Structural defects in 2D MoS2 nanosheets and their roles in the adsorption of airborne elemental mercury

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.

Atomic scale interfacial magnetism and origin of metal-insulator transition in (LaNiO[Formula: see text])[Formula: see text]/(CaMnO[Formula: see text])[Formula: see text] superlattices: a first principles study

Interfacial magnetism and metal-insulator transition at LaNiO[Formula: see text]-based oxide interfaces have triggered intense research efforts, because of the possible implications in future heterostructure device design and engineering. Experimental observation lack in some points a support from an atomistic view. In an effort to fill such gap, we hereby investigate the structural, electronic, and magnetic properties of (LaNiO[Formula: see text])[Formula: see text]/(CaMnO[Formula: see text])[Formula: see text] superlattices with varying LaNiO[Formula: see text] thickness (n) using density functional theory including a Hubbard-type effective on-site Coulomb term. We successfully capture and explain the metal-insulator transition and interfacial magnetic properties, such as magnetic alignments and induced Ni magnetic moments which were recently observed experimentally in nickelate-based heterostructures. In the superlattices modeled in our study, an insulating state is found for n=1 and a metallic character for n=2, 4, with major contribution from Ni and Mn 3d states. The insulating character originates from the disorder effect induced by sudden environment change for the octahedra at the interface, and associated to localized electronic states; on the other hand, for larger n, less localized interfacial states and increased polarity of the LaNiO[Formula: see text] layers contribute to metallicity. We discuss how the interplay between double and super-exchange interaction via complex structural and charge redistributions results in interfacial magnetism. While (LaNiO[Formula: see text])[Formula: see text]/(CaMnO[Formula: see text])[Formula: see text] superlattices are chosen as prototype and for their experimental feasibility, our approach is generally applicable to understand the intricate roles of interfacial states and exchange mechanism between magnetic ions towards the overall response of a magnetic interface or superlattice.

Insights into synergistic oxidation mechanism of Hg0 and chlorobenzene over MnCo2O4 microsphere with oxygen vacancy and acidic site

The simultaneous control of Hg⁰ and chlorinated organics has become the frontier of environmental engineering but still lacks the understanding of synergistic oxidation mechanism. Herein, we designed a Mn-Co catalyst with abundant oxygen vacancies and acidities, which delivered more than 90 % oxidation performance of Hg⁰ within 100-325 °C and achieved 90 % conversion of chlorobenzene at 220 °C. A synergistic effect was observed in the oxidation of Hg⁰ and chlorobenzene. Experimental and computational results revealed that Lewis acid over Mn site weakened C-Cl bands of chlorobenzene by electronic traction. The strong interaction between adsorbed mercury and Cl further promoted dechlorination process to generate HgCl₂ gas, while accelerating the nucleophilic substitution of Brønsted acid attacking the benzene ring over Co site, consequently triggering synergistic oxidation of Hg⁰ and chlorobenzene. Oxygen vacancies enhanced the initial adsorption of Hg⁰ and chlorobenzene. Meanwhile, the interfacial charge-transfer from Hg-d to Cl-p orbitals alleviated deactivation of Lewis acid and slowed down the consumption of Brønsted acid, which accelerated the conversion of intermediates to CO₂/H₂O and promoted deep oxidation of chlorobenzene. This work provides a unique insight into the promotion of the synergistic oxidation of Hg⁰ and chlorobenzene and is expected to guide the industrial applications.

Enhanced Tetracycline Adsorption of MoS2 via Defect Introduction Under Microwave Irradiation

Defect engineering is a promising method for improving the performance of MoS₂ in various fields. In this study, sulfur-defect-enriched MoS₂ (SD-MoS₂) nanosheets were fabricated via a facile microwave-hydrothermal strategy in 10 min for tetracycline (TC) adsorption applications. The introduction of sulfur defects in MoS₂ induced more exposed unsaturated sulfur atoms at the edge, enhancing the interaction between the adsorbent and antibiotic and improving the adsorption activity of the antibiotic. Density functional theory calculations further revealed that sulfur defects in MoS₂ could alter the electronic structure and exhibited low TC adsorption energy of -2.09 eV. This work provides a new method for fabricating MoS₂ nanosheets and other transition metal dichalcogenide-based adsorbents with enhanced antibiotic removal performance and a comprehensive understanding of antibiotic removal mechanisms in SD-MoS₂.

