The observation of distinct hexagonal crystal formation in FESEM images suggests a controlled synthesis process, leading to the formation of well-defined nanostructures. The crystallite size ZnO, Zn1-xFexO, and Zn1-xCuxO nano-adsorbents were calculated at 31.98, 32.09, and 58.82 nm, respectively. The calculated crystallite sizes provide valuable information about the nano-scale dimensions of the adsorbents, which are crucial for their adsorption performance. The significant morphological changes observed post-synthesis, as revealed by UV-Vis analysis, highlight the dynamic nature of the nanoparticles and their interaction with the dye molecules. This suggests that the adsorption process may involve not only surface adsorption but also structural transformations in the nanoparticles. The identification of key parameters influencing the adsorption process (adsorbent dosage, dye concentration, temperature, time, and pH) provides a basis for optimizing the adsorption conditions and enhancing the removal efficiency. The observed spontaneity of the adsorption process, as indicated by the negative ΔG° values, suggests that the process is thermodynamically favorable. The kinetic studies, which revealed a pseudo-second-order adsorption mechanism, provide insights into the rate-limiting steps of the adsorption process. The excellent fit of the Temkin and Langmuir isotherm models suggests that the adsorption process involves both adsorbate-adsorbent interactions and monolayer adsorption onto a homogeneous surface. The adsorption capacities (qmax) were 24.21, 11.29, and 19.92 mg g−1 for ZnO, Zn1-xFexO, and Zn1-xCuxO nanoparticles, respectively. The variation in qmax values among the different nanoparticles suggests that the composition and structure of the nanoparticles play a crucial role in their adsorption performance. Overall, this research provides valuable insights into the synthesis, characterization, and application of metal oxide nanoparticles for dye removal. The findings suggest that these nanoparticles have the potential to be used as effective adsorbents for wastewater treatment.
