Synthesis of carbon frameworks with N, O and S-lined pores from gallic acid and thiourea for superior CO2 adsorption and supercapacitors

Abstract

C 2 N"-species have emerged as a promising material with carbon-like applications in sorption, gas separation and energy storage, while with much higher polarity and functionality. Controlled synthesis of "C 2 N" structure is still based on complex and less-sustainable monomers, which prohibits its broader industrial application. Here we report a class of well-defined C 2 (N x O y S z ) 1 carbons with both high content of N/O/S heteroatoms and large specific surface area of up to 1704 m 2 g −1 , which can be efficiently synthesized through a simple additive condensation process using simple gallic acid and thiourea as the building blocks, without subtractive activation. This 1,4-para tri-doped C 2 (N x O y S z ) 1 structure leads to sufficient CO 2 adsorption capacity (3.0 mmol g −1 at 273 K, 1 bar) and a high CO 2 /N 2 selectivity (47.5 for a 0.15/0.85 CO 2 /N 2 mixture at 273 K). Related to the polarity, the polar frameworks can be used as supercapacitor electrodes, with record specific capacitances as high as 255 F g −1 at 3.5 V for a symmetric supercapacitor in ionic liquid electrolyte. This work discloses a general way for preparing a novel family of multifunctional, high heteroatomdoped porous materials for various applications. 1 Oschatz M, Antonietti M. A search for selectivity to enable CO 2 capture with porous adsorbents. Energy Environ Sci, 2018, 11: 57-70 2 Tian Z, Huang J, Zhang Z, et al. Organic-inorganic hybrid mi-

C2N: A Class of Covalent Frameworks with Unique Properties

“…As a result, we produced 1,4‐para N,O‐dual doped C 2 N x O 1‐ x and tri‐doped C 2 (N x O y S z ) 1 materials using similar salt melt synthesis and ring closure methods. [ 37,40 ] Gallic acid is considered to be a promising unit for ordered structure synthesis because it can easily decarboxylate at higher temperatures to generate pyrogallol. Therefore, the carboxylic acid unit can be regarded as a “protecting/leaving group” that controls preorganization, functionality, and N/O/S doping in the target carbon material.…”

“…Several theoretical predictions on the ability of C 2 N and metal composites to act as catalysts for diverse applications followed (e.g., HCOOH dehydrogenation, seawater desalination, and photocatalytic and electrocatalytic water splitting activity). [ 67–77 ] The predicted multipodal strong binding sites [ 66 ] play an important role when C 2 N combines with CO 2 , ionic liquids, and metal ions, such that C 2 N exhibits excellent gas adsorption/separation, supercapacitor, and battery performance, [ 38,40 ] which is discussed in detail in subsequent sections. Moreover, due to these unique pores, C 2 N itself can be used as a catalyst as well as a support, which can strongly bind large amounts of single metal atoms.…”

“…The C 2 N x O 1‐ x and C 2 (N x O y S z ) 1 materials reported by us have heterocyclic rings with approximately 30 wt% of heteroatoms. [ 37,40 ] The remarkably high content of heteroatoms can only be meaningfully assigned and included in the structure as phenazines, oxazine, dioxine rings, or thiazine/thiazole, which then define the pore surface. As a result, these materials also showed heat of adsorption values of ≈50 kJ mol −1 , which promote rather selective sorption processes.…”

“…The unique electronic properties of C 2 N could be complementary to the use of C 3 N 4 in application areas such as adsorption, [ 37,38 ] electrochemical catalysis and energy storage. [ 39,40 ]…”

“…We have discussed the influence of this pattern to explain the special performances in gas/water adsorption, [ 37,38 ] catalysis, [ 44 ] and energy storage. [ 40,45–48 ] Furthermore, the pores with six regularly spaced nitrogen lone pairs in the lining ring (N6‐cavities) are extremely suitable for anchoring metallic nanoparticles and single atoms, acting as an “active support.” [ 39–51 ]…”