Effects of ammonium dibasic phosphate pretreatment time on the structure and properties of PAN‐based activated carbon hollow fibers

Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate aqueous solution, then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of pretreatment time of PAN hollow fibers in ammonium dibasic phosphate aqueous solution on the microstructure, specific surface, pore‐size distribution, and adsorption properties of PAN‐based activated carbon hollow fibers (PAN‐ACHF) were studied in this work. After the activation process, the Brunaner–Emmett–Teller (BET) surface area of the PAN‐ACHF and surface area of mesopores in the PAN‐ACHF increases and reaches 513 m² g^?1 and 66 m² g^?1 respectively, when the dipping time of PAN hollow fibers in ammonium dibasic phosphate aqueous solution is 30 min. The adsorptions to creatinine and VB₁₂ of PAN‐ACHF are much high, reach 95% and 86% respectively, when dipping time is 30 min. The dominant pore sizes of mesopores in PAN‐ACHF range from 2 nm to 5 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2448–2453, 2006     

Effects of activation temperature on the properties and structure of PAN‐based activated carbon hollow fiber

Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate, then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of activation temperature of a precursor fiber on the microstructure, specific surface, pore‐size distribution, and adsorption properties of PAN‐based activated carbon hollow fibers (PAN‐ACHF) were studied in this work. After the activation process, the BET surface area of the PAN‐ACHF and surface area of mesopores in the PAN‐ACHF increased very remarkably and reached 1422 m² g^?1 and 1234 m² g^?1, respectively, when activation temperature is 1000°C. The adsorptions to creatinine and VB₁₂ of PAN‐ACHF were much high and reached 99 and 84% respectively. In PAN‐ACHF which went through the activation at 700°C and 800°C, the micropore filling mainly occurred at low relative pressures, multimolecular layer adsorption occurred with the increasing of relative pressure, and the filling and emptying of the mesopores by capillary condensation occurred at high relative pressures. But in PAN‐ACHF which went through the activation at 900°C, a mass of mesopores resulted in the large pore filling by capillary condensation. The dominant pore sizes of mesopores in PAN‐ACHF are from 2 nm to 5 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3778–3783, 2006     

Adsorption properties of polyacrylonitrile‐based activated carbon hollow fiber

In this work, polyacrylonitrile (PAN) hollow fibers are pretreated with ammonium dibasic phosphate and then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The adsorption properties of the resultant activated carbon hollow fibers (ACHF) prepared in different conditions were studied. The results show that the adsorption properties of ACHF change regularly with preparing conditions of ACHF. The different adsorption ratios to three adsorbates reflect the number of micropores and mesopores in PAN‐based ACHF. Pretreatment with phosphate can increase the number of mesopores. Proper oxidation temperature and time can increase the number of micropores and mesopores. When carbonization temperature is more than 900°C and carbonization time ranges from 50 to 90 min, the number of micropores and mesopores, especially mesopores, greatly increases. Compared with other treatments, activation treatment greatly increases the number of micropores and mesopores, and the dominant pore sizes of mesopores in PAN‐based ACHF are from 2 to 10 nm. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 602–607, 2004     

Effects of oxidation time on the structure and properties of polyacrylonitrile‐based activated carbon hollow fiber

Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate, then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of oxidation time of PAN hollow fiber precursor on the microstructure, specific surface, pore size distribution, and adsorption properties of PAN‐based activated carbon hollow fiber (PAN‐ACHF) were studied in this work. Both of specific surface area and adsorption ratio to VB₁₂ reach maximums when PAN hollow fibers are oxidized for 5 h in air. The adsorption ratios for creatinine are all higher than 90% over all oxidation time. After 5 h of oxidation, the number of pores on the surface obviously increases, and the pore size is uniform. After 7 h of oxidation, the number of macropores in PAN‐ACHF increases. The dominant pore sizes of mesopores in PAN‐ACHF range from 2 to 5 nm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Structure and properties of PAN‐based activated carbon hollow fibers: Effect of ammonium dibasic phosphate pretreatment

Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate aqueous solution, then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of pretreatment concentration of ammonium dibasic phosphate aqueous solution on the microstructure, specific surface, pore size distribution, and adsorption properties of PAN‐based activated carbon hollow fibers (PAN‐ACHF) were studied in this work. After the activation process, the Brunaner‐Emmett‐Teller (BET) surface area of the PAN‐ACHF and surface area of mesopores in the PAN‐ACHF increases and reaches 513 m²g^?1 and 66 m²g^?1 respectively when the concentration of ammonium dibasic phosphate aqueous solution is 4% (wt %). The adsorptions to creatinine are much high, reach more than 90% over all the concentration of ammonium dibasic phosphate aqueous solution. The adsorptions to VB₁₂ of PAN‐ACHF reach 86% when the concentration of ammonium dibasic phosphate aqueous solution is 4% (wt %). The dominant pore sizes of mesopores in PAN‐ACHF range from 2 to 5 nm. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effects of carbonization temperature on the properties and structure of PAN‐based activated carbon hollow fiber

Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate and then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of carbonization temperature of PAN hollow fiber precursor on the microstructure, specific surface, pore‐size distribution, and adsorption properties of PAN‐based carbon hollow fiber (PAN‐CHF) and PAN‐based activated carbon hollow fibers (PAN‐ACHF) were studied in this work. After the activation process, the surface area of the PAN‐ACHF increased very remarkably, reaching 900 m² g^?1 when carbonization is 1000°C, and the adsorption ratios to creatinine and VB₁₂ of ACHF were much higher than those of CHF, especially to VB₁₂. The different adsorption ratios to two adsorbates including creatinine and VB₁₂ reflect the number of micropores and mesopores in PAN‐ACHF. The dominant pore sizes of mesopores in PAN‐ACHF are from 2 to 5 nm. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2155–2160, 2005     

Effects of the oxidation temperature on the structure and properties of polyacrylonitrile‐based activated carbon hollow fiber

Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate, oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of the oxidation temperature of the PAN hollow fiber precursor on the microstructure, specific surface, pore size distribution, and adsorption properties of PAN‐based activated carbon hollow fiber (PAN‐ACHF) were studied. When PAN hollow fibers were oxidized at 270°C, because of drastic oxidation, chain scission occurred, and the number of pores within and on the surface of the resultant PAN‐ACHF increased, but the pores were just in the thinner region of the skin of PAN‐ACHF. The surface area of PAN‐ACHF reached a maximum when the oxidation temperature was 270°C. The adsorption ratios to creatinine were all higher than 90% at all oxidation temperatures, and the adsorption ratio to VB₁₂ reached a maximum (97%) at 230°C. The dominant pore sizes of the mesopores in PAN‐ACHF ranged from 2 to 5 nm. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 203–207, 2005     

Comparison about the structure and properties of PAN‐based activated carbon hollow fibers pretreated with different compounds containing phosphorus

Polyacrylonitrile (PAN) hollow fibers were pretreated with five different compounds containing phosphorus, including ammonium dibasic phosphate, ammonium dihydrogen phosphate, triammonium phosphate, phosphoric acid, and metaphosphoric acid, and then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of different compounds containing phosphorus as pretreating agents on the properties and structure of the resultant oxidized hollow fibers, carbon hollow fibers, and activated carbon hollow fibers are discussed. Comparing the Brunaner‐Emmett‐Teller (BET) surface area of PAN‐activated carbon hollow fibers (ACHF) pretreated with five different compounds, ammonium dibasic phosphate > triammonium phosphate > ammonium dihydrogen phosphate > phosphoric acid > metaphosphoric acid, and the surface area of mesopores in PAN‐ACHF pretreated with ammonium dibasic phosphate reaches maximum, 174 m² g^?1. The adsorption ratio to mesomolecule adsorbate, VB₁₂, of PAN‐ACHF pretreated with ammonium dibasic phosphate also reaches maximum, 97.7 wt %. Moreover, the dominant pore sizes of PAN‐ACHF range from 2 to 5 nm in diameter. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 294–300, 2005     

Influence of precursor structure on the properties of polyacrylonitrile-based activated carbon hollow fiber

Three types of precursors of polyacrylonitrile (PAN) hollow fibers were used to produce activated carbon hollow fibers (ACHF). These precursors are different in the structure and composition. Characterization were performed including tensile strength, modulus, x-ray diffraction, pore size distribution, and surface area measurement for the resulting ACHF. The results show that the ACHF produced from the precursor with larger crystal size and dense structure has higher mechanical properties, whereas the ACHF from the precursor with smaller crystal size and porous structure has larger surface area and broader pore size distribution. © 1996 John Wiley & Sons, Inc.     

