Sulfur Vacancy Concentration Research Articles

Sulfur vacancies-engineered CaIn2S4 microspheres for enhanced photocatalytic organic pollutant and antibiotic removal

It is an interesting research topic on construction of defect- rich structures to enhance the performance of photocatalysts. In this study, CaIn2S4 photocatalyst containing sulfur vacancy was successfully synthesized using a straightforward solvothermal method. The sulfur vacancy concentration in CaIn2S4 was controlled by adjusting the amount of thioacetamide added during preparation. Among the prepared samples, CaIn2S4-10 sample with excellent photocatalytic performance exhibits superior degradation efficiency (98.2 %) within 50 minutes when the initial methyl orange (MO) concentration was 20 mg/L. Similarly, it shows the highest degradation performance (94 %) against the antibiotic tetracycline hydrochloride (TCH) (20 mg/L). The phase structure, surface element composition, optical properties and other characteristics of the prepared samples were systematically investigated. The findings demonstrate that the CaIn2S4-10 sample exhibits a decreased band gap width and a negatively shifted conduction band position, which enhances its reduction ability and improves its photocatalytic activity.

Glutathione-mediated copper sulfide nanoplatforms with morphological and vacancy-dependent photothermal catalytic activity for multi-model tannic acid assays

Interface engineering and vacancy engineering play an important role in the surface and electronic structure of nanomaterials. The combination of the two provides a feasible way for the development of efficient photocatalytic materials. Here, we use glutathione (GSH) as a coordination molecule to design a series of CuxS nanomaterials (CuxS-GSH) rich in sulfur vacancies using a simple ultrasonic-assisted method. Interface engineering can induce amorphous structure in the crystal while controlling the formation of porous surfaces of nanomaterials, and the formation of a large number of random orientation bonds further increases the concentration of sulfur vacancies in the crystal structure. This study shows that interface engineering and vacancy engineering can enhance the light absorption ability of CuxS-GSH nanomaterials from the visible to the near-infrared region, improve the efficiency of charge transfer between CuxS groups, and promote the separation and transfer of optoelectronic electron-hole pairs. In addition, a higher specific surface area can produce a large number of active sites, and the synergistic and efficient photothermal conversion efficiency (58.01%) can jointly promote the better photocatalytic performance of CuxS-GSH nanomaterials. Based on the excellent hot carrier generation and photothermal conversion performance of CuxS-GSH under illumination, it exhibits an excellent ability to mediate the production of reactive oxygen species (ROS) through peroxide cleavage and has excellent peroxidase activity. Therefore, CuxS-GSH has been successfully developed as a nanoenzyme platform for detecting tannic acid (TA) content in tea, and convenient and rapid detection of tannic acid is achieved through the construction of a multi-model strategy. This work not only provides a new way to enhance the enzyme-like activity of nanomaterials but also provides a new prospect for the application of interface engineering and vacancy engineering in the field of photochemistry.

Bimetallic Sulfides with Vacancy Modulation Exhibit Enhanced Electrochemical Performance

AbstractTransition bimetallic sulfides show significant promise for energy‐related applications because of their plentiful active sites and synergistic redox activity. However, limited pore size and low‐conductivity issues hinder their application. The structure of NiCo–S with rich sulfur vacancies is first predicted by density functional theory (DFT) calculations. Different sulfur vacancy concentrations are modeled by DFT calculations, and the results confirm that sulfur vacancies enhance the conductivity of the electrode material and are more beneficial for the adsorption of OH* species. It is verified by the differential charge density that the electric field formed on the surface of the electrode can lead to strong interfacial interactions by electron aggregation, which promotes electron/ion transfer kinetics. Furthermore, NiCo–S nanosheets are prepared on carbon cloth enriched with different concentrations of sulfur vacancies (denoted as NiCo‐Sv‐x, with x representing the concentration of sulfur vacancies) by sulfide etching NiCo‐MOF and annealing under H2/Ar atmosphere. The NiCo‐Sv‐x electrodes obtained are applied to the cathode of supercapacitors and the anode of the oxygen evolution reaction. Through combining experimental and theoretical analysis, the effect of vacancy defect engineering on the electrochemical performance of the electrode materials is further confirmed.

Defect-Engineered Semiconducting van der Waals Thin Film at Metal-Semiconductor Interface of Field-Effect Transistors.

