HOMO/LUMO Orbital Distribution
The supposed structures of the PVA 4 monomers interactions with several metal oxides, including MgO, Al2O3, SiO2, TiO2, Fe3O4, NiO, CuO, ZnO, and ZrO2 and calculating HOMO/LUMO orbital distributions illustrated in figure (4). For 4 PVA monomers HOMO/LUMO orbital dispersion is distributed over all chain. In the presence of MOs interactions HOMO/LUMO orbitals were rearranged and localized around the MO. Table (1) introduce calculated TDM and band gap energy (∆E) of all structures. TDM of all MOs with PVA increased from 06.434 Debye to 29.420, 11.506, 15.823, 07.645, 09.481, 07.158, 08.512, 18.691, 12.910, 18.073, 07.977, 25.064 and 13.288 for MgO, OMg, Al2O3, O3Al2, SiO2, TiO2, Fe3O4, NiO, ONi, CuO, OCu, ZnO and OZn, respectively, except in case of ZrO2 the TDM decreased to 05.607 Debye. At the same time, band gap energy (∆E) of all MOs with PVA decreased from 6.989 eV to 0.330, 0.358, 1.291, 0.529, 0.788, 0.796, 1.289, 1.194, 0.626, 1.030, 1.076, 0.413, 0.394 and 0.904 for MgO, OMg, Al2O3, O3Al2, SiO2, TiO2, Fe3O4, NiO, ONi, CuO, OCu, ZnO, OZn and ZrO2, respectively. Because of rising TDM with decreasing band gap energy (∆E), the electronic characteristics improved, and the structure became more stable. As a result, PVA/MgO is the most electronic improved and stable structure.
Table 1
Optimised TDM (Debye) and ΔE (eV) using B3LYP/LANL2DZ for PVA and PVA interacted with different metal oxides
Structure
|
TDM (Debye)
|
∆E (eV)
|
PVA
|
06.434
|
6.989
|
PVA/MgO
|
29.420
|
0.330
|
PVA/OMg
|
11.506
|
0.358
|
PVA/Al2O3
|
15.823
|
1.291
|
PVA/O3Al2
|
07.645
|
0.529
|
PVA/OSiO
|
09.481
|
0.788
|
PVA/OTiO
|
07.158
|
0.796
|
PVA/Fe3O4
|
08.512
|
1.289
|
PVA/NiO
|
18.691
|
1.194
|
PVA/ONi
|
12.910
|
0.626
|
PVA/CuO
|
18.073
|
1.030
|
PVA/OCu
|
07.977
|
1.076
|
PVA/ZnO
|
25.064
|
0.413
|
PVA/OZn
|
13.288
|
0.394
|
PVA/OZrO
|
05.607
|
0.904
|
Molecular Electrostatic Potential (MESP):
MESP is a significant tool for estimating the electrostatic interaction of a chemical system with other molecules. MESP was used to investigate the sensitivity of a chemical system to explain its reactivity and stability. MESP is useful because it's can relate the impacts of the total charge distribution onto electronegativity, dipole moment, partial charges, and the chemical reactivity location of the structure [39]. Different MESP values appear on the molecule's surface in the form of a colour map, with the colours ordered as Red > Orange > Yellow > Green > Blue. The colour difference represented as red on the MESP surface refers to the richest charge area, the colour difference represented as blue refers to the poorest charge region, and the colour difference described as green represents zero electrostatic potential. The strongest potential is commonly found in red regions, whereas the weakest potential is found in blue regions. MESP of PVA and PVA reacted with some metal oxides, including MgO, Al2O3, SiO2, TiO2, Fe3O4, NiO, CuO, ZnO, and ZrO2 showed in figure (5). As a result, low potential red areas are used to quantify activity. The active PVA reactivity was found to be concentrated around the OH group of alcohol. When PVA interacted with various metal oxides, the red colour spread on the up and down terminals of the polymer chain, indicating that PVA's reactivity increased, and metal oxides enhanced PVA's active sides. When PVA interacted with MgO, Al2O3, SiO2, TiO2, Fe3O4, NiO, CuO, ZnO, and ZrO2, low potential red regions were localised mainly around the oxygen atom of metal oxide, whereas when PVA interacted with OMg, O3Al2, ONi, OCu, and OZn, the red regions were spread across the polymer chain and increased on the other side of the chain. As a result, PVA's electrical characteristics improved, and it may now be employed in a variety field of applications.
3-2 GQDs Interaction with PVA/MgO:
PVA/MgO is the most electrically improved, stable, and active structure chosen to interact with the four GQD forms ATRI, AHEX, ZTRI, and ZHEX, according to previous studies. HOMO/LUMO orbital distributions and MESP mapping were studied also for PVA/MgO/GQDs. The TDM of PVA/MgO was 29.420 Debye, and the band gap energy (∆E) was 0.330 eV. TDM, as recorded in table (2), for PVA/MgO reacted with four GQD forms altered to 59.831, 30.501, 14.879, and 26.963 Debye, while band gap energy (∆E) dropped to 0.273, 0.318, 0.201, and 0.312 for PVA/MgO/GQD ATRI C60, PVA/MgO/GQD AHEX C42, PVA/MgO/GQD ZTRI C46 and PVA/MgO/GQD ZHEX C54, respectively. The electrical properties of the structure improved as TDM increased with decreasing band gap energy (∆E), accordingly, the most electrically enhanced and stable structure is PVA/MgO/GQD ZTRI C46. Furthermore, as shown in figure (6), HOMO/LUMO orbital distributions and MESP mapping were disseminated across the GQDs sheet surface, indicating that the PVA/MgO/GQDs composition boosted the GQDs surface activity. As a result, the PVA/MgO/GQDs composite enhanced PVA sensitivity and selectivity, designed to function as a sensor.
Table 2
Optimised TDM (Debye) and ΔE (eV) using B3LYP/LANL2DZ for PVA/MgO reinforced with GQDs
Structure
|
TDM (Debye)
|
∆E (eV)
|
PVA/MgO/GQD ATRI C60
|
59.831
|
0.273
|
PVA/MgO/GQD AHEX C42
|
30.501
|
0.318
|
PVA/MgO/GQD ZTRI C46
|
14.879
|
0.201
|
PVA/MgO/GQD ZHEX C54
|
26.963
|
0.312
|