Growth Mechanism Of Nanoparticles Research Articles

Growth Mechanisms of Amorphous Nanoparticles in Solution and During Heat Drying

The purpose of this study was twofold: to identify the growth mechanisms of amorphous nanoparticles in solution and during the drying process at high temperatures, and to guide the process condition and stabilizer selection for amorphous nanoparticle formulations. In contrast to nanocrystals that are mostly mechanically robust, amorphous nanoparticles tend to undergo deformation under stress. As a result, development of a stable formulation and evaluation of the drying process for re-dispersible amorphous nanoparticles presents considerable challenges. Although amorphous nanoparticles have stability issues, they have several pros in terms of production, high monodispersity, and diverse applications in drug delivery. In this study, amorphous nanoparticles were prepared via liquid-liquid phase separation, and their growth mechanisms were investigated both in solution and during the drying process. In solution, particles were found to be susceptible to flocculation, crystallization, coalescence, and Ostwald ripening, with coalescence being a preliminary step providing the driving force for Ostwald ripening. However, during the heat drying process, coalescence and crystallization were found to be the primary mechanisms for particle growth, with Ostwald ripening being negligible due to reduced molecular mobility. The glass transition temperature (Tg) of these amorphous nanoparticles was found to be a crucial factor both in solution and during the drying process. At temperatures < Tg, particles remained in a rigid, glassy state thereby inhibiting coalescence, whereas at or above Tg, particles transition from glassy to rubbery state, making them more susceptible to deformation and coalescence. The mechanistic understanding of particle growth from this study can also be extended to the stabilization of other types of soft nanoparticles.

High-speed shearing: An ultra-fast internal energy accumulation method for nucleation of SnZnO in photocatalysis

Zinc oxide (ZnO) nanoparticles and their derivatives, appreciated for their cost-effectiveness, simplicity in synthesis, and versatile applications, have garnered considerable attention. However, unraveling the nucleation and growth mechanisms of ZnO nanoparticles remains a formidable challenge. By comparing the magnetic stirring synthesis (MSS) and high-speed shearing (HSS) methods, we conducted time-dependent calculations of pressure and velocity at various positions in the solution. Under the powerful shearing force, which is the key route to accumulate internal energy (Ein), molecules could achieve at most 174 eV Ein in HSS instead of 0.81 eV Ein in MSS. Molecules could obtain enough energy for nucleation in just 1.03 μs. HSS, utilizing a high-speed rotor for robust shear forces, not only modifies nucleation patterns but also facilitates effective mixing in multi-element systems. SnxZn1−xO1+x nanoparticles prepared through HSS display uniform size, markedly reduced agglomeration, homogeneous element distribution, and a more pronounced bandgap change, causing a decrease in photocatalytic activity to the original 11.2 %.

Highly controlled synthesis of symmetrically branched tripod and pentapod nanocrystals with enhanced photocatalytic performance

Anisotropic nanostructures with tunable optical properties induced by controllable size and symmetry have attracted much attention in many applications. Herein, we report a controlled synthesis of symmetrically branched AuCu alloyed nanocrystals. By varying Au:Cu atom ratio in precursor, Y-shaped tripods with three-fold symmetry and star-shaped pentapods with five-fold symmetry are synthesized, respectively. The growth mechanism of AuCu tripods from icosahedral seeds and AuCu pentapods from decahedral seeds is revealed. Aiming to excellent photocatalytic performance, CdS nanocrystals are controlled grown onto the sharp tips of AuCu tripods and pentapods. In addition, a carrier-selective blocking layer of Ag2S is introduced between AuCu and CdS, for achieving effective charge separation in AuCu-Ag2S-CdS nanohybrids. Through evaluating the photocatalytic performance by hydrogen generation experiments, the AuCu-Ag2S-CdS tripod nanocrystals exhibit an optimized hydrogen evolution rate of 2182 μmol·g−1·h−1. These findings will contribute greatly to the understanding of complex nanoparticle growth mechanism and provide a strategy for the design of anisotropic nanoalloys for widely photocatalytic applications.

