Aqueous-Phase Differentiation and Speciation of Fe³⁺ and Fe²⁺ Using Water-Stable Photoluminescent Lanthanide-Based Metal–Organic Framework

Abstract

Fe 2+ is vital to O 2 transportation and photosynthesis regulated by oxidases and reductases. On the other hand, Fe 3+ is detrimental due to its irreversible binding to O 2 . Hence there is a need for selective identification of Fe 3+ from aqueous systems in the presence of Fe 2+ . However, given their close chemical nature, it is not straightforward to differentiate them. Fe 2+ and Fe 3+ are typically sensed and differentiated using magnetic measurements, Mossbauer, X-ray absorption spectroscopy, or EXAFS, which are complex and equipment intensive techniques. In comparison, the fluorescence technique is advantageous in terms of time and accessibility. Although readily available lanthanide salts exhibit fluorescence, they are weak, and to serve as an optical probe, their luminescence has to be enhanced via ligand design. Hence we have designed a chromophoric ligand that can covalently bind to lanthanides and enhance its fluorescence intensity, and it binds selectively to Fe 3+ through its nitrogen centers. It detects Fe 3+ from low concentration (∼100 μM) aqueous solutions, with fast response time (<1 min) and with a detection limit of 3.6 ppm. Importantly, the Fe 3+ adsorbed MOF can be readily reactivated for the next cycle by merely washing with an aqueous ascorbic acid solution and can be used for multiple cycles without any appreciable loss in activity. This makes the Ln-MOF an environmentally benign, cost-effective, scalable, and recyclable probe.

Waste PET as a Reactant for Lanthanide MOF Synthesis and Application in Sensing of Picric Acid

“…Especially, luminescent lanthanide MOFs have received intense interest owing to their large Stokes shifts, high color purity, and long luminescent lifetime [5][6][7]. The combination of inherent luminescence properties, together with the porosity of lanthanide MOFs, is suitable for the sensing of chemicals [8][9][10][11][12][13][14] and temperatures [15,16].…”

Recent Advances in Nanocomposite Luminescent Metal-Organic Framework Sensors for Detecting Metal Ions

“…Remarkably, the fluorescence response was restored by reducing Fe 3+ to Fe 2+ by a simple chemical wash with ascorbic acid. [223] The Ti-based MOF, Ti 6 (μ 3 -O) 6 (μ 2 -OH) 6 (TCA) 2 (H 2 O)(DMF) 2 , exhibits highly efficient sensing of Fe 3+ ions at the nanoscale, reaching a detection limit of 63.8 nM with a strong binding affinity of 2.69 × 10 6 M −1. [240] Finally, the cluster {[Eu(L)(H 2 O) 2 ]•NMP•H 2 O}n, can detect Fe 2+ /Fe 3+ cations in different solvent systems with high selectivity and sensitivity over a wide linear range.…”

“…[222] Recently a chromophoric ligand (2,2′-((4carboxyphenyl)azanediyl)diacetic acid (H 3 CPADA)) that can covalently bind to lanthanides and enhance its fluorescence intensity was fabricated. [223] The obtained MOF was found to bind selectively to Fe 3+ through its nitrogen centers, where it detects Fe 3+ from low concentration (∼ 100 μM) aqueous solutions, with fast response time (<1 min), a detection limit of 3.6 ppm, and Ksv of 1.52 × 10 4 M −1. [223] Interestingly, a simple chemical wash with ascorbic acid reduces the Fe 3+ to Fe 2+ , which gets ejected out of the MOF, restoring the fluorescence, as presented in Figure 13.…”

“…[223] Interestingly, a simple chemical wash with ascorbic acid reduces the Fe 3+ to Fe 2+ , which gets ejected out of the MOF, restoring the fluorescence, as presented in Figure 13. [223]…”

Logic operation for differentiation and speciation of Fe3+ and Fe2+ based on two‐dimensional metal–organic frameworks with tunable emissions

“…Given the significant differences of the luminescent responses toward Fe 2+ and Fe 3+ , studies on the speciation of Fe 2+ and Fe 3+ were further carried out. It is well known that H 2 O 2 can oxidize Fe 2+ to Fe 3 + , [27] and the addition of H 2 O 2 in Fe 2+ solution leads to an obvious luminescence decrease with the generation of Fe 3+ in the detection system (Figures 2b and S10). Additionally, Fe 3+ can be reduced to Fe 2+ in the presence of ascorbic acid (AA).…”