Degradation of high-concentration Rhodamine-B using Cu-doped ZnO/Fe₃O₄ nanocomposites and assessment of its toxicity

This study was conducted to fabricate effective photocatalysts in the degradation of high concentrations of Rhodamine-B (RhB), to make the photocatalysts recyclable, and to determine the toxicity of the wastewater resulting from the degradation of RhB. Nanoparticles were synthesized by the hydrothermal method and magnetic nanocomposites by the thermal reflux method. The synthesized nanomaterials were characterized by SEM, EDX, Mapping, XRD, FTIR, UV-Vis, Zeta-potential, DLS, and bandgap energy analysis. The photocatalytic activity was performed under visible sunlight and in the presence of the variables of pollutant percentage, nanomaterial dose, pollutant concentration, and reaction time. Using 13 different groups, the toxicity of the synthesized nanomaterials, RhB and the resulting effluent was investigated through oxidative stress parameters and pathology of the liver, kidney, and testis tissues of the Syrian mice. The results showed that nanomaterials have a 1-100 nm diameter, high purity, and uniform distribution. Adding Cu dopant reduced the size of nanomaterials, reduced the bandgap energy, and increased their photocatalytic activity. The highest degradation efficiency of RhB, corresponding to 1.5 M% Cu doped ZnO and 1.0 M% Cu doped ZnO/Fe₃O₄, was 96, and 94 %, respectively. Using nanomaterials after four times decreased the photocatalytic activity of nanomaterials by 12-14 %. The highest toxicity was related to RhB group, then nanocomposites containing Fe₃O₄ followed by other types of nanomaterials. The toxicity of the dye decomposition effluent was lower than the group of pesticide toxins and nanomaterials. The difference in oxidative stress parameters between the studied groups was significant (p < 0.05). 1.5 M% Cu doped ZnO and 1.0 M% Cu doped ZnO/Fe₃O₄ had the highest photodegradation efficiency. The toxicity of the effluent resulting from the decomposition of RhB was lower than the toxicity of RhB itself.