Zeta Potential and Size Analysis of Zeolitic Imidazolate Framework-8 Nanocrystals Prepared by Surfactant-Assisted Synthesis.

The crystal nucleation and growth mechanism of monodispersed metal-organic framework nanoparticles were studied using time-resolved light dynamic, electrokinetic, and powder X-ray diffraction methods. We confirmed that zeolitic imidazolate framework-8 (ZIF-8) nanocrystals follow a nonclassical crystal growth pathway, where a fast nucleation occurs with dense liquid clusters or nanocrystals forming spontaneously when two precursors are mixed. We also explored the zeta potential and solvodynamic size changes of ZIF-8 prepared by a surfactant-assisted synthesis. Three modulators, including 1-methylimidazole (1-mIm), tris(hydroxymethyl)aminomethane (THAM), and (1-hexadecyl)trimethylammonium bromide (CTAB), were studied. We found that 1-mIm dramatically increases the rate of nucleation of ZIF-8. With an increasing amount of 1-mIm, which functions as a coordination modulator, the size increases, and the zeta potential of ZIF-8 decreases. Whereas THAM, as both a coordination and a deprotonation modulator, increases the size and zeta potential of ZIF-8 simultaneously, CTAB, as a long alkyl cationic surfactant, mainly adsorbs on the surface of ZIF-8, and the zeta potential of the formed ZIF-8 is controlled by the amount of CTAB in solution compared with its critical micelle concentration. Overall, we reveal that the modulator type and concentration can be used to control the size and zeta potential of the dispersed ZIF-8 nanocrystals in a colloid system. The experiments also enable identification of the nucleation and crystal growth processes of ZIF-8. The findings will be applicable to other nanocrystals in colloid systems, which are used for heterogeneous catalysis and guest molecular loadings.

Integrated microfluidic-based ultrafine water condensation particle counter (UWCPC) for monitoring of airborne nanoparticle generation and growth mechanisms

This study reports a newly developed condensation particle counter for nanoparticle source tracking, growth mechanism analysis, and wide area nanoparticle monitoring.

Growth mechanism prediction for nanoparticles via structure matching polymerization.

Exploring structural and component evolution remains a challenging scientific problem for nanoscience. We propose a novel approach called principle of minimization of structure matching polymerization (SMP) change to rapidly explore the global minimum structure on the potential energy surface (PES). The new method can map low-dimensional stable structures to high-dimensional local minima, and this will make it possible for us to study the growth mechanisms of nanoparticles. Some new lowest-energy structures were found by SMP methods for sulfuric acid (SA)-dimethylamine (DMA) systems relative to previous studies. Additionally, we found that the growth process of boron clusters is mainly that the small-size boron clusters are continuously added to large-size boron clusters by structure matching for Bn (n = 2-36) systems, Bm + Bk → Bn, where m + k = n and 1 ≤ k ≤ 3. The SMP approach can greatly improve the search efficiency of other unbiased global optimization algorithms, such as basin-hopping (BH) and genetic algorithm (GA), with an enhancement of up to 19- and 7-fold relative to traditional BH and GA algorithms for searching the global minima of Bn (n = 14-22) systems. The SMP approach is general and flexible and can be applied to different kinds of problems, such as material structure design, crystal structure prediction, and new drug generation.

