Nanosized Spinel Ferrites Synthesized by Sol-Gel Autocombustion for Optimized Removal of Azo Dye from Aqueous Solution

Table 6

Central composite design (CCD) of orthogonal type used for adsorption experiments (CR onto NiFe₂O₄).

	Factors (controllable input variables)						Responses (experimental values)
Run	, (min)		, (mg/L)		SD, (g/L)
						SD	, (%)	, (mg/g)
1	+1	180	+1	80.0	+1	5.00	79.057	10.209
2	−1	30	+1	80.0	+1	5.00	67.367	8.628
3	+1	180	−1	20.0	+1	5.00	97.143	3.184
4	−1	30	−1	20.0	+1	5.00	95.035	3.138
5	+1	180	+1	80.0	−1	1.00	22.026	14.634
6	−1	30	+1	80.0	−1	1.00	18.094	12.117
7	+1	180	−1	20.0	−1	1.00	59.247	10.127
8	−1	30	−1	20.0	−1	1.00	48.110	8.195
9	+α	196	0	50.0	0	3.00	77.902	10.868
10	−α	14	0	50.0	0	3.00	60.478	8.390
11	0	105	+α	86.5	0	3.00	54.426	12.956
12	0	105	−α	13.6	0	3.00	95.025	3.727
13	0	105	0	50.0	+α	5.43	93.258	7.198
14	0	105	0	50.0	−α	0.57	21.775	15.317
15	0	105	0	50.0	0	3.00	73.747	10.244
16	0	105	0	50.0	0	3.00	73.305	10.350