The significance of metal-semiconductor interfaces and their impact on electronic device performance have gained increasing attention, with a particular focus on investigating the contact metal. However, another avenue of exploration involves substituting the contact metal at the metal-semiconductor interface of field-effect transistors with semiconducting layers to introduce additional functionalities to the devices. Here, a scalable approach for fabricating metal-oxide-semiconductor (channel)-semiconductor (interfacial layer) field-effect transistors is proposed by utilizing solution-processed semiconductors, specifically semiconducting single-walled carbon nanotubes and molybdenum disulfide, as the channel and interfacial semiconducting layers, respectively. The work function of the interfacial MoS2 is modulated by controlling the sulfur vacancy concentration through chemical treatment, which results in distinctive energy band alignments within a single device configuration. The resulting band alignments lead to multiple functionalities, including multivalued transistor characteristics and multibit nonvolatile memory (NVM) behavior. Moreover, leveraging the stable NVM properties, we demonstrate artificial synaptic devices with 88.9% accuracy of MNIST image recognition.

Non-resonant absorption of the X-band electromagnetic wave power in a narrow-gap PbS semiconductor at temperatures of 2.6–8 K in the range of magnetic fields 0–100 mT

Studies of magnetically dependent effects of nonresonant absorption of electromagnetic wave energy in the resonator of the X-band EPR spectrometer related to the superconductivity of metallic lead inclusions and microscopic structural defects in crystals of narrow-band semiconductors PbS1 – x and PbS1 – x:Mn have been performed. It is shown that nanoscale lead particles present in polycrystalline material PbS0.96 with a high content of sulfur vacancies at temperatures of 2.6–8 K manifest themselves as superconductors of the 2nd kind and demonstrate high thermomagnetic stability. It was found that in a single-crystal sample PbS0.996 with a significantly lower concentration of sulfur vacancies under the influence of the electric component of the microwave field in the resonator of the ESR spectrometer, non-periodic bursts of microwave power absorption associated with avalanches of Abrikosov vortices and demonstrating the absence of thermomagnetic stability of superconducting regions associated with defects in the crystal structure of the sample PbS0.996 are observed.

Targeted fabrication of 1T-MoS2 enriched nanosheets vertically oriented on spiny-shaped nanospheres with sufficient sulfur vacancies and “rim” sites for co-enhancing the hydrodesulfurization activity and hydrogenation selectivity

The 1T-enriched spiny-shaped nanospheres with vertically oriented MoS2 nanosheets over the surface was successfully prepared with the novel solvent induced micelle-limited Mo-CTA+ composites self-assembly (SIMMS) strategy under the dual effects of mixed sulfur sources (thiourea and thioacetamide) and cetyltrimethylammonium bromide (CTAB). In the proposed strategy, the molybdenum source and CTAB are firstly assembled to Mo-CTA+ by strong electrostatic attraction to avoid the molybdenum source from polymerization and forming large polymolybdate anions. Meanwhile, the CTAB moleculars self-assemble to spherical micelles, which can adsorb Mo-CTA+ through van der Waals force and obtain spherical precursors with a controllable number of nucleation sites. Under the sulfurization from mixed sulfur source, appropriate reducibility can control the formation of crystal seeds and crystal growth during the crystallization process of MoS2, whereas CTAB can regulate and control the growth behavior and micro-morphology of MoS2, which is ultimately also retained between the MoS2 nanolayersto expand their interlayer spacing and stabilize the 1T phase. Therefore, the 1T-enriched spiny-shaped nanospheres with vertically oriented MoS2 nanosheets can be controllably prepared. In the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) over these catalysts, the MoS2-75%/0.25 catalyst with the highest concentration of sulfur vacancies as well as “rim” and “rim-like” sites can reach the highest HDS activity (99.1%) and HYD/DDS ratio (4.76), which are much higher than those of the MoS2-H catalyst prepared by conventional hydrothermal method (HDSDBT%=46.0%, HYD/DDS ratio=0.90).

