Study of light-driving reactions in oxidizing organic pollutants in liquid

Autor:	Wei-Lun Lee, 李偉綸
Rok vydání:	2011
Druh dokumentu:	學位論文 ; thesis
Popis:	99 Solar energy may enhance the auto-decomposition of peroxide and result in more hydroxyl radical production to speed the degradation of organic pollutants during in the chemical oxidation process. In addition, solar energy may promote the formations of electrons and electron holes on semi-conducting materials like Titanium dioxide (TiO2), and the latter can serve as electron hunters and act as oxidant like the peroxide. To combine the beneficial uses of solar energy with the patent awarded catalyst, EDTA-Fe, in degrading the targeted toxic organics, crystal violet (CV) and 3-, 3,4- and 3,5-chlorophenols (3-, 3,4- and 3,5-CPs), this study aimed to (1) study the degradation efficiency of the targeted compounds via auto-decomposition of peroxide, (2) investigate the degradation efficiency of the targeted compounds via TiO2-assisted photocatalysis, and (3) to determine the optimal conditions of using solar energy in treating toxic organic compounds. From the tests of EDTA-Fe catalyzed oxidation, the results concluded that by adding 0.18 μmole EDTA-Fe per mL of the target compound polluted solution with initial peroxide concentration at 0.1% the degradation of CV reached ~100% after 4 hours of reaction. At EDTA-Fe dosage of 0.108μmole EDTA-Fe per mL with initial peroxide concentration at 1.2%, all of the degradation efficiencies of the targeted chlorophenols were higher than 95%. From the tests of the auto-decomposition of peroxide, the results demonstrated that runs with peroxide alone raised their CV deduction by 43.9% after received 2-hours sun-light; runs with Fe2+ or EDTA-Fe as catalysts the CV deduction raised from 79.8 and 90, respectively, to 100%. In similar treatment but for four hours, the 3-MCP and 3,5-DCP had 12 and 7% more deduction compared with the ones receiving no sun-light. These results obviously indicated the solar energy enhanced the degradation efficiencies of the targe compounds in liquid. From the tests of TiO2-assisted photocatalysis, the results revealed a 12-25% increase of CV deduction after 2 hours of receiving sunlight. when receiving light, the runs containing EDTA or EDTA-Fe as catalyst had CV residuals of 4.49 (i.e., 47.8% degradation) and 4.25 mg/L (i.e., 50.6% degradation), respectively, which were 31.8 and 34.6% more deduction of CV than that of runs containing no catalyst or Fe2+ only. In treating CPs, the dosages of TiO2 had little effect on CPs degradation. Runs containing EDTA-Fe degraded about 30% of 3-MCP on average; runs containing no EDTA-Fe only 15% the most, which was 50% less than with EDTA-Fe runs.The optimal operating conditions of using electro-potential were set by using fluorine-doped tin oxide (FTO) glass as anode and TiO2-coated FTO (TiO2-FTO) as cathode at fixed current of 6 mA. After one hour of treatment, the CV deduction was ~92%. Results of a 24 factorial experiment demonstrated that additions of EDTA, EDTA-Fe, electrolyte and dye N719 decreased the CV reduction to 50%. When replacing the electropotential with sunlight for one hour using same electrodes, the results showed the CV degradation decreased about 75%; if using UV instead, the degradation was about 63% of that of runs receiving sunlight. Also the TiO2-FTO electrode showed the adsorption of CV (~40% of total CV added) and some detachment of TiO2 layer due to the reaction. The TiO2 detachment was fixed by soaking the TiO2-FTO electrode in 0.003 M EDTA-Fe solution for 12 hours. Connection of two electrodes by copper wire might further elliveate the detachment of TiO2 as well. Using the mentioned setup conditions, four potential affecting factors, namely, the addition of EDTA, Fe2+, electrolyte or phosphate buffer, were identified, and via a 24 and a 23 factory experiments, the additions of EDTA and buffer were identified as the most important factors that affected the degradation efficiency of CV in the treatment system. Soaking of TiO2-FTO electrode in EDTA solution was eliminated due to the instability of CV degradation if doing so. The optimal dosages of buffer and EDTA were determined at adding 1.37M buffer 0.375mL and 0.216M EDTA 0.75 mL in 23.75 mL of the targeted compound polluted solution. Under such optimal conditions, the degradation of CV over time was satisfactorily predicted by a first-order kinetic model with kinetic constant of 1.1171/hr if using sunlight and 0.385/hr if using UV light.When treating CPs at the optimal conditions, the run without sunlight showed 30-50% sorption of CPs, yet after a two-hours treatment around 15% of CPs degradation was observed.
Databáze:	Networked Digital Library of Theses & Dissertations
Externí odkaz:	http://ndltd.ncl.edu.tw/handle/15426573956714492857 Zobrazit plný text záznamu