Tuning the adsorption capability of multi-walled carbon nanotubes to polar and non-polar organic compounds by surface oxidation (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.
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.
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.
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
Heliyon, 2021
This study investigated the removal of Total Organic Carbon (TOC) from produced water by batch adsorption process using adsorbents developed from Multi-Walled Carbon Nanotubes (MWCNTs). The MWCNTs, synthesized by catalytic chemical vapour deposition method using kaolin-supported tri-metallic (iron-cobalt-nickel) catalyst were purified by H 2 SO 4 /HNO 3 and then functionalized with 1-pyrenebutanoic acid N-hydroxyl succinimidyl ester (PSE). The raw, purified and functionalized MWCNTs were characterized by High Resolution Scanning Electron Microscopy (HRSEM), High Resolution Transmission Electron Microscopy (HRTEM), Brunauer-Emmett-Teller (BET) and Fourier Transform Infrared Spectroscopy (FTIR). In the results, HRSEM/HRTEM revealed the structure, purity and also confirmed the attachment of the PSE molecule onto the nano-adsorbent(s). The BET surface areas of MWCNTs, PMWCNTs and FMWCNTs were 970.17, 869.25 and 831.80 m 2 /g, respectively while the FTIR established the existence of surface functional groups. The functionalized MWCNTs (FMWCNTs) nano-adsorbent showed superior performance efficiency (93.6%) than the purified MWCNTs (PMWCNTs) (79.2%) as examined under the same batch adsorption condition: 0.02 g adsorbent dosage, 10-90 min contact time and 30 C solution temperature probably, due the improved wettability resulted from incorporation of PSE. Subsequently, Central Composite Design (CCD) was applied to optimize the process parameters for the sorption of TOC onto FMWCNTs. The CCD in the response surface methodology predicted 260 mg/g adsorption capacity of FMWCNTs in the removal of TOC at the optimum condition of 49.70 min contact time, 34.81 C solution temperature, and 0.02 g adsorbent dosage. The kinetics data were best described by pseudo-second-order model and thermodynamic parameters suggested that the process was feasible, spontaneous and exothermic. It can be inferred from the various analysis conducted that the developed FMWCNTs nano-adsorbent is effective for removal of TOC from oilproduced water and may be explored for removal of organic contaminants from other industrial wastewater.
Green Processing and Synthesis, 2015
Multi-walled carbon nanotubes (MWCNTs) and their oxidized derivatives were used as adsorbents for the removal of methylene blue dye from aqueous solution. CNTs have consistent surface and distinct structure, thus they were selected as the novel adsorbents in this study. The site-energy distribution analysis could provide significant information for adsorption mechanisms. Therefore, this study concentrated on the site-sorption energy distribution analysis in combination with thermodynamic behavior of methylene blue adsorption on CNTs. The single point adsorption coefficient
Surface Modification of MWCNTs with Carboxylic-to-Amine and Their Superb Adsorption Performance
International Journal of Environmental Research, 2019
In this study, multi-walled carbon nanotubes (MWCNT) surface functionalization with amine group is studied for methyl orange (MO) dye removal from aqueous solution. The adsorbent was prepared using 1,2-ethylenediamine as amine via a microwave combination to functionalize the carbon nanotubes with carboxylic acid (-COOH) then converting to acyl chloride (-COCl) as intermediate using thionyl chloride. The prepared material shows a suburb adsorption performance of MO removal with a high adsorption capacity of 96 mg g −1. In addition, the equilibrium data are introduced by the Langmuir and Freundlich isotherms, and showed Langmuir is the best fit with the adsorption capacity of 25.73 mg g −1. Moreover, pseudosecond order is found to be the best kinetic model to fit the experimental data. According to kinetics results, the adsorption process involves chemisorption step. MWCNT-NH 2 is an excellent candidate to be used as an effective adsorbent for pollution removal from the aqueous environment.