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• Various synthetic methods for metal sulfides are introduced and compared. • Performances, merits, and flaws of metal sulfides are summarized and commented. • Layered metal sulfides, MoS 2 , WS 2 and SnS 2 , are the most promising mercury sorbents. • Effects of gas ingredients on the performances of metal sulfides are summed up. • Mercury capture mechanisms for metal sulfides are outlined and discussed. Mercury is largely emitted into the atmosphere during fossil fuel combustion or gasification, which causes a long-term contamination problem and poses great threats to human health. Currently, novel metal sulfides have been extensively investigated in capturing gaseous mercury because of their intense Hg0 affinities, large mercury uptakes, and distinguished tolerance to sulfur dioxide. This article overviews the recent progress on elemental mercury capture by diverse metal sulfides, i.e., CuS, ZnS, pyrite-phase metal sulfides, layered metal sulfides, Bi 2 S 3 and In 2 S 3. CuS and ZnS show good performances in a narrow temperature range due to the poor thermal stability and the compact crystal structure, respectively. Bi 2 S 3 and In 2 S 3 are also active in Hg0 adsorption, however, their performances are still unsatisfactory. Most pyrite-phase metal sulfides show moderate Hg0 capture abilities likely due to their compact crystal structures. Loading pyrites onto carriers or creating S vacancies in pyrite lattices seem to be feasible pathways to improve their performances. MoS 2 and WS 2 attained via molten salt method significantly outperform the ones obtained via hydrothermal method at elevated temperatures due to the production of ample sulfur variances and chemisorbed oxygen. Incorporating heteroatoms and expanding the interlayer distance by ions intercalation are effective routes to further strengthen their performances probably due to promoted electron transfer and increased accessibility of active sites, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • CoS 2 /SnO 2 composite adsorbent is facilely obtained via a molten salt method. • CoS 2 and SnO 2 exhibit a cooperative effect with respect to mercury capture. • SnO 2 addition can notably reinforce the Hg0 capture ability of cobalt disulfide. • NO and SO 2 negatively affect the Hg0 removal performance of CoS 2 /SnO 2. SnO 2 doped cobalt pyrite (CoS 2 /SnO 2) adsorbent is facilely prepared using a molten salt method and used to capture Hg0 capture in simulated flue gas. Bare CoS 2 and SnO 2 display relatively lower Hg0 adsorption ability. SnO 2 addition can evidently enhance the Hg0 capture ability of CoS 2 likely owing to the synergetic effect between CoS 2 and SnO 2. NO and SO 2 can negatively affect Hg0 capture processes due to competitive adsorption or side reaction. Co2+, S 2 2-, Sn4+ ions serve as the major adsorption sites for elemental mercury capture over CoS 2 /SnO 2. Chemisorbed oxygen may be participated in the mercury removale process. [ABSTRACT FROM AUTHOR]

A SnS 2 @Fe 3 O 4 composite has been easily synthesized via a KSCN fused salt approach and adopted for capturing elemental mercury at low temperature. Calcination temperature significantly impacts the mercury capture performance of SnS 2 -T. The optimal synthesis temperature for SnS 2 -T is 250 °C. Pristine SnS 2 -250 obtained at 250 °C exhibits a moderate Hg0 adsorption capability with mercury removing efficiency less than 65% within 80–120 °C. Fe 3 O 4 incorporation can notably improve the mercury capture ability of SnS 2 -250 probably due to the cooperative effect between SnS 2 nanoflakes and magnetic Fe 3 O 4 microspheres. SnS 2 -250@Fe 3 O 4 holds a good magnetism (saturation magnetization: 23 emu/g), which performs optimally at 100 °C with Hg0 capture efficiency of 95.2%. Sn4+, S2−, Fe3+ ions and chemisorbed oxygen species are principal active sites for Hg0 capture over SnS 2 -250@Fe 3 O 4 , which convert adsorbed Hg0 into HgO, HgS, and HgSO 4. • A SnS 2 @Fe 3 O 4 composite has been facilely obtained via a KSCN molten salt method. • Calcination temperature can notably influence the Hg0 capture performance of SnS 2. • SnS 2 nanoflakes and Fe 3 O 4 microspheres may show a synergy toward Hg0 capture. • Fe 3 O 4 addition can evidently enhance the mercury capture ability of tin disulfide. [ABSTRACT FROM AUTHOR]

