Regulation of the Sulfur Environment in Clusters to Construct a Mn-Sn2S6 Framework for Mercury Bonding

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

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 (Sd0) 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 Sd0 deposition, accompanied by the generation of unsaturated-coordinated polysulfide species (Sn2-, named Sd*) with significantly enhanced Hg0 adsorption performance. Surprisingly, the adsorption product, HgS (ZnS@HgS), can serve as a fresh interface for the activation of Sd0 to Sd* 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.

Biomimetic mercury immobilization by selenium functionalized polyphenylene sulfide fabric

Highly efficient decontamination of elemental mercury (Hg0) remains an enormous challenge for public health and ecosystem protection. The artificial conversion of Hg0 into mercury chalcogenides could achieve Hg0 detoxification and close the global mercury cycle. Herein, taking inspiration from the bio-detoxification of mercury, in which selenium preferentially converts mercury from sulfoproteins to HgSe, we propose a biomimetic approach to enhance the conversion of Hg0 into mercury chalcogenides. In this proof-of-concept design, we use sulfur-rich polyphenylene sulfide (PPS) as the Hg0 transporter. The relatively stable, sulfur-linked aromatic rings result in weak adsorption of Hg0 on the PPS rather than the formation of metastable HgS. The weakly adsorbed mercury subsequently migrates to the adjacent selenium sites for permanent immobilization. The sulfur-selenium pair affords an unprecedented Hg0 adsorption capacity and uptake rate of 1621.9 mg g-1 and 1005.6 μg g-1 min-1, respectively, which are the highest recorded values among various benchmark materials. This work presents an intriguing concept for preparing Hg0 adsorbents and could pave the way for the biomimetic remediation of diverse pollutants.

Sulfur Dioxide Promoted Mercury Fast Deposition over a Selenite-Chloride-Induced Surface from Wet Flue Gas

Gaseous elemental mercury (Hg0) extraction from industrial flue gases is undergoing intense research due to its unique properties. Selective adsorption that renders Hg0 to HgO or HgS over metal oxide- or sulfide-based sorbents is a promising method, yet the sorbents are easily poisoned by sulfur dioxide (SO2) and H2O vapor. The Se-Cl intermediate derived from SeO2 and HCl driven by SO2 has been demonstrated to stabilize Hg0. Thus, a surface-induced method was put forward when using γ-Al2O3 supported selenite-chloride (xSeO32--yCl-, named xSe-yCl) for mercury deposition. Results confirmed that under 3000 ppm SO2 and 4% H2O, Se-2Cl exhibited the highest induced adsorption performance at 160 °C and higher humidity can accelerate the induction process. Driven by SO2 under the wet interface, the in situ generated active Se0 has high affinity toward Hg0, and the introduction of Cl- enabled the fast-trapping and stabilization of Hg0 due to its intercalation in the HgSe product. Additionally, the long-time scale-up experiment showed a gradient color change of the Se-2Cl-induced surface, which maintained almost 100% Hg0 removal efficiency over 180 h with a normalized adsorption capacity of 157.26 mg/g. This surface-induced method has the potential for practical application and offers a guideline for reversing the negative effect of SO2 on gaseous pollutant removal.

Edge-Enriched Molybdenum Disulfide Ultrathin Nanosheets with a Widened Interlayer Spacing for Highly Efficient Gaseous Elemental Mercury Capture

Transition metal sulfides have exhibited remarkable advantages in gaseous elemental mercury (Hg⁰) capture under high SO₂ atmosphere, whereas the weak thermal stability significantly inhibits their practical application. Herein, a novel N,N-dimethylformamide (DMF) insertion strategy via crystal growth engineering was developed to successfully enhance the Hg⁰ capture ability of MoS₂ at an elevated temperature for the first time. The DMF-inserted MoS₂ possesses an edge-enriched structure and an expanded interlayer spacing (9.8 Å) and can maintain structural stability at a temperature as high as 272 °C. The saturated Hg⁰ adsorption capacities of the DMF-inserted MoS₂ were measured to be 46.91 mg·g^-1 at 80 °C and 27.40 mg·g^-1 at 160 °C under high SO₂ atmosphere. The inserted DMF molecules chemically bond with MoS₂, which prevents possible structural collapse at a high temperature. The strong interaction of DMF with MoS₂ nanosheets facilitates the growth of abundant defects and edge sites and enhances the formation of Mo⁵⁺/Mo⁶⁺ and S₂^2- species, thereby improving the Hg⁰ capture activity at a wide temperature range. Particularly, Mo atoms on the (100) plane represent the strongest active sites for Hg⁰ oxidation and adsorption. The molecule insertion strategy developed in this work provides new insights into the engineering of advanced environmental materials.

