Simultaneous Photocatalytic Reduction of Cr(VI) and Oxidation of Benzoic Acid in Aqueous N-F-Codoped TiO₂ Suspensions: Optimization and Modeling Using the Response Surface Methodology

Table 2

Analysis of variance (ANOVA) for % removal of Cr(VI).

Source	Sum of; squares	df	Mean; square	𝐹 value	𝑃 value; Prob>𝐹
Model	12510.88	9	1390.10	1841.56	<0.0001
𝑥1-TiO2 mg L^−1	2504.00	1	2504.00	3317.23	<0.0001
𝑥2-Cr/BA ratio	4710.52	1	4710.52	6240.35	<0.0001
𝑥3-pH	3593.50	1	3593.50	4760.57	<0.0001
𝑥1  𝑥2	21.35	1	21.35	28.29	0.0011
𝑥1  𝑥3	2.07	1	2.07	2.74	0.1416
𝑥2  𝑥3	276.95	1	267.95	366.89	<0.0001
𝑥^21	22.49	1	22.49	29.79	0.0009
𝑥^22	674.33	1	674.33	893.34	<0.0001
𝑥^23	294.43	1	294.43	390.05	<0.0001
Residual	5.28	7	0.75
Lack of fit	3.34	5	0.67	0.69	0.6829
Pure error	1.95	2	0.97