Size Of Nanocrystals Research Articles

Carbon nanotube-bridged MXene nanoarchitectures decorated with ultrasmall Rh nanoparticles for efficient methanol oxidation

Rational design and precise synthesis of cost-effective and highly-active Pt-alternative anode catalysts are important paths to accelerate the application and promotion of direct methanol fuel cell. Herein, a robust and controllable synthetic strategy is developed to bottom-up construction of carbon nanotube-bridged Ti3C2Tx MXene nanoarchitectures decorated with ultrasmall Rh nanoparticles (denoted as Rh/CNT-MX) through a facile co-assembly process. The existence of MXene nanosheets with abundant anchoring sites can immobilize nano-sized Rh crystals and facilitate their dispersion, while the integration of CNT skeletons effectively separates the neighboring MXene layers and offers unimpeded electron transport channels, which are conducive to making full use of respective catalytic functions for each component. As a consequence, the optimized Rh/CNT-MX catalyst expresses superior methanol oxidation performance with a considerable electrochemically active surface area of 89.4 m2/g, high mass/specific activity of 911.0 mA/mg/1.02 mA/cm2, and reliable long-term durability, which has obvious competitive advantages over the conventional Rh/carbon black, Rh/CNT, Rh/MXene, as well as commercial Pt/carbon black and Pd/carbon black catalysts.

InCl3-Assisted Surface Defects Restoring to Enhance Lead-Free Cs2ZrCl6 Nanocrystals for X-Ray Imaging and Blue LED Applications.

As one type of recent emerging lead-free perovskites, Cs2ZrCl6 nanocrystals are widely concerned, benefiting from the eminent designability, high X-ray cutoff efficiency, and favorable stability. Improving the luminescence performance of Cs2ZrCl6 nanocrystals has great importance to cater for practical applications. In view of the surface defects frequently formed by the liquid phase method, the particle morphology and surface quality of this material are expected to be regulated if certain intervention is made in the synthesis process. In the work, differing from normal cell lattice modulation based on the ion doping, the grain size and surface morphology of Cs2ZrCl6 nanocrystals are optimized via adding a certain amount of InCl3 to the synthetic solution. The surface defects are restored to inhibit the defect-induced non-radiative transition, resulting in the improvement of the luminescence properties. Moreover, a flexible Cs2ZrCl6@polydimethylsiloxane film with excellent heat, water, and bending resistance and a light-emitting diode (LED) device are fabricated, exhibiting excellent application potential for X-ray imaging and blue LED.

Development of a new family of hole transport semiconductor oxides for fully transparent optoelectronic devices

Highly crystalline p-type NbxNi1-xO films have been prepared at various concentrations of Nb doping (x = 0–0.17) using a solution growth approach. The films exhibit cubic crystal structures with preferential orientation along the (200) plane. The Nb-doping of NiO films increases the lattice constant, lattice strain, and deformation energy density. The SEM images depict the increase in the grain size of NiO nanocrystals with increasing the Nb concentration. The EDS spectra inspect the stoichiometry of the prepared films. The AFM measurements revealed that the surface roughness increases from 0.4 nm to 2.1 nm with increasing Nb doping. The deposited films showed high optical transparency reaching 80 %. The optical bandgap energy decreases from 3.35 eV to 2.63 eV, and the Urbach tail energy decreases from 0.78 eV to 0.52 eV with the increase of Nb doping. The photoluminescence measurements reveal the suppression of the density of the Ni and O vacancies by 70 % due to the inclusion of Nb doping in the Ni sites. The electrical resistivity of the Nb-doped NiO films decreased by 200 times, the hole mobility increased by 12-fold, and the carrier density increased by 15-fold compared to un-doped NiO films. Owing to these outstanding properties, NbxNi1-xO films are a promising alternative to PEDOT: PSS for developing durable and efficient optoelectronic devices.

Size and temperature dependent shapes of copper nanocrystals using parallel tempering molecular dynamics.

