Synergistic dual-pyrazol sites of metal-organic framework for efficient separation and recovery of transition metals from wastewater

Separation and recovery of metal ions with high value from industrial wastewaters is of significance due to the shortage of metal resources. A stable Al-based metal-organic framework (MOF-303) was used to selectively capture Cu2+ from Cu2+/Ni2+ and Cu2+/Co2+ binary systems. Due to the unique chelation effect of dual-pyrazol sites that are distributed parallel with the direction of the 1D channel, MOF-303 exhibited simultaneously a large capacity towards Cu2+ (330 mg g−1) and high separation selectivity (6076 and 2662 for Cu2+/Ni2+ and Cu2+/Co2+ respectively). The optimal pH for separation was found to 3.0–5.5, and the separation equilibrium was achieved at 3–4 h. Further, the recovery of the metals especially for Ni2+ and the regeneration of MOF-303 were achieved through a designed process. The Cu2+ selective adsorption mechanism based on the synergistic dual-pyrazol sites in MOF-303 was analyzed via a combination of experimental method and theoretical calculation. In conclusion, this work not only demonstrates MOF-303 is a promising adsorbent for the separation and recovery of the metals, but also highlights the unique dual-pyrazol sites in MOFs that can boost metal ions separation and recovery.