Advances in Natural Sciences: Nanoscience and Nanotechnology

In this study UiO-66 and UiO-66-NH₂ were synthesized by solvothermal method. The effect of preparation conditions on the quality of UiO-66-NH₂ was studied. The obtained material has been characterized by x-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimatric analysis (TGA), scanning electron microscopy (SEM) and nitrogen physisorption measurements (BET). The CO₂ and CH₄ physisorption measurements were carried out using a high pressure volumetric analyzer (Micromeritics HPVA—100). The results showed that the UiO-66-NH₂ of ball shape crystalline had been obtained and characterized by high surface area (BET) up to 876 m² g⁻¹, specific volume 0.379 cm³ g⁻¹, pore radius 9.5 Å and thermal stability up to 673 K, respectively. The experiments indicated that in comparison with UiO-66 the addition of NH₂ is able to increase the CO₂ and CH₄ storage capacity at 1 bar and 303 K twice from 28.43 cm³ g⁻¹ up to 52 cm³ g⁻¹ and from 6.68 cm³ g⁻¹ to 11.1 cm³ g⁻¹, respectively.

Mesoporous thiol-functionalized SBA-15 has been directly synthesized by co-condensation of tetraethyl orthosilicate (TEOS) and 3-mercaptopropyltrimethoxysilane (MPTMS) with triblock copolymer P123 as-structure-directing agent under hydrothermal conditions. Surfactant removal was performed by Soxhlet ethanol extraction. These materials have been characterized by powder x-ray diffraction (XRD), nitrogen adsorption/desorption (BET model), transmission electron microscopy (TEM), thermal analysis, infrared spectroscopy (IR) and energy-dispersive x-ray spectroscopy (EDX). The main parameters, such as the initial molar ratio of MPTMS to TEOS, the time of adding MPTMS to synthesized gel and the Soxhlet ethanol extraction on the thiol functionalized SBA-15 with high thiol content and highly ordered hexagonal mesostructure, were investigated and evaluated. The adsorption capacity of the thiol-functionalized and non-functionalized SBA-15 materials for ^Pb2+ ion from aqueous solution was tested. It was found that the ^Pb2+ adsorption capacity of the thiol functionalized SBA-15 is three times higher than that of non-functionalized SBA-15.

Copper nanoparticles, due to their interesting properties, low cost preparation and many potential applications in catalysis, cooling fluid or conductive inks, have attracted a lot of interest in recent years. In this study, copper nanoparticles were synthesized through the chemical reduction of copper sulfate with sodium borohydride in water without inert gas protection. In our synthesis route, ascorbic acid (natural vitamin C) was employed as a protective agent to prevent the nascent Cu nanoparticles from oxidation during the synthesis process and in storage. Polyethylene glycol (PEG) was added and worked both as a size controller and as a capping agent. Cu nanoparticles were characterized by Fourier transform infrared (FT-IR) spectroscopy to investigate the coordination between Cu nanoparticles and PEG. Transmission electron microscopy (TEM) and UV–vis spectrometry contributed to the analysis of size and optical properties of the nanoparticles, respectively. The average crystal sizes of the particles at room temperature were less than 10 nm. It was observed that the surface plasmon resonance phenomenon can be controlled during synthesis by varying the reaction time, pH, and relative ratio of copper sulfate to the surfactant. The surface plasmon resonance peak shifts from 561 to 572 nm, while the apparent color changes from red to black, which is partly related to the change in particle size. Upon oxidation, the color of the solution changes from red to violet and ultimately a blue solution appears.

In recent years the outbreak of re-emerging and emerging infectious diseases has been a significant burden on global economies and public health. The growth of population and urbanization along with poor water supply and environmental hygiene are the main reasons for the increase in outbreak of infectious pathogens. Transmission of infectious pathogens to the community has caused outbreaks of diseases such as influenza (A/H₅N₁), diarrhea (Escherichia coli), cholera (Vibrio cholera), etc throughout the world. The comprehensive treatments of environments containing infectious pathogens using advanced disinfectant nanomaterials have been proposed for prevention of the outbreaks. Among these nanomaterials, silver nanoparticles (Ag-NPs) with unique properties of high antimicrobial activity have attracted much interest from scientists and technologists to develop nanosilver-based disinfectant products. This article aims to review the synthesis routes and antimicrobial effects of Ag-NPs against various pathogens including bacteria, fungi and virus. Toxicology considerations of Ag-NPs to humans and ecology are discussed in detail. Some current applications of Ag-NPs in water-, air- and surface- disinfection are described. Finally, future prospects of Ag-NPs for treatment and prevention of currently emerging infections are discussed.

