MnO2/PSS/CNTs composite electrodes synthesized by a layer-by-layer deposition method and its application in the membrane capacitive deionization technology
Environmental issues, including water crisis, are under wide discussion nowadays and new technologies are needed to deal properly with them. Membrane capacitive deionization(MCDI) technology with added cation- and anion–exchange membrane is developed from the capacitive deionization (CDI) technology, which is an excellent alternative process for desalination and water purification and do not need high pressure pump, comprehensive operations or large amount of thermal energy. The additional ion-exchange membranes can selectively permeate ions. In both processes the charged ions, such as Na+,Cl-,Mg2+,Ca2+,Fe3+,SO42- ect., are electro-adsorbed on the surface of or into the pores of the porous electrodes when current electricity is applied; the ions are released from the electrodes when the charged are removed, thus the electrode can be used repeatly to treat large amount of water. Therefore, the performance of CDI/MCDI is largely affected by choice of electrodes.
This project goal is to develop an electrode material that possesses better electrosorption capacity. That is a material that possesses suitable pore structure, excellent electrical conductivity and electrochemical activity properties.
The manganese oxide (MnO2)/carbon nanotubes (CNTs) composite heritages not only the advantage of porous structure and excellent conductivity of CNTs but also the high capacitance as well as additional ions’ sorption/insertion ability of MnO2 was synthesised by a layer-by-layer deposition method with the assistance of Polystyrene Sodium Sulfonate (PSS). PSS being an anion surfactant facilitated the dispersion of CNTs and even growth of MnO2. The prepared composite materials were also characterized by nitrogen sorption/desorption at 77 K (BET, t-plot, αs-plot), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Fourier transform infrared spectrometry (FTIR), etc.
Lastly, desalting performances of the composites as electrode materials were tested under variety experimental conditions, including different feed solution concentration from 50 to 5500µS/cm and supplied voltage from 0.6 to 1.2V, and a highest salt removal efficiency of 96.8% was achieved when the feed NaCl solution concentrated 200µS/cm and external voltage supplied 1.2V.