We performed parallel-tempering molecular dynamics simulations to predict the temperature- and size-dependent equilibrium shapes of a series of Cu nanocrystals in the 100- to 200-atom size range. Our study indicates that temperature-dependent, solid-solid shape transitions occur frequently for Cu nanocrystals in this size range. Complementary calculations with electronic density functional theory indicate that vibrational entropy favors nanocrystals with a shape intermediate between a decahedron and an icosahedron. Overall, we find that entropy plays a significant role in determining the shapes Cu nanocrystals, so studies aimed at determining minimum-energy shapes may fail to correctly predict shapes observed at experimental temperatures. We also observe significant shape changes with nanocrystal size - sometimes with changes in a single atom. The information from this study could be useful in efforts to devise processing routes to achieve selective nanocrystal shapes.

Temperature dependence of the electron and hole Landé g-factors in CsPbI3 nanocrystals embedded in a glass matrix.

The coherent spin dynamics of electrons and holes in CsPbI3 perovskite nanocrystals in a glass matrix are studied by the time-resolved Faraday ellipticity technique in magnetic fields up to 430 mT across a temperature range from 6 K to 120 K. The Landé g-factors and spin dephasing times are evaluated from the observed Larmor precession of electron and hole spins. The nanocrystal size in the three studied samples varies from about 8 to 16 nm, resulting in exciton transition varying from 1.69 to 1.78 eV at a temperature of 6 K, allowing us to study the corresponding energy dependence of the g-factors. The electron g-factor decreases with increasing confinement energy in the NCs as a result of NC size reduction, and also with increasing temperature. The hole g-factor shows the opposite trend. Model analysis shows that the variation of g-factors with NC size arises from the transition energy dependence of the g-factors, which becomes strongly renormalized by temperature.

Catalysts Based on Iron Oxides for Wastewater Purification from Phenolic Compounds: Synthesis, Physicochemical Analysis, Determination of Catalytic Activity

In this work, the synthesis of magnetite nanoparticles and catalysts based on it stabilized with silicon and aluminum oxides was carried out. It is revealed that the stabilization of the magnetite surface by using aluminum and silicon oxides leads to a decrease in the size of magnetite nanocrystals in nanocomposites (particle diameter less than ~10 nm). The catalytic activity of the obtained catalysts was evaluated during the oxidation reaction of phenol, pyrocatechin and cresol with oxygen. It is well known that phenolic compounds are among the most dangerous water pollutants. The effect of phenol concentration and the effect of temperature (303–333 K) on the rate of oxidation of phenol to Fe3O4/SiO2 has been studied. It has been determined that the dependence of the oxidation rate of phenol on the initial concentration of phenol in solution is described by a first-order equation. At temperatures of 303–313 K, incomplete absorption of the calculated amount of oxygen is observed, and the analysis data indicate the non-selective oxidation of phenol. Intermediate products, such as catechin, hydroquinone, formic acid, oxidation products, were found. The results of UV and IR spectroscopy showed that catalysts based on magnetite Fe3O4 are effective in the oxidation of phenol with oxygen. In the UV spectrum of the product in the wavelength range 190–1100 nm, there is an absorption band at a wavelength of 240–245 nm and a weak band at 430 nm, which is characteristic of benzoquinone. In the IR spectrum of the product, absorption bands were detected in the region of 1644 cm−1, which is characteristic of the oscillations of the C=O bonds of the carbonyl group of benzoquinone. The peaks also found at 1353 cm−1 and 1229 cm−1 may be due to vibrations of the C-H and C-C bonds of the quinone ring. It was found that among the synthesized catalysts, the Fe3O4/SiO2 catalyst demonstrated the greatest activity in the reaction of liquid-phase oxidation of phenol.

Dual second harmonic generation and up-conversion photoluminescence emission in highly-optimized LiNbO3 nanocrystals doped and co-doped with Er3+ and Yb3.

Preparation from the aqueous alkoxide route of doped and co-doped lithium niobate nanocrystals with Er3+ and Yb3+ ions, and detailed investigations of their optical properties are presented in this comprehensive work. Simultaneous emission under femtosecond laser excitation of second harmonic generation (SHG) and up-conversion photoluminescence (UC-PL) is studied from colloidal suspensions according to the lanthanide ion contents. Special attention has been paid to produce phase pure nanocrystals of constant size (∼20 nm) thus allowing a straightforward comparison and optimization of the Er content for increasing the green UC-PL signals under 800 nm excitation. An optimal molar concentration at about 4 molar% in erbium ions is demonstrated, that is well above the concentration usually achieved in bulk crystals. Similarly, for co-doped LiNbO3 nanocrystals, different lanthanide concentrations and Yb/Er content ratios are tested allowing optimization of the green and red up-conversion excited at 980 nm, and analysis of the underlying mechanisms from excitation spectra. All together, these findings provide valuable insights into the wet-chemical synthesis and potential of doped and co-doped LiNbO3 nanocrystals for advanced applications, combining both SHG and UC-PL emissions from the particle core.

