Department of Chemical Engineering

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Author: search.filters.author.Garg, MohitSubject: search.filters.subject.Chemical Engineering

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Now showing 1 - 10 of 12
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    Novel Fe-doped TiO2 metal-organic framework for electrocatalytic hydrogen evolution reaction
    (Elsevier, 2024-07) Chatterjee, Somak; Pande, Surojit; Garg, Mohit
    A novel approach has been adopted to synthesize titanium oxide-based metal organic framework (MOF), which was doped with iron to increase its efficiency in hydrogen evolution reaction. Scanning electron microscopic images reveal the structure of bare titanium dioxide-based MOF as smooth and aggregated, while doping with iron renders a rough and irregular structure. Mineral phases of ferro-pseudobrookite, anatase, rutile and brookite were prevalent in the doped powder. The presence of iron and titanium in its structure is further confirmed by the deconvoluted spectra from x-ray photoelectron spectroscopy. 0.1 (M) iron doped powder showed an excellent current density of 10 mA/cm2 at an onset potential of 0.345 V, in a three-electrode system. Additionally, its Tafel slope value is 129.6 mV/dec, when compared to the undoped form (168.8 mV/dec), indicating the faster kinetics. Hydrogen evolution reaction is guided by Volmer-Heyrovsky pathway. Electrochemical active surface area of bare MOF powder is 0.62 cm2 while that for 0.1 (M) doped MOF powder is 0.965 cm2. This powder shows extremely good stability and retains its structural integrity even after 1000 linear sweep voltammetry cycles. Density functional theory calculations revealed an increase in the adsorption energy of water molecules attachment in the presence of iron, suggesting an enhanced HER activity.
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    Improving morphology of P3HT:PCBM bulk heterojunction solar cells with anisotropic shaped silica nanoparticles
    (Elsevier, 2023) Ghosh, Sarbani; Garg, Mohit
    Using coarse-grained molecular dynamics simulations we study blends of Poly(3-hexylthiophene-2,5-diyl) (P3HT), [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) and Silica nanoparticle (SiNP) to understand the effect of adding SiNP on morphology of P3HT:PCBM in Bulk heterojunction (BHJ) solar cells. We use an approximately 3 nm anisotropic shaped SiNP and predicted the morphology of BHJ upon its incorporation. The SiNP arrange themselves into anisotropic structures depending on the concentration of P3HT, PCBM and SiNP respectively creating a network like morphology. PCBM molecules utilize the surface energy of SiNP and gather at its surface forming a morphology which is beneficial for device efficiency. Our results suggest that an optimum weight fraction of all the three components leads to higher surface area of contact, optimum domain size and high percolation of domains throughout the system. The effective control of all the morphological parameters help in improving the charge generation, extraction and transport to electrodes, thereby improving the performance of BHJ solar cells.
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    Microscopic Insights of Electrochemical Switching of Poly(benzimidazobenzophenanthroline) (BBL) Thin Film: A Molecular Dynamics Study
    (ACS, 2009-04) Sarbani, Ghosh; Garg, Mohit
    Carbon nanotubes typically require the use of a dispersing or stabilizing agent to prevent significant aggregation during incorporation into a polymer matrix. These additives must be strongly associated, either covalently or physically, to achieve their purpose. In this study, multi-walled carbon nanotubes (MWNTs) were dispersed into an epoxy matrix using polyethylenimine (PEI) as a dispersant that was either covalently attached to the nanotubes or physically mixed to result in only noncovalent interaction. Epoxy composites containing covalently modified MWNTs exhibited greater storage modulus and reduced electrical conductivity.
