Synthesis of a Triangle-Fused Six-Pointed Star and Its Electrocatalytic CO2 Reduction Activity.

As electrocatalysts, molecular catalysts with large aromatic systems (such as terpyridine, porphyrin, or phthalocyanine) have been widely applied in the CO2 reduction reaction (CO2RR). However, these monomeric catalysts tend to aggregate due to strong π-π interactions, resulting in limited accessibility of the active site. In light of these challenges, we present a novel strategy of active site isolation for enhancing the CO2RR. Six Ru(Tpy)2 were integrated into the skeleton of a metallo-organic supramolecule by stepwise self-assembly in order to form a rhombus-fused six-pointed star R1 with active site isolation. The turnover frequency (TOF) of R1 was as high as 10.73 s-1 at -0.6 V versus reversible hydrogen electrode (vs RHE), which is the best reported value so far at the same potential to our knowledge. Furthermore, by increasing the connector density on R1's skeleton, a more stable triangle-fused six-pointed star T1 was successfully synthesized. T1 exhibits exceptional stability up to 126 h at -0.4 V vs RHE and excellent TOF values of CO. The strategy of active site isolation and connector density increment significantly enhanced the catalytic activity by increasing the exposure of the active site. This work provides a starting point for the design of molecular catalysts and facilitates the development of a new generation of catalysts with a high catalytic performance.

Constructing Heterointerfaces in Dual-Phase High-Entropy Oxides to Boost O2 Activation and SO2 Resistance for Mercury Removal in Flue Gas.

The low O2 activation ability at low temperatures and SO2 poisoning are challenges for metal oxide catalysts in the application of Hg0 removal in flue gas. A novel high-entropy fluorite oxide (MgAlMnCo)CeO2 (Co-HEO) with the second phase of spinel is synthesized by the microwave hydrothermal method for the first time. A high efficiency of Hg0 removal (close to 100%) is achieved by Co-HEO catalytic oxidation at temperatures as low as 100 °C and in the atmosphere of 145 µg m-3 Hg0 at a high GHSV (gas hourly space velocity) of 95,000 h-1. According to O2-TPD and in situ FT-IR, this extremely superior catalytic oxidation performance at low temperatures originates from the activation ability of Co-HEO to transform O2 into superoxide and peroxide, which is promoted by point defects induced from the spinel/fluorite heterointerfaces. Meanwhile, SO2 resistance of Co-HEO for Hg0 removal is also improved up to 2000 ppm due to the high-entropy-stabilized structure, construction of heterointerfaces, and synergistic effect of the multicomponents for inhibiting the oxidation of SO2 to surface sulfate. The design strategy of the dual-phase high-entropy material launches a new route for metal oxides in the application of catalytic oxidation and SO2 resistance.

Nafion-Mediated Proton Transfer Facilitates the Electroreduction of SO2 to H2S.

The electrocatalytic reduction of SO2 to produce H2S is a critical approach for achieving the efficient utilization of sulfur resources. At the core of this approach for commercial applications lies the imperative need to elevate current density. However, the challenges posed by high current density manifest in the rapid depletion of protons, leading to a decrease in SO2 partial pressure, consequently hampering the generation and separation of H2S. Here, we demonstrate an effective solution to alleviate the problem of insufficient supply of protons by employing Nafion polymer as the proton conductor to modified Cu catalysts surface, creating a proton-enriched layer to boost H2S generation. It was observed that Nafion shortens the hydrogen bonds with water molecules in the electrolyte via its sulfonic acid groups, benefiting the proton transfer and consequently increasing the proton density on the electrode surface by 5-fold. With the Nafion-modified catalyst, the H2S partial current density and separation efficiency reached 205.9 mA·cm-2 (1.01 mmol·cm-2·h-1) and 87.8%, which were 1.34 and 1.22 times that on unmodified Cu, respectively. This work highlights the practicality of fabricating a proton conductor via ionic polymer for the control over product selectivity in pH-sensitive reactions under high current density.

