Stability Of Nanocrystals Research Articles

Mg2+‐Doped Cesium Copper Halide for Bright Electroluminescent White Light‐Emitting Diodes

AbstractLead‐based perovskite nanocrystals (NCs) as one of the most promising materials in the fields of display and lighting, have outstanding optical performance and simple solution preparation process. However, the toxicity of lead and poor stability limit their commercialization. Meanwhile, as a key component of display and lighting, white light‐emitting diodes (WLEDs) still faces challenges such as low luminance and complex preparation process. A method is proposed for preparing nontoxic and stable Cs3Cu2I5 NCs by doping Mg2+ ions, achieved broadband blue light emission with a high PLQY of 96.2% and excellent thermal cycling stability and air stability. Then, the Mg2+ ions doped Cs3Cu2I5 NCs are used as emissive layer, while the 1,3,5‐Tri (m‐pyridine‐3‐ylphenyl) benzene (TmPyPb) is selected as electron transport layer to interact with Cs3Cu2I5 thin films for the formation of Cu‐I complex with broadband yellow light emission. This approach obviated the need for multi‐layer sedimentary emission layers, resulting in WLEDs featuring a high color rendering index (CRI) of 91, a peak external quantum efficiency (EQE) of 0.71% and maximum luminance of 2116 cd m−2 that is the highest values of lead‐free perovskite WLEDs at present. Therefore, Cs3Cu2I5 NCs have good application prospects in WLEDs.

Effect of salt ions (Na+, Ca2+ and Mg2+) and EOR anionic and nonionic surfactants on the dispersion stability of cellulose nanocrystals

The application of cellulose nanocrystals (CNCs) in enhanced oil recovery (EOR) is a developing hotspot. To improve the stability of CNCs in salt environments, the effects of sodium dodecylbenzene sulfonate (SDBS) and polyoxyethylene sorbitan monooleate (Tween 80) on the stability of CNCs in the presence of sodium (Na+), calcium (Ca2+) and magnesium (Mg2+) were investigated. The range of salt ions and the stability mechanism for improving the CNCs stability in the presence of SDBS and Tween 80 were pointed out. SDBS improved the stability of CNCs in the presence of 30–100 mM Na+, 1–2 mM Ca2+ and 2 mM Mg2+, respectively. Tween 80 improved the stability of CNCs in the presence of Na+ ≤ 300 mM, Ca2+ ≤ 10 mM and Mg2+ ≤ 10 mM, respectively. The mechanism was explained by the bridging effect of salt ions, electrostatic effect and spatial stability effect. The combined systems of surfactants (SDBS and Tween 80) with CNCs exhibited strong emulsifying properties, low interfacial tension (0.023 mN/m and 1.85 mN/m), and the ability to alter the wettability of oil wet rocks. This made the combined systems have better oil displacement performance.

Highly stable and bright CsPbI3 nanocrystal red emitters based on color-conversion from InGaN-based blue light-emitting diodes

Highly stable and bright CsPbI3 nanocrystal red emitters based on color-conversion from InGaN-based blue light-emitting diodes

Size and Shape Effect on Melting Temperature of Metallic Nanocrystals

The melting temperature serves as a pivotal physical property governing the thermal stability of metallic nanocrystals, notably exhibiting substantial variability with respect to size and dimensionality. While several quantitative models exist to elucidate how the melting temperature correlates with the size and dimensionality of metallic nanocrystals, these models often fall short of capturing the synergistic influence of both factors comprehensively. To address this gap, our study employs a novel thermodynamic framework grounded in cohesive energy theory, requiring no arbitrary adjustable parameters. We find that, under constant conditions, the melting temperature of metallic nanocrystals diminishes as their size decreases. In terms of dimensionality, we establish a hierarchy as follows: nanoparticles > nanowires > thin films. Moreover, we reveal a non-linear relationship between the melting temperature and the inverse of dimensionality. Through rigorous validation via both simulations and empirical experiments, we corroborate the high accuracy of this thermodynamic model in predicting the variations in the melting temperature of metallic nanocrystals due to changes in size and dimensionality. The model in this study is primarily applicable to metallic nanocrystals and the potential applicability to other types of nanocrystals under certain conditions is briefly mentioned..

