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Adsorption of Cu(II) on oxidized multi-walled carbon nanotubes in the presence of hydroxylated and carboxylated fullerenes.

Wang J, Li Z, Li S, Qi W, Liu P, Liu F, Ye Y, Wu L, Wang L, Wu W - PLoS ONE (2013)

Bottom Line: The effect of C60(OH)n on Cu(II) adsorption of oMWCNTs was not significant at low C60(OH)n concentration, whereas a negative effect was observed at higher concentration.The adsorption of Cu(II) on oMWCNTs was enhanced with increasing pH values at pH < 5, but decreased at pH ≥ 5.The double sorption site model was applied to simulate the adsorption isotherms of Cu(II) in the presence of C60(OH)n and fitted the experimental data well.

View Article: PubMed Central - PubMed

Affiliation: Radiochemistry Laboratory, School of Nuclear Science and Technology, Lanzhou University, Lanzhou, PR China.

ABSTRACT
The adsorption of Cu(II) on oxidized multi-walled carbon nanotubes (oMWCNTs) as a function of contact time, pH, ionic strength, temperature, and hydroxylated fullerene (C60(OH)n) and carboxylated fullerene (C60(C(COOH)2)n) were studied under ambient conditions using batch techniques. The results showed that the adsorption of Cu(II) had rapidly reached equilibrium and the kinetic process was well described by a pseudo-second-order rate model. Cu(II) adsorption on oMWCNTs was dependent on pH but independent of ionic strength. Compared with the Freundlich model, the Langmuir model was more suitable for analyzing the adsorption isotherms. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that Cu(II) adsorption on oMWCNTs was spontaneous and endothermic. The effect of C60(OH)n on Cu(II) adsorption of oMWCNTs was not significant at low C60(OH)n concentration, whereas a negative effect was observed at higher concentration. The adsorption of Cu(II) on oMWCNTs was enhanced with increasing pH values at pH < 5, but decreased at pH ≥ 5. The presence of C60(C(COOH)2)n inhibited the adsorption of Cu(II) onto oMWCNTs at pH 4-6. The double sorption site model was applied to simulate the adsorption isotherms of Cu(II) in the presence of C60(OH)n and fitted the experimental data well.

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Effect of C60(C(COOH)2)2 on Cu(II) adsorption onto oMWCNTs as a function of pH, m/V  = 0.5 g/L, T = 25±1°C, I = 0.01 mol/L NaCl, C[Cu2+]initial  = 1.87×10–4 mol/L.
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pone-0072475-g012: Effect of C60(C(COOH)2)2 on Cu(II) adsorption onto oMWCNTs as a function of pH, m/V  = 0.5 g/L, T = 25±1°C, I = 0.01 mol/L NaCl, C[Cu2+]initial  = 1.87×10–4 mol/L.

Mentions: Figure 12 illustrates the adsorption of Cu(II) on oMWCNTs as a function pH in the presence of C60(C(COOH)2)n. The adsorption of Cu(II) declines at pH 4–6 due to the inhibition of C60(C(COOH)2)n. Subsequently, Cu(II) adsorption gradually increases to a maximum and then remains stable. C60(C(COOH)2)n can be excluded from the interaction between C60(C(COOH)2)n and Cu(II) because there is no increasing adsorption of Cu(II). However, the adsorption mechanism of the combined impact of C60(C(COOH)2)n and C60(OH)n behaves differently. Due to the protonation of C60(C(COOH)2)n, the competition between H+ and Cu2+ for the adsorption site of oMWCNTs results in the declining adsorption of Cu(II) at pH 4–6. Because of the electron withdrawing effect of the carboxyl group on C60(C(COOH)2)n, the π-π stacking interactions of C60(C(COOH)2)n with the oMWCNTs benzene ring are weakened. Moreover, the steric hindered reaction of C60(C(COOH)2)n is stronger than that of C60(OH)n, and C60(C(COOH)2)n cannot easily be adsorbed onto oMWCNTs like C60(OH)n. This may be the reason why the TEM photos of the dispersion of oMWCNTs and C60(C(COOH)2)n have not shown C60(C(COOH)2)n connected to oMWCNT surfaces. Therefore, the increasing space hindrance effect of C60(C(COOH)2)n reduces the C60(C(COOH)2)n adsorption on oMWCNTs surfaces, and consequently Cu(II) adsorption on oMWCNTs gradually rises and then maintains steady state at pH >6.


