*3.5. Sorption Thermodynamics*

To estimate the thermodynamic action of the CIP and LEV adsorbed onto the Fe– Cu/Alg–LS nanocomposite, the thermodynamic factors were assessed in order to determine the thermodynamic viability and spontaneous nature of the process of adsorption. At varied temperatures (30, 40, and 60 ◦C), the findings were recorded. The formulae listed below were used to calculate the thermodynamic factors [56,57]:

$$
\Delta \mathbf{G}^{\odot} = -\mathbf{R} \mathbf{T} \ln \mathbf{K}\_{\mathbf{d}} \tag{11}
$$

$$
\Delta \mathbf{G}^{\diamond} = \Delta \mathbf{H}^{\diamond} - \mathbf{T} \Delta \mathbf{S}^{\diamond} \tag{12}
$$

$$
\ln \mathbf{K\_d} = -\Delta \mathbf{H^\diamond} / \mathbf{RT} + \Delta \mathbf{S^\diamond} / \mathbf{R} \tag{13}
$$

where T is the absolute temperature (K), Kd is the distribution coefficient, and R is the gas constant (8.314 J mol−<sup>1</sup> K−1). Using Equation (11), the Gibbs free energy was calculated. Furthermore, using Equation (12), G◦ might be calculated from H. Using Equation (13), the thermodynamic variables S◦ and H◦ were calculated (from the intercept and slope). The data showed that the amount of CIP and LEV ions taken up by nanocomposites slightly decreased in direct proportion to the temperature increase. In contrast to the adsorbent particles, the rise in degree of temperature increased the pollutants' solubility in a bulk solution to a larger extent [58]. Table 5 illustrates the Fe–Cu/Alg–LS nanocomposite components' thermodynamic sorption response to CIP and LEV ions.


**Table 5.** Thermodynamic conditions using 0.2 g/25 mL of the nanocomposite at pH 6 for CIP (10 ppm) and 7 for LEV (20 ppm), with contact times of 40 min and 45 min for CIP and LEV, respectively.

Negative G◦ show that the adsorption process is feasible and spontaneous. Additionally, negative findings of H◦ also suggest that LEV was adsorbed onto the Fe–Cu/Alg–LS nanocomposite in an exothermic manner. Positive readings of H◦ show that CIP was adsorbed endothermically. Given how CIP and LEV adsorbed onto the surfaces of the adsorbents, negative S◦ for the Fe–Cu/Alg–LS adsorbent demonstrated that randomness declined at the solid–liquid interfaces, demonstrating that the adsorption was energetically stable [59]. For G◦ values under 80 kJ mol−1, the sorption was of a physical origin. However, if G◦ was between 80 and 400 kJ mol−1, it might have been chemical [60]. Table 4 shows the "G" values, which show that CIP and LEV sorption were of a physical origin. These results support the D-R isotherm.
