Quantum dot-based non-volatile memory: a comprehensive outlook

With the rise of digital technology, the use of memory devices is swiftly expanding, and this trend is expected to continue in the forthcoming years. Accordingly, researchers are exploring materials that surpass the performance of those used in traditional memory devices, and notably, there is a considerable interest in quantum dots (QDs). This is primarily due to the fact that quantum dots possess exceptional optical and electric properties. As a result, they have become appealing materials to enhance the performance of non-volatile memory devices. In this review, we outlined the various approaches employed for the synthesis of quantum dots as well as different types of quantum dots used for prototyping different non-volatile memory technologies and their current perspective. Additionally, we compared various key parameters, such as the ON/OFF ratio, retention time, memory window, charge trapping capacity, and multiple voltage levels, of these QD-based memories together with future outlook.

Ionic liquid-assisted sustainable preparation of photo-catalytically active nanomaterials and their composites with 2D materials

The preparation of nanomaterials employing ionic liquids (ILs) and surface active ionic liquids (SAILs) in a relatively sustainable manner for different applications is reviewed. ILs offer structure directing and templating effects via inherent bi-continuous structures formed by the segregation of polar and non-polar domains. On the other hand, SAILs offer a structure-directing effect governed by their ability to lower the surface tension, self-assembling nature and interaction with precursors via ionic head groups. Binary mixtures of ILs with other relatively greener solvents or utilization of metal-based ILs (MILs), which act as precursors of metal ions, templates and stabilizing agents propose a new way to prepare a variety of nanomaterials. The introduction of SAILs that exfoliate 2D materials under low-energy bath sonication and also aid in photoreduction and stabilization of photocatalytically active nanomaterials at the surface of 2D materials poses a distinctive perspective in sustainable preparation and utilization of nanomaterials in different photocatalytic applications. The present feature article reviews the employment of distinctive properties of ILs in precise morphological control of nanomaterials, and their after-effects on their catalytic efficiencies.

Formation of ZnS quantum dots using green tea extract: applications to protein binding, bio-sensing, anti-bacterial and cell cytotoxicity studies

Biocompatible quantum dots (QDs) have attracted a lot of attention due to their potential biological applications (drug delivery, sensing and diagnosis). Here, we have synthesized 2-4 nm sized biocompatible zinc sulphide (ZnS) QDs using a plant leaf extract as an immobilizing and stabilizing agent via a green route. We have investigated the biological effects of ZnS QDs in a variety of applications, including (1) anti-bacterial activity, (2) cell cytotoxicity, (3) bio-sensing and (4) protein binding. Studies on the anti-bacterial activity of the as-synthesized ZnS QDs against E. coli and E. faecalis inhibited bacterial growth effectively and showed a cytotoxic effect on the HeLa cell line. The biosynthesized ZnS QDs act as a fluorescence probe to detect bilirubin and rifampicin (RFP) with a wide linear range, high sensitivity, good selectivity, and a low limit of detection (LOD), with LOD values of 22.12 ± 0.25 ng mL^-1 and 122.37 ± 0.42 ng mL^-1, respectively. In a biological matrix, the QDs can form a complex with biomacromolecules; therefore, we studied the interaction between a carrier protein (HSA) and the as-synthesized ZnS QDs. The surface functionalized and nano-sized ZnS-GT QDs were observed to form complexes with the human serum albumin (HSA) protein and quenched the intrinsic fluorescence of HSA through static and dynamic quenching modes. The binding affinity was observed to be of the order of 10⁵ M^-1 for the HSA-ZnS-GT QD interactions, which can be considered as a reversible mode of binding. The effect of the ZnS QDs on other ligands and protein interactions was also studied. Enhanced binding affinities for HSA-quercetin ((5.994 ± 0.139) × 10⁵ M^-1) and HSA-luteolin ((3.068 ± 0.127) × 10⁵ M^-1) interactions were also observed in the presence of ZnS-GT QDs.

