Clew-like Cu₂O/CuO Microsphere Adsorbents for Highly Efficient Anionic Dye Removal

Adsorbents with high selectivity and adsorption capacity are of significant interest for the removal of dye pollutants. Herein, we report a facile low-temperature solvothermal synthesis of clew-like Cu₂O/CuO microspheres by using cupric acetate monohydrate as the copper resource and ethylene glycol as the solvent and morphology modulator. The synthesized Cu₂O/CuO microspheres showed high selective adsorption to anionic dyes (e.g., methyl orange (MO) and Reactive Red 2 (RR2)) rather than to cationic dyes (e.g., methylene blue (MB), Rhodamine B (RhB)). MO was then selected to evaluate the parameters of adsorption due to the adsorbent exhibiting the highest adsorption capacity for MO. We demonstrate that the adsorption of MO by Cu₂O/CuO microspheres has a good correlation with the pseudo-second-order model and Langmuir isotherm with a maximum adsorption capacity of 826.45 mg/g, which is higher than that of previously reported metal oxide material adsorbents. The excellent adsorption ability of clew-like Cu₂O/CuO microspheres to MO may be attributed to the synergistic effects of electrostatic attraction, unique hierarchical structure, and crystal defects of the prepared Cu₂O/CuO microspheres. We believe our work provides new insight into the synthesis of high-performance adsorbents.