Table 2. Adsorption Isotherm Model Parameters at Different pH Values.

		pH
model parameters		2.0	3.0	3.5	4.0	5.0
Langmuir model	qm(mmol/g)	1.49	1.32	1.02	0.72	0.29
	kL(L/mol)	470.89	413.90	410.97	389.47	256.07
	R2	0.985	0.988	0.993	0.985	0.976
Freundlich model	kf(L/mol)	17.40	12.70	10.98	6.09	3.74
	n	1.87	1.97	1.85	2.01	1.68
	R2	0.934	0.958	0.961	0.984	0.956
Toth model	KT(L/mol)	580.64	473.77	402.24	391.42	65.70
	αT(L/mol)	107.32	157.50	313.18	1705.05	1.94 × 10–5
	τ	0.43	0.61	0.88	1.54	1.40 × 10–7
	R2	0.989	0.988	0.992	0.989	0.980
Sips model	qm(mmol/g)	1.25	1.26	0.89	1.01	0.22
	Ks(L/mol)	714.51	461.08	585.87	154.15	432.34
	ns	1.25	1.06	1.19	0.75	1.32
	R2	0.989	0.985	0.994	0.987	0.975