Influence of buffer on colloidal stability, microstructure, and rheology of cellulose nanocrystals in hyaluronic acid suspensions

Hyaluronic acid (HA) is a natural biopolymer found in various human tissues, while cellulose nanocrystals (CNCs) extracted from pulp fibers have unique rheological properties and biocompatibility. Due to the superior biomechanical properties of CNC and HA, a CNC-based HA suspension may be useful in biomedical applications. While buffers are an essential constituent of any suspension used for biomedical applications to maintain the desired pH level, they can significantly affect the properties of the suspension, including colloidal stability, microstructure, and rheological characteristics.To our knowledge, this is the first study analyzing the influence of buffer solutions on the suspension characteristics of HA/CNC systems, integrating both theoretical and experimental approaches. The results revealed an alignment between predictions of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and results from experiments characterizing a buffer-specific trend in colloidal stability. Suspensions with a higher energy barrier showed higher colloidal stability, with a lower tendency for phase separation and agglomerate formations. The microstructural analysis of CNC tactoids in the suspension revealed the existence of the hedgehog defect when dispersed in different buffer solutions. The defect is predicted to be caused by the pH-dependent protonation and deprotonation of HA. Furthermore, steady shear viscometry showed a microstructural-dependent shear viscosity trend, which, in turn, depends on the buffer solution.The study provides novel insights into the microstructural and bulk properties of HA and CNC suspensions in various buffer solutions. The results highlight the importance of solvent choice in tailoring the properties of the suspension for specific biomedical applications. These findings may be helpful in formulating HA and CNC suspensions for different biomedical applications, including drug delivery systems and viscosupplement injections.

Thermal stability and properties of silicon-germanium nanocrystals

Using first-principles calculations and ensemble theory, we have calculated the ground-state energy and electronic properties of SixGe10−xH16 nanocrystals, and analyzed their stability and properties at finite temperatures. We have determined the numerical correspondence between chemical potential and the proportion of element in SixGe10−xH16. The probability of various structures appearing within SixGe10−xH16 nanocrystals depends on temperature and chemical potential environment. The influence of vibrational free energy, as investigated by theoretical computations, is also summarized. The research results show that vibrational free energy enhances the structure stability by the occupation of Ge atoms and results in a more concentrated distribution of the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital.

The Thermal Stability and Photoluminescence of ZnSeO3 Nanocrystals Chemically Synthesized into SiO2/Si Track Templates

We report the effect of high-temperature treatment on the structure and photoluminescence of zinc selenite nanocrystals (ZnSeO3) deposited into SiO2/Si track templates. The templates were formed via irradiation with Xe ions (200 MeV, 108 ions/cm2) followed by etching in HF solution. ZnSeO3 nanocrystals were obtained via chemical deposition from the aqueous solution of ZnCl2 and SeO2 as Zn-, Se- and O-precursors. To estimate the thermal stability of the deposited precipitates, heat treatment was carried out at 800 and 1000 °C for 60 min in a vacuum environment. Scanning electron microscopy (SEM), X-ray diffractometry (XRD), photoluminescence (PL) spectroscopy, and electrical measurements were used for the characterization of ZnSeO3/SiO2nanoporous/Si nanocomposites. Thermal treatment of the synthesized nanocomposites resulted in structural transformations with the formation of ZnSe and ZnO phases while the content of the ZnSeO3 phase decreased. For the as-deposited and annealed precipitates, an emission in the range of (400 to 600) nm was observed. PL spectra were approximated by four Gaussian curves with maxima at ~550 nm (2.2 eV), 488 nm (2.54 eV), ~440 nm (2.82 eV), and 410 nm (3.03 eV). Annealing resulted in a decrease in PL intensity that was possibly due to the weight loss of the deposited substance during high-temperature treatment. The redistribution of maxima intensities after annealing was also observed with an increase in blue and violet emissions. The origin of the observed PL is discussed. The I–V curve analysis revealed an electronic type of conductivity for the ZnSeO3(NCs)/SiO2nanoporous/Si structure. The values of the specific conductivity were calculated within the percolation model. The sample annealed at 800 °C showed the highest specific conductivity of 8.5 × 10−6 Ohm−1·cm−1.

