High-magnification image (AR-TEM) showing the encapsulation of Fe/Fe3C nanoparticles within nitrogenated graphitic shells. Deconvulsed spectra of the Fe/Fe3C@C4N catalyst. a) CV curves of Pt/C and Fe/Fe3C@C4N samples prepared at different annealing temperatures.
Scalable Synthesis of Tetrapodal Octaamine
- Abstract
- Introduction
- Results and Discussion
- Experimental Section
- General Methods
- Synthesis of Tetra(p-nitrophenyl) methane (2)
- Synthesis of Tetra(p-aminophenyl) methane (3)
- N,N',N'',N'''-(methanetetrayltetrakis(2-nitrobenzene-4,1-diyl))tetraacetamide (4)
- Tetrakis(2,3-diphenylquinoxalin-6-yl) methane (7)
- Tetrakis(2,3-bis(4-methoxyphenyl) quinoxalin-6-yl) methane (8)
- Bis(2-(4-methoxyphenyl)-1H-benzo[d]imidazol-5-yl) bis(2-(4-methox-yphenyl)-1H-
- Bis(2-(4-nitrophenyl)-1H-benzo[d]imidazol-5-yl) bis(2-(4-nitrophenyl)-1H-
- References
Here, we report a facile route for the synthesis of soluble and air-stable methanetetrayltetrakis(benzene-1,2-diamine) without any purification by column chromatography. The synthesis of octaamine (6) starts with the protection of the amino groups of tetrakis(4-aminophenyl)-methane with acetic anhydride.
Scalable Synthesis of pure and stable saddle shaped octamine octahydrochloride
- Abstract
- Introduction
- Experimental Section
- General Methods
- Synthesis of tetraphenylene (2)
- Synthesis of 2,3,7,10,11,14,15-octabromotetraphenylene (3)
- Synthesis of N,N',N'',N''',N'''',N''''',N'''''',N'''''''-(tetraphenylene-2,3,6,7,10,11,14,15-octayl)
- Synthesis of tetraphenylene-2,3,6,7,10,11,14,15-octamine (5)
- Synthesis of (2,3,8,9,14,15,20,21-octakis(4-methoxyphenyl) cycloocta) tetraquinoxaline (6)
- Synthesis of (2,3,8,9,14,15,20,21-octaphenylcycloocta) tetraquinoxaline (7)
- References
While the synthesis of octamine starts with the bromination of tetraphenylene followed by substitution with an imine protecting group. The crude product was recrystallized in dichloromethane, during recrystallization we obtained two products, later we found that only the rearranged product was recrystallized, leaving the desired product in solution. Finally, the imine group was deprotected using aqueous HCl (2 M), resulting in a high yield of saddle-shaped octamine (Figures 2.7 and 2.8).
The crude product was then collected by solvent extraction and purified by column chromatography using hexane as an eluent to give the desired product as a white solid. The crude product was purified by column chromatography using ethyl acetate/hexane (20:80) as an eluent to give pure yellow solid. The mixture was diluted with CH2Cl2 and the product was collected by solvent extraction and dried under vacuum.
Finally, the crude product was recrystallized from hot aqueous HCl solution to obtain 5 as a brown crystal. Synthesis of benzo-fused tetraphenylenes and crystal structure of the clathrate inclusion compound 4:1 dibenzo [b, h] tetraphenylene with p-xylene.
Robust fused aromatic pyrazine-based two-dimensional network for stably cocooning iron
Abstract
Introduction
Non-precious metal-doped carbon-based materials are considered attractive alternative candidates due to their low cost and high ORR performance.34 However, these catalysts are too unstable to meet the demands of practical applications. In attempts to achieve both catalytic performance and stability, efforts have been made to develop methods to stably encapsulate non-noble metal nanoparticles with electrochemically stable carbon-based materials.35 However, such catalysts still suffer from poor stability, because pure carbon-based materials, such as carbon nanotubes and graphene, are not polar enough to provide a strong (bonding) interaction with the metal nanoparticles for stable, defect-free encapsulation.36. To achieve better interaction, hybrid systems consisting of polar heteroatoms containing carbon-based materials and metal nanoparticles are gaining increasing interest in the scientific community.24,37 Doping with electronegative nitrogen atoms changes the electron density of adjacent carbon atoms and polarizes adjacent carbon atoms , resulting in a net of unevenly charged centers for activating O2 adsorption, which can improve the oxygen reduction process.38.
