Preparation,Structure And Properties Of Porous Carbons Derived From Chinese Herbal Residues

As the energy crisis and global warming problems become more and more serious,the developments of the energy storage devices with high energy density and the efficient CO₂capture technologies have become increasingly important.Meanwhile,millions of tons of Chinese herbal residues are generated annually,which brings a heavy burden to our ecosystem.To effectively reuse and recycle CHR（Chinese herbal residues）,CHR-derived porous carbons with ultra-high specific surface area were synthesized to construct symmetric EDLCs devices.Also,the obtained CHR-derived porous carbons were used to evaluate the performance of the CO₂ capture and dye removal.The main research work is as follows:（1）To investigate the relationship between the structure of different kinds of CHR precursors and the electrochemical performance of their obtained carbons and to find the ideal precursors,20 kinds of roots and rhizomes（Radix and Rhizoma）,12 kinds of leaves and flowers（Folium and Flos）and 6 kinds of fruits and seeds（Fructus and Semen）herbal residues were directly carbonized to synthesize CHR-derived carbons.（2）To improve the textural parameters and electrochemical performance of the CHR derived carbons,the effects of different KOH activation conditions including activation times,activation temperatures and activator ratios were studied using Astragali Radix as the precursor.The relationship between pore structure and electrochemical performance was also discussed.In addition,other 7 kinds of roots and rhizomes residues derived porous carbons with ultra-high specific surface area(>3000 m² g^-1)were successfully synthesized under the optimal activation conditions.Dioscoreae Hypoglaucae Rhizoma derived porous carbon（DHRPC）electrode exhibited a specific capacitance of 291.6 F g^-1(1 A g^-1 current density)in 6 M KOH electrolyte.（3）To further verify the effects of surface chemistry and pore structure on electrochemical performance,SMPC（Salviae Miltiorrhizae Radix Et Rhizoma derived porous carbon）,ARPC（Astragali Radix derived porous carbon）and DHRPC（Dioscoreae Hypoglaucae Rhizoma derived porous carbon）were further characterized using different types of methods.In order to investigate the feasibility for supercapacitor devices,the SMPC,ARPC and DHRPC electrodes were further symmetrically assembled in CR2032-type coin cells.In 6 M KOH electrolyte and1 M H₂SO₄,the energy densities of CHRPC-based symmetric supercapacitors were higher than that of the commercial YP-80F device.The energy density of SMPC-based symmetric supercapacitor was calculated to be 13.0 Wh kg^-1 at the power density of 705 W kg^-1in 1 M Na₂SO₄ electrolyte.And even when the power density increased to 16711 W kg^-1,the cell still remained the energy density up to 10.7 Wh kg^-1,which was much higher than that of the commercial YP-80F device(～3.0 Wh kg^-1).（4）To evaluate the performance of CO₂ capture and separation,the static CO₂ uptake of different CHR-PCs samples was investigated in detail at 273 K and 298 K.At the pressure of1 bar,the DHRPC exhibited the highest CO₂ uptake among the samples(4.88 mmol g^-1 at 273 K and 2.52 mmol g^-1 at 298 K).The DHRPC showed CO₂ adsorption selectivity of 38.4 at 273 K,which is slightly better than those of SMPC and ARPC.The methyl orange adsorption capacity of DHRPC reached 498.4 mg g^-1 with the removal efficiency up to 99.7%,when the dosage of DHRPC was 0.6 g L^-1,indicating that the CHR derived porous carbons are also promising candidates for methyl orange adsorption.