Kinetics and Mechanism of Metal Nanoparticle Growth via Optical Extinction Spectroscopy and Computational Modeling: The Curious Case of Colloidal Gold

An overarching computational framework unifying several optical theories to describe the temporal evolution of gold nanoparticles (GNPs) during a seeded growth process is presented. To achieve this, we used the inexpensive and widely available optical extinction spectroscopy, to obtain quantitative kinetic data. In situ spectra collected over a wide set of experimental conditions were regressed using the physical model, calculating light extinction by ensembles of GNPs during the growth process. This model provides temporal information on the size, shape, and concentration of the particles and any electromagnetic interactions between them. Consequently, we were able to describe the mechanism of GNP growth and divide the process into distinct genesis periods. We provide explanations for several longstanding mysteries, for example, the phenomena responsible for the purple-greyish hue during the early stages of GNP growth, the complex interactions between nucleation, growth, and aggregation events, and a clear distinction between agglomeration and electromagnetic interactions. The presented theoretical formalism has been developed in a generic fashion so that it can readily be adapted to other nanoparticulate formation scenarios such as the genesis of various metal nanoparticles.Comment: Main text and supplementary information (accompanying MATLAB codes available on the journal webpage

A system for measuring particle size distribution of particles of a particulate matter

It is an objective of the present invention to provide a system for measuring the particle size distribution of the particles of a particulate matter and, simultaneously, its crystalline nature. This objective is achieved according to the present invention by a system for measuring the particle size distribution of the particles of a particulate matter; comprising: a) a particle separation unit (4), such as a decanter unit, a centrifugal unit or a magnetic/electric field unit, being designed to force the particles (10a, 10b) to move through a moderating agent (8), such as liquid or a suspension; b) a radiation source (12) and a respective detector (14) enabled to measure dynamically the transmitted and/or particle absorbed amount of the incident light in at least a section of said particle acceleration unit (4), said measurement being preferably performable during predetermined time intervals; c) a radiation source (12) and a respective detector (14) enabled to simultaneously measure dynamically the beam - particle interaction, such as diffraction pattern, of the particles (10a, 10b) moving along at least a section of said particle acceleration unit (4), said measurement being preferably performable during predetermined time intervals. The present system therefore allows to measure both the particle size distribution as well as the crystalline nature of the powders at the same time thereby achieving a higher resolution within a shorter investigation period as compared to the methods known so far

Synthesis of ZnO in aqueous media. Influence of several synthesis parameters on particle size and shape

No abstract availabl

Perovskite particles and nanostructures by self-assembly

Controlled self-organization of nanocrystals in aqueous media can be a powerful tool to obtain (nano)particles and more complex architectures with well-defined morphology and new modified properties. Aggregation of nanocrystals produces polycrystalline assemblies which can be ordered or disordered. The oriented aggregation of nano buildings blocks overcomes the classic concept of crystal growth, which is typically thought to accur via atom-by-atom or monomer-to-monomer addition of existing nucleous. Secondary nucleation on the surface of existing crystals represents a further mechanism for the growth of particles with some level of internal organization. We will show some examples of self-assembly processes in the synthesis of BaTiO(3) and SrTiO(3) mesocrystals from aqueous suspensions of amorphous titanium hydroxide. The assembly process can be controlled by varying the temperature and the concentration of the solution as well as by introducing suitable organic molecules. Core-shell structures can be obtained when the assembly process occurs at the surface of template particles suspended in the solution. The coating of BaTiO(3) spherical particles with SrTiO(3) and BaZrO(3) nanocrystals and the possible application of this process in the field of dielectric materials will be discussed

BaTiO(3)-(Ni(0.5)Zn(0.5))Fe(2)O(4) ceramic composites with ferroelectric and magnetic properties

No abstract availabl

Precipitation of Nanosized and Nanostructured Powders: Process Intensification and Scale-Out Using a Segmented Flow Tubular Reactor (SFTR)

