| At present, the pollution of indoor air has considerably been taken attention abroad as an important environmental problem. Formaldehyde as ubiquitous pollution species in the air is considered to cause cancer and abnormality by WHO. The effective treating process for decomposing formaldehyde have been increasingly concerned. However most of the studies on degradation of indoor air formaldehyde are concentrated on the operations using batch mode or continuous mode on low flow rate condition and thus this technique is still in experimental stage. Therefore how to explore some better techniques to clean the indoor air formaldehyde is the forward study in improved the air quality field.The dissertation studied the degradation of indoor air formaldehyde by photocatalytic oxidation process. The research mainly included the preparation and characterization of TiO2 catalysts. A series of factors on photocatalytic reaction process and reaction kinetics were also explored. The life of catalyst was investigated. The mechanism of photocatalytic decomposition of formaldehyde were preliminary discussed.TiO2 was prepared on the porous nickel plate by sol-gel process. The catalysts prepared were characterized by XRD, SEM, TEM and SPS. The results indicated that TiO2 was rutile-type. BET results indicated that the catalysts have surface areas of 69.27g/m2 and crystallite sizes of 23.4 nm.Batch reactor was employed in removal of formaldehyde gas. The effects of humidity, initial formaldehyde concentration, ozone amount and temperature on photocatalytical degradation of formaldehyde in gas-solid phase were investigated. The experimental results indicated that the best relative humidity was 30%,and the lower initial formaldehyde concentration, the higher its degradation. However, the degrading load of formaldehyde on the unit catalyst was increased at first and then decreased as increasing initial formaldehyde concentration. The decomposing efficiency of formaldehyde is direct proportion of temperature. Furthermore, addition of ozone can considerably increase decomposing of formaldehyde, and combination of ozonation with photocatalytic oxidation on formaldehyde showed a synergism. The kinetics of formaldehyde degradation reaction can be described by Langmuir-Hinshelwood model, that is, the degradation rate of formaldehyde can be expressed by first-order kinetics model.The degradation of gaseous formaldehyde was studied using continuous flow mode. A series of factors such as relative humidity, initial concentration, residence time and ozone adding amount was also investigated. Formaldehyde degradation efficiencies decreased from 72% to 21% as the concentration increased from 1.84mg/m3 to 24mg/m3 in the UV/TiO2; the formaldehyde degradation efficiencies decreased from 79.4% to 73.6% as the concentration increased from 1.84mg/m3 to 24mg/m3 in the UV/TiO2/O3 process. In the relative humidity range of study in this work, the degradation efficiencies achieved from 63.6% to 78.0% for UV/TiO2/O3 process but only 21.7% to 46.7% for UV/TiO2 process. When residence time is low ( 40 s), the degradation of formaldehyde is 33.3% for UV/TiO2 process, and 64.1% for UV/TiO2/O3 process, almost 2 times of that for UV/TiO2 process, indicating the UV/TiO2/O3 process was more efficient in decomposing formaldehyde than UV/TiO2 process at low residence time. When residence time increases to 300 s, almost same high formaldehyde degradations are achieved for both UV/TiO2 and UV/TiO2/O3 processes (96.2% for UV/TiO2 process and 98.5% for UV/TiO2/O3 process). Degradation of formaldehyde increases from 39.0 % to 94.1% when the ozone content increases from 49 to 141 mg/m3. So the process of UV/TiO2/O3 can degraded the formaldehyde more efficient than the UV/TiO2 process under all experimental conditions.The degradation of low-level formaldehyde gas was studied in the well-sealed room controlled by air-conditioning systems. The experimental results indicated that addition of ozone can considerably increase decomposing of formaldehyde, and combination of ozonation with photocatalytic oxidation on formaldehyde showed a synergetic effect.When the concentration of ozone reached 0.36mg/m3, ozone remains could not be detected, so the optimal ozone amount was around 0.36mg/m3 in the UV/TiO2/O3 process, and the formaldehyde residue (0.04mg/m3) is below the WHO guideline (0.1mg/m3).The mechanism of photocatalytic decomposition of formaldehyde were discussed. HCOOH and HCO3- as the intermediate were detected by GC-MS and Ion Chromatogram(IC).·OH,·HO2,·O2- and·CO2 radical were detected in the photo catalytic oxidation process by electron spin resonance (ESR) spectrum. The series of factors to affect the freedom radical production by different photo catalytic oxidation processes were investigated. The result indicated that the amount of water in reaction system decide the production of·OH,·HO2 or·O2- radical. The production of formaldehyde degradation was HCOOH at first, then oxidized to CO2 and H2O.In a word, combination of ozonation with photocatalytic oxidation process as an indoor air purification technology can be used to formaldehy degredation. This purification methods is a promising technology in cleaning the organic pollution.
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