Chemical Reaction Conditions Research Articles

The influence of chemical reaction conditions upon poly(styrene‐methyl methacrylate‐acrylic acid) synthesis: Variations in nanoparticle size, colour and deposition methods

AbstractMonodisperse latex nanospheres of poly(styrene‐methyl methacrylate‐acrylic acid) with different sizes were synthetised by soap‐free emulsion copolymerisation and applied onto polyamide 6,6 fabrics by two methods, ie, gravitational sedimentation and dip‐drawing. Different‐sized nanospheres were synthetised by varying temperature and stirring velocity as reaction parameters. Scanning electron microscopy and scanning transmission electron microscopy were used to evaluate nanosphere sizes and deposition structures. The results showed two different nanosphere structural arrangements on the fabric surface, a hexagonal packed centre structure in the even surfaces and a square arrangement in the out‐of‐plane surfaces. Different colours were observed according to particle size, namely, violet (ca. 170 nm), blue (ca. 190 nm), green (ca. 210 nm), yellow (ca. 230 nm) and red (ca. 250 nm). An iridescence effect was also observed, displaying different colours at different observation angles. By controlling the size of the nanospheres it was possible to obtain different, brilliant and iridescent colours. Using different nanosphere sizes it was possible to obtain different interplanar distances and to control the light scattering in the crystalline lattice planes, obtaining Bragg diffraction patterns.

UNSTEADY MHD MICROPOLAR FLUID IN A STRETCHING SHEET OVER AN INCLINED PLATE WITH THE EFFECT OF NON-LINEAR THERMAL RADIATION AND SORET-DUFOUR

The effect of unsteady MHD flow of a micropolar fluid over an inclined plate with thermal radiation and non-uniform heat source/sink, non-linear thermal radiation, chemical reaction and convective boundary conditions has been investigated in the present study. A mathematical model is developed to set of Partial differential equations into non-linear coupled ordinary differential equations and then solved numerically by spectral relaxation method (SRM) with finite difference scheme which employs the Gauss-Seidel type of relaxation approach to linearize and decouple the system of differential equations and then Chebyshev pseudo-spectral method was used to solve the equations. The influence of various physical parameters are depicted graphically and analyzed in details. An excellent agreement of accuracy has found after comparing present work with previously published work.

In Situ Preparation of Pr1-xCaxMnO3 and La1-xSrxMnO3 Catalysts Surface for High-Resolution Environmental Transmission Electron Microscopy

The study of changes in the atomic structure of a catalyst under chemical reaction conditions is extremely important for understanding the mechanism of their operation. For in situ environmental transmission electron microscopy (ETEM) studies, this requires preparation of electron transparent ultrathin TEM lamella without surface damage. Here, thin films of Pr1-xCaxMnO3 (PCMO, x = 0.1, 0.33) and La1-xSrxMnO3 (LSMO, x = 0.4) perovskites are used to demonstrate a cross-section specimen preparation method, comprised of two steps. The first step is based on optimized focused ion beam cutting procedures using a photoresist protection layer, finally being removed by plasma-etching. The second step is applicable for materials susceptible to surface amorphization, where in situ recrystallization back to perovskite structure is achieved by using electron beam driven chemistry in gases. This requires reduction of residual water vapor in a TEM column. Depending on the gas environment, long crystalline facets having different atomic terminations and Mn-valence state, can be prepared.

(Invited) Combined Ab Initio and Machine Learning Approaches to Discover Materials for Hydrogen Generation

In this talk we will present our results using ab initio and machine learned models to discover candidate perovskite STWS materials. This includes predicting the stability of these materials at the operating temperature, whether these materials form as perovskites and in what specific phase, the energy of oxygen vacancies and other defects that mediate the redox process, and finally the viability of these metal oxides as STWS redox materials. The Gibbs energy, G, determines the equilibrium conditions of chemical reactions and materials stability. Unfortunately, G has been tabulated for only a small fraction of known inorganic compounds, thus impeding an analysis of whether materials are stable and synthesizable at operating conditions. We used a statistical learning approach to identify a simple and accurate descriptor to predict G(T) for stoichiometric inorganic compounds with ~40 meV/atom resolution, and minimal computational cost, for temperatures between 300 K and 1800 K. We then applied this descriptor to screen various compositions for their stability at STWS temperatures. Candidate materials that form as perovskites were then analyzed using a machine learned one-dimensional tolerance factor, τ, that we developed that correctly predicts 92% of compounds as perovskite or non-perovskite to predict which of the predicted stable compounds form perovskites. Finally, we applied DFT on the remaining viable candidates to predict the thermodynamics of STWS reactions. This requires predicting the correct perovskite phase, symmetry breaking distortions and modeling the correct defect, spin and charge state of the defect mediating the oxidation and reduction processes at the operating conditions.

