Beyond Adsorption: The Effect of Sulfur Doping on Emerging Applications of Nanoporous Carbons

Abstract

Recently we have directed our attention to new applications of “old” materials, nanoporous carbons, as photocatalysts for oxidation of dibenzothiophenes, as water splitting catalysts, as gas sensors and as photosensitizers. Our inspiration was in graphene science. We found that both surface chemistry and porosity are crucial factors determining the specific performance. Since the effects are synergistic, it is not possible to totally separate the influence of these two factors. In terms of photoactivity and photosensitivity, surface chemistry was found as having the predominant effect on the catalytic performance. Sulfur containing groups were indicated as playing a major role in these processes. Of course physical adsorption was necessary to take place on the surface before further reactions promoted by absorption of photons occurred. Since some level of conductivity of the carbon matrix is important for an electron transfer, formation of radicals, and active oxygen species, the presence of sp² graphitic dots of 10 nm in size in the carbon matrix enhanced the photoactive performance. In the case of gas sensing where the reversibility of the signal is important, physical adsorption was a predominant factor. Here the specific polar or electrostatic interactions enhance the sensitivity and affect markedly the selectivity. A minireview of our recent work on these two emerging topics, photoactivity of carbon and their sensing application, is presented in this paper. The emphasis is on the importance of both, specific surface chemistry and developed porosity. The latter is a unique factor, which differentiates the performance of porous carbons from that of nanoforms of carbons such as graphene or carbon nanotubes.