Dual Role of MoS2 Quantum Dots in a Cross-Dehydrogenative Coupling Reaction

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.

Deep-Learning-Assisted Discriminative Detection of Vitamin B12 and Vitamin B9 by Fluorescent MoSe2 Quantum Dots

A facile and environmentally mindful approach for the synthesis of MoSe2 QDs was developed via the hydrothermal method from bulk MoSe2. In this, the exfoliation of MoSe2 was enhanced with the aid of an intercalation agent (KOH), which could reduce the exfoliation time and increase the exfoliation efficiency to form MoSe2 QDs. We found that MoSe2 QDs display blue emission that is suitable for different applications. This fluorescence property of MoSe2 QDs was harnessed to fabricate a dual-modal sensor for the detection of both vitamin B12 (VB12) and vitamin B9 (VB9), employing fluorescence quenching. We performed a detailed study on the fluorescence quenching mechanism of both analytes. The predominant quenching mechanism for VB12 is via Förster resonance energy transfer. In contrast, the recognition of VB9 primarily relies on the inner filter effect. We applied an emerging and captivating approach to pattern recognition, the deep-learning method, which enables machines to "learn" patterns through training, eliminating the need for explicit programming of recognition methods. This attribute endows deep-learning with immense potential in the realm of sensing data analysis. Here, analyzing the array-based sensing data, the deep-learning technique, "convolution neural networks", has achieved 93% accuracy in determining the contribution of VB12 and VB9.

Semiconductor Quantum Dots Act as Photocatalysts for Carbon-Carbon Bond Formation: Selective Functionalization of Xanthene's 9H Position

The potential of CdSe, CdS, MoS2, and WS2 QDs as semiconductor photocatalysts for selective functionalization of the xanthene 9H position through carbon-carbon bond formation has been investigated. Our study reveals valuable insights into the energy-transfer and electron-transfer pathways involved in these reactions, as well as the radical polar crossover (RPC) and triplet-to-triplet energy transfer (TTEnT) processes. Notably, this approach offers a range of intriguing features, including visible-light-mediated processes, inexpensive catalytic systems, mild reaction conditions, broad substrate scope, unfunctionalized starting materials, and suitability for gram-scale synthesis. This study makes a significant contribution to the newly emerging field of QD-catalyzed reactions, paving the way for future explorations.

Synthesis of biologically important tetrahydroisoquinoline (THIQ) motifs using quantum dot photocatalyst and evaluation of their anti-bacterial activity

Our study introduces an efficient photocatalytic approach for synthesizing biologically significant C1-substituted tetrahydroisoquinoline (THIQ) motifs, employing WS2 quantum dots (QDs) as catalysts. This method enables the formation of C-C and C-P bonds at the C1 position of the THIQ motif. The resulting compounds exhibit substantial antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) bacteria, with low minimum inhibitory concentration (MIC) values. Notably, the WS2 QD catalyst demonstrates recyclability and suitability for gram-scale reactions, underscoring the sustainability and scalability of our approach. Overall, our research presents a versatile and cost-effective strategy for synthesizing C1-substituted THIQ derivatives, highlighting their potential as novel therapeutic agents in biology and medicinal chemistry.

DoE-Assisted Development of a 2H-MoS2 -Catalyzed Approach for the Production of Indole Derivatives

2H-MoS2 is an appealing semiconductor because of its Earth-abundant nature, cheapness, and low toxicity. This material has shown promising catalytic activity for various energy-related processes, but its use in catalysis for C-C bond forming reactions towards useful organic compounds is still largely unexplored. The lack of examples in organic synthesis is mainly due to the intrinsic difficulties of using bulk 2H-MoS2 (e. g., low surface area), which implies the reliance on high catalytic loadings for obtaining acceptable yields. This makes the optimization process more expensive and tedious. Here, we report the development of a 2H-MoS2 -mediated synthesis of valuable bis(indolyl)methane derivatives, using indoles and benzaldehydes as starting materials. Exploiting the Design of Experiments (DoE) method, we identified the critical parameters affecting the catalytic performance of commercial 2H-MoS2 powder and optimized the reaction conditions. Lastly, we demonstrated that the catalytic system has versatility and good tolerance towards functional group variations of the reagents.

