Synthesis, characterization and photocatalytic activity of titanium dioxide (pure and doped) photocatalyst for the degradation of aqueous organic pollutants
Bibliographic record
Abstract
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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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".