Efficient and selective removal of Hg(II) from water using recyclable hierarchical MoS2/Fe3O4 nanocomposites

Developing practical and cost-effective adsorbents with satisfactory mercury (Hg) remediation capability is indispensable for aquatic environment safety and public health. Herein, a recyclable hierarchical MoS₂/Fe₃O₄ nanocomposite (by in-situ growth of MoS₂ nanosheets on the surface of Fe₃O₄ nanospheres) is presented for the selective removal of Hg(II) from aquatic samples. It exhibited high adsorption capacity (∼1923.5 mg g ^-1), fast kinetics (k₂ ∼ 0.56 mg g ^-1 min^-1), broad working pH range (2-11), excellent selectivity (K_d > 1.0 × 10⁷ mL g ^-1), and great reusability (removal efficiency > 90% after 20 cycles). In particular, removal efficiencies of up to ∼97% for different Hg(II) concentrations (10-1000 μg L ^-1) in natural water and industrial effluents confirmed the practicability of MoS₂/Fe₃O₄. The possible mechanism for effective Hg(II) removal was discussed by a series of characterization analyses, which was attributed to the alteration of the MoS₂ structure and the surface coordination of Hg-S. The accessibility of surface sulfur sites and the diffusion of Hg(II) in the solid-liquid system were enhanced due to the advantage of the expanded interlayer spacing (0.96 nm) and the hierarchical structure. This study suggests that MoS₂/Fe₃O₄ is a promising material for Hg(II) removal in actual scenarios and provides a feasible approach by rationally constructing hierarchical structures to promote the practical applications of MoS₂ in sustainable water treatments.

SO2-Driven In Situ Formation of Superstable Hg3Se2Cl2 for Effective Flue Gas Mercury Removal

Flue gas mercury removal is mandatory for decreasing global mercury background concentration and ecosystem protection, but it severely suffers from the instability of traditional demercury products (e.g., HgCl₂, HgO, HgS, and HgSe). Herein, we demonstrate a superstable Hg₃Se₂Cl₂ compound, which offers a promising next-generation flue gas mercury removal strategy. Theoretical calculations revealed a superstable Hg bonding structure in Hg₃Se₂Cl₂, with the highest mercury dissociation energy (4.71 eV) among all known mercury compounds. Experiments demonstrate its unprecedentedly high thermal stability (>400 °C) and strong acid resistance (5% H₂SO₄). The Hg₃Se₂Cl₂ compound could be produced via the reduction of SeO₃^2- to nascent active Se⁰ by the flue gas component SO₂ and the subsequent combination of Se⁰ with Hg⁰ and Cl^- ions or HgCl₂. During a laboratory-simulated experiment, this Hg₃Se₂Cl₂-based strategy achieves >96% removal efficiencies of both Hg⁰ and HgCl₂ enabling nearly zero Hg⁰ re-emission. As expected, real mercury removal efficiency under Se-rich industrial flue gas conditions is much more efficient than Se-poor counterparts, confirming the feasibility of this Hg₃Se₂Cl₂-based strategy for practical applications. This study sheds light on the importance of stable demercury products in flue gas mercury treatment and also provides a highly efficient and safe flue gas demercury strategy.

