Mechanism and Kinetics Study for Photocatalytic Oxidation Degradation: A Case Study for Phenoxyacetic Acid Organic Pollutant

Table 2

Central composite design with predictive values and their experimental results.

Standard	Point type	Experimental parameters				PAA degradation
		ZnO loading; (g/L)	Initial concentration of PAA (mg/L)	Solution pH	Reaction time (min)	Experimental; (%)	Predictive; (%)
1	Factorial	0.30	15.00	6.00	20.00	63.13	63.58
2	Factorial	0.50	15.00	6.00	20.00	54.68	55.27
3	Factorial	0.30	25.00	6.00	20.00	40.72	39.52
4	Factorial	0.50	25.00	6.00	20.00	35.59	38.14
5	Factorial	0.30	15.00	8.00	20.00	71.73	71.27
6	Factorial	0.50	15.00	8.00	20.00	63.36	65.60
7	Factorial	0.30	25.00	8.00	20.00	45.64	47.49
8	Factorial	0.50	25.00	8.00	20.00	47.66	48.21
9	Factorial	0.30	15.00	6.00	40.00	78.24	77.90
10	Factorial	0.50	15.00	6.00	40.00	68.37	68.88
11	Factorial	0.30	25.00	6.00	40.00	52.58	53.24
12	Factorial	0.50	25.00	6.00	40.00	50.47	51.14
13	Factorial	0.30	15.00	8.00	40.00	85.22	85.03
14	Factorial	0.50	15.00	8.00	40.00	76.71	78.12
15	Factorial	0.30	25.00	8.00	40.00	61.03	60.64
16	Factorial	0.50	25.00	8.00	40.00	58.74	60.65
17	Axial	0.20	20.00	7.00	30.00	44.12	45.22
18	Axial	0.60	20.00	7.00	30.00	40.58	36.92
19	Axial	0.40	10.00	7.00	30.00	89.82	89.27
20	Axial	0.40	30.00	7.00	30.00	49.76	47.75
21	Axial	0.40	20.00	5.00	30.00	49.09	48.43
22	Axial	0.40	20.00	9.00	30.00	67.53	65.63
23	Axial	0.40	20.00	7.00	10.00	62.77	61.04
24	Axial	0.40	20.00	7.00	50.00	88.65	87.81
25	Center	0.40	20.00	7.00	30.00	80.16	82.74
26	Center	0.40	20.00	7.00	30.00	83.22	82.74
27	Center	0.40	20.00	7.00	30.00	83.05	82.74
28	Center	0.40	20.00	7.00	30.00	81.55	82.74
29	Center	0.40	20.00	7.00	30.00	85.02	82.74
30	Center	0.40	20.00	7.00	30.00	83.41	82.74