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.