Study On Titanium Dioxide Assisted Egradation Of Cod

The study is on degradation treatment of papermaking wastewaterfrom Xi’an brothers and Paper enterprise through chemical coagulationand TiO₂photocatalytic method. First, selecting chemical coagulationmethod treated papermaking wastewater to determine the type ofcomposite coagulant in chemical flocculation process, the best ratio andconditions of composite coagulation treatment process. Thepapermaking wastewater was added in the process of coagulationtreatment according with the best ratio of the composite coagulation. Inthis way the COD value of5500mg·L^-1can be reduced to1000mg·L^-1.Then secondary treatment of wastewater was completed through theTiO₂photocatalytic oxidation after coagulation. Using two methods ofthe sol-gel and microwave-assisted sol-gel synthesis preparednano-titanium dioxide film in experiments. Meanwhile, multipleperformance were characterized which were formation mechanism,microscopic composition, surface properties, optical properties and soon. Secondary degradation of wastewater was completed viaphotocatalysis of two thin films after the composite coagulationtreatment. Then we explored the process parameters. In this study, thespecific content and conclusions are as follows.First, coagulation treatment of black liquor was mainly studiedthrough selecting a polyaluminum chloride （PAC）, cationicpolyacrylamide （CPAM） and polymeric ferric sulfate （PFS） ascoagulation reagents. Effects of single coagulant degradation,composite coagulant degradation and pH of composite coagulanttreatment were sufficiently investigated via the determination of COD,absorbance and precipitation amount. Afterwards wastewater aftercoagulation treatment was degradated by photocatalytic oxidationtechnique and was analyzed about effecting factors of photocatalytic process again. The consequences of composite coagulation treatmentwas superior to a single coagulation treatment. Using thePAC-PFS-CPAM as the complex flocculation withPAC:PFS:CPAM=5:3:2（volume rate） and pH value of6could get thebest result of degradation.Adopting Ti（OC4H9）4as the precursor solution of titanium, theanatase TiO₂thin films were prepared on the glass substrates with thedip-coating way through the Sol-gel method at500℃. The morphology,optical properties and surface properties of as-prepared samples werecharacterized by X-Ray Diffraction（XRD）, Scanning ElectronMicroscopy （SEM）, UV-vis absorption spectra analyses and contactangles of films. The results testified that this method could prepare theanatase phase of titanium dioxide films. The generated particles weresmall and arranged in dense, which of thin films（loading4layers） werebetter than the films（loading5layers）. By the energy spectrum analysisof the films, we can know that the number ratio of atom was1to2.Thus, we could obtain that the main composition of film was TiO₂.Thelarger absorbance is under the UV（λ=300nm）. Because the value ofcontact angle was in the less than90°, the results showed that thematerial surface could demonstrate hydrophilic properties and thehydrophilicity became strong with the smaller contact angle. Afterwards,the best degradation conditions of photocatalytic reaction process wereultimately gained that COD of wastewater can be reduced by77.9%with a concentration of wastewater about900mg·L^-1, pH of3.5,radiation time with UV light （80W,254nm） in10.0h and illuminationdistance of8cm. COD value of wastewater after degradation was only199mg·L^-1. The wastewater after degradation could be used as recycledpulp water.Based on sol-gel method, TiO₂films were prepared throughmicrowave assisted low temperature synthesis method. To comparewith traditional sol-gel, the microscopic structure, composition andsurface properties of as-prepared samples were characterized by X-RayDiffraction （XRD）, Scanning Electron Microscopy （SEM） and contact angle of films surface analyses and so on. Then using photocatalysis ofthese films treated the wastewater after coagulation and investigatedparameters of the reaction process. Making the contrast with the sol-gelmethod, the results indicated that this method can prepare good anatasephase of titanium dioxide films. The resultant particles became large,loosely arranged and uniformly distributed energy spectrum analysisknew the main composition of film was TiO₂, and content of Ti atomshad increased. The contact angles of the films with ultraviolet （UV）irradiation became smaller, which explained that the hydrophilicperformance was better than the traditional method. The bestdegradation conditions of photocatalytic reaction process wereultimately gained that COD of wastewater can be reduced by81.3%with a concentration of wastewater about950mg·L^-1, pH of4.0,radiation time with UV light （80W,254nm）of8.0h at35℃andillumination distance of8cm. Finally, COD value of wastewater afterdegradation was only178mg·L^-1. The research prove that this methodcan effectively improve the activity of the photocatalyst.