Influence of arylalkyl amines on the formation of hybrid CsPbBr3 nanocrystals via a modified LARP method.

Perovskite nanocrystals have attracted much attention in the last ten years due to their different applications, especially in the photovoltaic domain and LED performance. In this large family of perovskite nanocrystals, CsPbBr3 nanocrystals are attractive nanomaterials because they are good candidates for obtaining green emissions and exploring new synthesis routes. In this context, controlling the nanometric scale's morphology, particularly the size and monodispersity, is fundamental for exploring their photophysical properties and final applications. Currently, the nanometric size of nanocrystals is ensured by the presence of oleic acid and oleylamine molecules, in using Hot Injection (HI) or ligand-assisted reprecipitation (LARP) methods. If oleic acid plays a fundamental role, oleylamine can be easily substituted by other amino molecules, opening the way for the functionalization of CsPbBr3 nanocrystals and the obtention of new hybrid perovskite nanocrystal families. In this article, we describe the synthesis, by soft chemistry, of a new family of hybrid organic-inorganic CsPbBr3 nanocrystals, functionalized by aryl-alkylamine (AAA) molecules, through the modified LARP method. We highlight the mechanism for cutting submicron crystals into nanocrystals, using aryl-alkylamine molecules like scissors. The impact of these amino molecules on the final nanocrystals leads to different nanocrystal morphologies (nanocubes, nanosheets, or nanorods) and structures (monoclinic, rhombohedral, or tetragonal). In addition, this modified LARP method highlights, under certain experimental conditions, an unexpected formation of PbO ribbons.

Size-dependent cathodoluminescence properties of 5,5′-di(4-biphenylyl)-2,2′-bithiophene nanocrystals

Crystal-size-dependent cathodoluminescence measurements demonstrated that 0-1 band peak energy of BP2T nanocrystals gradually blue-shifted compared to that of the bulk crystal as the nanocrystal size decreased below 560 nm.

Degenerately doped metal oxide nanocrystals for infrared light harvesting: insight into their plasmonic properties and future perspectives.

The tuneability of the localized surface plasmon resonance (LSPR) of degenerately doped metal oxide (MOX) nanocrystals (NCs) over a wide range of the infrared (IR) region by controlling NC size and doping content offers a unique opportunity to develop a future generation of optoelectronic and photonic devices like IR photodetectors and sensors. The central aim of this review article is to highlight the distinctive and remarkable plasmonic properties of degenerately or heavily doped MOX nanocrystals by reviewing the comprehensive literature reported so far. In particular, the literature of each MOX NC, i.e. ZnO, CdO, In2O3, and WO3 doped with different dopants, is discussed separately. In addition to discussion of the most commonly used colloidal synthesis approaches, the ultrafast dynamics of charge carriers in NCs and the extraction of LSPR-assisted hot-carriers are also discussed in detail. Finally, future prospective applications of MOX NCs in IR photodetectors and photovoltaic (PV) self-powered chemical sensors are also presented.

Crystal structure of ZnO nanocrystals synthesized by the spray pyrolysis method

The paper discusses the issues related to the influence of technological conditions of synthesis by ultrasonic spray pyrolysis on the size and lattice parameters of ZnO:Mn nanocrystals. It is found that, depending on the concentration of zinc nitrate in the base solution from 5% to 10%, the synthesized nanocrystals have sizes ranging from 36÷40 nm for small solution droplets and 51÷55 nm for large droplets, respectively. Based on the X-ray diffraction data, it is found that the nanocrystals of small sizes have a more perfect crystal structure with a small number of intrinsic defects compared to the nanocrystals of larger sizes.

