Zeolite and metal-organic frameworks (MOFs) as typical NPCs have been studied and show great potential in gas storage, catalyst, and electronic devices. Therefore, we synthesized holey polybenzimidazole (HPBI) which is well matched with theoretical structure via condensation reaction using two types of aminobenzenes as monomer. The structure of Holey polybenzimidazole from Tetraaminobenzene (HPBI-Tetra). a) Schematic representation of the condensation reaction between hexaaminobenzene and tricarboxylic acid in PPA.
The structure of Holey polybenzimidazoles from hexaaminobenzene (HPBI-Hexa). a) the condensation reaction between hexaaminobenzene and tricarboxylic acid in PPA. The optical images; a) Hexaminobenzene in PPA at room temperature, b) Change of color to light blue and addition of trimesylic acid after removal of HCl, c) high viscosity of black final product, d) black powder resultant of HPBI-H. Figure 9. a) FT-IR spectra by granular composite ground sample and dried potassium bromide (KBr). Red arrow indicated C=N and C-N peaks. b) XRD pattern of HPBI-T. Inset box shows location over high intensity area.
Cyclic voltammograms in acetonitrile containing a 0.1 M TBAPF6 solution at a scan rate of 100 mV/s; a) HPBI-T on glassy carbon electrodes and b) ferrocene under nitrogen. Cyclic voltammograms in acetonitrile containing a 0.1 M TBAPF6 solution at a scan rate of 100 mV/s; a) HPBI-H on glassy carbon electrodes and b) ferrocene under nitrogen.
Introduction
Therefore, many attempts have been made to solve such problems, so far many scientists like a prof. Another example of nanoporous materials are metal-organic frameworks (MOFs), which coordinate organic ligands with metal ions or clusters.8 After the In the 1990s, many scientists have investigated the unique structure and properties of MOFs. Covalent organic frameworks (COFs) are considered a new material by polymer scientists. In COFs, all connected components are linked by a covalent bond which is strong and stable compared to coordinated bonds in MOFs and zeolites.
In addition, COFs are based on diverse organic and polymer synthesis, and then two- and three-dimensional compounds can be easily produced by controlling organic reactions. Until now, many studies have been carried out on imidazole in one-, two-, and three-dimensional domains, 12 but polyimidazole-based polymers with regular holes are still not well known. Here, we prepared 2D imidazole-based covalent organic frameworks with regular holes, called holey polybenzimidazoles (HPBIs).
Based on amine monomer, the hole size is different and the reactants are divided into HPBI-T (from 1,2,4,5-tetraaminobenzene) and HPBI-H (from hexaaminobenzene). We expected different properties between HPBI-T and –H; 1) gas absorptivity, 2) the size of the band gap. It is evidence from different gas absorptivity that Yaghi's group has reported that different hole sizes lead to trending absorbance of hydrogen, methane and carbon dioxide, respectively.13 Furthermore, graphene-like structure shows prominent band-gap electrical properties due to delocalization of electrons. movement by regularly placed hole in the structure.
Experimental section
- Materials
- Instrumentations
- Preparation of 1,5-dichloro-2,4-dinitrobenzene
- Preparation of 1,5-diamino-2,4-dinitrobenzene
- Preparation of 1,2,4,5-tetraaminobenzene (TAB)
- Synthesis of Holey-polybenzimidazole from TAB (HPBI-T)
- Synthesis of Holey-polybenzimidazole from HAB (HPBI-H)
The result was filtered several times with hot ethanol and water to purify the compound with poor solubility. The resulting solution was filtered into concentrated HCl (concentrated HCl or 37% HCl), which was at the bottom under reduced pressure above celite, to eliminate the Pd/C catalyst. The obtained powder was recrystallized with a mixture of water and concentrated HCl as solvent under nitrogen (N2) to prevent oxidation of amine.
Hole polybenzimidazole of TAB was prepared using TAB and trimesic acid (or 1,3,5-benzenetricarboxylic acid, TCB) as monomer in 30 g of polyphosphoric acid (PPA, 83 % P2O5 assay) in resin flask under nitrogen atmosphere with high torque mechanical stirrer The result was precipitated in D.I water and extracted with water in Soxhlet for 2 days and methanol for 3 days to purify from acidic solvent and unreacted monomer as well as small molecular impurities. For synthesis of hole-polybenzimidazole from Hexaaminobenzene (HAB), HAB was placed with a high torque mechanical stirrer with PPA as a solvent in resin flask under nitrogen inlet and.