In this study we report on the synthesis of silver nanoparticles (AgNPs) from the leaf extracts of Moringa oleifera using sunlight irradiation as primary source of energy, and its antimicrobial potential. Silver nanoparticle formation was confirmed by surface plasmon resonance at 450 nm and 440 nm, respectively for both fresh and freeze-dried leaf samples. Crystanality of AgNPs was confirmed by transmission electron microscopy, scanning electron microscopy with energy dispersive x-ray spectroscopy and Fourier transform infrared (FTIR) spectroscopy analysis. FTIR spectroscopic analysis suggested that flavones, terpenoids and polysaccharides predominate and are primarily responsible for the reduction and subsequent capping of AgNPs. X-ray diffraction analysis also demonstrated that the size range of AgNPs from both samples exhibited average diameters of 9 and 11 nm, respectively. Silver nanoparticles showed antimicrobial activity on both bacterial and fungal strains. The biosynthesised nanoparticle preparations from M. oleifera leaf extracts exhibit potential for application as broad-spectrum antimicrobial agents.

The present article is a review of research works on promising applications of graphene and graphene-based nanostructures. It contains five main scientific subjects. The first one is the research on graphene-based transparent and flexible conductive films for displays and electrodes: efficient method ensuring uniform and controllable deposition of reduced graphene oxide thin films over large areas, large-scale pattern growth of graphene films for stretchble transparent electrodes, utilization of graphene-based transparent conducting films and graphene oxide-based ones in many photonic and optoelectronic devices and equipments such as the window electrodes of inorganic, organic and dye-sensitized solar cells, organic light-emitting diodes, light-emitting electrochemical cells, touch screens, flexible smart windows, graphene-based saturated absorbers in laser cavities for ultrafast generations, graphene-based flexible, transparent heaters in automobile defogging/deicing systems, heatable smart windows, graphene electrodes for high-performance organic field-effect transistors, flexible and transparent acoustic actuators and nanogenerators etc. The second scientific subject is the research on conductive inks for printed electronics to revolutionize the electronic industry by producing cost-effective electronic circuits and sensors in very large quantities: preparing high mobility printable semiconductors, low sintering temperature conducting inks, graphene-based ink by liquid phase exfoliation of graphite in organic solutions, and developing inkjet printing technique for mass production of high-quality graphene patterns with high resolution and for fabricating a variety of good-performance electronic devices, including transparent conductors, embedded resistors, thin-film transistors and micro supercapacitors. The third scientific subject is the research on graphene-based separation membranes: molecular dynamics simulation study on the mechanisms of the transport of molecules, vapors and gases through nanopores in graphene membranes, experimental works investigating selective transport of different molecules through nanopores in single-layer graphene and graphene-based membranes toward the water desalination, chemical mixture separation and gas control. Various applications of graphene in bio-medicine are the contents of the fourth scientific subject of the review. They include the DNA translocations through nanopores in graphene membranes toward the fabrication of devices for genomic screening, in particular DNA sequencing; subnanometre trans-electrode membranes with potential applications to the fabrication of very high resolution, high throughput nanopore-based single-molecule detectors; antibacterial activity of graphene, graphite oxide, graphene oxide and reduced graphene oxide; nanopore sensors for nucleic acid analysis; utilization of graphene multilayers as the gates for sequential release of proteins from surface; utilization of graphene-based electroresponsive scaffolds as implants for on-demand drug delivery etc. The fifth scientific subject of the review is the research on the utilization of graphene in energy storage devices: ternary self-assembly of ordered metal oxide-graphene nanocomposites for electrochemical energy storage; self-assembled graphene/carbon nanotube hybrid films for supercapacitors; carbon-based supercapacitors fabricated by activation of graphene; functionalized graphene sheet-sulfure nanocomposite for using as cathode material in rechargeable lithium batteries; tunable three-dimensional pillared carbon nanotube-graphene networks for high-performance capacitance; fabrications of electrochemical micro-capacitors using thin films of carbon nanotubes and chemically reduced graphenes; laser scribing of high-performance and flexible graphene-based electrochemical capacitors; emergence of next-generation safe batteries featuring graphene-supported Li metal anode with exceptionally high energy or power densities; fabrication of anodes for lithium ion batteries from crumpled graphene-encapsulated Si nanoparticles; liquid-mediated dense integration of graphene materials for compact capacitive energy storage; scalable fabrication of high-power graphene micro-supercapacitors for flexible and on-chip energy storage; superior micro-supercapacitors based on graphene quantum dots; all-graphene core-sheat microfibres for all-solid-state, stretchable fibriform supercapacitors and wearable electronic textiles; micro-supercapacitors with high electrochemical performance based on three-dimensional graphene-carbon nanotube carpets; macroscopic nitrogen-doped graphene hydrogels for ultrafast capacitors; manufacture of scalable ultra-thin and high power density graphene electrochemical capacitor electrodes by aqueous exfoliation and spray deposition; scalable synthesis of hierarchically structured carbon nanotube-graphene fibers for capacitive energy storage; phosphorene-graphene hybrid material as a high-capacity anode material for sodium-ion batteries. Beside above-presented promising applications of graphene and graphene-based nanostructures, other less widespread, but perhaps not less important, applications of graphene and graphene-based nanomaterials, are also briefly discussed.

