3.1 Transmission Electron Microscope (TEM):
Typical nanostructures of prepared particles have been performed by TEM images. The TEM images of Fe3O4 (NP) coated with barbituric acid show uniformly dispersed nanoparticles of average diameter from 9-12nm associated with slight aggregation which confirm the presence of magnetite structure, while the TEM images of Fe3O4 –Ba complex confirm the synthesis of high quality, free, highly mono dispersed nano particles with average size from 5–10 nm. The average size of the complex is smaller than the coated nanoparticles because of coordination bond formation between barbituric acid and Fe3O4 NP.
- Scanning Electron Microscope (SEM):
The observation of SEM photographs of the dried barbituric acid with Fe3O4 NP demonstrated that most of the particles are completely spherical in shape, Fig. 3. The SEM photos of Fe3O4 –Ba complex, Fig. 4, show that the synthesized complex has an octahedral configuration with high density.
3.2 X- Ray Diffractometer:
The XRD diffraction pattern for Fe3O4 NPs, showed many peaks at 2θ values of 30.154, 31.677, 35.524, 43.109, 45.31, 53.523, 57.046, 62.699, 70.865 and 74.844. The maximum peaks corroborating the presence of magnetite structure.
The crystallinity of barbituric acid is determined by X-ray diffraction, Fig. 5, shows intense peaks of crystallinity. The 2θ peaks at 17.53, 19.765, 20.852, 22.231, 26.578, 29.231and 30.743.
Structural characterization of barbituric acid @ Fe3O4 NPs has been performed using XRD analysis. The 2θ maximum peaks at 29.258, 30.154, 35.524, and 49.503. Since these peaks are small, the possibility of a magnetite structure cannot be completely excluded. In addition to these four peaks there are unidentified peaks appear in the XRD pattern.
The crystal structure of Fe3O4 –Ba Complex was investigated using XRD. The 2θ peaks at 10.012, 16.548, 32.354, and 28.532. The spectra exhibited less intense peaks compared to barbituric acid @ Fe3O4 NPs, which indicates that the obtained sample is mostly amorphous instead of crystalline nature. On comparing between our XRD patterns, each component has its own crystal region in the hybrid nanoparticles.
3.3 Zeta potential:
Z - Potential measurements were made for coated nanoparticles. Barbituric acid @ Fe3O4 NPs shows a decrease of the negative surface charge − 1.5 mV., while for Fe3O4 –Ba complex shows a very low positive surface charge 0.135 mV. Such low values suggest weak negative and positive charges at the surface of the nanoparticles, yielding low stability of nanoparticles due to weak electrostatic repulsive forces between carboxyl groups.
3.4 Infrared (IR):
1- The IR spectral data of the ligand, its metal complex, and F3O4 coated NP are summarized in, Table 1. The strong bands are in the range at 3578 cm− 1 for the symmetric and asymmetric (OH) stretching of the ligand, while the (NH) band appears at 3192 cm− 1. The sharp band at 1750 cm− 1 was attributed to (C = 0), whereas the band at 1610 cm− 1 is for the (C = N). The information obtained suggested the existence of barbituric acid within the tautomeric forms.
2- A comparison of the IR spectra of the ligand, Fe3O4 –Ba Complex, and F3O4 coated NP, Table 1, brings out the subsequent facts.
a. The spectra of Fe3O4 –Ba Complex and F3O4 coated NP exhibited a broad band at 3500–3400 cm− 1, that attributed to ν OH of the associated water molecules, whereas the observed band at 860– 740 cm− 1 is referred to coordinated water molecules. [30]
b. The change in intensity and position of the carbonyl band indicate that at least one the carbonyl groups of the barbituric acid were coordinated with the metal. The νNH band at 3178 cm− 1 turned to a broad band at 3100 cm− 1 within the of Fe3O4 –Ba Complex suggesting that coordination bonds have been formed between the NH groups and the metal ion.
The appearance of ν C = N and ν C-O at 1650 and 1402 cm− 1, respectively, could be a robust proof that the ligand is tautomerized to the enol structure before complexation with the metal ion. [31] The appearance of weak bands at 536 and 449 cm− 1 respectively for Fe3O4 –Ba Complex offer a powerful proof for the formation of Fe –N and Fe –O bonds. [32, 33]
c. For F3O4 coated NP The absence of ν C = N and ν C-O bands indicates that there is no tautomerization and the ligand existed in the keto form when it is coated to the Fe3O4 Nano particle. The weak bands at 542 and 408 cm− 1 respectively prove the formation of Fe –N and Fe –O bonds
Table 1
IR spectra (cm− 1) of barbituric acid (H2L2), Fe3O4 –Ba Complex and F3O4 coated NP.