Mercury removal using various modified V/Ti-based SCR catalysts: A review

Growing levels of mercury pollution has made countries urgently need a suitable mercury treatment technology. Among various technologies, heterogeneous oxidative mercury removal via different modified V/Ti-based SCR catalysts is considered as a promising approach due to excellent economic value and removal efficiency. Although various related modification experiments have been worked in recent years, the research on the performance, including activity and resistance, and mechanism of catalysts still needs to be improved, so it is necessary to summarize these experiments to guide further work. This article will review many modifications start from the V/Ti catalyst. Not only the performance of these catalysts, but also a lot of speculation about the mercury removal mechanism are include in our research. In addition, the characteristics of some modified catalysts have been linked with their oxidation mechanism and structural changes by comparing many studies, and finally attributed to some special properties of the corresponding modifiers. We expect this study will clarify the research progress of modified V/Ti-based SCR catalysts in mercury removal, and guide future modification so that some properties of the catalyst can be improved in a targeted manner.

Aminated Multiwalled Carbon Nanotube-Doped Magnetic Flower-like WSe2 Nanosheets for Efficient Adsorption in Acidic Wastewater

The water body environment is related to ecological and human health. Adsorption is an effective means to remove pollutants from water bodies. Currently, the common adsorbents suffer from disadvantages such as structural instability and poor adsorption performance under acidic conditions, which not only affect the adsorption efficiency but also cause secondary pollution of water bodies. In this study, a novel aminated multiwalled carbon nanotube-doped flower-like nanocomposite was designed, where the anionic or neutral groups were protonated under acidic conditions, and it displayed a higher adsorption capacity for dyes by ion exchange, represented by methylene blue (MB) and rhodamine B (RB). WSe₂ in the composite increases its adsorption sites. The adsorption efficiency of pollutants in acidic wastewater was enhanced while avoiding secondary contamination. The synthesized composites showed maximum adsorptions of 27.55 and 27.47 mg/g for MB and RB, respectively. The current work offers a novel approach to treating acidic wastewater.

Efficient CO2 Capture and Activation on Novel Two-Dimensional Transition Metal Borides

The large-scale production of CO₂ in the atmosphere has triggered global warming, the greenhouse effect, and ocean acidification. The CO₂ conversion to valuable chemical products or its capture and storage are of fundamental importance to mitigate the greenhouse effect on the environment. Therefore, exploring new two-dimensional (2D) materials is indispensable due to their potential intriguing properties. Here, we report a new family of 2D transition metal borides (M₂B₂, M = Sc, Ti, V, Cr, Mn, and Fe; known as MBenes) and demonstrate their static and dynamic stability. These MBenes show a metallic nature and exhibit excellent electrical conductivity. The CO₂ adsorption energy on MBenes ranges from -1.04 to -3.95 eV and exhibits the decreasing order as Sc₂B₂ > Ti₂B₂ > V₂B₂ > Cr₂B₂ > Mn₂B₂ > Fe₂B₂. The spin-polarization calculation shows a reduction in the adsorption energy for magnetic systems. Bader charge transfer indicates the formation of CO₂^δ- moiety on the MBene surface, so-called activated CO₂, which is essential for its reaction with other surface chemicals. Differential charge density plots reveal a significant charge accumulation around the CO₂ molecule. Our theoretical results predict the usage of new MBenes as a cost-effective catalyst for CO₂ capture and activation.

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.

Catkin-derived mesoporous carbon-supported molybdenum disulfide and nickelhydroxyloxide hybrid as a bifunctional electrocatalyst for driving overall water splitting

