RhB-Embedded Zirconium–Biquinoline-Based MOF Composite for Highly Sensitive Probing Cr(VI) and Photochemical Removal of CrO₄^2–, Cr₂O₇^2–, and MO

Abstract

How to accurately detect and efficiently sweep Cr­(VI) from contaminated water has come into focus. Zirconium-based metal–organic frameworks (MOFs) play vital roles in water environmental chemistry due to excellent hydrolysis-resistant stability. However, as photochemical probes and photocatalysts, poor performances in detection sensitivity, selectivity, and photosensitiveness limit sole Zr-MOFs’ applications. So, it is urgent to quest valid strategies to break through the dilemmas. Embedding luminous dyes into MOFs has been considered one of the most feasible avenues. Herein, a dual-emissive RhB@Zr-MOF with orange-yellow fluorescence has been assembled by in situ-encapsulating rhodamine B (RhB) into a zirconium–biquinoline-based MOF. Actually, within RhB@Zr-MOF, the aggregation fluorescence quenching (ACQ) effect of RhB molecules was effectively avoided. Notably, RhB@Zr-MOF exhibits a rapid fluorescence quenching response toward Cr­(VI) ions with high selectivity, sensitivity, and anti-interference abilities. More interestingly, unlike the most widely reported fluorescence resonance energy transfer (FRET) between MOFs and encapsulated guest modules, photoinduced electron transfer from RhB to Zr-MOF has been confirmed by modeling the ground state and excited states of RhB@Zr-MOF using density functional theory (DFT) and time-dependent DFT (TD-DFT). The effective electron transfer makes RhB@Zr-MOF more sensitive in probing Cr2O7 2– and CrO4 2– ions with ultralow detection limit (DL) values of 6.27 and 5.26 ppb, respectively. Prominently, the detection sensitivity based on DL values has been increased about 6 and 9 times, respectively, compared with pristine Zr-MOF. Moreover, rather negative CB and positive VB potentials make RhB@Zr-MOF have excellent photochemical scavenging ability toward Cr­(VI) and MO.

Multifunctional In-MOF and Its S-Scheme Heterojunction toward Pollutant Decontamination via Fluorescence Detection, Physical Adsorption, and Photocatalytic REDOX

“…14 Metal−organic frameworks (MOFs) are novel porous solid materials self-assembled from metal nodes/clusters and diversified multifunctional organic connectors via powerful coordination bonding. 15−17 MOFs have attracted intensive attention due to the intriguing topological architectures, particularly versatile properties ranging from sensing, 18,19 capture, 20,21 and separation 22,23 to heterogeneous catalysis. 24−27 More recently, the assembly of high-performance MOFs for water environment monitoring and remediation has become a research focus.…”

A Tb3+-anchored Zr(iv)-bipyridine MOF to promote photo-induced electron transfer and simultaneously enhance photoluminescence ability and photocatalytic reduction efficiency towards Cr2O72−

“…11,12 Design of a versatile platform with highly sensitive uorescence detection and efficient photochemical removal capacity towards Cr(VI) ions thus has become a preferred research direction. 5,13 Metal-organic framework (MOF) materials are selfassembled from diversied organic units and metal nodes. MOFs provide a suitable platform to accommodate guest species and further adjust the properties by post-modication.…”

“…14,15 The photoluminescence of luminescent MOFs (LMOFs) is mainly caused by the aggregation-induced emission (AIE) effect of organic units, which leads to an increase in photoelectron ow. 13 LMOFs have been identied as potential candidates for uorescence sensing of various analytes, exhibiting a luminescence response (wavelength or intensity) to the interactions with the target analytes. 16 As the most usual phenomenon, the uorescence quenching response is oen caused by factors such as photo-induced electron transfer (PET) and uorescence resonance energy transfer (FRET).…”

“…17 Moreover, due to the organic-inorganic hybrid characteristics, a few LMOFs have been proven to generate sufficient negative conduction band potential or active species with suitable redox potential to reduce Cr( vi ) to Cr( iii ), under suitable light energy irradiation. 13 Nevertheless, since the dominant wavelength of UV light (around 365 nm) used to drive photocatalytic reactions often inevitably overlaps with the bands of excitation light deployed to excite aromatic ligands, strategies to achieve simultaneous enhancement of fluorescence sensing and photocatalytic reduction capabilities of MOFs have been rarely reported. And the smaller Stokes shift of most LMOFs makes the color difference between excitation and emission light indistinguishable to the naked eye.…”

“…11,12 Design of a versatile platform with highly sensitive fluorescence detection and efficient photochemical removal capacity towards Cr( vi ) ions thus has become a preferred research direction. 5,13…”