Enhancing Photocatalytic Pollutant Degradation through S-Scheme Electron Transfer and Sulfur Vacancies in BiFeO3/ZnIn2S4 Heterojunctions

Photocatalytic degradation plays a crucial role in wastewater treatment, and the key to achieving high efficiency is to develop photocatalytic systems that possess excellent light absorption, carrier separation efficiency, and surface-active sites. Among various photocatalytic systems, S-type heterojunctions have shown remarkable potential for efficient degradation. This work delves into the construction of S-type heterojunctions of ternary indium metal sulfide and bismuth ferrite nanofibers with the introduction of sulfur vacancy defects and morphology modifications to enhance the photocatalytic degradation performance. Through the impregnation method, BiFeO3/ZnIn2S4 heterojunction materials were synthesized and optimized. The 30% BiFeO3/ZnIn2S4 heterojunction exhibited superior photocatalytic performance with higher sulfur vacancy concentration than ZnIn2S4. The in-situ XPS results demonstrate that the electrons between ZnIn2S4 and BFO are transferred via the S-Scheme, and after modification, ZnIn2S4 has a more favorable surface morphology for electron transport, and its flower-like structure interacts with the nanofibers of BFO, which has a further enhancement of the reaction efficiency for degrading pollutants. This exceptional material demonstrated a remarkable 99% degradation of Evans blue within 45 min and a significant 68% degradation of ciprofloxacin within 90 min. This work provides a feasible idea for developing photocatalysts to deal with the problem of polluted water resources under practical conditions.

Regulation of sulfur vacancies in vertical nanolamellar MoS2 for ultrathin flexible piezoresistive strain sensors

• The vertical MoS 2 nanosheets prepared by magnetron sputtering displayed a piezoresistive effect, which has not been reported previously. • Contact and separation of channels between the vertical MoS 2 nanosheets under strain, leading to excellent piezoresistive properties. • Sulfur vacancies enhance electron transport of in-plane MoS 2 nanosheets. • The flexible sensors were excellent in human motion and bionic flight monitoring. Magnetron-sputtered MoS 2 has applications in piezoresistive functional materials research owing to its unique nanostructure. However, the controlled incorporation of sulfur vacancies and realization of enhanced piezoresistive performance remain significant challenges. In this work, the direct growth of large-area MoS 2 films with tunable sulfur vacancy concentrations was successfully achieved via magnetron sputtering at various temperatures. Microstructural analysis revealed that the application of strain altered the number of conductive channels between the vertical MoS 2 nanosheets, changing the measured resistance and leading to excellent piezoresistive properties. More importantly, the unsaturated electrons due to the sulfur vacancies increased the in-plane carrier concentration of the MoS 2 nanosheets. A deposition temperature of 50°C afforded the highest concentrations of sulfur vacancies and carriers. These MoS 2 films possessed a carrier concentration of 6.58 × 10 17 cm −3 , which was 40.9% higher than that obtained at 150°C, and displayed superior piezoresistive performance. The films exhibited high gauge factors of 2.66 and 23.22 under tensile and compressive strain of ≤0.29%, respectively. These values were 118% and 323% higher, respectively, than those obtained for films deposited at 150°C. This work provides an effective route for modulating and mass producing MoS 2 -based piezoresistive electronic devices.

Origin of electrically induced defects in monolayer MoS2 grown by chemical vapor deposition

Defects in MoS2 play substantial role in determining the performance of MoS2-based field-effect transistors. Typically, growth/synthesis process conditions determine the type and concentration of defects. Here, we show that defects are also introduced by prolonged operation of single crystal chemical vapor deposition-grown monolayer MoS2 transistors which hinder the overall performance. Depending on the electrical stress conditions, these defects result in threshold voltage instabilities, enhanced channel conductance, improved screening of charged impurity scattering sites and possibly better thermal management in MoS2 transistors. It turns out that a piezoelectric response in MoS2 leads to permanent change in the material’s molecular configuration thereby causing other effects like suppressed hopping transport within the channel, increased free electron concentration, prominent metal-insulator transition and reduction in channel potential with or without increasing sulfur vacancy concentration. As these defects are progressively introduced in the channel, the thermal dissipation capability of our MoS2 transistors improved due to enhanced channel-dielectric coupling. Such variations in the device performance due to spontaneous response to high electric field trigger a need to reconsider supply voltage requirements of MoS2-based electronic circuits for low-power logic applications.

