Table 1 Independent variables and their coded levels for the central composite design
From: Nb2O5 monolith as an efficient and reusable catalyst for textile wastewater treatment
Variables | Code | Units | Coded levels | ||
|---|---|---|---|---|---|
-1 | 0 | 1 | |||
pH | x1 | – | 4 | 6 | 8 |
CMB, 0 | x2 | (mg L− 1) | 15 | 30 | 45 |
\( {\mathrm{C}}_{{\mathrm{H}}_2{\mathrm{O}}_{2,0}} \) | x3 | (mM) | 40 | 60 | 80 |
ω | x4 | (\( {\mathrm{kg}}_{{\mathrm{Nb}}_2{\mathrm{O}}_5} \) m−3) | 2.62 | 5.24 | 7.86 |