Abstract
There is currently a pursuit of synthetic approaches for designing porous carbon materials with selective CO2 capture and/or excellent energy storage performance that significantly impacts the environment and the sustainable development of circular economy. In this study we prepared a new bio-based benzoxazine (AP-BZ) in high yield through Mannich condensation of apigenin, a naturally occurring phenol, with 4-bromoaniline and paraformaldehyde. We then prepared a PA-BZ porous organic polymer (POP) through Sonogashira coupling of AP-BZ with 1,3,6,8-tetraethynylpyrene (P-T) in the presence of Pd(PPh3)4. In situ Fourier transform infrared spectroscopy and differential scanning calorimetry revealed details of the thermal polymerization of the oxazine rings in the AP-BZ monomer and in the PA-BZ POP. Next, we prepared a microporous carbon/metal composite (PCMC) in three steps: Sonogashira coupling of AP-BZ with P-T in the presence of a zeolitic imidazolate framework (ZIF-67) as a directing hard template, affording a PA-BZ POP/ZIF-67 composite; etching in acetic acid; and pyrolysis of the resulting PA-BZ POP/metal composite at 500 °C. Powder X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller (BET) measurements revealed the properties of the as-prepared PCMC. The PCMC material exhibited outstanding thermal stability (Td10 = 660 °C and char yield = 75 wt%), a high BET surface area (1110 m2 g–1), high CO2 adsorption (5.40 mmol g–1 at 273 K), excellent capacitance (735 F g–1), and a capacitance retention of up to 95% after 2000 galvanostatic charge–discharge (GCD) cycles; these characteristics were excellent when compared with those of the corresponding microporous carbon (MPC) prepared through pyrolysis of the PA-BZ POP precursors with a ZIF-67 template at 500 °C.
Highlights
Benzoxazine (BZ) is a six-membered heterocyclic molecule, containing oxygen and nitrogen atoms, that is stable at room temperature or in humid environments; BZ derivatives are readily prepared through Mannich condensations of phenol derivatives with paraformaldehyde and primary amines in the melt or in solution [1–5]
Ring-opening polymerization (ROP) of the oxazine ring in a BZ precursor can be performed by applied heat, without adding any catalyst or initiator, to afford a polybenzoxazine (PBZ) as a thermosetting polymeric material [1–5]
The application of PBZ materials has been restricted industrially because the ROP of BZ resins to afford PBZs generally occurs at temperatures between 220 and 280 ◦ C [10–14]
Summary
Benzoxazine (BZ) is a six-membered heterocyclic molecule, containing oxygen and nitrogen atoms, that is stable at room temperature or in humid environments; BZ derivatives are readily prepared through Mannich condensations of phenol derivatives with paraformaldehyde and primary amines in the melt or in solution [1–5]. Extensive research efforts will be needed to develop novel materials possessing high specific surface areas that can increase the energy density of supercapacitors while maintaining their power density and cycling stability. In this regard, many porous organic polymers (POPs) featuring suitable pore size distributions—including covalent triazine frameworks (CTFs) [39], covalent organic frameworks (COFs) [40–42], hypercrosslinked porous polymers (HCPs) [43,44], conjugated microporous polymers (CMPs) [45–53], metal–organic framework [48–50], and ferrocene-based conjugated microporous polymers [51]—have been developed to improve the performance of supercapacitors.
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