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