ZnS Phase Research Articles

Luminescence properties of ZnSxO1-x:Ce3+ phosphors with tunable short fluorescence lifetime

Fluorescence lifetime of phosphors is a critical index in the field of high energy physics and astrophysical detection. A series of ZnSxO1-x:0.05Ce3+ phosphors with tunable short fluorescence lifetime were prepared by performing high temperature solid state reaction method. The phosphors exhibited two mixed phases consisting of the hexagonal phase ZnO and the hexagonal phase ZnS. They are spherical and the average particle size is 2.24 μm. As the component content of the ZnS in ZnSxO1-x:0.05Ce3+ phosphors varies, the emission wavelength can be tuned from 448 nm to 495 nm, the short fluorescence lifetime can be tuned within the range of 6 μs–200 μs. By performing exponential fitting, we obtained the equation for the variation of fluorescence lifetime of ZnSxO1-x:0.05Ce3+ phosphors with ZnS fraction.

Impedance Study of Zinc Sulphide Quantum Dots via One Step Green Synthesis

ZnS quantum dots were synthesized using green synthesis route which are cost effective and eco-friendly. X-ray diffraction study revealed the formation of single phase ZnS. Crystallite size and strain in the as synthesized material were calculated through Williamson-Hall and Size-Strain plot. UV-Vis spectroscopy investigations revealed the absorption region and optical band gap for the ZnS with refractive index analysis. Microstructural analysis of material was done using high resolution transmission electron microscope (HRTEM) which confirms the presence of quantum dots. Selected area electron diffraction pattern (SAEDP) of the corresponding area revealed the polycrystalline nature of as synthesized ZnS with fine crystallites oriented along (111) and (022) planes. Results of analysis of lattice fringe spacing’s of fine crystallites are found to be in good agreement with SAEDP data. Elemental compositional analysis was carried by using EDS as an attachment of TEM which showed the presence of Zinc and Sulphur only. Nyquist plot reported Warburg impedance which suggests the material for solar cell applications.

Environmentally safe ZVI/ZnS-based polymer composite for lindane degradation in water: Assessment of photocatalytic activity and eco-toxicity

Monolithic composite aerogel based on a photocatalytic system, constituted by Fe0 (ZVI) coupled with ZnS (FZ), embedded into syndiotactic polystyrene (sPS) matrix was used, for the first time, in the lindane degradation under UV light. The content of FZ photocatalyst inside the monolithic composite aerogel (FZsPS) composite was 3 wt%. FESEM images of FZsPS indicate that the FZ photocatalyst is well dispersed in the polymer matrix. EDS analyses and temperature-programmed reduction (TPR-H2) measurements revealed an interpenetrated structure of the ZVI and ZnS phases as well the presence of some iron in an oxidized form. Photocatalytic activity data showed that in presence FZsPS aerogel, the almost complete lindane degradation was achieved after only 30 min of UV irradiation time. FZsPS was also effective in the lindane mineralization since a TOC removal of about 94 % was detected after 180 min of treatment time. Remarkably, based on the toxicity evaluation on Artemia franciscana, while the bare FZ photocatalyst showed significant toxicity per se, no toxicity or genotoxicity was found in the water treated with the FZsPS composite system where FZ is immobilized into the sPS aerogel matrix. Therefore the proposed composite photocatalyst can be considered as a model for a strategy to eliminate the environmental impact of catalysts that would otherwise be harmful to water.