Adsorption of Cu(II) on oxidized multi-walled carbon nanotubes in the presence of hydroxylated and carboxylated fullerenes.

Wang J, Li Z, Li S, Qi W, Liu P, Liu F, Ye Y, Wu L, Wang L, Wu W - PLoS ONE (2013)

Effect of C60(C(COOH)2)2 on Cu(II) adsorption onto oMWCNTs as a function of pH, m/V  = 0.5 g/L, T = 25±1°C, I = 0.01 mol/L NaCl, C[Cu2+]initial  = 1.87×10–4 mol/L.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756995&req=5

pone-0072475-g012: Effect of C60(C(COOH)2)2 on Cu(II) adsorption onto oMWCNTs as a function of pH, m/V  = 0.5 g/L, T = 25±1°C, I = 0.01 mol/L NaCl, C[Cu2+]initial  = 1.87×10–4 mol/L.
Mentions: Figure 12 illustrates the adsorption of Cu(II) on oMWCNTs as a function pH in the presence of C60(C(COOH)2)n. The adsorption of Cu(II) declines at pH 4–6 due to the inhibition of C60(C(COOH)2)n. Subsequently, Cu(II) adsorption gradually increases to a maximum and then remains stable. C60(C(COOH)2)n can be excluded from the interaction between C60(C(COOH)2)n and Cu(II) because there is no increasing adsorption of Cu(II). However, the adsorption mechanism of the combined impact of C60(C(COOH)2)n and C60(OH)n behaves differently. Due to the protonation of C60(C(COOH)2)n, the competition between H+ and Cu2+ for the adsorption site of oMWCNTs results in the declining adsorption of Cu(II) at pH 4–6. Because of the electron withdrawing effect of the carboxyl group on C60(C(COOH)2)n, the π-π stacking interactions of C60(C(COOH)2)n with the oMWCNTs benzene ring are weakened. Moreover, the steric hindered reaction of C60(C(COOH)2)n is stronger than that of C60(OH)n, and C60(C(COOH)2)n cannot easily be adsorbed onto oMWCNTs like C60(OH)n. This may be the reason why the TEM photos of the dispersion of oMWCNTs and C60(C(COOH)2)n have not shown C60(C(COOH)2)n connected to oMWCNT surfaces. Therefore, the increasing space hindrance effect of C60(C(COOH)2)n reduces the C60(C(COOH)2)n adsorption on oMWCNTs surfaces, and consequently Cu(II) adsorption on oMWCNTs gradually rises and then maintains steady state at pH >6.

Bottom Line: The effect of C60(OH)n on Cu(II) adsorption of oMWCNTs was not significant at low C60(OH)n concentration, whereas a negative effect was observed at higher concentration.The adsorption of Cu(II) on oMWCNTs was enhanced with increasing pH values at pH < 5, but decreased at pH ≥ 5.The double sorption site model was applied to simulate the adsorption isotherms of Cu(II) in the presence of C60(OH)n and fitted the experimental data well.

View Article: PubMed Central - PubMed

Affiliation: Radiochemistry Laboratory, School of Nuclear Science and Technology, Lanzhou University, Lanzhou, PR China.

ABSTRACT
The adsorption of Cu(II) on oxidized multi-walled carbon nanotubes (oMWCNTs) as a function of contact time, pH, ionic strength, temperature, and hydroxylated fullerene (C60(OH)n) and carboxylated fullerene (C60(C(COOH)2)n) were studied under ambient conditions using batch techniques. The results showed that the adsorption of Cu(II) had rapidly reached equilibrium and the kinetic process was well described by a pseudo-second-order rate model. Cu(II) adsorption on oMWCNTs was dependent on pH but independent of ionic strength. Compared with the Freundlich model, the Langmuir model was more suitable for analyzing the adsorption isotherms. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that Cu(II) adsorption on oMWCNTs was spontaneous and endothermic. The effect of C60(OH)n on Cu(II) adsorption of oMWCNTs was not significant at low C60(OH)n concentration, whereas a negative effect was observed at higher concentration. The adsorption of Cu(II) on oMWCNTs was enhanced with increasing pH values at pH < 5, but decreased at pH ≥ 5. The presence of C60(C(COOH)2)n inhibited the adsorption of Cu(II) onto oMWCNTs at pH 4-6. The double sorption site model was applied to simulate the adsorption isotherms of Cu(II) in the presence of C60(OH)n and fitted the experimental data well.

Show MeSH
Related in: MedlinePlus