Low-defectiveness exfoliation of MoS2 nanoparticles and their embedment in hybrid light-emitting polymer nanofibers

Three-Dimensional Integrated Synaptic Devices Based on a Silver-Cluster Conduction Mechanism with High Thermostability

During the operation of synaptic devices based on traditional conductive filament (CF) models, the formation and dissolution of CFs are usually uncertain. Moreover, when the device is operated for a long time, the CFs may dissolve due to both the Joule heat generated by the device itself and the thermal coupling between the devices. These problems seriously reduce the reliability and stability of the synaptic device. Here, an artificial synapse device based on polyimide-molybdenum disulfide quantum dot (MoS2 QD) nanocomposites is presented. Research has shown that MoS2 QDs doped into the active layer can effectively induce the reduction of Ag ions into Ag atoms, leading to the formation of Ag clusters and thereby achieving control over the growth of the CFs. Therefore, the device is capable of stably realizing various basic synaptic functions. Moreover, the long-term potentiation/long-term depression (LTP/LTD) of this device shows good linearity. In addition, due to the change in the shape of the CFs, the highly integrated devices with a three-dimensional (3D) stacked structure can operate normally even in a high-temperature environment of 110 °C. Finally, the synaptic characteristics of the devices on learning and inference tests show that their recognition rates are approximately 90.75% (room temperature) and 90.63% (110 °C).

Elucidating the Role of Electron Transfer in the Photoluminescence of MoS2 Quantum Dots Synthesized by fs-Pulse Ablation

Herein, MoS2 quantum dots (QDs) with controlled optical, structural, and electronic properties are synthesized using the femtosecond pulsed laser ablation in liquid (fs-PLAL) technique by varying the pulse width, ablation power, and ablation time to harness the potential for next-generation optoelectronics and quantum technology. Furthermore, this work elucidates key aspects of the mechanisms underlying the near-UV and blue emissions the accompanying large Stokes shift, and the consequent change in sample color with laser exposure parameters pertaining to MoS2 QDs. Through spectroscopic analysis, including UV-visible absorption, photoluminescence, and Raman spectroscopy, we successfully unraveled the mechanisms for the change in optoelectronic properties of MoS2 QDs with laser parameters. We realize that the occurrence of a secondary phase, specifically MoO3-x, is responsible for the significant Stokes shift and blue emission observed in this QD system. The primary factor influencing these activities is the electron transfer observed between these two phases, as validated by excitation-dependent photoluminescence and XPS and Raman spectroscopies.

Controlled Differentiation of Human Neural Progenitor Cells on Molybdenum Disulfide/Graphene Oxide Heterojunction Scaffolds by Photostimulation

Ultrathin MoS₂-MoO_3-x heterojunction nanosheets with unique features were introduced as biocompatible, non-cytotoxic, and visible light-sensitive stimulator layers for the controlled differentiation of human neural progenitor cells (hNPCs) into nervous lineages. hNPC differentiation was also investigated on reduced graphene oxide (rGO)-containing scaffolds, that is, rGO and rGO/MoS₂-MoO_3-x nanosheets. In darkness, hNPC differentiation into neurons increased on MoS₂-MoO_3-x by a factor of 2.7 due to the excellent biophysical cues and further increased on rGO/MoS₂-MoO_3-x by a factor of 4.4 due to a synergistic effect induced by the rGO. The MoO_3-x domains with antioxidant activity and LSPR absorption induced p-type doping in MoS₂-MoO_3-x. Under photostimulation, the hNPCs on the MoS₂-MoO_3-x exhibited higher differentiation into glial cells by a factor of 1.4, and the decrease in photo-electron current to hNPCs due to the induction of more p-type doping in the MoS₂-MoO_3-x. While the increase in neuronal differentiation of hNPCs on rGO/MoS₂-MoO_3-x by a factor of 1.8 was ascribed to the presence of rGO as an ultrafast electron transferor which quickly transferred photogenerated electrons to hNPCs before their transfer to free radicals, these results demonstrated the promising potential of MoS₂-based scaffolds for applying in the controllable repair and/or regeneration of diseases/disorders related to the nervous system.

