## 3 Results and Discussion
### Adsorption of Reactive Orange 16 (RO 16) as an Indicator for Fabric Sorption Properties
#### 3.3.4 Thermodynamic Studies  
It is well known that thermodynamic experiments are important for probing the nature and mechanism of dye adsorption [48], hence, the impact of different temperatures (25, 35, 45, and 55 \({}^{\circ}\)C) on RO 16 adsorption onto investigated fabrics was examined. The data shown in Figure 10 point out that temperature has two different effects on the \(q\) of fabrics. Namely, with increasing the temperature from 25 to 55 \({}^{\circ}\)C, \(q\) of J, J.05% CS, and J1.0% CS decreased by about 46, 43, and 39%, respectively. It has been reported that an increase in the temperature beyond an optimum value can lead to the breakdown of weak interaction forces that are involved in the adsorption of the dye onto the adsorbent surface [45]. Interestingly, an inverse relationship between temperature and RO 16 adsorption onto J2.0% CS was observed. A significant increase (156%) in the \(q\) of J2.0% CS with increasing temperature was visible in Figure 10. Similar conclusions were recently drawn by [PERSON] et al. [45] and [PERSON] et al. [30] for the adsorption of RO 16 onto sunflower hairy roots, and lignocellulosic biomass waste supported with FeCl\({}_{3}\)/Zn(NO\({}_{3}\))\({}_{2}\), respectively. The data shown in Figure 10 were used for the calculation of the main thermodynamic parameters that were employed to determine the feasibility, spontaneity, and nature of the adsorption process by means of Gibbs free energy (\(\Delta G^{\circ}\)), enthalpy (\(\Delta H^{\circ}\)), and entropy (\(\Delta S^{\circ}\)), respectively. The values of the calculated thermodynamic parameters are summarized in Table 3. The obtained negative values for \(\Delta G^{\circ}\) proposed that, in the studied temperature range, the process under examination is spontaneous and thermodynamically feasible [51]. Moreover, the \(\Delta G^{\circ}\) values ranged between -20 and 0 kJ/mol, confirming the weak and physical nature of the interactions between fabrics and RO 16 [52]. In the case of the RO 16 adsorption onto J, J0.5% CS, and J1.0% CS, the process is exothermic, i.e., thermodynamically favored at lower temperatures (as already observed in Figure 10) and enthalpy driven since the negative \(\Delta H^{\circ}\) and \(\Delta S^{\circ}\) values were obtained, Table 3. Gradual increase of \(\Delta G^{\circ}\) value with an increase in the temperature from 298.15 to 328.15 K supports the dominant bonding between RO 16 and J, J0.5% CS, and J1.0% CS as was previously  
Figure 10: The influence of temperature (\(T\)) on the adsorption potential (\(q\)) of examined fabrics (\(c_{0}=100\) mg/L, \(t=21\) h, \(T=25\), 35, 45, or 55 \({}^{\circ}\)C, pH of 2.0 (for J, J0.5% CS, and J1.0% CS) and 4.0 (for J2.0% CS), the mass of adsorbent 0.25 g). proven by the Langmuir model [34]. Contrary to the above-discussed, the positive \(\Delta H^{\circ}\) and \(\Delta S^{\circ}\) values obtained for J2.0% CS evidenced that the adsorption of RO 16 onto this fabric is of endothermic character and some structurally-based dye-fabric complexes during the adsorption process coupled by an increased state of randomness at the solid/liquid interface [29]. According to [PERSON] et al. [32], the positive entropy reflects the release of high amounts of water molecules due to the sorption of large hydrated dye anions onto an adsorbent. The key to different RO 16 adsorption behavior depending on temperature lies in the different nature of binding mechanisms of J, J0.5% and J1.0% compared to J2.0% CS. In the case of the RO 16 adsorption onto J, J0.5% CS, and J1.0% CS, electrostatic interactions represent the main driving force for the adsorption, hence the positive charge of the fabric surface is neutralized through the interaction with negative moieties of the dye molecules.