Size-dependent optical properties of MoS2 nanoparticles and their photo-catalytic applications

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.

Green synthesis of ZnO nanoparticles from ball moss (Tillandsia recurvata) extracts: characterization and evaluation of their photocatalytic activity

Green synthesis (GS), referred to the synthesis using bioactive agents such as plant materials, microorganisms, and various biowastes, prioritizing environmental sustainability, has become increasingly relevant in international scientific practice. The availability of plant resources expands the scope of new exploration opportunities, including the evaluation of new sources of organic extracts, for instance, to the best of our knowledge, no scientific articles have reported the synthesis of zinc oxide nanoparticles (ZnO NPs) from organic extracts of T. recurvata, a parasitic plant very common in semiarid regions of Mexico.This paper presents a greener and more efficient method for synthesizing ZnO NPs using T. recurvata extract as a reducing agent. The nanoparticles were examined by different techniques such as UV-vis spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and BET surface analysis. The photocatalytic and adsorptive effect of ZnO NPs was investigated against methylene blue (MB) dye in aqueous media under sunlight irradiation considering an equilibrium time under dark conditions. ZnO nanoparticles were highly effective in removing MB under sunlight irradiation conditions, showing low toxicity towards human epithelial cells, making them promising candidates for a variety of applications. This attribute fosters the use of green synthesis techniques for addressing environmental issues.This study also includes the estimation of the supported electric field distributions of ZnO NPs in their individual spherical or rounded shapes and their randomly oriented organization, considering different diameters, by simulating their behavior in the visible wavelength range, observing resonant enhancements due to the strong light-matter interaction around the ZnO NPs boundaries.

Recent progress in MoS2 nanostructures for biomedical applications: Experimental and computational approach

In the category of 2D materials, MoS2 a transition metal dichalcogenide, is a novel and intriguing class of materials with interesting physicochemical properties, explored in applications ranging from cutting-edge optoelectronic to the frontiers of biomedical and biotechnology. MoS2 nanostructures an alternative to heavy toxic metals exhibit biocompatibility, low toxicity and high stability, and high binding affinity to biomolecules. MoS2 nanostructures provide a lot of opportunities for the advancement of novel biosensing, nanodrug delivery system, electrochemical detection, bioimaging, and photothermal therapy. Much efforts have been made in recent years to improve their physiochemical properties by developing a better synthesis approach, surface functionalization, and biocompatibility for their safe use in the advancement of biomedical applications. The understanding of parameters involved during the development of nanostructures for their safe utilization in biomedical applications has been discussed. Computational studies are included in this article to understand better the properties of MoS2 and the mechanism involved in their interaction with biomolecules. As a result, we anticipate that this combined experimental and computational studies of MoS2 will inspire the development of nanostructures with smart drug delivery systems, and add value to the understanding of two-dimensional smart nano-carriers.

TMDC ternary alloy-based triboelectric nanogenerators with giant photo-induced enhancement

Multifunctional self-powered energy harvesting devices have attracted significant attention for wearable, portable, IoT and healthcare devices. In this study, we report transition metal dichalcogenide (TMDC) ternary alloy (Mo0.5W0.5S2)-based self-powered photosensitive vertical triboelectric nanogenerator (TENG) devices, where the ternary alloy functions both as a triboelectric layer and as a photoabsorbing material. The scalable synthesis of the highly crystalline Mo0.5W0.5S2 ternary alloy can overcome the limitations of binary TMDCs (MoS2, WS2) by utilizing its superior optical characteristics, enabling this semiconductor-based TENG device to simultaneously exhibit photoelectric and triboelectric properties. Benefiting from visible light absorption, this vertical TENG device generates higher triboelectric outputs and exhibits excellent power harvesting properties under visible light illumination. The open circuit voltage and short circuit currents of the devices under illumination (410 nm, 525 μW cm-2) are enhanced by 62% and 253%, respectively, while in the darkness, a very high photoresponsivity of ∼45.5 V mW-1 (voltage mode) is exhibited, indicating the superior energy harvesting potential under ultralow illumination. Furthermore, the energy harvesting ability from regular human activities and the operation as artificial e-skin expands the multi-functionality of this TENG device, paving a pathway for simultaneous mechanical and photonic energy harvesting with self-powered sensing.

