Adsorption thermodynamic, kinetic and desorption studies of Pb2+ on carbon nanotubes
Introduction
Recently, an increasing interest has been focused on removing Pb2+ ions from drinking water due to its supreme toxicity to our health. Drinking those that contain Pb2+ ions for a long term, even if in a very low concentration, could lead to a wide range of spectrum health problems, such as nausea, convulsions, coma, renal failure, cancer and subtle effects on metabolism and intelligence (Friberg et al., 1979; Rashed, 2001).
Different approaches to remove Pb2+ ions from wastewater, including chemical precipitation, ion exchange, reverse osmosis and adsorption, have been reported. One of which, adsorption method, is simple and cost-effective, thus has been widely used. Various adsorbents such as activated carbon (Lee et al., 1998; Reed et al., 1996), iron oxides (Liu and Huang, 2003), filamentous fungal biomass (Lo et al., 1999) and natural condensed tannin (Zhan and Zhao, 2003) have been explored and the results are promising.
Carbon nanotubes (CNTs), a new member of the carbon family, have attracted special attentions to many researchers after their discovery in 1991 (Iijima, 1991) because they possess unique morphologies and have showed excellent properties and great potential for engineering applications such as composite reinforcement (Wagner et al., 1998), field emission element (Wang et al., 1998), nanodevice component (Collins et al., 1997), gas adsorption materials (Dillon et al., 1997) and catalyst support phases (Planeix et al., 1994). CNTs are also good anion and cation adsorption materials for wastewater treatment, as they exhibit exceptionally large specific surface areas which are easy to decorate (Li et al., 2001, Li et al., 2002, Li et al., 2003). We have previously demonstrated that CNT supported alumina is a good fluoride adsorbent whose adsorption capacity is 15–25 times higher than that of the activated carbon (Li et al., 2001). CNTs oxidized with nitric acid showed very good cation adsorption capability, e.g., their lead and cadmium (II) adsorption capacities being 15.6 and 3.6 mg/g, separately, at metal ion equilibrium concentration of 2.7 mg/L (Li et al., 2002, Li et al., 2003).
In this paper, we will investigate the thermodynamic and kinetic of the Pb2+ absorption onto CNTs, in order to obtain the thermodynamic parameters, to establish the adsorption rate equation and to assess the reuse capacity of CNTs in wastewater treatment.
Section snippets
Experimental
CNTs were prepared by Ni nanoparticle catalysed pyrolysis of propylene in a hydrogen flow at 750 °C. The as-grown CNTs were dispersed in concentrated HNO3 and were refluxed for 30 min at 140 °C, to remove the catalyst. By dissolving lead nitrate in deionized water, we obtained the lead containing stock solution (1000 mg/L), which was further diluted to the required concentrations before being used.
To evaluate the thermodynamic properties, we first prepared various solutions with initial Pb2+
Results and discussion
The CNT starting materials usually exhibit curved features, with ca. 30 nm o.d. and 10 nm i.d., and hundreds of nm to μm long. Their specific surface areas are 122 and 153 m3/g, respectively, before and after oxidation treatment by nitric acid.
Fig. 1 shows the adsorption isotherms of Pb2+ on CNTs at 280, 298 and 321 K. These data could be approximated by the Freundlich isotherm model, which depicts the relationship between the amount of Pb2+ adsorbed by per unit mass of CNTs (qe, mg/g) and the
Conclusion
Adsorption thermodynamics and kinetics of Pb2+ on CNTS have been studied. A positive value of the standard enthalpy change suggests that the interaction of Pb2+ adsorbed by CNTs is endothermic. The negative adsorption standard free energy changes and positive standard entropy changes indicate that the adsorption reaction is spontaneous process. The kinetic adsorption process can be well described by the pseudo-second-order rate model. Pb2+ can be easily desorbed from CNTs by adjusting the
Acknowledgements
This work was funded by the State Key Project for the Fundamental Research of MOST of China (Grant No. 20000264-04) and by the open funds of State Key Laboratory of Environmental Aquatic Chemistry.
References (20)
- et al.
Cadmium removal from aqueous solutions by chitinkinetic and equilibrium studies
Water Res.
(2002) - et al.
A study of the factors affecting the removal of humic acid by activated carbon prepared from biomass material
Colloid Surf. APhysicochem. Eng. Aspects
(2004) - et al.
Adsorption of fluoride from water by amorphous alumina supported on carbon nanotubes
Chem. Phys. Lett.
(2001) - et al.
Lead adsorption on carbon nanotubes
Chem. Phys. Lett.
(2002) - et al.
Adsorption of cadmium(II) from aqueous solution by surface oxidized carbon nanotubes
Carbon
(2003) - et al.
Kinetics of lead adsorption by iron oxides formed under the influence of citrate
Geochim. Cosmochimi. Acta
(2003) - et al.
A comparative investigation on the biosorption of lead by filamentous fungal biomass
Chemosphere
(1999) - et al.
The adsorption of phosphamidon on the surface of styrene supported zirconium tungstophophatea thermodynamic study
Colloid. Surf. APhysicochem. Eng. Aspects
(2000) - et al.
Mechanism of lead adsorption from aqueous solutions using an adsorbent synthesized from natural condensed tannin
Water Res.
(2003) - et al.
Nanotube nanodevice
Science
(1997)
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