Gas-phase Method Research Articles

Population Balance-Monte Carlo Simulation for Gas-to-Particle Synthesis of Nanoparticles

The process simulation of nanoparticle synthesis via the gas-phase method is essential to understanding the detailed dynamic evolution of nanoparticles within a very short time period under high temperature. The task is, however, very challengeable up to now as the conversion of the gaseous precursor to the end-use nanoparticle is a complex physicochemical process involving nucleation of the particulate phase, agglomeration between particles and sintering under industrial production conditions. In this article, we extended the differentially weighted Monte Carlo method for population balance to simulate the dynamic evolution of titania (TiO2) nanoparticles synthesized by gas-to-particle conversion in a single aerosol reactor, considering simultaneous nucleation, agglomeration, and sintering. The simulated size distribution of TiO2 agglomerate and primary particles produced by the thermal decomposition of titanium tetraisoproxide agreed well with the experimental data. In the simulation, the fast population balance-Monte Carlo method was utilized to accelerate the process simulation on a desktop PC. Results were obtained up to 178 times faster than that of a normal Monte Carlo method. The inhomogeneous internal structure of primary particles was considered through solving population balance of polydisperse primary particles within agglomerate. It was found the polydisperse model could predict the primary particle size distribution better. Simulation results revealed a complex competition relation among nucleation, agglomeration and sintering. Copyright 2013 American Association for Aerosol Research

Implementation of the CCSD-PCM linear response function for frequency dependent properties in solution: Application to polarizability and specific rotation

This work reports the first implementation of the frequency dependent linear response (LR) function for the coupled cluster singles and doubles method (CCSD) combined with the polarizable continuum model of solvation for the calculation of frequency dependent properties in solution. In particular, values of static and dynamic polarizability as well as specific rotation are presented for various test molecules. Model calculations of polarizability show that a common approximation used in the definition of the LR function with solvation models recovers over 70% of the full response while maintaining a computational cost comparable to gas phase LR-CCSD. Calculations of specific rotation for three compounds for which gas phase methods predict the wrong sign of the rotation show that accounting for the electronic response of the solvent may be essential to assign the correct absolute configuration of chiral molecules.

Melt Infiltration: an Emerging Technique for the Preparation of Novel Functional Nanostructured Materials

The rapidly expanding toolbox for design and preparation is a major driving force for the advances in nanomaterials science and technology. Melt infiltration originates from the field of ceramic nanomaterials and is based on the infiltration of porous matrices with the melt of an active phase or precursor. In recent years, it has become a technique for the preparation of advanced materials: nanocomposites, pore-confined nanoparticles, ordered mesoporous and nanostructured materials. Although certain restrictions apply, mostly related to the melting behavior of the infiltrate and its interaction with the matrix, this review illustrates that it is applicable to a wide range of materials, including metals, polymers, ceramics, and metal hydrides and oxides. Melt infiltration provides an alternative to classical gas-phase and solution-based preparation methods, facilitating in several cases extended control over the nanostructure of the materials. This review starts with a concise discussion on the physical and chemical principles for melt infiltration, and the practical aspects. In the second part of this contribution, specific examples are discussed of nanostructured functional materials with applications in energy storage and conversion, catalysis, and as optical and structural materials and emerging materials with interesting new physical and chemical properties. Melt infiltration is a useful preparation route for material scientists from different fields, and we hope this review may inspire the search and discovery of novel nanostructured materials.

Magnetic nanoparticles of core-shell structure for recoverable photocatalysts

Si doped iron-iron oxide core-shell magnetic nanoparticles are presented in this paper for photocatalysis applications. The nanoparticles were fabricated by a gas phase method with control of small size. Enhanced optical absorption was observed in them compared to the ones without Si, particularly in the 310 nm–450 nm wavelength range. This active optical property is beneficial for photocatalysis in terms of the efficient hole transfer from the catalysts to the reacting chemistry groups. The nanoparticles also possess a strong and active magnetic property which provides an easy way for recyclable usage. This work offers a route towards the improvement of a photocatalytic system which integrates a nanoparticulate structure of a large surface area with effective doping and recoverability by a magnetic field.

