The Photosensitizer-Assisted Photocatalytic Degradation Of Organic Chlorine Contaminants And Its Kinetic Model

Organic chlorine compounds with macro rings are a series of dangerous contaminants, for they can hardly be degraded. Semiconductor photocatalytic oxidation is a newly developed technique for wastewater treatment. It has been applied for oxidizing and degrading many organic contaminants, which usually are hardly degraded by other methods, into CO2, H2O and other harmless small molecules. Therefore, studies on the photocatalytic reaction mechanism, reaction engineering and preparation of high active catalysts are important for contamination control, environmental and water resource protection.In this dissertation, we employed a cylinder photocatalytic reactor, a low-pressure Hg lamp as light source, and TiO2 as catalyst to investigate degradation of simulating organic chlorine wastewater with outer circulation photoreactor. The effects of preparation temperature of micro scale TiO2 on the catalytic activities have been explored. The catalysts were also characterized with SEM, XRD and FTIR. Na-PCP, p-benzenediol and 4-chloro -2-methoxyphenol were chose for degradation studies. The results showed the catalyst heating at 500℃ for 24 hours has the highest catalytic activity. Their crystal size is equivalent and crystal face is clear. Both the size and specific areas have been changed, but no big difference found for their crystal structure after heating. These studies showed that TiO2 in micro scale could also be applied as nanoscale TiO2 for the degradation of wastewater. However, TiO2 in micro scale is cheaper and easy to recover.When Na-PCP and 4-chloro -2-methoxyphenol were used as simulating compounds, the photocatalytic oxidation reaction and the reference reaction have been investigated. Experimental results showed the adsorption of solid catalyst reaches equilibrium in 20 minutes. The reaction kinetics were studied based on Na-PCP photocatalytic degradation experimentations, including initial concentration of Na-PCP, dosage of catalyst TiO2, pH of solution and UV-radiation intensity etc. A kinetic model was proposed from pseudo first order Langmuir-Hinshelwood equation to describe heterogeneous photocatalytic system.The designation and development of large-scale photocatalytic reactor for wastewater treatment is one of the major challenges for the industrial application of this technique. We used a tubular continuous-flow and outer circulation photo-reactor with titanium dioxide in suspension for the photocatalytic study. The kinetic process in the reactor system has been studied with 4-chloro-2-methoxyphenol as model reactant in different catalyst concentration (100mg/L and 200mg/L). A mathematical model has been proposed for the process by using a fourth-order Runge-Kutta scheme and MATLAB to calculate the differential equations. 3D graphs describing the distribution of radiant energy and the concentration of 4-chloro-2-methoxyphenol in the reactor were achieved with Origin software. The results indicated the radiant energy decrease gradually in the radial and the concentration of 4-chloro-2-methoxyphenol is decreased in the axes direction (either liquid flow direction), but is increased radically.The degradation of 4-chloro -2-methoxyphenol, the main contaminant in bleach wastewater, has been studied with photocatalytic oxidation method. The results show TiO2 can effectively photocatalyze the oxidation of 4-chloro -2-methoxyphenol. The optimal reaction conditions have been concluded with orthogonal method. The initial concentration of organic compounds is the key factor for the reaction. The pH of solution is the second important factor affecting the reaction. Increasing reaction times would raise the degradation rate of photocatalytic reaction. The photocatalyst dosage and the circulationflow rate of reactor also have contributions on the reaction. The optimal conditions are: initial concentration 0.05 mmol/L, the circulation flow rate 20L/h, dosage of catalyst 250 mg/L and pH of solution is 10, the degradation rates up to 83%.The photosensitizer-assisted photocatalytic oxidation of organic chlorine compounds...