Surface-Engineered Sponge Decorated with Copper Selenide for Highly Efficient Gas-Phase Mercury Immobilization

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.

DFT study of mercury adsorption on Al2O3 with presence of HCl

mercury emission control from flue gas is a crucial issue for environment protection. Alumina is an important alkali metal oxide for mercury adsorption in particulate, meanwhile is the potential adsorbent for mercury removal. The cognition on mercury heterogeneous reaction mechanism with alumina in presence of hydrogen chloride is inadequate. In this work, the DFT calculation was applied to detect mercury's chlorides adsorption on α-Al2O3 (001) surface, the Bader charge analysis was used to estimate electron transfer and the transition state theory was used to clarify reaction pathway and energy barrier, besides, the kinetic analysis based on Gibbs free energy was conducted to study the impact of temperature on chemical reaction. The results show that Hg can be captured by weak chemisorption on α-Al2O3 (001) surface with the adsorption energy of -56.37 kJ/mol, HgCl, HgCl2 are intensively bonded on surface with adsorption energies of -276.90 kJ/mol and -231.87 kJ/mol, the surface unsaturated Al and O atoms are the active sites. Charge transfer and PDOS analysis prove that the forming of covalent bonding is responsible for Hg species adsorption. Two possible reaction pathways of Hg oxidization to HgCl2 are discussed, in which a smaller energy barrier of 0.1 eV implies the dominant pathway 1 via Eley-Rideal mechanism: two adsorbed HCl molecules dissociate on surface and then react with one Hg atom. High temperature can promote the reaction rate constants of pathway 1 and 2, but is only favorable for reducing energy barrier of pathway 2.

Efficient immobilization and detoxification of gaseous elemental mercury by nanoflower/rod WSe2/halloysite composite: Performance and mechanisms

Gaseous mercury pollution control technologies with low stability and high releasing risks always face with great challenges. Herein, we developed one halloysite nanotubes (HNTs)-supported tungsten diselenide (WSe2) composite (WSe2/HNTs) by one-pot solvothermal approach, curing Hg0 from complicated flue gas (CFG) and reducing second environment risks. WSe2 as a monolayer with nano-flower structure and HNTs with rod shapes in the as-prepared sorbent exhibited outstanding synergy efficiency, resulting in exceptional performance for Hg0 removal with high capture capacity of 30.6 mg·g-1 and rate of 9.09 μg·g-1·min-1, which benefited from the high affinity of selenium and mercury (1 ×1045) and the adequate exposure of Se-terminated. The adsorbent showed beneficial tolerance to high amount of NOx and SOx. An online lab-built thermal decomposition system (TPD-AFS) was employed to explore Hg species on the used-sorbent, finding that the adsorbed-mercury species were principally mercury selenide (HgSe). Density functional theory calculations indicated that the hollow-sites were the major adsorption sites and exhibited excellent selectivity for Hg0, as well as HgSe generation needed to overcome the 0.32 eV energy barrier. The adsorbed mercury displayed high environmental stability after the leaching toxicity test, which significantly decreased its secondary environmental risks. With these advantages, WSe2/HNTs possess enormous potential to achieve the effective and permanent immobilization of gaseous mercury from CFG in the future.

Effecting pattern study of SO2 on Hg0 removal over α-MnO2 in-situ supported magnetic composite

α-MnO₂ was in-situ supported onto silica coated magnetite nanoparticles (MagS-Mn) to study the adsorption and oxidation of Hg⁰ as well as the effecting patterns of SO₂ and O₂ on Hg⁰ removal. MagS-Mn showed Hg⁰ removal capacity of 1122.6 μg/g at 150 °C with the presence of SO₂. Hg⁰ adsorption and oxidation efficiencies were 2.4% and 90.6%, respectively. Hg⁰ removal capability deteriorated at elevated temperatures. Surface oxygen and manganese chemistry analysis indicated that SO₂ inhibited the Hg⁰ removal through consumption of adsorbed oxygen and reduction of high valence manganese. This inhibiting effect was observed to be counteracted by O₂ at lower temperatures. O₂ tended to compete with SO₂ for active sites and further create additional adsorbed oxygen sites for Hg⁰ surface reaction via surface dissociative adsorption rather than replenish the active sites consumed by SO₂. The high valence manganese was also preserved by O₂ which was essential to Hg⁰ oxidation. The intervention of O₂ in the inhibition of SO₂ on Hg⁰ removal was weakened at temperatures higher than 250 °C. Aa a result, Hg⁰ tends to be catalytic oxidized in the condition of low reaction temperatures and with the presence of O₂ over α-MnO₂ oriented composites.

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.

