2. Thesis and Dissertations
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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 Higher Order Asymptotics and Viscosity Method to Burgers Solutions(National Institute of Technology Karnataka, Surathkal, 2018) M, Manasa; E, SatyanarayanaThe viscous Burgers equation ut +uux = νuxx is a nonlinear partial differential equation, named after the great physicist Johannes Martinus Burgers (1895-1981). We focused on the study of the large time asymptotic for solutions to the viscous Burgers equation and also to the adhesion model via heat equation. Using generalization of the truncated moment problem to a complex measure space, we construct asymptotic N-wave approximate solution to the heat equation subject to the initial data whose moments exist up to the order 2n + m and i-th order moment vanishes, for i = 0; 1; 2 : : : m − 1. We provide a different proof for a theorem given by Duoandikoetxea and Zuazua (1992), which plays a crucial role in error estimations. In addition to this we describe a simple way to construct an initial data in Schwartz class whose m moments are equal to the m moments of given initial data. Secondly, we focus on the Riemann problem for de-coupled system and obtain the weak solutions explicitly. It is to be noted here that real valued solution for the system exists in the case of rarefaction wave and the weak solution consist of δ- measures in the case of raising the speed of characteristics. Eventually, we consider inviscid Burgers equation with a forcing term, this is in fact the first equation in the de-coupled system, but with a general initial function u0(x) = o(jxj); as jxj ! 1: We then pick up an explicit solution from Satyanarayana et al. (2017) for the parabolic approximation of the hyperbolic partial differential equation using vanishing viscosity method, we construct weak solutions for the considered hyperbolic partial differential eq