Top-Down Approach for the Preparation of Colloidal Carbon Nanoparticles

An aluminosilicate MCM-41 with a highly ordered mesoscopic structure and Si/Al molar ratio of 1.25 has been synthesized in basic medium in the presence of sodium ions. Standard procedures to exchange Na+ for other cations in calcined MCM-41 led to a gradual collapse of the structure along with a partial dealumination. Various [Me]AlMCM-41, with Me = K+, Cs+, Ca2+, could be obtained by completely exchanging sodium ions prior to calcination, i.e., in the presence of surfactant molecules. These molecules prevent framework dealumination during exchange, while preserving the long-range mesoscopic ordering of the parent [Na]AlMCM-41. The [Me]AlMCM-41 thus obtained possessed all the properties of materials that would have been obtained directly in the presence of the corresponding cations. Moreover, structural and textural properties of the calcined products are very similar to those of the directly calcined [Na]AlMCM41, suggesting that the nature of the charge compensating cation has little influence on the thermal stability.