预氧化时间对中空形态的聚丙烯腈基活性碳纤维性能的影响

聚丙烯腈(PAN)中空纤维在空气中250℃分别预氧化不同的时间,在N2气氛下于900℃进行碳化60min,随后用CO2气体在800℃活化40min,得到PAN基活性中空碳纤维(PAN-ACHF)。测定了PAN-ACHF对碘和亚甲基蓝的吸附量,考察了预氧化时间对PAN预氧化纤维的收缩率和芳构化指数以及对PAN-ACHF的活化收率和吸附性能的影响。     

Preparation and characterization of polymer‐based spherical activated carbons with tailored pore structure

A series of spherical activated carbons (SACs) with different pore structure were prepared from divinylbenzene‐based polymer through CO₂ activation. The effect of activation temperature and retention time on the yield and textural properties of the resulting SACs were studied. The SACs were characterized by N₂ adsorption, X‐ray diffraction, scanning electron microscopy, and aqueous adsorption assays. Either increasing activation temperature or extending retention time decreases the yield of SACs. The BET surface area and pore volume increase with activation temperature and reach a maximum at 1000°C and then decrease at higher activation temperatures. At 1000°C, BET surface area, total pore volume, and mesopore pore volume increase with retention time from 0.5 to 2 h, and meanwhile micropore volume decreases. The micropores are gradually widened into mesopores with increasing activation temperature or extending retention time. SEM and XRD analyses of SAC10 verify the presence of developed porous structure composed of disordered micrographite stacking. Aqueous adsorption assays indicate that SACs have good adsorption capacity for phenol. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of activation time on the properties of polyacrylonitrile-based activated carbon hollow fiber

Activated carbon hollow fiber (ACHF) was prepared from polyacrylonitrile (PAN) hollow fiber through carbonization in nitrogen and activation with carbon dioxide. The effect of the activation time on the pore size distribution and the surface structure of the resulted ACHF was investigated. The results show that increasing the activation time at 800°C can increase the number of pores and reduce the crystal size, the tensile strength, the modulus, and the elongation. © 1995 John Wiley & Sons, Inc.     

Preparation of ultra-thin PAN-based activated carbon fibers with physical activation

This study elucidates the stabilization and activation in forming activated carbon fibers (ACFs) from ultra-thin polyacrylonitrile (PAN) fibers. The effect of stabilization time on the properties and structure of resultant stabilized fibers was investigated by thermal analysis, X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy (SEM). Stabilization was optimized by the pyrolysis of ultra-thin PAN fibers in air atmosphere at 280°C for 15 min, and subsequent activation in steam at 1000°C for 0.75 to 15 min. Resultant ACFs were characterized by N₂ adsorption at 77 K to evaluate pore parameters, XRD to evaluate structure parameters, and field emission scanning electron microscopy (FESEM) to elucidate surface morphology. The produced ACFs had surface areas of 668–1408 m²/g and a micropore volume to total pore volume ratio from 78 to 88%. Experimental results demonstrate the surface area and micropore volume of 1408 m²/g and 0.687 cm³/g, respectively, following activation at 1000°C for 10 min. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Removal of formaldehyde at low concentration using various activated carbon fibers

Adsorption of low concentration formaldehyde on pitch‐based, rayon‐based, and PAN‐based activated carbon fibers (ACFs) and an unactivated PAN‐based carbon fiber (PAN‐CF) was investigated by a dynamic method. The pore structure and surface chemistry of these samples were characterized by liquid nitrogen adsorption, elemental analysis, and X‐ray photoelectron spectroscopy. Results revealed that the pore structure, especially surface chemical composition, greatly influence the formaldehyde adsorption. PAN‐based ACFs showed the highest formaldehyde adsorption capacity because there are more abundant nitrogen‐containing groups, especially pyrrolic, pyridonic, pyridinic, and quaternary on the surface. The breakthrough time and formaldehyde adsorption capacity of one kind of PAN‐ACF were 361 min and 0.478 mmol/g, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

