Preparation of N/O co-doped biochar by microwave-assisted one-step method for adsorption removal of gaseous H2S

In this article, a simple and effective microwave-assisted one-step modification method was used to prepare nitrogen/oxygen co-doped straw biochar, and then the prepared adsorbent was used for efficient removal of gaseous hydrogen sulfide. The influences of preparation and process parameters on desulfurization performance of the adsorbents were assessed. The H₂S adsorption mechanism and kinetic laws, and the regeneration characteristics of the adsorbent were studied. Results showed that the microwave-assisted nitrogen/oxygen co-doping one-step modification technology significantly optimized the pore structure of the biochar, and achieved the synchronous loading of nitrogen-containing and oxygen-containing functional groups on the surface of biochar. The optimal preparation conditions were 10 % ammonia concentration and 20 min microwave radiation time. Increasing H₂S inlet concentration reduced the H₂S breakthrough time, while increasing water vapor content and raising adsorption temperature both significantly promoted the H₂S removal. The maximum adsorption capacity of the modified biochar for H₂S reached 62.61 mg/g. It was demonstrated that H₂S was converted into elemental sulfur, organic sulfur, bisulfate, and sulfate on the modified biochar surface through the co-action of nitrogen-containing and oxygen-containing functional groups. The desulfurization process over the modified biochar followed a pseudo-first-order kinetic model, and thus external mass transfer was the main controlling step for H₂S adsorption. The developed regeneration method can effectively restore the desulfurization ability of the saturated biochar.