Adsorption Of Ni(?)and Cr(?)from Water By Polydopamine-modified Magnetic Carbon Nanotubes

Electroplating wastewater was directly discharged into the natural water environment causing serious consequences to the ecological environment and human health.Adsorption method was used to remove Ni(II)and Cr(VI)from the water in this study,which were two representative heavy metal ions in the electroplating wastewater.Carbon nanotubes(MWNTs),dopamine,ammonium ferrous sulfate and ammonium ferric sulfate are the main raw materials.Magnetic carbon nanotubes(mMWNTs)were prepared by chemical co-precipitation method,and dopamine-coated magnetic carbon nanotubes(mMWNTs@-PDA)were obtained with in situ oxidative polymerization of dopamine onto the surface of magnetic carbon nanotubes.Materials before and after modification were characterized by Fourier transform infrared spectroscopy,Scanning electron microscope and X-ray diffraction.The adsorption performance of Ni(II)in water were investigated by modified materials under the conditions of pH,reaction time,temperature,initial concentration and adsorbent dosage,and the adsorption performance of Ni(II)were investigated by raw materials under the first four influencing factors.The results showed that the adsorption quantity increased with the increase of pH,reaction time,temperature,initial concentration and adsorbent dosage,the adsorption properties of Ni(II)by modified materials are generally better than those raw materials.When the temperature is 25?,the pH value is 6,and the Ni(II)concentration is 40mg/L,mMWNTs@PDA and MWNTs reached adsorption equilibrium at240 min and 120 min,respectively.The adsorption capacities were 27.98mg/g and 23.23 mg/g,respectively.At the same time,adsorption kinetics and adsorption isotherm were analyzed based on the adsorption process.The results showed that the adsorption process of Ni(II)in aqueous solution by modified materials was more in line with the pseudo-second-order kinetic model(correlation coefficient R~2=0.9989)and Freundlich isotherm adsorption model(correlation coefficient R~2=0.9961).The regeneration experiment showed that the adsorption effect of the modified material on Ni(II)was still good after 5 cycles of regeneration.The adsorption performance of Cr(VI)in water were investigated by modified materials under the conditions of pH,reaction time,temperature,initial concentration and absorbent dosage.The results showed that the adsorption decreased with the increase of pH and increased with the increase of reaction time,temperature,initial concentration and adsorbent dosage.The temperature was 25?,the concentration of Cr(VI)solution was 40 mg/L,the pH value was 3,and the adsorption equilibrium was reached by oscillating for 240 min.The adsorption capacity of mMWNTs@PDA was 49.82 mg/g.At the same time,adsorption kinetics and adsorption isotherm were analyzed based on the adsorption process.The results showed that the adsorption process of Cr(VI)in aqueous solution by modified materials was more in line with the pseudo-second-order kinetic model(correlation coefficient R~2=0.9989).The intraparticle diffusion model shows that the adsorption process is a combination of membrane diffusion and intraparticle diffusion,and the isotherm adsorption model was consistent with the Langmuir and Freundlich isotherm adsorption models(correlation coefficient R~2 was both bigger than 0.99).The adsorption thermodynamics study found that the adsorption process of Cr(VI)in aqueous solution was a spontaneous adsorption reaction.The regeneration experiment showed that the adsorption effect of the modified material on Cr(VI)was still good after 5 cycles of regeneration.