Continuous-flow synthesis of CsPbI3/TiO2 nanocomposites with enhanced water and thermal stability.

The inherent poor stability of CsPbI3 nanocrystals hinders the practical application of this material. Therefore, it is still a challenge to improve the stability of CsPbI3 nanocrystals and realize their large-scale continuous preparation. In this work, we report the preparation of CsPbI3/TiO2 nanocomposites with high stability by a microfluidic method. After the combination of CsPbI3 nanorods with TiO2, the PL intensity increased by 1.3 times under excitation at 577 nm due to the passivating effect of TiO2 on the surface of CsPbI3 nanorods and its carrier transport characteristics. Meanwhile, due to the coating of TiO2, the surface exposure area of CsPbI3 nanorods is reduced, which blocks external environmental effects to some extent and effectively improves the stability of CsPbI3 nanorods. Finally, an LED with a color gamut of 142% NTSC and a color temperature (CCT) of 3952 K was obtained by combining CsPbI1.5Br1.5/TiO2 and CsPbBr3/TiO2 nanocomposites with a blue light chip (455 nm). This study shows that the continuous and controllable synthesis of all inorganic halide perovskite nanocrystals by a microfluidic method is of great significance in the fabrication of high-performance optoelectronic materials and display devices.

Improvements in Photoluminescence Efficiency and Stability of CsPbBr3 Nanocrystals Through 3-Aminopropyltriethoxysilane Treatment

Improvements in Photoluminescence Efficiency and Stability of CsPbBr3 Nanocrystals Through 3-Aminopropyltriethoxysilane Treatment

(Invited) Transformation Mechanism of Quantum-Sized Semiconductor Nanocrystals Revealed by in Situ Transmission Electron Microscopy

Semiconductor nanocrystal quantum dots are renowned for their remarkable properties, including tunable bandgap, pure color emission with exceptionally narrow bandwidths, and high luminescence efficiency. A thorough understanding of the transformation mechanism of quantum-sized semiconductor nanocrystals is essential for their practical application, as their properties are determined by their structure. This presentation will focus on exploring these mechanisms using in-situ transmission electron microscopy (TEM). The first part of the talk will examine the moisture-induced degradation of quantum-sized semiconductor nanocrystals, highlighting a notable finding: the formation of amorphous intermediates on the surfaces of these nanocrystals during degradation. This insight is crucial for developing strategies to enhance the stability and durability of nanocrystals, thereby extending their practical application. Next, I will discuss the crystal phase transition mechanism in II-VI semiconductor nanocrystals, triggered by off-stoichiometry. This discussion will shed light on the determinants of the crystal phase in these nanocrystals, a key to understanding their functionality. Lastly, the presentation introduces the application of in-situ X-ray scattering. This technique offers structural insights that complement those obtained from in-situ TEM, significantly enriching our understanding of the structural dynamics in semiconductor nanocrystals.

Dandelion inspired microparticles with highly efficient drug delivery to deep lung

Active pharmaceutical ingredient (API) embedded dry powder for inhalation (AeDPI) shows higher drug loading and delivery dose for directly treating various lung infections. Inspired by the dandelion, we propose a novel kind of AeDPI microparticle structure fabricated by spray freeze drying technology, which would potentially enhance the alveoli deposition efficiency. When inhaling, such microparticles are expected to be easily broken-up into fragments containing API that acts as ‘seed’ and could be delivered to alveoli aided by the low density ‘pappus’ composed of excipient. Herein, itraconazole (ITZ), a first-line drug for treating pulmonary aspergillosis, was selected as model API. TPGS, an amphiphilic surfactant, was used to achieve stable primary ITZ nanocrystal (INc) suspensions for spray freeze drying. A series of microparticles were prepared, and the dandelion-like structure was successfully achieved. The effects of feed liquid compositions and freezing parameters on the microparticle size, morphology, surface energy, crystal properties and in vitro aerosol performance were systematically investigated. The optimal sample (SF(-50)D-INc7Leu3-2) in one-way experiment showed the highest fine particle fraction of ∼ 68.96 % and extra fine particle fraction of ∼ 36.87 %, equivalently ∼ 4.60 mg and ∼ 2.46 mg could reach the lung and alveoli, respectively, when inhaling 10 mg dry powders. The response surface methodology (RSM) analysis provided the optimized design space for fabricating microparticles with higher deep lung deposition performance. This study demonstrates the advantages of AeDPI microparticle with dandelion-like structure on promoting the delivery efficiency of high-dose drug to the deep lung.