In this work, a two-dimensional heterostructure of molybdenum disulfide (MoS₂) and nickelhydroxyloxide (NiOOH) nanosheets supported on catkin-derived mesoporous carbon (C-MC) was constructed and exploited as an efficient electrocatalyst for overall water splitting. The C-MC nanostructure was prepared by pyrolyzing biomass material of catkin at 600 °C in N₂ atmosphere. The C-MC network exhibited hollow nanotube structure and had a large specific surface area, comprising trace nitrogen and a large amount of oxygen vacancies. It further served as the support for the growth of NiOOH nanosheets (NiOOH@C-MC), which was combined with MoS₂ nanosheets by in situ growth, yielding a multicomponent electrocatalyst (MoS₂@NiOOH@C-MC). By integrating the superior hydrogen evolution reaction (HER) performance of MoS₂, oxygen evolution reaction (OER) performance of NiOOH, and the fast electron transfer capability of C-MC, the prepared MoS₂@NiOOH@C-MC illustrated a low potential of - 250 mV for HER and 1.51 V for OER at the current density of 10 mV cm^-2. Consequently, when applied as the working electrode for driving overall water splitting in a two-electrode system, the bifunctional MoS₂@NiOOH@C-MC electrocatalyst displayed a low cell voltage of 1.62 V at the current density of 10 mA cm^-2. The present work provides a new strategy that uses biomass material for developing bifunctional electrocatalyst for overall water splitting.

Evolution of low-dimensional material-based field-effect transistors

Field-effect transistors (FETs) have tremendous applications in the electronics industry due to their outstanding features such as small size, easy fabrication, compatibility with integrated electronics, high sensitivity, rapid detection and easy measuring procedures. However, to meet the increasing demand of the electronics industry, efficient FETs with controlled short channel effects, enhanced surface stability, reduced size, and superior performances based on low-dimensional materials are desirable. In this review, we present the developmental roadmap of FETs from conventional to miniaturized devices and highlight their prospective applications in the field of optoelectronic devices. Initially, a detailed study of the general importance of bulk and low-dimensional materials is presented. Then, recent advances in low-dimensional material heterostructures, classification of FETs, and the applications of low-dimensional materials in field-effect transistors and photodetectors are presented in detail. In addition, we also describe current issues in low-dimensional material-based FETs and propose potential approaches to address these issues, which are crucial for developing electronic and optoelectronic devices. This review will provide guidelines for low-dimensional material-based FETs with high performance and advanced applications in the future.

Mechanistic investigation of elemental mercury adsorption over silver-modified vanadium silicate: A DFT study

Ag-modified vanadium silicate (EVS-Ag) has been regarded as a superior sorbent for elemental mercury (Hg⁰) capture from coal-fired flue gas. However, the atomic-level reaction mechanism which determines Hg⁰ adsorption capacity of EVS-Ag sorbent remains elusive. Reaction mechanism and active sites of Hg⁰ adsorption over EVS-Ag sorbent were studied using density functional theory (DFT) calculations systematically. DFT calculation results indicate that silver exchange shows little effects on the geometric structure of EVS-10 sorbent. Hg⁰ adsorption on EVS-10 and EVS-Ag surfaces is controlled by the physisorption and chemisorption mechanisms, respectively. Ag₂ cluster is determined to be the most active site of Hg⁰ adsorption over Ag-modified EVS sorbent. The adsorption energy of Hg⁰ on Ag₂ cluster is -51.93 kJ/mol. The orbital hybridization and electron sharing between Ag and Hg atoms are responsible for the strong interaction between EVS-Ag surface and Hg⁰. HgO prefers to adsorb on Ag₂ cluster of EVS-Ag sorbent, and yields an energy release of 306.21 kJ/mol. HgO desorption from EVS-Ag sorbent surface needs a higher external energy, and occurs at the relatively higher temperatures. O₂ molecule promotes Hg⁰ adsorption over EVS-Ag sorbent. HgO species can be easily formed during Hg⁰ adsorption over EVS-Ag sorbent in the presence of O₂.

Outstanding performance of ZnS/TiO2 for the urgent disposal of liquid mercury leakage indoors: Novel support effect, reaction mechanism and kinetics