Photocatalytic active ZnO1−x S x @CNTs heteronanostructures

Herein, we report on the use of vertically aligned multiwall carbon nanotubes (CNTs) films as support for ZnO/ZnS photocatalytic active nanostructures. The CNTs were synthetized via a hot-filament chemical vapor deposition (HfCVD), using Fe catalyst on top of Al2O3 buffer layer. Controlled point defects in the CNTs outer walls were created by exposure to a low pressure nonthermal water vapors diffusive plasma and acted as seeds for subsequent pulsed-electrodeposition of Zn nanoparticles. This was to achieve a direct and improved contact between the nanoparticles and CNTs. To obtain ZnO, ZnS and mix phase of ZnO/ZnS spread on CNTs, the oxidation, sulfurization and 2 steps subsequent annealing in oxygen and sulfur rich atmospheres were applied. High resolution transmission electron microscopy with energy dispersive x-rays spectroscopy in scanning mode, provided the chemical mapping of the structures. X-ray diffraction (XRD) analyses proved the hexagonal phase of ZnO and ZnS, obtained after oxidation in H2O and S vapors, respectively. In the case of the samples obtained by the 2 steps subsequent annealing, XRD showed mainly the presence of ZnO and a small amount of ZnS. The benefit of the secondary annealing in S vapor was seen as an absorption enhancement of the ZnO1−x S x @CNTs sample having the absorption edge at 417 nm, whereas the absorption edge of ZnO@CNTs was 408 nm and of ZnS@CNTs 360 nm. For all the samples, compared to the bare ZnO and ZnS, the absorption red shift was observed which is attributed to the CNTs involvement. Therefore, this study showed the double sides benefit to induce the absorption of ZnO of the visible light, one from S doping and second of CNTs involvement. The absorption enhancement had a positive impact on photocatalytic degradation of methyl blue dye, showing that ZnO1−x Sx@CNTs heteronanostructure was the best photocatalyst among the studied samples.

Electrospun Nanofiber Mats with Embedded Zinc Oxysulfide for Photoreduction of Nitrobenzene to Aniline under Mild Condition.

In this work, electrospun nanofiber embedded with zinc oxysulfide (Zn(O,S)) has been demonstrated as an efficient and robust photocatalyst for hydrogenation of nitrobenzene to aniline under solar light irradiation at mild conditions with methanol as the hole scavenger. The solid solution state of Zn(O,S) in electrospun nanofiber was successfully revealed by high-resolution transmission electron microscopy and X-ray diffraction analyses in which the lattice fringes and diffraction planes located in between those of ZnO and ZnS phases. Moreover, the electrochemical and optical properties of Zn(O,S) embedded in polyethylene oxide (PEO) nanofiber are found to be better than those of ZnO and ZnS indicating more efficient photocatalytic activities as well. The photocatalytic hydrogenation of nitrobenzene to aniline occurred completely within 2 h of the photocatalytic reaction with a reusability of 95% after five consecutive runs. Finally, the mechanism of photocatalytic hydrogenation by Zn(O,S) embedded in the PEO (PZOS) nanofiber involves a total of six electrons (e-) and six protons (H+) to hydrogenate nitrobenzene to nitrosobenzene, phenylhydroxylamine, and aniline.

ZnSSe Decorated Reduced Graphene Oxide for Enhanced Photoelectric Properties

AbstractZSSG (ZnSSe/rGO) composites are prepared by a hydrothermal method. The structure, morphology and material properties are investigated by various tests. Compared to ZnSe, the diffraction peaks of ZnSSe are moved to a larger angle and located between cubic phase ZnSe and cubic phase ZnS. The photocurrent density of ZSSG20 with 20 wt.% graphene is 2.17×10−5 A cm−2, which is 8.9 times higher than that of pure ZnSSe. ZSSG20 has the minimum charge transfer resistance and highest carrier density. The decreased fluorescence intensity in PL spectra indicates that graphene can effectively prevent the recombination of electron‐hole pairs.

