We prepared novel ZnO nanoparticles (NPs) modified with humic acid (Zn-H), extractant of Walnut shell (ZN-W) and 1,5 diphenyl carbazon (Zn-C). Three modified nanoparticles (MNPs) were characterized by SEM, XRD, FT-IR spectra, and EDX analysis. The images showed that Zn-H, Zn-W, and Zn-C particles had mean diameters of about 52, 56, and 76 nm, respectively. We explored the ability of the MNPs for removing heavy metal ions (Cd2+, Cu2+, and Ni2+) from aqueous phase in single and multiple solutions. Based on the average metal removal by the three NPs, the following order was determined for single and multiple component solutions: Cu2+ > Cd2+ > Ni2+. We investigated the adsorption capacity of MNPs as a function of contact time, pH, and metal ions concentration (isotherm). Among different isotherm models, it was found that the Langmuir model showed better correlation with the experimental data than Freundlich model. Spectroscopic analyses such as SEM–EDX and saturation indexes have been investigated to study the mechanism of sorption of metal ions by MNPs. The high adsorption capacities of the MNPs shown from the results make them promising candidates for removal of the tested heavy metal ions.