In this work we have demonstrated a powerful disinfectant ability of colloidal silver nanoparticles (NPs) for the prevention of gastrointestinal bacterial infections. The silver NPs colloid was synthesized by a UV-enhanced chemical precipitation. Two gastrointestinal bacterial strains of Escherichia coli (ATCC 43888-O157:k-:H7) and Vibrio cholerae (O1) were used to verify the antibacterial activity of the as-prepared silver NPs colloid by means of surface disinfection assay in agar plates and turbidity assay in liquid media. Transmission electron microscopy was also employed to analyze the ultrastructural changes of bacterial cells caused by silver NPs. Noticeably, our silver NPs colloid displayed a highly effective bactericidal effect against two tested gastrointestinal bacterial strains at a silver concentration as low as ∼3 mg l⁻¹. More importantly, the silver NPs colloid showed an enhancement of antibacterial activity and long-lasting disinfectant effect as compared to conventional chloramin B (5%) disinfection agent. These advantages of the as-prepared colloidal silver NPs make them very promising for environmental treatments contaminated with gastrointestinal bacteria and other infectious pathogens. Moreover, the powerful disinfectant activity of silver-containing materials can also help in controlling and preventing further outbreak of diseases.

Direct wafer bonding processes are being increasingly used to achieve innovative stacking structures. Many of them have already been implemented in industrial applications. This article looks at direct bonding mechanisms, processes developed recently and trends. Homogeneous and heterogeneous bonded structures have been successfully achieved with various materials. Active, insulating or conductive materials have been widely investigated. This article gives an overview of Si and ^SiO₂ direct wafer bonding processes and mechanisms, silicon-on-insulator type bonding, diverse material stacking and the transfer of devices. Direct bonding clearly enables the emergence and development of new applications, such as for microelectronics, microtechnologies, sensors, MEMs, optical devices, biotechnologies and 3D integration.

Electrospinning is a process used to fabricate continuous nanoscale fibers with diameters in the sub-micrometer to nanometer range using a high-voltage power supply. Electrospun (e-spun) fibers and the non-woven webs manufactured from them have attracted considerable attention due to their outstanding characteristics, such as high porosity, small diameter, excellent pore interconnectivity and high surface-to-volume ratio. Because of the useful properties of e-spun fibers, many synthetic and natural polymers, including single and blended polymers, have been electrospun into fibers that can be employed in a variety of applications such as filtration and thermal insulation, and in the manufacture of protective clothing, sensors, conducting devices, wound dressings and scaffolds for tissue engineering. Utilizing the electrospinning technique and its product, some studies on its applications have been conducted in our lab. They included the fabrication of a conducting composite mat for electrical applications, an antibacterial web for a biomedical sector and PCM containing e-spun mat for energy storage.