Single-Layer MoS2-MoO3-x Heterojunction Nanosheets with Simultaneous Photoluminescence and Co-Photocatalytic Features

Single-layer MoS2-MoO3-x heterojunction nanosheets with visible-light-sensitive band gap energy and average lateral dimensions of ~70 nm were synthesized by using a two-step combined exfoliation method. The exfoliation was initiated from pristine MoS2, while some sulfur sites in expanded MoS2 sheets during exfoliating were substituted by ambient non-thermal oxygen, resulting in formation of α-MoO3-x crystalline domains. The morphological features, crystalline structure, phase formation, number of layers, and optical properties of the MoS2-MoO3-x nanosheets were determined by atomic force microscopy; X-ray diffraction; field emission electron microscopy; transmission electron microscopy; and Raman, UV–visible–NIR, diffuse transmittance, and photoluminescence spectroscopies. The produced α-MoO3-x domains displayed a narrower indirect band gap energy (~1.95 eV) than that of stoichiometric MoO3 (~3 eV), and a broad light absorption range from visible to near-infrared region can act as a plasmonic material facilitating the separation of the photoinduced carriers and enhancing the photocatalytic activity of the MoS2 domain, having ~1.75(2.16) eV indirect (direct) band gap energy. In this regard, the MoS2-MoO3-x heterojunction nanosheets showed single-layer-based excitation-dependent luminescence emissions and visible-light-induced photocatalytic features, at the same time. This study can contribute to promising applications of sheet-like nanomaterials for purposes requiring simultaneous photoluminescence and photocatalytic features, such as in-vivo monitoring and targeting.

Energy Dissipation and Asymmetric Excitation in Hybrid Waveguides for Routing and Coloring

The delivery of optical signals from an external light source to a nanoscale waveguide is highly important for the development of nanophotonic circuits. However, the efficient coupling of external light energy into nanophotonic components is difficult and still remains a challenge. Herein, we use an external silica nanofiber to light up an organic-inorganic hybrid nanowaveguide, namely, a system composed of a polymer filament doped with MoS₂ quantum dots. Nanofiber-excited nanowaveguides in a crossed geometry are found to asymmetrically couple excitation signals along two opposite directions, with different energy dissipation resulting in different colors of the light emitted by MoS₂ quantum dots and collected from the waveguide terminals. Interestingly, rainbow-like light in the hybrid waveguide is achieved by three-in-one mixing of red, green, and blue components. This heterodimensional system of dots in waveguide represents a significant advance toward all-optical routing and full-color display in integrated nanophotonic devices.

Silver decorated 2D nanosheets of GO and MoS2serve as nanocatalyst for water treatment and antimicrobial applications as ascertained with molecular docking evaluation

In this work, synthesis of graphene oxide (GO) and reduced graphene oxide (rGO) was realized through a modified Hummers route. Different concentrations (5 and 10 wt%) of Ag were doped in MoS₂and rGO using a hydrothermal technique. Synthesized Ag-MoS₂and Ag-rGO were evaluated through XRD that confirmed the hexagonal structure of MoS₂along with the transformation of GO to Ag-rGO as indicated by a shift in XRD peaks while Mo-O bonding and S=O functional groups were confirmed with FTIR. Morphological information of GO and formation of MoS₂nanopetals as well as interlayer spacing were verified through FESEM and HRTEM respectively. Raman analysis was employed to probe any evidence regarding defect densities of GO. Optical properties of GO, MoS₂, Ag-rGO, and Ag-MoS₂were visualized through UV-vis and PL spectroscopy. Prepared products were employed as nanocatalysts to purify industrial wastewater. Experimental results revealed that Ag-rGO and Ag-MoS₂showed 99% and 80% response in photocatalytic activity. Besides, the nanocatalyst (Ag-MoS₂and Ag-rGO) exhibited 6.05 mm inhibition zones againstS. aureusgram positive (G+) and 3.05 mm forE. coligram negative (G-) in antibacterial activity. To rationalize biocidal mechanism of Ag-doped MoS₂NPs and Ag-rGO,in silicomolecular docking study was employed for two enzymes i.e.β-lactamase and D-alanine-D-alanine ligase B (ddlB) from cell wall biosynthetic pathway and enoyl-[acylcarrier-protein] reductase (FabI) from fatty acid biosynthetic pathway belonging toS. aureus. The present study provides evidence for the development of cost-effective, environment friendly and viable candidate for photocatalytic and antimicrobial applications.

Preparation of a polymer nanocomposite via the polymerization of pyrrole : biphenyldisulfonic acid : pyrrole as a two-monomer-connected precursor on MoS2 for electrochemical energy storage

We prepared a poly(pyrrole : biphenyldisulfonic acid : pyrrole (Py:BPDSA:Py)) nanocomposite of molybdenum disulfide (MoS₂), P(Py:BPDSA:Py)-MoS₂, with high crystallinity. The composite is synthesized by oxidative polymerization of Py:BPDSA:Py as a two-monomer-connected precursor (TMCP) linked by ionic bonding on a molybdenum disulfide (MoS₂) monolayer. The chemical, structural and morphological characterization of this composite is confirmed by Raman spectroscopy, FT-IR, X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), and scanning electron microscopy (SEM). The crystal structure is analysed by X-ray diffraction (XRD) and high-voltage electron microscopy (HVEM), which shows a face-centered cubic (FCC) crystal structure for the composite. Nitrogen adsorption-desorption isotherms show an improved specific surface area (91.3 m² g^-1). The electrochemical properties of the composite with a unique crystal structure and a large specific surface area are analysed through cyclic voltammetry (CV), which shows a specific capacitance of 681 F g^-1 demonstrating that the composite can be used as an efficient electrode active material for electrochemical energy storage systems.