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    Electrocoagulation Influencing Parameters Investigation on Reactive Dyes in Textile Wastewater
    (CRC Press, 2021) Garg, Mohit
    Textile industry discharges lot of waste into the water body in terms of high color, dissolved organic and inorganic salt which causes serious concern to the environment. The present chapter reports experimental study on electrocoagulation (EC) process to remove color and chemical oxygen demand (COD) from a real textile waste water obtained from dyeing cotton fiber industries consisting reactive dye. A batch of experimental studies have been performed and effect of various operating parameters such as, contact time (t: 0–150 min), initial pH (pH0: 4–10), current density (j: 20–80 mA/cm2) and electrode spacing (z: 0.5–1.5 cm) on color and COD removal efficiency have been studied. The results indicate that pH of the solution significantly influences the removal efficiency in terms of COD and does not have significant effect on color removal efficiency. High current density and minimum distance between two electrodes favors the process. The scum and sludge are produced during color removal. The treatment of waste water for removal of color and COD together with proposed cost-effective method is useful for many industrial applications.
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    Ion Diffusion through Nanocellulose Membranes: Molecular Dynamics Study
    (ACS, 2021-12) Garg, Mohit
    One of the most promising applications of nanocellulose is for membranes for energy storage devices including supercapacitors, batteries, and fuel cells. Several recent studies reported the fabrication of cellulose-based membranes where ionic conductivity was confined to channels. So far, theoretical understanding of the effect of the nanoconfinement and surface charged groups on the diffusion coefficient of ions in cellulose nanochannels is missing. In the present study, we perform atomistic molecular dynamics simulations to provide this theoretical understanding and unravel mechanisms affecting the ionic diffusion in nanochannels. We demonstrate that the diffusion coefficient of ions in cellulose nanochannels is reduced in comparison to its bulk value. The change of the diffusion coefficient depends on the density of charged surface groups in nanochannels and the channel height, and it is primarily caused by the Coulomb interaction between the ions and the surface. We believe that our results reveal an important structure/property relationship in cellulose nanochannels, and they show that accounting for the dependence of the diffusion coefficient on the charge of the surface groups and channel height can be important for the Nernst–Plank–Poisson modeling of the ion conductivity in nanomembranes as well as for accurate fitting the experimental data to extract the material parameters.
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    Moisture uptake in nanocellulose: the effects of relative humidity, temperature and degree of crystallinity
    (Institute for Metals Superplasticity Problems, 2021-08) Garg, Mohit; Ghosh, Sarbani
    Hydrogen has the potential to be an alternative source of energy. However, most of the research on hydrogen storage carried out in the past is based on low temperature (<80 K) whereas storage near room temperature is desired. Here, we report room-temperature hydrogen storage capacity of defective single-walled carbon nanotubes (SWCNT) investigated using molecular dynamics simulations and density functional theory. Four different types of defective SWCNTs are considered to study room temperature hydrogen storage. We observed maximum adsorption capacity of SWCNT with 5 and 8-membered ring defects, namely, D1. The SWCNT with other three defects studied here, Stone-Wales with 5- and 7-membered ring defect (D2), 5-membered ring defect (D3), and 3-, 5- and 8-membered ring defect (D4) have negative adsorption effect compared to the defect-free SWCNT. The highest gravimetric capacity of 1.82 wt.% is found for the D1 defective SWCNT at room temperature, 298 K and 140 atm. The DFT calculations show that hydrogen adsorption strongly depends on the type of defect where the 8-membered ring has the highest adsorption energy and the 3-membered ring has the lowest adsorption energy. A combination of 5- and 8-membered defective rings can increase hydrogen adsorption significantly even at room temperature.
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    Humidity-Dependent Thermal Boundary Conductance Controls Heat Transport of Super-Insulating Nanofibrillar Foams
    (Elsevier, 2021-01) Garg, Mohit
    Cellulose nanomaterial (CNM)-based foams and aerogels with thermal conductivities substantially below the value for air attract significant interest as super-insulating materials in energy-efficient green buildings. However, the moisture dependence of the thermal conductivity of hygroscopic CNM-based materials is poorly understood, and the importance of phonon scattering in nanofibrillar foams remains unexplored. Here, we show that the thermal conductivity perpendicular to the aligned nanofibrils in super-insulating ice-templated nanocellulose foams is lower for thinner fibrils and depends strongly on relative humidity (RH), with the lowest thermal conductivity (14 mW m−1 K−1) attained at 35% RH. Molecular simulations show that the thermal boundary conductance is reduced by the moisture-uptake-controlled increase of the fibril-fibril separation distance and increased by the replacement of air with water in the foam walls. Controlling the heat transport of hygroscopic super-insulating nanofibrillar foams by moisture uptake and release is of potential interest in packaging and building applications.
