A hierarchical porous carbon membrane from polyacrylonitrile/polyvinylpyrrolidone blending membranes: Preparation,characterization and electrochemical capacitive performance

Novel hierarchical porous carbon membranes were fabricated through a simple carbonization procedure of well-defined blending polymer membrane precursors containing the source of carbon polyacrylonitrile (PAN) and an additive of polyvinylpyrrolidone (PVP), which was prepared using phase inversion method. The as-fabricated materials were further used as the active electrode materials for supercapacitors. The effects of PVP concentration in the casting solution on structure feature and electrochemical capacitive performance of the as-prepared carbon membranes were also studied in detail. As the electrode material for supercapacitor, a high specific capacitance of 278.0 F/g could be attained at a current of 5 mA/cm² and about 92.90% capacity retention could be maintained after 2000 charge/discharge cycles in 2 mol/L KOH solution with a PVP concentration of 0.3 wt% in the casting solution. The facile hierarchical pore structure preparation method and the good electrochemical capacitive performance make the prepared carbon membrane particularly promising for use in supercapacitor.     

壳聚糖基多孔碳材料的制备及其超级电容性能

以胶态SiO₂纳米粒子为模板,壳聚糖为碳源,ZnCl2为活化剂,制备了具有不同比表面积和孔体积的氮掺杂介孔碳。采用多种表征手段对碳材料的微观形貌、比表面积和孔道结构进行了表征,探究了壳聚糖与SiO₂纳米粒子的比例以及ZnCl2活化剂对碳材料孔体积和比表面积的影响。结果表明,在未使用活化剂时碳材料(CSi-1.75)的孔体积高达4.53 cm³·g^-1,但其比表面积最小(729 m²·g^-1);使用ZnCl₂作为活化剂制备的碳材料(CSi-1.75-Zn)比表面积为1032 m²·g^-1,但其孔体积下降到1.99 cm³·g^-1,且具有最多的吡啶氮和吡咯氮。在以6.0 mol·L^-1 KOH为电解液的三电极体系中,当电流密度为0.5 A·g^-1时,CSi-1.75-Zn的比电容为344 F·g^-1,而CSi-1.75的比电容仅为255 F·g^-1。这表明碳材料的比表面积对超级电容性能影响最大,而孔体积影响较小。电容贡献分析结果表明,相对于CSi-1.75,CSi-1.75-Zn的双电层电容和赝电容都得到了提高,这表明更大的比表面积和更多的吡啶氮和吡咯氮有利于提高碳材料的超级电容性能。     

壳聚糖基多孔碳材料的制备及其超级电容性能

以胶态SiO₂纳米粒子为模板,壳聚糖为碳源,ZnCl₂为活化剂,制备了具有不同比表面积和孔体积的氮掺杂介孔碳。采用多种表征手段对碳材料的微观形貌、比表面积和孔道结构进行了表征,探究了壳聚糖与SiO₂纳米粒子的比例以及ZnCl₂活化剂对碳材料孔体积和比表面积的影响。结果表明,在未使用活化剂时碳材料(CSi-1.75)的孔体积高达4.53 cm³·g^-1,但其比表面积最小(729 m²·g^-1);使用ZnCl₂作为活化剂制备的碳材料(CSi-1.75-Zn)比表面积为1 032 m²·g^-1,但其孔体积下降到1.99 cm³·g^-1,且具有最多的吡啶氮和吡咯氮。在以6.0 mol·L^-1KOH为电解液的三电极体系中,当电流密度为0.5 A·g^-1时,CSi-1.75...     

Preparation of a magnetic porous carbon with hierarchical structures from waste biomass for the extraction of some carbamates

In this study, corn stalk was used to synthesize a magnetic adsorbent by pyrolysis together with KHCO₃ as the chemical activator and iron(III) salt as the magnetic reagent. The characterization by scanning electron microscopy, transmission electron microscopy and N₂ adsorption–desorption analysis showed that the magnetic carbon adsorbent had a structure of hierarchical pores with a high specific surface area. To evaluate its adsorption performance, the adsorbent was used for the extraction of carbamates pesticides (propoxur, isoprocarb and fenobucarb) from water and zucchini samples before high‐performance liquid chromatography analysis. The result showed that the adsorbent had a good adsorption capability for the analytes. Under the optimized conditions, a good linearity for the analytes existed in the range of 0.1–100.0 ng/mL for water samples and 0.5–100.0 ng/g for zucchini samples with the correlation coefficients of 0.9992–0.9998. The limits of detection for the analytes at a signal to noise ratio of 3 were 0.03 ng/mL for water samples and 0.20–0.50 ng/g for zucchini samples.     

