M.Phil / MS
Permanent URI for this collectionhttps://repository.cuilahore.edu.pk/handle/123456789/30
This collection archives the complete set of theses produced by students of the COMSATS University Islamabad, Lahore Campus.
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Item Hydrogen Splitting using Single Metal Atom Doped Zinc Oxide Nanocage as a Catalyst: A DFT Study(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2023) Ali Hussain; FA21-R06-016; LHR TP 8447; Dr. Mazhar Amjad GilaniHydrogen dissociation reaction is a key step in sustainable, non-toxic and renewable energy production and single atom catalysts have shown promising catalytic activity in facilitating this reaction. The world is currently facing major challenges related to the environment, including climate change and the depletion of non-renewable energy sources. As a potential solution to these challenges, the use of clean and renewable energy sources, such as hydrogen, has gained increasing attention. Herein we employed DFT calculation on single atom catalyst-based study to investigate the adsorption and dissociation of H2 molecule over TM@ Zn12O12 catalysts. The analysis of the interaction energy reveals the stability of all transition metal doped complexes (Sc-Mn), with the highest interaction energy (-4.27 eV) observed in the Cr@Zn12O12 complex. Furthermore, electronic properties (FMOs, NBO analysis) confirm the electropositive nature of transition metal atoms. QTAIM and IRI analysis are employed to interpret shared or partially covalent interactions in TM@ Zn12O12 complexes. The mechanism of hydrogen dissociation reaction is studied for all the complexes (Sc-Mn), and it is found that Sc@Zn12O12 is the most efficient catalytic agent for the hydrogen dissociation reaction, with the lowest activation barrier (0.09 eV). EDD isosurface and NBO analysis confirm the charge transfer from metal to antibonding orbital of hydrogen which facilitates the hydrogen splitting. The pivotal insights gained from this study enhance our understanding about the stability, electronic properties, and hydrogen dissociation reaction of various transition metal doped Zn12O12complexes.Item Exploration of Diradical Graphene Nanoflakes (GNFs) as NLO based Sensors for NOx(Library Information Services COMSATS University Islamabad Lahore Campus, 2023-02-27) Mawra Nasir; SP22-R06-009; Dr. Mazhar Amjad Gilani; LHR TP 8648Approximately 78% of the air is composed of nitrogen, which, in its elemental form, is not harmful. However, nitrogen oxides (NO, NO2, N2O) present in the air can have adverse effects on both human health and the environment. In the realm of environmental monitoring, the crucial task of adsorbing or detecting small (toxic) gas molecules relies on appropriate semiconductors. Although graphene nanoflakes (GNFs) find extensive applications in energy storage and optoelectronics, their potential as sensors is not extensively explored. This study investigates the adsorption of nitrogen-containing gaseous molecules i.e NO, NO2, and N2O on trigonal, rhombic, and bowtie GNFs sheets through Density Functional Theory (DFT) simulations. The analysis encompasses optimized geometries, adsorption energies, as well as Natural Bond Orbital (NBO) and Electron Density Differences (EDD) analyses to interpret the interaction between GNFs sheets and NOx gases. The theoretical findings reveal strong binding between GNFs sheets and NO2 molecule, with adsorption energies of -30.2, - 17.1, and -29.8 kcalmol-1 for NO2@t-GNFs, NO2@r-GNFs, and NO2@b-GNFs, respectively. Furthermore, Frontier Molecular Orbital (FMO), and Density of State (DOS) analyses underscore the significant impact of gas adsorption on GNF sheets. Interaction Region Indicator (IRI) and Quantum Theory of Atoms in Molecules (QTAIM) analyses indicate the covalent interactions between GNFs sheets and NO, NO2 gases, while van der Waals interactions are confirmed with N2O gases. UV-Vis and IR analyses demonstrate the selectivity of b-GNFs towards NO2 and NO, respectively. Based on Nonlinear Optical (NLO) response, b-GNFs exhibit the highest sensitivity towards NOx. In conclusion, GNFs sheets exhibit promising sensitivity to gaseous molecules, positioning them as potential multimode sensors, including UV, IR, and NLO-based applications. This theoretical insight aids experimentalists