Effectively weakening the bond strength of Zn-S in S-Zn-S on ZnS is of great significance to the improvement of its performance for the urgent disposal of liquid Hg⁰ leakage indoors. In this work, ZnS was loaded on three common supports (i.e., TiO₂, SiO₂, and Al₂O₃) to further improve its performance for capturing high concentrations of Hg⁰ indoors. After being loaded on TiO₂, the S-Zn-O bond was present on ZnS, and the bond strength of Zn-S in S-Zn-O was significantly weaker than that in S-Zn-S because Zn²⁺ preferred to O^2- than S^2-. Hence, physically adsorbed Hg⁰ was much easier to bond with S in S-Zn-O than that in S-Zn-S to form HgS. Therefore, TiO₂ showed a novel support effect on ZnS for Hg⁰ capture, and the Hg⁰ capture performance of ZnS/TiO₂ was greatly better than those of ZnS, ZnS/SiO₂, and ZnS/Al₂O₃. Moreover, the promotion mechanism of ZnO loading on Hg⁰ adsorption onto TiO₂-S was discovered after comparing the Hg⁰ adsorption kinetic parameters of TiO₂-S and ZnS/TiO₂. The promotion of ZnO loading was primarily related to the notable increase in the content of S^2- that can bond with physically adsorbed Hg⁰, which predominantly resulted from the strong interaction of ZnO/TiO₂ with H₂S.

Binary mineral sulfides sorbent with wide temperature range for rapid elemental mercury uptake from coal combustion flue gas

Developing efficient sorbents with rapid kinetics is the main challenge encountered for Hg⁰ capture from coal combustion flue gas in a sorbent injection scenario. Binary mineral sulfide-based materials combining copper sulfide (CuS) and zinc sulfide (ZnS) to exert their capabilities for Hg⁰ capture at the low- and high-temperature was for the first time reported for Hg⁰ removal to realize a wide temperature range sorbents. When the molar ratio between CuS and ZnS was 10%, the as-synthesized 10Cu-Zn nanocomposite exhibited excellent Hg⁰ uptake rate at 150°C that could degrade 40 μg/m³ of Hg⁰ to undetectable level at the end of a 60-s experiment with the dosage of only 1 mg. This Hg⁰ uptake rate is folds higher compared to that when bare CuS or ZnS was adopted alone at this specific temperature. The typical flue gas atmospheres had negligible effect on Hg⁰ removal over 10Cu-Zn in a short contact time, which further suggests that the binary sorbents were proper to be injected before the electrostatic precipitator system. Moreover, it is found that, by adjusting the ratio between CuS and ZnS, it is potential to develop binary sorbent suiting any temperature conditions that may achieve an exceedingly high Hg⁰ capture performance. Thus, this work not only justified the candidature of 10Cu-Zn as a promising alternative to traditional activated carbon for Hg⁰ capture from coal combustion flue gas but also guided the future development of multi-component mineral sulfide-based sorbents for Hg⁰ pollution remediation from various industrial flue gases.

Direct Tellurization of Pt to Synthesize 2D PtTe2 for High-Performance Broadband Photodetectors and NIR Image Sensors

Platinum telluride (PtTe₂) has garnered significant research enthusiasm owing to its unique characteristics. However, large-scale synthesis of PtTe₂ toward potential photoelectric and photovoltaic application has not been explored yet. Herein, we report direct tellurization of Pt nanofilms to synthesize large-area PtTe₂ films and the influence of growth conditions on the morphology of PtTe₂. Electrical analysis reveals that the as-grown PtTe₂ films exhibit typical semimetallic behavior, which is in agreement with the results of first-principles density functional theory (DFT) simulation. Moreover, the combination of multilayered PtTe₂ and Si results in the formation of a PtTe₂/Si heterojunction, exhibiting an obvious rectifying effect. Moreover, the PtTe₂-based photodetector displays a broadband photoresponse to incident radiation in the range of 200-1650 nm, with the maximum photoresponse at a wavelength of ∼980 nm. The R and D* of the PtTe₂-based photodetector are found to be 0.406 A W^-1 and 3.62 × 10¹² Jones, respectively. In addition, the external quantum efficiency is as high as 32.1%. On the other hand, the response time of τ_rise and τ_fall is estimated to be 7.51 and 36.7 μs, respectively. Finally, an image sensor composed of a 8 × 8 PtTe₂-based photodetector array was fabricated, which can record five near-infrared (NIR) images under 980 nm with a satisfying resolution. The result demonstrates that the as-prepared PtTe₂ material will be useful for application in NIR optoelectronics.