Size-Dependent Graphene Support for Decorating Gold Nanoparticles as a Catalyst for Hydrogen Evolution Reaction with Machine Learning-Assisted Prediction

Size-dependent two-dimensional (2D) materials (e.g., graphene) have been recently used to improve their performance in various applications such as membrane filtration, energy storage, and electrocatalysts. It has also been demonstrated that 2D nanosheets can be one of the promising support materials for decorating nanoparticles (NPs). However, the optimum nanosheet size (lateral length and thickness) for supporting NPs has not yet been explored to enhance their catalytic performance. Herein, we elucidate the mechanism behind size-dependent graphene (GP) as a support due to which gold nanoparticles (AuNPs) are used as an active catalyst for the hydrogen evolution reaction (HER). Surprisingly, the decoration of AuNPs increased with the increasing nanosheet size, counter to what is widely reported in the literature (high surface area for smaller nanosheet size). We found that a large graphene nanosheet (lGP; ∼800 nm) used as the AuNP support (lGP/AuNPs) exhibited superior performance for the HER with long-term stability. The lGP/AuNPs with a suitable content of AuNPs provides a low overpotential and a small Tafel slope, being lower than that of other reported carbon-based HER electrocatalysts. This results from highly exposed active sites of well-dispersed AuNPs on lGP giving high conductivity. The laminar structure of the stacked graphene nanosheets and the high wettability of the lGP/AuNPs electrode surface also play crucial roles in enhancing electrolytes for penetration in the electrode, suggesting a highly electrochemical surface area. Moreover, machine learning (Random Forest) was also used to reveal the essential features of the advanced catalytic material design for catalyst-based applications.

Exfoliation of MoS2 Quantum Dots: Recent Progress and Challenges

Although, quantum dots (QDs) of two-dimensional (2D) molybdenum disulfide (MoS₂) have shown great potential for various applications, such as sensing, catalysis, energy storage, and electronics. However, the lack of a simple, scalable, and inexpensive fabrication method for QDs is still a challenge. To overcome this challenge, a lot of attention has been given to the fabrication of QDs, and several fabrication strategies have been established. These exfoliation processes are mainly divided into two categories, the 'top-down' and 'bottom-up' methods. In this review, we have discussed different top-down exfoliation methods used for the fabrication of MoS₂ QDs and the advantages and limitations of these methods. A detailed description of the various properties of QDs is also presented.

Casted MoS2 nanostructures and their Raman properties

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been widely investigated for optoelectronic applications. Here, by employing the nanocasting method, molybdenum disulfide (MoS₂) nanostructures, including supercrystals, nanoparticles and nanowires, are synthesized with curved features by changing the precursor concentration and template types. The Raman properties of different MoS₂ nanostructures are investigated by varying the laser power under both resonant and non-resonant excitations. The defect disorder induced LA(M) mode and other silent Raman modes in planar 2D materials are clearly observed under the resonant excitation. We believe that the varying optical properties of TMDC nanostructures will greatly broaden the optoelectronic applications of 2D materials.

Tuning the photocatalytic/electrocatalytic properties of MoS2/MoSe2 heterostructures by varying the weight ratios for enhanced wastewater treatment and hydrogen production

Two-dimensional (2D) heterojunctions with layered structures give high flexibility in varying their photocatalytic/electrocatalytic properties. Herein, 2D/2D heterostructures of MoS₂/MoSe₂ with different weight-ratios (1 : 1, 1 : 3, and 3 : 1) have been prepared by a simple one-step microwave-assisted technique. The characterization studies confirm formation of crystalline MoS₂/MoSe₂ nanoparticles with a high surface area (60 m² g⁻¹) and porous structure. The high synergistic-effect (1.73) and narrow bandgap (∼1.89 eV) of the composites result in enhanced photo-degradation efficiency towards methylene blue dye (94%) and fipronil pesticide (80%) with high rate constants (0.33 min⁻¹ and 0.016 min⁻¹ respectively) under visible light. The effect of pH, catalyst dose, and illumination area on photodegradation has been optimized. Photodegradation of real-industrial wastewater shows 65% COD and 51.5% TOC removal. Trapping experiments confirm that holes are mainly responsible for degradation. The composites were highly reusable showing 75% degradation after 5-cycles. MoS₂/MoSe₂ composites show excellent electrochemical water-splitting efficacy through hydrogen-evolution-reaction (HER) exhibiting a stable high current density of −19.4 mA cm⁻² after 2500 cyclic-voltammetry (CV) cycles. The CV-plots reveal high capacitance activity (C_dl value ∼607 μF cm⁻²) with a great % capacitance retention (>90%). The as-prepared 2D/2D-catalysts are highly active in sunlight and beneficial for long-time physico-chemical wastewater treatment. Moreover, the electrochemical studies confirm that these composites are potential materials for HER activity and energy-storage applications.