ZnS/ZnSe heterojunction photocatalyst for augmented hydrogen production: Experimental and theoretical insights

A facile chemical process for the synthesis of ZnS/ZnSe composites and theoretical and experimental insights into their sunlight-driven photocatalytic H2 production via water-splitting reactions are demonstrated. ZnSe systems are varied by synthesizing at various temperatures such as 80, 150, and 180 °C for 12 h via hydrothermal process to tune their crystalline properties while maintaining ZnS as the host material, which is the main driving force to achieve increased photocatalytic H2 production efficiency in this study. The prepared composite photocatalyst is found to have cubic ZnS and wurtzite ZnSe phases with good overall crystalline properties. The morphological investigation revealed that the composite consists of ZnS with a spherical structure coupled with irregular-structured ZnSe particles. The optimized ZnS/ZnSe (ZnSe prepared at 150 °C) photocatalyst showed the highest H2 generation of around 84.8 mmol h−1 g−1cat, with a UTH (i.e., UV–visible-to-H2) conversion efficiency and turnover frequency of 20.4% and 0.097 Atom−1 s−1, respectively. This observed photocatalytic efficiency is presumed to be the formation of type-I heterojunction channelizing the effective transfer of hot photocarriers from ZnS to ZnSe for the rapid production of protons (H+) and their subsequent reduction to H2 molecules. The achieved highest efficiency of the composite is around 56.4 and 4.2 folds higher than the pristine ZnSe and ZnS, respectively. In addition, the recycle experiments of the optimized catalyst showed consistent H2 production for upto 5 cycles. Further, the developed composite systems are investigated via density functional theory and validated through various physio and electrochemical analyses to understand their structure-property relationships and photocatalytic mechanisms toward water splitting for H2 production.

Facile synthesis and characterization of ZnO:Al/ZnS/NiO heterojunction thin films with enhanced photocatalytic activities

This study covers a physical investigation of ZnO:Al/ZnS/NiO heterojunction thin films and their photocatalytic activities. The obtained samples were analyzed using XRD, FTIR, SEM/EDS, AFM, and UV–vis spectroscopy. The XRD and FTIR results confirmed that the nanocrystalline ZnO, ZnS, and NiO phases were successfully prepared. SEM morphological analysis of the multilayer film indicated that depositing different nanocrystalline layers above one another could deteriorate the adherence of the upper layer. In addition, AFM shows acceptable surface roughness for application as a photocatalyst. Optical analysis revealed that the ZnO:Al/ZnS/NiO multilayer film exhibited an average transmittance of 65%. The Eg value of the ZnO:Al monolayer of 3.26 eV is decreased to 3.15 eV after Al–ZnO/ZnS coupling, whereas ZnO:Al/ZnS/NiO exhibits an additional absorption value of 3.52 eV due to the NiO layer. The photocatalytic activity of ZnO:Al/ZnS/NiO under visible light exhibited an approximately 96% photodegradation efficiency against methylene blue after only 50 min. However, under sunlight, the degradation rates reached 90, 85, and 65% for methylene blue, crystal violet, and Congo red, respectively, in 90 min. This study shows that a synthesized ZnO:Al/ZnS/NiO heterojunction multilayer photocatalyst can efficiently degrade organic pollutants.

Solid-state synthesis of ZnS/ZnO nanocomposites and their decoration with NiS cocatalyst for photocatalytic hydrogen production

Herein was demonstrated the facile solid-state synthesis of ZnS/ZnO nanocomposites using planetary ball milling followed by subsequent thermal treatment. X-ray diffraction analysis has shown that the ZnS/ZnO products are nanocrystalline with an estimated crystallite size of less than 60 nm. A transmission electron microscope has demonstrated the presence of spherical heterostructures and core-shell structured ZnS/ZnO nanocomposites with the size being 40–80 nm in diameter. Fourier transform infrared spectroscopy analysis confirmed the presence of Zn–O and Zn–S bonds. The formation of a thin boundary between the ZnS and ZnO phases, where the sulfur oxidation state varies from −2 to +6, was determined by X-ray photoelectron spectroscopy. Degradation of methylene blue and Orange II organic dyes was used to assess the photocatalytic activity of ZnS/ZnO nanocomposites, and the nanocomposites of ZnS/ZnO, with a mass ratio of ∼1:1, demonstrated the highest visible light photocatalytic activity. For photocatalytic hydrogen production experiments, the surface of ZnS/ZnO nanocomposites was in situ decorated with NiS nanoparticles, where the mass content of NiS was 1.5%. The presence of NiS cocatalyst promotes the separation and transfer of photogenerated charges, thereby increasing the photocatalytic activity of ZnS/ZnO nanocomposites during hydrogen generation. The apparent quantum efficiency of photocatalytic hydrogen generation using ZnS/ZnO-3h-NiS photocatalyst was equal to 1.13%. This contribution shows the possibility to prepare nano-structured photocatalysts via mechanochemistry.