A simplified approach for the fabrication of CuO/TiO 2 was demonstrated. In this study, low cost CuO/TiO 2 photocatalysts (CuO loading 0–15 wt.%) were prepared, characterized and evaluated for gas-phase Hg 0 oxidation. The obtained CuO/TiO 2 photocatalysts were used to remove gaseous elemental mercury under UV light and visible light (both xenon lamp and LED), respectively, and the optimum doping levels of CuO and optimum illumination conditions were determined. The results showed that the CuO/TiO 2 photocatalysts were highly efficient in oxidizing Hg 0 , reaching above 70% in all cases under UV light, peaking at 57.8% with 1.25 wt.% CuO under visible light and peaking at about 60% with 1.25 wt.% CuO under LED light. We have proposed that the probable mechanism by which CuO/TiO 2 photocatalysts removes gaseous elemental mercury is two-fold: the CuO not only prevents electrons and holes from recombining, but also narrows the band gap of TiO 2 . [ABSTRACT FROM AUTHOR]

[Display omitted] • The different morphologies of BiOI and Bi modified Bi 4 O 5 I 2 catalysts were successfully synthesized by three methods. • The synergistic effect of oxygen vacancies and built-in electric field promotes the separation of photogenerated electron-holes. • The 3D Bi/Bi 4 O 5 I 2 microspheres with rich oxygen vacancies exhibits an excellent photocatalytic activity and durability. • Possible photo-induced charges transfer mechanism and photocatalytic reaction mechanism were proposed. A 3D hierarchical metallic Bi modified Bi 4 O 5 I 2 microspheres with rich oxygen vacancies (Vos) was successfully prepared via a one-pot solvothermal method. In this work, the different morphologies of BiOI and Bi modified Bi 4 O 5 I 2 were prepared by precipitation, hydrothermal and solvothermal methods. It was discovered that using the solvothermal method with ethylene glycol as the solvent could not only prepare microspheres Bi 4 O 5 I 2 with rich oxygen vacancies but also control the content of Bi by changing the reaction duration. The doping of metallic Bi created a built-in electric field between Bi and Bi 4 O 5 I 2 , which is helpful to improve the efficiency of carrier separation. Benefited from the synergistic effect of oxygen vacancies and built-in electric field, the as-prepared Bi/Bi 4 O 5 I 2 exhibits an excellent mercury removal efficiency, high-performance stability, and satisfactory sulfur resistance as well as nitric oxide resistance. Finally, the mechanism of catalytic oxidation reaction was proposed, photo-generated holes and superoxide radicals were predominant in the photocatalytic reaction. [ABSTRACT FROM AUTHOR]

• The prospect and limitation of low-dimensional carbon for Hg0 removal are commented. • Bio-char, carbon nitride, and metal-organic framework are promising mercury sorbents. • The performances and mechanisms of diverse carbon-based sorbents are fully discussed. Mercury emission, derived from natural gas exploitation, metal sintering, coal gasification and combustion, gold mining, etc., has posed great threaten to the environment and human beings due to its volatility, mobility, toxicity, and bioaccumulation in ecosystem and food chains. Adsorption using carbon materials is regarded as one of the most promising techniques for mercury emission control due to its simple equipment, convenient operation, high removing efficacy, less secondary pollution, etc. This review comments the new research progress of elemental mercury capture by novel carbon-based sorbents in recent five years, particularly emerging carbon materials, such as bio-chars, graphene and graphene oxide, carbon nanotubes and nanofibers, carbon spheres, carbon aerogels, metal-organic frameworks, and graphitic carbon nitrides. The mercury removal performances and reaction mechanisms of diverse carbon-based sorbents along with their merits and drawbacks are fully discussed, which aims to strengthen the understanding of this emerging research topic and outline future research directions for the development of sustainable, recyclable, and cost-effective carbon-based mercury sorbents. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbon nitride microsphere (CNS) is synthesized via a hydrothermal method. • Heterojunction interface between CNS and CeO 2 activate Hg0 adsorption process. • DFT guided design of microstructure is used to construct efficient mercury sorbents. • Hg0 is chemically adsorbed on the heterojunction interface of CeO 2 /CNS sorbent. Engineering sorbent microstructure to regulate their interfacial activity is a promising strategy for enhancing mercury adsorption activity. In this work, carbon nitride microsphere (CNS) synthesized via a hydrothermal route is used for Hg0 adsorption. Bare CNS shows a moderate Hg0 capture performance with mercury removal efficiency of 43.1%. To accomplish effective mercury capture by CNS, the heterojunction structure is rationally developed via density functional theory (DFT). Calculation results reveal a considerable charge interaction at the heterojunction interface of CNS and CeO 2. Mercury adsorption energy at the heterojunction interface is significantly higher than that of pristine CNS. x CeO 2 /CNS composites are prepared by wetness impregnation method under the guidance of DFT results. Optimal performance is observed over 5CeO 2 /CNS with Hg0 removal efficiency of 98.3%, which testifies that constructing a heterojunction interface can distinctly enhance the mercury capture ability of CNS. These results contribute a lot to the deep understanding of the structural properties and mercury adsorption behaviors of x CeO 2 /CNS composites, which also indicate that DFT-assisted design of the microstructures of sorbents is a feasible way to improve their mercury removal performances. [ABSTRACT FROM AUTHOR]