Multiscale structural control of thiostannate chalcogels with two-dimensional crystalline constituents

Chalcogenide aerogels (chalcogels) are amorphous structures widely known for their lack of localized structural control. This study, however, demonstrates a precise multiscale structural control through a thiostannate motif ([Sn₂S₆]^4-)-transformation-induced self-assembly, yielding Na-Mn-Sn-S, Na-Mg-Sn-S, and Na-Sn(II)-Sn(IV)-S aerogels. The aerogels exhibited [Sn₂S₆]^4-:Mn²⁺ stoichiometric-variation-induced-control of average specific surface areas (95-226 m² g^-1), thiostannate coordination networks (octahedral to tetrahedral), phase crystallinity (crystalline to amorphous), and hierarchical porous structures (micropore-intensive to mixed-pore state). In addition, these chalcogels successfully adopted the structural motifs and ion-exchange principles of two-dimensional layered metal sulfides (K_2xMn_xSn_3-xS₆, KMS-1), featuring a layer-by-layer stacking structure and effective radionuclide (Cs⁺, Sr²⁺)-control functionality. The thiostannate cluster-based gelation principle can be extended to afford Na-Mg-Sn-S and Na-Sn(II)-Sn(IV)-S chalcogels with the same structural features as the Na-Mn-Sn-S chalcogels (NMSCs). The study of NMSCs and their chalcogel family proves that the self-assembly principle of two-dimensional chalcogenide clusters can be used to design unique chalcogels with unprecedented structural hierarchy.

Controllable Disordered Copper Sulfide with a Sulfur-Rich Interface for High-Performance Gaseous Elemental Mercury Capture

Copper sulfide (CuS) has received increasing attention as a promising material in gaseous elemental mercury (Hg⁰) capture, yet how to enhance its activity at elevated temperature remains a great challenge for practical application. Herein, simultaneous improvement in the activity and thermal stability of CuS toward Hg⁰ capture was successfully achieved for the first time by controlling the crystal growth. CuS with a moderate crystallinity degree of 68.8% showed a disordered structure yet high thermal stability up to 180 °C. Such disordered CuS can maintain its Hg⁰ capture activity stable during longtime test at a wide temperature range from 60 to 180 °C and displayed strong resistance to SO₂ (6%) and H₂O (8%). The significant improvement can be attributed to the synergistic effect of a moderately crystalline nature and a unique sulfur-rich interface. Moderate crystallinity guarantees the thermal stability of CuS and the presence of abundant defects, in which copper vacancy enhances significantly the Hg⁰ capture activity. The sulfur-rich interface enables CuS to provide plentiful highly active S_x^2- sites for Hg⁰ adsorption. The interrelation between structure, reactivity, and thermal stability clarified in this work broadens the understanding toward Hg⁰ oxidation and adsorption over CuS and provides new insights into the rational design and engineering of advanced environmental materials.

Structure-Directing Role of Support on Hg0 Oxidation over V2O5/TiO2 Catalyst Revealed for NOx and Hg0 Simultaneous Control in an SCR Reactor

The crystal structure of TiO₂ strongly influences the physiochemical properties of supported active sites and thus the catalytic performance of the as-synthesized catalyst. Herein, we synthesized TiO₂ with different crystal forms (R = rutile, A = anatase, and B = brookite), which were used as supports to prepare vanadium-based catalysts for Hg⁰ oxidation. The Hg⁰ oxidation efficiency over V₂O₅/TiO₂-B was the best, followed by V₂O₅/TiO₂-A and V₂O₅/TiO₂-R. Further experimental and theoretical results indicate that gaseous Hg⁰ reacts with surface-active chlorine species produced by the adsorbed HCl and the reaction orders of Hg⁰ oxidation over V₂O₅/TiO₂ catalyst with respect to HCl and Hg⁰ concentration were approximately 0 and 1, respectively. The excellent Hg⁰ oxidation efficiency over V₂O₅/TiO₂-B can be attributed to lower redox temperature, larger HCl adsorption capacity, and more oxygen vacancies. This work suggests that to achieve the best simultaneous removal of NO_x and Hg⁰ on state-of-the-art V₂O₅/TiO₂ catalyst, a combination of anatase and brookite TiO₂-supported vanadyl tandem catalysts is supposed to be employed in the SCR reactor, and the brookite-type catalyst should be on the downstream of the anatase-based catalyst due to the inhibition of NH₃ on Hg⁰ oxidation.