The removal percentages of Br

The removal percentages of Br.G, To.B and Tr.B were plotted against the solution temperature (Fig. 3a). It is very obvious that temperature has little effect on the adsorption of Br.G except at temperature 59°C there is a slight decrease from 100% to 99% at 76°C, on the contrary for Tr.B and To.B by increasing temperature, the removal percentage of those dyes decrease. The [email protected] will be more efficient for removal of Br.G from hot wastewater industries. For Br.G, elevation of temperature makes increasing for the mobility of the large dye ions. Furthermore, increasing the temperature may produce a swelling effect within the internal structure of [email protected] enabling the large dyes to penetrate further (Mckay et el., 1982), so it makes a change for pore-geometry of the sorbent. In Tr.B which has a higher molecular weight than others, so it cannot enter the pores of the sorbent.
Thermodynamic behavior of sorption of Br.G, Tr.B and To.B dyes on [email protected] was studied and thermodynamic parameters were calculated using the following equations:
(12)
(13)
Where Kc is the equilibrium constant of adsorption, T is the temperature (K) and R is the gas constant. Plots of ln K versus 1/T were linear (R2 = 0.753, 0.929 and 0.953) and the numerical values of enthalpy (?H°) and entropy (?S°) were obtained from the slope and the intercept (Fig.3b). For extraction of Br.G, Tr.B and To.B dyes, respectively. The values of thermodynamic parameters are presented in Table 6. The change in free energy (?G) can be calculated from the relation:. Negative values of ?G° represent spontaneous adsorption process and exothermic in nature. Decreasing negativity of (?G°) values indicate that movement of molecules is less freedom and adsorption process is less spontaneous (Dahri et el., 2017) with increase temperature as in adsorption of To.B and Tr.B. also having ?G° between ( means adsorption of Br.G, To.B and Tr.B onto [email protected] is a physisorption process (Chieng et el., 2015) . Positive value of ?H° (56.06 KJ/mol) indicate that the reaction is endothermic for Br.G only, besides its values higher than 8 KJ/mol means adsorption of Br.G is a physisorption type (Nandi et el., 2009; Rehman et el., 2013).This theory supported by increasing of amount of dye adsorbed by increasing temperature and this totally different from To.B and Tr.B which have (?H°=-0.077 and -14.84 KJ/mol) means that the reaction is exothermic as with increasing temperature amount of dyes adsorbed decrease. ?S° values were negative in To.B and Tr.B (?S°=-0.04,-31.8 KJ/mol K) means To.B more restricted to the surface than Tr.B (decrease randomness) compared to a positive value in Br.G (?S°= 0.21KJ/mol K) means the increasing of randomness at the interface between solid and solution (increase freedom of adsorbed species) (Purkait et el., 2007; Selvam et el., 2008).