in developing novel GNFs-based sensors for the detection of toxic gases.Item Hydrogen Adsorption and Dissociation Using Single Metal Atom Doped Mg12O12 Nanocage as a Catalyst: A DFT Study(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2025) Irsa Nageen; FA22-R06-008; Dr. Mazhar Amjad Gilani; LHR TP 9309Energy is the keystone of life on Earth, powering everything from microscopic levels to large scale chemical reactions. The expanding population and increasing industrial activities have reinforced the energy demands, traditionally sourced from fossil fuels. However, the finite nature of these resources and their detrimental environmental impacts necessitate a transition to sustainable energy solutions. Currently, hydrogen emerges as the outstanding substitute for fossil fuels, making it a more valuable energy source due to its high energy density, renewability, and clean burning nature, producing only water as a by-product. Hence, efficient hydrogen utilization requires its dissociation because molecular hydrogen is not an effective energy source as the atomic form. In this regard, hydrogen dissociation reaction on single-atom catalysts (SAC) is an essential step in sustainable and non-toxic energy production. Our study employed DFT calculations to investigate the adsorption and dissociation of molecular hydrogen on 3d transition metal atoms doped onto Mg12O12 nanocages. Each TM@Mg12O12 complex is evaluated to identify the most stable spin state for the catalytic reaction. The energetic analysis reveals that the Sc@Mg12O12 and Ti@Mg12O12 complexes exhibit high and identical interaction energy (-2.13eV) among the studied complexes. Further evaluation using NBO, FMO, IRI, and QTAIM analysis revealed the charge transfer carried from nanocage to metal and confirmed the partial covalent interactions between the TM-doped complexes. The adsorption of molecular hydrogen on the TM-doped nanocage exhibits negative adsorption energy which confirms the exothermic nature of H2 adsorption. Notably, the homolytic dissociation of H2 on the Ti@Mg12O12 complex displayed the lowest activation barrier (0.23eV), highlighting its potential as an efficient catalyst for hydrogen dissociation reactions. QTAIM of H2TM@Mg12O12 studies the interaction between the hydrogen and catalyst and confirms the covalency. NBO and EDD analysis confirm the transfer of charge from metal bonding to hydrogen antibonding orbital which leads to the dissociation of the H-H bond and facilitates the adsorption of hydrogen atoms on the catalyst. Our investigation sheds light on the factors that govern the electronic properties and catalytic ability of TM-doped Mg12O12 nanocage complexes in hydrogen dissociation reactions and paving the way for the development of improved hydrogen energy technology.Item Detection of Histamine and Serotonin as Chronic Stress Biomarkers Using Graphyne-based Sensor: A DFT Study(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2025) Amina Haq; FA22-R06-027; Dr. Mazhar Amjad Gilani; LHR TP 9317Chronic stress is a leading cause of mental illnesses that is interceded by neuroinflammation and poses one of the most critical public health challenges globally therefore, a theragnostic strategy is needed for effective diagnosis of stress. Neuroinflammation induces an increase in histamine and a decrease in serotonin levels in blood during chronic stress. The sensitivity of pristine and alkali metal (IA = Li, Na, and K) doped C24H12 toward histamine and serotonin are probed herein at DFT/ωB97XD/6 31+G (d, p) level of theory in the water phase. The -NH2 group of histamine and -OH group of serotonin are coordinated with pristine and metal-doped C24H12 nanosheets. The adsorption of histamine and serotonin is an exothermic process and physi-chemisorbed as their adsorption energies range from -40 to -60 kJ/mole per atom for all complexes except His@C24H12, His@KC24H12, and Ser@C24H12. Considerable, charge transfer from biomarkers to the C24H12 except for Ser@C24H12 is revealed via NBO analysis and confirmed by.MEP, UV-visible, and IR spectroscopic analyses. Upon the adsorption of the biomarkers, the λmax of pristine C24H12 remains unchanged but, in metal-doped C24H12, a bathochromic effect is observed. The significant shift in vibrational frequencies of -NH and -OH stretch occurred due to