Impact of H₂S on Hg⁰ capture performance over nitrogen-doped carbon microsphere sorbent: experimental and theoretical insights

Abstract

A nitrogen-doped carbon microsphere sorbent with a hierarchical porous structure was synthesized via aggregation-hydrothermal carbonization. The Hg⁰ adsorption performance of the nitrogen-doped carbon microsphere sorbent was tested and compared with that of the coconut shell activated carbon prepared in the laboratory. The effect of H₂S on Hg⁰ adsorption was also investigated. The nitrogen-doped carbon microsphere sorbent exhibited superior mercury removal performance compared with that of coconut shell activated carbon. In the absence of H₂S at a low temperature (≤ 100 °C), the Hg⁰ removal efficiency of the nitrogen-doped carbon microsphere sorbent exceeded 90%. This value is significantly higher than that of coconut shell activated carbon, which is approximately 45%. H₂S significantly enhanced the Hg⁰ removal performance of the nitrogen-doped carbon microsphere sorbent at higher temperatures (100–180 °C). The hierarchical porous structure facilitated the diffusion and adsorption of H₂S and Hg⁰, while the nitrogen-containing active sites significantly improved the adsorption and dissociation capabilities of H₂S, contributing to the generation of more active sulfur species on the surface of the nitrogen-doped carbon microsphere sorbent. The formation of active sulfur species and HgS on the sorbent surface was further confirmed using X-ray photoelectron spectroscopy and Hg⁰ temperature-programmed desorption tests. Density functional theory was employed to elucidate the adsorption and transformation of Hg⁰ on the sorbent surface. H₂S adsorbed and dissociated on the sorbent surface, generating active sulfur species that reacted with gaseous Hg⁰ to form HgS.

Key words： nitrogen-doped carbon microsphere; H₂S; Hg⁰ removal; adsorption mechanism

Competing interests

The authors declare that they have no competing interests.

Acknowledgements

This work was supported by National Natural Science Foundation of China (Grant Nos. 51976108 and U1906232), and Shihezi University Self Funded Support Project (ZZZC2023069).

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