Facile synthesis of single-phase spherical α″-Fe16N2/Al2O3 core-shell nanoparticles via a gas-phase method

When nitrogen was inserted into the spherical α-Fe/Al2O3 core shell of 45 nm nanoparticles, the XRD pattern showed a clear change in the crystal modification from a body-centered cubic crystal to that of a single-phase α″-Fe16N2 structure. SEM, TEM, and energy-dispersive X-ray spectroscopy mapping analysis gave the particle size distributions, the shell thickness, and the Fe and Al elements. An examination of the total electron yield (surface sensitive) and fluorescence yield (bulk sensitive) of X-ray absorption fine structure on Fe and N atoms of these core shell nanoparticles confirmed the nitriding of the core iron and showed iron oxide formations on the core surface, indicating stability and resistivity performance. The nitriding process also changed the magnetic properties from paramagnetic to ferromagnetic with a coercivity above 3000 Oe, indicating a promising material for a “rear-earth-free” giant magnet.

Theoretical Study of the Substituent and Solvent Effects on the Reaction Enthalpies of the Antioxidant Mechanisms of Tyrosol Derivatives

Abstract In this paper, the study of various ortho- and meta-substituted tyrosol derivatives is presented. The reaction enthalpies related to three antioxidant action mechanisms HAT, SET-PT, and SPLET for substituted tyrosols have been calculated using the DFT/B3LYP method in gas phase and water. Calculated results show that electron-withdrawing substituents increase the bond-dissociation enthalpy (BDE), ionization potential (IP), and electron-transfer enthalpy (ETE), while electron-donating ones cause a rise in the proton-dissociation enthalpy (PDE) and proton affinity (PA). In the ortho-position, substituents show larger effect on reaction enthalpies than at the meta-position. In comparison to the gas phase, water attenuates the substituent effect on all reaction enthalpies. In the gas phase, BDEs are lower than PAs and IPs, i.e., HAT represents the thermodynamically preferred pathway. On the other hand, SPLET mechanism represents the thermodynamically favored process in water. Results show that calculated enthalpies can be correlated with Hammett constants (σm) of the substituted tyrosols successfully. Furthermore, calculated IP and PA values for substituted tyrosols show linear dependence on the energy of the highest occupied molecular orbital (EHOMO).

Photo-initiated chemical vapor deposition as a scalable particle functionalization technology (a practical review)

Chemical vapor deposition (CVD), and its variants, is a more viable technology than the addition of surface active agents to modify nanoparticle surfaces. While thermally-activated CVD simply works by initiating the monomers using heat, some other techniques are more powerful and versatile. Indeed, higher energy CVD methods open up possibilities to a wider range of monomers. Unfortunately, different terminologies and classifications due to parallel work have led to confusion. This paper presents and explains the different techniques as well as their equivalent terminologies to clarify the big picture. While the demand for functionalized nanoparticles grows rapidly, current functionalization methods are still too expensive for most applications. This paper is intended to be a practical review of the gas phase methods available in order to identify a potential candidate for large scale functionalization of nanoparticles. This study identifies photo-initiated CVD (PICVD) as an ideal solution for scalable particle functionalization technology. This paper is intended to be a practical review of the gas phase methods available in order to identify a potential candidate for large-scale functionalization of nanoparticles. The focus is put on photo-initiated CVD (PICVD) as an ideal solution for scalable particle functionalization technology. ► Review of gas-phase nanoparticle surface treatment technologies ► Ranking based on technique scalability and versatility ► Equivalence between existing terminologies and proposal of a common terminology ► Identification of avenues of research for one promising technique: PICVD

Discrete particle simulation of jet-induced cratering of a granular bed

Abstract Jet-induced catering in a granular bed is an interesting phenomenon observed in nature and in many industries. This paper presents a numerical study of this process by the combined approach of computational fluid dynamics (CFD) for gas phase and discrete element method (DEM) for solid phase. The applicability of the model is verified by comparing the numerical results with experimental measurements of crater depth and crater shape in the cratering regime of Diffusion Driven Flow. The sensitivity of numerical results to model parameters such as restitution coefficient, sliding friction coefficient and Young's modulus is also examined. Then, the effect of jet velocity is quantified, followed by a detailed analysis of flow characteristics and forces between particles, as well as between particles and fluid, to understand the underlying mechanisms. Based on the simulated results, two equations are respectively formulated to estimate the asymptotic crater depth and crater width.

