Carbon Nanosheet Preparation By Low-Temperature Two-Step Carbonization: A Study of Their Properties and Mechanism of Adsorption of Oxidized H2S.

Abstract

Straw, as a kind of biomass waste, has the advantages of low cost and abundant storage, which makes it a promising renewable resource. Using rice straw as a carbon source, carbon nanosheets were prepared by a two-step carbonization method combining low-temperature pyrolysis and low-temperature hydrothermal, and they were used as H2S removal agents. The results showed that during the two-step carbonization process, the adsorption performance of carbon nanosheets for H2S showed a tendency of enhancing and then weakening with the increase of pyrolysis temperature in the first step, and the sulfur capacity could reach 3.1 mg/g at the maximum of the pyrolysis temperature of 200 °C, which was superior to or close to that of the modified or activated carbon. The XPS, EPR, and CO2-TPD tests showed that the surface of carbon nanosheets was alkaline, containing a large number of hydroxyl groups and the presence of phenoxy persistent free radicals or semiquinone persistent free radicals. It was analyzed that the direct or indirect oxidation of H2S by the persistent radicals under an alkaline environment could convert the -2-valent sulfur into -1-, 0- and +6-valent sulfur to realize the adsorption and removal of H2S. This work, while offering the possibility of utilizing carbon nanosheets made from straw as a material for H2S adsorption and removal, also expands the application of straw waste in exhaust gas treatment.