Synthesis, characterization and photocatalytic activity of titanium dioxide (pure and doped) photocatalyst for the degradation of aqueous organic pollutants
Notice bibliographique
Résumé
Recently the advantages derived from titanium dioxide (TiO2) as a photocatalyst for the degradation of organic pollutants in waste water has prompted a great deal of research. TiO2 exist in nature in three crystalline forms; anatase, brookite and rutile. Although anatase is recognized to be more active as a photocatalyst than the other two, there are reports in the literature that a mixture of anatase-rutile may exhibit higher photocatalytic activity. Under visible light irradiation the photocatalytic activity of TiO2 is negligible because of its wide band gap (~3.2eV) which corresponds to UV light. In addition, the recombination rate of photogenerated electron-hole pairs is very high compared to the rate of charge transfer to the catalyst surface for the redox reactions. To overcome these limitations, doping is a promising approach which not only extends the TiO2 response to the visible region but also helps to decrease the recombination of charge carriers thus enhancing the interfacial charge transfer rate.The objective of this dissertation is to address the effects of the dopants (molybdenum, vanadium, iron and selenium) and chelating agents (acetic acid, formic acid and oxalic acid) on TiO2 physiochemical and UV/vis photocatalytic properties. The synthesis of doped TiO2 from titanium oxysulfate precursor showed a decrease in the band gap value implying an increase in visible light absorption following the order of Mo-TiO2 < V-TiO2 < Fe-TiO2. Increase in the concentration of Mo leads to the transformation of brookite into anatase. In contrast Fe and V favor the formation of brookite phase. In the degradation of methylene blue (MB) under visible light the 0.25mol% Fe-TiO2 achieved the highest apparent reaction rate constant (kapp) value of 1.2min-1 which is 6.6 times higher compared to undoped TiO2 (0.18min-1) and commercially available Degussa P25 (0.17min-1).Chelating agents (carboxylic acids) and solvents (alcohols) are added to modify the titanium alkoxide precursors (titanium butoxide, titanium isopropoxide) to control the very fast hydrolysis and condensation reactions occurring during the synthesis of the photocatalyst. Due to the chelation of the formate group with titanium atoms, a mixture anatase-brookite (86-14wt.%) was obtained in contrast to pure anatase formation in the absence of formic acid at 400oC. The formic acid modified TiO2 (anatase-rutile; 94-6wt.%) calcined at 600oC showed enhanced UV photocatalytic activity compared to Degussa P25 for the decomposition of methylene blue dye. The variation in the synthesis method may also affect the physical properties of the final material. V-TiO2 was prepared by a modified sol gel method from TTIP mixed with acetic acid. In undoped TiO2 the acetate group was binded by bidentate bridge mode to the titanium atoms compared to bidentate chelating mode in V-TiO2. This result verified that the presence of vanadium ions affect the chelation of acetate group with titanium atoms, and this may be the reason that anatase to rutile transformation is suppressed. In the photocatalytic tests, V-TiO2 (100:1, V:Ti molar ratio) powder showed enhanced visible activity for methylene blue degradation due to small crystallite size, high surface area, lower band gap and the presence of oxygen vacancies. The synthesis of undoped, mono and codoped TiO2 with Mo and V was carried out by ultrasonic assisted sol-gel method. It was observed that due to ultrasonication TiO2 composed of anatase with minor brookite and rutile was produced compared to pure anatase formed when mechanical stirring was used. In the UV/vis photocatalytic tests codoped powders showed enhanced activity compared to undoped and mono doped powders in the degradation of methylene blue and sulfamethoxazole. The enhanced catalyst activity was attributed to composite mixture of TiO2 polymorphs, enhanced dye adsorption at the surface, dopant impurity bands, Ti+3 centers and oxygen vacancies.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,001 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,000 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».