Study On The Adsorption Of Heavy Metal Ions With Carbon Xerogels Modified By Nitrogen Functional Groups

Recently, carbon xerogels and their modified materials are widely used in the field of chemical industry and environmental protection. In this work, two kinds of nitrogen-modified carbon xerogels were prepared by using sol-gel and impregnation method. Moreover, their adsorption performance for the removal of heavy metal ions were evaluated.The obtained samples were characterized by scanning electron microscopy (SEM), specific surface area analyzer (BET) and elemental analyzer (EA).The results showed that the specific surface area of melamine doped carbon xerogels were between530.0m2/g and573.3m2/g. Nitrogen functional groups in melamine doped carbon xerogels were mainly existed in the form of pyrodone-N or pyrrolic-N (N-5) groups, where secondary amine and primary amine is given priority in Polyethylene imine impregnated carbon xerogels.Three heavy metal ions were used for the research of the adsorption performance of melamine doped carbon xerogels. The results demonstrated that the adsorbed amounts of metal ions were significantly increased due to the introduction of N functional groups. Among them, the best sample is NCX-150-2, its removal efficiencies for Pb, Zn and Cu by NCX are74.4%,80.3%, and83.1%, respectively, which are1.97,1.67and1.64times of those by CX. The adsorption process followed the pseudo-second-order kinetic and Langmuir model. Adsorption thermodynamics showed that the adsorption process is an endothermic process with spontaneous nature, hi addition, lead ions was used for the research of the adsorption performance of polyethylene imine impregnated carbon xerogels. The remove efficiency is higher than traditional carbon xerogels, sample CX-PEI-0.5has the best performance with a removal of74%, which is1.96times of CX. The adsorption process also followed the pseudo-second-order kinetics.The regeneration experiment results showed that after three times adsorption, regeneration rate of sample NCX-150-2was80.4%and88.1%for CX-PEI-0.5, which indicated good stability for both materials. Through the pH changes before and after adsorption and characterization results, we found that ion exchange and surface complexation existed for the adsorption process of melamine doped carbon xerogels, where surface complexation is dominated; Polyethylene imine impregnated carbon xerogels for lead ions adsorption is given priority to ion exchange.