Nanosized Copper Selenide Functionalized Zeolitic Imidazolate Framework‐8 (CuSe/ZIF‐8) for Efficient Immobilization of Gas‐Phase Elemental Mercury

Abstract

A key challenge in elemental mercury (Hg 0 ) decontamination from flue gas lies in the design of a sorbent with abundant reactive adsorption sites that exhibit high affinity toward Hg 0 to simultaneously achieve rapid capture and large capacity. Herein, zeolitic imidazolate framework-8 (ZIF-8) supported copper selenide (CuSe) nanocomposites are synthesized by a newly designed two-step surfactant-assisted method. The as-prepared CuSe/ZIF-8 with CuSe to ZIF-8 mass ratio of 80% (0.8NC-ZIF) exhibits unparalleled performance toward Hg 0 adsorption with equilibrium capacity and average rate reaching 309.8 mg g −1 and 105.3 µg g −1 min −1 , respectively, surpassing all reported metal sulfides and traditional activated-carbon-based sorbents. The impressive performance of 0.8NC-ZIF for Hg 0 immobilization is primarily attributed to the adequate exposure of the Se-terminated sites with high affinity toward Hg 0 resulted from the layered structure of CuSe. The adsorbed mercury selenide exhibits even higher stability than the most stable natural mercury ore-that is, mercury sulfide-hence minimizing its environmental impact when the CuSe/ZIF-8 sorbent is dumped. This work provides a new mindset for future design of sorbents for efficient Hg 0 capture from industrial flue gas. The results also justify the candidature of CuSe/ZIF to be applicable for mercury pollution remediation in real-world conditions.

Density Functional Theory Study of Elemental Mercury Immobilization on CuSe(001) Surface: Reaction Pathway and Effect of Typical Flue Gas Components

“…The CuSe crystal exhibited excellent performance for Hg 0 immobilization was proven in our previous study to be klockmannite with the P 63/ mmc space group ( a = b = 3.98 Å, c = 17.38 Å, α = β = 90°, γ = 120°, as shown in Figure a) . Klockmannite preferentially grows along six energetically equivalent (110) surfaces as they exhibited relatively narrow lattice fringes, thus exposing the CuSe(001) facet to a large extent.…”

“…In the fixed-bed reactor, 1 mg of the CuSe sorbent was mixed with 499 mg of silicon dioxide (SiO 2 ) and pretreated with 100 μg m –3 Hg 0 carried by air at 50 °C for 30 min, and the as-obtained CuSe was called the Hg-laden sorbent. Moreover, the Hg-saturated CuSe was prepared by pretreating 500 mg of CuSe–SiO 2 mixture in a nested-tube reactor for 4 h. SiO 2 was proven to be inert for Hg 0 capture in our previous study, which can make sure that CuSe primarily accounted for the Hg 0 adsorbed. Subsequently, 500 mg of Hg-laden CuSe–SiO 2 mixture was purged by air until the outlet Hg 0 concentration equaled zero stably, while for Hg-saturated CuSe–SiO 2 mixture, 5 mg of it was weighed out and purged by N 2 as Hg-saturated CuSe adsorbed redundant Hg 0 exceeding the testing limit of the mercury analyzer.…”

“…Among various mineral selenides, hexagonal copper selenide (CuSe) based sorbent was found as the first example and a potential candidate for efficient and permanent Hg 0 sequestrations. The Hg 0 adsorption capacity of CuSe reached more than 200 mg g –1 , which surpassed the Hg 0 adsorption capacities of traditional ACs by at least two orders of magnitude . However, although HgSe was experimentally evidenced to be the final product after Hg 0 immobilization on CuSe surface, the intermediates and reaction pathways are rarely revealed by only experimental studies, which significantly impedes a molecular-level insight into the adsorption mechanisms and hence a wise design of future mineral selenide sorbents.…”

“…As an immediate response to the forces of the Minamata Convention and the defects of AC techniques, mineral selenides have been recently found as potential alternatives to traditional AC sorbents for Hg 0 capture from various industrial processes. ,− The mineral selenides significantly outperformed traditional ACs because (1) mineral selenides are adequately covered by active selenide sites that are the one of the best-known antidotes against mercury and could achieve extremely high Hg 0 capture performances; and (2) mineral selenides could chemisorb Hg 0 and convert Hg 0 into metabolically inactive mercury selenide (HgSe), which exhibited much lower leachability than Hg 0 adsorbed on ACs by orders of magnitude . Among various mineral selenides, hexagonal copper selenide (CuSe) based sorbent was found as the first example and a potential candidate for efficient and permanent Hg 0 sequestrations.…”

“…However, although HgSe was experimentally evidenced to be the final product after Hg 0 immobilization on CuSe surface, the intermediates and reaction pathways are rarely revealed by only experimental studies, which significantly impedes a molecular-level insight into the adsorption mechanisms and hence a wise design of future mineral selenide sorbents. Moreover, the Hg 0 adsorption performance of CuSe was only tested under relatively simple gas compositions, i.e., pure nitrogen (N 2 ) or nitrogen and oxygen (N 2 + O 2 ) . In this case, the role of typical flue gas components widely existing in coal combustion flue gases, i.e., SO 2 and H 2 O, on Hg 0 immobilization over CuSe remains to be clarified to justify its applicability in a real-world condition.…”