Study of evolution of three-dimensional porous structure in zeolite-templated carbons

The clogging of zeolites with carbon-containing precursors is an industrial challenge in some applications but when the deposition of carbon is deliberate and ‘works well’, a source of carbon material with intriguing properties in others. Zeolite-templated carbons (ZTCs) are often compared to activated carbons due to their shared characteristics, such as high surface area, chemical composition, and thermal and chemical stability under various conditions. However, the key distinction lies in their controllable pore size, which makes ZTCs exceptionally interesting materials. Since the late 1990s, extensive research has been conducted on ZTCs, exploring different zeolite templates, carbon precursors, and synthesis parameters. Yet, despite significant progress, the field still faces unresolved questions, controversies, and aspects that have been overlooked. We report synthesis and characterization of three-dimensional porous carbon structures by using ion-exchanged faujasite zeolite as template. The progression of carbon networks from the initial to the final stages of growth inside zeolite channels was studied by transmission and scanning electron microscopy, gas adsorption, thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, and solid state nuclear magnetic resonance. Atomic-resolution images obtained with integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM) were used to study both the zeolite and carbon structure inside the zeolite pores. Argon and CO2 adsorption isotherms show that the inner and the outer pore volumes (that we label V1 and V2) and surface areas (that we label S1 and S2) of the hollow carbon networks can be distinguished in the pore size distribution curves; to the best of our knowledge, this is the first time that these pore volumes and BET surface areas have been separately determined. For this porous carbon product, V1=0.14 cm3/g and S1=500 m2/g, and V2=0.99 cm3/g and S2=1640 m2/g. The iDPC-STEM and gas adsorption studies, as a function of time of exposure to acetylene during synthesis, provide new insights into the growth of zeolite-templated carbons and thus of carbons having both “inner” (enclosing V1 and generating S1) and “outer” (enclosing V2 and generating S2) volumes and surfaces after removal of the zeolite.