In-situ low-temperature sulfur CVD on metal sulfides with SO₂ to realize self-sustained adsorption of mercury.

Abstract

Capturing gaseous mercury (Hg⁰) from sulfur dioxide (SO₂)-containing flue gases remains a common yet persistently challenge. Here we introduce a low-temperature sulfur chemical vapor deposition (S-CVD) technique that effectively converts SO₂, with intermittently introduced H₂S, into deposited sulfur (S_d⁰) on metal sulfides (MS), facilitating self-sustained adsorption of Hg⁰. ZnS, as a representative MS model, undergoes a decrease in the coordination number of Zn-S from 3.9 to 3.5 after S_d⁰ deposition, accompanied by the generation of unsaturated-coordinated polysulfide species (S_n^2-, named S_d^*) with significantly enhanced Hg⁰ adsorption performance. Surprisingly, the adsorption product, HgS (ZnS@HgS), can serve as a fresh interface for the activation of S_d⁰ to S_d^* through the S-CVD method, thereby achieving a self-sustained Hg⁰ adsorption capacity exceeding 300 mg g^-1 without saturation limitations. Theoretical calculations substantiate the self-sustained adsorption mechanism that S₈ ring on both ZnS and ZnS@HgS can be activated to chemical bond S₄ chain, exhibiting a stronger Hg⁰ adsorption energy than pristine ones. Importantly, this S-CVD strategy is applicable to the in-situ activation of synthetic or natural MS containing chalcophile metal elements for Hg⁰ removal and also holds potential applications for various purposes requiring MS adsorbents.