Study On Codoped TiO₂Degradation Of Indoor Formaldehyde And The Design Of Photocatalytic Reactor

According to statistics,more than80%of time are spent indoors for modern people. Forworldwide,2.8million people directly or indirectly died of decoration pollution each year andabout4%of the diseases are related with indoor air pollution. Formaldehyde is dangeroussubstance with high toxicity which can induce cancer and abnormality and it is one of themajor pollutants of indoor air pollution. In1995, formaldehyde was identified as a suspectcarcinogen by the International Agency for Research on Cancer.Nano TiO₂is the most studied photocatalyst,it can degradate most organic pollutant byphotocatalytic oxidation in water and air,include dye,surfactant,and various nonbiodegradabletoxic organic pollutant,its final degradation product is H20,C02and nontoxic ion or salts.TiO₂photocatalytic oxidation is considered the most promising photocatalytic oxidation forits nontoxicity,chemical stability,inexpensiveness and non-secondary pollution.But,thesemiconductor TiO₂-based photocatalysis technology still exists two key difficult problems ofscience and technology:both of the quantum production and the utilization of solar energy arelow. Considering those two difficult problems above,the research work has been carried out asfollow:1.In this paper, L9(34)orthogonal experiment and sol-gel method were used to determinethe optimum preparation of TiO₂,N/TiO₂,Ce/TiO₂,Ce/N/TiO₂. The results show, theoptimum preparation of TiO₂,N/TiO₂,Ce/TiO₂,Ce/N/TiO₂are T=500℃,t=2h；T=500℃,t=2h,N/TiO₂(mol%)=10%；T=500℃,t=2h,Ce/TiO₂(mol%)=3.0%；T=400℃,t=3h,N/TiO₂(mol%)=15%,Ce/TiO₂(mol%)=3.0%respectively.2. To TiO₂,N/TiO₂,Ce/TiO₂and Ce/N/TiO₂which were prepared under optimumconditions, influencing factors such as the initial formaldehyde concentration,temperature,theamount of catalyst,UV lamp intensity and other factors on the formaldehyde degradationwere studied. The results show:when one single factor was changed,the formaldehydedegradation rate of TiO₂,N/TiO₂,Ce/TiO₂and Ce/N/TiO₂increased and then decreased.Whenother conditions were certain, the formaldehyde degradation rate of the four groups shownfollowing order: Ce/N/TiO₂>Ce/TiO₂>N/TiO₂>TiO₂； Under the same conditions, theformaldehyde degradation rate of TiO₂,N/TiO₂,Ce/TiO₂and Ce/N/TiO₂under the xenon lightsource were higher than the formaldehyde degradation rate under the8w fluorescent light source.3. The surface microstructure and morphology of TiO₂,N/TiO₂,Ce/TiO₂and Ce/N/TiO₂were characterized by X-ray diffraction (XRD) and UV-visible spectra,trying to explore themechanism of the degradation of formaldehyde. The results show:when2θ=25.160,TiO₂,N/TiO₂,Ce/TiO₂and Ce/N/TiO₂which were prepared under optimum conditions showndiffraction peaks.Compared with other diffraction peaks,the diffraction peak of TiO₂wasweak.The four samples were up to the nanometer level,the particle size'order: TiO₂﹥N/TiO₂﹥Ce/TiO₂﹥Ce/N/TiO₂. TiO₂,N/TiO₂,Ce/TiO₂and Ce/N/TiO₂shown different redshift,theextent of redshift'order: TiO₂﹥N/TiO₂﹥Ce/TiO₂﹥Ce/N/TiO₂.4. A formaldehyde degradation device was designed,charcoal supported Ce/N/TiO₂usedas photocatalyst.The effect of the load,charcoal interval of the catalytic unit on theformaldehyde degradation were discussed.Charcoal supported TiO₂used as a comparativeexperiment.And the device's formaldehyde degradation rate was tested. The resultsshow:when the device was designed into gata structure, the light surface of the catalyst waseffectively increased and the block of the charcoal to the UV light source was reduced,whichcan improve the photocatalytic reaction rate.When the thickness of catalyst layer is2mm andits intervals is20mm, the formaldehyde degradation rate is better,up to94%.