Aggregation Of Nanocrystals Research Articles

Modification of Copper-based chalcogenide nanocrystals' interconnections for efficient hole transportation in perovskite solar cell

Cu-based chalcogenide p-type semiconductors in the form of nanocrystals can be used to deposit low-temperature and stable hole-transport layers (HTL) for n-i-p perovskite solar cells (PSCs). In this study, the synthesis parameters are modified to improve the hole-extraction of CuIn0.75Ga0.25S2 (CIGS) layer. By optimizing the amount of oleylamine as the capping agent, the internal series resistance of PSCs decreases significantly while preventing aggregation of CIGS nanocrystals. Increasing the growth temperature from 220°C to 275°C leads to an increase in the size of CIGS nanocrystals. This results in an improvement in the open-circuit voltage of PSCs with FTO/c-TiO2/m-TiO2/Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3/CIGS/Au structure from 0.941 to1.092 V, and Fill Factor from 60 to 73 on average. Finally, a nanocomposite of CIGS and a small amount of doped Spiro-OMeTAD is applied in PSCs with ITO/SnO2/(FA,MA)Pb(I,Cl,Br)3/HTL/Au structure. The achieved efficiency of 18.72% is comparable to that of PSCs with highly doped Spiro OMeTAD (18.5%).

Photostability of CsPbBr3 nanocrystals modified with poly(ethylene adipate)

All inorganic CsPbBr3 nanocrystals (NCs) have gained significant attention due to their potential as light-emitting diodes, solar cells and other optoelectronic devices. However, to a certain extent, the stability issues of CsPbBr3 NCs under water, light, and thermal conditions limit their further applications. In order to improve stability, this article proposes a strategy of modifying CsPbBr3 NCs with poly(ethylene adipate) (PEA). The surface passivation of macromolecular polymer PEA not only increases the distance between NCs which inhibits the aggregation of small NCs, but also provides a dense protective layer to protect NCs from corrosion by water, air and light. Therefore, the performance of PEA-modified CsPbBr3 NCs in terms of optical properties and stability is significantly improved. The photoluminescence intensity of PEA-modified CsPbBr3 NCs remains at about 40% of the initial intensity when heated to 100 °C, while that of pure CsPbBr3 NCs has decreased to less than 10%. The photoluminescence intensity of PEA-modified CsPbBr3 NCs decreased to 83% of the initial intensity after 7 cycles of heating to 100 °C and then cooling to room temperature, while that of pure CsPbBr3 NCs decreased to 13%. Meanwhile, the PL intensity of PEA-modified CsPbBr3 NCs remained at 66% of the initial intensity after 10 h under 365 nm ultraviolet light, and there is no obvious red shift in PL spectra, while the PL intensity of pure CsPbBr3 NCs only maintained 21% of the initial intensity, accompanied by obvious red shift in PL spectra. The results show that the PEA-modified CsPbBr3 NCs have a positive effect on stability.

Liquid lasing from solutions of ligand-engineered semiconductor nanocrystals.

Semiconductor nanocrystals (NCs) can function as efficient gain materials with chemical versatility because of their surface ligands. Because the properties of NCs in solution are sensitive to ligand-environment interactions, local chemical changes can result in changes in the optical response. However, amplification of the optical response is technically challenging because of colloidal instability at NC concentrations needed for sufficient gain to overcome losses. This paper demonstrates liquid lasing from plasmonic lattice cavities integrated with ligand-engineered CdZnS/ZnS NCs dispersed in toluene and water. By taking advantage of calcium ion-induced aggregation of NCs in aqueous solutions, we show how lasing threshold can be used as a transduction signal for ion detection. Our work highlights how NC solutions and plasmonic lattices with open cavity architectures can serve as a biosensing platform for lab-on-chip devices.

2D kinetic Monte-Carlo model of nanocrystal aggregation within a liquid matrix: Simulation and experimental study

A stochastic model of nanocrystals (NC) aggregation governing mobilities both of individual nanocrystals and its clusters is developed. The influence of the model parameters on the NC morphology is considered and an analysis is made of the applicability of the model to describe various real physical systems. The model is applied to simulate an aggregation of cadmium sulfide nanocrystals upon evaporation of the Langmuir–Blodgett matrix and as a result a comparison of simulations and experimental results is carried out. We give a comprehensive analysis of the patterns simulated by the model, and study an influence of the surrounding medium (solvent) on the aggregation processes. This system is a typical example from real life and is noteworthy in that the morphology of NC after evaporation of the matrix cannot be described exactly by a model based only on the motion of individual nanocrystals or by a cluster–cluster aggregation model.

