Effects of CO2 activation on electrochemical performance of microporous carbons derived from poly(vinylidene fluoride)
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The microvoid activated carbon with large specific surface area was prepared from reed pulping black liquor through chemical activation with K2CO3 as activator. The effect of activation temperature on the specific surface area, micropore volume and mesopore volume of the prepared activated carbon BET was closely investigated. The optimum temperature for preparing large specific surface area activated carbon is 800℃. The BET surface area and pore volume of the carbon activated at 800℃ were 1401 m2/g and 0.79 ml/g respectively. XRD shows that silicon crystals appeared in the activated carbon. The activated carbon had a good adsorption of heavy metal C(rVI)at pH=7 and the maximum adsorptive capacity could reach 54.23 mg/g and Langmuir model was better for describing the adsorption process than Freundlich model.
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The effect of pressure, temperature, microporous size of activated carbon on adsorption process of isopro-pyl alcohol on activated carbon was studied by Grand Canonical Monte Carlo Simulation. The result shows that the adsorption process can be described reliably by the activated carbon microporous model. When the pressure is 1kPa, the adsorption quantity of activated carbon with microporous size of 1. 7nm is higher. While activated carbon with microporous size of 2. 0nm has higher adsorption quantity when the pressure is 2-4kPa. At the pressure of 4 -10kPa, the adsorption quantity of activated carbon with microporous size of 2. 5nm is higher. The adsorption quantity of the system which jaws width of activity carbon is 2. 5nm is higher. The best recovery temperature of iso-propyl alcohol desorbed from activated carbon is 140℃.
Isopropyl alcohol
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A methodology for determining the micropore, mesopore, and external surface areas of hierarchical microporous/mesoporous materials from N2 adsorption isotherms at 77 K is described. For FAU-Y zeolites, the microporous surface area calculated using the Rouquerol criterion and the Brunauer–Emmett–Teller (BET) equation is in accord with the geometrical surface determined by the chord length distribution method. Therefore, BET surface area (SBET) is the well representative of micropore surface areas of microporous materials and of total surface area of microporous/mesoporous materials. Mechanical mixtures of mesoporous MCM-41 and microporous FAU-Y powders of known surface areas were used to calculate the respective surface areas by weighted linear combination and the results were compared to the values obtained by the t-plot method. The first slope of the t-plot determined the mesopore and external surface areas (Smes+ext). The linear fit of the first slope is in general in the range 0.01 < p/p0 < 0.17 and contains the volumes and relative pressures at which all micropores are filled (p/p0 > 0.10). Overestimation of Smes+ext values was evident and appropriate corrections were provided. External surface areas (Sext) were obtained from the second slope of the t-plot, without noting an overestimation of Sext, thus allowing the determination of mesopore surface areas (Smes) by difference. Micropore surface areas were calculated by subtracting Smes+ext from the total surface area, SBET. As an example, this methodology was applied to characterize a family of hierarchical microporous/mesoporous FAU-Y (FAUmes) synthesized from H-FAU-Y (H-Y, Si/Al = 15) using C18TAB as the surfactant and different NaOH/Si ratios (0.05 < NaOH/Si < 0.25). By increasing the NaOH/Si ratio in the synthesis of FAUmes, it was shown that as the micropore surface area decreases, the mesopore surface area increases, whereas the micropore and mesopore surface area remains constant. This methodology allows accurate characterization of the surface areas of microporous/mesoporous materials.
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Activated carbon electrode material for supercapacitor was prepared from polyvinylidene chloride(PVDC) as raw material by steam activation.The specific surface area and pore structure of the material were studied by N2 adsorption method.The electrochemical performance of the material in 6 mol/L KOH solution was analyzed by galvanostatic charge-discharge and cyclic voltammetry tests.The results showed that activated carbon material with high specific surface area(2 296 m2/g) and abundant mesopores(mesoporosity ratio was 42.7%) could be prepared by this method at 900 ℃.It was suitable for electrode material of supercapacitor.The activated carbon prepared at 880 ℃ and activated for 1 h had the specific capacitance of 177 F/g(50 mA/g) and good large current rate performance.
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Searching for good-natured feedstocks and understanding the texture property of porous carbon/specific capacitance relationships have long been highly desirable. Herein, hydrothermal and KOH were used to assist the synthesis of lignin-derived porous carbons (LPCs) with high specific surface area for supercapacitors. The as-synthesized LPC-150 and LPC-200 had a specific surface area of 3033.88 m2/g and 3178.36 m2/g, respectively, with a specific capacitance of 214.03 F/g and 201.69 F/g at 0.50 A/g. In the range from 2448 m2/g to 3178 m2/g, increasing the specific surface area again possesses no remarkable effect on the specific capacitance. Meanwhile, the specific surface area and the pore-wall thickness together determine the specific capacitance. When using a three-electrode configuration with a 6 mol/L KOH electrolyte, the volumetric surface area rather than the ultrahigh specific surface area can be employed as a general predictor of specific capacitance in the low current density ranging from 0.50 to 10.00 A/g.
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BET equation was used to calculate surface area of different powder solids,such as mesoporous Al_2O_3 and microporous zeolites,at different relative pressure(P/P_0).The results showed that when relative pressure is in the range of 0.01-0.10,surface area of microporous materials calculated is more reliable.For most microporous materials,BET surface area calculated at P/P_0=0.05-0.20 is less than that at P/P_0=0.01-0.10.For some hydrothermally-treated ZSM-5 samples,their isotherms have hysteresis loop at lower relative pressure;BET surface area calculated at P/P_0=0.05-0.20 is smaller that that calculated at P/P_0=0.01-0.10.The more microporous material in the catalysts,the larger the difference in BET surface area calculated at the two relative pressure ranges.For some pure zeolites,this difference can be up to 15%.
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Activated carbons are prepared from hemp stem with KOH as activating agent under different ratio of KOH to carbon conditions. The BET(Brunauer Emmett and Teller) specific surface area of the hemp stem-based activated carbons first increases and then decreases with the increasing ratio of KOH to carbon. The specific surface area, micropore surface area and volume of the activated carbons reach a maximum of 1589.27m 2 /g 1420.52m 2 /g, 89% of the total area, 0.751m 3 /g at the ratio of 4.5:1. The micropore size distribution shows the activated carbons contain a large number of ultramicropore and supermicropore.
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To quantitatively describe and analyze specific surface area and pore structure of graphite fibers,in this paper,nitrogen adsorption-desorption isotherms of graphite fibers were measured by low temperature nitrogen adsorption method at liquid nitrogen temperature and different pressures.It showed that graphite fibers are microporous material which contains a large number of microporous and a few of mesoporous;the BET specific surface area,total pore volume and average pore size of graphite fibers were 541.00m2/g,0.2436cm3/g and 1.8010nm,respectively,and the specific surface area,pore volume and pore diameter of its microporous were 535.53m2 / g,0.2331cm3/g and 0.9896nm,respectively;there is a narrow pore size distribution of graphite fibers,which are a large number of microporous about 1.4nm and a few of mesoporous about 2.0-7.7nm,and the microporous is the greatest contribution to the specific surface area and the pore volume.
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