Characterization of Nanocellulose from Orange Peel Waste

Orange peel is a commercially available natural fiber with an increasing interest in using it as a raw material in a variety of applications due to its high cellulose concentration in the plant. This research aims to determine the preparation of nanocellulose from orange peel waste (OPW) by using chemical treatment of acid hydrolysis method. In order to provide the optimum conditions of nanocellulose of OPW which are possessed high crystallinity in their crystal structure by using acid hydrolysis method and the effects of various acid concentrations on the crystallinity index, crystallite size and morphology of cellulose nanocrystals were studied. However, based on the previous study, using OPW there is limited study has been reported on type of acid and optimum acid concentration as a parameter of using hydrolysis method. Therefore, in this study, the process of preparation OPW nanocellulose by using acid hydrolysis method with the best type of acid used of sulphuric acid (H2SO4) and hydrochloric acid (HCl), optimum acid concentration (30-40 wt%), constant hydrolysis time (120 min) and constant temperature (45 °C) is comprehensively studied. Based on the achieved outcomes, the H2SO4 emerges as the most favorable approach for acid hydrolysis technique, effectively yielding finely dispersed crystalline cellulose while mitigating undesirable aggregation effects. The optimal acid concentration of 30 wt%, coupled with a 120 minute hydrolysis duration and a temperature of 45 °C, yields the most favorable results in terms of both crystallinity index and crystallite size, reaching remarkable values of 87.69 % and 3.19 nm, respectively. The nanocellulose derived from OPW holds significant potential as an environmentally sustainable material, aligning harmoniously with prevailing global trends in design and development for enhanced sustainability.

Effect of gamma irradiation on the size of cellulose nanocrystals with polyethylene glycol and sodium hydroxide/Gd2O3 nanocomposite as contrast agent in magnetic resonance imaging (MRI)

The attractive properties of gadolinium-based nanoparticles as a positive contrast agent for magnetic resonance imaging (MRI) have piqued the interest of both researchers and clinicians. Nonetheless, due to the biotoxicity of gadolinium (III) ions' free radicals, there is a need to address this issue. Therefore, this research aimed to develop a biocompatible, dispersible, stable, hydrophilic, and less toxic cellulose nanocrystals/gadolinium oxide nanocomposite as contrast agent properties for MRI purposes. This study aimed to synthesize gadolinium oxide nanoparticles coated with cellulose nanocrystals with polyethylene glycol and sodium hydroxide (CNCs-PEG/NaOH)/Gd2O3 using the gamma irradiation method to reduce the particle size. The results showed that using a gamma irradiation dose of 10 kGy, quasi-spherical morphology with a size of approximately 5.5 ± 0.65 nm could be produced. Furthermore, the cytocompatibility of (CNCs-PEG/NaOH)/Gd2O3 nanocomposite synthesized was assessed through MTT assay tests on Hep G2 cells, which demonstrated good cytocompatibility without any cytotoxic effects within a concentration range of (10 μg/mL −150 μg/mL) and had sufficient cellular uptake. Moreover, the T1-weighted MRI of (CNCs-PEG/NaOH)/Gd2O3 nanocomposite revealed promising results as a positive contrast agent. It is envisaged that the gamma irradiation method is promising in synthesizing (CNCs-PEG/NaOH)/Gd2O3 nanocomposite with nanoscale for different applications, especially in the radiotherapy field.

Effect of substrate roughness on the nucleation and growth behaviour of microwave plasma enhanced CVD diamond films – a case study

The influence of substrate surface roughness on the nucleation and growth of diamond films by chemical vapour deposition (CVD) is investigated. Silicon substrates were grinded with six different grit sizes of abrasive papers with a rotating wheel. Si was also etched by Ar+ ions to produce average surface roughness Ra = 11.29 nm on the mirror polished side (Ra = 1.17 nm). A comparison of the results of the effect of substrate roughness, on the growth behaviour of nanocrystalline diamond (NCD) films, by using both the resonant cavity and the linear antenna CVD systems, are presented here. Scanning electron microscopy (SEM) images and Raman spectroscopy reveal that under both the linear antenna and the resonant cavity microwave plasma CVD conditions, grown films are NCD. The diamond nanocrystals sizes vary from 80 to 180 nm, grown by both the reactors after few hours of deposition, irrespective of the substrate roughness, whereas their quality (defined by the relative percentage ratios of the Raman sp3 peak intensity to the non-sp3 peak intensity) varies from 33% to 45%, depending on the substrate surface roughness. Such nanocrystals grew into plate-like flat 1–6 μm size diamond grains after prolonged hours (64–69 h) of CVD growth. It is found specifically that the roughness created by the argon plasma treatment of the silicon substrate surfaces effectively enhances the nucleation and growth behaviour of the diamond films.

