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Experimental levels of independent factors and their codes in a Box–Behnken design.
| Codes | Variables | Low Level (−1) | Central Point (0) | High Level (+1) |
|---|---|---|---|---|
| For adsorption experiments | ||||
| A | pH | 2 | 6 | 10 |
| B | Adsorbent dose (g L−1) | 0.2 | 0.4 | 0.8 |
| C | Contact time (min) | 30 | 60 | 120 |
| D | Temperature (°C) | 10 | 25 | 50 |
| For photocatalytic experiments | ||||
| A | pH | 3 | 5 | 9 |
| B | Photocatalyst dose (g L−1) | 0.2 | 0.4 | 0.8 |
| C | Contact time (min) | 30 | 60 | 120 |