The authors report the synthesis of Fe₃O₄ nanoparticles by wet chemical reduction technique at ambient temperature and its characterization. Ferric chloride hexa-hydrate (FeCl₃ · 6H₂O) and sodium boro-hydrate (NaBH₄) were used for synthesis of Fe₃O₄ nanoparticles at ambient temperature. The elemental composition of the synthesized Fe₃O₄ nanoparticles was determined by energy dispersive analysis of x-rays technique. The x-ray diffraction (XRD) technique was used for structural characterization of the nanoparticles. The crystallite size of the nanoparticles was determined using XRD data employing Scherrer's formula and Hall–Williamson's plot. Surface morphology of as-synthesized Fe₃O₄ nanoparticles was studied by scanning electron microscopy. High resolution transmission electron microscopy analysis of the as-synthesized Fe₃O₄ nanoparticles showed narrow range of particles size distribution. The optical absorption of the synthesized Fe₃O₄ nanoparticles was studied by UV–vis–NIR spectroscopy. The as-synthesized nanoparticles were analyzed by Fourier transform infrared spectroscopy technique for absorption band study in the infrared region. The magnetic properties of the as-synthesized Fe₃O₄ nanoparticles were evaluated by vibrating sample magnetometer technique. The thermal stability of the as-synthesized Fe₃O₄ nanoparticles was studied by thermogravimetric technique. The obtained results are elaborated and discussed in details in this paper.

The demand for efficient energy storage solutions has become increasingly imperative in today's rapidly evolving technological landscape. Researchers from various disciplines have been diligently exploring potential avenues for enhancing the performance of electrode materials. Various materials have been explored for electrode materials. Among these, binary spinels such as MnCo₂O₄, NiCo₂O₄, Co₂TiO₄, etc, have emerged as promising candidates due to their exceptional super-capacitive properties. This review article aims to provide an in-depth exploration of recent developments in the synthesis, charge-storage mechanism, and utilization of different MnCo₂O₄-based nanostructures for energy storage applications. The discussion encompasses a comprehensive analysis of synthesis methods and further highlights their potential in electrochemical properties. Through a systematic examination of the latest research findings, this review seeks to shed light on the evolving landscape of spinel-based nanostructures and their pivotal role in advancing energy storage technologies. By consolidating the current state of knowledge and identifying areas for further investigation, this work contributes to the collective effort to develop sustainable and high-performance energy storage solutions.

The field of cancer treatment is undergoing a paradigm shift with the emergence of nanotechnology, particularly the use of nanoparticles (NPs) and their potential synergy with cold atmospheric plasma (CAP) and electroporation. This paper provides a comprehensive review of the current progress, challenges, and future prospects in utilizing NPs, CAP, and electroporation for cancer therapy. The investigated studies highlight the advantages of NPs, such as their small size, large surface area, and controlled drug release properties, making them efficient in delivering therapeutic agents to specific targets. Additionally, they explore the potential of metallic NPs, such as gold, silver, titanium, and palladium, in targeted drug-delivery systems, showcasing their ability to enhance cancer treatment through properties like tunable optical properties and increased drug circulation time. The combination of NPs with CAP and electroporation is shown to amplify cytotoxicity and therapeutic efficacy, leading to increased cancer cell death and improved treatment outcomes. Furthermore, the studies address the molecular mechanisms and outcomes of these combination therapies, emphasizing the potential for enhanced targeted drug delivery and improved therapeutic outcomes in cancer therapy. This review aims to contribute towards the development of future therapeutic strategies and optimized cancer treatment modalities.

Considering the wide range of applications in the pharmaceutical, cosmetics, food, and biomedical research industries, developing protein sources that are nutritious, easy to cultivate, and environmentally friendly, like microalgae Porphyridium cruentum is crucial to realising the rising demand. This study aims to explore the potential aspects of hydroxyapatite/lignocellulose using phycobiliproteins (PBPs) from red algae that have been purified and determine the material characteristics such as crystallinity, structure-function relation, morphology, elemental composition, and purification ability that have been addressed. The HAp/lignocellulose was successfully synthesized using the precipitation method. X-ray diffraction results show that the highest diffraction peak of HAp is at an angle of 33.0° with a lattice plane (211). The characterization results showed that the size of HAp was 16.5 nm, and that of the HAp/lignocellulose composite was 34.9 nm. Fourier transform infrared analysis showed the presence of the Ca-O functional group, confirming the formation of HAp/lignocellulose. The UV-visible spectra showed absorption peaks at 220, 254, and 360 nm. Then, the purity value obtained from PBP crude extract reached 4.00 with a yield of 60%. Therefore, HAp/lignocellulose materials can be relied upon to purify PBPs and have high selectivity capabilities such as bioactivities against cancer, diabetes, hypertension, and antioxidants for future studies.

