3.2 Carbon Nanotubes (CNTs) Carbon nanotubes have remarkable adsorption behavior in purification and detoxification of the environmental pollutants[12]. Their characteristics of being highly porous, having large specific area and being not solvable in aqueous solution because of the high Van der Waals interaction forces on the tube walls(pi-stacking) allow them to be great environmental pollutants adsorbent in solution. Thus, researchers have been concentrated on aqueous solution purification with single-walled carbon nanotubes(SWCNTs) and multi-walled carbon nanotubes(MWCNTs). In the past few years, CNTs have been proved to be great pollutants adsorbent for pollutants such as penta-chlorophenol(PCP)[13], polycyclic aromatic hydrocarbons (PAH)[14],
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Researches related to SW/MWCNTs that shown great adsorption behavior toward heavy metallic ions possess negative Gibb’s free energy change, positive enthalpy change and positive entropy change which is the same result as studies for activated carbons[19][20][24]. The negative value of ∆G reflects feasibility and spontaneity of adsorption processes. The more negativity of ∆G marks greater driving force for adsorption, which implies a higher adsorption capacity. The positive value of ∆S indicates increased randomness at reacting interface and the increased occurrence tendency of adsorption reaction. The increased occurrence tendency is caused by the pore growth or the change of surface activation[27][28]. The positive value of ∆H is supported by the prediction of Langmuir which indicates the endothermic behavior of the overall adsorption with the increment of temperature. The magnitude of ∆H gives an insight view of adsorption thermos-mechanisms, as ∆H for chemical adsorption is typically in the range of 40-800 (kJ/mol) and the corresponding ∆H specified for physical adsorption process, though may have other effect that affect the value, is usually within 5-40 (kJ/mol)[29]. Researches showed that the ∆H magnitude order of metallic ions could be explained that ions with larger charge surface and more charges could cause higher ∆H and thus higher tendency for the adsorption reaction to take place and have better adsorption behavior which is the same result as Gibb’s free energy and entropy
Researches related to SW/MWCNTs that shown great adsorption behavior toward heavy metallic ions possess negative Gibb’s free energy change, positive enthalpy change and positive entropy change which is the same result as studies for activated carbons[19][20][24]. The negative value of ∆G reflects feasibility and spontaneity of adsorption processes. The more negativity of ∆G marks greater driving force for adsorption, which implies a higher adsorption capacity. The positive value of ∆S indicates increased randomness at reacting interface and the increased occurrence tendency of adsorption reaction. The increased occurrence tendency is caused by the pore growth or the change of surface activation[27][28]. The positive value of ∆H is supported by the prediction of Langmuir which indicates the endothermic behavior of the overall adsorption with the increment of temperature. The magnitude of ∆H gives an insight view of adsorption thermos-mechanisms, as ∆H for chemical adsorption is typically in the range of 40-800 (kJ/mol) and the corresponding ∆H specified for physical adsorption process, though may have other effect that affect the value, is usually within 5-40 (kJ/mol)[29]. Researches showed that the ∆H magnitude order of metallic ions could be explained that ions with larger charge surface and more charges could cause higher ∆H and thus higher tendency for the adsorption reaction to take place and have better adsorption behavior which is the same result as Gibb’s free energy and entropy