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 S22- 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.

Achieving Large-Capability Adsorption of Hg0 in Wet Scrubbing by Defect-Rich Colloidal Copper Sulfides under High-SO2 Atmosphere.

This paper reports on a novel method to remove Hg0 in the wet scrubbing process using defect-rich colloidal copper sulfides for reducing mercury emissions from non-ferrous smelting flue gas. Unexpectedly, it migrated the negative effect of SO2 on mercury removal performance, while also enhancing Hg0 adsorption. Colloidal copper sulfides demonstrated the superior Hg0 adsorption rate of 306.9 µg·g-1·min-1 under 6% SO2 + 6% O2 atmosphere with a removal efficiency of 99.1%, and the highest-ever Hg0 adsorption capacity of 736.5 mg·g-1, which was 277% higher than all other reported metal sulfides. The Cu and S sites transformation results reveal that SO2 could transform the tri-coordinate S sites into S22- on copper sulfides surfaces, while O2 regenerated Cu2+ via the oxidation of Cu+. The S22- and Cu2+ sites enhanced Hg0 oxidation, and the Hg2+ could strongly bind with tri-coordinate S sites. This study provides an effective strategy to achieve large-capability adsorption of Hg0 from non-ferrous smelting flue gas.

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 Sx2- 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.

Formation of sulfur oxide groups by SO2 and their roles in mercury adsorption on carbon-based materials.

The presence of SO2 display significant effect on the mercury (Hg) adsorption ability of carbon-based sorbent. Yet the adsorption and oxidation of SO2 on carbon with oxygen group, as well as the roles of different sulfur oxide groups in Hg adsorption have heretofore been unclear. The formation of sulfur oxide groups by SO2 and their effects on Hg adsorption on carbon was detailed examined by the density functional theory. The results show that SO2 can be oxidized into SO3 by oxygen group on carbon surface. Both C-SO2 and C-SO3 can improve Hg adsorption on carbon site, while the promotive effect of C-SO2 is stronger than C-SO3. Electron density difference analyses reveal that sulfur oxide groups enhance the charge transfer ability of surface unsaturated carbon atom, thereby improving Hg adsorption. The experimental results confirm that surface active groups formed by SO2 adsorption is more active for Hg adsorption than the groups generated by SO3.

The Design of Sulfated Ce/HZSM-5 for Catalytic Decomposition of CF4.

CF4 has a global warming potential of 6500 and possesses a lifetime of 50,000 years. In this study, we modified the HZSM-5 catalyst with Ce and sulfuric acid treatment. The S/Ce/HZSM-5 catalyst achieves 41% of CF4 conversion at 500 °C, which is four times higher than that over Ce/HZSM-5, while the HZSM-5 exhibits no catalytic activity. The effects of modification were studied by using NH3-TPD, FT-IR of pyridine adsorption, and XPS methods. The results indicated that the modification, especially the sulfuric acid treatment, strongly increased the Lewis acidic sites, strong acidic sites, and moderate acidic sites on catalysts, which are the main active centers for CF4 decomposition. The mechanism of acidic sites increases by modification and CF4 decomposition is clarified. The results of this work will help the development of more effective catalysts for CF4 decomposition.

Low-temperature Hg0 abatement by ionic liquid based on weak interaction.

Low-temperature gaseous elemental mercury (Hg0) abatement is an objective demand in industrial flue gas treatment. In this work, we proposed a new approach for Hg0 capture via weak interaction of ionic liquids. Ionic liquids with varied anions (1-butyl-3-methylimidazolium thioacetate ([Bmim][ThAc]), 1-butyl-3-methylimidazolium diethyldithiocarbamate ([Bmim][DTCR]), and 1-butyl-3-methylimidazolium ethylxanthate ([Bmim][EX])) were designed and synthesized. The interaction energies between ionic liquids and elemental mercury were proved to be positively related to mercury removal efficiency, revealing that the electrostatic interaction derived physical adsorption from anions is the dominant factor affecting mercury removal performance. [Bmim][ThAc] with the largest anionic electrostatic interaction energy showed the best mercury abatement performance, achieving a Hg0 removal efficiency of over 98% and an adsorption capacity of 10.66 mg/g at 50 °C. The influence of temperature and the results of mercury temperature-programmed desorption (Hg-TPD), X-ray photoelectron spectroscopy (XPS) further confirmed that the ionic liquid combines with elemental mercury through physical adsorption. The work provides a new perspective on designing high-efficiency sorbents for mercury removal at low temperature.