Insight into organophosphate chemical warfare agent simulant hydrolysis in metal-organic frameworks.

Metal-organic frameworks (MOFs) are porous 3-dimensional crystalline structures that have shown promise for a variety of applications including adsorption, catalysis, and sensing. Modern warfare has placed chemical warfare agent (CWA) destruction at the forefront of chemical applications for MOFs. However, experiments involving CWAs can only be performed by a small number of highly trained individuals as they are extremely dangerous and available only to certain laboratories. As such, it is imperative that suitable chemical simulants and reaction conditions are determined for CWAs of interest. In this work, we determine the reaction rate for heterogeneous catalytic hydrolysis of eight commonly used G-agent simulants with zirconium-based MOFs. Of the simulants tested, only dimethyl chlorophosphate (DMCP), diisopropylfluorophosphate (DFP), and dimethyl p-nitrophenylphosphate (DMNP) exhibit the ability to be catalytically hydrolyzed in a manner similar to the G-agents by the MOFs studied. Two different base-catalyzed reaction mechanisms are proposed for the hydrolysis reaction on the different MOF secondary building units, and the effect of pH and buffer properties is determined using an N-ethylmorpholine (NEM) buffer at pH 8-10 and a 3-(cyclohexylamino)-1-propanesulofinic acid (CAPS) buffer at pH 10-11.

Characteristics of chemical reaction and convective boundary conditions in Powell-Eyring nanofluid flow along a radiative Riga plate

A typical base fluid such as water, oil or glycol is poor conductor of heat due to deficient thermo-physical properties. This deficiency is normally addressed by saturation of thermally strong conductive metallic nanoparticles such as Fe, Ti, Hg, Cu, Au into the base fluid resulting a stronger thermal conductivity, electric conductivity, heat and mass flux of the so formulated nanofluid. Nanoparticles having a diameter size less than 100 nano-meter are preferred in this formulation because these nano-sized particles stay suspended into the base fluid for a longer time-period. This communication aims to investigate the salient features of a nanofluid flow along a radiative Riga plate using Powell-Eyring model and convective boundary conditions. The flow model involves the effect of first order chemical reaction as well as the Brownian motion diffusion and Thermophoresis effects. Governing PDEs are transformed into ODEs using suitable transformations. HAM is applied for convergent series solutions to the boundary value problem. Impact of various parameters including Brownian motion, Thermophoresis, modified Hartman number, Lewis and Prandtl number on flow profiles is analyzed graphically. Parameters of physical interest like Skin-friction, Nusselt and Sherwood numbers are illustrated through numerical data. Effect of modified Hartman number is significant on flow profiles due to involvement of Riga plate. An efficiency is achieved in fluid flow and heat-mass flux through suspension of nanoparticles in base fluid.

Cross-diffusion Effects on MHD Mixed Convection over a Stretching Surface in a Porous Medium with Chemical Reaction and Convective Condition

In this paper, we investigate the Dufour and Soret effects on MHD mixed convection of a chemically reacting fluid over a stretching surface in a porous medium with convective boundary condition. The similarity transformation is used to reduce the governing non-linear partial differential equations into an ordinary differential equations. Then, they are solved analytically by using homotopy analysis method (HAM) and are solved numerically by Runge-Kutta fourth order method. The analytical and numerical results for the velocity, temperature, concentration, skin friction, Nusselt number and Sherwood number are discussed.

Magnetohydrodynamic mixed convection flow of Jeffery fluid with thermophoresis, Soret and Dufour effects and convective condition

The aim of this paper is to investigate heat and mass transfer of Jeffery fluid on a stretching sheet. Moreover, the influence of magnetic field with mixed convection, convective boundary condition and Soret and Dufour effects is also brought into the consideration along with chemical reaction and thermophoresis condition. The problem is modeled by system of partial differential equations and solutions are obtained by optimal homotopy analysis method. In addition, for comprehensive interpretation of the influence of the system parameters results are shown by graphs and tables.

High-Performance Materials for 3D Printing in Chemical Synthesis Applications.