纳米CeO<sub> 2</sub>制备方法研究进展

综述了纳米CeO 2 的几种主要制备方法及其研究进展。对比分析了气相、固相、液相三种主要方法的优缺点，气相法所制备的样品纯度高、团聚小，但设备昂贵不易普及。液相法设别简单易普及但所制备的样品团聚严重，固相法工艺简单污染少但所制样品均匀性可控性较差。并对未来纳米CeO 2 制备方法的发展方向进行分析与展望。 Several main preparation methods of nano-CeO 2 and their research progress are reviewed. The advantages and disadvantages of three major methods including gas phase, solid phase and liquid phase are analyzed and com- pared separately. Sample prepared by gas phase method has high purity and small reunion, but the expensive equipment makes it difficult to popularize. Liquid phase method is easy to popularize, but its sample has heavy reunion. The solid phase method has outstanding merits of simple production process and low pollution, while the uniformity of sample which prepared via this method is hard to control. The future directions of the preparation methods of nano-CeO 2 are analyzed and prospected too.

Single-crystal growth of organic semiconductors

Abstract

DFT/B3LYP Study of the Substituent Effects on the Reaction Enthalpies of the Antioxidant Mechanisms of Magnolol Derivatives in the Gas-Phase and Water

In this paper, the study of various ortho- and meta-substituted Magnolol derivatives is presented. The reaction enthalpies related to three antioxidant action mechanisms HAT, SET-PT and SPLET for substituted Magnolols have been calculated using DFT/B3LYP method in gas-phase and water. Calculated results show that electron-withdrawing substituents increase the bond dissociation enthalpy (BDE), ionization potential (IP) and oxidation/reduction enthalpy (O/RE), while electron-donating ones cause a rise in the proton dissociation enthalpy (PDE) and proton affinity (PA). In ortho- position, substituents show larger effect on reaction enthalpies than in meta-position. In comparison to gas-phase, water attenuates the substituent effect on all reaction enthalpies. In gas-phase, BDEs are lower than PAs and IPs, i.e. HAT represents the thermodynamically preferred pathway. On the other hand, SPLET mechanism represents the thermodynamically favored process in water. Results show that calculated enthalpies can be successfully correlated with Hammett constants () of the substituted Magnolols. Furthermore, calculated IP and PA values for substituted Magnolols show linear dependence on the energy of the highest occupied molecular orbital ().

Density functional conformational study of 2-O-sulfated 3,6 anhydro-α-D-galactose and of neo-κ- and ι-carrabiose molecules in gas phase and water

We examined the conformational preferences of the 2-O-sulfated-3,6-α-D-anhydrogalactose (compound I) and two 1,3 linked disaccharides constituting-κ or ι-carrageenans using density functional and ab initio methods in gas phase and aqueous solution. Systematic modifications of two torsion angles leading to 324 and 144 starting geometries for the compound I and each disaccharide were used to generate adiabatic maps using B3LYP/6-31G(d). The lower energy conformers were then fully optimized using B3LYP, B3PW91 and MP2 with several basis sets. Overall, we discuss the impact of full relaxation on the energy and structure of the dominant conformations, present the performance comparison with previous molecular mechanics calculations if available, and determine whether our results are impacted, when polarization and diffuse functions are added to the 6-31G(d) basis set, or when the MP2 level of theory is used.