DFT and Experimental Studies on the Mechanism of Mercury Adsorption on O2-/NO-Codoped Porous Carbon.

The utilization of O2 and NO in flue gas to activate the raw porous carbon with auxiliary plasma contributes to an effective mercury (Hg)-removal strategy. The lack of in-depth knowledge on the Hg adsorption mechanism over the O2-/NO-codoped porous carbon severely limits the development of a more effective Hg removal method and the potential application. Therefore, the generation processes of functional groups on the surface during plasma treatment were investigated and the detailed roles of different groups in Hg adsorption were clarified. The theoretical results suggest that the formation of functional groups is highly exothermic and they preferentially form on a carbon surface, and then affect Hg adsorption. The active groups affect Hg adsorption in a different manner, which depends on their nature. All of these active groups can improve Hg adsorption by enhancing the interaction of Hg with a surface carbon atom. Particularly, the preadsorbed NO2 and O3 groups can react directly with Hg by forming HgO. The experimental results confirm that the active groups cocontribute to the high Hg removal efficiency of O2-/NO-codoped porous carbon. In addition, the mercury temperature-programmed desorption results suggest that there are two forms of mercury present on O2-/NO-codoped porous carbon, including a carbon-bonded Hg atom and HgO.

High-efficient adsorption and removal of elemental mercury from smelting flue gas by cobalt sulfide.

Nonferrous metal smelting produces a large amount of Hg0 in flue gas, which has caused serious damage to the environment and human health. In this work, amorphous cobalt sulfide was synthesized by a liquid-phase precipitation method and was used for capturing gaseous Hg0 from simulated smelting flue gas at low temperatures (50~150 °C). In the adsorption process, Hg0 can be transformed into the stable mercury compound, which is confirmed to be HgS by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption of Hg (Hg-TPD) analysis. Meanwhile, XPS results also demonstrate that S22- species on the surface of cobalt sulfide play an important role in Hg0 transformation. At the temperature of 50 °C (inlet Hg0 concentration of 214 µg·m-3), the Hg0 adsorption capacity of cobalt sulfide (penetration rate of 25%) is as high as 2.07 mg·g-1, which is much higher than that of popular adsorbents such as activated carbons and metal oxides. In addition, it was found that the Hg0 removal efficiency by cobalt sulfide in the flue gas with high concentration of SO2 (5%) remained more than 94%. The good adsorption and Hg0 removal performance guarantee cobalt sulfide the great superiority and application potential in the treatment of Hg0 in smelting flue gas with high concentration of SO2.

Transport and transformation of mercury during wet flue gas cleaning process of nonferrous metal smelting.

Reducing mercury emission is hot topic for international society. The first step for controlling mercury in fuel gas is to investigate mercury distribution and during the flue gas treatment process. The mercury transport and transformation in wet flue gas cleaning process of nonferrous smelting industry was studied in the paper with critical important parameters, such as the solution temperature, Hg0 concentration, SO2 concentration, and Hg2+ concentration at the laboratory scale. The mass ratio of the mercury distribution in the solution, flue gas, sludge, and acid fog from the simulated flue gas containing Hg2+ and Hg0 was 49.12~65.54, 18.34~35.42, 11.89~14.47, and 1.74~3.54%, respectively. The primary mercury species in the flue gas and acid fog were gaseous Hg0 and dissolved Hg2+. The mercury species in the cleaning solution were dissolved Hg2+ and colloidal mercury, which accounted for 56.56 and 7.34% of the total mercury, respectively. Various mercury compounds, including Hg2Cl2, HgS, HgCl2, HgSO4, and HgO, existed in the sludge. These results for mercury distribution and speciation are highly useful in understanding mercury transport and transformation during the wet flue gas cleaning process. This research is conducive for controlling mercury emissions from nonferrous smelting flue gas and by-products.