硼、氮共掺杂多孔碳的制备及其超电容性能

分别以含氮菲咯啉、四硼酸钾和醋酸锌为碳源、活化剂和模板,制备了B、N共掺杂多孔碳(BN-PC),并探究模板质量对BN-PC结构和储电性能的影响。当醋酸锌质量为5g时,所得BN-PC₅中B、N杂原子含量分别为 20.21%、18.29%。电化学测试结果表明,以6 mol·L^-1 KOH为电解液,BN-PC₅电极展现出高的比电容(在0.05 A·g^-1电流密度下为255 F·g^-1)、优异的倍率性能(在20A·g^-1电流密度下为188F·g^-1)和卓越的循环稳定性(在5 A·g^-1的电流密度下循环10 000次比电容保持率为97%)。以3 mol·L^-1 ZnSO₄为电解液,在平均功率密度为56W·kg^-1时,BN-PC₅电容器的能量密度可达27Wh·kg^-1。     

硼、氮共掺杂多孔碳的制备及其超电容性能

分别以含氮菲咯啉、四硼酸钾和醋酸锌为碳源、活化剂和模板,制备了B、N共掺杂多孔碳(BN-PC),并探究模板质量对BN-PC结构和储电性能的影响。当醋酸锌质量为5 g时,所得BN-PC₅中B、N杂原子含量分别为20.21%、18.29%。电化学测试结果表明,以6 mol·L^-1KOH为电解液,BN-PC₅电极展现出高的比电容(在0.05 A·g^-1电流密度下为255 F·g^-1)、优异的倍率性能(在20 A·g^-1电流密度下为188 F·g^-1)和卓越的循环稳定性(在5 A·g^-1的电流密度下循环10 000次比电容保持率为97%)。以3mol·L^-1ZnSO₄为电解液,在平均功率密度为56 W·kg^-1时,BN-PC₅电容器的能量密度可达27 Wh·kg^-1。     

金属改性与碳包覆的多孔硅微球复合材料的制备及其电化学储锂性能

以工业级SiAl合金微球为前驱物,采用多步刻蚀-热处理策略,制备了金属(Sb-Sn)改性与碳包覆的多孔硅微球复合材料(pSi/Sb-Sn@C)。pSi/Sb-Sn@C具有以 Sb-Sn改性的多孔硅微球(pSi/Sb-Sn)为核、碳包覆层为壳的三维结构。碳外壳可以提高多孔硅微球的电子导电性和机械稳定性,有利于获得稳定的固体电解质界面(SEI)膜;而三维多孔核可以促进锂离子的扩散,增加嵌/脱锂活性位,缓冲嵌锂过程中的体积膨胀。此外,活性金属(Sb-Sn)的引入能够提高复合材料的导电性,并可以贡献一定的储锂容量。由于其特殊的组成和独特的微观结构,pSi/Sb-Sn@C复合材料在1.0 A·g^-1电流密度下充放电300次后的可逆容量为1 247.4 mAh·g^-1,显示了良好的高速率储锂性能和优异的电化学嵌/脱锂循环稳定性。     

氢氧化镁-硼酸锌复合阻燃剂辅助制备产率高和电容性能优异的煤焦油沥青基多孔碳

以煤焦油沥青为前驱体,氢氧化镁-硼酸锌复合阻燃剂为助剂,直接在空气条件下高温碳化制备了煤沥青基多孔碳,并探究其电化学性能。得益于阻燃剂的阻燃协同其活化、掺杂功能化作用,得到了高产率(55.1%)、多原子(N、B、O)掺杂且具有分级多孔结构的多孔碳。将其作为超级电容器电极材料,在三电极体系中0.5 A·g^-1电流密度下比电容可达344 F·g^-1。此外,以制备的多孔碳和壳聚糖基氨基酸质子盐凝胶电解质组装的柔性对称电容器具有29.3 Wh·kg^-1的高能量密度,在50 000次循环后电容保持率为96.9%,且在-25~75℃温度区间内可正常工作,显示出宽的温度使用范围。     

