Study On Adsorption Of Specific Organic Pollutants In Water By Carbon Nanotubes

Carbon nanotubes（CNTs） were used as a new type of one-dimensional nano materials.The adsorption properties were excellent because of their unique physical and chemical properties such as high specific surface area and high reaction activity,etc.Due to their potential value in environmental protection of trace organic pollutants removal CNTs have been widely concerned.This paper investigated CNTs’ adsorption properties,with CNTs as solid-phase sorbents and representative organic pollutants in environmental water as target.At the same time,CNTs were purified and modified.The influence of modification on adsorption properties was discussed by determining specific surface area and particle size of CNTs before and after modification.The research can provide theory basis for industrial wastewater treatment by CNTs and create conditions for the future further exploitation and application of CNTs.The objects were 2-nitrophenol and 2,4-dichlorophenol.Adsorption characteristics of important kind of pollutant phenols in environment on CNTs were mainly studied.The process of adsorption of CNTs reached equilibrium at 293 K in 80 minutes for 2-Nitrophenol and 300 minutes for 2,4-dichlorophenol.The saturated adsorption capacities of 2-Nitrophenol and 2,4-dichlorophenol were 24.54mg/g and 30.53mg/g,espectively.The adsorption process conformed to the Freundlich isotherm equation with correlation coefficients were all above 0.95.With temperature in the range of 293 K～353K,â–³H,â–³G andâ–³S of the process of adsorption were -7.74～-7.05 kJ/mol,-6.14～-4.80 kJ/mol and -3.00～-8.33 J/（mol·k） for 2-nitrophenol,while were-24.75～-17.78 kJ/mol,-6.79～-6.22 kJ/mol and -32.75～-61.29 J/（mol·k） for 2,4-dichlorophenol.It was proved to be a exothermal,spontaneous and reducing entropy physical adsorption process.The objects were BPA and 4-NP.Adsorption characteristics and mechanism of persistent organic pollutants on CNTs were studied.For the sake of effective determination of trace objects after the process of adsorption,the sample solution was loaded and the analytes were then preconcentrated onto the preconcentration column using the cigarette filter as sorbent.The analytes were subsequently eluted with a mobile phase of methanol/water（90:10,V/V）.An on-line solid phase extraction（SPE） protocol coupled with high performance liquid chromatography（HPLC） was developed for the simultaneous determination of trace BPA and 4-NP in water samples.The adsorption of CNTs was a quick adsorption for the two compounds.When the concentrations of the two aqueous solutions samples were both 10 mg/L,the adsorption of BPA reached equilibrium in 60 minutes with the adsorption amount of 3.75 mg/g,while the adsorption of NP reached equilibrium in 10 minutes with the adsorption amount of 4.91 mg/g.The adsorption amount was increased with increasing of initial concentration or dropping of temperature.The correlation coefficients were larger than 0.99 when both Freundlich equation and Langmuir equation were used to fit data.Thermodynamic functions such asâ–³G,â–³H andâ–³S of the process of adsorption for BPA were -39.48 KJ/mol～-43.51 KJ/mol, -18.06 KJ/mol and 71.73 J/（mol·k）,respectively.â–³G,â–³H andâ–³S of the process of adsorption for NP were -39.89～-46.15 KJ/mol,-9.49 KJ/mol and 103.60 J/（mol·k）,respectively.The adsorption was a exothermal, increased entropy,spontaneous process having a character of physical adsorption.The enthalpy change and entropy increase were the main driving forces for the adsorption.CNTs were purified by microwave radiation and modified by oxidizing methods such as nitric acid soaking and so an.The object was heterocylic compound-pyridine.The adsorption characteristics of heterocyclic small molecules compound adsorption from aqueous solution by unmodified and modified CNTs were examined.Microwave radiation and modification by nitric acid oxidation both could effectively remove amorphous carbon impurities from multi-wall carbon nano-tubes.The purity and the specific surface area of CNTs increased.CNTs were primarily purified by microwave radiation for 60～120 s with low power. The specific surface area increased to 108.33 m²/g from 66.49 m²/g.CNTs were modified by four methods as follows:refluxing in concentrated nitric acid（CNTs-HNO₃）,refluxing in concentrated nitric acid and roasting（CNTs-HNO₃-OX）,ultrasonic vibration and refluxing in concentrated nitric acid（CNTs-ULTRA-HNO₃）,refluxing in concentrated nitric acid and polyvinyl alcohol treatment（CNTs-HNO₃-POLY） The followed conclusions were obtained by specific surface area and particle size analysis.The specific surface area increased to 112.88,117.34, 113.17,70.95 m²/g from 66.49 m²/g,respectively.The particle size of CNTs-HNO₃,CNTs-ULTRA-HNO₃ and CNTs-HNO₃-POLY was smaller than that of original-CNTs.It decreased to 27.15μm,31.33μm and 23.24μm from 31.59μm respectively,but the particle size of CNTs-HNO₃-OX decreased to 34.89μm.The adsorption of pyridine on all the four kinds of modified CNTs was basically saturated in 120 minutes and the adsorption capacity reached the maximum at pH=8.55.When the concentration of pyridine was 80 mg/L,the adsorption capacity of original-CNTs was 3.80 mg/g.It increased to 4.36 mg/g,4.28 mg/g and 4.07 mg/g for CNTs-ULTRA-HNO₃,CNTs-HNO₃ and CNTs-HNO₃-OX.Instead,it decreased to 2.58 mg/g for CNTs-HNO₃-POLY.The adsorption amount was increased with increasing of initial concentration or dropping of temperature under the same condition.With temperature in the range of 293 K～313 K,experimental data of adsorption for all modified CNTs were fitted to the Freundlich equation with the correlation coefficients all over 0.99.