The presence of a high concentration of silver metal ions can lead to soil and water toxicity, resulting in skin irritation, nausea, diarrhoea, argyria, kidney, neuronal and liver dysfunction. The study highlights the development of sensitive and selective nano sensors for the detection of toxic metal ion Ag⁺ in aqueous solution. Gum acacia-capped selenium nanoparticles (GA-SeNPs) were synthesized using the chemical reduction method which is a simple, eco-friendly method employing ascorbic acid as a reducing agent. The nanoparticles were characterized using techniques such as UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy (SEM), and dynamic light scattering (DLS), confirming their stability, morphology, and surface chemistry. SEM and DLS studies have confirmed the particle size to be approximately 66 nm, XRD confirmed the crystalline structure and FTIR confirmed the capping of gum acacia over the selenium surface. GA-SeNP was screened for the anions and cations in aqueous solution which has shown selective detection towards Ag⁺ ions with a detection limit in the nanomolar range. The limit of detection and quantification for Ag⁺ was 0.127 ppm and 0.387 ppm, respectively. SeNP were deposited on a paper strip and silver metal ion detection was performed, showing a quick colour change of the paper strip within seconds from orange to black with a single drop of minimum 2.8 ppm of Ag⁺ metal. Thus GA-SeNP can be used as an efficient nanoprobe for selective, sensitive, real-time quick analysis and detection of an impermissible limit (>1 mgL⁻¹ i.e. 1 ppm) of silver metal ions in our food, water and cosmetic samples.

The development of cost-effective materials that are catalytically efficient under both dark and light conditions remains a challenging goal in the field of water remediation. In this work, mesoporous SnS nanoparticles, synthesized using the ball-milling method, are demonstrated as a suitable and reusable candidate for the catalytic degradation of methylene blue under both dark and light conditions. A more detailed analysis is carried out on the dark activity which has been less explored. The prepared SnS particles are characterized using XRD, XPS, TEM, BET, UV–vis spectrophotometer, cyclic voltammetry and DLS techniques. Preliminary studies on the catalytic performance of various sizes of SnS nanoparticles are conducted under visible light, with 15 nm particles showing the best efficiency. Further studies are carried out with different quantities of 15 nm sized SnS catalyst under dark and degradation rate increased to as high as 0.1 min⁻¹. The surface electron transfer mechanism is identified as the driving force behind the dark catalysis, which is validated by the HOMO–LUMO alignment between the dye and the SnS nanoparticle. Moreover, the negative surface charge of SnS nanoparticles is expected to increase the electrostatic attraction and thereby the adsorption to the cationic dye molecules. The reusability of the catalyst is analysed using the repeatability studies and the structural stability is confirmed using x-ray diffraction and FTIR spectroscopy.

The demand for efficient energy storage solutions has become increasingly imperative in today's rapidly evolving technological landscape. Researchers from various disciplines have been diligently exploring potential avenues for enhancing the performance of electrode materials. Various materials have been explored for electrode materials. Among these, binary spinels such as MnCo₂O₄, NiCo₂O₄, Co₂TiO₄, etc, have emerged as promising candidates due to their exceptional super-capacitive properties. This review article aims to provide an in-depth exploration of recent developments in the synthesis, charge-storage mechanism, and utilization of different MnCo₂O₄-based nanostructures for energy storage applications. The discussion encompasses a comprehensive analysis of synthesis methods and further highlights their potential in electrochemical properties. Through a systematic examination of the latest research findings, this review seeks to shed light on the evolving landscape of spinel-based nanostructures and their pivotal role in advancing energy storage technologies. By consolidating the current state of knowledge and identifying areas for further investigation, this work contributes to the collective effort to develop sustainable and high-performance energy storage solutions.

The field of cancer treatment is undergoing a paradigm shift with the emergence of nanotechnology, particularly the use of nanoparticles (NPs) and their potential synergy with cold atmospheric plasma (CAP) and electroporation. This paper provides a comprehensive review of the current progress, challenges, and future prospects in utilizing NPs, CAP, and electroporation for cancer therapy. The investigated studies highlight the advantages of NPs, such as their small size, large surface area, and controlled drug release properties, making them efficient in delivering therapeutic agents to specific targets. Additionally, they explore the potential of metallic NPs, such as gold, silver, titanium, and palladium, in targeted drug-delivery systems, showcasing their ability to enhance cancer treatment through properties like tunable optical properties and increased drug circulation time. The combination of NPs with CAP and electroporation is shown to amplify cytotoxicity and therapeutic efficacy, leading to increased cancer cell death and improved treatment outcomes. Furthermore, the studies address the molecular mechanisms and outcomes of these combination therapies, emphasizing the potential for enhanced targeted drug delivery and improved therapeutic outcomes in cancer therapy. This review aims to contribute towards the development of future therapeutic strategies and optimized cancer treatment modalities.