氢氧化镁-硼酸锌复合阻燃剂辅助制备产率高和电容性能优异的煤焦油沥青基多孔碳

以煤焦油沥青为前驱体,氢氧化镁-硼酸锌复合阻燃剂为助剂,直接在空气条件下高温碳化制备了煤沥青基多孔碳,并探究其电化学性能。得益于阻燃剂的阻燃作用协同其活化、掺杂功能化作用,得到了高产率(55.1%)、多原子(N、B、O)掺杂且具有分级多孔结构的多孔碳。将其作为超级电容器电极材料,在三电极体系中0.5 A·g^-1电流密度下比电容可达344 F·g^-1。此外,以制备的多孔碳和壳聚糖基氨基酸质子盐凝胶电解质组装的柔性对称电容器具有29.3 Wh·kg^-1的高能量密度,在50 000次循环后电容保持率为96.9%,且在-25~75℃温度区间内可正常工作,显示出宽的温度使用范围。     

A facile synthesis of hierarchical porous carbon derived from renewable lignin for high-performance supercapacitor

In this work, we proposed a facile one-pot pyrolysis method to conveniently manufacture lignin-derived carbon materials with graded porous construction for use in supercapacitors. The renewable lignin was selected as precursor, while the potassium citrate was used as a pore-forming agent. The properties of the prepared lignin-derived carbon (LAC) and the performance for supercapacitor application were thoroughly evaluated. The LAC at optimal preparation conditions shows a layered porous structure with a large specific surface area of 3174 cm² g⁻¹ and pore volume of 2.796 cm³ g⁻¹, where the specific capacitance reach to 241 F g⁻¹ at 1 A g⁻¹ scan rate in 6 M KOH electrolyte solution. At the same time, the specific capacitance remains at 220 F g⁻¹ even at an excessive scan velocity of 20 A g⁻¹, while the capacitance retention is still close to 91.3%. The capacitance retention rate is stable above 95% after 10,000 charge/discharge cycles, which shows the desired long-time stability. All these results demonstrate the outstanding properties of the new prepared LAC material and the considerable application potential in the field of electrical energy storage.     

多孔雪花状氧化锌分级纳米结构的制备、表征及其光催化性能研究

在H2O和乙二醇(EG)构成的二元体系中,通过Zn AC2与NH4F和H2O的水热反应制备了六角雪花状Zn OHF。Zn OHF在空气中退火,制备出了由单晶Zn O纳米片构建的多孔六角雪花状Zn O。用X射线衍射(XRD),扫描电子显微镜(SEM),透射电子显微镜(TEM)及其热重等多种手段对产物进行结构表征,并提出了可能的化学反应。以甲基橙和酸性大红为例,研究了其光催化性能,结果表明,多孔雪花状Zn O是一种有效的光催化剂。     

Fabrication of carbon fibers with nanoporous morphologies from electrospun polyacrylonitrile/poly(L‐lactide) blends

Porous carbon nanofibers were prepared through electrospinning a blend solution of polyacrylonitrile and poly(L ‐lactide), followed by carbonization at different temperatures and in different atmospheres. Structural features of these porous carbon nanofibers were characterized using scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, X‐ray powder diffraction, and Raman spectroscopy. Surface area and pore structure were evaluated using the nitrogen adsorption technique. It was found that carbon fibers prepared by this scalable and relatively economical method exhibited a porous surface morphology with high specific surface area and large pore volume. The fiber diameter, surface area, pore volume, bulky crystalline structure, and surface crystalline structure of these carbon nanofibers showed a strong dependence on the polymer precursor composition and carbonization condition. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 493–503, 2009     

Trimodel hierarchical yolk-shell porous materials TS-1@mesocarbon:Synthesis and catalytic application

