Preparation and Characterization of Chitosan/Feldspar Biohybrid as an Adsorbent: Optimization of Adsorption Process via Response Surface Modeling

Table 3

Central composite design (CCD) for the four independent variables and corresponding dye adsorption (mg/g).

CCD term	Number of experiments	Coded values of process variables				Adsorption (mg/g)
		𝐶0	𝐷	pH	𝑇
Factorial 2^𝑛	16	−1, +1	−1, +1	−1, +1	−1, +1	1–9.5
Axial (2𝑛)	8	−2, 0, +2	−2, 0, +2	−2, 0, +2	−2, 0, +2	1.23–14
Center (𝑛𝑐)	7	0	0	0	0	2.65–3.53