Removal of Hg²⁺ and methylmercury in waters by functionalized multi-walled carbon nanotubes: adsorption behavior and the impacts of some environmentally relevant factors

Figures & data

Figure 1. TEM images of pristine and functionalized MWCNTs. (a) MWCNTs; (b) MWCNTs-COOH; (c) MWCNTs-NH₂; (d) MWCNTs-OH.

Figure 2. FTIR of pristine and functionalized MWCNTs.

Figure 3. Effect of pH on removal of Hg²⁺ (a) and MeHg (b) by MWCNTs.

Notes: In the solutions were spiked with 0.5 g/L different MWCNTs, and 100 μg/L Hg²⁺ and MeHg, respectively. The solution pH was adjusted by using 10 mmol/L phosphate buffer.

Figure 4. Effect of NOM on the removal of Hg²⁺ (a) and MeHg (b) by MWCNTs.

Notes: In the solutions were spiked with 0.5 g/L different MWCNTs, and 100 μg/L Hg²⁺ and MeHg, respectively. The solution pH was adjusted to pH 7.0 by using 10 mmol/L phosphate buffer.

Figure 5. Effect of Cl⁻ on the removal of Hg²⁺ (a) and MeHg (b) by MWCNTs.

Notes: In the solutions were spiked with 0.5 g/L different MWCNTs, different concentration of Cl⁻, and 100 μg/L Hg²⁺ and MeHg, respectively. The solution pH was adjusted to pH 7.0 by using 10 mmol/L phosphate buffer.

Figure 6. Effect of adsorbent dose on removal of Hg²⁺ (a) and MeHg (b).

Notes: In the solutions were spiked with 100 μg/L Hg²⁺ and MeHg, respectively. The solution pH was adjusted to pH 7.0 by using 10 mmol/L phosphate buffer.

Table 1. Parameters of isotherms for Hg²⁺ adsorption on MWCNTs (mean ± SD, n = 3).

Model	Parameter	MWCNTs	MWCNTs-OH	MWCNTs-COOH	MWCNTs-NH2
Langmuir	Qm (mg/g)	71.1 ± 7.3	78.9 ± 4.7	134 ± 20	205 ± 10
	RL (C0 = 0.1 mg/L)	0.13 ± 0.01	0.13 ± 0.03	0.06	0.03
	b (L/mg)	0.07 ± 0.01	0.07 ± 0.02	0.17	0.30 ± 0.01
	R^2	0.719	0.935	0.914	0.865
Freundlich	n	0.84 ± 0.01	0.97 ± 0.03	0.81 ± 0.05	0.60 ± 0.02
	KF (mg^1 ‒ n L^n/g)	8.63 ± 0.82	18.3 ± 0.3	33.9 ± 0.3	48.0 ± 0.3
	R^2	0.862	0.960	0.956	0.931
Dubinin-Radushkevich	E (kJ/mol)	9.13 ± 0.08	9.97 ± 0.21	9.29 ± 0.29	8.15 ± 0.17
	β (mol^2/kJ)	0.006	0.005	0.006	0.008
	R^2	0.977	0.969	0.977	0.805
Temkin	bT (kJ/mol)	12.6 ± 0.6	10.6 ± 0.1	10.1 ± 0.6	7.79 ± 0.27
	BT (kJ/mol)	194 ± 9	229 ± 2	242 ± 14	313 ± 11
	AT	2.67 ± 0.05	1.49 ± 0.15	1.18 ± 0.16	1.44 ± 0.11
	R^2	0.944	0.849	0.790	0.695

Table 2. Parameters of isotherms for MeHg adsorption on MWCNTs (mean ± SD, n = 3).

Model	Parameter	MWCNTs	MWCNTs-OH	MWCNTs-COOH	MWCNTs-NH2
Langmuir	Qm (mg/g)	184 ± 8	237 ± 12	265 ± 38	334 ± 11
	RL (C0 = 0.1 mg/L)	0.24 ± 0.02	0.17 ± 0.01	0.27 ± 0.02	0.16 ± 0.02
	b (L/mg)	0.03	0.03	0.05	0.05 ± 0.01
	R^2	0.997	0.995	0.998	0.964
Freundlich	n	1.47 ± 0.04	1.60 ± 0.04	1.34 ± 0.01	1.28 ± 0.02
	KF (mg^1 ‒ n L^n/g)	9.40 ± 0.12	10.5 ± 0.1	10.6 ± 0.1	23.9 ± 0.4
	R^2	0.996	0.997	0.997	0.922
Dubinin-Radushkevich	E (kJ/mol)	11.8 ± 0.2	12.4 ± 0.1	11.4 ± 0.1	11.1 ± 0.1
	β (mol^2/kJ)	0.004	0.003	0.004	0.004
	R^2	0.999	0.999	0.998	0.917
Temkin	bT (kJ/mol)	36.4 ± 2.5	30.2 ± 1.6	21.6 ± 0.5	14.1 ± 0.2
	BT (kJ/mol)	67.2 ± 4.6	80.9 ± 4.4	112 ± 2	173 ± 2
	AT	3.44 ± 0.21	3.01 ± 0.15	3.16 ± 0.17	1.59 ± 0.03
	R^2	0.838	0.829	0.806	0.936

Table 3. Kinetic parameters for adsorption of Hg²⁺ onto MWCNTs.

Model	Parameter	MWCNTs	MWCNTs-OH	MWCNTs-COOH	MWCNTs-NH2
Pseudo-first order	k1 (min^−1)	0.0146	0.0412	0.0287	0.0314
	qe(mg/g)	5.96	85.9	47.0	45.0
	R^2	0.564	0.938	0.862	0.962
Pseudo-second order	k2( g mg^−1 min^−1)	0.0321	0.00210	0.000537	0.00572
	qe(mg/g)	46.0	93.9	120	140
	R^2	0.999	0.999	0.997	0.994

Table 4. Kinetic parameters for adsorption of MeHg onto MWCNTs.

Model	Parameter	MWCNTs	MWCNTs-OH	MWCNTs-COOH	MWCNTs-NH2
Pseudo-first order	k1 (min^−1)	0.00867	0.00815	0.00880	0.0117
	qe (mg/g)	4.89	5.43	4.85	3.67
	R^2	−0.101	0.564	0.204	0.835
Pseudo-second order	k2 (g mg^−1 min^−1)	0.0161	0.0115	0.0428	0.0229
	qe (mg/g)	20.2	28.1	40.2	91.6
	R^2	0.986	0.992	0.990	0.995