Different Crystal Forms of ZnS Nanomaterials for the Adsorption of Elemental Mercury.

ZnS is a promising sorbent in recovering Hg from industrial flue gas due to its excellent Hg adsorption capacity. However, the internal structure-activity relationship still needs to be further clarified. In this work, ZnS sorbents with different structures were synthesized with the hydrothermal method by tuning the temperature. The samples had significant differences in the crystallinity, morphology, particle size, and sulfur (S) active sites. The results indicated that Hg removal performance was determined by the specific surface area and S active sites. ZnS synthesized at low temperatures (80-ZnS and 120-ZnS) had a larger surface area, while the S sites on the high-temperature-synthesized sample (160-ZnS) were more active for Hg adsorption. The 160-ZnS sample exhibited a much higher Hg adsorption amount per unit surface area. Further characterization revealed that S and S were the main active sites for Hg adsorption. S existed in the form of long-chain polysulfur (L-S) on 80-ZnS and 120-ZnS, while it exhibited in the form of short-chain polysulfur (S-S) on 160-ZnS. L-S had negligible adsorption ability, while S-S had a high affinity for Hg. Hg can react with S and S-S, forming α-HgS and β-HgS, respectively. The new insight in this work can provide theoretical guidance for the design and structure optimization of ZnS, facilitating its practical industrial application.