charge transfer toward C24H12. Furthermore, the band gap of the pristine C24H12 is 6.86 eV which remains constant even after histamine and serotonin adsorption. However, the doping of alkali metals leads toward a significant decrease of the band gap of about 4.60 eV revealing that doping facilitated the charge transfer from biomarkers to graphyne for effective sensing. The QTAIM and IRI studies show the presence of non-covalent interactions among the biomarkers and C24H12. Finally, a shorter recovery time (fast desorption) is found in vacuum ultraviolet light, indicating the pristine and metal-doped C24H12 nanosheets as a reusable or non-disposable sensor. Therefore, it concludes that metal-doped C24H12 nanosheets are more sensitive toward histamine and serotonin adsorption than pristine C24H12.Item Hydrogen Splitting Using Single Metal Atom Doped C3N Nanosheet as a Catalyst: A DFT Study(Library Information Services COMSATS University Islamabad Lahore Campus, 2022-02-26) Zulqarnain Haider; FA20-R06-010; Dr. Mazhar Amjad Gilani; LHR TP 7881Atomic hydrogen is the most intriguing free radical for high-energy applications. The ability of atomic hydrogen to protect DNA and mitochondria from oxidative damage may be advantageous in the treatment of chronic illnesses including cancer. When dissociation energy is supplied, a molecule of hydrogen dissociates into two atoms (H2 → 2H). In contrast to other radicals, hydrogen recombination requires no activation energy. The highest efficiency and stability for heterogeneous catalysis of hydrogen splitting are provided by single-atom catalysts adsorbed on the active surface. For support of single-atom catalyst (SAC), carbon nanotubes, graphene, metal hydrides, metal-organic frameworks, graphene, graphdiyne, carbon nitride, and silanes surfaces have been employed recently. The presence of nitrogen in carbon nitride surfaces is shown to be much more effective for hydrogen dissociation and considered as the most suitable substrate for SAC. Because of their varying oxidation states, transition metals have several spin states that can be tested, and the most stable spin states based on thermodynamic energy data may be determined. The optimized C3N nanosheet is doped with 3d transition metals. The lowest energy spin state of each doped metal is considered for further calculations. The stabilities of complexes have been measured by calculating the interaction energies of optimized geometries. Adsorption energies of H2 on metal doped carbon nitride surface are computed to investigate the adsorption mechanism and characterize the energetic heterogeneity of solid surfaces. The energy barrier (activation energy) and reaction energies are required to determine the splitting of hydrogen. This study shows that SAC can be used as the most efficient doping technique for hydrogen splitting.Item A Theoretical Exploration of Supramolecular Architectures as High Performance Nonlinear Optical (NLO) Materials(Library Information Services COMSATS University Islamabad Lahore Campus, 2022-02-26) FA20-R06-001; Aqsa Nisar; Dr. Mazhar Amjad Gilani; LHR TP 7876Density functional theory (DFT) calculations have been performed for a series of supramolecular assemblies containing azobenzene (Azo-X where X=I, Br and H) and alkoxystilbazole subunits to evaluate their electronic, linear and nonlinear optical properties. These assemblies are derivatives of azobenzene, obtained by the substitution of electron-withdrawing and electron-donating groups onto the molecular skeleton. The interaction energies (Eint) of all the designed supramolecular complexes (IA-IF, IIA-IIF and IIIA-IIIF) range from -1.02 kcal/mol to -7.70 kcal/mol. Electronic properties of these hydrogen/halogen bond driven supramolecular assemblies such as, vertical ionization energies (VIE), HOMO-LUMO energy gap (GH-L), excitation energies, density of states (DOS) and natural bond orbital (NBO) analyses were also computed. The non-covalent interaction index (NCI) and quantum theory of atoms in molecules (QTAIM) analyses have also been performed to validate the nature of inter- and intra-molecular interactions in these complexes. A substantial enhancement in the first hyperpolarizability (βₒ) values of the designed supramolecular complexes has been observed driven by the charge transfer from the pyridyl moiety of