Formation and characterization of ZnS and CdZnS films using open-air chemical vapor deposition for buffer layers of compound semiconductor solar cells

ZnS and CdZnS (a mixed crystal phase of ZnS and CdS) were formed using the open-air CVD method. Cadmium diethyldithiocarbamate (C10H20CdN2S4) and zinc diethyldithiocarbamate (C10H20ZnN2S4) were used as the source materials for CdS and ZnS, respectively. By changing the ratio of source materials, it was found that the bandgap and the lattice constant of the CdZnS film were continuously changing without a miscibility gap. Furthermore, the bandgap of the obtained ZnS films was less than the reported bandgap of ZnS (3.68 eV) due to incorporation of oxygen. X-ray diffraction analysis revealed that the increase of Zn in CdZnS film generated a crystalline disorder. When the substrate temperature was changed from 421 °C to 464 °C, the deposition rate increased fourfold for the CdS and ZnS films. The impact of substrate temperature on the bandgap and lattice constant was found to be less pronounced.

Spectral and structural properties of CuO doped ZnS-MoS2 nanocomposites synthesized by hydrothermal method

ZnS-MoS2 nanocomposite powders (with CuO and without CuO doping) were prepared by well-known eco-friendly hydrothermal method, to study the structural and spectral properties of the prepared materials. The XRD investigations confirm the presence of hexagonal phase of MoS2 and the cubic & hexagonal phases of ZnS. Also XRD results confirms that the prepared samples were in the limits of 4–20 nm. Captured SEM images showed ZnS spheres and MoS2 flakes sheet. EDAX study corroborated the presence of various elements in the prepared samples. From UV–Vis DRS studies, with the hike of CuO doping in the ZnS-MoS2 lattice, the optical bandgap energy values of CuO doped samples are found to decreases. FT-IR spectra confirm the presence of various functional groups related to prepared samples.

Synthesis of a Hexagonal Phase ZnS Photocatalyst for High CO Selectivity in CO2 Reduction Reactions.

ZnS materials exhibit very negative potential of the conduction band, which is promising in photocatalytic reduction reactions. Unfortunately, previously reported ZnS materials for photocatalysis are mainly in the cubic phase, which produce high activity for H2 evolutions and low activity toward CO2 reductions. Herein, a hexagonal phase ZnS photocatalyst is fabricated for highly efficient CO2 reduction reactions. The hexagonal ZnS nanoplates with the pure phase and well crystallization are synthesized via three-step solvothermal methods. In photocatalytic CO2 reduction reactions under an aqueous solution environment, the hexagonal ZnS produces a CO selectivity of 21%, which is distinctly higher than that of 0.2% for commonly used cubic ZnS. The energy band study suggests that hexagonal ZnS possesses a slightly more negative conduction band and wider bandgap than cubic ZnS. Theoretical calculations reveal that the hexagonal ZnS possesses increased electron density around Zn atoms as that of cubic ZnS. Furthermore, hexagonal ZnS exhibits relatively reduced absorption energy of CO2 reduction intermediates and increased absorption energy of H* as cubic ZnS, which result in better selectivity toward CO2 reduction reactions. This study offers deep insights into the synthesis and electronic structure of hexagonal ZnS for CO2 reduction reactions, which inspire the design of highly active photocatalysts for artificial photosynthesis.