Trimodal hierarchical yolk-shell materials consisting of TS-1 core and mesoporous carbon shell(YS-TS-1@MC) was successfully synthesized by using TS-1@mesosilica as hard template,sucrose as carbon source and organic base tetrapropylammonium hydroxide(TPAOH) as silica etching agent.The resultant YS-TS-1@MC contains the micropores(0.51 nm) in TS-1 core,the mesopores(2.9 nm) in carbon shell as well as a void or a stack pore between TS-1 fragcments(TS-1 intercrystal mesopores,～18.4 nm).Under the rigorous etching conditions,the crystalline structure of TS-1 core was well retained.The YS-TS-1@MC served as a good support for palladium nano-particles(Pd NPs) or Rh(OH)x species,giving rise to efficient bifunctional catalysts for the tandem reactions including one-pot synthesis of propylene oxide or amides.     

Leaching of PVP from polyacrylonitrile/PVP blending membranes: A comparative study of asymmetric and dense membranes

Poly(N‐vinyl‐2‐pyrrolidone) (PVP) has been often used as an additive to improve the structure and performances of asymmetric membrane. In this work, we examined the leaching of PVP from polyacrylonitrile/PVP asymmetric membranes regarding the effect of leaching time, PVP content, and the molecular weight of PVP. Also, comparative studies of dense membranes were performed. It was found that the water contact angle on the dense membrane surface is very low compared with that on the asymmetric membrane surface. Results from X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy‐attenuated total reflection (FTIR‐ATR) showed that more amount of PVP exists at the surface layer of the dense membrane than at the asymmetric one. If the dense membrane was immersed into water for several hours and then dried in the air, the water contact angle increases and closes to that on the asymmetric membrane surface. Although leaching time was extended from 2 h to 15 days, PVP leaches out little from the asymmetric membrane. The leaching of PVP mainly occurs during the phase‐inversion process. Furthermore, the surface features were examined by atomic force microscopy and field emission scanning electron microscopy, respectively. In comparison with PVP K30, more PVP K90 remains in the asymmetric membrane based on the FTIR‐ATR spectra. However, it can be concluded from the results of XPS that at the most outer surface of the asymmetric membrane (e.g., in depth about 1～2 nm), the residual PVP K90 is almost the same with PVP K30. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1490–1498, 2006     

Preparation and electrochemical performance of activated carbon thin films with polyethylene oxide-salt addition for electrochemical capacitor applications

The effect of polymer–salt addition in the activated carbon electrode for electric double-layer capacitor (EDLC) has been investigated. A series of composite thin film electrode consisting of activated carbon, carbon black, polytetrafluoroethylene and polymer–salt complex (polyethyleneoxide–LiClO₄) with an appropriate weight ratio were prepared and examined their performance for EDLCs using 1 mol L⁻¹ LiClO₄ in ethylene carbonate:diethylcarbonate electrolyte solution. The electrochemical capacitance performances of these electrodes with different compositions were characterized by cyclic voltammetry, galvanostatic charge–discharge cycling, and AC impedance measurements. By comparison, the best results were obtained with a composite electrode rich in polymer–salt additive (132 F g⁻¹ at 100 mA g⁻¹ of galvanostatic experiment). In general, the polymer–salt-containing electrode had shown improved performance over activated carbon electrodes without polymer–salt at high current density.     

