Luminescent Metal–Organic Framework for Lithium Harvesting Applications

We have synthesized a stable luminescent metal–organic framework (LMOF) through modification of an established Zr-based structure. The three-dimensional porous network of LMOF-321 represents a step forward in the development of robust, dual-ligand Zr-MOFs. This material is based on Zr6-nodes, which underlie chemically and thermally stable frameworks. LMOF-321 exhibits notable durability in diverse types of water samples (deionized, acidic/basic, seawater). The porosity, luminescence, and specific functionality from LMOF-321 establishes itself as a fluorescent chemical sensor and adsorbent for aqueous analytes. Studies have been implemented to analyze interactions of LMOF-321 with Li+ and other metals commonly found in water. The fluorescence intensity from LMOF-321 is responsive to Li+ at a parts per billion level (3.3 ppb) and demonstrates high selectivity for Li+ over other light metals, with detection ratios of 6.2, 14.3, and 44.9 for Li+/Na+, Li+/Ca2+, and Li+/Mg2+, respectively. These performances were maintained in ion-doped deionized and seawater samples, highlighting the potential of LMOF-321 for field applications. The Li+ KSV value for LMOF-321 (6549 M–1) sets the standard for LMOF sensors. ICP-OES reveals the selective adsorption of Li+ over other light metals, consistent with fluorescence measurements. LMOF-321 has a maximum uptake capacity of 12.18 mg/g, on par with lithium extraction materials. The adsorption data was fitted using Langmuir adsorption model with a high correlation factor (>0.999). XPS and FTIR studies provide insight to help understand the interaction mechanism between Li+ and LMOF-321, focusing on the bis(sulfonyl)imide functionality in the pillaring coligand. No other MOFs have been utilized for both the detection and extraction of Li+, rendering this work one step further toward more efficient harvesting procedures.