The Characteristics Of Chlorophenols Adsorption On Single-walled Carbon Nanotubes

Chlorophenols,which are highly toxic and carcinogenic,have been widly used as intermidates to produce other chemical materials.The environmental risks caused by their existence in aqueous environment have attracted increasing interest.In this study,the adsorption of 6 kinds of chlorophenols on single-walled carbon nanotube(SWCNT),which is a new kind of adsorbent,was investigated.A linear solvation energy relationship model was developed to predict the ability of SWCNT to adsorb other phenols.The molecular dynamics simulation was performed to analyze the adsorption mechanism.The adsorption of 6 chlorophenols on three kinds of SWCNT(pristine SWCNT,SWCNT-OH,SWCNT-COOH)was studied.Pseudo-first order and pseudo-second order models were applied to fit the kinetic curves.The time needed to reach adsorption equilibrium was about 2 hours.The adsorption isotherms obtained from the experiment were all well fitted by Langmuir,Freundlich and Polanyi–Manes models,with the corresponding correlation coefficients all above 0.95.The oxidation of SWCNT would depress the adsorption capacity of chlorophenols significantly.When pH was above the pKa of 2,6-DCP,the removal decreased dramatically.The adsorption capacity of 2,6-DCP decreased slightly when ionic strenghth increased.The powdered activated carbon(PAC)has higher adsorption capacity for chlorophenols than SWCNT,while SWCNT adsorbs chlorophenols much faster than PAC.A linear solvation energy relationship(LSER)model was built and validated using the data on the adsorption of 40 organic compounds,including six chlorophenols from this study.This model can be used to predict the adsorption coefficient of organic compounds on SWCNT.The adjusted R2,root mean square error(RMSE)and external RMSE were 0.84,0.49 and 0.50,respectively.The Q2 and external Q2 calculated with leave-one-out cross-validation method were 0.79 and 0.72,respectively.These characteristic parameters indicate that the LSER model has good fitness,robustness and predictive ability.Hydrogen bond donating ability and cavity formaition and dispersion interactions were two key factors controlling the adsorption process.The variance of equilibrium concentration would influence the predictive ability of themodel.The adsorption of benzene,phenol and 4-CP was investigated with molecular dynamics simulation.The adsorption energy for each adsorbate was calculated.The interactions between adsorbate molecules and SWCNT's surface were visualized.The results indicate that the adsorption capacities of SWCNT for adsorbates are highly correlated with the corresponding adsorption energy.A second layer was formed on(5,5)SWCNT and diminished with the increase in diameter.The distances between adsorbed molecules and(5,5)SWCNT surface were determined by radial distribution function(RDF).The distances for benzene,phenol and 4-chlorophenol are 5.00 ?,4.85 ?,4.75 ? respectively.The visualization of ?-? interation indicates that attractive and repulsive forces co-exist in the complicated interaction.