Dynamic Nanocrystal Superlattices with Thermally Triggerable Lubricating Ligands.

The size-dependent and collective physical properties of nanocrystals (NCs) and their self-assembled superlattices (SLs) enable the study of mesoscale phenomena and the design of metamaterials for a broad range of applications. However, the limited mobility of NC building blocks in dried NCSLs often hampers the potential for employing postdeposition methods to produce high-quality NCSLs. In this study, we present tailored promesogenic ligands that exhibit a lubricating property akin to thermotropic liquid crystals. The lubricating ability of ligands is thermally triggerable, allowing the dry solid NC aggregates deposited on the substrates with poor ordering to be transformed into NCSLs with high crystallinity and preferred orientations. The interplay between the dynamic behavior of NCSLs and the molecular structure of the ligands is elucidated through a comprehensive analysis of their lubricating efficacy using both experimental and simulation approaches. Coarse-grained molecular dynamic modeling suggests that a shielding layer from mesogens prevents the interdigitation of ligand tails, facilitating the sliding between outer shells and consequently enhancing the mobility of NC building blocks. The dynamic organization of NCSLs can also be triggered with high spatial resolution by laser illumination. The principles, kinetics, and utility of lubricating ligands could be generalized to unlock stimuli-responsive metamaterials from NCSLs and contribute to the fabrication of NCSLs.

Nanoarchitectonics of ultrafine molybdenum carbide nanocrystals into three-dimensional nitrogen-doped carbon framework for capacitive deionization.

Molybdenum carbide (MoC) has emerged as a promising material for capacitive deionization (CDI), but the poor electrochemical kinetics in conventional MoC owing to the bulk structure and low electric conductivity limit its CDI performance. To address this challenge, herein, we develop a novel strategy to synthesize ultrafine MoC nanocrystals that are embedded within a three-dimensional nitrogen-doped carbon framework (NC/MoC). This synthesis method involves the space-confined pyrolysis of molybdate precursors within metal-organic frameworks (MOFs). In this process, molybdates are confined into the MOF crystalline structure, where MOFs provide a confined reactor and carbon source. The resulting NC/MoC with the uniformly distributed MoC nanocrystals provides sufficient active sites for the electrosorption of salt ions, while the MOF-derived NC matrix facilitates charge transfer and provides the space-confined effect for preventing the possible aggregations of MoC nanocrystals during the CDI process. The NC/MoC exhibits an impressive salt adsorption capacity (SAC, 84.2 mg g-1, 1.2 V), rapid desalination rate, and high cycling stability (91.4% SAC retention after 200 cycles), better than those of most previously reported carbon-based CDI materials. Besides, the possible mechanisms are systematically investigated by ex situ characterization and density functional theory calculations. This study opens up new avenues for the construction of metal carbide-based nanocrystals for CDI and other electrochemical applications.

The Impact of Ligand Removal on the Optoelectronic Properties of Inorganic and Hybrid Lead Halide Perovskite Nanocrystal Films

AbstractLigand exchange performed during or after the colloidal synthesis of nanocrystals (NCs) provides an efficient way to produce conductive NC solids for optoelectronics. Herein, a post‐synthetic ligand washing process is developed and applied to two different combinations of ligands and perovskite NCs, namely robust green CsPbBr3 NCs capped by didodecyldimethylammonium bromide and near‐infrared FAPbI3 NCs decorated by weakly bound oleic acid ligands. The impact of such processes on the morphological and optoelectronic NC properties is examined while exploring parameters such as the reaction time and the influence of oxygen and humidity. For the FAPbI3 NCs, ligand washing results in extended NC aggregation and substantial photoluminescence loss, with the treatment becoming more aggressive for air‐exposed films. For the CsPbBr3 NCs, the process is insensitive to the environmental conditions and results in partial ligand shell loss and NC close packing rather than bulk‐like aggregation while affecting less the optical properties. Upon ligand removal, the photoconductance increases by up to ≈90% and ≈60% for FAPbI3 NCs and CsPbBr3 NCs, respectively. THz spectroscopy produces qualitatively similar trends of the conductivity with ligand removal time, with THz mobility values as high as 30 and 6 V−1s−1cm2 for glove box prepared FAPbI3 and CsPbBr3 NCs, respectively.