3D printing has emerged as an enabling technology for miniaturization. High-precision printing techniques such as stereolithography are capable of printing microreactors and lab-on-a-chip devices for efficient parallelization of biological and biochemical reactions under reduced uptake of reactants. In the world of chemistry, however, up until now, miniaturization has played a minor role. The chemical and thermal stability of regular 3D printing resins is insufficient for sustaining the harsh conditions of chemical reactions. Novel material formulations that produce highly stable 3D-printed chips are highly sought for bringing chemistry up-to-date on the development of miniaturization. In this work, a brief review of recent developments in highly stable materials for 3D printing is given. This work focuses on three highly stable 3D-printable material systems: transparent silicate glasses, ceramics, and fluorinated polymers. It is further demonstrated that 3D printing is also a versatile technique for surface structuring of polymers to enhance their wetting performance. Such micro/nanostructuring is key to selectively wetting surface patterns that are versatile for chemical arrays and droplet synthesis.

PH Sensitive Peptide Functionalized High Stability Polymeric Nanoparticles for Mitochondria Targeted Cancer Drug Delivery

A major focus of cancer nanomedicine is to achieve a high therapeutic index for cancer therapy. Despite the unprecedented growth in the development of polymeric self-assembled nanosystems, only a few of them end up in clinics (e.g. Doxil) as a result of (i) poor stability, (ii) drug leakage and (iii) dissociation kinetics due to the strong influence of blood components in vivo. The most common method for improving nanocarrier stability is to tune the drug hydrophobicity and polymer matrix miscibility under complex chemical reaction conditions, that leads to poor drug cytotoxicity and attenuation of therapeutic efficacy. To address these challenges, we have designed a simple and robust poly (lactide-co-glycolide) (PLGA) and bovine serum albumin (BSA) hybrid nanoparticles to provide high stability and trigger drug release inside cancer cells. The hybrid nanoparticles were prepared by covalently wrapping BSA over the surface of drug-loaded PLGA nanoparticles using simple carbodiimide-chemistry in mild reaction conditions. To increase the stability, the BSA shells were crosslinked. The BSA shells can be dissociated in the high redox microenvironment of the tumor and within the cancer cells. Subsequently, the drugs loaded into the PLGA core can be released by accelerated degradation (hydrolysis) due to the low pH conditions in the tumor microenvironment and lysosomal compartments. The cancer cell targeting ability of the hybrid NPs was achieved by coupling of the amino groups of the BSA shell with a pH-sensitive peptide (acidity-triggered rational membrane peptide, ATRAM). The insertion of the ATRAM-BSA-PLGA nanoparticles into cancer cell membranes occurs at the peritumoral pH (6.5). In vitro studies showed highly-efficient pH-dependent uptake and remarkable cytotoxicity of doxorubicin triphenylphosphine loaded ATRAM-BSA-PLGA NPs. Our results demonstrate that the novel pH-sensitive peptide-functionalized high stability BSA-PLGA nanoparticles are a highly promising nanoplatforms.

Renormalization group analysis of heat transfer in the presence of endothermic and exothermic chemical reactions.

In the present paper, renormalization group methods are used to develop a macroscopic turbulence model for thermal diffusivity in turbulent fluid flow under conditions of endothermic and exothermic chemical reactions in flow. The temperature field is divided into slow (large-scale) and fast (small-scale) modes. With the help of the renormalization procedure, energy equations for the large-scale modes and relations for effective turbulent thermal diffusivity were obtained. It was shown how the type of the chemical reaction affects turbulent thermal diffusivity. In addition, the conditions were identified where effective thermal diffusivity undergoes a sharp growth.

Numerical Analysis of Heat and Mass Transfer Flow of Nanofluid over a Moving Wedge Using Spectral Quasilinearization Method

In this paper the problem of unsteady two-dimensional heat and mass transfer flow of nanofluid past a moving wedge is considered. The effects of nanoparticle volume fraction, viscous dissipation, chemical reaction, and convective boundary conditions are studied. The physical problem is modeled using partial differential equations. Using suitable similarity variables, the governing equations and their related boundary conditions are transformed into dimensionless forms of a system of coupled nonlinear ordinary differential equations. The resulting systems of equations are then solved numerically using spectral quasilinearization method (SQLM). The results reveal that the skin friction coefficient increases with increasing the values of nanoparticle volume fraction, unsteadiness and permeability parameters. The local Nusselt number reduces with increasing the value of nanoparticle volume fraction, Prandtl number and Eckert number. The local Sherwood number enhances with greater the value of nanoparticle volume fraction, unsteadiness, pressure gradient and chemical reaction parameters. Moreover, the method is checked against the previously published results and a very good agreement have been obtained.