Fabrication of Faceted Metal Nanocrystal Electrodes By Solid-State Dewetting

Electrochemical reactions are electrode-structure sensitive and hence microstructural properties of the (electro)-catalysts such as size, shape, exposed facets, and grain boundaries, among others, strongly affect the activity, selectivity, and stability.1, 2 Conventional methods based mainly on wet-chemistry have been widely adopted to synthesize nanocrystal (NC) electrocatalysts, and proved suitable to control their features. However, these methods require several synthesis steps, which increase the production time and complexity, and resulting particles often feature a complex composition (due to impurities such as ligands or templating agents) and suffer from durability issues, due e.g. to particle detachment from the substrates.We explore solid-state dewetting (SSD) as an alternative way to produce metal nanocrystal electrocatalysts while overcoming various challenges intrinsic of conventional approaches.3, 4 Dewetting is the heat induced agglomeration of thin metal films into particles. Taking Pt as a case study, we have investigated the effect of various SSD parameters such as metal film thickness, substrate crystallographic features, and dewetting conditions (time/temperature/atmosphere) on the physicochemical properties of the resulting dewetted metal NCs. Under optimized conditions, dewetting forms monodispersed faceted Pt nanocrystals of tunable size. Low- or high-index facets can be designed (as shown in the figure below) by tuning the substrate orientation and dewetting conditions (e.g., T, dewetting gas). In general, dewetted Pt NCs show higher (ESCA-normalized) activity towards hydrogen evolution reaction (HER) compared to Pt thin films, and their mass activity is comparable to the state-of-the-art Pt/C. The talk will delve into correlations between microstructure (grain size, shape and facets etc.) and the electrochemical performance of dewetted NCs.From a general point of view, dewetted NCs show intriguing electrochemical and mechanical properties, and hence dewetting appears to be a promising approach for preparing active and robust nanostructured (electro)-catalysts for various applications. In ongoing work, we investigate dewetting to deposit catalysts on gas diffusion layer (GDL) electrodes and test their performance in PEM lab-scale electrolyzers. Figure 1

Hot Excitons Cool in Metal Halide Perovskite Nanocrystals as Fast as CdSe Nanocrystals.

The idea of phonon bottlenecks has long been pursued in nanoscale materials for their application in hot exciton devices, such as photovoltaics. Decades ago, it was shown that there is no quantum phonon bottleneck in strongly confined quantum dots due to their physics of quantum confinement. More recently, it was proposed that there are hot phonon bottlenecks in metal halide perovskites due to their physics. Recent work has called into question these bottlenecks in metal halide perovskites. Here, we compare hot exciton cooling in a range of sizes of CsPbBr3 nanocrystals from weakly to strongly confined. These results are compared to strongly confined CdSe quantum dots of two sizes and degrees of quantum confinement. CdSe is a model system as a ruler for measuring hot exciton cooling being fast, by virtue of its efficient Auger-assisted processes. By virtue of 3 ps time resolution, the hot exciton photoluminescence can now be directly observed, which is the most direct measure of the presence of hot excitons and their lifetimes. The hot exciton photoluminescence decays on nearly the same 2 ps time scale on both the weakly confined perovskite and the larger CdSe quantum dots, much faster than the 10 ps cooling predicted by transient absorption experiments. The smaller CdSe quantum dot has still faster cooling, as expected from quantum size effects. The quantum dots of perovskites show extremely fast hot exciton cooling, decaying faster than detection limits of <1 ps, even faster than the CdSe system, suggesting the efficiency of Auger processes in these metal halide perovskite nanocrystals and especially in their quantum dot form. These results across a range of sizes of nanocrystals reveal extremely fast hot exciton cooling at high exciton density, independent of composition, but dependent upon size. Hence these metal halide perovskite nanocrystals seem to cool heavily following quantum dot physics.