alkoxystilbazole to Azo-X. The highest first hyperpolarizability (βₒ) value of 1.3×104 au is observed for supramolecular complex of p-nitro substituted azobenzene with alkoxystilbazole (ID complex). It was confirmed on a purely theoretical basis that both the type of noncovalent interactions present and the substituent group incorporated influence the nonlinear optical response (NLO) of the systems.Item Theoretical Design of Alkali and Alkaline Earth Metals Doped Cubanes (C8H8) as Novel Nonlinear Optical Materials(Library Information Services COMSATS University Islamabad Lahore Campus, 2021-02-25) Javaria Naeem; SP20/R06/013; Dr. Mazhar Amjad Gilani; LHR TP 7567Novel organic materials have spark the attention of many scientists to design the high performance NLO materials. In the current study, the effect of alkali and alkaline earth metals doped cubanes have been studied by using density functional theory. The strong influence of doped metal atoms on structural, electronic and nonlinear optical prosperities have been investigated. The results have revealed thermodynamic stability of the doped complexes. The HOMO-LUMO energy gap is reduced upto 4.43 eV. Density of state analysis confirmed the formation of new highest occupied molecular orbital that contributes in the reduction of energy gap. The NBO analysis is performed to evaluate the charge transfer between metal atoms and the cubane ring. The NCI and QTAIM studies also validated the nature of the intramolecular interaction. Doping of metal atoms significantly boosts the hyperpolarizability of the complexes. The first hyperpolarizability (βₒ) of 3.01×104 au is observed for K@Cubane. Moreover, second hyperpolarizability (γtot), second harmonic generation (SHG), electro-optic Pockel’s effect (EOPE), electric field-induced second harmonic generation (EFISHG), electro-optic Kerr effect (EOKE), hyper-Rayleigh scattering coefficient (βHRS) and nonlinear refractive indices (n2) are also calculated for the designed complexes. The highest dc-Kerr of 2.03 × 1011 au and EFISHG of 2.06 × 1012 au are observed at ω= 0.0856 au along with large refractive index (1.15 × 10-5 au ). These remarkable findings offer new perspectives for designing new materials for their future applications in optoelectronics.Item A First Principle Study on Sensing Properties of Twisted Nanographenes Towards Phosgene, Thiophosgene and Formaldehyde(Library Information Services COMSATS University Islamabad Lahore Campus, 2021-02-24) Naila Sattar; FA19-R06-007; Dr. Mazhar Amjad Gilani; LHR TP 7324The harmful chemicals like chemical warfare agents (CWAs) and toxic industrial chemicals (TICs) are extremely pernicious to the climate and living systems. The efficient detection and removal of these noxious chemicals in limited time span is essential for the human health and environmental security. Twisted nanographenes have great applications in the fields of energy storage and optoelectronics, but their applications as sensors are rarely described. Therefore, we have explored theoretically the sensitivity and selectivity of twisted nanographenes C32H16, C64H32 towards the harmful chemicals like phosgene, thiophosgene and formaldehyde. Here, we elaborate the phenomena of adsorption of the selected toxic chemicals on twisted nanographenes' surface within the framework of density functional theory (DFT). Adsorption interpretation is depending upon the optimized geometries, adsorption energies, NBO (natural bond orbital) charge transfer, frontier molecular orbital (FMO), absorption (UV-Vis), NCI (non-covalent interaction) and QTAIM (quantum theory of atoms in molecules) analyses. Results of interaction energies reveal the physiosorption of the toxic chemicals on the twisted nanographenes surface, which mainly arise due to the non-covalent interactions. The non-covalent nature of adsorption of toxic chemicals on twisted nanographenes surface is also ascribed by the NCI and QTAIM analyses. Most favorable adsorptions of the selected toxic chemicals occur at the edges of the distorted moiety (central ring). The average band gap changes (%Eg) and %sensitivity is quantitatively determined by the molecular orbital analysis, to evaluate the sensitivity of twisted nanographenes. Among the selected chemicals, the sensing of thiophosgene (ThP) is prominent on the twisted nanographenes