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 3

Analysis of variance (ANOVA) for % degradation of benzoic acid.

Source	Sum of; squares	df	Mean; square	𝐹 value	𝑃 value; Prob>𝐹
Model	3908.5	9	434.28	426.95	<0.0001
𝑥1-TiO2 mg L^−1	311.69	1	311.69	306.43	<0.0001
𝑥2-Cr/BA ratio	236.80	1	236.80	232.80	<0.0001
𝑥3-pH	2616.02	1	2616.02	2571.86	<0.0001
𝑥1  𝑥2	9.05	1	9.05	8.90	0.0204
𝑥1  𝑥3	75.34	1	75.34	74.07	<0.0001
𝑥2  𝑥3	10.33	1	10.33	10.15	0.0153
𝑥^21	1.77	1	1.77	1.74	0.2284
𝑥^22	374.00	1	374.00	367.69	<0.0001
𝑥^23	382.08	1	382.08	375.63	<0.0001
Residual	7.12	7	1.02
Lack of fit	6.24	5	1.25	2.84	0.2805
Pure error	0.88	2	0.44