Adsorption of emerging pollutants on functionalized multiwall carbon nanotubes (original) (raw)
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Water Research, 2010
With the significant increase in the production and use of carbon nanotubes (CNTs), they will be inevitably released into aquatic environments. Therefore, the fate and transport of CNTs in aqueous solutions have attracted extensive attention. In the present work, the effects of natural organic matter (NOM), solution pH and ionic strength on adsorption of three synthetic organic chemicals (SOCs) by both pristine and surface functionalized single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) were investigated. The three SOCs (phenanthrene, biphenyl, and 2-phenylphenol) with different planarity, polarity, and hydrogen/electron-donor/acceptor ability, representing typical scenarios for the SOC-CNT interactions, were employed as probe molecules. Among the three background solution characteristics examined, NOM showed the most significant effect on SOC adsorption, while solution pH and ionic strength exhibited minimal or negligible impacts. The presence of NOM greatly suppressed the SOC adsorption by CNTs, and the impact on the SWNTs was higher than that on the MWNTs. The planarity and hydrophobicity of SOCs were two important factors determining the effects of NOM, solution pH and ionic strength on their adsorption by CNTs.
Journal of Solution Chemistry, 2010
Multi-walled carbon nanotubes (MWCNTs) were chemically modified with octadecyl amine or polyethyleneglycol and then used as solid phase adsorbents for the adsorption from aqueous solution of different polyhalogenated organic pollutants: pentachlorophenol, 2,4,5-trichlorophenol, 3,3 ,4,4-tetrachlorobiphenyl and 2,2 ,5,5-tetrabromobiphenyl from model aqueous solutions. The effects of temperature were measured and thus the Gibbs energy, enthalpy, and entropy of adsorption were calculated. In general, the Gibbs energy of adsorption was negative for the target analytes, indicating that adsorption was spontaneous at all temperatures. On the other hand, the values of the enthalpy and entropy of adsorption were significantly dependent on the type of modified MWCNTs as well as the analytes used. Computer modeling was used to simulate the adsorption process and calculate the Gibbs energies of adsorption. The results showed moderate agreement with the experimentally determined values. Keywords Multi-walled carbon nanotubes • Modification • Polyhalogenated organic pollutants • Adsorption • Thermodynamics • Computer modeling 1 Introduction Recently, releases of different pollutants to the water environment have drawn the attention of scientists due to their toxic effects. Most of these pollutants have limited solubility in Electronic supplementary material The online version of this article
In this work, the single species and competitive (multispecies) adsorption of pyridine, phenol, and p-nitrophenol present in aqueous solution on multiwalled carbon nanotubes (MWCNTs), and nitrogen-doped carbon nanotubes (CNx) were studied. The physicochemical properties of MWCNTs and CNx were related to their capability for the adsorption of the organic molecules. Adsorption isotherms were developed at 25 °C, at pH 7 and 10. All compounds were favorably adsorbed on both materials, with differences in the adsorption capacities. The CNx phenol adsorption capacity outperformed that of MWCNTs; however, CNx demonstrated a lower adsorption capacity for pyridine and p-nitrophenol than MWCNTs. The adsorption capacities for each material could be associated with the particular adsorption mechanisms that control the adsorption of the organic molecules. Based on the results, it is proposed that three mechanisms might be responsible for the adsorption of the organic molecules: hydrogen bonding, π-π interactions , and electron-donor reactions. The prevalence of any of the specific mechanism depends on the geometry of the carbon nanotubes, the size and shape of the organic target molecules to adsorb, and the presence of other organic molecules in solution. The aqueous chemistry of the adsorbates at the solution pH during adsorption, played a relevant role during adsorption as well. The differences in nanotube selec-tivity were attributed to the presence of oxygen and nitrogen in the adsorbent structure.
