Spectral Dependence and Wavelength Selectivity in Heterogeneous Photocatalysis. I. Experimental Evidence from the Photocatalyzed Transformation of Phenols
Bibliographic record
Abstract
The photocatalyzed transformation of phenol (PhOH) and 4-chlorophenol (ClPhOH) in air-equilibrated TiO 2 dispersions has been used to examine the spectral behavior of the quantum yields Φ (and photonic efficiencies, η) of loss of these two substrates at various wavelengths. Contrary to the band model of semiconductors and conventional wisdom which predict rapid thermalization of photogenerated charge carriers to the lowest energy levels in their respective conduction and valence band states, and consequently to spectrally independent quantum yields, experimental results demonstrate that in fact the quantum yields of loss of PhOH and ClPhOH are spectrally dependent, displaying well resolved band structures at 3.13, 3.21, 3.32, 3.60, 3.81, 4.28 and 4.57 eV for phenol and at 3.16, 3.25, 3.41, 3.59, 3.70 and 4.15 eV for 4-chlorophenol. These energies correlate with absorption and emission band energies of direct and indirect band-to-band transitions reported earlier by Serpone et al. ( J. Phys. Chem ., 1995, 99, 16655) and with theoretical estimates by Daude and co-workers ( Phys. Rev. B, 1977, 15, 3229) for TiO 2 crystals. Both the spectral dependence of Φ and η and the wavelength selectivity of TiO 2 ( S e and S h ) are discussed in terms of theoretical predictions based on the solution of the continuity equation. The implicit emphasis of this study is the need to rethink the predictions based on the conventional band model of semiconductors. Thermalization of hot carriers may not (in some cases) be as rapid as once envisaged.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".