Luminescent Metal–Organic Framework for Lithium Harvesting Applications

Abstract

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+ K SV 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.

Vibrational Paddlewheel Cu–Cu Node in Metal–Organic Frameworks: Probe of Nonradiative Relaxation

“…The wide chemical variety of MOFs results in the tunability of both their modular topologies and their physicochemical functions, which has accelerated the investigation of MOFs for various applications, including luminescence-based chemical sensing. However, developing luminescent MOFs in this context has been challenging due to the requirements for chemical sensors that aim to replace conventional sensors. − To date, four components yielding luminescence in MOFs have been elucidated: − (i) luminescent organic linkers that are typically π-conjugated, (ii) luminophores entrapped in MOF pores or bound to the external surface of MOF crystals, (iii) exciplexes formed by π–π interactions between adjacent conjugated linkers or between a conjugated linker and a guest molecule, and (vi) luminescent framework metal ions. Among these components, in particular, framework metal ions make a substantial contribution to luminescence depending on their electronic configurations and orbital energies, which are strongly associated with metal-to-ligand or ligand-to-metal charge transfer.…”

Room-Temperature Quantitative Quantum Sensing of Lithium Ions with a Radical-Embedded Metal–Organic Framework

“…It suggests that sensing with MgHOTP is reserved to Li + ions proximal to the pore surface, as would be expected given the fast decay of the radical– 7 Li hyperfine interaction with distance. Interestingly, the Langmuir behavior provides thermodynamic data that calibrate the strength of Li + adsorption onto MgHOTP: fitting the data to the above equation gives K eq = 49.5 ± 10.2 L/mol, consistent with a weak Li + –MOF interaction . Altogether, these results demonstrate that using CP-ESEEM with MgHOTP enables quantitative sensing of Li + ions in the range 5 × 10 –3 –0.5 mol/L under ambient conditions, a 2 orders of magnitude improvement over relaxometry.…”

“…Interestingly, the Langmuir behavior provides thermodynamic data that calibrate the strength of Li + adsorption onto MgHOTP: fitting the data to the above equation gives K eq = 49.5 ± 10.2 L/mol, consistent with a weak Li + −MOF interaction. 61 Altogether, these results demonstrate that using CP-ESEEM with MgHOTP enables quantitative sensing of Li + ions in the range 5 × 10 −3 −0.5 mol/L under ambient conditions, a 2 orders of magnitude improvement over relaxometry. CP-ESEEM and relaxometry are nevertheless complementary: their combination enables an effective quantum sensing range of 5 × 10 −3 −2 mol/L.…”

Room-Temperature Quantitative Quantum Sensing of Lithium Ions with a Radical-Embedded Metal‒Organic Framework

“…Interestingly, the Langmuir behavior provides thermodynamic data that calibrate the strength of Li + adsorption onto MgHOTP: fitting the data to the Langmuir model gives an adsorption equilibrium constant of 49.5 ± 10.2 L/mol, consistent with a weak Li + -MOF interaction. 55 Altogether, these results demonstrate that using CP-ESEEM with MgHOTP enables quantitative sensing of Li + ions in the range of 5 × 10 -3 mol/L -0.5 mol/L under ambient conditions, two-order of magnitude improvement over relaxometry. CP-ESEEM and relaxometry are nevertheless complimentary: their combination enables an effective quan- Crucially, the principles and methods above can be extended for the detection of other metal ions with nonzero nuclear spin and, by extension, should allow simultaneous detection of multiple metal ions that display distinguishable Larmor frequencies.…”