Unveiling Step-by-Step the Bottom-Up Kinetics and Growth Mechanism of Laser-Induced Colloidal Gold Nanoparticles

Unveiling Step-by-Step the Bottom-Up Kinetics and Growth Mechanism of Laser-Induced Colloidal Gold Nanoparticles

Study the growth mechanism of AgNi nanoparticles by surface diffusion

Quantifying the kinetic processes of the diffusion and growth of adsorbed atoms on the surface of nanoparticles at the atomic level enables the control of nanomaterial structures. To examine the diffusion and growth of adsorbed atoms on the surface of nanoparticles, this study adopts AgNi nanoparticles as an example, comprehensively explores surface diffusion, and reveals the physical causes of the growth results from the perspective of surface diffusion. Molecular dynamics, Monte Carlo, and nudged elastic band methods are utilized. Many studies have been conducted on the diffusion barriers of adsorbed atoms. On the basis of these studies, the current work classifies the diffusion paths of adsorbed atoms on the surface of nanoparticles in detail and determines the optimal surface diffusion paths. It reveals the formation mechanism of AgNi nanoparticles from the perspective of surface diffusion and the physical causes of the clustering of surface atoms into islands during growth. Among all the surface exchange diffusion paths defined in this study, the center exchange diffusion paths, especially CPDE, are the best when the system energy decreases after the substrate boundary atom is exchanged with an adatom. The relative magnitude of the exchange energy barriers between hetero adsorbed atoms and atoms on the substrate surface is a major determinant of the formation of core–shell and three-layer onion-like structures and the degree of surface alloying of the nanoparticles. In addition, the appearance of surface energy trap sites during the growth of AgShellNiCore nanoparticles leads to the diffusion of surface Ag atoms to these sites and their aggregation into Ag islands.

Multifunctional Tb-doped SnO2 based photocatalytic agent for water remediation: Study of defect-related properties

A new methodology to obtain Tb-doped SnO2 nanoparticles based on precipitation method followed by hydrothermal treatment was developed. Two series of nanoparticles with various Tb concentrations were fully characterized with large number of methods, including XRD method, FTIR, XPS, and Raman spectroscopy, TEM imaging, SSA estimation, optical transmittance study, luminescence spectroscopy and quantum-chemical calculations.The oriented attachment mechanism of nanoparticle growth is shown to occur under hydrothermal treatment. Computational study of interaction energies of mutually oriented nanoparticles and role of ions in the synthesis media was performed. Study of photoluminescence characteristics of the obtained nanoparticles is provided. The presence of blue and green luminescence is shown. The blue luminescence is related to SnO2 self-luminescence, while the green is related to Tb. Increase of Tb concentration suppress blue self-luminescence of SnO2, and promote green luminescence due to an increase of the energy transfer from crystal host to doping Tb ions.The nanoparticles are shown to possess photocatalytic activity of 97–100% under Vis light irradiation. Using a complex of modern physicochemical methods, a new factor affecting photocatalytic efficiency was revealed – the ratio of vacancies to defects (Vac/Def). A clear dependency of photocatalysis and normalized Vac/Def ratio to interaction energy between pollutant and catalysts surface is explained via quantum-chemical calculations for the first time, and demonstrated on examples of colored solution of organic dye methylene blue and colorless solution of oxytetracycline. Detailed study of the relation between morphological and structural properties of nanoparticles and their photocatalytic properties is provided. High degradations percent are achieved under simple LED light bulb. A concept of a chemical and computational experiments-based route for the development of effective photocatalysts is suggested.

Hot-Injection Synthesis of HgTe Nanoparticles: Shape Control and Growth Mechanisms.

Understanding the growth mechanisms of HgTe nanoparticles (NPs) with varied shapes is crucial for their applications in infrared photodetection. Here, we investigated the growth mechanisms of HgTe NPs with nanorod, sphere, and tetrahedral shapes in depth. The HgTe NPs with a nanorod shape are obtained at low reaction temperatures and formed by breaking tetrapod branches, while HgTe NPs with sphere and tetrahedron shapes have been further achieved at increased reaction temperatures. The systematic crystal analyses demonstrate this effective shape control is related to the synergic effect among the anisotropic passivation of oleylamine, surface free energy, and reaction temperatures. Our findings have deepened the understanding of shape control of the HgTe NPs and inspired a growing passion in the design and engineering of infrared photodetectors using HgTe NPs.

Fractal Design of Hierarchical PtPd with Enhanced Exposed Surface Atoms for Highly Catalytic Activity and Stability.

