A Novel Viologen‐Derived Covalent Organic Framework Based Metal Free Catalyst for Nitrophenol Reduction

Abstract

It is highly desirable to develop new metal free catalysts to reduction of toxic organic pollutants such as 4-nitrophenol (4-NP). Viologens are efficient electron-transfer mediators (ETMs) for reduction reactions with NaBH 4 as an effective hydrogen source. NaBH 4 -assisted reduction of 4-NP via a novel viologenbased covalent organic framework as metal free catalyst has been reported. The butyl bridge between the pyridine moieties at viologen based COF-TPCBP structure provides flexibility to the framework and gives the structure and amorphous character according to SEM, TEM and XRD results. The flexible 3D structure was also demonstrated by the geometric optimization. The structure without any metal moiety was fully completed to 4-NP reduction in only 12 minutes and have 88 % efficiency after 5 catalytic cycles because of the porous surface of the COF-TPCBP powder.

Boosting Photocatalytic Metal-Free Hydrogen Production of Viologen-Based Covalent Organic Frameworks

“…The carbazole in the repeating CBP units, which is the hole transport material, is responsible for the oxidation peak seen at approximately 1.0 V (vs Ag/AgCl) in the anodic scan of the CV measurements . Furthermore, the observed reduction–oxidation behavior in the cathodic scan of COF-MB-TPCBP, ranging around −0.8, is attributed to the radical cation of the viologen units in the structure . Here, the reduction and oxidation potentials of COF-MB-TPCBP demonstrate that it is suitable for the distance between the carbazole and viologen electroactive moieties for use in photocatalytic applications.…”

“…31 Furthermore, the observed reduction−oxidation behavior in the cathodic scan of COF-MB-TPCBP, ranging around −0.8, is attributed to the radical cation of the viologen units in the structure. 32 Here, the reduction and oxidation potentials of COF-MB-TPCBP demonstrate that it is suitable for the distance between the carbazole and viologen electroactive moieties for use in photocatalytic applications. Additionally, with a band gap value of 1.5 eV, a calculated highest occupied molecular orbital (HOMO) value of −5.47 eV, and a lowest unoccupied molecular orbital (LUMO) value of −3.97 eV with respect to standard hydrogen electrode (SHE), it indicates that the synthesized COF-MB-TPCBP is highly appropriate for the process of photocatalytic and photoelectrocatalytic hydrogen production (Table S1).…”

Enhanced Photocatalytic Hydrogen Evolution by Star-Shaped Viologen-Sensitized TiO2 Nanoparticles

“…The star-shaped viologen derivatives were synthesized in four steps (Figure S1). The tetra-pyridine functionalized bicarbazole compound (TPCBP) in the third step was prepared using the procedure described in our previous publication . In the final step, TPCBP-X compounds were obtained by refluxing in acetonitrile (ACN) in the presence of an excess amount of alkyl bromide, resulting in precipitation of the compounds in the reaction medium.…”

“…The tetra-pyridine functionalized bicarbazole compound (TPCBP) in the third step was prepared using the procedure described in our previous publication. 42 In the final step, TPCBP-X compounds were obtained by refluxing in acetonitrile (ACN) in the presence of an excess amount of alkyl bromide, resulting in precipitation of the compounds in the reaction medium. Characterization of the TPCBP-X was carried out using Fourier-transform infrared (FTIR) spectroscopy and 1 H NMR techniques, and the results exhibited successful synthesis of all compounds (Figures S2−S6).…”

Heterosporous Phenylpyridine-Based Covalent Organic Framework Microflowers for Highly Selective Sensing of Hydrogen Sulfide

“…In the recent literature, there have been reports on the rational design of COF nanomaterials with precise crystalline forms and consistent pore size distributions, aiming to enhance their characteristics and expand their potential uses . The enhancement of π-stacking interactions between layers of COFs and the manipulation of the stiffness or flexibility of the constituent monomers will have an impact on the crystalline structure of the resulting COFs. , Various kinds of well-defined crystallites, such as fabric fibers, belts, cubes, sheets, platelets, and spheres, are being created effectively for COFs. − Nevertheless, the occurrence of all-in-one COF microflowers possessing prospective characteristics has been scarcely documented in the literature.…”