Photodegradation of Pharmaceuticals and Organic Contaminants in Water Using TiO2 and BiOCL-BiOI
Heterogeneous photocatalysis using semiconductors is an emerging green technology, suitable and recently applied for removal of these recalcitrant contaminants in waste water. The advantage of this technology is based on the generation of highly oxidizing radicals for degradation of organic pollutants to nontoxic intermediates or inorganic compounds such as water and carbon dioxide. Recent studies focus on improving the efficiency of the photocatalysis by immobilizing the photocatalyst on a substrate, preparing visible light photoactive catalysts in a cost effective way and optimizing photocatalytic reactors. The focus of this thesis is to develop a technique for immobilizing catalyst on polymeric substrates and prepare a visible light active photocatalyst for effective degradation of organic contaminants in waste water effluent. A novel low temperature heat attachment technique for immobilizing catalyst film on polymeric materials at low temperature was developed using Dimethylacetamide (DMAC) as the immobilization solvent. The catalyst was successfully immobilized on Poly methyl methacrylate (PMMA) and Polyvinylidene fluoride (PVDF) at low temperature of 55 °C. Immobilized catalyst adhesion test was carried out using two different techniques: by measuring the turbidity of water under maximum speed magnetic stirring in the reactor and by using adhesive tape scratch method. Both methods proved that the catalyst film on the polymeric substrate was strongly attached on the substrate. The turbidity of water measured during the adhesion test was relatively constant at 0.135 NTU after four hours of agitation for TiO2 immobilized on PMMA which implied that catalyst attrition was not experienced in the process. The immobilized photocatalyst was characterized using scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Atomic Force Microscopy (AFM). The TiO2 film was observed to be evenly distributed with an average thickness of 14 μm after the third coating. The immobilized catalyst activity was tested by degrading a recalcitrant pharmaceutical in a batch reactor under UVC irradiation. Experimental results showed that the photocatalysis followed pseudo first order reaction kinetics. 100% degradation of carbamazepine was achieved after 3 hours irradiation. Comparison study of reaction kinetics performed with other works indicated that the technique is a potential candidate for treating waste water. NOM in tertiary and secondary wastewater effluents resulted in 16% and 33% decrease in reaction rate constant respectively. Increase in number of substrates resulted to an increase in photodegradation rate constant, and a correlation between reaction rate constant and immobilized surface area was obtained as Y = 0.00134 X + 5.03 * 10-4. The results also indicated that the photodegradation efficiency of the catalyst film on PMMA is in the order of P25 > Anatase TiO2 > P25/AC. The film catalyst was also found to be highly stable, self-regenerating and reusable after an additional 3 cycles of experiment. A continuous flow photocatalytic reactor was also designed and fabricated using galvanized steel with TiO 2 immobilized on a highly porous ceramic substrate at 400°C using 5.5% (v/v) phosphoric acid as binder. BiOClx/BiOI(1-x) which is a visible light heterojunction catalyst was rapidly prepared at room temperature and calcined under microwave irradiation. The prepared photo-catalysts were identified and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–VIS diffused reflectance spectroscopy (DRS) analysis, and N2 adsorption-desorption isotherms. The characterization revealed that the catalyst composite formed a spherical hierarchical 3D structure with nano pore size of 19.81 nm, average particle size of 155.2 nm and band gap of 2.75 eV. Photo-catalyst experiment performed in degrading Tartrazine affirmed that BiOCI/BiOI composite with a molar ratio of 0.85 to 0.15 exhibited the highest photo-activity and achieved 100% degradation of 20 mg/l of Tartrazine in 60 minutes and 140 minutes in a reacting volume of 100 ml under simulated solar light and LED visible light irradiation respectively. Results also showed that the photo-catalysis followed pseudo first order reaction mechanism with kinetic rate constants of 0.097 min-1 and 0.048 min-1 for BiOCl0.85/BiOI 0.15 under simulated solar light and LED visible light irradiation respectively. BiOCl0.85/BiOI0.15 was also found to be five times better than P25 and fourteen times better than BiOI. Under both simulated solar light and LED visible light irradiation, effect of water depth was investigated, and the result showed that the degradation rate constant decreases with increase in water depth. Comparison based on Electrical Energy per Order (EEO) reveals that water depth of 5.08 cm with EEO of 63.12 and 273.375 for irradiation under both solar light and LED visible light irradiation respectively is the optimum height for the degradation. (Abstract shortened by ProQuest.)
Nnanna, Purdue University.
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