Order of chemical reaction and convective boundary condition effects on micropolar fluid flow over a stretching sheet

The study of chemical reaction and convective boundary conditions on thermosolutal behavior of magneto hydrodynamic (MHD) fluid flow above a stretching sheet has been investigated in the current investigation. A mathematical model is established and the governing partial differential system is modified into a set of nonlinear coupled ordinary differential system and it is evaluated by using the numerical scheme of RK method. The physical importance of different flow variables such as the magnetic parameter, vortex viscosity parameter, order of chemical reaction, Prandtl, skin friction coefficient and Eckert numbers are discussed in detailed through graphical representation.

Multi-objective optimization of chemical reaction conditions based on a kinetic model

The main purpose of the study is to introduce the multi-objective optimization using Pareto approximations to problems of chemical kinetics. We report the setting up and solution of the multi-objective optimization problem for conditions of a chemical reaction on the basis of a kinetic model. The study addresses the reaction of alcohols with dimethyl carbonate catalyzed by cobalt or tungsten carbonyl. The objective functions for optimization of chemical reaction conditions based on a kinetic model are presented. The NSGA-II algorithm was applied to determine the Pareto set and front for the multi-objective optimization problem applied to the reaction of alcohols with dimethyl carbonate for two catalysts, which make it possible to find the compromise values of variable parameters providing extrema of the objective functions.

Physical descriptor for the Gibbs energy of inorganic crystalline solids and temperature-dependent materials chemistry

The Gibbs energy, G, determines the equilibrium conditions of chemical reactions and materials stability. Despite this fundamental and ubiquitous role, G has been tabulated for only a small fraction of known inorganic compounds, impeding a comprehensive perspective on the effects of temperature and composition on materials stability and synthesizability. Here, we use the SISSO (sure independence screening and sparsifying operator) approach to identify a simple and accurate descriptor to predict G for stoichiometric inorganic compounds with ~50 meV atom−1 (~1 kcal mol−1) resolution, and with minimal computational cost, for temperatures ranging from 300–1800 K. We then apply this descriptor to ~30,000 known materials curated from the Inorganic Crystal Structure Database (ICSD). Using the resulting predicted thermochemical data, we generate thousands of temperature-dependent phase diagrams to provide insights into the effects of temperature and composition on materials synthesizability and stability and to establish the temperature-dependent scale of metastability for inorganic compounds.

Real-time monitoring of N2O production in a catalytic reaction process using mid-infrared quantum cascade laser

In the context of climate change mitigation, reuse of carbon dioxide (CO2) represents an alternative with important applications in chemical industry and power generation. For this purpose, CO2 must be purified. Combustion processes lead to high amounts of CO2 but still with impurities and also accompanied by toxic gases (mainly NO and CO). A catalytic reduction process of NO (to N2) while oxidizing CO into CO2 is a promising method to purify the CO2. However, nitrous oxide (N2O) with a global warming potential of 300 times greater than CO2 may be a by-product from this process. It is therefore necessary to optimize the chemical reaction conditions to minimize N2O production. A room-temperature continuous-wave (CW) external cavity quantum cascade laser (EC-QCL)-based optical sensor was developed for real-time monitoring N2O production during the whole catalytic reaction process. A well-isolated N2O absorption line, located at 1261.0598 cm−1, of the ν1 fundamental vibrational band was selected for sensitive and selective measurement of N2O concentration by direct absorption spectroscopy. Using a modified-Herriot multi-pass cell with an effective path-length of 50 m, the limit of detection (1σ) of 32.3 ppbv was obtained in 12 s with 1.1% relative uncertainty in measurement precision. N2O productions through the catalytic reduction of NO by CO over Pt/SiO2 catalyst under different temperatures were investigated. High N2O production of up to ∼6.1 ppmv at 190 °C was observed. The optimal reaction conditions for zero N2O production were found at a temperature higher than 340 °C where 47% of NO was converted to N2.

Формирование границ раздела полупроводник-сера-переходный металл

Выполнены термодинамические расчеты при стандартных условиях химических реакций, протекающих при сульфидной пассивации поверхности элементарных полупроводников (Si, Ge), нитридов галлия, индия, алюминия (GaN, InN, AlN). Осуществление сульфидной пассивации нитрида алюминия, кремния и германия термодинамически вероятнее для неокис-ленной поверхности полупроводников, контактирующей с газовой фазой, содержащей серу или сероводород. Существует термодинамическая вероятность сульфидирования окисленной поверхности германия из газовой фазы. Сульфидирование нитридов галлия и индия самопроизвольно возможно из водных растворов сульфидов щелочных металлов. Сравнение кристаллохимических параметров атомов (ковалентные и атомные радиусы), типов симметрии возможных фазовых соединений на границах раздела полупроводник-сульфид-металл и полупроводник-оксид-металл показало, что для сульфидированной поверхности полупроводника имеется большее структурное соответствие, чем для окисленной поверхности полупроводника, контактирующего с переходным металлом. При замещении атомов кислорода на атомы серы в приграничном слое между переходным металлом и полупроводником наблюдается меньший скачок в величинах электроотрицательностей элементов, образующих границу раздела фаз. Формирование с помощью сульфидной пассивации поверхности полупроводника более совершенной и стабильной (по химическим и физическим свойствам) границы раздела фаз способствует созданию выпрямляющих контактов металл-полупроводник с улучшенными электрофизическими параметрами.DOI 10.14258/izvasu(2018)4-02

