PHOTODEGRADATION OF DYES IN THE PRESENCE OF BISMUTH-TREATED APATITES AS HETEROGENEOUS CATALYSTS IN WATER

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In viewpoint of development of photocatalyst for water purification based on advanced oxidation process, hydroxyapatite (HAP-400) and fluoraptite (FAP) were treated with Bi(NO₃)₃ in DMSO/H₂O mixed solvent (DMSO = dimethylsufoxide) to give the corresponding Bi-treated apatites, HAP-400-Bi and FAP-Bi, respectively. The treated apatites were investigated as catalysts in photodegradation of dyes, alizarin red S (ARS) and methyl orange (MO), in water under H₂O₂-absent/present condition. Photodegradation rates of ARS under H₂O₂-absent condition reached 73% for HAP-400-Bi and 83% for FAP-Bi, accompanied with the corresponding ARS adsorption rates at 62% for HAP-400-Bi and 69% for FAP-Bi, respectively. On the other hand, MO was photodegraded at less than 4% under the same condition, possibly attributed to little adsorbabilities of MO on the prepared Bi catalysts. Eventually, photodegradation of ARS by using HAP-400-Bi or FAP-Bi under H₂O₂-present condition, namely photo-Fenton like condition, resulted in the complete ARS consumption rate of 100% for both of the catalysts, and considerably high mineralization rates of 40% for HAP-400-Bi and 62% for FAP-Bi. Generation of hydroxyl radical •OH as an activated oxygen species was confirmed by the following two methods: One employs 2-propanol as a •OH scavenger; The other employs N, N-dimethylamino-4-nitrosoaniline (DMNA) as an indirect •OH detector. It was found that •OH radical species is predominantly formed via the prepared Bi catalysts under photo-Fenton like condition to offer an oxidative reaction field, and that self-photodegradation of dye, especially ARS, partly proceeds by electron transferring interaction between dye and Bi catalyst.