Tunning active oxygen species for boosting Hg0 removal and SO2-resistance of Mn-Fe oxides supported on (NH4)2S2O8 doping activated coke

Active oxygen species (AOS) play an essential role in modulating the activity of activated coke (AC) based samples. In this paper, AC was endowed with abundant AOS by modifying with (NH₄)₂S₂O₈ and MnO_x-FeO_x for Hg⁰ removal. (NH₄)₂S₂O₈ treatment induced abundant micropores and oxygen-containing functional groups, and thus provided more anchoring sites for the dispersion of MnO_x-FeO_x. The synergy of MnO_x-FeO_x and interaction between MnO_x-FeO_x and NAC support contributed to a larger surface area, highly-dispersed active components, stronger reducibility, and more metal ions with high valence of MnFe/NAC. The optimal MnFe/NAC exhibited superior Hg⁰ removal efficiency above 90% at 120∼180 ℃, as well as excellent performance for simultaneous removal of Hg⁰ and NO, and 600 ppm SO₂ and 8 vol.% H₂O addition led to a slight deterioration. XPS and Hg-TPD revealed that mercury adsorbed on MnFe/NAC included phy-Hg, C=O-Hg, COO-Hg, and O_L-HgO. Besides, the priority of AOS for Hg⁰ chemisorption was C=O > COO- > O_L, and Hg²⁺ was also detected in the outlet. Moreover, the SO₂-poisoning effect was ascribed to the sulfation of MnO_x and the occupation of COO- and C=O, and FeO_x incorporation enhanced the SO₂-resistance through weakening SO₂ adsorption on C=O and COO-. The motivation of O₂ mainly contributed to the regeneration of AOS, especially O_L. The excellent regeneration performance and stability further affirmed the application potential of MnFe/NAC for Hg⁰ capture from coal-fired flue gas.

Covalent and Non-covalent Functionalized Nanomaterials for Environmental Restoration

Nanotechnology has emerged as an extraordinary and rapidly developing discipline of science. It has remolded the fate of the whole world by providing diverse horizons in different fields. Nanomaterials are appealing because of their incredibly small size and large surface area. Apart from the naturally occurring nanomaterials, synthetic nanomaterials are being prepared on large scales with different sizes and properties. Such nanomaterials are being utilized as an innovative and green approach in multiple fields. To expand the applications and enhance the properties of the nanomaterials, their functionalization and engineering are being performed on a massive scale. The functionalization helps to add to the existing useful properties of the nanomaterials, hence broadening the scope of their utilization. A large class of covalent and non-covalent functionalized nanomaterials (FNMs) including carbons, metal oxides, quantum dots, and composites of these materials with other organic or inorganic materials are being synthesized and used for environmental remediation applications including wastewater treatment. This review summarizes recent advances in the synthesis, reporting techniques, and applications of FNMs in adsorptive and photocatalytic removal of pollutants from wastewater. Future prospects are also examined, along with suggestions for attaining massive benefits in the areas of FNMs.

Comparison of pyrite-phase transition metal sulfides for capturing leaked high concentrations of gaseous elemental mercury in indoor air: Mechanism and adsorption/desorption kinetics

Understanding the characteristics of pyrite-phase transition metal sulfides for the adsorption and desorption of gaseous elemental mercury (Hg⁰) is of vital significance for their applications in gaseous Hg⁰ capture. In this study, the adsorption and desorption of gaseous Hg⁰ onto pyrite-phase transition metal sulfides (i.e., FeS₂/TiO₂, CoS₂/TiO₂, and NiS₂/TiO₂) were compared, and the mechanisms of their differences were revealed by the kinetic analysis. The Co/NiS and SS bonds in dumbbell-shaped CoS₂ and NiS₂ were not entirely broken after oxidizing physically adsorbed Hg⁰, whereas the FeS and SS bonds in dumbbell-shaped FeS₂ were. Thus, the activation energies of CoS₂/TiO₂ and NiS₂/TiO₂ for oxidizing physically adsorbed Hg⁰ were smaller than that of FeS₂/TiO₂, causing the stronger abilities of CoS₂/TiO₂ and NiS₂/TiO₂ to oxidize physically adsorbed Hg⁰ than that of FeS₂/TiO₂. However, the bonding strengths of Hg-S in HgS adsorbed on dumbbell-shaped CoS₂ and NiS₂ were relatively weaker because of the sharing of S^2- in HgS with S^- and Co²⁺/Ni²⁺, causing the decreases in heat stabilities of HgS adsorbed on CoS₂/TiO₂ and NiS₂/TiO₂. Therefore, HgS adsorbed on CoS₂/TiO₂ and NiS₂/TiO₂ can be voluntarily decomposed to release gaseous Hg⁰, which should be combined with FeS₂/TiO₂ for the emergency treatment of liquid Hg⁰ leakage indoors.