Emerging research in conductive and composite polymer nanoinks (CCPNIs) demonstrate remarkable advantages in electrical, thermal, and mechanical properties which are highly desired for printable applications. The development of suitable scalable production techniques can address the demand for wearable, printable, and flexible nanoink-based electronic applications. In this review we present a comparative analysis for contact based techniques such as screen printing (SP), nano imprint lithography (NIL) and non-contact printing techniques such as inkjet printing (IJP), aerosol jet printing (AIP) and 3D printing with a focus on CCPNIs. We discuss the application of these techniques across various electronic domains such as wearable electronics, flexible sensors and robotics which rely on scalable printing technologies. Among the techniques reviewed, SP stands out as particularly suitable and sustainable, primarily due to its scalability and efficiency. It is capable of producing between 1,000 and 5,000 parts per hour, while maintaining a practical resolution range of 1000 μm (±5–10%). SP is suitable for applications in printed electronics, where cost-effectiveness, simplicity, and scalability are of focus. In contrast, for complex and multidimensional printing, 3D printing shows promise with an excellent resolution which are crucial for industrial-scaled production.

Cancer remains a formidable global health challenge, with millions of lives lost annually and a projected increase in cases, particularly in regions like South Central Asia, Europe, Eastern Europe, etc, Traditional cancer treatments, including chemotherapy, radiotherapy, and surgery, face limitations in effectively managing the complex tumor microenvironment and addressing the diverse characteristics of cancer cells. Nano-oncology has emerged as a promising frontier in cancer therapy, utilizing nanoscale materials to deliver therapeutic agents with precision and efficacy. The benefits of nanoparticle-based drug delivery systems are the ability to target tumor cells while minimizing adverse effects and overcoming multidrug resistance. Advancements in hybrid nanoparticle development have further enhanced the stability and performance of drug delivery systems, offering new avenues for cancer treatment. Moreover, nanoparticle-based therapies hold the potential to modulate the immunosuppressive tumor microenvironment and improve outcomes in immunotherapy. The review provides a comprehensive overview of nanotherapeutic products currently in various preclinical and clinical study stages, focusing on their success rates in lung and breast cancers compared to conventional chemotherapeutic drugs. By elucidating the landscape of nano-oncology and evaluating its efficacy in specific cancer types, this review aims to shed light on the transformative potential of nanoparticle-based approaches in cancer treatment and diagnosis. They are exploring nano-oncology promises to pave the way for innovative strategies in combating cancer and improving patient outcomes globally.

Highly luminescent nanocrystals (NCs), including semiconductor quantum dots (QDs), have been synthesized as light emitters for various applications during the last three decades. Recently, light-emitting diodes based on NCs or QDs (hereafter commonly called QLEDs) have been fabricated, achieving an external quantum efficiency of more than 20%, closely approaching practical requirements. In the QLED structure, the outermost shell of the luminescent NCs or QDs plays a crucial role, as it needs to simultaneously meet the following requirements: (i) to act as an effective shell to passivate imperfections or traps on the NC surface, while confining injected charge carriers within the emitting QDs/NCs; and (ii) to possess compatibility with both the electron transport layer (ETL) and the hole transport layer (HTL) for efficient injection of electrons and holes into the core NCs/QDs. Additionally, the outermost shell of the NCs/QDs should be environmentally friendly. Practically, the outermost ZnS shell appears to satisfy all the above requirements for various types of emitting NCs/QDs, including II-VI (CdSe, CdTe, ZnSe), III-V (InP, GaP), I-III-VI (CuInS₂, AgInS₂, AgInSe₂), and metal halide perovskites. This has naturally led to numerous studies conducted on different NCs and QDs with the same outermost ZnS shell. Using a ZnS shell is also advantageous for designing uniform QLED structures with different NCs or QDs to emit a variety of wavelengths. In this article, we review the recent development of QLEDs using various NCs or QDs as light emitters, where the spectral emission range can be controlled by simply adjusting the size or composition of the core NCs/QDs. We also discuss why ZnS is suitable for shelling various types of NCs/QDs and how it aligns appropriately with the ETLs and HTLs being studied for facilitating the injection of charge carriers in QLEDs.