Department of Chemical Engineering

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Ferrimagnetic nanoparticles (FMNPs) were synthesized using different wet chemical synthesis methods. In particular, the chemical co-precipitation method (CCPM), sol-gel method (SGM), hydrothermal method (HM), and sonochemical method (SM) were used for the preparation of FMNPs. The work aims to explore the influence of different synthesis methods on the structural and magnetic properties of synthesized FMNPs. The physical morphology, chemical composition, and magnetic properties of the FMNPs were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Zeta potential, particle size distribution, and vibrating sample magnetometer (VSM). The experimentations observed that the FMNPs obtained through CCPM exhibited a stable cubical shape of 11.80 nm. The chemical co-precipitation method was also more cost-effective and time-efficient than the other wet-chemical methods. On the other hand, FMNP prepared by the hydrothermal method showed higher magnetic strengths of 89.34 emu/g with a suitable particle size distribution of −24.43 mV. The highest synthesis time was required for the sol-gel method, followed by the hydrothermal, sonochemical, and co-precipitation methods. © 2022 Elsevier B.V.

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Powder Technology

Synthesis and effect on the surface morphology &amp; magnetic properties of ferrimagnetic nanoparticles by different wet chemical synthesis methods

In this paper, a method of designing control inputs for stochastic nonlinear processes under state-feedback is proposed. The objective is to determine a control input that minimizes the expected value of the integral of error between the set-point and the states. Since the states may not be measured, they are estimated using a particle filtering algorithm. The optimal control design is then reformulated as a parameter estimation problem using control vector parameterization where the inputs are considered as a nonlinear function of the error between the state estimates and the set-point. The parameters are then computed through a homotopy based optimization method. The control performance resulting from proposed homotopy based optimization method is compared with that of direct optimization and an existing nonlinear control method on a Solid Oxide Fuel Cell (SOFC) stack model. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

International Journal of Dynamics and Control

Stochastic state-feedback control using homotopy optimization and particle filtering

Journal of Molecular Liquids

Molecular simulation of separation of gadolinium ions from aqueous waste using directional solvent extraction

Cerium oxide (ceria) contains two stable states of cerium ions (Ce3+and Ce4+). The presence of these two states and the ability to swap from one state to another (Ce3+Ce4+) by scavenging the highly reactive oxygen species (ROS) generated from radiolysis of water, ensure the enhanced stability of polysulfone (Psf) membranes in the γ-radiation environment. In this study, the ROS scavenging ability of ceria was studied. Ceria nanoparticles were found to scavenge ROS like hydroxyl radicals and hydrogen peroxide (H2O2). The H2O2scavenging is due to the peroxidase-like catalytic activity of ceria nanoparticles. The ROS scavenging is responsible for offering protection to the Psf host matrix and in turn the stability to the Psf-ceria mixed-matrix membranes( MMMs) in γ-radiation environment. Thus, presence of ceria nanoparticles provides an opportunity for utilizing PsfceriaMMMsin ionizing radiation environment with increased life span, without compromise in the performance. © 2021 De Gruyter. All rights reserved.

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International Journal of Chemical Reactor Engineering

Kinetics studies on free radical scavenging property of ceria in polysulfone-ceria radiation resistant mixed-matrix membrane

Molecular dynamics simulations and complementary experiments are used to understand the inter- and intramolecular structures and conformational properties of ionenes (i.e., cationic polymers formed from condensation reactions) dissolved in an ionic liquid, 1-ethyl-3-methylimidazolium bistriflimide [C2mim+][Tf2N-]. The simulated structural properties are benchmarked against experimental analyses of these same polymers, mainly using dynamic light scattering experiments. Four different imidazolium ionenes are considered, corresponding to variations in the chemistry and structure of the repeat units including: (1) poly(decylimidazolium) (PD10); (2) poly(tetraethyleneglycolimidazolium) (PE10); (3) alternating copolymer (P(ED)5); and (4) a block copolymer (PE5D5). Detailed computational analyses of the polymer structure and conformational properties were performed, including the radius of gyration, end-to-end distance, torsional distributions, and site-site and spatial distribution functions. Overall, there is a competition between intramolecular associations between the imidazolium groups and the ether sites in the polymers versus the intermolecular interactions of the polymer imidazolium groups with the surrounding anion molecules. The polymer with only ether linkages (PE10) results in the most intramolecular interactions, leading to significant coiling behavior and chain contraction. These strong interactions reduce chain flexibility but they also result in much more linear chain configurations and alignment of the imidazolium groups. The polymer structure is strongly affected as the concentration of alkyl groups is increased, and we find that the polymer architecture (alternating vs block copolymer) also has an important influence. These detailed observations are important for understanding the connection between the molecular design of imidazolium polymers and their emergent structural properties, which could lead to unique opportunities for creating polymer composites. ©

Macromolecules

How Do Ionic Liquids "fold" Ionenes? Computational and Experimental Analysis of Imidazolium Polymers Based on Ether and Alkyl Chain Variations Dissolved in an Ionic Liquid

All-atom molecular dynamics simulations are used to understand the structural and thermodynamic behavior of water in a biphasic system composed of a brine solution in contact with two different amine-based solvents, diisopropylamine (DiPA) and tripropylamine. As compared to the bulk brine solution, the biphasic system leads to significant salt aggregation and crystallization, and this behavior is observed over a relatively broad range of temperatures, from 278 to 343 K. In general, there are stronger hydrogen bond interactions between DiPA and water, leading to more favorable solvation and reduced diffusion rates. Detailed analysis of the solvation behavior is provided by using thermodynamic integration to calculate the free energy of water solvation in different brine and solvent mixtures. This also indicates a stronger interaction of water with the DiPA solvent, and this occurs mainly via interactions of the oxygen atoms in water with the nitrogen atoms of the solvent molecules. Overall, the structural and thermodynamic analyses in this study provide a better molecular-level understanding of solvent-based desalination of high-salinity brines. © 2021 American Chemical Society.