Tunable Molybdenum Disulfide-Enabled Fiber Mats for High-Efficiency Removal of Mercury from Water

The application of molybdenum disulfide (MoS₂) for water decontamination is expanded toward a novel approach for mercury removal using nanofibrous mats coated with MoS₂. A bottom-up synthesis method for growing MoS₂ on carbon nanofibers was employed to maximize the nanocomposite decontamination potential while minimizing the release of the nanomaterial to treated water. First, a co-polymer of polyacrylonitrile and polystyrene was electrospun as nanofibrous mats and pretreated to form pristine carbon fibers. Next, three solvothermal methods of controlled in situ MoS₂ growth of different morphologies were achieved on the surface of the fibers using three different sets of precursors. Finally, these MoS₂-enabled fibers were extensively characterized and evaluated for their mercuric removal efficiency. Two mercury removal mechanisms, including reduction-oxidation reactions and physicochemical adsorption, were elucidated. The two nanocomposites with the fastest (0.436 min^-1 mg^-1) and highest mercury removal (6258.7 mg g^-1) were then further optimized through intercalation with poly(vinylpyrrolidone), which increased the MoS₂ interlayer distance from 0.68 nm to more than 0.90 nm. The final, optimal fabrication technique (evaluated according to mercuric capacity, kinetics, and nanocomposite stability) demonstrated five times higher adsorption than the second-best method and obtained 70% of the theoretical mercury adsorption capacity of MoS₂. Overall, results from this study indicate an alternative, advanced material to increase the efficiency of aqueous mercury removal while also providing the basis for other novel environmental applications such as selective sensing, disinfection, and photocatalysis.

Fast Evolution of Sulfuric Acid Aerosol Activated by External Fields for Enhanced Emission Control

Sulfuric acid aerosol (SAA) can considerably deteriorate air visibility, which poses a threat to human health. Pretreatment methods that enlarge SAA sizes are crucial to enhanced emission control from industrials. This study provides an insight into SAA growth in terms of aerosol dynamics simulation and growth experiments under simulated flue gas conditions. Results show that SAA growth dynamics are dominated by coagulation and condensation mechanisms for small and large aerosols, respectively. The two mechanisms are coupled mainly in SAA sizes smaller than 0.05 μm. A large amount of time was allotted for the SAA distribution to grow into an approximately log-normal form without the use of any activation methods. Cooling gas and corona discharge can both enhance SAA growth. Cooling gas is in charge of condensation, whereas corona discharge mainly acts on coagulation. They exhibited 14.3% and 12.3% increases in mean diameter and 12.3% and 69.1% decreases in number concentration. In contrast, adding vapor led to a 1.58% decrease in mean diameter and a 9.4% increase in number concentration. Findings suggest that combining cooling gas and corona discharge to simultaneously promote coagulation and condensation and reduce SAA emission from humid flue gas is possible.

The tesseract in two dimensional materials, a DFT approach

A series of novel two-dimensional materials inspired from a 4D polytope, tesseract, have been proposed by density functional theory (DFT) based computations. Both C24X12 and C16X16 (X = O, S and Se) are found to have great thermodynamic and dynamic stabilities, and C24X12 exhibited excellent thermal stability up to 1000 K. All these 2D crystals are semiconductors with 2.17 eV to 3.35 eV band gaps at the HSE06 theoretical level, except for C24S12 (4.14 eV energy gap). Moreover, the intrinsic pore sizes of C24Se12 are suitable to sieve He from the He/CH4 mixture, with over 80% separation ratio and nearly 100% selectivity. Our findings not only enlarged the boundary of the 2D family, but also offered another potential method to recover helium from natural gas at ambient conditions.

Scalable and Universal Route for the Deposition of Binary, Ternary, and Quaternary Metal Sulfide Materials from Molecular Precursors

A range of binary, ternary (CFS), and quaternary (CZTS) metal sulfide materials have been successfully deposited onto the glass substrates by air-spray deposition of metal diethyldithiocarbamate molecular precursors followed by pyrolysis (18 examples). The as-deposited materials were characterized by powder X-ray diffraction (p-XRD), Raman spectroscopy, secondary electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy, which in all cases showed that the materials were polycrystalline with the expected elemental stoichiometry. In the case of the higher sulfides, EDX spectroscopy mapping demonstrated the spatial homogeneity of the elemental distributions at the microscale. By using this simple and inexpensive method, we could potentially fabricate thin films of any given main group or transition metal chalcogenide material over large areas, theoretically on substrates with complex topologies.