To remove the HCl used for reducing the amine reactivity, the medium was stirred at R.T and 50 °C for 12 h and 12 h until the color of the mixture became transparent blue. Then the black result was poured into the D.I water to make the precipitate and washed using Soxhlet extractor with water and methanol for 2 and 3 days, respectively.
Results and Discussion
Synthesis of 1,2,4,5-tetraaminobenzene (TAB)
Photographs; a) 1,5-dichloro-2,4-dinitrobenzene after recrystallization, b) 1,5-diamino-2,4-dinitrobenzene with a washing process to completely remove impurities, and c) recrystallized TAB.
Polybenzimidazole
Synthesis of Holey-polybenzimidazole
Different hole sizes lead to different properties such as the following results (specific surface area, band gap). Similar results by Yaghi's group show that the diverse structure based on boron-based COFs has different hole sizes and affected the gas absorption ability without reference to different gases. 13 Since HPBIs have many nitrogen components in the imidazole ring, they can be used for many applications. , such as catalysts, sensors and electronic devices. For example, nitrogen has the ability to withdraw electrons with an electronegativity of 3.0 on the Pauling scale and can act as an active site for the reaction.
The optical images; a) Hexaminobenzene in PPA at room temperature, b) Change of color to pale blue and addition of trimesic acid after removal of HCl, c) high viscosity of black final product, d) black powder resultant of HPBI-H.
Elemental analysis
The structure of HPBIs is characterized through quadruple transform infrared spectroscopy (FT-IR), powder X-ray diffraction pattern (PXRD or XRD), and thermogravimetric analyzer (TGA). Although the trends of HPBIs are similar, here is the difference in the 3500-3000 cm-1 region due to the amount of limited water. This phenomenon comes from the following reasons; HPBI-H has a large amount of water trapped between the layers due to the high nitrogen content (correlated with EA and EDX data in Section 3.4).
Wide-angle X-ray scattering (WAXS) pattern was obtained from powder samples to determine the crystallinity of HPBIs. HPBIs are shown similar pattern with broadening of each other in Figures 9a and 11a because hole structure was shown scattered around dangling powder samples.11 The highest peaks are shown at 24.62° and 26.04° with 3.61 Å and 3 .42 Å d-spacing. As a result, we can expect the HPBIs to be stacked like graphite (like a stacked graphene) with a d-spacing of 3.4 Å between the interlayers.
Compared between HPBI-T and –H, HPBI-H has narrow width in each peak and it is evidence of high crystallinity of well-stacked structure by the large frequency of hydrogen bonding of imidazole in smaller pores. The samples without pretreatment showed a broad 5% weight loss around 150 °C which caused expulsion of confined water. Therefore, we annealed the samples to 200 °C for 10 min in the chamber of TGA before measuring each time for outside interruption.
According to the experimental data, HPBIs show the main decomposition at 550 and 558 °C, which is related to the pyrolysis of the imidazole ring, respectively in Figure 10a and 12a, because generally the imidazole group of linear polybenzimidazole (PBI) is pyrolyzed at 580 °C in air.20 There are minor decompositions at 350 °C approximately from the edges of the HPBIs and impurities trapped by the high polarity of the imidazole in the interlayer. Like the atmosphere under air, there are two decomposition steps at about 430 and 710 °C under nitrogen atmosphere in HPBI-T and HPBI-H (Figures 10b and 12b). As a result, we can confirm the thermal stability of HPBIs which is known as a type of thermally stable polymer.15b.
Scanning Electron Microscopy (SEM)
Specific surface area study
Band-gap calculation
Cyclic voltammogram in acetonitrile containing 0.1 M TBAPF6 solution at a scan rate of 100 mV/s; a) HPBI-T on glassy carbon electrodes and b) ferrocene under nitrogen. Cyclic voltammogram in acetonitrile containing 0.1 M TBAPF6 solution at a scan rate of 100 mV/s; a) HPBI-H on glassy carbon electrodes and b) ferrocene under nitrogen.
Conclusion
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