Valorization of citrus peel industrial wastes for facile extraction of extractives, pectin, and cellulose nanocrystals through ultrasonication: An in-depth investigation

In this work we developed an eco-friendly valorisation of Citrus wastes (CWs), through a solvent-assisted ultrasonication extraction technique, thus having access to a wide range of bio-active compounds and polysaccharides, extremely useful in different industrial sectors (food, cosmetics, nutraceutical). Water-based low-amplitude ultrasonication was examined as a potential method for pectin extraction as well as polar and non-polar citrus extractives (CEs), among which hesperidin and triglycerides of 18 carbon fatty acids were found to be the most representative ones. In addition, citric acid:glycerol (1:4)-based deep eutectic solvent (DES) in combination with ultrasonic extraction was utilized to extract microcellulose (CMC), from which stable cellulose nanocrystals (CNCs) with glycerol-assisted high amplitude ultrasonication were obtained. The physical and chemical properties of the extracted polysaccharides (pectin, micro and nanocellulose) were analysed through DLS, ζ-potential, XRD, HP-SEC, SEM, AFM, TGA-DSC, FTIR, NMR, and PMP-HPLC analyses. The putative structure of the extracted citrus pectin (CP) was analysed and elucidated through enzyme-assisted hydrolysis in correlation with ESI-MS and monosaccharide composition. The developed extraction methods are expected to influence the industrial process for the valorisation of CWs and implement the circular bio-economy.

Luminescence Nanothermometry: Investigating Thermal Memory in UiO-66-NH2 Nanocrystals.

Metal-organic frameworks (MOFs), a diverse and rapidly expanding class of crystalline materials, present many opportunities for various applications. Within this class, the amino-functionalized Zr-MOF, namely, UiO-66-NH2, stands out due to its distinctive chemical and physical properties. In this study, we report on the new unique property where UiO-66-NH2 nanocrystals exhibited enhanced fluorescence upon heating, which was persistently maintained postcooling. To unravel the mechanism, the changes in the fluorescence signal were monitored by steady-state fluorescence spectroscopy, lifetime measurements, and a fluorescence microscope, which revealed that upon heating, multiple mechanisms could be contributing to the observed enhancement; the MOFs can undergo disaggregation, resulting in a fluorescent enhancement of the colloidally stable MOF nanocrystals and/or surface-induced phenomena that result in further fluorescence enhancement. This observed temperature-dependent photophysical behavior has substantial applications. It not only provides pathways for innovations in thermally modulated photonic applications but also underscores the need for a better understanding of the interactions between MOF crystals and their environments.

MgO/Ni nanocomposite and its PVP-modified derivative for catalytic CO2 methanation and photocatalytic hydrogen production

In this study, we show that MgO/Ni nanocomposite (NC) synthesized using Laurus nobilis leaf extract display high catalytic activity toward CO2 methanation and photocatalytic hydrogen production. The polyvinylpyrrolidone (PVP)-modified NC displayed improved dispersion and charge separation, hence enhanced performance. The physicochemical characterization of the NCs revealed thermally stable (<0.5 wt% loss up to 400 °C) single nanocrystals, which may aggregate depending on the preparation technique. Fourier transform infrared spectroscopy coupled with thermogravimetry confirmed the incorporation of 0.45 g PVP per 1 g MgO/Ni. Catalytic performance evaluation showed peak CO2 conversion of 94.56 % and 98.74 % for MgO/Ni and MgO/Ni@PVP, respectively, at 390 °C, with higher selectivity towards CH4 observed for MgO/Ni@PVP across all temperatures. Similarly, MgO/Ni@PVP exhibited higher hydrogen production reaching 1.68 mmol/g.h compared with 1.30 mmol/g.h for MgO/Ni. These results underscore the potential of MgO/Ni@PVP NC as an effective catalyst for renewable energy production and carbon utilization.

