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The U.S.Geological Survey found that there is 96.5% water in the oceans and sea,1.7% in the ice caps,1% in brackish water,and only 0.8% fresh water [1].1.2 billion people lack access to safe drinking water,millions of people die annually from diseases transmitted through unsafe water [2].The best answer to solve the water shortage issue is transform sea water into fresh water.This paper proposes to employ the stacking of two nano desalinators in parallel for water purification.Based on the overlapping of electro-double-layer (EDL) inside the anodic aluminum oxide (AAO) nanochannels as virtual filter,each desalinator can select uni-ions for desalination [our previous paper].This study extends the previous result further,to apply electrical field throughout the stacking region of double desalinators from outside,thus both positive and negative ions can be separated at the same time.The operation principle of the desalination system is shown in Fig.1.The surface of the nano desolinator was coated with a conductive metal layer and an insulation layer.When enough voltages applied on the nano channel,the thickness of the EDL will increase to overlap owning to the increment of the charge density on the channel[3].When water passing through the channel,the co-ions are kept in the enter side due to electrostatic expelling while the counter-ions and water can go through the channel rapidly.A concept-testing model is designed as shown in Fig.2(a)un-ion separation testing,and it consists of two chambers stacking on a piece of nano desalinator.1M NaCl solution and pure water were loaded into the upper and lower chamber,respectively.When stacked nano-desalinator is shown in Fig.2(b)consisting of two nano desalinators under electric field to filter out both positive and negative ions.The result of the concept-testing model for NaCl solution is shown Fig.3.After the applications of +0.1V,+0.3V and +0.5V onto the desalinator membrane,the concentrations were reduced to 14.96 mM,12.12 mM,and 8.98 mM,respectively.When salt water through the parallel nano desalinator and electric field,higher voltage provide better desalination result,as shown in Fig.4,by adding 15V a desalination result with a 10% desalination rate is obtained.