Separating Pb²⁺ And Na⁺ From Wastewater By Electrochemically Switched Ion Exchange Based On Organic-Inorganic Composite Film Electrodes

Electrochemically switched ion exchange?ESIX?is a novel ion exchange technology,which has the advantages of no secondary pollution and fast processing speed.The key issue of ESIX technology for water treatment is to develop new type of electroactive ion exchange materials?EIXMs?,including organic conductive polymer,inorganic ferricyanide and organic-inorganic composite materials.Among EIXMs,the organic-inorganic composite materials have attracted wide attention due to their excellent conductivity stability and ion exchange performance.In this paper,aiming at the separation of heavy metal lead ions and metal sodium ions,the SBA-15/PANI/PSS and PPy/UiO-66composite film electrodes have been developed.Lead is a neurotoxic heavy metal,which can enter the body and accumulate in the body through various ways.A certain accumulation can be seriously harmful to human health.Inorganic mesoporous SBA-15,with a large specific surface area and excellent stability,has been favored by researchers.In this study,for the removal of Pb²⁺ions,a novel potential-triggered electroactive composite film consisting of mesoporous silica SBA-15,polyaniline?PANI?and polystyrenesulfonate(PSS^n-)was fabricated in an aqueous electrolyte solution via a facile pulse potentiostatic method.The obtained composite film was characterized by Fourier transform infrared spectroscopy?FT-IR?,scanning electron microscopy?SEM?and thermo gravimetric?TG?.The ion exchange properties were evaluated in a 0.1 M Pb?NO₃?₂ solution by using an electrochemical quartz crystal microbalance?EQCM?as well as cyclic voltammetry?CV?method.It was indicated that the uptake/release of Pb²⁺ions in/from SBA-15/PANI/PSS composite film were successfully achieved by modulating the redox states of the electroactive composite film.Investigating the effect of scan rate on the exchange behavior of SBA-15/PANI/PSS composite film,the low ion transfer resistance was achieved and it exhibited different ion exchange behavior at different scan rates.Compared with PANI/PSS film,SBA-15/PANI/PSS composite film had higher adsorption capacity as well as higher selectivity towards Pb²⁺ions,and the ion exchange of SBA-15/PANI/PSS composite film maintained a high stability over 97%even after 500 successive cycles.The reuse of reclaimed water alleviates the shortage of water resources.However,due to the high concentration of sodium ions in the reclaimed water,long-term use will cause problems such as salinization and alkalization of the soil,which will cause damage to the soil.In this work,we synthesized a composite film consisting of metal organic framework Ui O-66 and conducting polymer PPy for the treatment of Na⁺ions.The Na⁺ion exchange performance and adsorption/desorption performance of composite film were investigated respectively.The results show that the composite film exhibits good ESIX behavior for Na⁺ions due to the properties of the channel and affinity of the organic ligands with the UiO-66 materials.Through periodic repeatedly monitoring the redox state of composite film,the rapid Na⁺ions adsorption/desorption performance can be achieved.The Na⁺ions exchange capacity of PPy/UiO-66 composite film can reach 30 mg g^-1 and keep saturated within 50 s.Compared with different electrolyte solutions,the PPy/UiO-66composite film exhibts excellent exchange performance for Na⁺ions.In contrast to PPy film,PPy/UiO-66 composite film electrode possesses higher Na⁺ion exchange capacity.