Effect of alloying elements on mechanical behaviour of Cu-Zn-Sn bronzes

Abstract The effect of Fe, P and Mn on microstructure and fatigue properties of CuZnSn bronzes investigated with optical microscopy and scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, hardness, tensile and fatigue tests. The addition of Fe, Mn and P to Cu-Zn-Sn bronzes formed Cu31Sn8, Cu6Sn5, ZnSn2, PbSnS2, ZnS, Cu2S, FeZn9 and FeZn21 phases. These phases were deposited between the dendrite arms and were dissolved in the matrix in small amounts. Especially, these precipitated phases were effective in fatigue properties. The formation of Cu-Sn, Cu-Zn and Zn-Sn intermetallic phases emitted due to the addition of Fe, Mn and P increased the fatigue strength. The spread of ferrous phases caused an increase in mechanical properties. The beneficial effect of P addition on the fatigue life far surpassed that of Mn and Fe additives.

Carbonization of MOF-5/Polyaniline Composites to N,O-Doped Carbon/ZnO/ZnS and N,O-Doped Carbon/ZnO Composites with High Specific Capacitance, Specific Surface Area and Electrical Conductivity.

Composites of carbons with metal oxides and metal sulfides have attracted a lot of interest as materials for energy conversion and storage applications. Herein, we report on novel N,O-doped carbon/ZnO/ZnS and N,O-doped carbon/ZnO composites (generally named C-(MOF-5/PANI)), synthesized by the carbonization of metal-organic framework MOF-5/polyaniline (PANI) composites. The produced C-(MOF-5/PANI)s are comprehensively characterized in terms of composition, molecular and crystalline structure, morphology, electrical conductivity, surface area, and electrochemical behavior. The composition and properties of C-(MOF-5/PANI) composites are dictated by the composition of MOF-5/PANI precursors and the form of PANI (conducting emeraldine salt (ES) or nonconducting emeraldine base). The ZnS phase is formed only with the PANI-ES form due to S-containing counter-ions. XRPD revealed that ZnO and ZnS existed as pure wurtzite crystalline phases. PANI and MOF-5 acted synergistically to produce C-(MOF-5/PANI)s with high SBET (up to 609 m2 g-1), electrical conductivity (up to 0.24 S cm-1), and specific capacitance, Cspec, (up to 238.2 F g-1 at 10 mV s-1). Values of Cspec commensurated with N content in C-(MOF-5/PANI) composites (1-10 wt.%) and overcame Cspec of carbonized individual components PANI and MOF-5. By acid etching treatment of C-(MOF-5/PANI), SBET and Cspec increased to 1148 m2 g-1 and 341 F g-1, respectively. The developed composites represent promising electrode materials for supercapacitors.

Sedimentary cycling of zinc and nickel and their isotopes on an upwelling margin: Implications for oceanic budgets and paleoenvironment proxies