Hierarchical assembly of arc-like fractal nanostructures not only has its unique self-similarity feature for stability enhancement but also possesses the structural advantages of highly exposed surface-active sites for activity enhancement, remaining a great challenge for high-performance metallic nanocatalyst design. Herein, we report a facile strategy to synthesize a novel arc-like hierarchical fractal structure of PtPd bimetallic nanoparticles (h-PtPd) by using pyridinium-type ionic liquids as the structure-directing agent. Growth mechanisms of the arc-like nanostructured PtPd nanoparticles have been fully studied, and precise control of the particle sizes and pore sizes has been achieved. Due to the structural features, such as size control by self-similarity growth of subunits, structural stability by nanofusion of subunits, and increased numbers of exposed active atoms by the curved homoepitaxial growth, h-PtPd displays outstanding electrocatalytic activity toward oxygen reduction reaction and excellent stability during hydrothermal treatment and catalytic process.

Understanding the growth mechanism of Al-bearing hematite nanoparticles via two-dimensional oriented attachment

Hematite occurs ubiquitously in nature and is important for controlling the migration and conversion of various nutrients and pollutants. The morphology of hematite is a key factor affecting its reactivity. Naturally occurring hematite usually contains an amount of aluminum (Al) impurities. Al has a significant effect on the morphology of hematite. However, the details of Al-bearing hematite formation and the role of Al in the morphological evolution remain poorly understood. In this work, a series of Al-bearing hematite were synthesized using hydrothermal methods. Their growth process was followed by examining the intermediate products harvested at different intervals of reaction time using the XRD and electron microscopy. DFT calculations were used to investigate the effect of Al on the stability of hematite {001} and {110} crystal facets. The results indicate that the formation of Al-bearing hematite follows two stages: the initial nucleation of hematite nuclei and the subsequent ripening of nuclei into nanoplates. The nucleation process involves the formation of ferrihydrite, followed by the amorphous nanoparticles undergoing phase transition into more thermodynamically stable hematite nuclei. In the ripening stage, hematite nuclei aggregate into single-crystalline hematite particles through oriented attachment and then crystallize into nanoplates. The surface energy of the {110} crystal facet is higher than the {001} crystal facet at high concentrations of Al, which promotes oriented attachment of {110} facets between hematite nuclei. The proposed mechanism in this article not only provides deep insight into the formation of naturally occurring hematite but also a path for the efficient fabrication of environmentally friendly iron oxide materials.

In Situ Insights into the Nucleation and Growth Mechanisms of Gold Nanoparticles on Tobacco Mosaic Virus.

Biotemplated syntheses have emerged as an efficient strategy to control the assembly of metal nanoparticles (NPs) and generate promising plasmonic properties for sensing or biomedical applications. However, understanding the nucleation and growth mechanisms of metallic nanostructures on biotemplate is an essential prerequisite to developing well-controlled nanotechnologies. Here, we used liquid cell Transmission Electron Microscopy (TEM) to reveal how the formation kinetics of gold NPs affects their size and density on Tobacco Mosaic Virus (TMV). These in situ insights are used as a guideline to optimize bench-scale synthesis with the possibility to homogenize the coverage and tune the density of gold NPs on TMV. In line with in situ TEM observations, fluorescence spectroscopy confirms that the nucleation of NPs occurs on the virus capsid rather than in solution. The proximity of gold NPs on TMV allows shifting the plasmonic resonance of the assembly in the biological window.