The FA-PON structure consists of fused aromatic ring systems, which provide tremendous stability, and tunable pore sizes, which can be tailored by changing any of the repeating units in the building blocks. Nitrogen-rich FA-PON structures, due to their basicity and coordinating ability with metal ions, are receiving increasing attention as a new design for indirect contact catalyst structures39. In an effort to explore the diverse potential of PON structures, we report here for the first time a new FA-PON structure synthesized via the polycondensation of triphenylenehexamine (TPH) and hexaketocyclohexanone (HKH) with the empirical formula of C4N1. 18 The FA-PON (C4N1) contains uniform pores.
Each pore contains six nitrogen atoms, which provide good chelating ability for non-noble metals such as Fe. This enables FA-PON to stably fixate Fe ions and then encapsulate Fe nanoparticles within the graphite shells, making them an efficient and stable indirect contact ORR catalyst.
Results and Discussion
To investigate the morphology of the Fe/Fe3C@C4N1 catalyst, FE-SEM and TEM analyzes were performed. The XPS survey spectrum of the Fe/Fe3C@C4N1 catalyst showed the presence of C, N, O and Fe (Figure 3.9b). The TGA curve of Fe/Fe3C@C4N1 catalyst recorded in air atmosphere showed a residual amount of 9.60 wt % above 800 °C.
The Tafel slope of the Fe/Fe3C@C4N catalyst was smaller (92 mV dec−1) than that of commercial Pt/C (96 mV dec−1) (Figure 3.12c), indicating its excellent catalytic activity. These results further confirmed that the Fe/Fe3C@C4N1 catalyst is more suitable than commercial Pt/C in DMFCs. These results show that the superior activity and better durability of the Fe/Fe3C@C4N1 catalyst compared to commercial Pt/C can be.
The limiting current density of the Fe/Fe3C@C4N1 catalyst was higher than that of Pt/C (Figure 3.14d). The cyclic performance of a rechargeable Zn-air battery with Fe/Fe3C@C4N1 was also evaluated (Figure 3.14d).
Conclusion
Experimental Section
- Materials
- Synthesis of the Fe/Fe 3 C@C 4 N catalyst
- Hybrid Li-air battery and Zn-air battery tests
- Instrumentation
- Electrochemical measurements
The results presented in this work suggest that it is one of the best performing non-precious metal-based indirect contact catalysts for practical applications. For zinc (Zn) air battery tests, a Zn metal foil (Alfa Aesar) of 0.25 mm thickness was used as the anode of the cell, and 6 M KOH in DI water was used as the aqueous electrolyte. High-resolution transmission electron microscopy (TEM) was performed using a JEM-2100F microscope (JEOL, Japan) under an operating voltage of 200 keV.
Thermogravimetric analysis (TGA) was performed in air and nitrogen atmosphere at a rate of 10 °C min-1 using a Q200 thermogravimetric analyzer (TA Instrument Inc., USA). The spectrum recorded under cross-polarization conditions (13C ← 1H), the magic angle spinning sample with high 1H decoupling power. Electrochemical tests were performed using an electrochemical workstation (Ivium, The Netherlands) with a typical three-electrode cell.
A graphite rod was used as a counter electrode and an Ag/AgCl (saturated KCl) electrode as the reference electrode. Each catalyst dye (22.7 µL) was cast onto a rotating ring disk electrode (RRDE, 4 mm diameter) and further dried thoroughly at room temperature before electrochemical tests.
Y.; Baek, J.-B., Strong Pyrazine-Based Two-Dimensional Fused Aromatic Network for Stable Encapsulation of Iron Nanoparticles as an Electrocatalyst for Oxygen Reduction. Yang, W.; Liu, X.; Yue, X.; Jia, J.; Guo, S., Bamboo-like carbon nanotube/Fe3C nanoparticle hybrids and their highly efficient catalysis for oxygen reduction. Ren, G.; Lu, X.; Li, Y.; Zhu, Y.; Dai, L.; Jiang, L., Carbon nanofibers embedded with porous Fe3C core-shells as an effective electrocatalyst for oxygen reduction reaction.
Wu, Z.-S.; Yang, S.; Sun, Y.; Parvez, K.; Feng, X.; Müllen, K., 3D Fe3O4 nanoparticles supported on nitrogen-doped graphene airgel as efficient electrocatalysts for the oxygen reduction reaction. Zhang, Y.; Jiang, W.-J.; Guo, L.; Zhang, X.; Hu, J.-S.; Wei, Z.; Wan, L.-J., Confinement of iron carbide nanocrystals within CN x@ CNTs toward an efficient electrocatalyst for oxygen reduction reaction. Shui, J.; Wang, M.; Du, F.; Dai, L., N-doped carbon nanomaterials are sustainable catalysts for the oxygen reduction reaction in acidic fuel cells.
