Selective uptake of cationic organic dyes in a series of isostructural Co2+/Cd2+ metal-doped metal–organic frameworks.

Abstract We study adsorption behaviors of isomorphic metal-doped metal-organic frameworks in the field of dyeing wastewater treatment technology. Herein, a series of 3D isostructural Co2+/Cd2+ metal-doped metal-organic frameworks named compounds 1 – 5 were successfully synthesized under hydrothermal conditions and used in adsorbing and separation dyes. We demonstrate that dye molecules can be adsorbed on the external surface of the MOFs and their loadings can be tuned by adjusting the rate of the central metal atoms. We show that compound 5 crystals containing Cd2+ are selective adsorbent for pH, temperature, ionic strength responsive adsorption. Their adsorptive properties of cationic dyes in aqueous solutions are higher than that of neutral and anionic dyes. Our method of isomorphic metal-doped opens new possibilities to construct adsorption strength regulation systems for a wide range of applications and facilitates new efforts in environmental purification. Graphical abstract fx1 Highlights • Study on the effect of metal ions on the adsorption of dyes by isomorphic metal doping. We characterize the synthesized compounds, which adsorb a series of dyes (cationic, neutral and anionic dyes). • Some typical organic dyes such as Methylene Blue(MB), Methyl Violet(MV), Phenol Red(PR), Methyl Orange(MO) and Congo Red(CR) were selected as targeted models. For compounds 1 – 5 doped with different contents of metal, the adsorption amount of MV increased with the increasing content of Cd2+ which is in the frameworks. The compound 5 has maximum adsorption amount which can reach 5.93 mg g−1. • Compounds 1-5 have the adsorption capacity for cationic dyes, and the adsorption capacity for MV is better than MB. Compound 5 almost don't carry the neutral dye PR, while compound 5 hardly adsorb anionic dye, such as MO and CR. • We study many factors (pH, temperature, ionic strength)of the adsorption of dye on the compound 5. The experiment shows that the increase of temperature is beneficial to the adsorption in a specific range and the dye adsorption is better under alkaline conditions. • Compound 5 successfully adsorbed MV and MB from mixed dyes with removal percentages of 80% and 90%, respectively. it is stable in the solvent environment. The recyclability of compound 5 adsorbed MV which was investigated over five cycles, the fluctuation of the adsorption capacity was less than 5%. Perform correlation calculations between adsorption kinetics and thermodynamics. [ABSTRACT FROM AUTHOR]