Multifunctional Polymer Restraint of the Agglomeration of SnO2 Nanocrystals for Efficient and Stable Planar Perovskite Solar Cells.

The aggregation of SnO2 nanocrystals due to van der Waals interactions is not conducive to the realization of a compact and pinhole-free electron transport layer (ETL). Herein, we have utilized potassium alginate (PA) to self-assemble SnO2 nanocrystals, forming a PA-SnO2 ETL for perovskite solar cells (PSCs). Through density functional theory (DFT) calculations, PA can be effectively absorbed onto the surface of SnO2. This inhibits the agglomeration of SnO2 nanocrystals in solution, forming a smoother pinhole-free film. This also changes the surface contact potential (CPD) of the SnO2 film, which leads to a reduction in the energy barrier between the ETL and the perovskite layers, promotes effective charge transfer, and reduces trap density. Consequently, the power conversion efficiency (PCE) of PSCs with a PA-SnO2 ETL increased from 19.24% to 22.16%, and the short-circuit current (JSC) was enhanced from 23.52 to 25.21 mA cm-2. Furthermore, the PA-modified unpackaged device demonstrates better humidity stability compared to the original device.

Study of Structural and Optical Properties of Zirconium Oxide Nanoparticles

In present study Zirconium dioxide (ZrO2) nanoparticles (NPs) were synthesized by using the chemical method. For the synthesis of desired NPs, oleyl amine (OA) was used as a surfactant material. OA plays a crucial role in inhibiting the aggregation of ZrO2 nanocrystals. Particle surface stabilisation is facilitated by it. The average crystallite size estimated from X-ray diffraction (XRD) using Scherrer equation, to be 6.15nm. UV-vis absorption spectra in the wavelength range of 200-900 nm were obtained; energy band gap obtained approximately 2.52 eV in as prepared ZrO2 NPs. Using FT-IR, the functional group and band structure of ZrO2 were studied.

Synthesis of calcium silicate hydrate nanoparticles and their effect on cement hydration and compressive strength

This study aims to synthesize calcium silicate hydrate (CSH) nanoparticles at room temperature using a liquid-phase reaction method, to incorporate the synthesized material into a cement composite, and to study its hydration characteristics. The optimal amount of polycarboxylate-based dispersant, in terms of nanocrystal size and CSH particle aggregation state, was obtained using scanning electron microscopy. The concentration of the generated harmful ions during the synthesis was reduced via a cleaning procedure. The experiments confirmed that the CSH nanoparticles acted as nucleation sites. Moreover, the initial hydration calorific value and early-age compressive strength increased with the amount of CSH nanoparticles.

Microwave-assisted dry synthesis of hybrid electrode materials for supercapacitors: Nitrogen-doped rGO with homogeneously dispersed CoO nanocrystals

In this research work, we have applied a dry microwave (MW) strategy to synthesize uniformly sized CoO nanocrystals homogeneously dispersed on the basal plane of nitrogen-doped reduced graphene oxide nanosheets (N-rGO NSs). The MW treatment is an ultra-fast process for exfoliation and in-situ reduction of graphite oxide and simultaneous decomposition of the cobalt precursor. The results show that during the MW-assisted synthesis process, the graphite oxide is exfoliated, reduced and combined with the available nitrogen from the precursor to form N-rGO NSs. Simultaneously; the Co ions react with oxygen functionalities on surface of N-rGO NSs to form CoO ([email protected]) nanocrystals. These processes, when combined, effectively prevented the aggregation of the CoO nanocrystals and the re-stacking of the N-rGO layers. The resulting [email protected] nanocomposites exhibited unique surface morphology and electrochemical performance for supercapacitor (SC) applications. As the SC electrode, the nanocomposite delivered high specific capacitance (744.1 F/g at 5 mV/s) and excellent cyclic stability (91.3 % over 5000 cycles). Thus, the MW-processing method proved to be a rapid, effective, and simple approach for single step synthesis of doped rGO-metal oxide electrodes for SC applications.