Mercury in natural gas streams: A review of materials and processes for abatement and remediation

The role of natural gas in mitigating greenhouse gas emissions and advancing renewable energy resource integration is undoubtedly critical. With the progress of hydrocarbons exploration and production, the target zones become deeper and the possibility of mercury contamination increases. This impacts on the industry from health and safety risks, due to corrosion and contamination of equipment, to catalyst poisoning and toxicity through emissions to the environment. Especially mercury embrittlement, being a significant problem in LNG plants using aluminum cryogenic heat exchangers, has led to catastrophic plant incidents worldwide. The aim of this review is to critically discuss the conventional and alternative materials as well as the processes employed for mercury removal during gas processing. Moreover, comments on studies examining the geological occurrence of mercury species are included, the latest developments regarding the detection, sampling and measurement are presented and updated information with respect to mercury speciation and solubility is displayed. Clean up and passivation techniques as well as disposal methods for mercury-containing waste are also explained. Most importantly, the environmental as well as the health and safety implications are addressed, and areas that require further research are pinpointed.

Catalytic oxidation of Hg0 with O2 induced by synergistic coupling of CeO2 and MoO3

Based on Volcano plotting, the controlled combination of weak and strong bond strengths of a bimetallic catalyst has the potential to maximize the catalytic effect via the formation of intermediate bond strength between the reactant and the two different types of active sites. In this study, a rational design approach was adopted to couple MoO₃ and CeO₂ to maximize the catalytic oxidation of Hg⁰ using oxygen as the oxidizing agent. It is found that CeO₂ displayed a relatively strong bond strength with Hg⁰ while MoO₃ has relatively weak bond strength with Hg⁰; the pre-doping of MoO₃ results in the transformation of CeO₂ from clusters to the form with additional exposed CeO₂ (111) surface; the CeO₂ and MoO₃ show synergistic effect on the formation of Brønsted acid sites. Moreover, the results show that there is an overlap between the Hg⁰ desorption region of MoO₃ and the Hg⁰ adsorption region of CeO₂ (with adjusted optimum bond strength with Hg⁰), which contributes to the catalytic reaction of Hg⁰ by O₂. Therefore, this study reveals that the synergistic effects of the coupling of CeO₂ and MoO₃ induced the reaction between Hg⁰ and O₂, which is otherwise difficult.

Preparation of MoS2 nanoflowers with rich active sites as an efficient adsorbent for aqueous organic dyes

In this study, molybdenum disulfide (MoS₂) was used as an adsorbent to quickly and efficiently remove Rhodamine B (RhB) from wastewater.

Mutual effects behind the simultaneous removal of toxic metals and cationic dyes by interlayer-expanded MoS2 nanosheets

Simultaneous removal of coexisting metals and dyes from industrial wastewaters is challenging, and the mutual effects behind the co-adsorption of these pollutants remain unclear. Herein, interlayer-expanded MoS₂ (IE-MoS₂) nanosheets prepared by a one-pot simple and scalable method were tested to simultaneously remove toxic metals and cationic dyes. The adsorption capacities of IE-MoS₂ nanosheets were 499, 423, 500, 355, and 276 mg/g for Pb(II), Cu(II), methylene blue, malachite green, and rhodamine B, respectively, in a mono-contaminant system. Interestingly, the sequestration amount of Pb(II) was dependent on the concentrations of dyes in the binary Pb(II)-dye systems, while uptake of cationic dyes was almost not influenced by coexisting Pb(II). The simultaneous adsorption mechanism was further confirmed by spectroscopic methods. The IE-MoS₂ nanosheets were easily regenerated and reused for six adsorption-desorption cycles without structure destruction, thus avoiding the potential hazards of nanomaterial to the ecosphere. More interestingly, high-efficiency uptake of Pb(II) from intentionally contaminated natural water and model textile effluent was obtained by using a column filled with IE-MoS₂ nanosheets. In summary, IE-MoS₂ nanosheets with facile and scalable synthesis method, efficient adsorption performance, and excellent reusability showed potential promise for the integrative treatment of complex wastewater bearing both metals and organic pollutants.