An Accelerated Method for Investigating Spectral Properties of Dynamically Evolving Nanostructures

The discrete-dipole approximation (DDA) is widely applied to study the spectral properties of plasmonic nanostructures. However, the high computational cost limits the application of DDA in static geometries, making it impractical for investigating spectral properties during structural transformations. Here we developed an efficient method to simulate spectra of dynamically evolving structures by formulating an iterative calculation process based on the rank-one decomposition of matrices and DDA. By representing structural transformation as the change of dipoles and their properties, the updated polarizations can be computed efficiently. The improvement in computational efficiency was benchmarked, demonstrating up to several hundred times acceleration for a system comprising ca. 4000 dipoles. The rank-one decomposition accelerated DDA method (RD-DDA) can be used directly to investigate the optical properties of nanostructural transformations defined by atomic- or continuum-scale processes, which is essential for understanding the growth mechanisms of nanoparticles and algorithm-driven structural optimization toward enhanced optical properties.

Effect of chemical potential on the structural modification of titanate-based photocatalysts: Fast dye degradation efficiency and adsorption power

In this work, the impact of the chemical potential of sodium hydroxide concentration was evaluated in the synthesis of titanate-based photocatalysts prepared by the microwave-assisted hydrothermal method. The materials were characterized by techniques that made it possible to unveil their structural, morphological, and electronic properties, corroborating the formation of a heterojunction of sodium titanate (Na2Ti6O13) and hydrated hydrogen titanate (H2Ti3O7·H2O). The results demonstrated that the increased chemical potential of NaOH caused an ionic exchange between Na+ and H+ ions, making the H2Ti3O7·H2O phase more stable. The oriented attachment (OA) growth mechanism was predominant, resulting in nanoparticles with nanosheet-like morphology. The photocatalytic efficiency of the materials was tested for the discoloration of Rhodamine B (RhB) and Methylene Blue (MB) dyes. The photocatalyst with the best efficiency showed a half-life time for RhB discoloration of only 5 min and a high capacity of adsorption in the MB medium (∼90% in 10 min). The details of the nanoparticle growth mechanism, the charge transport in the heterojunction, and the stability and reusability of the materials were clarified.

Shape control with atomic precision: anisotropic nanoclusters of noble metals.

When plasmonic metal nanoparticles become smaller and smaller, a new class of nanomaterials-metal nanoclusters of atomic precision-comes to light and has become an attractive research topic in recent years. These ultrasmall nanoparticles (or nanoclusters) are unique in that they are molecularly uniform and pure, often possess a quantized electronic structure, and can grow into single crystals as do protein molecules. Exciting achievements have been made by correlating their properties with the precise structures at the atomic level, which has provided a profound understanding of some mysteries that could not be elucidated in the studies on conventional nanoparticles, such as the critical size at which plasmons are emergent. While most of the reported nanoclusters are spherical or quasi-spherical owing to the reduced surface energies (and hence stability), some anisotropic nanoclusters of high stability have also been obtained. Compared to the anisotropic plasmonic nanoparticles, the nanocluster counterparts such as rod-shaped nanoclusters can provide insights into the growth mechanisms of plasmonic nanoparticles at the early stage (i.e., nucleation), reveal the evolution of properties (e.g., optical), and offer new opportunities in catalysis, assembly, and other themes. In this Review, we highlight the anisotropic nanoclusters of atomic precision obtained so far, primarily gold, silver, and bimetallic ones. We focus on several aspects, including how such nanoclusters can be achieved by kinetic control, and how the anisotropy gives rise to new properties over the isotropic ones. The anisotropic nanoclusters are categorized into three types, (i) dimeric, (ii) rod-shaped, and (iii) oblate-shaped nanoclusters. For future research, we expect that anisotropic nanoclusters will provide exciting opportunities for tailoring the physicochemical properties and thus lead to new developments in applications.

Growth-control of hexagonal CdS-decorated ZnO nanorod arrays with low-temperature preheating treatment for improved properties and efficient photoelectrochemical applications.