Synthesis and Characterization of Multistage Porous Sodalite Nanocrystal Aggregate

Using the mixed solution of [Formula: see text]-butanol and ethanol as solvent, the sodalite nanocrystal aggregate was prepared by the solvothermal method. The influences of crystallization temperature, molar ratio Na/Al, crystallization time and silane concentration on the morphology, crystallite size, degree of crystallization and pore structure of the as-prepared samples were investigated by X-ray diffraction (XRD), BET, FTIR, Transmission Electron Microscopy (TEM) and scanning electron microscope (SEM). The results reveal that the sodalite nanocrystals are aggregated by self-assembly into the micropore–mesopore–macropore structure. Higher crystallization temperature and longer crystallization time are conducive to the growth of sodalite nanocrystals. It is a necessary condition for the formation of sodalite nanocrystals to keep high molar ratio Na/Al. The higher the molar ratio Na/Al, the more favorable the crystallization of sodalite nanocrystals. The appropriate concentration of silane agent is conducive to the preparation of smaller crystal-sized sodalite nanocrystals. After removing the silane agent by pickling, the sodalite nanocrystal aggregate is a multistage porous structure with the pore volume of 1.0133[Formula: see text]mL/g and the specific surface area of 449.73[Formula: see text]m2/g.

Surfactant-Dependent Bulk Scale Mechanochemical Synthesis of CsPbBr3 Nanocrystals for Plastic Scintillator-Based X-ray Imaging.

We report a facile, solvent-free surfactant-dependent mechanochemical synthesis of highly luminescent CsPbBr3 nanocrystals (NCs) and study their scintillation properties. A small amount of surfactant oleylamine (OAM) plays an important role in the two-step ball milling method to control the size and emission properties of the NCs. The solid-state synthesized perovskite NCs exhibit a high photoluminescence quantum yield (PLQY) of up to 88% with excellent stability. CsPbBr3 NCs capped with different amounts of surfactant were dispersed in toluene and mixed with polymethyl methacrylate (PMMA) polymer and cast into scintillator discs. With increasing concentration of OAM during synthesis, the PL yield of CsPbBr3/PMMA nanocomposite was increased, which is attributed to reduced NC aggregation and PL quenching. We also varied the perovskite loading concentration in the nanocomposite and studied the resulting emission properties. The most intense PL emission was observed from the 2% perovskite-loaded disc, while the 10% loaded disc exhibited the highest radioluminescence (RL) emission from 50 kV X-rays. The strong RL yield may be attributed to the deep penetration of X-rays into the composite, combined with the large interaction cross-section of the X-rays with the high-Z atoms within the NCs. The nanocomposite disc shows an intense RL emission peak centered at 536 nm and a fast RL decay time of 29.4 ns. Further, we have demonstrated the X-ray imaging performance of a 10% CsPbBr3 NC-loaded nanocomposite disc.

Synthesis and Specific Properties of the Ceria and Ceria-Zirconia Nanocrystals and Their Aggregates Showing Outstanding Catalytic Activity in Redox Reactions—A Review

Non-stoichiometric CeO2−y, especially in the form of nanocrystal aggregates, exhibits exceptional catalytic activity in redox reactions. It significantly improves the activity of transition metals and their oxides dispersed on/or in it, also acting as an oxygen buffer. Particularly, active oxygen species (O2n−, O−) are generated at the M/CeO2−y nanoparticle interface, as well as in the surface layer of their solid-state solutions MxCe1−xO2−y. The crystal structure of CeO2, ZrO2 and (Ce, Zr)O2 and its defects are discussed in connection with the resulting specific catalytic activity. All the methods (simple precipitation and co-precipitation from mother liquors, sol–gel methods, precipitation from nanoemulsions, hydrothermal and solvothermal techniques, combustion and flame spray pyrolysis, precipitation using molecular and solid-state matrices, 3D printing and mechanochemical methods) used for the synthesis of these nanomaterials are comprehensively reviewed, describing the rules of individual procedures and preparation details. Methods of deposition of metal catalysts and their oxides on CeO2 nanoparticles, such as impregnation, washcoating and precipitation deposition, were also discussed. This review contains more than 160 references to representative papers wherein the reader can find further details on individual syntheses of effective ceria-based catalysts for redox reactions.

