Metal Ion Doped TiO₂ Photocatalytic Degradation Of Phenolic Compounds

Industrial wastewater containing organic pollutants has always been a main environmental concern throughout the world. A proper method of treating is the main objective to sustaining water resources. Among several methods of water purification, semiconductor photocatalysis is a competent technique for degradation of various hazardous substances. It can degrade various organic chemicals which have not been tackled by other methods of purification. This dissertation incorporates the studies on various aspects of photocatalytic degradation of phenolic compounds.The photocatalytic degradation of three phenolic compounds namely phenol, 4-chlorophenol and 4-nitrophenol over UV-irradiated TiO₂ was investigated in aerated aqueous solution. The effects of various operational parameters such as pH, catalyst concentration, phenol concentration, anions, metal ions, electron acceptors, surfactants and power of UV lamp on the photocatalytic degradation of phenol were investigated. The degradation kinetics was computed by measuring the change in phenol concentration employing UV-visible spectroscopy as a function of irradiation time. The degradation kinetics of phenol follows pseudo first-order kinetics. The results showed a significant dependence of the photocatalytic degradation of phenol on the operational parameters. The probable promising roles of the additives on the degradation process were discussed. This study also includes the effect of photocatalyst such as TiO₂ (anatase) and TiO₂-P25, and alignment of UV-lamp on the photocatalytic degradation of phenol. TiO₂-P25 was found to be more active than TiO₂ (anatase) which is attributed to small crystalline size. Horizontal position of the lamp was found to be better than vertical position of lamp. The degradation was also enhanced with increasing UV lamp power.The influence of temperature at optimized pH and TiO₂ concentration was studied for three phenolic compounds. The degradation kinetics were somewhat accelerated by increase in temperature in the range 25-45°C and apparent activation energy was calculated to be 9.68-21.44 kJ mol-1. Thermodynamic parameters of activation were also assessed for the degradation process. Formation of acidic species results in decrease in pH of solution. The appearance and the evolution of main intermediate species like hydroquinone, benzoquinone and catechol during the degradation process were computed by UV-vis spectral analysis. The effect of different supporting materials such as activated carbon, ZSM-5 and silica mixed physically with titanium dioxide on the photocatalytic degradation of phenolic compounds has also been studied in aqueous suspension under UV irradiation. TiO₂ with all supports exhibited good degradation efficiency for phenolic compounds and was better than TiO₂ alone within 120 min photocatalysis. The degradation was also significantly enhanced in the presence of cheaper rice husk and the activity was close to activated carbon.The Fe³⁺-doped and undoped TiO₂ nanoparticles have been prepared employing sol-gel method with hydrolysis mechanism using ferric nitrate aqueous solution and tetrabutyl titanate. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and ultraviolet-visible spectroscopy (UV-visible) diffuse reflectance spectra (DRS) were used to characterize the nanoparticles. The experimental results revealed that Fe³⁺-doped TiO₂ nanoparticles possessed the anatase structures, which were composed of 8-11 nm of crystallite size. The photocatalytic performance of the nanoparticles was examined for degradation of phenol in aqueous dispersion under UV light. The most favorable efficiency of Fe doping on TiO₂ occurs at 0.5 mol% in this study. 0.5 mol% Fe³⁺-doped TiO₂ has also been calcined at various temperature to assess the calcination effect. Catalytic activity increased with the increase in calcination temperature and maximum efficiency was observed at 450°C. Beyond 450°C, decrease in photocatalytic activity was observed and approaches to zero at 750°C due to rutilation. An attempt has been made to correlate the degradation of phenol with partition coefficient of phenol in sodium dodecyl sulfate micelles and water as a function of irradiation time.Fe³⁺/M codoped TiO₂ nanoparticles (where M = Ba²⁺, Co²⁺ and La³⁺) were also prepared using TiO₂ as a starting material. Prepared catalysts were calcined at 450°C and characterized by XRD, SEM and EDX. The photocatalytic activity was evaluated by the photodegradation of phenolic compounds at pH 5 under both UV and visible irradiation. Prepared catalysts retained their UV light activity. This section also shows that the role of oxygen is important for improving the photocatalytic degradation. Comparable radii of the dopant metal ion have significant influence on the photocatalytic activity of codoped catalysts.