2.5 Investigation and study of the curcumin absorption process
To investigate the process of absorption of curcumin solution on the
synthesized adsorbents, 100 ml of the curcumin solution was taken as a
sample and the adsorbent was added to it and placed on the shaker at
room temperature for 2 hours. After a while, the sample was taken and
centrifuged for better separation. The concentration of curcumin
solution in the samples taken at different times and were measured using
a UV light spectrometer.
Finally, using equation (1), the absorption percentage of curcumin
solution and using equation (2), the adsorption capacity of the
synthesized magnetic metal-organic framework nanocomposite was
calculated and determined.
%Adsorption= (C0 - Ct /
C0)*100 (1)
qt = (C0-Ct) V/m (2)
Where C0 and Ct are the initial
concentration of curcumin solution and the concentration of curcumin
solution at time t respectively, V is the volumes of curcumin solution
per liter, m the amount of adsorbent (gr) and qt are the
adsorption capacity of the magnetic metal-organic framework
nanocomposite in terms of (mg.g-1) [26-29].
Finally, the effect of parameters such as adsorbent dose, adsorbent type
and concentration of curcumin solution on the adsorption of curcumin
solution by synthesized magnetic metal-organic framework nanocomposites
was studied.
To investigate the behavior of the synthesized adsorbent, the
relationship between the absorbing sample and the adsorbent surface and
sample interaction with the adsorbent requires the equations that are
used to investigate this adsorption behavior. There are several ways to
look at absorption isotherms. These isotherms include the Langmuir,
Freundlich and the Temkin. In this study, two isotherms of Langmuir and
Freundlich with the following equations have been used to investigate
the ruling isotherm to the absorption process [29-31].
The Langmuir adsorption isotherm model is examined and calculated with
Equation 3 and its variables are presented in Table 6. The Langmuir
adsorption isotherm is based on the single-layer adsorption of the
adsorbent, which here is the curcumin solution, on the adsorbent
surface, indicating that no reaction occurs between the absorbed sample
and adsorbent molecules.
Ce/qe = 1/KL.
qL + Ce/qL (3)
In this equation, Ce is the concentration of curcumin
solution at equilibrium (mg.l-1), qeis the amount of material absorbed per unit mass of the adsorbent,
qL the maximum absorption capacity is synthesized on the
nanocomposites of the magnetic metal-organic framework, and
KL is the Langmuir constant which refers to the energy
of absorption.
The Freundlich isotherm model is examined and calculated with Equation 4
and its variables are presented in Table 6. Frondelich adsorption
isotherm is synthesized on the adsorbent based on multi-layered and
heterogeneous adsorption of the adsorbent. The closer value of 1/n to
zero showing more heterogeneous absorption and if the value is
0.1>1/ n> 1, the absorption process is optimal
[32].
Ln qe = Ln KF + (1/nF)
Ln Ce (4)
In the above relation Ce the concentration of curcumin
solution at equilibrium (mg.l-1), qe the amount of
material absorbed per unit mass of the adsorbent, 1/n the heterogeneous
factor that indicates the type and severity of absorption and
KF is the constant isotherm of the Frondelich.
The third isothermal model studied is Temkin isotherm with linear
equation 5, this calculation model and its variables are presented in
Table 6.
qe = B1 Ln KT+B1 Ln Ce (5)
In the above relation Ce the concentration of curcumin
solution at equilibrium (mg.L-1), qethe amount of substance absorbed per unit mass of the adsorbent,
KT isotonic absorption coefficient of Temkin and
B1 is the slope of the diagram of this isotherm
[32-36].
Absorption kinetics is used to determine the mechanism and rate of the
kinetic of the synthesized magnetic metal-organic framework nanoparticle
and to control the absorption processes [37]. There are several
different kinetic models used in this study to better understand the
experimental data of the process of absorption of curcumin solution by
magnetic metal-organic framework nanocomposite synthesized from
quasi-first and second-order kinetics and intramolecular penetration to
quantify the quantitative absorption kinetics. The quasi-first-order
model occurs with an equation of 6 expressing penetration into the
single layer, and the changes in adsorption value over time are
proportional to the number of unoccupied adsorbent sites [38-40].
Ln (qe – qt) = Ln qe –
k1t (6)
In equation 6, K1 equilibrium constant quasi-first order
velocity (min-1), qe the amount of
curcumin absorbed in equilibrium (mg/g) and qt is the
amount of curcumin absorbed at time t (mg/g). The quasi-second order
model with Equation 7 represents the chemical adsorption rate with a
slowing speed which controls surface absorption where the square of the
number of unoccupied sites in the adsorbent is proportional to the
occupancy rate of the absorbed sites [41].
t / qt = 1 / K2qe2 + t / qe (7)
In this regard, K2 is the equilibrium constant of the
second-order kinetic and in terms of (g/mg .min). The parameters
qe and qt, indicate the amount of
curcumin absorbed in equilibrium and the amount of curcumin absorbed at
time t and in terms of (mg/g) respectively. Finally, by comparing these
three kinetic models, it can be estimated which synthesized
metal-organic framework nanocomposite follows which kinetics model and
its adsorption rate are calculated [42-45].