Growth of CsPbX3 nanocrystals using sol–gel SiO2 solid powders as reactors without capping agents towards anomalous stable emission membranes

To overcome the poor stability of metal halide perovskite nanocrystals (NCs) prepared in organic solvents, a solid reaction method at high temperature was developed using sol–gel porous SiO2 as a reactor. Sol-gel SiO2 powders were used to encapsulate CsPbX3 NCs at high temperatures (600–800 °C) in air to get SiO2/CsPbX3 glass by dispersing growth cites in advance and no ligands added. After NaOH etching, a thin dense SiO2 shell was remained on the surface of CsPbX3 NCs (named as CsPbX3@SiO2).The photoluminescence (PL) quantum yield of the CsPbX3@SiO2 was 86.7 %, in which their PL peak wavelengths were adjusted from 410-707 nm by changing halogen components. The dense SiO2 shell on CsPbX3 NCs blocked the connection of CsPbX3 cores with water and oxygen in the external environment, resulting in CsPbX3@SiO2 revealed extraordinary high stability. After immersing in water for half year, the PL intensity of CsPbX3@SiO2 composites was remained unchanged and the composites still revealed bright PL after heat-treating in boiling water for 14 h. These highly stable composites were used to fabricate a white light-emitting diode, in which the color coordinates are located at (0.36, 0.33), and the color temperature reaches 5169 K which belongs to the warm white light range.

Active Learning of Ligands That Enhance Perovskite Nanocrystal Luminescence.

Ligands play a critical role in the optical properties and chemical stability of colloidal nanocrystals (NCs), but identifying ligands that can enhance NC properties is daunting, given the high dimensionality of chemical space. Here, we use machine learning (ML) and robotic screening to accelerate the discovery of ligands that enhance the photoluminescence quantum yield (PLQY) of CsPbBr3 perovskite NCs. We developed a ML model designed to predict the relative PL enhancement of perovskite NCs when coordinated with a ligand selected from a pool of 29,904 candidate molecules. Ligand candidates were selected using an active learning (AL) approach that accounted for uncertainty quantified by twin regressors. After eight experimental iterations of batch AL (corresponding to 21 initial and 72 model-recommended ligands), the uncertainty of the model decreased, demonstrating an increased confidence in the model predictions. Feature importance and counterfactual analyses of model predictions illustrate the potential use of ligand field strength in designing PL-enhancing ligands. Our versatile AL framework can be readily adapted to screen the effect of ligands on a wide range of colloidal nanomaterials.

Efficient nanostructured Cs2CuBr2Cl2 perovskite as a fluorescent sensor for the selective “Switch Off” detection of nitrobenzene

Lead halide nanostructured perovskites are well known for their excellent photoluminescence and optoelectronic properties. However, lead toxicity and instability in moisture impedes its suitability for material use. Here we synthesized a highly efficient, lead free, economical, stable Cs2CuBr2Cl2 perovskite nanocrystals (PNCs) via Ligand Assisted Re-Precipitation (LARP) method which is less explored. The sensing application of the synthesized PNCs towards nitro explosives and other small organic compounds were studied. The probe exhibited high selectivity towards nitrobenzene with a lowest detection limit of 57.64 nM. The fluorescent emission intensity was drastically quenched upon the addition of 32 µM nitrobenzene. A Stern-Volmer plot was utilized for the quantification of fluorescence quenching. Further to investigate the quenching mechanism, time correlated single photon counting spectroscopy and other photoluminescence studies were performed pointing out the possibility of fluorescence resonance energy transfer. The work has been further extended to test the capability of the probe to detect nitrobenzene in real water samples and a good recovery percentage ranging from 93-98 % was obtained. Further, a paper strip assay was designed which successfully detected nitrobenzene and can be clearly noticed even with our naked eye making the probe an excellent sensor for nitrobenzene detection.

