange and congo red) under the simulated sunlight. We have measured the HO generated in the above process by terephthalic acid indirectly. Both BiOCl and BiOBr have been characterized by XPS, DRS, SEM, TEM, XRD and ξ potential. XPS data indicate that the surfaces of the BiOX samples are covered by low amounts of adsorbed azo dye molecules or/and intermediates produced during the dye photodecomposition.Graphical abstractHighlights► It is very easy to prepare pure BiOX quickly and directly from BiX3 by the hydrolysis. ► BiOCl and BiOBr show photocatalytic activity. ► HO can be generated in the process of photocatalytic degradation of azo dyes by BiOX.