Barbituric acid
|
F3O4 coated NP
|
Fe3O4 –Ba Complex
|
Assignment
|
3578
3192
3095
2874
1755 − 1710
1610
1421 − 1354
1291,1244
933
781
|
3464 − 3238
3100 (b)
2924,2859
2879(b)
1699(s)
-
1429
1347
1091 − 1040
1092 − 1041
784
542 − 509
408
|
3423
3205(b)
2362
1703 (b)
1650 − 1607
1428 − 1402
1347
1292
1095 (b)
771
536
449
|
ν (as & sy) OH
ν NH
ν OH
ν C = O
ν C = N
ν CH2δ NH
ν (C–O), ν C = N
δ O-H
ν (CN), ν CCH
coordinated (H2O)
ν Fe-N
ν Fe-O
|
3.5 Nujol spectra:
Table 2
Nujol mull electronic absorption spectra and geometries of barbituric iron metal complex at room temperature
Complex
|
λ max (nm)
|
Geometry
|
Fe3O4 –Ba Complex
|
319, 354, 461
|
Oh
|
Fe3O4 –Ba Complex Table 2, gave bands at 319, 354, 461 nm. These bands are because of CT (t2g → π*) and CT (π →eg) confirm the existence of Octahedral configuration. [34, 35]
3.6 Thermal studies: -
3.6a TGA analysis: The TGA of the naked Fe3O4 nanoparticles was studied by Asgari et al.[36–39] The TGA of naked Fe3O4 magnetic nanoparticles shows that it lost about 5% of its weight within the temperature range from 25 to 300°C due to the loss of residual water in the sample. On the other hand, for F3O4 nanoparticles coated with Barbituric acid, Fig. 6, owing to the removal of absorbed water, the weight loss of the entire nanocomposite is slightly below 200°C. Then the barbituric acid begins to decompose within the range from 183°C to 500°C and the weight loss was 72%. At higher temperature (500 to 800°C), there is no significant weight lost and the remaining weight is 17% from the initial weight. From the previous study it has been found that the ratio of barbituric acid to Fe3O4 nanoparticles is (15:2)
- Fe3O4 –Ba Complex, lost 4.685% of its weight below 191°C due to the removal of the inner and outer sphere water. Then the degradation of complex began at 200°C and therefore the final temperature of decomposition is around 479°C
3.6b Differential scanning calorimetry (DSC):
DSC technique used to determine the thermal transitions of a compound like glass transition, melting and crystallization. Plotting heat flow against temperature gave 3 regions. within the initial region, glass transition temperatures are often determined by taking the center of the incline, within the second region the crystallization are often determined by taking the temperature at the lowest point of the dip and within the third region, melting temperature are often determined by taking the temperature at the top of the peak.[40–45] The glass transition and crystallization temperatures have been determined from DSC graph for the Fe3O4 –Ba Complex and F3O4 coated NP, Fig. 7 and Table 3. The crystallization temperatures for Fe3O4 –Ba Complex was 258.19 and 67.4 ºC, 228.48 ºC for F3O4 coated NP in which the compounds have gained enough energy to be in order arrangements subsequently it gave off heat through an exothermic transition.
Table 3
Thermal transitions of Fe3O4 –Ba Complex and F3O4 coated NP.
Compound
|
Peak (type)
|
Tc (ºC)
|
Tm (ºC)
|
Tg (ºC)
|
Enthalpy (ΔH) (J/g)
|
Fe3O4 –Ba Complex
|
a(endo)
|
258.19
|
-------
|
270.33
|
-197.27
|
F3O4 coated NP
|
a(endo)
b(endo)
|
67.41
228.48
|
-------
-------
|
68.77
224.66
|
-79.63
-35.96
|
However, the Debye model is applied to explain capacity modification over an outsized temperature vary. [46–48] The Cp has been represented as the following empirical form:
A straight line is obtained by plotting Cp versus T, thus, "a" and "b" parameters will be determined, respectively, from the slope and intercept of the line, Fig. 8 (a) and Table 4.
Further applications depend on Debye model on the complexes are given from the scope of the subsequent equations:
$$\frac{Cp}{T}= {T}^{2}+{\gamma }$$
$$Cp \text{C}\text{v}={T}^{3}+{\gamma }\text{T}$$
Where, the electronic and lattice heat capacities coefficients are γ and α, respectively. Cp is assumed to be equal to Cν that represents the heat capacity at constant volume. Plotting of Cp / T versus T2 yield straight lines with slopes α and intercepts γ, Fig. 8(b), Table 5.