Hydrothermal Synthesis of CuS Catalysts for Electrochemical CO2 Reduction: Unraveling the Effect of the Sulfur Precursor

Copper-based catalysts have been recognized as promising candidates for electrochemical conversion of CO2 to value-added chemicals and synthetic fuels. Yet, the challenges of high overpotential and low product selectivity have motivated the rational electrode engineering. In the present work, we prepared CuS catalysts using different sulfur precursors, and we aimed to elucidate the precursor-dependent effect on their structure–property–activity relationships for electrochemical CO2 reduction. The different sulfur precursors exhibited varied S release rates in hydrothermal synthesis, which had induced distinct surface morphological features and diverse sulfur vacancy concentrations, and the intrinsic catalytic activity and product selectivity would be affected. The desired CuS-TU catalyst synthesized using thiourea as the sulfur precursor featured a flower-like morphology and had the highest sulfur vacancy concentration. The nanoflower morphology offered expanded space and considerable undercoordinated sites for facilitated interfacial mass transfer in electrochemical CO2 reduction. Density functional theory calculations confirmed that the abundant sulfur vacancy played an important role in strengthening the adsorption of the *COOH intermediates on the surface, which promoted CO production via the *COOH pathway. The CuS-TU catalyst therefore exhibited a relatively higher CO selectivity of 72.67% at −0.51 V vs RHE. These findings will provide more insights into improving the electrochemical CO2 reduction performance of copper-based catalysts by structure engineering.

Sulfur vacancy in SnS2 nanoflake adjusted by precursor and improved photocatalytic performance

SnS2 with nanoflake-based microstructure and different concentrations of sulfur vacancy (SV) has been synthesized. The valence state of tin cation in the precursors is found to be closely related to the SV concentration in SnS2 nanoflake. SnS2 nanoflake with unsaturated tin cation in tin salt precursor (SnCl2·2H2O) favors to create SV. Sufficient SV is found to bring about a number of advantages such as smaller energy band gap, larger electrochemical active surface Area (ECSA), improved light absorption and separation efficiency of photogenerated charge carriers, which results in superior photocatalytic activities for degradation of RhB and CO2. SnS2 with more sulfur vacancies exhibits better photocatalytic activity for RhB degradation with a degradation rate 1.02×10−2min−1 and for CO2 reduction with an average CO production rate 2.44μmol∙g−1∙h−1. Above results not only reveal the importance of defect engineering, but also provide valuable guide to develop effective metal-sulfide photocatalysts for organic pollutant degradation and CO2 reduction.

Decreased n-type behavior of monolayer MoS2 crystals annealed in sulfur atmosphere

Herein, we report decreased n-type behavior of mechanically exfoliated monolayer MoS2 crystals via annealing in sulfur atmosphere. The Raman, photoluminescence, and X-ray photoelectron spectroscopy (XPS) measurements consistently suggested decreased n-type behavior of the monolayer MoS2 crystals after an hour of thermal annealing at 200 °C in sulfur atmosphere. Such decreased n-type behavior could be attributed to the reduced concentration of sulfur vacancies after the annealing, suggested by the analysis of XPS spectra. Furthermore, after the annealing in sulfur atmosphere, the monolayer MoS2 transistors exhibited positively shifted threshold voltages and reduced on-currents, confirming decreased n-type conduction. These results demonstrate that the reduction of the concentration of sulfur vacancies decreases n-type behavior in monolayer MoS2, providing valuable information on understanding the effect of sulfur vacancies on the performance of monolayer MoS2 devices.

Tuning sulfur vacancies in CoS2 via a molten salt approach for promoted mercury vapor adsorption

Metal sulfides are emerging and efficient adsorbents for mercury removal. However, the major active sites responsible for their superior Hg0 adsorption ability are still disputable. Here, we proposed that sulfur vacancies play an important role in Hg0 removal over metal sulfides. Moreover, tuning the sulfur vacancies in CoS2 appears to be a feasible route to strengthen its mercury adsorption ability. Since traditional methods for adjusting the sulfur vacancies in metal sulfides are very complicated and hard to scale up, a simple, and cost-effective molten salt approach is employed to tune the concentrations of the sulfur vacancies in CoS2. The Hg0 removal efficiency of CoS2 is positively correlation with the density of sulfur vacancies, which can be facilely tuned by altering the cobalt precursors and annealing temperatures. The CoS2 derived from cobalt chloride and cobalt sulfate with higher concentrations of sulfur vacancies distinctly outperforms the ones derived from cobalt nitrate and cobalt acetate. Higher annealing temperature can generate higher concentration of sulfur vacancies, leading to a better mercury capture performance. CoS2-500-CA attained by annealing treatment of KSCN and cobalt acetate at 500 °C displays excellent mercury capture ability with Hg0 removal efficiency of 100% at reaction temperatures of 80–100 °C plausibly due to its high density of sulfur vacancies and big pore diameter. CoS2-500-CA is insusceptible to 100–200 ppm NO or 150–300 ppm SO2.