Effect of Fe substitution over ZSM-48 on performance of n-dodecane hydroisomerization and distribution of isomers

A series of Fe substituted ZSM-48 nanocrystal aggregates were synthesized by the dynamic hydrothermal method. Through incorporation of Fe into ZSM-48 framework, the acidity of ZSM-48 zeolites has been modified. The hydroisomerization performances of n-dodecane were investigated on Pt supported ZSM-48 and Fe incorporated ZSM-48 zeolites. Fe incorporated ZSM-48 catalysts show higher n-C12 hydroisomerization selectivity compared with parent sample due to weaker acid strength of Si–OH–Fe than Si–OH–Al. High temperature favor the generation of the multi-branched isomers (mainly dimethyl isomers) following the “Key-Lock” mode. Meanwhile, 5-methylundecane is the main product in the monomethyl isomers (MOB) and 2,6-dimethyldecane is the main product in the multi-branched isomers (MUB), which suggests the excellent shape selectivity of ZSM-48 and the “Key-Lock” mode is preferred on ZSM-48 catalysts regardless Fe substituted or not. The relationship between the mono-methyl isomers and the butene-TPD results has been correlated and investigated. Four desorption peaks corresponding to butene weakly adsorbed over Si–OH, Fe–OH or Lewis acid sites, the “Key-Lock” mode adsorbed butene, the “Pore-Mouth” mode adsorbed butene and the strongly adsorbed butene respectively, can be distinguished. ZLC results indicate that Fe modified ZSM-48 can effectively increase n-hexane diffusion rate and reduce the activation energy of diffusion of n-hexane, which is benefit for the hydroisomerization performance. SMOB/SMUB can be altered by Fe modification, however, the distribution of the mono-methyl isomers can hardly be affected.

Core-shell metal-organic framework/silica hybrid with tunable shell structure as stationary phase for high performance liquid chromatography

Metal-organic framework/silica composite (SSU) were prepared by growing UiO-66 on the amino-functionalized SiO2 core-shell spheres (SiO2@dSiO2) via a simple one-pot synthesis approach. By controlling the concentration of Zr4+, the obtained SSU have two different morphologies: spheres-on-sphere and layer-on-sphere. The spheres-on-sphere structure is formed by the aggregation of UiO-66 nanocrystals on the surface of SiO2@dSiO2 spheres. SSU-5 and SSU-20, which contain spheres-on-sphere composites have mesopores with a pore size of about 45 nm in addition to the characteristic micropores of UiO-66 with a pore size of 1 nm. In addition, UiO-66 nanocrystals were grown both inside and outside the pores of SiO2@dSiO2, resulting in a 27% loading of UiO-66 in the SSU. The layer-on-sphere is the surface of SiO2@dSiO2 covered with a layer of UiO-66 nanocrystals. SSU with this structure has only a characteristic pore size of about 1 nm belonging to UiO-66 and is therefore not suitable as a packed stationary phase for high performance liquid chromatography. The SSU spheres were packed into columns and tested for the separation of xylene isomers, aromatics, biomolecules, acidic and basic analytes. With both micropores and mesopores, SSU with spheres-on-sphere structure achieved baseline separation of both small and large molecules. Efficiencies up to 48,150, 50,452 and 41,318 plates m − 1 were achieved for m-xylene, p-xylene and o-xylene, respectively. The relative standard deviations of the retention times of anilines for run-to-run, day-to-day and column-to-column were all less than 6.1%. The results show that the SSU with spheres-on-sphere structure has great potential for high performance chromatographic separation.

