Adsorption of hazardous Cr(VI) on CoMnZnO nanomaterials: experimental and statistical approach

The removal of hexavalent chromium Cr(VI) from contaminated water remains a critical environmental challenge due to its high toxicity and carcinogenicity. In this study, a novel Co₃O₄–MnO₂–ZnO nanocomposite (CoMnZnONs) was synthesized via a co-precipitation method and evaluated as an efficient adsorbent for Cr(VI) removal. Structural and morphological characterization using HRTEM, SAED, EDS, XRD, and FTIR confirmed the formation of uniformly distributed, polycrystalline nanoparticles with an average size of 20–30 nm. Batch adsorption experiments demonstrated that adsorption performance is strongly influenced by pH, contact time, and adsorbent dosage, with optimal removal achieved at pH 4 and equilibrium attained within 60 min. Kinetic studies indicated that the adsorption process follows a pseudo-second-order model (R2 ≈ 1), suggesting a chemisorption mechanism. Isotherm analysis revealed a better fit with the Freundlich model (R2 = 0.9958), indicating heterogeneous multilayer adsorption. The maximum adsorption capacity was determined to be 294.11 mg/g, exceeding many reported adsorbents. Thermodynamic parameters confirmed that the process is spontaneous and exothermic. Statistical physics modeling further suggested a double-layer adsorption mechanism with multi-docking interactions. The adsorbent exhibited excellent reusability, retaining over 92% of its efficiency after five cycles. These findings highlight the potential of CoMnZnONs as a cost-effective and sustainable material for advanced wastewater treatment applications.