Ligand Exchange on MoS2 Nanosheets: Applications in Array-Based Sensing and Drug Delivery

Two-dimensional MoS2 nanosheets (2D-MoS2) have been widely used in many biological applications due to their distinctive physicochemical properties. Further, the development of surface modification using thiolated ligands allows us to use them for many specific applications. But the effect of possible ligand exchange on 2D-MoS2 has never been explored, which can play an important role in diverse biological applications. In this study, we have observed the ligand-exchange phenomenon on 2D-MoS2 in the presence of different thiolated ligands. The initial study proceeded with boron-dipyrromethene (BODIPY) functionalized MoS2 with different concentrations of glutathione (GSH), which is the most abundant thiol species in the cytoplasm of various cancer cells. It was found that in the presence of GSH the fluorescence of BODIPY can be regenerated, which is time and concentration dependent. We have also examined this phenomenon with different thiol ligands and transition-metal dichalcogenides (TMDs). We observed a variable rate of ligand exchange in different solvents, surface functionality, and receptor environments that helped us to construct sensor arrays. Interestingly, a ligand-exchange process was not observed in the presence of dithiols. Further, this concept was applied to a cancerous cell line for in vitro delivery. We found that BODIPY-functionalized 2D-MoS2 undergoes thiol exchange by intracellular GSH and subsequently enhanced the fluorescence in the cytoplasm of cancer cells. This strategy can be applied to the development of 2D-TMD-based materials for various biological applications related to ligand exchange.

Molybdenum disulfide (MoS2) based photoredox catalysis in chemical transformations

Photoredox catalysis has been explored for chemical reactions by irradiation of photoactive catalysts with visible light, under mild and environmentally benign conditions. Furthermore, this methodology permits the activation of abundant chemicals into valuable products through novel mechanisms that are otherwise inaccessible. In this context, MoS2 has drawn attention due to its excellent solar spectral response and its notable electrical, optical, mechanical and magnetic properties. MoS2 has a number of characteristic properties like tunable band gap, enhanced absorption of visible light, a layered structure, efficient photon electron conversion, good photostability, non-toxic nature and quantum confinement effects that make it an ideal photocatalyst and co-catalyst for chemical transformations. Recently, MoS2 has gained synthetic utility in chemical transformations. In this review, we will discuss MoS2 properties, structure, synthesis techniques, and photochemistry along with modifications of MoS2 to enhance its photocatalytic activity with a focus on its applications and future challenges.

Fe-Doped MoS2 Nanozyme for Antibacterial Activity and Detoxification of Mustard Gas Simulant

The peroxidase-like catalytic activity of various nanozymes was extensively applied in various fields. In this study, we have demonstrated the preparation of Fe-doped MoS₂ (Fe@MoS₂) nanomaterials with enhanced peroxidase-like activity of MoS₂ in a co-catalytic pathway. In view of Fenton reaction, the peroxidase-like Fe@MoS₂ nanozyme prompted the decomposition of hydrogen peroxide (H₂O₂) to a reactive hydroxyl radical (·OH). The efficient decomposition of H₂O₂ in the presence of Fe@MoS₂ has been employed toward the antibacterial activity and detoxification of mustard gas simulant. The combined effect of Fe@MoS₂ and H₂O₂ showed remarkable antibacterial activity against the drug-resistant bacterial strain methicillin-resistant Staphylococcus aureus and Escherichia coli with the use of minimal concentration of H₂O₂. Fe@MoS₂ was further applied for the detoxification of the chemical warfare agent sulfur mustard simulant, 2-chloroethyl ethyl sulfide, by selective conversion to the nontoxic sulfoxide. This work demonstrates the development of a hybrid nanozyme and its environmental remediation from harmful chemicals to microbes.