Highly Selective Separation of Rare Earth Elements by Zn-BTC Metal-Organic Framework/Nanoporous Graphene via In Situ Green Synthesis

Rare earth elements (REEs) are used widely in devices of many fields, but it is still a troublesome task to achieve their selective separation and purification. Metal-organic frameworks (MOFs) as an emerging porous crystalline material have been used for selective separation of REEs using the size-selective crystallization properties. However, so far, almost all MOFs cannot be used directly for selective separation of REEs in strong acid via solid-state adsorption. Herein, a zinc-trimesic acid (Zn-BTC) MOF is grown by solid synthesis in situ on ZnO nanoparticles covering nanoporous graphene for preparing Zn-BTC MOF/nanoporous graphene composites with strong acid resistance. The adsorption capacity of the resulting composites to REEs is highly sensitive to the ionic radius, which may be attributed to the fact that the REE ions coordinate with O to form a stable structure. The selectivity of Ce/Lu is approximate to 10,000, and it is extremely important that the selectivity between adjacent REEs (e.g., Nd/Pr) is as high as approximate to 9.8, so the composite exhibits the best separation performance so far. This work provides a green, facile, scale, and effective synthesis strategy of Zn-BTC MOF/nanoporous graphene, which is hopefully applied directly in the separation industries of REEs.

Automated summary

Rare earth elements are widely used in various devices, but achieving their selective separation and purification remains a challenge. Metal-organic frameworks (MOFs) have been utilized for selective separation of REEs, but most cannot be used for solid-state adsorption of REEs in strong acid. A new composite material was developed with the best separation performance for REEs.