Grafting of phosphorus-containing tetrahydroxy(thia)calixarenes on silica enhances europium(III) adsorption

Figures & data

Scheme 1. Grafting of silica gel surface with the upper rim phosphorylated (thia)calixarenes

Table 1. Content of calixarenes grafted on silica gels 4, 5.

Silica, No.	4a	4b	4c	4d	4e	5a	5b	5c
Content, (mmol/g)	0.16	0.18	0.18	0.16	0.06	0.1	0.1	0.1

Figure 1. Microphotographs of silica gels 4a (a), 4b (b), 5a (c), 5с (d).

Table 2. pH Dependence of Eu(III) sorption by silica gels 1, 4 and 5 from nitric acid solutions.

pH	1	4a	4b	5a	5c
1	0%	0%	2.91%	1.94%	21.3%
2	0.94%	8.49%	41.7%	47.6%	63.1%
3	24.5%	71.7%	98.3%	88.3%	93.8%
4	60.4%	89.6%	93.3%	97.8%	97.8%
5	76.4%	93.1%	93.3%	98.5%	98.3%
6	88.7%	97.9%	95.0%	99.1%	99.3%
7	99.9%	94.0%	96.9%	95.5%	88.3%

Table 3. Sorption parameters obtained according to Langmuir and Freundlich models.

Langmuir model
Silica gel	Maximum sorption capacity q∞, mg/g	Langmuir constant KL	R^2
4a	14.4	1.8	0.95
4b	11.3	1.8	0.95
5a	6.2	0.1	0.77
5c	6.4	5.8	0.75
Freundlich model
	Freundlich constant KF	n	R^2
4a	7.3	6.2	0.83
4b	6.6	8.2	0.84
5a	1.1	2.9	0.89
5c	4.6	12.9	0.70

Figure 2. Sorption isotherms of europium(III) by silica gels 4a, b and 5a, c: Langmuir model (a) and Freundlich model (b).

Figure 3. General structures of model calixarene 7' (a), and its Eu(III) complexes 7′Eu (b) and 7′Eu⋅3H₂O (c).

Figure 4. Optimized (RI-BP86/def-TZVP) structures of model calixarene 7′, and its Eu(III) complexes 7′Eu and 7′Eu⋅3H₂O. Color coding: gray – C, red – O, beige – Si, light green – Eu. Hydrogen atoms are omitted for clarity (the structures are graphically presented with Jmol program^[12]).

Katz, A.; Da Costa, P.; Lam, A.; Notestein, J. The First Single-Step Immobilization of a Calix[4]arene onto the Surface of Silica. Chem. Mater. 2002, 14, 3364–3368. DOI: 10.1021/cm020082l.

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