Zinc oxide quantum dots for textile dyes and real industrial wastewater treatment: Solar photocatalytic activity, photoluminescence properties and recycling process

•Zinc oxide quantum dots (ZnO QDs) were successfully prepared via a modified sol–gel method.•XRD and TEM proved the formation of high purity single phase of ZnO QDs prepared samples.•Quantum size has an interesting effect on photocatalytic activity processes by the fluorescent probe method.•The mineralization efficiency of real industrial wastewater carried out by sunlight for six months as a study case.•Recycle process for reusable of 8 times for ZnOQDs and nano ZnO prepared samples investigated and evaluated.