Synthesis of green fluorescent carbon materials using byproducts of the sulfite-pulping procedure residue for live cell imaging and Ag+ ion determination

A simple synthesis strategy was designed and applied to synthesize nitrogen and sulfur co-doped aminated ligninsulfonate/graphene quantum dots (ASL/GQDs) composites using citric acid monohydrate and byproducts of the sulfite-pulping procedure (sodium lignosulfonate). The combination of these two materials improves surface chemical activities and electronic characteristics. As a result，the combination offers excellent photoluminescence properties and sensitivity. The fluorescence intensity of the as-prepared ASL/GQDs composites is more than three times that of the free GQDs. ASL/GQDs based fluorescent probe was applied to sensitively determine Ag⁺ with a good linearity in a range from 0.005 to 500 μM with a correlation coefficient of 0.99. The method was also used successfully to determine the amount of Ag⁺ in environmental water samples. Using an MTT assay, the ASL/GQDs have low toxicity and are biocompatible with A549 cells, and may be successfully used to image A549 cells.

A comparative study of mechanisms of the adsorption of CO2 confined within graphene-MoS2 nanosheets: a DFT trend study

The space within the interlayer of 2-dimensional (2D) nanosheets provides new and intriguing confined environments for molecular interactions. However, atomic level understanding of the adsorption mechanism of CO₂ confined within the interlayer of 2D nanosheets is still limited. Herein, we present a comparative study of the adsorption mechanisms of CO₂ confined within graphene-molybdenum disulfide (MoS₂) nanosheets using density functional theory (DFT). A comprehensive analysis of CO₂ adsorption energies (E _AE) at various interlayer spacings of different multilayer structures comprising graphene/graphene (GrapheneB) and MoS₂/MoS₂ (MoS₂B) bilayers as well as graphene/MoS₂ (GMoS₂) and MoS₂/graphene (MoS₂G) hybrids is performed to obtain the most stable adsorption configurations. It was found that 7.5 Å and 8.5 Å interlayer spacings are the most stable conformations for CO₂ adsorption on the bilayer and hybrid structures, respectively. Adsorption energies of the multilayer structures decreased in the following trend: MoS₂B > GrapheneB > MoS₂G > GMoS₂. By incorporating van der Waals (vdW) interactions between the CO₂ molecule and the surfaces, we find that CO₂ binds more strongly on these multilayer structures. Furthermore, there is a slight discrepancy in the binding energies of CO₂ adsorption on the heterostructures (GMoS₂, MoS₂G) due to the modality of the atom arrangement (C-Mo-S-O and Mo-S-O-C) in both structures, indicating that conformational anisotropy determines to a certain degree its CO₂ adsorption energy. Meanwhile, Bader charge analysis shows that the interaction between CO₂ and these surfaces causes charge transfer and redistributions. By contrast, the density of states (DOS) plots show that CO₂ physisorption does not have a substantial effect on the electronic properties of graphene and MoS₂. In summary, the results obtained in this study could serve as useful guidance in the preparation of graphene-MoS₂ nanosheets for the improved adsorption efficiency of CO₂.

Fault Diagnosis for a Bearing Rolling Element Using Improved VMD and HT

The variational mode decomposition (VMD) method for signal decomposition is severely affected by the number of components of the VMD method. In order to determine the decomposition modal number, K, in the VMD method, a new center frequency method of the multi-threshold is proposed in this paper. Then, an improved VMD (MTCFVMD) algorithm based on the center frequency method of the multi-threshold is obtained to decompose the vibration signal into a series of intrinsic modal functions (IMFs). The Hilbert transformation is used to calculate the envelope signal of each IMF component, and the maximum frequency value of the power spectral density is obtained in order to effectively and accurately extract the fault characteristic frequency and realize the fault diagnosis. The rolling element vibration data of the motor bearing is used to test the effectiveness of proposed methods. The experiment results show that the center frequency method of the multi-threshold can effectively determine the number, K, of decomposed modes. The proposed fault diagnosis method based on MTCFVMD and Hilbert transformation can effectively and accurately extract the fault characteristic frequency, rotation frequency, and frequency doubling, and can obtain higher diagnostic accuracy.