Investigations of the structure and tunable magnetic properties of Cu doped cobalt chromite nanoparticles

This article reports the synthesis, microstructural, magnetic and optical properties of copper ions substituted cobalt chromite nanoparticles. We have prepared four nanosized chromite samples with a general composition of CuxCo1-xCr2O4 (x = 0.0, 0.1, 0.2 and 0.3) using conventional wet chemical co-precipitation method. The x-ray diffraction profiles verified the presence of pure spinel crystal structure of the samples. Using the Williamson-Hall (W-H) method, the average crystallite size of all the samples were calculated to be between 11 nm and 16 nm. A tensile microstrain in all the samples was noticed. Surface morphology and average particle size of doped cobalt chromite nanocrystals was examined using HRTEM images. A moderate increment in the optical band gap was detected with increasing Cu ions in cobalt chromite nanoparticles which is attributed to the nanosize effect of the samples. The presence of all five distinctive Raman active modes in the chromite samples ensured phase purity and a decrease in crystal symmetry was also observed as the amount of Cu dopants was increased. Due to low magnetic moment of Cu2+ ions when compared with Co2+ ions, incorporation of copper ions reduces the coercive field of the host chromite system. With increasing Cu percentage in chromite especially for 30 % Cu doped sample, the spin-spiral transition TS vanishes which indicates TS is affected by the dopant concentrations.

Directing polymorph specific calcium carbonate formation with de novo protein templates

Biomolecules modulate inorganic crystallization to generate hierarchically structured biominerals, but the atomic structure of the organic-inorganic interfaces that regulate mineralization remain largely unknown. We hypothesized that heterogeneous nucleation of calcium carbonate could be achieved by a structured flat molecular template that pre-organizes calcium ions on its surface. To test this hypothesis, we design helical repeat proteins (DHRs) displaying regularly spaced carboxylate arrays on their surfaces and find that both protein monomers and protein-Ca2+ supramolecular assemblies directly nucleate nano-calcite with non-natural {110} or {202} faces while vaterite, which forms first in the absence of the proteins, is bypassed. These protein-stabilized nanocrystals then assemble by oriented attachment into calcite mesocrystals. We find further that nanocrystal size and polymorph can be tuned by varying the length and surface chemistry of the designed protein templates. Thus, bio-mineralization can be programmed using de novo protein design, providing a route to next-generation hybrid materials.

Effect of oleic acid on morphologies of BaTi5O11 nanocrystals synthesized by hydrothermal method

Abstract BaTi5O11 nanocrystals were synthesized by a hydrothermal method, and the effect of oleic acid (OA) in the Ba–Ti precursors on morphologies of BaTi5O11 nanocrystals was investigated. As the OA/(Ba2+ + Ti4+) molar ratio ranged from 0 to 8, single-phase BaTi5O11 nanocrystals were synthesized at 260 °C for 20 h. When OA reagent was not added to the precursors, rice-like BaTi5O11 nanocrystals were obtained. As the OA/(Ba2+ + Ti4+) molar ratio was 1, elongated lath-like BaTi5O11 nanocrystals were synthesized with the width of about 130 nm, thickness of about 50 nm and length of about 400 nm. With increasing the OA/(Ba2+ + Ti4+) molar ratio from 1 to 6, the grain size of elongated lath-like BaTi5O11 nanocrystals gradually decreased. As the OA content increased, the amount of adsorbed OA molecules on the surface of Ti(OH) x nucleus increased and hindered the reaction of Ba2+ ions with Ti(OH) x nucleus, which caused the decrease of grain size of lath-like BaTi5O11 nanocrystals. When the BaTi5O11 nanocrystals were synthesized at OA/(Ba2+ + Ti4+) molar ratio of 1, they had the largest dielectric constant (ε r) of 40.9 at 5 GHz.

Optimizing crystallinity and particle size of cellulose nanocrystals from rice straw biomass: an integrated sonication-assisted acid hydrolysis approach

Optimizing crystallinity and particle size of cellulose nanocrystals from rice straw biomass: an integrated sonication-assisted acid hydrolysis approach