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    Theoretical Rationalization of Self-Assembly of Cellulose Nanocrystals: Effect of Surface Modifications and Counterions
    (ACS, 2020-07) Garg, Mohit
    The hierarchical self-assembly of cellulose nanocrystals (CNCs) is an important phenomenon occurring naturally in plant cell walls. Utilization of this assembly for advanced applications requires a fundamental theoretical understanding of interactions between the CNCs, which is still incomplete. Hence, in this work, we used molecular dynamics simulations to study the effect of surface modification on the interactions between the CNCs and the resulting bundling process. We consider two types of common surface modifications of native CNCs, sulfated CNCs (SCNCs) and TEMPO-oxidized CNCs (TCNCs), in the presence of two types of counterions, Na+ and Ca2+, in solution. We used the umbrella sampling method to calculate the potential of the mean force (PMF), and we found that the strength of interaction between the modified CNCs decreases, compared with the native CNCs. The strength of interaction for TCNCs is almost similar to that for SCNCs at the same level of surface substitution, whereas the type of counterion has a strong effect on the PMF with a higher interaction energy between the CNCs in the presence of a divalent counterion as compared to a monovalent counterion. Finally, we studied the self-assembly of CNCs into a hexagonal bundle for the native CNCs and sulfated CNCs focusing on the twist of the bundle, bound water inside the bundle, inter-CNC gap, and interaction energy between the CNCs in the bundle, and the effect of the counterions on the morphology of the bundle. The equilibrium spacing of the CNCs within the bundle is found to be consistent with the results of PMF calculations for the minimum separation distance between the respective crystal surfaces.
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    New Patchy Particle Model with Anisotropic Patches for Molecular Dynamics Simulations: Application to a Coarse-Grained Model of Cellulose Nanocrystal
    (ACS, 2020-05) Garg, Mohit
    Self-assembly is ubiquitous in nature and underlies the formation of many complex systems from the molecular to the macroscopic scale. Kern–Frenkel-like patchy particles are powerful models to investigate this phenomenon by computational methods such as Monte Carlo or molecular dynamics simulations. However, in these models the interactions are mediated by circular patches at the particle surface, which can be hardly mapped to realistic systems, containing for instance faceted particles with rectangular surfaces. In this paper we extend the model to take into account such geometries, and we use it to build a supra coarse-grained model of the cellulose nanocrystal where the interactions are parametrized against all-atomistic molecular dynamics simulations. The formation of cholesteric ribbons and defects in cholesteric droplets of the cellulose nanocrystal are investigated and confirm experimental behavior reported in the literature. The flexibility of this new patchy particle model makes it a powerful tool to develop supra coarse-grained models of self-assembly for large space and time scales and should find a broad range of applications for self-assembly in chemical and biological systems.
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    A novel supra coarse-grained model for cellulose
    (Springer, 2020-03) Garg, Mohit
    Cellulose being the most widely available biopolymer on Earth is attracting significant interest from the industry and research communities. While molecular simulations can be used to understand fundamental aspects of cellulose nanocrystal self-assembly, a model that can perform on the experimental scale is currently missing. In our study we develop a supra coarse-grained (sCG) model of cellulose nanocrystal which aims to bridge the gap between molecular simulations and experiments. The sCG model is based on atomistic molecular dynamics simulations and it is developed with the force-matching coarse-graining procedure. The validity of the model is shown through comparison with experimental and simulation results of the elastic modulus, self-diffusion coefficients and cellulose fiber twisting angle. We also present two representative case studies, self-assembly of nanocrystal during solvent evaporation and simulation of a chiral nematic phase ordering. Finally, we discuss possible future applications for our model.