Preparation And Properties Of Sodium Titanium Phosphate/graphene Composites

Hybrid capacitive deionization is a new type of desalination technology developed by capacitive deionization,which has attracted much attention due to the high adsorption capacity of battery-type electrodes and the high adsorption rate of capacitive electrodes.Sodium titanium phosphate is considered to be a promising electrode material due to its high theoretical capacity and high sodium ion conductivity,but its poor electronic conductivity and volume expansion during ion intercalation/deintercalation limits the development in hybrid capacitive deionization.However,three-dimensional holey graphene with high conductivity and rich pore structure is considered as ideal carbon composite matrix.In order to obtain hybrid capacitive deionization electrode material with high adsorption capacity,high adsorption rate and high cycle stability,the three-dimensional sodium titanium phosphate/graphene composites are prepared by hydrothermal,double carbon coating and hetero atom doping.The specific research contents are as follows:(1)The sodium titanium phosphate/reduced holey graphene oxide(NTP/rHGO)composites with three-dimensional porous structure were prepared by hydrothermal method combined with carbonization.The NTP/rHGO-2 with holey graphene oxide content of 0.15 g exhibited highest specific capacity(396.42 F·g-1)at the scan rate of 0.2 mV·s-1 and capacity retention rate(90.61%)at 2 A·g-1.When NTP/rHGO-2 was used as the hybrid capacitive deionization electrode,the electrosorption capacity was 33.25 mg·g-1 and the average adsorption rate was 0.3 mg·g-1 s-1 in sodium chloride solution with the initial conductivity of 1600 ?S·cm-1 under 1.4 V.(2)The sodium titanium phosphate/reduced holey graphene oxide(NTP/rGO@rHGO)composites with three-dimensional porous structure were prepared by double carbon coating.The NTP/rGO@rHGO-2 prepared with graphene oxide and holey graphene oxide content of 0.05 g and 0.1 g exhibited highest specific capacity(420.36 F·g-1)at the scan rate of 0.2 mV·s-1 and ultrahigh capacity retention rate(93.46%)at 2 A·g-1.When NTP/rGO@rHGO-2 was used for desalination of hybrid capacitive deionization,the electrosorption capacity was 35 mg·g-1 and the maximum ion removal rate was 0.53 mg·g-·1s-1 in sodium chloride solution with the initial conductivity of 1600 ?S·cm-1 under 1.4 V.(3)Nitrogen-sulfur co-doped sodium titanium phosphate/reduced holey graphene oxide(N,S-NTP/rHGO)composites with three-dimensional porous structure were prepared by hydrothermal method.The N,S-NTP/rHGO-2 with thiourea content of 0.45 g exhibited highest specific capacity(530.46 F·g-1)at the scan rate of 0.2 mV·s-1 and high capacity retention rate(92%)at the current density of 4 A·g-1.When N,S-NTP/rHGO-2 was used for desalination of hybrid capacitive deionization,the electrosorption capacity was 36.87 mg·g-1 and the maximum ion removal rate was 0.66 mg·g-1·s-1 in sodium chloride solution with initial concentration of 800 mg·L-1 under 1.4 V.