Size Effect of Activated Carbons on Catalytic Degradation of Nitroaromatic Compounds in Carbon-Sulfide Reduction Systems

Carbon materials for catalytic degradation of organic compounds in carbon-sulfide systems have received great interest for potential environmental remediation application. Either the surface oxygen functional groups or the graphite/graphene region on the carbon surface is commonly recognized as the controlling factor in mediating the reductive degradation. In this study, by introducing 21 carbon materials for catalytic degradation of nitro-aromatic compounds (NACs) in a carbon-sulfide system, we found a new mechanism that the particle size of carbon materials played a more dominant role in the reaction. This is because only the mesopores and the exterior carbon surface are accessible for the reaction. The measured double-layer capacitances of carbons could be used for indicating the accessible surface area. However, further adsorption experiments suggested that the reduction of nitrobenzene in the carbon-sulfide system might not be merely adsorption controlled. We hypothesized that the nonadsorbed NACs might be directly reduced via an outer-sphere electron transfer pathway. The influence of ionic strength and the molecular charges of NACs provided the necessary evidence. These results improve our understanding about the catalytic role of carbon materials and highlight the advantage of the smaller sized activated carbons for degradation of NACs in carbon-sulfide systems.