The 2D/2D-MoS₂/MoSe₂ catalysts with good photocatalytic/electrocatalytic properties can be potential materials for wastewater treatment and hydrogen production.

Construction of 2D layered TiO2@MoS2heterostructure for efficient adsorption and photodegradation of organic dyes

In this work, heterostructures of coupled TiO₂@MoS₂with different phases of MoS₂were synthesized via hydrothermal technique. The prepared materials were thoroughly characterized using various techniques, including XRD, SEM, transmission electron microscopy, Brunauer-Emmet-Teller, XPS, Zeta potential and UV-vis spectroscopy. The optimized nanocomposites were tested for the photocatalytic degradation of methyl Orange (MO) under visible light as well as the adsorption of Rhodamine b (RhB) and methelene blue (MB) dyes. The TiO₂@1T/2H-MoS₂heterostructures exhibited a narrow bandgap compared to the other studied nanomaterials. A remarkable photodegradation efficiency of TiO₂@1T/2H-MoS₂was observed, which completely degraded 20 ppm of MO after 60 min with high stability over four successive cycles. This can be assigned to the formation of unique heterostructures with aligned energy bands between MoS₂nanosheets and TiO₂nanobelts. The formation of these novel interfaces promoted the electron transfer and increased the separation efficiency of carriers, resulting in high photocatalytic degradation. Furthermore, the adsorption efficiency of TiO₂@1T/2H-MoS₂was unique, 20 ppm solutions of RhB and MB were removed after 1 and 2 min, respectively. The superior adsorption performance of the TiO₂@1T/2H-MoS₂can be attributed to its high surface area (279.9 m²g^-1) and the rich concentration of active sites. The kinetics and the isothermal analysis revealed that the TiO₂@1T/2H MoS₂heterstructures have maximum adsorption capacity of 1200 and 970 mg g^-1for RhB and MB, respectively. This study provides a powerful way for designing an effective photocatalyst and adsorbent TiO₂-based nanocomposites for water remediation.

Bacterial Nanocellulose/MoS2 Hybrid Aerogels as Bifunctional Adsorbent/Photocatalyst Membranes for in-Flow Water Decontamination

To address the problems associated with the use of unsupported nanomaterials, in general, and molybdenum disulfide (MoS₂), in particular, we report the preparation of self-supported hybrid aerogel membranes that combine the mechanical stability and excellent textural properties of bacterial nanocellulose (BC)-based organic macro/mesoporous scaffolds with the excellent adsorption-cum-photocatalytic properties and high contaminant removal performance of MoS₂ nanostructures. A controlled hydrothermal growth and precise tuning of the synthetic parameters allowed us to obtain BC/MoS₂-based porous, self-supported, and stable hybrid aerogels with a unique morphology resulting from a molecular precision in the coating of quantum-confined photocatalytic MoS₂ nanostructures (2-4 nm crystallite size) on BC nanofibrils. These BC/MoS₂ samples exhibit high surface area (97-137 m²·g^-1) and pore volume (0.28-0.36 cm³·g^-1) and controlled interlayer distances (0.62-1.05 nm) in the MoS₂ nanostructures. Modification of BC with nanostructured MoS₂ led to an enhanced pollutants removal efficiency of the hybrid aerogels both by adsorptive and photocatalytic mechanisms, as indicated by a detailed study using a specifically designed membrane photoreactor containing the developed photoactive/adsorptive BC/MoS₂ hybrid membranes. Most importantly, the prepared BC/MoS₂ aerogel membranes showed high performance in the photoassisted in-flow removal of both organic dye (methylene blue (MB)) molecules (96% removal within 120 min, K_obs = 0.0267 min^-1) and heavy metal ions (88% Cr(VI) removal within 120 min, K_obs = 0.0012 min^-1), separately and/or simultaneously, under UV-visible light illumination as well as excellent recyclability and photostability. Samples with interlayer expanded MoS₂ nanostructures were particularly more efficient in the removal of smaller species (CrO₄^2-) as compared to larger (MB) dye molecules. The prepared hybrid aerogel membranes show promising behavior for application in in-flow water purification, representing a significant advancement in the use of self-supported aerogel membranes for photocatalytic applications in liquid media.