Department of Chemical Engineering

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IIT Jodhpur

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

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

Chemical Engineering Science

Molecular-level behavior of imidazolium-based ionic liquid mixtures

Evolution in material centric devices like batteries and electrocatalytic reactors have predominantly been made possible via the exploitation of the thermodynamic ground state of pristine or defective bulk crystal, referred to as the “Native polymorph” (NP) here. A significant increase in the material search space is possible by utilizing “Non-Native polymorphs (NNP),” which are materials that have different translational symmetry with respect to NP. As the NNP have a distinct coordination structure from that of the NP, critical material properties can be anticipated to be different, making NNP a potential substitute material for the aforementioned applications, which are the focus of this review. To obtain a structure–function relationship, systematic approaches to the synthesis of NNP has been demonstrated. Following certain generalities behind NNP, we classify synthesis techniques into few categories with the hope of rationalizing the underlying mechanism of these synthesis and stabilization strategies. We discuss the utility of NNPs in the context of electrochemical water electrocatalytic reactions. Typically, the NNPs have more open volume space enabling lower lithium-ion diffusion barrier, higher lithium-ion binding energies, thereby making NNP efficient in the context of energy storage material. However, NNP have lesser stability than the NP and methods to calibrate and improve the stability of NNP are important. Overall, the discussion of polymorphic materials by demarcating them as NP and NNP provides a systematic approach towards modulating material properties as a trade-off between thermodynamics and kinetics of physicochemical processes. Finally, the challenges and perspectives in this emerging field are discussed. This article is categorized under: Fuel Cells and Hydrogen > Science and Materials Energy Research & Innovation > Science and Materials Energy and Development > Science and Materials. © 2020 Wiley Periodicals LLC

Wiley Interdisciplinary Reviews: Energy and Environment

Stabilization of non-native polymorphs for electrocatalysis and energy storage systems

US Patent App. 17/059,242

System and method facilitating decision making for disinfectant dosing in water in water distribution networks

We explore the effect of sulfur doping in Co3V2O8 on the electrochemical performance of supercapacitors in terms of enhanced lattice spacing, electrochemical surface area (ECSA), electronic conductivity, and density of states. The sulfur-doped Co3V2O8 (S-Co3V2O8) nanosheets were grown in situ as a binder-free synthesis on nickel foam by the hydrothermal method. The electrochemical performance was analyzed in an aqueous alkaline electrolyte where the S-Co3V2O8 electrode exhibited a specific capacity of 410 mAh/g at 2 A/g with enhanced rate capability and capacity retention of 94.2% at 5 A/g specific currents after 4000 cycles, whereas the undoped Co3V2O8 electrode exhibited a specific capacity of 337.8 mAh/g at 2 A/g. The high capacity of S-Co3V2O8 is attributed to the enhanced ECSA (by ∼45%) and improved electrical conductivity (by ∼22%) upon doping with sulfur. Furthermore, these results corroborated with density functional theory results. The calculations suggest an increase in lattice parameters and the introduction of additional density of states near the valence-band edge due to the doping of sulfur, resulting in a decrease in charge-transfer resistance. An asymmetric supercapacitor was fabricated, using S-Co3V2O8 nanosheets as the cathode and activated carbon as the anode, which shows a high specific capacity (or capacitance) value of 485 mAh/g, an energy density of 36.4 W h/kg, and a power density of 740 W/kg at 2 A/g with 98.4% specific capacity retention after 4000 consecutive charge-discharge cycles. Furthermore, the analysis was extended in a nonaqueous medium for Li-ion storage where S-Co3V2O8 exhibits a specific capacity of 994 mA h/g and a specific energy density of 828 W h/kg at 1 A/g making it a promising candidate for future high-energy storage systems. The concept of doping is extended to other chalcogenide (e.g., selenium) doping (Se-Co3V2O8), which also shows improved device performance and makes this a versatile approach for high-performance devices. ©

ACS Applied Energy Materials

Chalcogenide Dopant-Induced Lattice Expansion in Cobalt Vanadium Oxide Nanosheets for Enhanced Supercapacitor Performance

The aldol condensation of acetaldehyde with other carbonyl molecules is a complex reaction wherein there is often formation of multiple undesirable side products. These side products include higher oligomers, which not only reduce the selectivity for the main product but also prevent the use of heterogeneous catalysts due to rapid deactivation. 3-Methylpent-3-en-2-one (MPO) is an important fine chemical used as a key intermediate in the fragrance and flavor industry and is produced by the aldol condensation of acetaldehyde (AcH) with methyl ethyl ketone (MEK). In this work, we investigate the continuous production of MPO in the presence of a cation exchange resin (Amberlyst-15) in a fixed-bed reactor. Our earlier work on batch kinetics reveals that a higher feed molar ratio of AcH:MEK results in a higher yield of MPO. Accordingly, reactions are performed in a laboratory fixed-bed reactor at different feed molar ratios, reaction temperatures, and residence times. The effect of side injection of acetaldehyde into the flow reactor was also investigated and found to favorably influence the selectivity toward MPO. A crucial observation was that maintaining a low concentration of acetaldehyde helps in reducing catalyst deactivation and hence extends its life. Based on the results obtained in the lab-scale reactor, MPO was successfully produced in the pilot-scale fixed-bed reactor by performing the reaction for an extended duration (570 h), indicating that the catalyst is sufficiently active under the conditions of interest without loss of activity. The intrinsic kinetic model developed earlier using the batch reactor data is incorporated in the fixed-bed reactor model and it was found that the predictions agree reasonably well with the experimental results. © 2021 American Chemical Society