Ph.D Defence of Hamid Khan

Mr. Hamid Khan Ph.D. Research Scholar has submitted thesis on “Improvement of the Photo Response and Photocataltic Activity of TiO2 for Photoelectrochemical Applications” to the University of Peshawar, in partial fulfillment of the requirements for the award of degree of Doctor of Philosophy (Ph.D.) in Physics The oral examination (Public Defence) is scheduled to be held on September 14th, 2026 at 10.30 a.m in the Department of Physics, University of Peshawar. The abstract of the thesis is attached herewith.

All those interested in, the said research work may participate in the event. They may raise relevant questions during presentation by the scholar for further evaluation.

ABSTRACT

Titanium dioxide (TiO2) has emerged as a leading semiconductor material for photo catalytic and photo electrochemical (PEC) applications attributed to its low toxicity, natural abundance, and remarkable stability. On the other hand, its large band gap (3.2 eV for anatase), constraints its photo catalytic activity within the ultraviolet (UV) range, which constitutes only a limited part of the sun spectrum. For improvement of visible light activity, extensive research has focused on band gap engineering through mono-, co-, and tri-doping strategies with various metal and non- metal elements using both theoretical and experimental approaches. Within this study, synthesis of TiO2 nanoparticles doped with Mo was carried out using a hydrothermal route, which offers advantages such as uniform morphology, controlled crystallinity, and better dopant dispersion. Various techniques of characterization were employed to confirm the successful doping of Mo into the TiO2 lattice and to evaluate the crystallographic, microstructural and light interaction characteristics of the prepared samples. X-ray diffraction (XRD) verified the persistence of the iC2 anatase phase with slight peak shifts indicating Mo incorporation. Scanning electron microscopy (SEM) revealed the presence of uniform spherical nanoparticles a subtle reduction in particle size due to doping. UV-Vis spectroscopy showed a shift in the absorption edge towar! the visible zone, confirming band gap reduction. The band gap energy reduction from 3.48 eV (pure TiO2) to around 2.79 eV (Mo-doped TiO2) indicates improved visible light response. The catalytic degradation of methylene blue dye under light in the visible region revealed that Mo- doped TiO2 achieved over 90% degradation efficiency, significantly outperforming pure TiO2. To supplement and verify the experimental results, density functional theory (DFT) simulations were undertaken in this study. Theoretical modelling confirmed that Mo doping introduces mid- gap states, which reduce the band gap and facilitate visible light excitation. Density of states OS) analysis revealed improved enhanced Photocatalytic activity due to modified electronic structures. Pb-doped TiO2 has been the subject of computational research. Recently, the impact of Pb-doping upon red shift in TiO2 light absorption edge has been investigated. The present results demonstrate a significant decrease in the TiO2 band gap within the visible spectrum which lead to improvement in optical absorption. Pb-doped titanium dioxide was found capable of absorbing a considerable percentage of the solar spectrum. Simulation studies have shown that Pb-doping of TiO2 produced an optical absorption spectrum to shift toward the red. Further, it was discovered that the co-doping of anatase (TiO2) with Pb and (N, Sn, C and Cr) dopants was an excellent method for causing red shifting. While studying the density of stares (DOS), it was found that the variations in band structure are caused via N 2p and Pb 2p orbitals. In the analysis  of optical absorption spectra, the Pb and N co-doped system demonstrated an increase in the amount of absorption that occurred in the visible spectrum. Among all models, the Pb and N co- adoped TiO2 exhibits the strongest and most prominent optical absorption peak. In another theoretical study, the route was altered to examine the influence of doping with molybdenum (Mo), yttrium (Y), and nitrogen (N) on the red shifting of the optical absorption, edge. It was reported that the geometrical model, the band gap, and the photo response were all estimated in the model of anatase. Comparison showed that there was not much difference in the tri-doped structure and pure TiO2 model. As a consequence of the mixing of Mo and Ti 3d states, it was noticed that a reduction in the band gap occurred. Y-doped TiO2 was reported to be the first material to introduce Y 2p levels in the vicinity of the band gap's centre. Both the produced states and the band gap of the tri-doped TiO2 model were occupied, and there was a discernible decrease in the band gap. In the case of a tri-doped model, the substitution of oxygen (O) for nitrogen (N) resulted in the introduction of states into the band gap. These states were the consequence of the inter mixing of nitrogen (2p) and oxygen (2p) states. In conclusion, results of both from experiments and calculations based on DFT appear to be promising and provide a great deal of potential for the photo electrochemical applications of the tri-doped TiO2. Furthermore, Mo doping has proven to be a good strategy for optimization the photo, response and Photocatalytic activity of TiO2. The combination of hydrothermal synthesis, detailed material characterization, photo catalytic performance testing, and theoretical simulations provides a comprehensive understanding of the materials behaviour. These findings contribute to the development and designing of efficient photoactive materials for solar driven environmental and applications.