surface, having interaction energies of -8.19 and -12.14 kcal mol-1 (in case of C32H16 and C64H32 tNGs), respectively. Therefore, it is concluded that twisted nanographenes can be applied as a potential sensing agent for the detection of toxic chemicals, especially thiophosgene. This x research will help the experimentalists to devise novel sensors based on twisted nanographenes.Item Theoretical Prediction of Nocturnal/Diurnal and Seasonal Real World Absorption Spectra of Polycyclic Aromatic Hydrocarbons and their Derivatives in Two Chinese Polluted Cities(Library Information Services COMSATS University Islamabad Lahore Campus, 2021-02-24) Sahiba Fareed; FA19-R06-014; Dr. Mazhar Amjad Gilani; LHR TP 7320Brown carbon (BrC) is an organic aerosol, released during combustion of organic matter. It strongly absorbs solar radiations hence, plays an important role in radiative forcing. Neglecting brown carbon from climate models leads to difference between theoretical and experimental works. Polycyclic aromatic hydrocarbons (PAHs) and their derivatives such as oxygenated polycyclic aromatic hydrocarbons (OPAHs) and nitrated polycyclic aromatic hydrocarbons (NPAHs) are the major constituents of the BrC and they are persistent environmental pollutants. Their study is the need of hour as they are ubiquitous in atmosphere and carcinogenic in nature. Our strategy here is to utilize time dependent-density functional theory (TD-DFT) to model the absorption spectra of PAHs and their derivatives in two Chinese industrial sites: Qingcheng district (site A) and Longtang town of Qingyuan (site B). These data are corrected for “Real-world” experimental concentrations of PAHs over these cities. For the first time, nocturnal/diurnal and seasonal variations of PAHs are being studied at a time in these Chinese regions. These findings show that most relevant absorption regions for climate forcing are ~320nm, ~380nm and ~430nm. Moreover, almost all the absorption at site A and B takes place mainly due to PAHs while OPAHs and NPAHs play a very negligible part in absorption. Site A is highly affected by climate forcing caused by these PAHs. Absorption in winter is higher as compared to that of in summer. Furthermore, this model infers that relevant contributors to absorption at ~320nm are PAHs and OPAHs while absorption at ~380nm is attributed only to PAHs. Absorption at ~430nm is mainly explained by PAHs and NPAHs. Most of the absorption takes place in UVA and visible regions of the electromagnetic spectrum. More specifically, from the 35 studied PAHs and their derivatives, the major contributors towards radiative forcing are DBA (dibenzo[ah]anthracene), BaA (benz[a]anthracene) and BkF (benzo[k]fluoranthene) (PAHs). While among OPAHs and NPAHs, major contributors are Bpone (6H-benzo[c,d]pyrene-6-one), Bzdion (Benzo[a]anthracene-7,12-dione) and 7NBaA (7-nitrobenz[a]anthracene). Thus, our x theoretical modeling approach remarkably identifies the most relevant PAHs, OPAHs and NPAHs for climate forcing in this Chinese region.Item Design of Novel Lanthanum Doped Al12P12 Nanocages with High Nonlinear Optical Response(Library Information Services COMSATS University Islamabad Lahore Campus, 2020-02-20) Faiqa Khaliq; SP19-R06-022; Dr. Mazhar Amjad Gilani; LHR TP 6523In current study, the effect of lanthanum doping over Al12N12 and Al12P12 nanocages has been investigated using density functional theory. The strong influence of lanthanum doping on geometrical, electronic, linear, and nonlinear optical properties of Al12N12 and Al12P12 nanocages has been observed. The results revealed that doped nanoclusters possess high thermodynamic stability upto -37.37 kcal/mol and HOMO-LUMO gap is reduced upto 0.89 eV. NBO analysis confirms the charge transfer from metal towards nanocage. The Partial Density of States (PDOS) and Total Density of States (TDOS) strongly support the formation of new HOMO energy level which contributes in the reduction of HOMO-LUMO orbital energy gap. Doping of lanthanum remarkably increases the first hyperpolarizability (βₒ) of the complexes. The highest first hyperpolarizability of 4.43 × 104 au is observed for La@endo-Al12N12 complex. The present investigations intrigue the designing of high performance NLO materials that can be beneficial for their use in modern optoelectronic applications.