Banham, D.; Yes.; Pei, K.; Ozaki, J.-i.; Kishimoto, T.; Imashiro, Y., A review of the stability and durability of non-precious metal catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells. Liu, J.; Song, P.; Ning, Z.; Xu, W., Recent advances in heteroatom-doped metal-free electrocatalysts for highly efficient oxygen reduction reaction.
Three-dimensional porous fused aromatic networks for high performance gas and iodine
Abstract
Introduction
Nitrogen-containing structures formed by the condensation reactions of aromatic aldehydes and amines have attracted considerable attention for heterogeneous catalysis and gas adsorption, due to their high nitrogen content and large specific surface area.27 A series of nitrogen-containing conjugated polymers have been reported to have exceptional gas adsorption capacity27-29 The majority of these structures however, has been devised from flatter building blocks, while highly twisted three-dimensional (3D) monomers such as triptycene, triphenylamine, tetrahedral tetraphenylene, and spirobifluorene have rarely been used. The tight spacing resulting from packing the planner monomers into 2D layered organic network structures can be sufficiently reduced by forming 3D structures from the non-planner monomers. Considering the above-mentioned problems, two new stable fused aromatic nitrogen-rich PONs were synthesized via double condensation between tetrapodal octamine and pyrenetetraketone (PTK) or hexaketocyclohexane (HKH).
Due to the non-shared electron pair containing nitrogen and partially positively charged carbon as well as its π-electron conjugated backbone, the PONs showed a good tendency for gas storage and iodine trapping. In addition to this, the presence of the covalent bond provides thermal and physiochemical stability to PON's structure, one of the necessities for practical applications. The resulting PONs were investigated to determine their performance for the capture and adsorption of small molecules such as (CO2, H2, CH4 and I2).
Results and discussion
Schematic illustration of the synthesis of fused aromatic networks (PONs): P-PON formed by double condensation between tetrapodal octamine and pyrenetetraketone (PTK). Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was used to investigate the chemical structures of the resulting PONs. The chemical environment and bonding nature of the samples were resolved using X-ray photon spectroscopy (XPS). a) Powder X-ray diffraction patterns (PXRD).
The content of elements in PON was calculated based on the structural repeating units, excluding edge contributions. The thermal stability of PON was investigated by thermogravimetric analysis (TGA) in both air and nitrogen atmospheres (Figure 4.5a,b). Another weight loss is associated with the degradation of PON skeletons, which is similar to that of intact PONs (Figure 4.5a, b).
Gravimetric iodine uptake capacity of H-PON in relation to time. e) TGA thermogram of the H-PON under nitrogen conditions. f) High-resolution XPS spectrum of I@H-PON. One of the most important factors in evaluating the performance of an absorbent is its recyclability.
Conclusions
Experimental section
- Materials
- Synthesis of P-PON
- Synthesis of H-PON
After completion of the reaction, the precipitates were collected and Soxhlet extracted with methanol and water for two days each.
W.; Cheng, Y.; Wei, H.; Nguyen, N.; Wojtas, L.; Ma, S., Postsynthetically modified covalent organic frameworks for efficient and effective mercury removal. Qian, H.-L.; Yang, C.-X.; Yan, X.-P., Bottom-up synthesis of chiral covalent organic frameworks and their tethered capillaries for chiral separation. Zhang, J.; He, X.; Wu, X.; Liu, Y.; Cui, Y., Multivariate chiral covalent organic frameworks with controlled crystallinity and stability for asymmetric catalysis.
I also want to convey my heartiest gratitude to all the esteemed committee members Professor Hu Young Jeong, Professor Guntae Kim, Professor In Yup Jeon and Professor Sung-Yeon Jang for their timely suggestions to complete this thesis. I want to say a special thanks to my mother who always misses my presence at home. Last but not least, I want to offer special prayers to my late grandfather and grandmother, who have always been a source of spiritual support to me.
Mechanically Assisted Synthesis of a Ru Catalyst for Hydrogen Evolution with Performance Superior to Pt in Both Acid and Alkaline Media Adv. Encapsulation of Iridium Nanoparticles within 3D Cage-like Organic Networks as an Efficient and Durable Catalyst for Hydrogen Evolution Reaction Adv Mater.
