where kc is the equilibrium constant, Cs is the equilibrium
concentration on the adsorbent and Ce is the equilibrium concentration
of dye in the solution. R is the universal gas constant
(8.314 J mol−1 K−1), and T is the absolute temperature. The values
of G◦ and H◦ are obtained from the slope and intercept by plotting
ln kc versus 1/T. The thermodynamic parameters are listed in
Table 3. The negative value of G◦ indicates the spontaneity and
feasibility of the sorption of RR228 on the adsorbent. The negative
value of H◦ reflects that the sorption is exothermic in nature. The
negative value of S◦ shows that a decrease in randomness occurs
at the interface during the sorption process. The results indicate
that the adsorption capacity decreases with increasing temperature;
therefore, lower temperature is favorable to the adsorption.