Preparation And Application Of Activated Carbon From Heavy Metal Hyperaccumulator Perilla Frutescens

Perilla frutescens is an annual herb of the genus Perilla in the Lamiaceae family,which has strong adaptability and widely distributed throughout our country.As a kind of spice and medicinal crops,perilla frutescens has a long history of cultivation in China.Previous studies showed that perilla frutescens had strong tolerance and enrichment ability to cadmium.In this study,activated carbons were prepared from perilla frutescens by phosphoric acid activation and potassium hydroxide activation.The preparation technology was optimized according to different uses of activated carbon.Samples were characterized by N2 adsorption-desporption isotherms,Fourier transform infrared spectroscopy and scanning electron microscopy.The application of activated carbon in adsorption of heavy metals form the wastewater,supercapacitor electrode materials,and modified electrodes had been studied.The main results were as follows:(1)A series of activated carbons prepared from perilla frutescens by using phosphoric acid activation were studied in order to show the influence on adsorption performance of the carbons of main activation parameters such as concentration of phosphoric acid,impregnation ratio,activation temperature and activation time.In order to obtain the optimum preparation conditions,orthogonal experiments were carried out.Results showed that the optimum conditions were phosphoric acid concentration of 60%,impregnation ratio of 200%,activation temperature of 400℃ and activation time of 60 min.Under these conditions,the yield was 40%,the iodine adsorption value and the methylene blue adsorption value of activated carbon were 910 mg·g-1 and 202.5 mg·g-1,respectively.The specific surface area was 1101.26 m2·g-1,the total pore volume was 0.89 m3·g-1 and the average pore size was 3.23 nm.The surface of activated carbon was uneven and honeycomb,containing a variety of oxygen functional groups.(2)The activated carbons prepared by phosphoric acid activation under the optimal conditions were modified to use for the adsorption of lead and cadmium ions in wastewater.Results showed that the adsorption of lead and cadmium ions on activated carbon tended to balance at about 30 min,the adsorption capacity increased with the increased of pH value and initial concentration but decreased with the increased of activated carbon dosage.The adsorption process was well fitted to the pseudosecond order model.Under the optimal conditions,the adsorption efficiency of lead ion on activated carbon was better than that of cadmium ion,and the equilibrium adsorption capacity of lead and cadmium ions was 141.805 mg·g-1 and 46.083 mg·g-1,respectively.Furthermore,the effect of magnetic modification on activated carbon was good,and it can be separated quickly and completely from the solution by external magnetic field.(3)A high specific surface area activated carbons used as electrode materials of supercapacitor were prepared from perilla frutescens by potassium hydroxide activation.The effects of alkali-carbon ration,activation temperature and activation time on the capacitive performance of activated carbon were investigated.Results showed that,the specific surface area of activated carbon was 3094.08 m2·g-1,the total pore volume was 1.65 cm3·g-1 and the specific capacitance of activated carbon electrode was 255 F·g-1 under the conditions that the ratio of alkali to carbon was 4:1,the activation temperature was 800℃,and the activation time was 60 min.In addition,the electrode was charged and discharged 5000 times at a current density of 5 A·g-1,and the capacitance retention rate was 90%,suggesting that the electrode had good cycling stability.(4)The high surface area activated carbon modified electrode was used for the determination of hydroquinone and catechol in water,and the detection conditions were optimized.The results showed that the optimium detection conditions were as follows:the dosage of activated carbon dispersion was 6.0 μL,the scanning speed was 100 mV·s-1,and the pH value of the supporting electrolyte(0.2 mol·L-1 Na2HPO4-NaH2PO4 buffer solution)was 7.0.Under the optimal conditions,there was a good linear relationship between the oxidation peak current and the concentration of hydroquinone and catechol in the range of 1.0×10-6～2×10-4 mol·L-1;and 1.0×10-6～1.5×10-4 mol·L-1,and the correlations were 0.9907 and 0.9908,the limits were 2×10-7 mol·L-1 and 3×10-7mol·L-1,respectively.The modified electrode showed good repeatability,stability and antiinterference.The proposed method was used for the detection of two kinds of hydroquinone isomers in the actual water samples meet the requirements of analysis and determination.