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Table 1 Independent variables and their levels

From: Optimization of phenol adsorption from synthetic wastewater by synthesized BiFeO3 perovskite material, using split-plot central composite design

Independent variable

Unit

Symbol

Levels

− α

− 1

0

 + 1

 + α

pH

 

a

2

4

7

10

12

Time

Min

B

30

87

165

243

300

Dosage

G

C

0.2

0.4

0.6

0.8

1.0