DFT/B3LYP Study of the Substituent Effects on the Reaction Enthalpies of the Antioxidant Mechanisms of Sesamol Derivatives in the Gas phase and water

In this paper, the study of various ortho and meta–substituted Sesamol derivatives is presented. The reaction enthalpies related to three antioxidant action mechanisms HAT, SET–PT, and SPLET for substituted Sesamols, have been calculated using the DFT/B3LYP method in gas phase and water. Calculated results show that electron-withdrawing substituents increase the bond dissociation enthalpy (BDE), ionization potential (IP), and electron transfer enthalpy (ETE), while electron-donating ones cause a rise in the proton dissociation enthalpy (PDE) and proton affinity (PA). In the ortho position, substituents show a larger effect on reaction enthalpies than in the meta position. In comparison with the gas phase, water attenuates the substituent effect on all reaction enthalpies. In the gas phase, BDEs are lower than PAs and IPs, i.e., HAT represents the thermodynamically preferred pathway. On the other hand, the SPLET mechanism represents the thermodynamically favored process in water. Results show that calculated enthalpies can be successfully correlated with Hammett constants (σm) of the substituted Sesamols. Furthermore, calculated IP and PA values for substituted Sesamols show linear dependence on the energy of the highest occupied molecular orbital (EHOMO).

Quantitative Studies on the Oxygen and Nitrogen Functionalization of Carbon Nanotubes Performed in the Gas Phase

Gas-phase methods were applied for the oxygen and nitrogen functionalization of multiwalled carbon nanotubes (CNTs). The oxygen functionalization was performed by HNO3 vapor treatment at temperatures from 200 to 250 °C for 12 h up to 120 h. The oxygen-functionalized CNTs were used as the starting material for nitrogen functionalization through thermal treatment under NH3. The BET surface area increased after the treatment in HNO3 vapor, which also caused the weight loss due to carbon corrosion. The oxygen content increased with increasing treatment time but decreased with increasing temperature, as disclosed by elemental analysis, X-ray photoelectron spectroscopy, and temperature-programmed desorption (TPD) results. The surface acidity increased with increasing treatment time as shown by TPD using NH3 as a probe molecule. As to nitrogen functionalization, the amount of nitrogen was correlated with the oxygen amount in the starting CNTs. A higher NH3 concentration caused a lower BET surface area due to carbon corrosion. The incorporation of both oxygen and nitrogen lowered the thermal resistance of CNTs. The nitrogen-functionalized CNTs showed only a slight decrease, in contrast to a significant decrease observed for O-functionalized CNTs. The formation or removal of coordinatively unsaturated carbon like amorphous carbon or defects was found to be involved in all of the functionalization, desorption, and oxidation processes.

Effect of the multistage chemical treatment of carbon nanotubes on their purity and quality of walls

The effect of chemical methods that include the gas-phase and liquid-phase selective oxidation methods, of hydrochloric acid when used in different sequences, and of concentrated nitric acid on the purification efficiency of carbon nanotubes after their synthesis is studied. Changes in the quality of walls of this material at different stages of purification are studied physicochemically.

Electronic spectra of C4H3Cl+ isomers

Two experimental methods were applied to identify the structure and electronic transitions of C4H3Cl+ isomers. The first is a direct absorption technique where mass-selected ions are embedded in 6 K neon matrices using a mass-selected ion beam and absorption spectra of different C4H3Cl+ isomers were thus observed. The second is a gas phase method on ions which have been collisional cooled with cryogenic helium inside of a 22-pole ion trap. The c-type (1)2 A′ ← X 2 A″ electronic transition of a C4H3Cl+ isomer could then be measured by a one-colour, two-photon technique at 20 and 50 K in the gas phase. The two sets of data, complemented by calculated excitation energies, allowed the assignment of particular isomers. Rotational structure in the gas phase spectra was resolved for C4H3 35Cl+ and C4H3 37Cl+ isomers of cis-1-chlorobutenynylium. The analysis leads to the spectroscopic constants: T 00 = 19 184.680(5), , , , , and (all in cm−1).

