1. Ph.D Theses
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Item Perovskite Alkaline Earth Titanates Based Nanomaterials as Photocatalysts(National Institute of Technology Karnataka, Surathkal, 2023) B, Harsha; Bhat, D. KrishnaThe research thesis entitled ‘Perovskite alkaline earth titanates based nanomaterials as photocatalysts’ deals with the synthesis, characterization and photocatalytic studies of some doped perovskite alkaline earth titanates and porous graphene-perovskite alkaline earth titanate nanocomposites. The present study reports the successful synthesis of seven different series of novel perovskite alkaline earth titanate-based materials namely, Rh-doped SrTiO3, V-doped SrTiO3, porous graphene-SrTiO3 nanocomposite (PGST), Rh-doped BaTiO3, porous graphene-BaTiO3 nanocomposite (PGBT), V-doped CaTiO3 and porous graphene-CaTiO3 nanocomposite (PGCT) using facile solvothermal/hydrothermal method. All the synthesized materials were carefully characterized for their elemental composition, structural, morphological, and optical properties by employing appropriate techniques such as XRD, FESEM, EDS, TEM, HRTEM, Raman Spectroscopy, XPS, BET, DRS, and PL spectroscopy. Thereafter, each material was investigated for its catalytic efficiency towards the degradation of methylene blue dye under visible light irradiation. The synthesized materials exhibited enhanced photocatalytic efficiency which could be attributed to the efficient visible light harvesting capacity and reduced rate of recombination of photoinduced charges.Item Synthesis of Boron and Cerium Codoped Titanium Dioxide Photocatalysts For Antibiotic Degradation And Microbial Disinfection Under Solar Light(National Institute of Technology Karnataka, Surathkal, 2022) M, Manasa; Mahalingam, Harin recent years, antimicrobial resistance has been a global emerging problem due to the emergence of superbugs which poses a major threat to human health and the environment. The presence of antibiotic residues is the primary source of this emerging problem. Photocatalysis, for decades, has been a promising treatment technology in removing recalcitrant organic compounds from the environment. In this study, a systematic series of B and Ce monodoped (0.1 and 1 at.% Ce-TiO2, 1 and 2 at.% B-TiO2) and codoped (BxCe1-xTiO2, x = 0.9, 0.8 and 0.7 at.%) catalysts were synthesized using a facile green EDTA-citrate method. The synthesized catalysts were evaluated for the degradation of ciprofloxacin (CIP, antibiotic) and disinfection of E.coli under sunlight in both suspended and immobilized forms. For immobilization, waste expanded polystyrene (EPS) beads were used as a substrate along with the best performing codoped catalyst. The catalysts were characterized for particle size, BET surface area, surface morphology (SEM and TEM analysis), crystal structure (XRD analysis), surface chemistry (XPS and RAMAN analysis), bandgap (DRS analysis), and recombination (PL analysis). XRD analysis showed anatase rutile and Ce peaks, and no B peaks were detected which is due to the difference in ionic radius of the dopants. From XPS analysis, the elemental compositions of the doped catalysts (suspended form) and the actual amount of photocatalyst added during the film preparation (immobilized form) were in accordance with the selected compositions. Lesser recombination with lower PL intensity was observed for the doped catalysts. The reaction parameters such as catalyst loading, initial concentrations of antibiotic, mineralization (COD/TOC reduction), and reusability were studied, and the degradation pathways were elucidated (LC-MS analysis). The degraded sample was evaluated for the residual antibacterial activity to confirm the degradation of antibiotic. Real water matrices (tap water and river water) were considered in the study. Among the monodoped series, highest degradation of 93.22% was shown by 1 at.% Ce-TiO2 and 93.16% by 1 at.% B-TiO2 after 180 min. Whereas, among the codoped series of catalysts, B0.8Ce0.2TiO2 showed the highest degradation of 97.43% (suspended form) and 81.36% (immobilized form) after 180 min. Immobilized form ii showed 89.17% degradation of CIP at the end of 240 min. In terms of disinfection, the codoped catalyst was found to be 10 times more effective (corresponding to 1 log higher reduction) than the monodoped catalysts. Low molecular weight and less harmful degraded products were observed from LC-MS analysis. Reusability studies up to five consecutive runs proved the stability of these catalysts both in suspended and immobilized forms. The active role of electrons, holes, and OH ̇ species in the degradation was observed from the scavenging studies. The degradation and disinfection efficiencies in the real water samples were slightly lesser than the deionized water, which might be due to the presence of anions and