Industrial and Engineering Chemistry Research

Molecular Simulation of High-Salinity Brines in Contact with Diisopropylamine and Tripropylamine Solvents

Here, we demonstrate a material design strategy to enhance the electrocatalytic activity for oxygen evolution reaction (OER) by repetitive charge/discharge supercapacitor cycling of Co3V2O8. The charge/discharge cycle helps to alter the electronic structure via stabilizing more active components on the surface and increases the electronic conductivity by increasing the oxygen vacancies. X-ray photoelectron spectroscopy and X-Ray Diffraction assists in identifying the chemical states and the structure of different components. The electrochemical techniques suggest that an increase in Co3+ on the surface with the available oxygen vacancies at 2500 charge/discharge cycled sample promotes intermediates like CoOOH, which help in decreasing the overpotential for the OER. We report specific current density with respect to the electrochemical surface area (ECSA), and our best sample shows a specific activity of ~6.2 µA/cm2ECSA with Tafel slope 85.12mV/dec. Further, the reaction mechanism and different interfacial resistances are identified with the help of electrochemical impedance spectroscopy. This study suggests that an optimum number of charge/discharge cycles are needed to balance the competing factors of electrocatalysts activation and decomposition of the active material. © 2020 Elsevier Ltd

Electrochimica Acta

Surface-enhanced OER activity in Co3V2O8 using cyclic charge-discharge to balance electrocatalytic active site generation and degradation

The present numerical work explores the fluid flow and heat transfer characteristics due to combined forced and natural convection in a tall lid-driven cavity containing uniformly heated equilateral triangular block. The flow is assumed to be steady, laminar, and two dimensional with incompressible non-Newtonian power-law fluids. The study is carried out to illustrate the convection behavior in tall cavities of different aspect ratios (AR = length / height = 0.25 , 0.5 , 0.75) at different Richardson numbers (Ri=0.1,1and10), non-Newtonian power-law index (0.6 ≤ n≤ 1.4) and Prandtl number (1 ≤ Pr ≤ 100) for a constant Grashof number of 104. The flow circulation is observed to be limited near the region of the moving wall irrespective of Richardson number for lower Pr. With the increase in the AR of the cavity, fluid–structure becomes more dispersed within the cavity. Higher heat transfer rates are obtained for the low AR (AR = 0.5). © 2020, Akadémiai Kiadó, Budapest, Hungary.

Journal of Thermal Analysis and Calorimetry

Mixed convection in a tall lid-driven cavity with a triangular heat source for non-Newtonian power-law fluids

The study of hydrodynamics and thermal characteristics inside a lid-driven cavity has been one of the most captivating problems in computational fluid dynamics. In this numerical work, the mixed convection phenomenon inside a two-dimensional, tall lid-driven cavity with top and bottom lids moving in opposite directions, +x and –x, respectively, has been explored for non-Newtonian power-law fluids. The cavity contains a uniformly heated equilateral triangular obstacle at its geometric center. Numerical experimentation is performed for a range of flow governing parameters, such as aspect ratio (0.25, 0.5, and 0.75), Prandtl number (1, 50, and 100) Richardson number (0.1, 1, and 10), power-law index (0.6–1.4) and Grashof number of 104. The physical perceptions of the cavity are explained by using streamline and isotherm contours. The fluid movement is limited adjacent to the moving wall concerning the Richardson number at the lower Prandtl number. With a rise in the aspect ratio of the cavity, the flow-pattern becomes more dispersed inside the cavity. Heat transfer enhancement is observed at a lower aspect ratio equal to 0.25. © 2021 Wiley Periodicals LLC

Heat Transfer

A numerical study of mixed convection in a two-sided lid-driven tall cavity containing a heated triangular block for non-Newtonian power-law fluids

Understanding the molecular-level organization of anions and cations in a mixture of different ionic liquids (ILs) is challenging, but it can be very important for designing solvents and IL-based membrane materials. Here, we perform all-atom molecular dynamics (MD) simulations to understand the intermolecular interactions and structuring of both neat and mixed IL compositions containing 1-benzyl-3-methylimidazolium [ZMIM+], 1-butyl-3-methylimidazolium [BMIM+], bistriflimide [Tf2N−], and tetrafluoroborate [BF4−]. We observe very strong underlying molecular-level migrations in these mixtures, and this tends to mainly involve the anion species. As compared to the systems with a single anion, the mixed anions lead to large increases/decreases in the radial distribution function peak heights, whereas the cation mixing is relatively benign. The [BF4−] anions have a strong tendency to displace the [Tf2N−] anions in the mixtures, and this is seen with respect to both [BMIM+] and [ZMIM+]. © 2020 Elsevier Ltd