Research On Nanoporous Graphene In Heavy Water Separation And Its Electrochemical Performance

Hydrogen is the lightest element in nature and has three isotopes:hydrogen（¹H）,deuterium（²H,D）and tritium（³H,T）.Deuterium has a wide range of uses in military,energy,medical and scientific research.However,deuterium is extremely low natural abundance（about 0.015%）,and tritium only exists in nuclear reactors or accelerators.Meanwhile,deuterium（tritium）-containing wastewater from nuclear facilities which has great damage to staff and environment,needs to be properly recycled.So deuterium（tritium）must be concentrated from water solution.There are many separation methods of hydrogen isotope,and the GS（Girdler-Sulfied）method still be used in most plants.The hydrogen sulfide gas used in this method is not only corrosive to equipment,but also has strong toxicity.Therefore,it is necessary to develop a new method to separate hydrogen isotope.Nanoporous graphene was used to separate deuterium and hydrogen in first part of this paper.First,graphene oxide was synthesized by modified Hummer’s method and the nanoporous graphene was prepared by combustion method.They were characterized by infrared spectroscopy,X-ray powder crystal diffraction（XRD）,Raman spectroscopy,N₂physical adsorption specific surface area test（BET）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,etc.The nanoporous graphene was prepared successfully verified by characterization.Afterwards,the nanoporous graphene were used for concentrating deuterium from water solution by liquid adsorption and gas phase static adsorption experiments.It is found that the nanoporous graphene can be used to concentrate deuterium from water solution and big pore size of the nanoporous graphene is benefit to deuterium concentration.A dynamic gaseous experimental device was designed to finish adsorption and desorption experiments.The dynamic adsorption equilibrium time is about 45min,the optimal adsorption temperature is 85°C and the desorption temperature is 120°C.The content of ¹⁷O in water solution was used to study effect of the molecular mass in isotope concentration experiment,and the effect of oxygen-containing functional groups was also studied.It is shown that the concentration rate of deuterium by the nanoporous graphene is not only related to molecular mass,but also the oxygen-containing functional groups on the nanoporous graphene.A one-step method to obtain nitrogen/sulfur doped nanoporous graphene（NS-NG）is first used in the second part of this paper.Zinc nitrate and dye containing nitrogen or sulfur were mixed in graphene oxide solution,and the film was prepared by vacuum filtration.The nitrogen/sulfur doped nanoporous graphene（NS-NG）was successfully prepared by burning the film at 550°C.NS-NG was used to study its electrical storage performance of supercapacitors.The two-electrode symmetric supercapacitor device were assembled in 0.5 M Na₂SO₄aqueous solution and the measurement of electrochemical performance was finished at the current density was 2 A·g^-1.It was found that the NS-NC not only holds a high specific capacitance of 325 F g^-1,and also have a high energy density of 25 Wh kg-1 at a high power density of 1906 W kg^-1.Meanwhile the supercapacitors had an excellent capacity retention of 86%after10,000 cycles.