natural organic matter. The performance of the codoped catalysts (in terms of both degradation and disinfection) was better than monodoped catalysts and superior when compared to TiO2. Overall, these boron and cerium (monodoped and codoped) doped catalysts can serve as an efficient solar light active catalysts for both antibiotic degradation and bacterial disinfection.Item Doping of Vacuum Deposited Zinc Oxide Thin Films(National Institute of Technology Karnataka, Surathkal, 2013) Palimar, Sowmya; Shivakumar, G. K.; Bangera, Kasturi. V.The main objective of present work is to study the doping of vacuum evaporated zinc oxide (ZnO) thin films. Initially, optimum conditions required to obtain good quality of undoped ZnO thin films is determined by depositing films using two evaporation sources (boats) namely molybdenum and tungsten and annealing them under different conditions. Compositional analysis of films showed incorporation of boat atoms in to ZnO thin films prepared using molybdenum as well as tungsten boat. A considerable reduction in atomic percentage incorporated boat atoms on annealing was observed in both cases. ZnO thin films obtained under optimum conditions were found to be amorphous in nature with good combination of visible region transmittance of up to 90% and room temperature conductivity of 92 Ω−1cm−1. XPS analysis has shown that the film is approximately stoichiometric with slight oxygen deficiency. From the measurements of activation energy it is observed that ZnO thin film is having two donor levels below the conduction band. Further, ZnO films are doped with third group dopants to improve their n-type conductivity. Investigation has been carried out to know the optimum percentage of dopnat to be added to retain the transmittance of the film. Role of third group elements as n-type dopants in the form of pure metals and metal oxides is studied by doping the film with indium and indium oxide separately. It is observed that contribution of indium oxide dopants is more than indium dopants in improving the conductivity of films. ZnO films were then doped with other two third group oxides, namely gallium oxide and aluminum oxide. From structural, optical and electrical properties of these oxide doped ZnO films it is found that all films have smooth surface with visible region transparency of above 90% and significantly high room temperature conductivity of the order of 103 Ω−1cm−1, which are well suited for the application of transparent electrodes.Item Study of Doping In Zinc Oxide in Thin Films Grown by Spray Pyrolysis Technique(National Institute of Technology Karnataka, Surathkal, 2014) Kumar N, Sadananda; Bangera, Kasturi V.; Shivakumar, G. K.The main objective of present work is to study the effect of doping on the optical and electrical properties of spray deposited zinc oxide (ZnO) thin films. The optimum conditions required to obtain quality of ZnO thin films is determined initially by varying the deposition parameters such as substrate temperature, spray rate and precursor molarity. Later film thickness and annealing temperature is fixed by considering the transmittance and conductivity of the films. ZnO thin films obtained under optimum conditions were found to be crystalline in nature with the combination of visible region transmittance of 78 % and room temperature conductivity of 0.156 S/cm. XPS analysis has been shown that the as-deposited film is oxygen deficient and annealed films are oxygen rich. Further, ZnO films were doped with group V and group III dopants to improve their conductivity. Investigation has been carried out to know the optimum percentage of dopant to be added to retain the transmittance of the films by varying dopant concentration from 0 to 5%. The effect of group V elements as dopants in the form of pure metals has been studied by doping the film with antimony and bismuth separately. A slight improvement in the conductivity of the films was observed with antimony and bismuth doping without changing optical transmittance in the visible region. ZnO film doped with Sb (3% and above) shows ptype conductivity. Role of group III elements as n-type dopants in the form of pure metals is studied by doping the film with aluminium, indium and gallium separately. It has been observed that all the doped films possess transparent and highly conducting properties. The 3% doping concentration and annealing at 450°C for 4hr is the optimum condition to achieve transparent and high conductive ZnO films doped with Al, In and Ga. From the structural, optical and electrical properties of these doped ZnO films it is found that all films have smooth surface with visible region transparency of 80% and significantly high electrical conductivity of the order of 102 S/cm at room temperatures, which are well suited for the transparent electrodes application.