Chemical modification of multi-walled carbon nanotubes and their potential applications as new adsorbents for solid phase extraction from aqueous solutions.

摘要

The adsorptive potential of pristine and chemically modified multi-walled carbon nanotubes (MWCNTs) for solid phase extraction (SPE) of polar analytes; 2,4,5-trichlorophenol (TCP) and pentachlorophenol (PCP), and non polar analytes; 3,3',4,4'-tetrachlorobiphenyl (PCB77) and 2,2',5,5'-tetrabromobiphenyl (PBB52), from aqueous solution was investigated.; Chemical modification of MWCNTs via oxidation followed by side wall functionalization using polyethylene glycol (PEG) or octadecylamine (ODA) was studied. Different characterization techniques were used to investigate the oxidized MWCNTs, MWCNTs-PEG and MWCNTs-ODA. The characterization techniques proved the presence of the functional groups on the MWCNTs surface.; Both pristine and chemically modified MWCNTs were good adsorbents for the elimination of organic pollutants from aqueous solution using SPE.; The kinetics of adsorption were investigated and showed that the process is diffusion controlled, but that this step is followed by intra-particle diffusion. Equilibrium adsorption on pristine and chemically modified MWCNTs at different temperatures was studied and the adsorption isotherms were well described using different adsorption models. The thermodynamic parameters of adsorption were measured; free energy, enthalpy and entropy. Small values for the enthalpy of adsorption indicated that adsorption is mainly physical. The trend for the thermodynamic parameters was mostly dependent on type of analyte and the type of adsorbent. Computer modeling was used to estimate the free energy of adsorption and the results showed a good correlation with the experimental free energy.; The SPE process was greatly affected by different factors such as the type of adsorbent, type of adsorbate, flow rate, mass of adsorbent, and pH of the aqueous solution.; Method development was performed to investigate the applicability of pristine and chemically modified MWCNTs as packing materials for SPE using model solution and freshwater samples. The method detection limits of SPE with different adsorbents were studied and were found to be 1.0 ng/ml for the chlorophenols, and 6.0 ng/ml for the PCB77 and PBB52, all with very good recoveries, especially when MWCNTs-ODA was used as the adsorbent. The regeneration and reusability of the different MWCNTs SPE cartridges were studied and the results showed that the SPE cartridge could be used for three cycles of adsorption/desorption with excellent efficiency.; Finally, it was found that MWCNTs-ODA was the best adsorbent and could be used successfully in SPE for the extraction of different organic pollutants; polar and non polar, with great efficiency, recovery, reproducibility, sensitivity and precision, and high dynamic range.