The influence of microporosity creation in highly mesoporous N-containing carbons obtained from chitosan on their catalytic and electrochemical properties

Abstract

Highly mesoporous novel nitrogen-containing, silica templated carbons, obtained from chitosan were described in the present study to demonstrate the effects of ZnCl2, KOH and CO2, widely used carbon activators, on the development of their micro/mesoporsity by means of nitrogen sorption, elemental analysis, X-ray diffraction, cyclic voltammetry and SO2 oxidation reaction. The latter two activation methods were post-synthesis treatments as opposite to the first one in which ZnCl2 was added directly to the solution of colloidal silica template and chitosan. We confirmed that chemical activation using KOH or ZnCl2 generates microporosity as opposite to physical activation which only slightly enhances micro/mesoporosity. All the activation methods studied resulted in a wider mesopore size distribution. The KOH was the most effective activator for the creation of narrow micropores with the diameter of ca. 0.6nm, and it was the most widely used one.The microporosity development was also reflected in capacitance measured in 6M KOH solution and high rate of catalytic SO2 oxidation in solution. The higher the activation temperature the less the nitrogen was preserved in the structure modified with KOH. No significant changes in nitrogen percentage have been found after two other activation treatments.Microporosity development reflects in an improvement of the ability to accumulate the charge and an increase in a rate of SO2 oxidation in solution. The studied carbons exhibited a specific surface area up to 1800m2/g, and a quite high capacitance up to 245F/g, as for carbons having such a low microporosity contribution of up to 32% to the overall pore volume, and SO2 oxidation rate up to 4.42μmol/s/g.A creation of appropriate microporosity is extremely important for a particular process/reaction. The diameter of pores within the range of 0.7–0.9nm is demanded for SO2 oxidation. However, slightly smaller pores (0.6nm) improve the ability to store the charge in 6M KOH.