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Adsorption Kinetics of WS2 Quantum Dots onto a Polycrystalline Gold Surface.

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Title: Adsorption Kinetics of WS2 Quantum Dots onto a Polycrystalline Gold Surface.
Authors: Valappil, Manila Ozhukil1,2, Alwarappan, Subbiah1,2, Pillai, Vijayamohanan K.1,2, Roopesh, Mekkat3
Source: Langmuir. 5/15/2018, Vol. 34 Issue 19, p5474-5380. 7p.
Subjects: Adsorption kinetics, Tungsten compounds, Quantum dots, Langmuir isotherms, Thermodynamics
Abstract: In this work, we report the adsorption kinetics of electrochemically synthesized WS2 quantum dots (QDs) (ca. 3 nm) onto a polycrystalline gold electrode. The Langmuir adsorption isotherm approach was employed to explore the temperature and adsorbate concentration dependence of the experimentally calculated equilibrium constant of adsorption (Keq) and the free energy for adsorption (ΔGads). Subsequently, we extract other thermodynamic parameters, such as adsorption rate constant (Kads), desorption rate constant (Kd), the enthalpy of adsorption (ΔHads), and the entropy of adsorption (ΔSads). Our findings indicate that ΔGads is temperature-dependent and ca. -7.64 ± 0.6 kJ/mol, ΔHads = -43.72 ± 1.7 kJ/mol, and ΔSads = -0.126 ± 0.017 kJ/(mol K). These investigations on the contribution of the enthalpic and entropic forces to the total free energy of this system underscore the role of entropic forces on the stability of the WS2 QDs monolayer and provide new thermodynamic insights into other transition-metal dichalcogenide quantum dot (TMDQD) monolayers as well. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:In this work, we report the adsorption kinetics of electrochemically synthesized WS2 quantum dots (QDs) (ca. 3 nm) onto a polycrystalline gold electrode. The Langmuir adsorption isotherm approach was employed to explore the temperature and adsorbate concentration dependence of the experimentally calculated equilibrium constant of adsorption (Keq) and the free energy for adsorption (ΔGads). Subsequently, we extract other thermodynamic parameters, such as adsorption rate constant (Kads), desorption rate constant (Kd), the enthalpy of adsorption (ΔHads), and the entropy of adsorption (ΔSads). Our findings indicate that ΔGads is temperature-dependent and ca. -7.64 ± 0.6 kJ/mol, ΔHads = -43.72 ± 1.7 kJ/mol, and ΔSads = -0.126 ± 0.017 kJ/(mol K). These investigations on the contribution of the enthalpic and entropic forces to the total free energy of this system underscore the role of entropic forces on the stability of the WS2 QDs monolayer and provide new thermodynamic insights into other transition-metal dichalcogenide quantum dot (TMDQD) monolayers as well. [ABSTRACT FROM AUTHOR]
ISSN:07437463
DOI:10.1021/acs.langmuir.7b03321