Nanoparticle Fabrication on Bacterial Microcompartment Surface for the Development of Hybrid Enzyme-Inorganic Catalyst

Bacterial microcompartments (MCPs) are polyhedral organelles containing an enzyme cluster wrapped inside a protein shell and carry out specific enzyme reactions in bacteria. These organelles have been explored meticulously using genetic, structural, and biochemical tools; however, their application in material science has not been explored much. In this study, we have used the external shell surface of MCP as a scaffold for the fabrication of gold nanoparticles displayed in 3D. This resulted in the formation of a protein scaffolded gold nanoparticle shell enclosing an active enzyme cluster. The surface scaffolded gold nanoparticles demonstrated standard catalysis, while the internal enzyme cluster of the MCPs demonstrated no loss in activity due to this fabrication. Under ambient conditions for in vitro inorganic reaction, the shell proteins sturdily maintain the barrier between the luminal enzyme and the surface inorganic catalysts and preserve the functionality of the core enzyme cluster. The MCP-AuNPs hybrid catalysts inspire a pristine class of resources that can be used in a chemical reaction condition without perturbing core biological environment for enzymatic activity. This system provides insight for fabricating uniform size nanoparticles in 3D for the development of orthogonal hybrid catalytic material.

Biomechanically driven flow of a magnetohydrodynamic bio-fluid in a micro-vessel with slip and convective boundary conditions

The main objective of the present study is to model the peristaltic transport of an incompressible couple stress fluid in an inclined asymmetric channel under the impact of porous medium, inclined magnetic field, heat and mass transfer. The effects of viscous dissipation, thermal radiation, Joule heating, chemical reaction, slip and convective boundary conditions are also taken into account. The entropy generation analysis is also studied. The non-dimensional and non-linear partial differential equations that govern the fluid flow model are simplified under the long wavelength and low Reynolds number assumptions. The entropy generation number due to heat transfer, fluid friction and magnetic field is formulated. The exact solutions for the stream function, pressure gradient, temperature, concentration, heat transfer coefficient and Nusselt number are derived. The trapping phenomenon is also presented for different wave shapes through streamline patterns. The comparison has been made with the results obtained in the symmetric and asymmetric channel, and Newtonian and couple stress fluid model. The results indicate that the entropy generation number achieves higher values in the region close to the walls of the channel, while it gains low values near the center of the channel. Temperature is a decreasing function of radiation parameter, Prandtl number and thermal Biot number. The size of the trapped bolus is greater in the Newtonian fluid model than the couple stress fluid model.

Evolution of the feruloyl esterase MtFae1a from Myceliophthora thermophila towards improved catalysts for antioxidants synthesis.

The chemical syntheses currently employed for industrial purposes, including in the manufacture of cosmetics, present limitations such as unwanted side reactions and the need for harsh chemical reaction conditions. In order to overcome these drawbacks, novel enzymes are developed to catalyze the targeted bioconversions. In the present study, a methodology for the construction and the automated screening of evolved variants library of a Type B feruloyl esterase from Myceliophthora thermophila (MtFae1a) was developed and applied to generation of 30,000 mutants and their screening for selecting the variants with higher activity than the wild-type enzyme. The library was generated by error-prone PCR of mtfae1a cDNA and expressed in Saccharomyces cerevisiae. Screening for extracellular enzymatic activity towards 4-nitrocatechol-1-yl ferulate, a new substrate developed ad hoc for high-throughput assays of feruloyl esterases, led to the selection of 30 improved enzyme variants. The best four variants and the wild-type MtFae1a were investigated in docking experiments with hydroxycinnamic acid esters using a model of 3D structure of MtFae1a. These variants were also used as biocatalysts in transesterification reactions leading to different target products in detergentless microemulsions and showed enhanced synthetic activities, although the screening strategy had been based on improved hydrolytic activity.