Activation Strategy of MoS2 as HER Electrocatalyst through Doping-Induced Lattice Strain, Band Gap Engineering, and Active Crystal Plane Design

Doping engineering emerges as a contemporary technique to investigate the catalytic performance of MoS₂. Cation and anion co-doping appears as an advanced route toward electrocatalytic hydrogen evolution reaction (HER). V and N as dopants in MoS₂ (VNMS) build up a strain inside the crystal structure and narrow down the optical band gaps manifesting the shifting of the absorbance band toward lower energy and improved catalytic performance. FE-SEM, HR-TEM, and XRD analysis confirmed that V and N doping decreases agglomeration possibility, particle size, developed strain, and crystal defects during crystal growth. Frequency shift and peak broadening in Raman spectra confirmed the doping induced strain generation in MoS₂ leading to the modification of acidic and alkaline HER (51 and 110 mV @ 10 mAcm^-2, respectively) performance. The improved donor density in VNMS was confirmed by the Mott-Schottky analysis. Enhanced electrical conductivity and optimized electronic structures facilities H* adsorption/desorption in the catalytically active (001) plane of cation and anion co-doped MoS₂.

Dye Stabilization and Wavelength Tunability in Lasing Fibers Based on DNA

Lasers based on biological materials are attracting an increasing interest in view of their use in integrated and transient photonics. Deoxyribonucleic acid (DNA) as optical biopolymer in combination with highly emissive dyes has been reported to have excellent potential in this respect. However, achieving miniaturized lasing systems based on solid-state DNA shaped in different geometries to confine and enhance emission is still a challenge, and the physicochemical mechanisms originating fluorescence enhancement are not fully understood. Herein, a class of wavelength-tunable lasers based on DNA nanofibers is demonstrated, for which optical properties are highly controlled through the system morphology. A synergistic effect is highlighted at the basis of lasing action. Through a quantum chemical investigation, it is shown that the interaction of DNA with the encapsulated dye leads to hindered twisting and suppressed channels for the nonradiative decay. This is combined with effective waveguiding, optical gain, and tailored mode confinement to promote morphologically controlled lasing in DNA-based nanofibers. The results establish design rules for the development of bright and tunable nanolasers and optical networks based on DNA nanostructures.

Promising performance of chemically exfoliated Zr-doped MoS2 nanosheets for catalytic and antibacterial applications

Nanostructured materials incorporated with biological reducing agents have shown significant potential for use in bactericidal applications. Such materials have also demonstrated considerable efficacy to counter effects of chemical toxicity. In this study, nanostructured molybdenum disulfide (MoS₂) was doped with various concentrations (2.5, 5, 7.5, 10 wt%) of zirconium (Zr) using a hydrothermal route in order to assess its antimicrobial and catalytic potential. Doped and control samples were characterized with various techniques. X-ray diffraction (XRD) analysis confirmed the presence of the hexagonal phase of MoS₂ and identification of various functional groups and characteristic peaks (Mo bonding) was carried out using FTIR spectra. Micrographs obtained from FESEM and HR-TEM showed a sheet-like surface morphology, while agglomeration of nanosheets was observed upon doping with nanoparticles. To seek further clarity regarding the layered features of S–Mo–S planes, the defect densities and electronic band structure of pure MoS₂ and doped MoS₂ samples were investigated through Raman analysis. Optical properties of Zr-doped MoS₂ nanosheets were assessed using a UV-vis spectrophotometer and the results indicated a red-shift, i.e., movement of peaks towards longer wavelengths, of the material. Dynamics of migration and recombination of excited electron–hole pairs were investigated using PL spectroscopy, which was also used to confirm the presence of exfoliated nanosheets. In addition, the synthetic dye degradation potential of pure and doped samples was investigated in the presence of a reducing agent (NaBH₄). It was noted that doped MoS₂ showed superior catalytic activity compared to undoped MoS₂. The nanocatalyst synthesized in this study exhibited enhanced antibacterial activity against E. coli and S. aureus at high concentrations (0.5, 1.0 mg/50 μl). The present study suggests a cost-effective and environmentally friendly material that can be used to remove toxins such as synthetic dyes and tannery pollutants from industrial wastewater.

Nanostructured materials incorporated with biological reducing agents have shown significant potential for use in bactericidal applications.