4.8 kinetics Studies on the methylene blue
To study the removal behavior of dye and the degradation mechanism and rate of its removal from first- and second-rate kinetic equation and intramolecular infiltration was used to analyze the obtained data. Initially, different kinds of magnetic metal-organic framework nanocomposites synthesized with different weight percentages at different concentrations were studied. Then the magnetic metal-organic framework with higher removal efficiency was studied.
Kinetic of methylene blue dye degradation by magnetic metal-organic framework nanocomposites synthesized by weight percentages (30 and 50) was investigated and calculated and the methylene blue adsorption kinetics were investigated at different concentrations of solution (Fig 20). Initially, the methylene blue degradation kinetics on metal-organic framework nanocomposites was calculated using pseudo-first-order kinetic having the following formula.
Ln (qe - qt) = Ln qe – K1t
Where qe is the equilibrium adsorption (mg.g-1) and qt is adsorbed at different times (mg.g-1) and k1 is the constant rate of absorption (min-1) and t represents time. In the second step, the adsorption kinetics was calculated using the pseudo-second-order equation which has the following formula:
t/q = 1/K2 qe 2 + t/qe
Which, like the above equation K2, is the rate of absorption constant (min-1). The intramolecular diffusion kinetic method was used to study the third kinetic, which can also be used to investigate the kinetic and compared the amount of dye penetrating into the nanocomposite molecules. The following equation was used for the intramolecular diffusion method:
qe = Kp t1/2 + I
Where KP is the rate of diffusion within the molecule. Finally, by comparing these three kinetic models, it can be estimated which kinetic nickel-ferrous magnetic metal-organic nanocomposites in the silica substrate follow and calculated its absorption rate [64-70].
Fig (20): Examination of different kinetic types for methylene blue degradation with different nanocomposites a) The pseudo-first-order kinetics b) pseudo-second-order kinetic c) kinetic of intramolecular penetration
The pseudo-second-order kinetic model fits better than the other two models for synthesized metalorganic framework nanocomposites because as calculated from the above relation, the coefficient of determination R2 for the pseudo-second-order model is calculated and all coefficients are very close to one. Whereas the two pseudo-first-order models and the intramolecular diffusion are more distant than the second-order ones. Therefore, it can be concluded that the methylene blue dye kinetic using a variety of synthesized nanocomposites follows the pseudo-second-order kinetic. On the other hand, the amount of (qe)cel obtained from the above equations in the pseudo-second-order kinetic model is much closer to the empirical value of (qe)ex Table 4 presents the values of the coefficient of determination R2, as well as the rate of degradation and the amount of degradation for each of the three kinetic models given. Table 4 data obtained from the calculation of different kinetic models for different types of synthesized nanocomposites.
Table (4): Values of the coefficient of determination R2 and rate of degradation and the amount of degradation for each of the three kinetic models given.