The successful scale-out and process intensification using a segmented flow tubular reactor (SFTR) for ultrafine CaCO3, BaTiO3, and nanosized ZnO from optimized minibatch (20 mL) conditions is presented. The capacity of the SFTR in process intensification was demonstrated by producing ∼ 5 kg batches of BaTiO3 powders with excellent batch-to-batch reproducibility. The SFTR scale-out or numbering-up capacity was demonstrated for a nanostructured CaCO3 in 500 g batches by scaling-out from one to six segmented flow tubular reactors run in parallel (scale-out/-up ratio of 5000 compared to lab batch experiments). The SFTR was then used to demonstrate its potential for nanosized ZnO powders producing 50 g lots of these nanopowders in a continuous process, a scale-out/-up ratio of 250 compared to lab batch experiments without any loss of powder quality. The SFTR allows a precise control of precipitation conditions, leading to an excellent reproducibility in powder characteristics, and shows great promise as a simple production process of powders and advanced nanomaterials with highly controlled properties

Influence of Irradiance, Flow Rate, Reactor Geometry, and Photopromoter Concentration in Mineralization Kinetics of Methane in Air and in Aqueous Solutions by Photocatalytic Membranes Immobilizing Titanium Dioxide

Photomineralization of methane in air (10.0–1000 ppm (mass/volume) of C) at100%relative humidity (dioxygen as oxygen donor) was systematically studied at318±3 K in an annular laboratory-scale reactor by photocatalytic membranes immobilizing titanium dioxide as a function of substrate concentration, absorbed power per unit length of membrane, reactor geometry, and concentration of a proprietary vanadium alkoxide as photopromoter. Kinetics of both substrate disappearance, to yield intermediates, and total organic carbon (TOC) disappearance, to yield carbon dioxide, were followed. At a fixed value of irradiance (0.30 W⋅cm-1), the mineralization experiments in gaseous phase were repeated as a function of flow rate (4–400 m3⋅h−1). Moreover, at a standard flow rate of 300 m3⋅h−1, the ratio between the overall reaction volume and the length of the membrane was varied, substantially by varying the volume of reservoir, from and to which circulation of gaseous stream took place. Photomineralization of methane in aqueous solutions was also studied, in the same annular reactor and in the same conditions, but in a concentration range of 0.8–2.0 ppm of C, and by using stoichiometric hydrogen peroxide as an oxygen donor. A kinetic model was employed, from which, by a set of differential equations, four final optimised parameters,k1andK1,k2andK2, were calculated, which is able to fit the whole kinetic profile adequately. The influence of irradiance onk1andk2, as well as of flow rate onK1andK2, is rationalized. The influence of reactor geometry onkvalues is discussed in view of standardization procedures of photocatalytic experiments. Modeling of quantum yields, as a function of substrate concentration and irradiance, as well as of concentration of photopromoter, was carried out very satisfactorily. Kinetics of hydroxyl radicals reacting between themselves, leading to hydrogen peroxide, other than with substrate or intermediates leading to mineralization, were considered, and it is paralleled by a second competition kinetics involving superoxide radical anion

The impact of sorbent geometry on the sulphur adsorption under supercritical water conditions: a numerical study

A numerical model to show the impact of the adsorption bed geometry on the desulfurization process of wet biomass under supercritical water (SCW) gasification process has been developed. Three different geometries, straight channels (pipe), sharp-edged channels (sharp) and packed bed of particles (pebbles) have been considered for the sorbent bed. The influence of the flow patterns on the sulphur distribution inside the bed and on the saturation of the sorbent has been analysed. The results show that, when the flow is unidirectional with a parabolic profile, as in the pipe geometry, the adsorption process can be explained based on the 1D plug-flow model. In the case of more complex flow structures, when torus-shaped vortices appeared in the sharp or pebbles geometries, the 3D flow effects should be considered. The present work might provide useful information for the evaluation of sulphur sorption under SCW conditions. The models obtained by computational fluid dynamic, which are under experimental validation using neutron imaging, will help for the sorbent design and production by 3D printing techniques, which represent an advanced engineered tool to improve the process efficiency and sorbent material selection