Estimating the Adsorption Thermodynamics of a Toxic Pollutant by Activated Carbon Coated with Superparamagnetic Nanoparticles Using Isothermal Titration Calorimetry

Abstract

In the present work, the thermodynamic parameters for the adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D), a herbicide, onto biomass-based activated carbon coated with magnetite nanoparticles (ACM) were estimated using a high-precision isothermal titration calorimeter (ITC). The obtained thermodynamic parameters, such as change in Gibb’s free energy (ΔG), change in enthalpy (ΔH), and change in entropy (ΔS), were compared with the values computed applying conventional methods using equilibrium isotherm model parameters. The thermodynamic parameters suggested that the adsorption of 2,4-D onto ACM was spontaneous and exothermic. ITC proved to be an efficient experimental method in determining the thermodynamic parameters for the adsorption process with minimal adsorbent, adsorbate, and time consumption. The application of ITC can also be extended to determine the thermodynamic parameters of various solid–liquid interactions involved in different processes. The 2,4-dichlorophenoxyacetic acid (2,4-D) is commonly used as a herbicide, and its occurrence is reported widely in aquatic bodies. Adsorption process using activated carbon impregnated with iron nanoparticles proved to be effective in removing these 2,4-D from the aquatic phase. In general, adsorption dynamics are demonstrated by isotherm, kinetics, and thermodynamic studies so that it can be extended to real-world applications. Conventionally, adsorption thermodynamic parameters are estimated from equilibrium isotherm constants. However, the determination of these parameters using the isotherm constants may not be accurate. Hence, sophisticated equipment such as isothermal titration calorimeter (ITC) can be used as an efficient tool to accurately compute the thermodynamic parameters in less time with minimal requirement of reagents.