The hierarchical pore structures of carbons are significant for their properties. The template strategy is a typical pore-making approach of carbons. However, few reports on the micropore templates of porous carbons have been found. Herein, a micropore template is incorporated into a carbon precursor by adopting a post-impregnation approach for the first time, thus preparing hierarchically porous carbons. Polystyrene-b-poly(ethylene oxide) (PS-b-PEO) micelles are used as a soft template. Poly(3-aminophenyl) boronic acid-encapsulated PS-b-PEO composite micelles are assembled on the surface of graphene oxide, forming sandwich aggregations. They are immersed in a zinc acetate solution and then directly pyrolyzed into porous carbons. During pyrolysis, the PS cores of micelles are decomposed to generate abundant mesopores, while the coordinated zinc ions are reduced to zero-valent zinc and then evaporated above its boiling temperature, creating numerous micropores. This in situ-reduced metallic zinc functions as a micropore template. The resulting carbons achieve hierarchical pore structures and a high specific surface area. As an application demonstration, they show one of the best catalytic performances for the oxygen reduction reaction among metal-free doped carbons. This post-impregnation approach can be extended to apply to numerous polar carbon precursors, thus preparing many hierarchically porous carbons with abundant micropores.
Chan Wang,Miao Yang,Peng Tian,Shutao Xu,Yue Yang,Dehua Wang,Yangyang Yuan,Zhongmin Liu
A spherical self-assembly of SAPO-34 nanosheets was hydrothermally synthesized by using a quaternary ammonium-type organosilane surfactant [3-(trimethoxysilyl)propyl]octadecyldimethylammonium chloride (TPOAC) as the mesoporogen and a part of the silica source, and diethylamine (DEA) as the microporous template. The prepared materials were well characterized by XRD, XRF, SEM, TEM, N2 adsorption–desorption, NH3-TPD, NH3-adsorbed IR and pyridine-adsorbed IR measurements. It revealed that the morphologies, compositions and acidity of the SAPO-34 products changed significantly with the increased TPOAC/TEOS ratio, showing that the TPOAC/TEOS ratio had a significant impact on the crystallization process of SAPO-34. Solid state 13C, 29Si NMR and TG-DTA analyses were further conducted to investigate the status of TPOAC in the final products. A possible crystallization process involving TPOAC was proposed. The catalytic performances of the synthesized SAPO-34s were evaluated using the MTO reaction. The optimal SAPO-34 nanosheet assemblies with a hierarchical porous structure displayed a remarkably enhanced catalytic lifetime and high yields of light olefins.
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