Research On Photoregeneration Of Activated Carbon And Synergy Effect Of TiO₂--Activated Carbon

Modification of photocatalyst anatase TiO2 and photoregeneration of activated carbon under irradiation of UV light were studied in this thesis as well as its photoregeneration mechanism and synergy effect of TiO2 and activated carbon.The activity of nanometric-sized Zhengyuan TiO2 and Aldrich Chemicals Companies' TiO2 was analyzed. Compared to Zhengyuan TiO2, Aldrich Chemicals Companies Ti02 had higher photocatalyst activity, which was selected as an optimal photocatalyst for modification and light regeneration of activated carbon. The reason of low activity of nanometric-sized Zhengyuan TiO2 was analyzed.Effects of heat treatment and noble metal doping of Aldrich Companies TiO2 was investigated on photocatalyst activity. Heat treatment of TiO2at various temperature (400-900C) and time was carried out and its activity and XRD were analyzed. The results showed that TiO2 treated at 500C for 2 hours, consisting of 96% anatase type and 4% rutile type, had optimal crystal structure and high activity. TiO2 treated at 900C for 6 hours had 3% anatase type and 97% rutile type. This indicated that anatase type in TiO2 was transformed into rutile type when increasing treatment temperature. Coagulation of photocatalytic particles, however, was observed during the heat treatment process. Ag-TiO2 photocatalyst was achieved by doping noble metal Ag on TiO2 through reaction of AgNO3 and Na2CO3. The optimal synthesis condition of Ag-TiO2 was obtained through photodegradation of methylene blue as follows: 7 ml 0.2 M AgNO3 /g TiO2, 2:1 AgNO3 : Na2CO3 (v/v). The results showed that Ag-TiO2 activity was higher than heated TiO2. Ag-TiO2 activity was 7.7 times as high as regular TiO2. Mechanism of enhancing activity of noble metal additive was discussed.By using TiO2 and Ag-TiO2 as photocatalyst, 257 nm wavelength UV as light source, methylene blue and phenol as model compounds, photoregenerations of wooden and coaly activated carbons were performed in suspension system and immobilized system respectively. Photocatalyst was fixed on activated carbon through impregnation-desiccation. When methylene blue as model compound, 60-80 meshes wooden activated carbon loaded with suitable content Ag-TiO2 was regenerated under 50C for 72 hours and its absorbing capacity was recovered by 81%. Under the same condition, it took 86 hours to obtain the same regeneration efficiency for 20-28 meshes activated carbon. When phenol as model compound, coaly activated carbons loaded with suitable content Ag-TiO2 was regenerated under 50C and pH 13 for 72 hours and it's absorbing capacity was recovered by 79.6%. Main factors effecting regeneration efficiency were discussed including the applying method, activity of the photocatalyst, particle size of activated carbon, time, temperature, pH, frequency, oxidant, and inorganic ion. The regeneration efficiencyIIIof activated carbon treated with Ag-TiO2 was higher than that treated with TiO2. Higher regeneration efficiency was achieved for smaller particle size of activated carbon at extended time and higher temperature. For activated carbon absorbing acidic or alkaline material, pH showed to some extent effect on regeneration efficiency. Regeneration efficiency decreased significantly when activated carbon was recycled many times. Most of inorganic ions have no effect on photoregeneration efficiency except trace Mn2+ that greatly decreased photoregeneration efficiency.The results showed that model compound and its photodegraded intermediate had similar structure and its components couldn't be thoroughly separated through HPLC and GC. MS results showed that phenol's photocatalytic intermediate structure has changed greatly compared to phenol. The result from loaded activated carbon microstructure analysis showed that the photocatalyst were mainly adsorbed on the macro-pore and hollow site and distributed unevenly. The adsorbed photocatalyst jammed only a part of adsorption pathway and specific area of loaded carbon decreased slightly. As the photoregeneration proceeded, saturated carbon's spec...