兼具高孔隙率和梯度孔隙结构的多孔钯块材的制备、表征及其电化学性能研究

钯材料广泛用于氢同位素储存和分离、催化和传感等领域.传统的负载钯催化材料具有优异的乙醇和甲醇等电化学催化氧化性能.除此之外,负载钯催化材料还具有优异的甲烷催化燃烧性能.然而,很多研究显示负载钯催化材料存在很多不足,例如在工程应用过程中不稳定,纳米颗粒会发生聚集和长大,进而引起材料性能急剧下降等.不同于钯片、海绵钯粉末和负载钯催化材料,多孔钯具有三维连通的孔隙结构,可避免团聚现象的发生.同时,多孔钯还具有一些特殊的物理化学性能.研究表明,梯度孔隙结构是一种高效的电化学催化结构.因而近年来很多研究者都致力于探索具有高孔隙率和梯度孔隙结构多孔钯块材的制备方法.已有的研究包括造孔剂法和模板法等,但上述方法制得的多孔钯块材均存在比表面积低或难以获得块体材料缺点.我们研究组发展了一种制备兼具高孔隙率和梯度孔隙结构的多孔钯块材的新方法.即通过以一定粒度的NaCl颗粒作为造孔剂放电等离子烧结制备PdAl合金复合块材,然后通过去离子水溶解获得多孔PdAl合金,最后经过在盐酸溶液中去合金化得到具有数十微米的宏观大孔和约10纳米的纳米孔等梯度孔隙结构的多孔钯块材.当造孔剂添加量为20 vol.%,制得了孔隙率高达88%且完整的多孔钯块材.对该多孔钯块材的力学性能进行了测试,其压缩强度为0.5 MPa.对该块材进行氮吸附测试,测试结果显示其比表面积达到54 m2/g.我们进一步对该多孔钯块材的乙醇电化学催化氧化性能进行了研究.对不同扫描速度下多孔钯块材在KOH(1 mol/L)+乙醇(0.8 mol/L)溶液中电催化活性进行分析.随着扫描速率从10 mV/s提高到50 mV/s,正扫描峰电流密度也逐渐提高,且峰电位向正电位方向移动.对峰电流密度和扫描速率的平方根进行拟合,发现它们之间存在明显的线性关系,表明该电催化氧化行为是一个受扩散控制的过程.随着溶液中乙醇浓度不断增加,正扫描方向乙醇氧化峰的峰电流呈现出先增大后减小的趋势.这是因为乙醇基和羟基在钯表面的竞争性吸附造成的.当乙醇浓度较高时,乙醇基会占据钯表面大量的活性位,从而阻碍和抑制羟基的吸附.此时,羟基在钯表面的吸附成为电氧化反应的控制因素.因此,只有选择合适的乙醇浓度,才能更好地发挥材料的电催化性能.当乙醇浓度为2 mol/L时,峰电流最大,达到120 mA/cm2,表明多孔钯块材具有优异的电催化性能,这与该材料的梯度孔隙结构、高比表面积和高孔隙率密切相关.进一步对多孔钯块材的催化稳定性进行研究.该多孔钯块材显示出了优异的催化稳定性,当经过50次循环后,乙醇氧化峰的峰电流仅下降到~110 mA/cm2.     

Chitosan/polyvinyl alcohol/amino functionalized multiwalled carbon nanotube pervaporation membranes: Synthesis,characterization, and performance

In the present study, novel biodegradable nanocomposite membranes were prepared by adding the amino functionalized multiwalled carbon nanotube (NH₂‐MWCNT) to the chitosan/polyvinyl alcohol blend polymers, and the obtained membranes were used for dehydration of isopropyl alcohol through pervaporation process. For this purpose, the membranes were prepared with chitosan/polyvinyl alcohol ratio of 4:1 on the basis of “solution casting” method and then crosslinked using glutaraldehyde, after addition of different amounts of NH₂‐MWCNT. The prepared membranes were characterized using scanning electron microscopy, contact angle, mechanical strength, degree of swelling (DS), and biodegradability. Also, the ability of the prepared membranes in dehydration of isopropyl alcohol was determined using pervaporation experiments. Results indicated that contact angle, mechanical resistance, separation factor (α), and pervaporation separation index were increased with the addition of NH₂‐MWCNT up to 10 wt% (relative to the total amount of polymer) and then decreased in the higher presence of nanotubes (15 wt%). Furthermore, the DS and permeate flux were first decreased and then increased for the same mentioned amounts of additive. In this study, optimized membrane was obtained by the addition of 10 wt% NH₂‐MWCNT. This membrane showed the maximum α (99.5), pervaporation separation index parameter (78.29 kg m⁻² h⁻¹), biodegradability, and mechanical stability as well as minimum DS.     