Zinc and Ni are essential micronutrients whose stable isotope systematics in marine sediments represent promising, but still developing, tracers of past ocean chemistry and biology. Sediments from upwelling continental margins have been identified as important sinks for Zn and Ni, driven by high productivity, incorporation of the metals into cells and organic carbon burial. At present, however, our understanding of how Zn and Ni isotope composition of upwelling sediments reflects specific processes in the water column is incomplete. Here, we present coupled Zn and Ni abundance and isotope data for both solid phase and porewater in a series of sediment cores collected on a shelf-to-slope transect across an oxygen minimum zone (OMZ) from the southwest African margin off Namibia.Zinc/Al and Ni/Al ratios in Namibian margin sediments are elevated relative to the lithogenic background, by factors of 1.4–2.4 and 1.7–5.7, respectively. Systematic relationships between solid phase Zn and Ni concentrations and organic carbon accumulation corroborate the view that authigenic Zn and Ni are mainly delivered to these sediments via export production from the photic zone. Corrections for detrital Ni are sometimes substantial, but authigenic δ60Ni values are within uncertainty of the modern deep ocean, at 1.38 ± 0.18 ‰ (mean and 1SD, n = 42). Authigenic δ66Zn is more variable, at −0.09 to 0.50 ‰, at or below the value for the deep ocean average. This latter observation can be attributed to Zn isotope fractionation during sequestration into authigenic ZnS phases in the sediments, either quantitatively, or partially.Porewater systematics are more complex and the profiles do not necessarily reflect the redox state of the sediment-porewater system at the time of sampling, but rather characteristics inherited from more reducing conditions in a temporally heterogeneous system. Porewater zinc concentrations (30–369 nM) are much higher than the deep ocean and increase with depth beneath the sediment–water interface. Despite this prominent increase in Zn concentrations, δ66Zn is rather constant and lighter than the deep ocean average, at 0.18 ± 0.06 ‰ (mean and 1SD, n = 33). These observations are most consistent with the buffering of the small porewater pool by the dissolution of a previously formed sulfide phase. Porewater Ni concentrations are closer to the deep ocean, mostly at 5–15 nM. The lightest porewater isotope compositions (δ60Ni as low as 0.15 ‰) are consistent with a Mn-oxide source of Ni, whereas the heaviest isotope compositions (up to 1.76 ‰) clearly reflect uptake of light Ni into sulfide at depth within the sediment.Our data, for the largest upwelling site in the modern ocean, add to sparse data from the eastern Pacific, and confirm that upwelling margin sediments bury Ni that is close to the deep ocean in isotope composition, but Zn that is generally lighter. The data thus confirm the importance of such margins in setting the heavy isotope composition of oceanic Zn. Sediments from this kind of setting hold significant potential for the construction of records of past oceanic Ni isotopes.

Structural, Mechanical and Thermodynamic properties of Manganese Monocarbide (MnC) in ZnS phase under High Pressure: a DFT Study

The structural, elastic and thermodynamic properties of the manganese monocarbide in ZnS (B3) phase were investigated using the DFT calculation with the PBE functional. The ground state properties of this materials such as lattice constant, bulk modulus, pressure derivatives of bulk modulus and Young’s modulus are calculated and the obtained results show a good agreement with the experimental data. Moreover, the estimated values of elastic constants indicate that the studied material is found to be mechanically stable. The results show also that the heat capacity of this materials as a function of the temperature is close to the Dulong-Petit limit (49.6 J/mol.K)at higher temperatures. The thermal expansion( α) and Debye parameter were also calculated at the different temperatures. The pressure effects on the above parameters were computed and their values are compared with the experimental results.

Zinc-induced changes on structural pathways, optical parameters, optical constants extracted by Kramers-Kronig Formulas, Photoluminescence Spectra and photovoltaic characteristics of n-Cd50-xZnxS50/i-AgSe/p-Si solar cells

In highlighted our study's scenarios, the importance of using a buffer layer of AgSe between an absorbent silicon substrate and a Cd50-xZnxS50 window layer with different Zn content with (x = 0, 10, 20, 30, 40, and 50 wt%) was discussed. The significant influence of the window layer on the properties of fabricated designs: (front electrode) Nickel (Ni)/n-Cd50-xZnxS50/i-AgSe/p-Si/(pt), platinum (back electrode) was also studied. This work devoted a large portion of its parts to investigate the structural, optical, photoluminesce, and thermopower properties of the CdZnS window layer to highlight the rationale for its application in the solar cells fabricated in this study. Pure phases of CdS and ZnS were confirmed through XRD and SEM analysis for the CdZnS window layers. Based on Tauc and Urbach's relationships, the optical parameters (bandgap energy Eg, tail energy Ee) were extracted. The optical constants (refractive index n, absorption index k) were calculated via the Kramers-Kronig formulas. In the visible region at 300–800 nm, the CdZnS thin layers showed a sharp peak in photoluminescence PL study results. The current density-voltage (J-V) characteristics in dark and illumination conditions were discussed. The highest power conversion efficiency (PCE) was for the last window layer. Thus, this layer was appropriate for the fabricated solar cells to obtain good photovoltaic properties.