Controllable fabrication of sulfur-vacancy-rich Bi2S3 nanorods with efficient near-infrared light photocatalytic for nitrogen fixation

Herein, orthorhombic phase Bi2S3 nanorods with different concentration of sulfur vacancies (SVs) were controllably synthesized via a facile solvothermal strategy. Benefited from the high specific surface area, proper band gap, good reduction capacity andabundant SVs, the Bi2S3 nanorods exhibit remarkable photocatalytic nitrogen fixation performance. The ammonia yield of the sulfur-vacancy-rich Bi2S3-3is around 51.04 μmol g−1 h−1 under full solar irradiation. Moreover, Bi2S3-3 also responds sensitively to near-infrared (NIR) light, and the nitrogen reduction rate is 33.37 μmol g−1 h−1. The superior photocatalytic performance of Bi2S3 is mainly attributed to SVs, which can absorb nitrogen and afford plentiful active sites to activate molecular nitrogen.Moreover, SVs also can trap the photoinduced electrons and contribute to the separation of the interfacial charge. This work provides a promising and sustainable defect-rich photocatalyst for the fixation of atmospheric nitrogen using solar energy.

Facile Synthesis of Template‐Free SnS2 with Different Morphologies and Excellent Gas‐Sensing Performance for NO2 Gas‐Sensor Applications

Herein, SnS2 particles with two different morphologies are synthesized using a template‐free one‐step hydrothermal method. Flower‐ and plate‐like SnS2 are obtained using different solvents, ethyl alcohol, and deionized water, respectively, under the same synthesis conditions. The flower‐like SnS2 had a larger surface area and higher concentration of sulfur vacancies than plate‐like SnS2. The effects of the specific surface area and the number of sulfur vacancies in the gas‐sensing materials are studied using the gas‐sensing characteristics of SnS2 in the two morphologies. The gas sensitivities at 25 °C under 1 ppm NO2 are 73.5 and 129.5 for flower‐ and plate‐like SnS2, respectively. Both the flower‐ and plate‐like SnS2 gas sensors exhibited good gas selectivity for NO2 against SO2, CO, and NH3 at 25 °C. The response and recovery times are 540 and 1407 s for the flower‐like SnS2 and 214 and 18 s for the plate‐like SnS2, respectively. It is confirmed that a large specific surface area and the number of sulfur vacancies adversely affected the response and recovery times. Therefore, the plate‐like gas sensor is expected to be a good candidate for NO2 gas‐sensing applications at 27 °C.

Binder-free SnS2 sheet array with high sulfur vacancy concentration for enhanced lithium storage performance

Vacancy could not only offer extra active sites for electrochemical reactions, but also induce the change of band gap of electrode materials to enhance the electronic conductivity. In this work, binder-free SnS2 sheet array with high S vacancy concentration was fabricated on carbon paper (CP) by hydrothermal synthesis. When employed as the anode for lithium-ion battery, the SnS2/CP delivers greatly improved capacity, coulombic efficiency, high-rate discharge-ability as well as cycling performance from that of SnS2 powders. The results were analyzed and discussed with density functional theory based theoretical calculation, electrochemical impedance spectra combining diverse physicochemical techniques.

