Preparation Of Carbon Nanofiber Aerogels And Its Adsorption Properties For Pb²⁺

In this work,a carbon aerogel based on electrospun nanofibers was prepared and applied to the adsorption of heavy metal ions in wastewater.First,the spinning solution was electrospun,and the nanofibers were received through a water bath,then transferred to a mold for freeze-drying.Finally,a polyacrylonitrile(PAN)/graphene nanofiber aerogel with a three-dimensional structure was obtained.The effects of different concentrations of PAN and graphene on the prepared nanofiber aerogel were investigated.The results show that as the concentration of PAN increases,the fiber diameter increases.And the addition of graphene enhances the conductivity of the spinning solution,thereby reducing the fiber diameter.At the same time,the greater the concentration of graphene,the more obvious the agglomeration phenomenon in the fiber,which affects the mechanical stability of the aerogel.It was found that the aerogel properties obtained at 10 wt%PAN and 0.5 wt%graphene concentration were optimal.The prepared PAN(10%)/graphene(0.5%)aerogel was subjected to carbonization treatment in three different processes to obtain three carbon nanofiber aerogels(CNFA-1,CNFA-2,CNFA-3).The results show that CNFAs are successfully produced by three carbonization processes,among which CNFA-2 has the smallest carbon fiber diameter,uniform size,continuous fiber,and minimal carbon fiber bonding.All three CNFAs have carbon structure defects,which are typical amorphous carbon.CNFA-2 has the lowest degree of carbonization and the largest internal defect of carbon structure.XPS test results show that CNFA-2 has the lowest carbon content,and the main forms of carbon atoms are C-C,C-OH,C=O.Since CNFA-2 has more reactive groups,it was selected as the final sample for adsorption of Pb2+.The effects of single factors on the adsorption of Pb2+by CNFAs were investigated.Adsorption kinetics and adsorption isotherm fitting were applied to the adsorption data to explore its adsorption mechanism.The results showed that the adsorption amount of Pb2+by CNFAs was positively correlated with pH,contact time and initial concentration were negatively correlated with the amoUnt of CNFAs.The kinetic experimental data of CNFAs adsorption Pb2+ follows the pseudo-second-order kinetic model,indicating that the whole adsorption process mainly involves chemical adsorption of covalent electrons or ion exchange,and the experimental adsorption equilibrium amount is well fitted by the Langmuir isotherm model.Under the same conditions,the adsorption amount of CNFAs on different heavy metal ions is Pb2+>Cu2+>Cd2+>Co2+>Cr3+.