How do zeolite-templated carbons grow?

Major insights into the formation mechanism of zeolite-templated carbons (ZTCs) were achieved via a thorough ex situ kinetic study of the hybrid (carbon/zeolite) and carbon materials. In depth characterization of the chemical, electrical, textural, and morphological properties of the materials allowed us to draw a precise picture of the key steps of the ZTC formation. An in situ time resolved GC study enabled us to achieve complementary insights into the ethylene consumption and hydrogen production during ZTC synthesis. Three stages could be disclosed: nucleation, growth and condensation. During nucleation, individual polyaromatic hydrocarbons (PAHs) develop through the aromatization of ethylene. These PAHs present high spin concentration and react upon zeolite dissolution, leading to unstructured carbon particles of undefined morphology. These carbons feature persistent radicals. During growth, the PAHs evolve to form more complex rylene-type molecules. Typical structural, textural, and morphological features of ZTCs start to emerge during this second stage. The evolution of electrical conductivity of hybrid materials indicates partial condensation of PAHs throughout the zeolite crystals leading to their connection. The carbon materials achieved during the second stage can be described as composites of ZTCs and randomly reacted PAHs. Condensation, which is importantly induced by heat treatment, triggers full connection of the ZTC network. Textural, morphological, structural, and electrical features develop, which result directly from zeolite templating. Final ZTCs feature carbonyl functionalization, which is inherent to the zeolite dissolution step and probably results from radical quenching with water.