Covalent immobilization of single-walled carbon nanotubes and single-stranded deoxyribonucleic acid nanocomposites on glassy carbon electrode: Preparation, characterization, and applications

Single-stranded deoxyribonucleic acid (ssDNA)-wrapped single-walled carbon nanotubes (SWNTs) were modified on the surface of glassy carbon electrode (GCE) by covalent modification technique. Field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectrum (XPS), electrochemical impedance spectroscopy (EIS), and cyclic voltammetric (CV) were used to characterize the properties of this modified electrode. The results showed that SWNTs-ssDNA composites were successfully immobilized onto the surface of GCE. Moreover, this modified electrode exhibited high stability, largely active areas, and efficiently electrocatalytic activities. It had been used for the analysis of various biomolecules, such as dopamine (DA), uric acid (UA), and ascorbic acid (AA), and the results were satisfactory.     

Hierarchically porous carbon membranes derived from PAN and their selective adsorption of organic dyes

Porous carbon membranes were favorably fabricated through the pyrolysis of polyacrylonitrile(PAN) precursors, which were prepared with a template-free technique-thermally induced phase separation. These carbon membranes possess hierarchical pores, including cellular macropores across the whole membranes and much small pores in the matrix as well as on the pore walls. Nitrogen adsorption indicates micropores(1.47 and 1.84 nm) and mesopores(2.21 nm) exist inside the carbon membranes, resulting in their specific surface area as large as 1062 m2/g. The carbon membranes were used to adsorb organic dyes(methyl orange, Congo red, and rhodamine B) from aqueous solutions based on their advantages of hierarchical pore structures and large specific surface area. It is particularly noteworthy that the membranes present a selective adsorption towards methyl orange, whose molecular size(1.2 nm) is smaller than those of Congo red(2.3 nm) and rhodamine B(1.8 nm). This attractive result can be attributed to the steric structure matching between the molecular size and the pore size, rather than electrostatic attraction. Furthermore, the used carbon membranes can be easily regenerated by hydrochloric acid, and their recovery adsorption ratio maintains above 90% even in the third cycle. This work may provide a new route for carbon-based adsorbents with hierarchical pores via a template-free approach, which could be promisingly applied to selectively remove dye contaminants in aqueous effluents.     

A universal model for nanoporous carbon supercapacitors applicable to diverse pore regimes, carbon materials, and electrolytes

Supercapacitors, commonly called electric double-layer capacitors (EDLCs), are emerging as a novel type of energy-storage device with the potential to substitute batteries in applications that require high power densities. In response to the latest experimental breakthrough in nanoporous carbon supercapacitors, we propose a heuristic theoretical model that takes pore curvature into account as a replacement for the EDLC model, which is based on a traditional parallel-plate capacitor. When the pore size is in the mesopore regime (2-50 nm), counterions enter mesoporous carbon materials and approach the pore wall to form an electric double-cylinder capacitor (EDCC); in the micropore regime (<2 nm), solvated/desolvated counterions line up along the pore axis to form an electric wire-in-cylinder capacitor (EWCC). In the macropore regime (>50 nm) at which pores are large enough so that pore curvature is no longer significant, the EDCC model can be reduced naturally to the EDLC model. We present density functional theory calculations and detailed analyses of available experimental data in various pore regimes, which show the significant effects of pore curvature on the supercapacitor properties of nanoporous carbon materials. It is shown that the EDCC/EWCC model is universal for carbon supercapacitors with diverse carbon materials, including activated carbon materials, template carbon materials, and novel carbide-derived carbon materials, and with diverse electrolytes, including organic electrolytes, such as tetraethylammonium tetrafluoroborate (TEABF(4)) and tetraethylammonium methylsulfonate (TEAMS) in acetonitrile, aqueous H(2)SO(4) and KOH electrolytes, and even an ionic liquid electrolyte, such as 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI). The EDCC/EWCC model allows the supercapacitor properties to be correlated with pore size, specific surface area, Debye length, electrolyte concentration and dielectric constant, and solute ion size It may lend support for the systematic optimization of the properties of carbon supercapacitors through experiments. On the basis of the insight obtained from the new model, we also discuss the effects of the kinetic solvation/desolvation process, multimodal (versus unimodal) pore size distribution, and exohedral (versus endohedral) capacitors on the electrochemical properties of supercapacitors.