BACKGROUND: Organic dyes are extremely hazardous waste toxins because they can harm all living organisms as well as the environment. Among them, azo dyes are the most harmful, containing a non‐degradable azo group (NN); these dyes are highly hazardous for both humans and animals, even in low concentration. This research study aims to remove hazardous anionic azo dyes from aqueous solutions by a simple adsorption method using zinc oxide quantum dots (ZnO QDs) synthesized by a facile precipitation method. RESULTS: As synthesized, ZnO QDs were characterized by transmittance electron microscopy, atomic force microscopy, X‐ray powder diffraction, Fourier transform infrared spectroscopy, zeta potential and Brunauer–Emmett–Teller. The azo dyes Methyl Orange (MO), Congo Red (CR) and Eriochrome Black‐T (EBT) have been removed actively from an aqueous solution using the high adsorption characteristic of ZnO QDs. The results demonstrated that the adsorbent was efficient even at a low concentration at 0.05 g L−1. The maximum adsorption capacity of ZnO QDs at 27 ± 1 °C was 102.9, 124.3 and 60 mg L−1 for MO, CR and EBT, respectively, and all these results have been observed in just 30 min. A pseudo‐second‐order and Langmuir isotherm model satisfactorily suited the dye adsorption data and, up to three cycles, the ZnO QDs demonstrated outstanding reusability. CONCLUSION: ZnO QDs showed not only efficient removal of individual dyes but also simultaneous removal of azo dyes from mixture solution and proved to be an effective, eco‐friendly, low‐cost adsorbent for dye decontamination in wastewater. © 2022 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]