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

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.