Tailoring S-vacancy concentration changes the type of the defect and photocatalytic activity in ZFS

Defect engineering is crucial in the development of semiconductor catalyst activity. However, the influence of defect/vacancy density and states on catalysis remains vague. Thus, the optimized sulfur vacancy (SV) state is achieved among Fe-ZnS models (ZFS) via a chemical etching strategy for photocatalytic degradation (PD). As the SV concentration (ρSV) increases, the predominant state of vacancies changes from isolated defects－a state to a combination of a state and vacancy clusters－e state, as verified by positron annihilation and X-ray absorption fine structure spectra. However, the two types of defect states activated the intrinsic activity of the crystal via radically different mechanisms and exerted different degrees of influence on PD activity, as revealed by first-principles calculations and quantitative structure-activity relationship. Our results suggest that the SV activity is strongly influenced by its concentration in the ZFS crystal, while the vacancy concentration is not a control parameter for the PD activity, but a defect form. The underlying essence of atomic defects behavior affecting crystal catalytic activity at the atomic level is also revealed in this paper. Uncovering these structural relationships provide a theoretical basis for designing effective catalysts.

NIR light responsive MoS2 nanomaterials for rapid sterilization: Optimum photothermal effect via sulfur vacancy modulation

As the increasing problem of bacterial resistance has become the threaten to human health and environmental protection, the explorations of efficient and environmental-friendly antimicrobial agents are highly desired. Recently, vacancy engineering is regarded as the quite novel strategy to regulate the electronic structure of semiconductor Nanomaterials (NMs), largely improving their photocatalytic performance in rapid and safe sterilization. In this study, molybdenumsulfide(MoS2) NMs with different concentrations of sulfur vacancies (Vs) were synthesized through annealed at different temperature (i.e., 150 °C, 250 °C and 350 °C), providing the platform for studying the efficient bacterial inactivation of defective MoS2 NMs under the near-infrared light irradiation. The optimum photothermal conversion efficiency could be achieved with the appropriate concentration of Vs, through improving the light adsorption and preventing the recombination of photogenerated e−/h+ pairs. In addition, MoS2 NMs with the abundant Vs exhibited hyperthermia and strong binding ability to bacteria, leading to the severe damage to cell wall integrity, energy supply and antioxidant system. Collectively, these results focused on the relationship between optimum antibacterial efficiency and appropriate concentrations of Vs, providing new insights into the designation of photocatalysts with highly efficient sterilization.

Nitrogen-Doped Metallic MoS2 Derived from a Metal-Organic Framework for Aqueous Rechargeable Zinc-Ion Batteries.

Molybdenum disulfide (MoS2) has been extensively studied as a potential storage material for batteries. However, the electrochemical performance of MoS2 is far from ideal, and it exhibits severe activity fading resulting from its low electronic conductivity. The present work synthesizes nitrogen (N)-doped 1T MoS2 nanoflowers made of ultrathin nanosheets via the one-step hydrothermal sulfurization of a molybdenum-based metal-organic framework precursor. The resulting metallic phase shows improved conductivity and hydrophilicity, and characterization demonstrates that N doping effectively expands the interlayer spacing and increases the concentration of sulfur vacancies serving as defects. This material demonstrates high rate performance and good cycling stability when used as the cathode in an aqueous rechargeable zinc-ion battery (ARZIB). Its performance is superior to those of pure 1T MoS2 and 2H MoS2 synthesized with MoO3 as the molybdenum source. Ex situ X-ray photoelectron spectroscopy and X-ray diffraction analyses are performed to explore the reaction mechanism during charging and discharging of the N-doped 1T MoS2. A three-cell series ARZIB system containing this material is used to power five light-emitting diodes to confirm the possible practical applications of this technology.

First-principles study of sulfur vacancy concentration effect on the electronic structures and hydrogen evolution reaction of MoS2

Defect engineering has been widely used in experiments to modulate the electrocatalytic properties of molybdenum disulfide (MoS2). However, the effect of vacancy concentration on the vacancy distribution, electronic properties, and hydrogen evolution reaction (HER) activity remains elusive. Herein, we perform density functional theory (DFT) studies to investigate defective MoS2 with different numbers of sulfur vacancies. In the case of low S-vacancy concentration, the vacancies prefer to agglomerate rather than being dispersed, while at the higher-vacancy concentration, the combination of local point defect and clustered vacancy chain is preferred. The coupling between S-vacancies leads to decreased band gap and increased Mo–H adsorption strength with increasing vacancy concentration. The optimal HER activity is identified to occur below vacancy concentration of 12.50%. Our work provides an atomic-level understanding about the role of S-vacancies in the HER performance of MoS2, and offers useful guidelines for the design of defective MoS2 and other TMDs electrocatalysts.