A Molten-Salt Pyrolysis Synthesis Strategy toward Sulfur-Functionalized Carbon for Elemental Mercury Removal from Coal-Combustion Flue Gas

The emission of mercury from coal combustion has caused consequential hazards to the ecosystem. The key challenge to abating the mercury emission is to explore highly efficient adsorbents. Herein, sulfur-functionalized carbon (S-C) was synthesized by using a molten-salt pyrolysis strategy and employed for the removal of elemental mercury from coal-combustion flue gas. An ideal pore structure, which was favorable for the internal diffusion of the Hg0 molecule in carbon, was obtained by using a SiO2 hard template and adjusting the HF etching time. The as-prepared S-C with an HF etching time of 10 h possessed a saturation Hg0 adsorption capacity of 89.90 mg·g−1, far exceeding that of the commercial sulfur-loaded activated carbons (S/C). The S-C can be applied at a wide temperature range of 25–125 °C, far exceeding that of commercial S/C. The influence of flue gas components, such as SO2, NO, and H2O, on the Hg0 adsorption performance of S-C was insignificant, indicating a good applicability in real-world applications. The mechanism of the Hg0 removal by S-C was proposed, i.e., the reduced components, including sulfur thiophene, sulfoxide, and C-S, displayed a high affinity toward Hg0, which could guarantee the stable immobilization of Hg0 as HgS in the adsorbent. Thus, the molten-salt pyrolysis strategy has a broad prospect in the application of one-pot carbonization and functionalization sulfur-containing organic precursors as efficient adsorbents for Hg0.

Coordinatively Unsaturated Selenides over CuFeSe2 toward Highly Efficient Mercury Immobilization

Metal selenides have been demonstrated as promising Hg⁰ remediators, while their inadequate adsorption rate primarily impedes their application feasibility. Based on the critical role of coordinatively unsaturated selenide ligands in immobilizing Hg⁰, this work proposed a novel strategy to enhance the Hg⁰ adsorption rate of metal selenides by magnitudes by purposefully adjusting the selenide saturation. Copper iron diselenide (CuFeSe₂), in which the surface reconstruction tended to occur at ambient temperature, was adopted as the concentrator of unsaturated selenides. The adsorption rate of CuFeSe₂ reached as high as 900.71 μg·g^-1·min^-1, far exceeding those of the previously reported metal selenides by at least 1 magnitude. The excellent resistance of CuFeSe₂ to flue gas interference and temperature fluctuation warrants its applicability in real-world conditions. The theoretical investigations and mechanistic interpretations based on density functional theory (DFT) calculation further confirmed the indispensable role of unsaturated selenides in Hg⁰ adsorption. This work aims not only to develop a Hg⁰ remediator with extensive applicability in coal combustion flue gas but also to take a step toward the rational design of selenide-based sorbents for diverse environmental remediation by the facile surface functionalization of coordinatively adjustable ligands.

Strengthen the Affinity of Element Mercury on the Carbon-Based Material by Adjusting the Coordination Environment of Single-Site Manganese

Mercury, as a highly poisonous pollutant, poses a severe threat to the global population. However, the removal of Hg⁰ can only be carried out at below 100 °C due to the weak binding of the adsorbent. Herein, a series of carbon-based materials with different coordination environments and atomic dispersion of single-site manganese were prepared, and their elemental mercury removal performance was systematically investigated. It was demonstrated that the coordination environment around manganese determines its electronic structure and size, thus affecting its affinity with mercury. The obtained best adsorbents atomically dispersed Mn with atom size near 0.2 nm, achieves high Hg⁰ removal efficiency and over 13 mg/g Hg⁰ adsorption capacity at 200 °C. And the SO₂ resistance performance of single atoms (∼0.2 nm) is much better than clusters (∼1-2 nm) because of its high selectivity, that the effect of SO₂ is only 3%. Density functional theory (DFT) reveals that Mn with four-nitrogen atoms (Mn-N₄-C═O) is more active than other number nitrogen coordination materials. Moreover, the presence of carboxyl groups around manganese also promotes affinity for Hg⁰. This work might shed new light on the enhancement of Hg⁰ affinity in carbon-based materials and the rational design of the coordination structure of the tunable Hg⁰ activities.

Effect of Sonochemical Treatment on Thermal Stability, Elemental Mercury (Hg0) Removal, and Regenerable Performance of Magnetic Tea Biochar

Elemental mercury (Hg⁰) removal from a hot gas is still challenging since high temperature influences the Hg⁰ removal and regenerable performance of the sorbent. In this work, a facile yet innovative sonochemical method was developed to synthesize a thermally stable magnetic tea biochar to capture the Hg⁰ from syngas. A sonochemically synthesized magnetic sorbent (TUF_0.46) exhibited a more prodigious surface area with developed pore structures, ultra-paramagnetic properties, and high dispersion of Fe₃O₄/γ-Fe₂O₃ particles than a simply synthesized magnetic sorbent (TF_0.46). The results showed that TUF_0.46 demonstrated strong thermostability and attained a high Hg⁰ removal performance (∼98.6%) at 200 °C. After the 10th adsorption/regeneration cycle, the Hg⁰ removal efficiency of TUF_0.46 was 19% higher than that of TF_0.46. Besides, at 23.1% Hg⁰ breakthrough, TUF_0.46 achieved an average Hg⁰ adsorption capacity of 16.58 mg/g within 24 h under complex syngas (20% CO, 20% H₂, 5% H₂O, and 400 ppm H₂S). In addition, XPS results revealed that surface-active components (Fe⁺, O^2-, O*, C=O) were the key factor for high Hg⁰ removal performance over TUF_0.46 from syngas. Hence, sonochemistry is a promising practical tool for improving the surface morphology, thermal resistance, renewability, and Hg⁰ removal efficiency of a sorbent.