Multifunctional Zr-MOF Based on Bisimidazole Tetracarboxylic Acid for pH Sensing and Photoreduction of Cr(VI)

Abstract

Herein, a new luminescent zirconium MOF [Zr-BBI, BBI = 4,4′,4″,4‴-(1,4-phenylenebis(1H-imidazole-2,4,5-triyl))tetrabenzoic acid] was successfully constructed by a rationally designed functionalized bisimidazole tetracarboxylic acid ligand. Zr-BBI consists of eight-connected Zr 6 clusters and four-connected BBI ligands. The high connection mode must be responsible for the high stabilities of Zr-BBI in both acidic and basic systems. Apart from the high stability, the inherent bisimidazole units endow Zr-BBI with the traits of intense fluorescent emission as well as the protonation/ deprotonation behavior. Therefore, Zr-BBI could display a highly sensitive fluorescence response along with the varying pH values in the aqueous solutions and act as a pH sensing scaffold, especially in the pH value range from 4.6 to 7.12. Zr-BBI also shows good fluorescence detection performance toward Cr 2 O 7 2− at a low concentration with a high K SV value up to 6.49 × 10 4 M −1 . Moreover, by the utilization of Zr-BBI as a catalyst, Cr(VI) could be effectively photoreduced to Cr(III) in aqueous solution under visible light irradiation, in which the introduction of a hole scavenger (benzyl alcohol) could further significantly enhance the photocatalytic efficiency. Compared to that of the recently representative MOFs, the k value of the photocatalytic reaction over Zr-BBI is as high as 0.073 min −1 . With the consideration of the presented results, Zr-BBI can serve as a multifunctional platform for efficiently sensing and photoreducing Cr 2 O 7 2− in an aqueous system, which fully illustrates the feasibility that introducing specific functional groups in the framework of MOFs would enhance the related photocatalytic activity.

Application of Copper(II)–Organic Frameworks Bearing Dilophine Derivatives in Photocatalysis and Guest Separation

“…With the measurement of UV–visible absorption diffuse reflectance spectra (UV–vis DRS) (Figure S14) and Mott–Schottky curves, the energy band structure of the catalyst was explored. The band gap energy ( E g ) of Cu-MOF can be calculated by the Kubelka–Munk equation α h ν = B ( h ν – E g ) 1/2 , where α, B , h , and ν represent the absorption coefficient, the proportionality constant, Planck’s constant, and the light frequency, respectively. , The curve of (α h ν) with photon energy ( h ν) was fitted linearly (Figure a), and the gap band energy ( E g ) of Cu-MOF was calculated to be 3.29 eV. In addition, Mott–Schottky plot results based on different frequencies (1200 and 1500 Hz) further illustrate the intrinsic electronic properties of Cu-MOF.…”

Photoluminescence Quenching in Recyclable Water-Soluble Zn-Based Metal–Organic Framework Nanoflakes for Dichromate Sensing

“…Through formula 3σ/ K , we calculated the detection limit of the tested object to be 0.09 μM (where σ is expressed as the relative standard deviation of 10 blank measured values and K is expressed as the slope value between the concentration of the measured object and relative fluorescence intensity). Compared with some methods reported in the literature ,,− for the detection of Cr 2 O 7 2– , although the proposed method is not optimal, it still has certain advantages in the detection limit and linear range compared with most methods (Table S3). It can fully meet the requirements of measuring Cr 2 O 7 2– in actual water samples.…”

pH-Stable Luminescent Metal–Organic Frameworks for the Selective Detection of Aqueous-Phase FeIII and CrVI Ions

“…Recently, MOF-based luminescent sensors for the detection of targeted analytes are emerging because of their several advantages, i.e., ease of use, low operation cost, and very high sensitivity and selectivity. , The organic ligand used to construct the framework commonly contains aromatic or conjugated π moieties, making them promising luminophore candidates. − In addition, the metal components can also contribute to the photoluminescence (PL); for example redox-inert Zn II of d 10 , lanthanides, or various inorganic clusters are often involved. − Meanwhile, the mixed-ligand strategy has been widely used for the construction of multifunctional MOFs; however, developing luminescent MOFs using such a strategy have been rarely explored . Naturally, the luminescent properties of MOFs can potentially be deployed for real-world sensory applications. − The sensors based on MOFs have evidenced several advantages over other chemical sensors because their high selectivity, easy operability, fast response time, and recyclability. − As a result, a growing number of luminescent MOFs are prevalent in the literature, which manifests their excellent ability to sense various analytes including anions, cations, pH, small molecules, gases, and explosives. − …”