Preparation Of Modified Rice Husk Porous Carbon Electrode And Capacitive Deionization Performance Study

Capacitive deionization technology(CDI),also known as electrosorption technology(EST),is a new water treatment technology that concentrates charged particles in solution on the surface of electrode plates.As a new sewage treatment technology with high efficiency and low consumption,electroadsorption technology is often used in the fields of seawater desalination and water resource pollution treatment,and has broad application prospects in these fields.The electrode is an important part of the CDI module,and the performance of the electrode can directly determine the removal effect of the electrosorption device on the target ions.In this study,rice husks were used as raw materials,and rice husks were precarbonized at 300 °C at low temperature,and then rice husk charcoal was impregnated and modified with different concentrations of zinc acetate.Finally,zinc-loaded modified rice husk biochar was prepared by secondary high-temperature carbonization,the rice husk biochars prepared before and after modification were named RHC and MRHC,respectively.The physical and chemical properties of RHC and MRHC were characterized by means of SEM,BET,and XRD.Then RHC and MRHC were made into electrodes,and their electrochemical properties were tested by cyclic voltammetry,AC impedance method,and constant current charge-discharge method.After a series of characterization and analysis,MRHC-0.3(modified biochar when the concentration of zinc acetate is 0.3 mol/L)has the best comprehensive performance.This material was applied to the capacitive deionization experiment to evaluate the electrode’s electrosorption performance in a simulated desalination experiment.The experimental results are as follows:(1)Through SEM,it can be seen that the surface of rice husk carbon modified by zinc acetate is rough,with well-developed pores and white particles are distributed.XRD shows that the white particles loaded on the surface are oxides containing zinc.Zinc acetate impregnation modification can make rice husk charcoal form more porous structure,increase specific surface area and increase mesoporosity.Due to the large specific surface area and more mesopores,this can lead to higher specific capacity and superior rate performance of MRHC electrodes than RHC electrodes.(2)Compared with the unmodified rice husk biochar,the specific capacitance of the modified biochar was significantly increased,the electrical resistance was significantly reduced,and the cycle performance and rate performance were improved.When the concentration of zinc acetate was 0.3 mol/L,MRHC-0.3 electrode is at 0.5 A/g,the specific capacitance reaches 191.94 F/g.After charging and discharging 2000 times at 2 A/g,its capacitance retention rate is 92.16%,which is higher than that of the unmodified biochar electrode(75.81%),good cycle stability.(3)The optimal operating parameters of the capacitive deionization experiment were determined by the single-factor method,and the results showed that the optimal operating voltage was 1.5 V,the pole plate spacing was 2 mm,and the inlet water flow rate was 20 m L/min.At the voltage of 1.5 V,the pole plate spacing was 2mm,and the inlet water flow rate was 20 m L/min,the Na Cl solution with an initial concentration of 400 mg/L was configured,and the initial conductivity of the solution was 795 μs/ cm,when the adsorption equilibrium was reached,the adsorption capacity and removal rate of the electrode were 9.36 mg/g and 46.79%,respectively.The electrode was desorbed by short connection desorption with a desorption time of 12 min.After eight successive adsorption-desorption processes,the electrode regeneration rate was 98.99%,which has a strong cyclic regeneration capability.(4)The electrosorption process of Na Cl in salt solution by rice husk charcoal electrode MRHC-0.3 at different working voltages and different initial concentrations was more consistent with the quasi-first-order kinetic equation.The adsorption capacity and adsorption rate of the electrode were effectively enhanced with the increase of the working voltage and initial concentration.The adsorption thermodynamics study showed that the electrode’s electrosorption process of Na Cl in salt solution fit the Freundlich adsorption isotherm model more closely,and since n was between 2 and 10,it indicated that the electrode’s adsorption process of NaCl was easier to carry out.