Photocatalytic degradation of alachlor by TiO₂ nanoparticles from aqueous solutions under UV radiation

Figures & data

Figure 1. The specification of the photochemical reactor.

Table 1. The parameters and levels used for the experimental design.

Parameters	Levels
	Units	–α	Low	Center	High	+α
		(–2)	(–1)	(0)	(+1)	(+2)
pH (A)	__	3	5	7	9	11
Initial alachlor concentration (B)	(mg/L)	15	30	45	60	75
TiO2 concentration (C)	(mg)	25	50	75	100	125
Temperature (D)	(°C)	20	25	30	35	40
Time (E)	(min)	15	30	45	60	75

Figure 2. The XRD pattern of synthesised TiO₂ NPs. The most important peaks of rutile TiO₂ have been marked by “*” on the figure.

Figure 3. SEM image of TiO₂ (a) and elemental analysis (EDX) for TiO₂ (b).

Table 2. Analysis of variance to evaluate the significance of the model obtained by CCD for alachlor removal.

Source	Sum of squares	df	Mean square	F-value	p-Value (prob > F)
Model	970.41	11	88.22	19.56	<0.0001	significant
A-pH	53.42	1	53.42	11.85	0.0012
B-Initial alachlor concentration	37.60	1	37.60	8.34	0.0058
C-TiO2 concentration	123.52	1	123.52	27.39	<0.0001
D-temperature (°C)	0.03	1	0.03	0.01	0.9353
E-time	213.03	1	213.05	47.23	<0.0001
AB	14.82	1	14.82	3.29	0.0761
BC	52.12	1	52.12	11.56	0.0014
A^2	149.18	1	149.18	33.08	<0.0001
B^2	210.94	1	210.94	46.77	<0.0001
C^2	47.16	1	47.16	10.46	0.0022
D^2	242.42	1	242.42	53.75	<0.0001
Residual	216.49	48	4.51
Lack of fit	168.06	31	5.421277	1.902919	0.0816	Not significant
Pure error	48.43	17	2.848926
Cor total	1186.90	59
SD	2.12		R^2		0.818
Mean	89.586		R^2Adj		0.776
C.V. %	2.371		R^2pred		0.717
PRESS	335.709		Adeq precision		19.463

Figure 4. Normal probability plot of the studentised residual (a) and alachlor removal observed in the experiment versus predicted values by the model (b).

Figure 5. Response surface plot of the interactive effect of the initial alachlor concentration and pH on alachlor removal. Actual value of other factors: TiO₂ concentration = 75.0 mg, temperature = 30.0 °C and time = 45.0 min. Response surface plot of the interactive effect of the initial alachlor concentration and TiO₂ concentration on alachlor removal percentage. Actual values of other factors: pH = 7.0, temperature = 30.0 °C and time = 45.0 min.