Abstract
The adsorption of Th(IV) onto the surface of oxidized multi-walled carbon nanotubes (oMWCNTs) in the absence and presence of hydroxylated fullerene (C60(OH)n) and carboxylated fullerene (C60(C(COOH)2)n) has been investigated. C60(OH)n, C60(C(COOH)2)n and oMWCNTs have been chosen as model phases because of their representative in carbon nano-materials family. Adsorption experiments were performed by batch procedure as a function of contact time, pH, ionic strength, and temperature. The results demonstrated that the adsorption of Th(IV) was rapidly reached equilibrium and the kinetic process could be described by a pseudo-second-order rate model very well. Th(IV) adsorption on oMWCNTs was dependent on pH but independent on ionic strength. Adsorption isotherms were correlated better with the Langmuir model than with the Freundlich model. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that Th(IV) adsorption on oMWCNTs was spontaneous and endothermic. Compared with the adsorption of Th(IV) on the same oMWCNTs free of C60(OH)n or C60(C(COOH)2)n, the study of a ternary system showed the inhibition effect of C60(OH)n at high concentration on the adsorption of Th(IV) in a pH range from neutral to slightly alkaline; whereas the promotion effect of C60(C(COOH)2)n, even at its low concentration, on Th(IV) adsorption was observed in acid medium.
Highlights
Multiwalled carbon nanotubes (MWCNTs) have raised much interest during recent years due to their inherent extraordinary structural, mechanical, and electronic properties [1,2,3]
The adsorption behavior of actinide and lanthanide ions onto oxidized multi-walled carbon nanotubes (oMWCNTs) is investigated in a limited number of studies [5,6,7,11,20,21], and the sorption mechanism is still unclear, especially in the presence of other nano-materials
Th(IV) onto oMWCNTs is rapid at the initial contact time, and the adsorption equilibrium is reached within 3 h
Summary
Multiwalled carbon nanotubes (MWCNTs) have raised much interest during recent years due to their inherent extraordinary structural, mechanical, and electronic properties [1,2,3]. Within the remarkable progress for industrial scale application, the toxicity of MWCNTs must be considered. Once they are released into the environment, the human health and environmental may suffer serious risks. Thorium exists only stable as Th(IV) in solution, which is an important model element for other tetravalent actinides such as Np(IV), U(IV), and Pu(IV) It is profit as a tracer for studying environmental important processes [16]. The adsorption behavior of actinide and lanthanide ions onto oMWCNTs is investigated in a limited number of studies [5,6,7,11,20,21], and the sorption mechanism is still unclear, especially in the presence of other nano-materials. The adsorption of soluble fullerene and Th(IV) on oMWCNTs for understanding the radionuclide pollution and the potential impact evaluation of CNTs on radionuclide behavior
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