Enhanced photoluminescence emission intensity and stability of deep blue-emissive (Et3NH)PbBr3 perovskite nanocrystals by using metal-organic frameworks

The primary obstacle faced by researchers in the field of luminescent metal-halide perovskites is their inherent instability, prompting a shift in focus towards enhancing the stability of perovskite nanocrystals (PNCs). One of the promising approaches to address this challenge involves the utilization of metal-organic frameworks (MOFs) to fabricate PNCs@MOF composites. The present study reports a facile and low-cost colloidal strategy to prepare (Et3NH)PbBr3 PNCs followed by their encapsulation within UiO-67 to enhance their photoluminescence (PL) emission stability. The PNCs and modified UiO-67 were prepared separately via simple and efficient ligand-assisted reprecipitation (LARP) and hydrothermal methods, respectively. After modification of the UiO-67, the pore sizes experienced a substantial increase from 1.90 to 28.84 nm which significantly facilitated the localization of PNCs within the porous matrix. Under a full survey of experimental conditions, the resulting (Et3NH)PbBr3@UiO-67 composite exhibited a bright deep-blue emission at around 410 nm with an emission quantum yield of 52 %. The emission durability of the fabricated PNCs@MOF composites was assessed against temperature and long-time of storage, confirming the superior advantages of MOF even at elevated temperatures of up to 100 °C. The stable and luminous deep-blue emission displayed by the PNCs@MOF composites in this investigation, offers a promising advancement in materials development for optoelectronic applications.

Ligand engineering for improving the stability and optical properties of CsPbI3 perovskite nanocrystals

Inorganic lead halide perovskite nanocrystals (NCs) have recently become one of the research topics for optoelectronic applications due to their excellent photophysical properties. Despite their notable thermal stability over organic-inorganic halide perovskites, CsPbI3 NCs suffer from the phase instability of α-CsPbI3 phase at room temperature and under ambient conditions. Here, the effects of 4-Hydroxybenzoic acid (4-HBA) as an additive to standard oleic acid – oleylamine pair on the stability and optical properties of CsPbI3 perovskite NCs are discussed. 4-HBA addition into perovskite NC systems causes a compressive strain on perovskite lattice, which leads to the formation of a mixed phase α- and γ-CsPbI3 phases while pristine perovskite has α-CsPbI3 phase. Time-dependent stability of the perovskite NCs was tested under an ethanol (EtOH) medium. After EtOH exposure of the perovskite NCs, CsPbI3 NCs transformed to non-perovskite phase in 1 h while 4-HBA added CsPbI3 NCs still have perovskite phase after 48 h. In addition to the improved optical properties of the perovskite NCs, 4-HBA addition remarkably improves CsPbI3 perovskite stability.

Enhanced stability and dissolution of curcumin nanocrystals stabilized by octenyl succinic anhydride modified starch

Curcumin (CUR) has known to have poor oral bioavailability due to its poor aqueous solubility and stability in gastrointestinal fluid condition as well as its limited permeability which greatly limits its applications in food and medical fields. The present study reported the development of CUR nanocrystal suspension (CUR-NS) for enhanced bioavailability, stabilized with octenyl succinic anhydride modified starch (OSA-S), a naturally renewable and biocompatible biomolecule. This preparation was achieved via an antisolvent precipitation combined with ultrasonic dispersion method, following which the suspension was freeze-dried to form powder CUR nanocrystals (CUR-NCs). Physicochemical properties of the prepared CUR-NS and CUR-NCs powders were extensively characterized. The particle size of the nanocrystals was found to be around 322.8 ± 15.7 nm with a small polydispersity index (PDI) of about 0.230 ± 0.039. Rod like crystal shape was observed by the SEM. Results from powder X-ray diffraction (pXRD) and differential scanning calorimetry (DSC) indicated that the crystal form of CUR in CUR-NCs was a monoclinic polymorph Form 2. Stability results indicated that CUR-NCs possessed an excellent storage-, thermal-, and photo-stabilities. CUR-NCs had a significantly higher dissolution rate, a 68-fold increase in its solubility than that of raw CUR. The cytotoxicity assay demonstrated that CUR-NCs exhibited lower toxicity towards normal human kidney epithelial cells compared to raw CURs. Parallel artificial membrane permeability assay (PAMPA) characterization confirmed that the flux of CUR was significantly enhanced after forming nanocrystals with OSA-S, probably resulting from its increased solubility and dissolution rate. The study showed that OSA-S could effectively stabilize CUR-NCs, and CUR-NCs developed in the current work exhibited significant enhancement in the stability and dissolution rate leading to an improved bioavailability which might be helpful for further development of CUR based products.