| Electroplating,printing and dyeing,metal smelting and other industrial processes often produce wastewater containing large amounts of copper ions.As a common heavy metal ion,copper ions can cause serious harms to human health and ecological environment.Activated carbon has pore structure well developed and rich surface active functional groups,which are usually used as adsorbents.The adsorption process includes physical adsorption and chemical adsorption.Chemical adsorption plays an important role during the adsorption process.In order to increase the Cu(?)adsorption capacity,this study proposes to apply non-thermal plasma to modify the surface of activated carbon,and promote the formation of oxygen-functional groups.The phosphoric acid activated carbon was modified by using dielectric barrier discharging non-thermal plasma.The effect of modification time(2.5,5,7.5,10,12.5,15min)on Cu(?)adsorption capacity of activated carbons was investigated.Results showed that plasma modification improves Cu(?)adsorption capacity remarkably.Importantly,the Cu(?)adsorption capacity of activated carbons shows a non-monotonic variation(increasing firstly and then decreasing)with the plasma modification time.The modification time of 7.5min reached the best adsorption capacity compared to unmodified activated carbon.The adsorption equilibrium curves of modified activated carbon with different initial concentrations of copper ion solution(60,100,200mg/L)were studied.It was concluded that the adsorption of copper ions on activated carbon at different initial concentrations of copper ions at equilibrium time was 120min.The adsorption equilibrium curves of different initial copper ion concentration is fitted based on the adsorption kinetic model.The determination coefficients for both the surface diffusion model and chemical adsorption model are high,whereas the coefficient of determination for the internal diffusion model is low.Hence,the change of copper ion adsorption activated carbon after adsorption is chemical-based,which is supplemented by surface diffusion.The influence of activated carbon with different adsorption temperatures before and after modification on the adsorption effect of copper ions was studied.The influence of activated carbon with different adsorption pH,different adsorption dose and different rotational speed on the adsorption effect of copper ions was studied.The optimum adsorption conditions are as follows:the modified time is 7.5min,the adsorption temperature is 40,the pH is 5,the input of activated carbon is 3g/L,and the speed is 300rpm.Infrared spectra analysis of activated carbons before and after modified 7.5min adsorption showed that C=O and carboxyl groups and functional groups of phosphorus on the surface of activated carbons promoted the adsorption of Cu(?).The SEM-EDX of activated carbon after modified 7.5min adsorption is analyzed.It is concluded that the phosphorus in the pores of activated carbon is more than that outside the hole,and the copper in activated carbon hole is also more than that outside the hole.It is further conjectured that the phosphorous functional groups on the surface of the activated carbon can promote the adsorption of copper ions.The XPS of phosphorus containing functional groups of activated carbons and activated carbons activated by phosphoric acid at different time is obtained.It is concluded that phosphate and pyrophosphate can promote the chemisorption of copper ions.XPS analysis of carbon containing functional groups of activated carbons and phosphoric acid activated carbons at different time was carried out.It was found that carboxyl functional groups promoted the adsorption of Cu(?).Based on the above experiments and mechanism studies,the carboxyl groups of phosphorus containing functional groups,including pyrophosphates and phosphates and functional groups of carboxyl groups,can promote the adsorption of Cu(?). |
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