Table 4
The slopes "a" and intercept "b" for DSC curves of the compounds
compound
|
a1
[b1]
|
a2
[b2]
|
a3
[b3]
|
a4
[b4]
|
a5
[b5]
|
a6
[b6]
|
a7
[b7]
|
Fe-Ba complex
|
-0.347
[190.7]
504–532 ºK
|
0.988
[-522.57]
536–551 ºK
|
0.0575
[-8.833]
569–599 ºK
|
-0.0331
[46.384]
619–651ºK
|
-0.4429
[-246.09]
651–696 ºK
|
|
-
|
F3O4 coated NP
|
0.009
[-0.0008]
300–303 ºK
|
0.0081
[0.0077]
303–338 ºK
|
0.0084
[-0.0009]
338–358 ºK
|
0.0148
[-0.06562]
350–463ºK
|
0.013
[-0.0016]
500–512 ºK
|
0.0164
[-0.1109]
540–631 ºK
|
0.0268
[-0.0940]
664–706 ºK
|
Table 5
The slopes “α” and intercept “γ” for DSC curves of the compounds
Compound
|
α1
[γ1]
|
α2
[γ2]
|
α3
[γ3]
|
α4
[γ4]
|
α5
[γ5]
|
α 6
[γ6]
|
α 7
[γ7]
|
Fe3O4 –Ba Complex
|
-0.0009
[0.0625]
311–463 ºK
|
-0.0054
[0.1643]
483–536 ºK
|
0.0231
[-0.6539]
536–547 ºK
|
0.0003
[-0.345]
559–599 ºK
|
0.0044
[-0.1501]
655–696 ºK
|
|
|
F3O4 coated NP
|
-0.0275
[0.3339]
315–331 ºK
|
0.0512
[-522.57]
338–344 ºK
|
0.0014
[0.0577]
369–433 ºK
|
0.0029
[0.1371]
463–484 ºK
|
0.0283
[-0.54]
500–507 ºK
|
0.0025
[0.0115]
552–611 ºK
|
0.00109
[-0.3519]
648–705 ºK
|
- Determination of kinetic parameters from thermal degradation:
The thermo gravimetric data were used to evaluate kinetic parameters of solid-state reactions involving weight loss (or gain) has been investigated. [49–51]
Broido’s technique: [52, 53]
The activation energy related to each stage of decomposition was conjointly evaluated by Broido’s technique. The following equation is used to calculate the activation energy (Ea):
$${ln}{ln}\left(\frac{1}{Y}\right)=\left(\frac{-{E}_{a}}{R}\right)\frac{1}{T}+constant$$
Where \(Y=\frac{Wt-W\infty }{Wo-W\infty }\)
Where, Y is the fraction of the number of initial molecules that do not decomposed; Wt, W ∞ and W0 represent the weight at any time t, the weight at infinite and the initial weight, respectively. By blotting ln ln (1/Y) vs. 1/T a straight line was obtained and the activation energy could be evaluated from the slope, Fig. 9.
The kinetic parameters of the Fe-Ba complex and F3O4 coated NP are given in Table 6.
Table 6
Kinetic parameters of Fe3O4 –Ba Complex and F3O4 coated NP by Broido method
Compound
|
Decomposition Temperature range (oC)
|
Regression value (R2 )
|
Activation energy in Kcal/mol
|
Fe3O4 –Ba Complex
|
190–279
279–429
|
0.809
0.9929
|
6.705
22.655
|
F3O4 coated NP
|
24–84
84–183
183–261
261–385
385–503
|
0.757
0.970
0.978
0.989
0.947
|
69.033
5.387
9.523
1.471
12.518
|
3.7 Computer simulation technology (CST)
3.7a SAR Measurement
Dielectric properties at frequency 915 MHz, and thermal properties of the human tissues are shown in Table 7. [54–57] The effect of microwave imaging using FEM for the designed 3D model was studied. Figure 10, indicates a localized region of the highest SAR value (yellow region) that coincides with the position of the inserted tumor cells at 915 MHz. SAR is determined by the “rate of temperature rise”.
Table 7
Dielectric properties and thermal properties at frequency 915 MHz
Dielectric Properties
|
Electrical permittivity Ɛr
|
38.84 (F/m)
|
Conductivity σ
|
0.59 (S/m)
|
Thermal Properties
|
Heat capacity C
|
3621 (J/kg. ÛC)
|
Thermal conductivity K
|
0.5 (W/m. ÛC)
|
3.7b Temperature Distribution ͦ
The effect of MFH treatment at 915 MHz using FEM for designed model was studied, Figures (11, 12), Show the presence of nanoparticles which cause an increase in the tumor’s temperature to exceed 42oC and are sufficient for hyperthermia treatment and destroy tumor cells. Also, the temperature outside the tumor is below 38oC which keeps the surrounding tissues healthy unharmed.
The relation between temperature and distance shows a localized high temperature at the center of the tumor (approximately 42o C) and it decreases as moving away from the center of the tumor as shown in, Fig. 13F.