| Due to population growth and environmental pollution,human society is facing the critical problem of shortage of clean water.Water resources in many regions are contaminated with various harmful compounds,among which the monovalent anion pollution represented by fluoride?F-?pollution is listed as the main inorganic pollutant.Therefore,the efficient removal of fluoride from wastewater has become an increasingly important issue.Compared with traditional defluorination technology,capacitive deionization?CDI?is an emerging technology for desalination,which has the advantages of high efficiency,simplicity and safety,low energy consumption,and no secondary pollution.The key of CDI technology is the development of electrode materials.The poor selectivity and low adsorption capacity of carbon materials limit their application as CDI electrodes.Therefore,it is necessary to develop new electrode materials with high adsorption capacity,excellent selectivity and excellent regeneration performance.In recent years,Layered Double Hydroxide?LDHs?,which has the advantages of adjustable metal ions and interlamellar anion types and composition,simple synthesis method and low price,has been regarded as one of the ideal choices for CDI electrode materials.One of the most important characteristics of LDHs is its"memory effect",that is,when it is heated to a certain temperature,LDHs can be converted into mixed layered metal oxides,which have a good adsorption effect on anions in water.At present,the research mainly focuses on binary hydrotalcites and its metal oxides,and there are few studies on ternary hydrotalcites.The synergy between ternary hydrotalcite metals and the good pseudocapacitance behavior of transition metals are expected to improve their CDI performance.Therefore,this paper focuses on the preparation of ternary hydrotalcite and its application in CDI defluorination.The properties of defluorination and cyclic stability were investigated,and the electrosorption mechanism was analyzed.The details are as follows:?1?A ternary hydrotalcite?NiFeMn-LDH?containing nickel,iron,and manganese was successfully synthesized by co-precipitation method at room temperature,and then calcined at500°C for 4 h to obtain a metal oxide?NiFeMn-LMO?.NiFeMn-LMO was used as the CDI positive electrode,and the activated carbon treated by nitric acid was used as the negative electrode.An asymmetric CDI module was assembled for CDI defluorination research.The results showed that Mn doping regulated the electronic structure of NiFeMn-LMO and improved its pseudocapacitor behavior,.At an initial NaF concentration of 500 mg L-1and a voltage of 1.4 V,the defluorination amount of NiFeMn-LMO could reach 16.7 mg/g,and it could still maintain 93.3% of the initial amount after 30 cycles of cyclic testing.?2?NiCoAl-LDH/rGO composites were successfully synthesized by homogeneous urea precipitation method,that cobalt was introduced into LDH interlayer to improve its pseudocapacitor behavior,and graphene was introduced to enhance its conductivity.NiCoAl layered metal oxide/graphene nanosheets?NiCoAl-LMO/rGO?were prepared by high-temperature roasting,and asymmetric CDI modules were assembled with nitric acid-treated activated carbon for defluorination testing.The results showed that the maximum adsorption capacity of NiCoAl-LMO/rGO was 24.5 mg/g at the applied voltage of 1.4 V when the initial NaF concentration was 500 mg L-1.At the same time,the composites also showed good cyclic stability during 40 consecutive CDI defluorination cycles. |
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