The electrochemical selective reduction of NO using CoSe2@CNTs hybrid.

Converting the NO from gaseous pollutant into NH4+ through electrocatalytical reduction using cost-effective materials holds great promise for pollutant purifying and resources recycling. In this work, we developed a highly selective and stable catalyst CoSe2 nanoparticle hybridized with carbon nanotubes (CoSe2@CNTs). The CoSe2@CNTs hybrid catalysts performed an extraordinary high selectivity for NH4+ formation in NO electroreduction with minimal N2O production and H2 evolution. The specific spatial structure of CoSe2 is conductive to the predominant formation of N-H bond between the N from adsorbed NO and H and inhibition of N-N formation from adjacent adsorbed NO. It was also the first time to convert the coordinated NO into NH4+ using non-noble metal catalysis. Moreover, the original concept of employing CoSe2 as eletrocatalyst for NO hydrogenation presented in this work can broaden horizons and provide new dimensions in the design of new highly efficient catalysts for NH4+ synthesis in aqueous solution.

Selenium catalyzed Fe(III)-EDTA reduction by Na2SO3: a reaction-controlled phase transfer catalysis.

Fe(II)-EDTA, a typical chelated iron, is able to coordinate with nitric oxide (NO) which accelerates the rates and kinetics of the absorption of flue gas. However, Fe(II)-EDTA can be easily oxidized to Fe(III)-EDTA which is unable to absorb NO. Therefore, the regeneration of fresh Fe(II)-EDTA, which actually is the reduction of Fe(III)-EDTA to Fe(II)-EDTA, becomes a crucial step in the denitrification process. To enhance the reduction rate of Fe(III)-EDTA, selenium was introduced into the SO3 (2-)/Fe(III)-EDTA system as catalyst for the first time. By comparison, the reduction rate was enhanced by four times after adding selenium even at room temperature (25 °C). Encouragingly, elemental Se could precipitate out when SO3 (2-) was consumed up by oxidation to achieve self-separation. A catalysis mechanism was proposed with the aid of ultraviolet-visible (UV-Vis) spectroscopy, Tyndall scattering, horizontal attenuated total reflection Fourier transform infrared (HATR-FTIR) spectroscopy, and X-ray diffraction (XRD). In the catalysis process, the interconversion between SeSO3 (2-) and nascent Se formed a catalysis circle for Fe(III)-EDTA reduction in SO3 (2-) circumstance.

Controllable synthesis of hierarchical porous Fe3O4 particles mediated by poly(diallyldimethylammonium chloride) and their application in arsenic removal.

Hierarchical porous Fe3O4 particles with tunable grain size were synthesized based on a facile poly (diallyldimethylammonium chloride) (PDDA)-modulated solvothermal method. The products were characterized with scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), N2 adsorption-desorption technique, vibrating sample magnetometer (VSM), and dynamic light scattering (DLS). The results show that increasing the PDDA dosage decrease the grain size and particle size, which increased the particle porosity and enhanced the surface area from 7.05 to 32.75 m(2) g(-1). Possible mechanism can be ascribed to the PDDA function on capping the crystal surface and promoting the viscosity of reaction medium to mediate the growth and assembly of grain. Furthermore, the arsenic adsorption application of the as-obtained Fe3O4 samples was investigated and the adsorption mechanism was proposed. High magnetic Fe3O4 particles with increased surface area display improved arsenic adsorption performance, superior efficiency in low-level arsenic removal, high desorption efficiency, and satisfactory magnetic recyclability, which are very promising compared with commercial Fe3O4 particles.