Study On Electrosorption Of Cu²⁺ In Aqueous Solution With CNT/PANI Electrodes

Cu2+ is a common heavy metal which is poisonous for aquatic organism and harmful to human health.As a result,it’s significant to study the treatment of copper ion-containing wastewater.As for traditional treatment method,such as adsorption and chemical precipitation,there are many disadvantages existing like high energy consumption,high investment,complex operations and secondary pollution,etc.Capacitive deionization is a new technology with low energy consumption and maintenance cost,no secondary pollution and has well prospect of development.At present,capacitive deionization is mainly applied to desalination rather than removal of heavy metal in wastewater.So it has theoretical and social value to investigate the application of capacitive deionization in this field.This study investigated the application of CNT and CNT/PANI electrodes in capacitive deionization,the synthesis of CNT/PANI composites,influence of experimental condition and electrosorption mechanism.The CNT/PANI composites were synthesized via in situ chemical oxidation polymerization and the electrodes were prepared by coating method,the wastewater with Cu2+ circulated through the electrodes by a peristaltic pump.In this study,the morphology of CNT/PANI composites was observed by Scanning Electron Microscope(SEM)and the composites were characterized by Fourier Transform Infrared(FTIR)spectroscopy and X-ray Photoelectron Spectroscopy(XPS).Their specific areas were determined by N2 adsorption-desorption tests and electrochemical capacitance was measured by Cyclic Voltammetry(CV)in copper solutions.The results show that the CNT/PANI composites have a networked-rod nanostructure and the inner layer CNTs are wrapped by PANI and their specific area and pore volume decreased compared to CNT.The electrochemical capacitance of CNT/PANI increased 1.25 times and the removal rate of Cu2+ increased 94.39%.This study also investigated the influence factors of electrosorption experiment,including working voltage,circulation velocity,electrode spacing,initial concentration of Cu2+,temperature and pH.The results showed that the electrosoption capacity of CNT and CNT/PANI electrodes increased with the growth of working voltage and initial concentration but decreased with the growth of electrode spacing and temperature.In acid conditions,H+ would compete with Cu2+ and influence the removal efficiency.As a result,the removal rate decreased along with the reduction of pH.Circulation velocity has no effect on the equilibrium absorption capacity of electrodes while it only influences the equilibrium time.The electrosorption mechanism of CNT and CNT/PANI electrodes on the removal of Cu2+ was investigated with adsorption kinetics and isotherm models.The results showed that the adsorption process of Cu2+ removal by the two kinds of electrodes well fitted the pseudo-first-order kinetic and Langmuir isotherm models.the adsorption process was dominated by monolayer adsorption and the adsorption type is single molecule layer adsorption.