Separation and Purification Technology, 2013
This current study addresses the inter-relationship between the surface oxidation of multi-walled carbon nanotubes (MWCNTs) and the polarity of organic solutes and its effect on the adsorption reaction between them. Results indicated that pristine MWCNTs exhibited a stronger affinity toward non-polar compounds such as phenanthrene compared to that of ozone-oxidized MWCNTs (O-MWCNTs). On the contrary, the adsorption of polar compounds, such as phenol, on MWCNTs occurred to a much less extent compared to that on O-MWCNTs as indicated by a smaller Freundlich affinity coefficient. The adsorption capability of various organic compounds on MWCNTs could be tuned. It was found that the stability of MWCNTs did not control the adsorption capacity. The solution chemistry only had minimal influence on the adsorption of phenanthrene on MWCNTs. Results demonstrated the importance of surface chemistry and the properties of adsorbates on the adsorption process. Overlooking either aspect might lead to a misinterpretation of the adsorption reaction. Understanding the interactive nature of MWCNTs adsorption provides information on the preparation of green and ''smart'' adsorbents according to the nature of adsorbates.
Monoaromatic Pollutant Removal by Carbon Nanotubes from Aqueous Solution
Advanced Materials Research, 2012
The removal of monoaromatic (benzene (B) and toluene (T)) from aqueous solution by multi walled, single walled, and hybrid carbon nanotubes (MWCNTs, SWCNTs, and HCNTs) was evaluated for a nanomaterial dose of 1 g/l, concentration of 10-100 mg/l, and pH 7. The equilibrium amount removed by SWCNTs (B: 9.98 mg/g and T: 9.96 mg/g) was higher than for MWCNTs and HCNTs. Toluene has a higher adsorption tendency on CNTs than benzene, which is related to the increasing water solubility and the decreasing molecular weight of the compounds. The SWCNTs performed better for B and T sorption than the MWCNTs and HCNTs. Isotherms study based on isofit program, indicate that the Generalized Langmuir-Freundlich (GLF) isotherm expression provides the best fit for benzene sorption and Brunauer-Emmett-Teller (BET) isotherm is the best fit for toluene adsorption by SWCNT. SWCNTs are efficient B and T adsorbents and possess good potential applications to water and wastewater treatment and maintain water of high quality that could be used for cleaning up environmental pollution.
Adsorption, 2014
The surface heterogeneity of multiwalled carbon nanotubes (MWCNTs) is studied on the basis of adsorption isotherms from dilute aqueous phenol and dopamine solutions at various pH values. The generalized Langmuir-Freundlich (GLF) isotherm equation was applied to investigate the cooperative effect of the surface heterogeneity and the lateral interactions between the adsorbates. The theoretical isosteric heats of adsorption were obtained assuming that the heat of adsorption profile reveals both the energetic heterogeneity of the adsorption system and the strength of the interactions between the neighboring molecules. The adsorption energy distribution (AED) functions were calculated by using algorithm based on a regularization method. The great advantage of this method is that the regularization makes no assumption about the shape of the obtained energy distribution functions. Analysis of the isosteric heats of adsorption for MWCNTs showed that the influence of the surface heterogeneity is much stronger than the role of the lateral interactions. The most typical adsorption heat is 20-22 kJ/mol for both phenol and dopamine. After purification of nanotubes, heat value for phenol dropped to 16-17 kJ/mol. The range of the energy distribution is only slightly influenced by the surface chemistry of the nanotubes in the aqueous conditions.
Modifying the sorption properties of multi-walled carbon nanotubes via covalent functionalization
Analyst, 2009
We demonstrate that the functionalization of carbon nanotubes dramatically alters their sorption characteristics. The effect of covalent functionalization of multiwalled carbon nanotubes (MWNTs) on the gas phase adsorption and desorption of polar and nonpolar organics is presented. Carboxylation and nitration led to the generation of polar functional groups on the nanotube surface. The derivatized nanotubes showed strong adsorption of polar analytes such as alcohols and relatively weaker adsorption for nonpolar and aromatic compounds. The breakthrough volume of ethanol increased by 300%, where as that of hexane decreased by 75% after functionalization. The functionalized MWNT also showed rapid desorption of the polar as well as nonpolar compounds.