The limitations of oxide semiconductor-based solar cells in achieving high energy conversion efficiencies have prompted incessant research efforts towards the creation of efficient heterostructures. Despite its toxicity, no other semiconducting material can fully replace CdS as a versatile visible light-absorbing sensitizer. Herein, we explore the aptness of preheating treatment in the successive ionic layer adsorption and reaction (SILAR) deposition technique and improve the understanding of the principle and the effects of a controlled growth environment on thus-formed CdS thin films. Single hexagonal phases of nanostructured cadmium sulfide (CdS)-sensitized zinc oxide nanorods arrays (ZnO NRs) have been developed without the support of any complexing agent. The influences of film thickness, cationic solution pH and post-thermal treatment temperature on the characteristics of binary photoelectrodes have been investigated experimentally. Interestingly, the preheating-assisted deposition of CdS, which is rarely applied for the SILAR technique, resulted in improved photoelectrochemical performance similar to the post-annealing effect. The X-ray diffraction pattern revealed that optimized ZnO/CdS thin films were polycrystalline with high crystallinity. Examination of the morphology of the fabricated films via field emission scanning electron microscopy showed that film thickness and medium pH altered the growth mechanism of nanoparticles, thereby changing their particle sizes, which had a significant influence on the film's optical behavior. The effectiveness of CdS as a photosensitizer and the band edge alignment for ZnO/CdS heterostructures were evaluated using ultra-violet visible spectroscopy. Facile electron transfer in the binary system as evidenced in electrochemical impedance spectroscopy Nyquist plots, therefore, promotes higher photoelectrochemical efficiencies from 0.40% to 4.30% under visible light illumination as compared with the pristine ZnO NRs photoanode.

Insight on the growth mechanism of TiO2 nanoparticles via gaseous detonation intercepting collection

In a closed tube, TiO2 nanoparticles can be prepared by hydrolyzing TiCl4 under extreme conditions of hydrogen-oxygen explosion. In this process, the chemical reaction is complex and violent, and TiO2 nanoparticles can achieve particle growth and phase transition in a very short time. The photocatalytic activity of TiO2 is closely related to its particle size and phase composition, however, it is difficult to observe the growth process of TiO2 in the explosion process. An intercepting collection scheme was proposed to explore the growth mechanism of TiO2 nanoparticles during gaseous detonation. The characterization results illustrated that the TiO2 nanoparticles were successfully collected by the intercepting device. The particle size of intercepted powders is smaller than that of the powders precipitated on the tube wall, and as the distance between the intercept position and the initiation point increases, the particle size decreases. The growth of TiO2 nanoparticles closely depends on the propagation and attenuation of detonation wave. After detonation nucleation and combustion sintering, TiO2 nanoparticles with anatase phase and rutile phase are fabricated. The proposed intercepting collection method is helpful to reveal the dynamic growth mechanism of nanomaterials under the extreme conditions of gaseous detonation.

UV-Induced Gold Nanoparticle Growth in Polystyrene Matrix with Soluble Precursor

It is demonstrated that UV (LED at 365 nm) irradiation with subsequent heating (90–110 °C) of the polystyrene matrix containing a soluble Au(I) compound ((Ph3P)Au(n-Bu)) results in the growth of gold nanoparticles within the sample bulk, as confirmed by UV-vis spectroscopy and TEM electron microscopy. Pure heating of the samples without previous UV irradiation does not provide gold nanoparticles, thereby facilitating optical image printing. Comparing the nanoparticles’ growth kinetics in samples with different precursor content suggests the nanoparticle growth mechanism through Au(I) autocatalytic reduction at the surface of a gold nanoparticle. Within the polymer matrix, this mechanism is suggested for the first time.

In-situ preparation of carbon nanotubes on CuO nanowire via chemical vapor deposition and their growth mechanism investigation

In-situ growth of carbon nanotubes (CNTs) on CuO nanowires is realized by chemical vapor deposition method, in which hydrogen/argon mixed gas and acetylene are used as pretreatment gas and carbon source, respectively. CuO nanowires are formed uniformly on the surface of copper wire (CW) through thermal oxidation method, which generates CW@CuO@CNTs with a good hierarchical structure. Also, many copper nanoparticles are formed on the surface of CNTs. The growth mechanisms of CNTs and copper nanoparticles are investigated in this paper.