| The fresh water scarcity has become a severe global challenge threatening human survival and affecting economic development nowadays.The seawater desalination technology can provide an effective way to alleviate the freshwater crisis.The dominant industrial desalination technologies are mainly relied on multistage flash distillation,multiple-effect distillation and reverse osmosis.Nevertheless,these technologies still suffer from seversl drawbacks,for instance,high energy consumption,low desalination efficiency and expensive operating cost.Capacitive deionization(CDI)is an emerging desalination technology based on the electrochemical double layer(EDL).Carbon materials are used as the working electrodes for traditional CDI,resulting in low desalination capacity as well as low charge efficiency which hardly meet the requirments of brine water treatment.Hybrid capacitive deionization(HCDI)system was adopted to improve the desalination performance in our research,where sodion intercalation materials operated as sodion intercalation/deintercalation electrode and carbons severed as chlorid ion intercalation electrode.Pseudocapacitance reaction was introduced to embed sodion into sodium ionic intercalation materials by chemical bonds,meanwhile chloridion was adsorbed and stored in the EDL by electrostatic adsorption.In addition,we also proposed a novel pseudo-capacitive behaviors induced dual-ion hybrid deionization(Di-HCDI)system to further promote the capacitance desalination property,where Na1.1V3O7.9@rGO applied as sodion de-intercalation electrode and Ag@rGO used as chloridion one to realize the matching electrochemical reactions on two electrodes.The main research contents of this paper are as follows:1.The carbon@Na4Ti9O2O(C@NTO)core-shell nanotubes with a carbon layer thickness of?1.6 nm were synthesized via secondary hydrothermal reaction and annealing.As electrochemical results shown,the specific capacity of C@NTO electrode at the scan rate of 1 mV/s was 153.34 F/g,which was significantly improved compared with NTO(62.84 F/g).Finally,C@NTO(NTO)and actived carbon were selected to constitute a HCDI system to investigate their capacitance deionization performance.The salt removal capacivity of C@NTO HCDI system has reached up to 66.14 mg/g and the corresponding charge efficiency was close to 100%,which was promoted obviously compared with NTO HCDI system.Moreover,C@NTO HCDI system exhibated excellent cyclic regeneration capability,there was only 3.78 mg/g decay after 50 cycles.2.The Na1.1V3O7.9(NVO)nanoribbon with an average width of?50 nm was prepared by hydrothermal reaction and annealing.Then NVO-250 nanoribbon obtained under 250? annealing treatment was selected to embedd into rGO network to get NVO-250@rGO composite.As electrochemical results shown,the specific capacity of NVO-250 electrode was superior to NVO-350 and NVO-450 electrode at different scanning rates.And the specific capacity of NVO-250@rGO electrode at the scan rate of 1 mV/s was 241.38 F/g,which was greatly improved compared with NTO(190.58 F/g).NVO-250@rGO(NVO-250)and rGO were selected to form a HCDI system.The results showed that the salt removal capacivity of NVO-250@rGO HCDI system has reached up to 49.71 mg/g and the corresponding charge efficiency was close to 100%.3.Ag@rGO composite was synthesized via Alkali reduction reaction in a water bath,and massive Ag particles with diameter of?30 nm distributed in the rGO network uniformly.A novel Di-HCDI system was proposed where Na1.1V3O7.9@rGO applied as sodion electrode and Ag@rGO used as chloridion one.An optimal salt removal capacity of 60.26 mg/g was achieved,simultaneously the charge effciency was close to 100%,which was far superior to rGOINVO-250@rGO HCDI system.Moreover,Ag@rGOINVO-250@rGO Di-HCDI system showed excellent recycling capacity.Finally,the crystal structure change of Ag@rGO and NVO-250@rGO electrodes before and after desalination was detected to explore the desalination mechanism of Di-HCDI system. |
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