Firmly interlocked Janus-type metallic Ni3Sn2S2-carbon nanotube heterostructure suppresses polysulfide dissolution and Sn aggregation

Ternary transition-metal tin chalcogenides, with their diverse compositions, abundant constituents, high theoretical capacities, acceptable working potentials, excellent conductivities, and synergistic active/inactive multi-components, hold promise as anode materials for metal-ion batteries. However, abnormal aggregation of Sn nanocrystals and the shuttling of intermediate polysulfides during electrochemical tests detrimentally affect the reversibility of redox reactions and lead to rapid capacity fading within a limited number of cycles. In this study, we present the development of a robust Janus-type metallic Ni3Sn2S2-carbon nanotube (NSSC) heterostructured anode for Li-ion batteries (LIBs). The synergistic effects of Ni3Sn2S2 nanoparticles and a carbon network successfully generate abundant heterointerfaces with steady chemical bridges, thereby enhancing ion and electron transport, preventing the aggregation of Ni and Sn nanoparticles, mitigating the oxidation and shuttling of polysulfides, facilitating the reforming of Ni3Sn2S2 nanocrystals during delithiation, creating a uniform solid-electrolyte interphase (SEI) layer, protecting the mechanical integrity of electrode materials, and ultimately enabling highly reversible lithium storage. Consequently, the NSSC hybrid exhibits an excellent initial Coulombic efficiency (ICE > 83 %) and superb cyclic performance (1218 mAh/g after 500 cycles at 0.2 A/g and 752 mAh/g after 1050 cycles at 1 A/g). This research provides practical solutions for the intrinsic challenges associated with multi-component alloying and conversion-type electrode materials in next-generation metal-ion batteries.

Synthesis and characterization of bulk mechanical properties of a bio-based resin filled by graphene nanoplatelets and cellulose nanocrystals

In the present paper, a novel bio-based resin derived from epichlorohydrin was reinforced by Graphene NanoPlatelets (GNPs) and Cellulose NanoCrystals (CNCs) in different weight ratios and characterized experimentally through tension tests and fracture toughness tests on bulk specimens. The nanofillers were applied separately. The experimental results showed that the neat resin has a Young’s modulus of 3.29 GPa, a tensile strength of 45.15 MPa, a stress intensity factor of 0.61 MPa m1/2 and a critical strain energy release rate of 0.091 kJ/m2. The level of the properties reveal that the bio-based adhesive can be used for cosmetic and for some structural applications. The addition of cellulose nanocrystals in the epoxy resin didn’t improve the mechanical properties of the neat resin mainly due to the development of intense aggregation of cellulose nanocrystals. On the other hand, the addition of graphene has led to the increase of the Young’s modulus and the fracture toughness and to the decrease of the tension strength of the resin. Development of agglomerations of graphene were also present in this case. The contradictory findings on the mechanical properties of the reinforced resin gives a clear message about the need for optimizing the manufacturing process. Both nanocomposites have undergone a complete life-cycle analysis which has shown that they are far more environmentally friendly than a conventional epoxy resin.

Phosphate Capture Enhancement Using Designed Iron Oxide-Based Nanostructures.

Phosphates in high concentrations are harmful pollutants for the environment, and new and cheap solutions are currently needed for phosphate removal from polluted liquid media. Iron oxide nanoparticles show a promising capacity for removing phosphates from polluted media and can be easily separated from polluted media under an external magnetic field. However, they have to display a high surface area allowing high removal pollutant capacity while preserving their magnetic properties. In that context, the reproducible synthesis of magnetic iron oxide raspberry-shaped nanostructures (RSNs) by a modified polyol solvothermal method has been optimized, and the conditions to dope the latter with cobalt, zinc, and aluminum to improve the phosphate adsorption have been determined. These RSNs consist of oriented aggregates of iron oxide nanocrystals, providing a very high saturation magnetization and a superparamagnetic behavior that favor colloidal stability. Finally, the adsorption of phosphates as a function of pH, time, and phosphate concentration has been studied. The undoped and especially aluminum-doped RSNs were demonstrated to be very effective phosphate adsorbents, and they can be extracted from the media by applying a magnet.

Fluorescence decay enhancement and FRET inhibition in self-assembled hybrid gold CdSe/CdS/CdZnS colloidal nanocrystal supraparticles.

We report on the synthesis of hybrid light emitting particles with a diameter ranging between 100 and 500 nm, consisting in a compact semiconductor CdSe/CdS/CdZnS nanocrystal aggregate encapsulated by a controlled nanometric size silica and gold layers. We first characterize the Purcell decay rate enhancement corresponding to the addition of the gold nanoshell as a function of the particle size and find a good agreement with the predictions of numerical simulations. Then, we show that the contribution corresponding to Förster resonance energy transfer is inhibited.