Free radical scavenging activity of morin 2′-O− phenoxide anion

Due to intramolecular H-atom transfer, deprotonation of the most acidic 3-OH group of morin yields 2′-O− phenoxide anion. The reaction enthalpies related to mechanisms of free radical scavenging activity of this dominant species at a physiological pH of 7.4 were calculated by PM6 and DFT methods in gas-phase, water, benzene and DMSO. Results indicate the 4′-OH group of 2′-O− phenoxide anion is the active site for radical inactivation. The thermodynamically favoured mechanism depends on the polarity of the reaction media: in polar solvents (water and DMSO), the sequential proton loss electron transfer (SPLET) mechanism is preferred while in non-polar benzene (and in gas-phase), the hydrogen atom transfer (HAT) mechanism is responsible for the free radical scavenging activity of the morin phenoxide anion. Results show that the fast, semiempirical PM6 method fairly mimics more accurate, though time-consuming DFT methodologies.

Absorption and emission properties of various substituted cinnamic acids and cinnamates, based on TDDFT investigation

AbstractAbsorption and emission properties of the hydroxy‐, nitro‐, and fluoro‐group substituted at the ortho‐, meta‐, and para‐positions of cinnamic acids (1A–9A) and cinnamates (1E–9E) were investigated using the density functional theory (DFT) and time‐dependent DFT (TDDFT) calculations. The ground (S0)‐ and excited (S1)‐state geometries were obtained at the B3LYP/6‐31G(d) and TD‐B3LYP/6‐31G(d) methods, respectively. On the basis of the optimized structures of the S0‐ and S1‐states, the TDDFT calculations with B3LYP and CAM‐B3LYP functionals were performed to compute the absorption and emission energies of the various substituted cinnamic acids and cinnamates. The solvent effect was examined by the polarizable continuum model in methanol solution. As result, all compounds had the local minimum at the planar structure conformation due to π‐conjugation. The characteristics of the absorption spectra for cinnamic acid and cinnamate derivatives were satisfactorily reproduced by TDDFT method in gas phase and in methanol solution in both peak position and intensity. The emission from the local minimum in the planar structure was calculated for various substituted cinnamic acids and cinnamates. The results obtained by TDDFT investigation provide a useful insight into the detailed information on the optical and electronic properties of these compounds and a useful tool for designing and developing the superior UV absorber compounds. © 2012 Wiley Periodicals, Inc.

Electrospray–Differential Mobility Analysis as an Orthogonal Tool to Size-Exclusion Chromatography for Characterization of Protein Aggregates

The biopharmaceutical industry characterizes and quantifies aggregation of protein therapeutics using multiple analytical techniques to cross-validate results. Here, we demonstrate the use of electrospray-differential mobility analysis (ES-DMA), a gas-phase and atmospheric pressure ion-mobility method for characterizing protein aggregates. Two immunoglobulin Gs are systematically heat treated to induce aggregation and characterized using size-exclusion chromatography (SEC) and ES-DMA. Although ES-DMA is a gas-phase characterization method, we find that aggregation kinetic rate constants determined by ES-DMA is in good agreement with those determined by SEC. ES-DMA appears to have a higher resolution and lower limit of detection as compared with SEC. Thus, ES-DMA can potentially become an important orthogonal tool for characterization of nascent protein aggregates in the biopharmaceutical industry.

PM6 and DFT study of free radical scavenging activity of morin

Flavonoids have long been recognised for their general health-promoting properties, of which their antioxidant activity may play an important role. In this work, we have studied the properties of flavonoid morin using semiempirical and density functional theory (DFT) methods in order to validate the application of the recently developed parametric method 6 (PM6). Reaction enthalpies related to mechanisms of free radical scavenging by flavonoid morin were calculated by DFT and PM6 methods in gas-phase, water, DMSO and benzene. It has been shown that fast semiempirical PM6 method can mimic results obtained by means of more accurate time consuming DFT calculations. Thermodynamically favoured mechanism depends on reaction medium: SPLET (sequential proton loss electron transfer) is preferred in water and DMSO, and HAT (hydrogen atom transfer) is predominant in gas-phase. In benzene these two mechanisms are competitive.