Effect of Al concentration on the structural and thermoelectric properties of ZnAlS alloy

In the present study, we have successfully controlled the structural and thermoelectric properties of ZnAlS nanoparticles alloy by varying the concentration of Al atoms (1, 2, 3 and 4 %). The samples under investigation were prepared by the solid state reaction method and were characterized using X-ray Diffraction (XRD), Raman spectroscopy measurements and Seebeck data. XRD data have confirmed the cubic phase of ZnS with specific planes 100), (1 1 1), (2 2 0), and (3 1 1). XRD data also verified that structure quality of prepared samples was found to be decreased as we increased the concentration of Al atoms up to 4 %. Raman data demonstrated two peaks at 285 and 348 cm−1 which are assigned as TO and LO modes of cubic ZnS respectively. Seebeck coefficient/thermomotive force and electrical conductivity values are increased to 153.5 μV/°C and 1011.11 S/µm respectively, when the concentration of Al atoms increased to 4 % and measurement temperature reached at 100 °C. The simultaneous enhancement in conductivity and Seebeck data suggested the formation of secondary phases when we increased the concentration of Al atoms because extra Al atoms are unattended by the ZnS structure therefore these atoms are involved in the formation of secondary phases.

First principles calculations of structural, electronic and optical properties of Sn-doped ZnS

Using the full potential linearized augmented plane wave approach within the density functional theory (DFT), the structural, electronic and optical properties of Zn1−xSnxS (x= 6.25, 12.5 and 25%) solid solutions in most stable cubic phase of ZnS are computed. The bandgap values are calculated by using Tran–Blaha approach of modified Becke and Johnson (TB-mBJ) local spin density approximation. For Sn-doped ZnS, the compounds are non-magnetic indirect bandgap semiconductors with narrow bandgaps. The contribution of the Sn-5p state near Fermi level in the valance band reduces the bandgap of the doped systems. Optical characteristics are estimated using the dielectric function spectra as well as other associated optical properties such as absorption coefficient, reflectivity, refractive index, extinction coefficient and conductivity. The investigation shows that this compounds might be a good choice for optoelectronic devices.

Boxlike Assemblages of Few-Layer MoS2 Nanosheets with Edge Blockage for High-Efficiency Hydrogenation of CO2 to Methanol

Direct hydrogenation of CO2 into methanol is a promising strategy for reducing excessive dependence on fossil fuels and alleviating environmental concerns. Recently, in-plane sulfur vacancies in two-dimensional MoS2 nanosheets were unveiled as efficient catalytic active sites for methanol synthesis from CO2, whereas edge vacancies facilitated hydrogenation of CO2 to methane. Herein, we developed boxlike assemblages of quasi-single-layer MoS2 nanosheets, which were edge-blocked by ZnS crystallites (denoted as h-MoS2/ZnS) via a metal–organic framework (MOF)-engaged solvothermal route and subsequent heat treatments. The spatial confinement of the ZnS can restrain the growth and aggregation of MoS2 and ensure the stability of few-layer or even single-layer MoS2 in the assemblages. More importantly, the presence of ZnS can prevent reactants from approaching the edge sulfur vacancies of MoS2. With more exposed in-plane sulfur vacancies and less edge sulfur vacancies, the h-MoS2/ZnS exhibits 67.3% methanol selectively, 9.0% CO2 conversion, and a high methanol space-time yield of up to 0.93 gMeOH·gMoS2–1·h–1 at 260 °C, 5 MPa, and 15 000 mL·gcat.–1·h–1. The catalytic activity was stable for at least 120 h. By removing the ZnS phase from h-MoS2/ZnS and thus deliberately creating more edge sulfur vacancies, it was further confirmed that edge sulfur vacancies are active catalytic sites for excessive hydrogenation of CO2 to methane. Furthermore, the reaction mechanism of our catalyst was also investigated by a high-pressure in situ DRIFTS study. Thus, this MOF-templated strategy for assembling and confining quasi-single-layer MoS2 provides insights into the development of highly efficient transition-metal dichalcogenide catalysts for CO2 hydrogenation with excellent stability.