Photocatalytic degradation of Congo Red by zinc sulfide quantum dots produced by anaerobic granular sludge

ABSTRACTSulfate reducing bacteria present in anaerobic granular sludge mediate the metabolic conversion of sulfate to sulfide. In the presence of heavy metals, sulfides precipitate as metal sulfides. In this study, dissimilatory sulfate reduction was coupled to the precipitation of zinc as ZnS quantum dots (QDs) at ambient conditions. The biogenic ZnS QDs had average sizes of 5-7 nm and were formed within 2-4 days of incubation. X-ray diffraction analysis indicated that the biosynthesised ZnS QDs possessed a crystalline cubic lattice structure. The organics present during ZnS biosynthesis were characterized using 3D-fluorescence excitation-emission measurements (FEEM) and the presence of an organic coating on the biogenic ZnS QDs was affirmed using FTIR analysis. The UV-visible absorption spectra of the samples exhibited a prominent absorption peak below 325 nm, which is the characteristic of the surface plasmon resonance of ZnS QDs. The band gap energy of the biogenic ZnS QDs was estimated to be 3.84 eV, comparable to the values reported for chemically synthesised ZnS QDs. The direct band gap energy indicates a large redox potential and carrier mobility, which capacitate the application of these QDs as effective photocatalysts for the photo-assisted decolourization of dyes, as illustrated for the dye congo red.

Synthetic Approaches, Modification Strategies and the Application of Quantum Dots in the Sensing of Priority Pollutants

Polycyclic aromatic hydrocarbons (PAHs) and nitro-aromatic compounds (NACs) are two classifications of environmental pollutants that have become a source of health concerns. As a result, there have been several efforts towards the development of analytical methods that are efficient and affordable that can sense these pollutants. In recent decades, a wide range of techniques has been developed for the detection of pollutants present in the environment. Among these different techniques, the use of semiconductor nanomaterials, also known as quantum dots, has continued to gain more attention in sensing because of the optical properties that make them useful in the identification and differentiation of pollutants in water bodies. Reported studies have shown great improvement in the sensing of these pollutants. This review article starts with an introduction on two types of organic pollutants, namely polycyclic aromatic hydrocarbons and nitro-aromatic explosives. This is then followed by different quantum dots used in sensing applications. Then, a detailed discussion on different groups of quantum dots, such as carbon-based quantum dots, binary and ternary quantum dots and quantum dot composites, and their application in the sensing of organic pollutants is presented. Different studies on the comparison of water-soluble quantum dots and organic-soluble quantum dots of a fluorescence sensing mechanism are reviewed. Then, different approaches on the improvement of their sensitivity and selectivity in addition to challenges associated with some of these approaches are also discussed. The review is concluded by looking at different mechanisms in the sensing of polycyclic aromatic hydrocarbons and nitro-aromatic compounds.

Inorganic Synthesis Based on Reactions of Ionic Liquids and Deep Eutectic Solvents

Ionic liquids and deep eutectic solvents are of growing interest as solvents for the resource‐efficient synthesis of inorganic materials. This Review covers chemical reactions of various deep eutectic solvents and types of ionic liquids, including metal‐containing ionic liquids, [BF₄]⁻‐ or [PF₆]⁻‐based ionic liquids, basic ionic liquids, and chalcogen‐containing ionic liquids. Cases in which cations, anions, or both are incorporated into the final products are also included. The purpose of this Review is to raise caution about the chemical reactivity of ionic liquids and deep eutectic solvents and to establish a guide for their proper use.

Recyclable ZnS QDs as an efficient photocatalyst for dye degradation under the UV and visible light

Energy-efficient synthesized ZnS QDs with unique visible range absorption through defects show the best photocatalytic activity under UV light and best degradation under visible light.

Sustainable preparation of sunlight active α-Fe2O3 nanoparticles using iron containing ionic liquids for photocatalytic applications

Inspired by the nano-segregation of ionic liquids (ILs) into bi-continuous structures constituting of arrays of ionic and non-ionic components, herein, a new and sustainable strategy for preparation of mesh-like nano-sheet α-Fe₂O₃ nanoparticles and their photo-catalytic activity under sunlight, is presented. For the purpose, metal (iron) containing ionic liquids (MILs), 1-alkyl-3-methylimidazolium tetrachloroferrates, [C_nmim][FeCl₄], (n = 4, 8 and 16), which not only act as precursors and solvents but also as structure directing agents have been used. Thus prepared NPs show MIL dependent structural, photophysical and magnetic properties. The catalytic efficiency of NPs has been tested for the photo-degradation of organic dyes (Rhodamine B) in aqueous solution under sunlight. The NPs are found to exhibit comparable catalytic efficiency under sunlight as compared to that observed under high intensity visible lamplight, without showing a decline in their catalytic efficiency even after 4 catalytic cycles. It is anticipated that the present work will provide a new platform for preparation of sunlight active nanomaterials for photo-catalytic applications with control over the structural and physical properties via varying the molecular structure of MILs.

Inspired by nanosegregation of ionic liquids into bicontinuous structures of arrays of ionic and non-ionic components, we present a new sustainable strategy for preparation of mesh-like nano-sheets of α-Fe₂O₃ nanoparticles and their photocatalytic activity under sunlight.