Common Experimental Protocol v1.0
Results can be compared and pooled only when labs run experiments the same way.
Reference conditions
| Item | Reference | Variable range |
|---|---|---|
| Catalyst loading | 1.0 g/L | 0.25–2.0 g/L |
| Initial methyl orange | 10 mg/L | 5–20 mg/L |
| Volume | 100 mL | Fixed |
| Initial pH | Not adjusted, measure and record | 3–11 (ZnO may dissolve below pH 6) |
| Light source | UV-A 365 nm | Visible, sunlight |
| Temperature | 25 ± 2 °C | 15–40 °C |
| Dark equilibrium | 30 min | Fixed |
| Sampling times | 0, 15, 30, 60, 90, 120 min | May add |
| Wavelength | 464 nm (check λmax) | — |
| Replicates | 3 runs | At least 2 |
In variable experiments, change one condition at a time and record which one.
Required controls
Run the main run (catalyst + light), a dark control (catalyst only) and a photolysis control (light only) on the same day with the same solution, grouped as one series.
Must-dos
- Time zero is when the light turns on, after a 30-minute dark equilibrium.
- Remove ZnO particles by centrifuge or 0.22 µm filter before measuring; leftover particles raise absorbance.
- Methyl orange is a pH indicator. Match the pH of samples and calibration standards.
- Make the calibration curve on the same instrument; R² ≥ 0.99 is recommended. Dilute and re-measure out-of-range samples.
- Never write 0 for a value you could not measure; leave it empty and record the reason.
Safety
Students must work under a teacher's or PI's supervision. Wear UV goggles, avoid inhaling ZnO powder, and dispose of waste under your institution's rules.
The full document is shared via the Participate page.