炭化过程对聚丙烯腈基活性中空炭纤维性能的影响

聚丙烯腈(PAN)中空纤维在空气中250℃预氧化2 h后,在氮气气氛中炭化,得到PAN基中空炭纤维(PAN-CHF),再在二氧化碳气氛中活化,得到PAN基活性中空炭纤维(PAN-ACHF)。考察了炭化温度和炭化时间对PAN-CHF的收缩率、PAN-ACHF的收缩率、活化收率、比表面积和吸附性能的影响。结果表明:炭化温度为1 000℃时,PAN-CHF和PAN-ACHF的收缩率相同;炭化温度为900℃时,PAN-ACHF的比表面积最大,吸附性能最好,炭化时间对PAN-CHF和PAN-ACHF的收缩率影响不大,但活化收率随炭化时间延长呈上升趋势,比表面积先增后降,炭化时间为60 min时达到最大,其吸附量最大。     

Preparation and characterization of trilobal activated carbon fibers

The objective of this research was to evaluate the effectiveness of several different methods for controlling the pore size and pore size distribution in activated carbon fibers. Variables studied included fiber shape, activation time, and the addition of small amounts of silver nitrate. Pure isotropic pitch and the same isotropic pitch containing 1 wt.% silver were melt spun to form fibers with round and trilobal cross sections. These fibers were then stabilized, carbonized, and activated in carbon dioxide. Field emission scanning electron microscopy (FE SEM), electron dispersive spectra (EDS), and wavelength dispersive spectra (WDS) were used to monitor the size and distribution of the silver particles in the fibers before and after activation. Each of these analyses showed that the distribution of silver particles was extremely uniform before and after activation. The fibers were also weighed before and after activation to determine the percent burn-off. The BET specific surface areas of the activated fibers were determined from N₂ adsorption isotherms measured at −196 °C. The results showed that round and trilobal fibers with equivalent cross-sectional areas yielded similar burn-off values and specific surface areas after activation. Also, activation rates were found to be independent of CO₂ flow rate. The porosity of the activated fibers depended on the total time of activation and the cross-sectional area of fibers. The N₂ adsorption measurements showed that the activated fibers had extremely high specific surface areas (greater than 3000 m²/g) and high degrees of meso- and macro-porosity. FE SEM was also used to investigate surface texture and size of pore openings on the surfaces of the activated fibers. The photos showed that silver particles generated surface macro- and mesopores, in agreement with the inferences from N₂ adsorption measurements.     

活化温度对聚丙烯腈基活性中空炭纤维结构和吸附性能的影响

用质量分数为4%的磷酸氢氨溶液预处理聚丙烯腈(PAN)中空纤维,经预氧化及炭化后,用二氧化碳气体在不同温度下活化40 min,得到PAN基活性中空炭纤维(PAN-ACHF)。考察了活化温度对PAN-ACHF的比表面积、孔径分布、形态和吸附性能的影响。结果表明,随着活化温度的升高,PAN-ACHF表面的孔逐渐加深,且数目逐渐增多,比表面积逐渐增大;当活化温度为900℃时,BET比表面积最大为1 422 m2/g,中孔的比表面积也达到最大,为1 234 m2/g,且孔径主要集中在2~5 nm;PAN-ACHF对肌酐和VB12的吸附率都随着活化温度的升高而增大,当活化温度为900℃时,PAN-ACHF对肌酐和VB12的吸附率都达到最大值.分别为99%和84%。     

Preparation and characterization of PAN-based ultra-fine activated carbon fiber adsorbent

Polyacrylonitrile-based (PAN) ultra-fine fibers were made from electrospining with dimethylformamide as a solvent. And then the fibers were processed via pre-oxidization, carbonization, and steam activation to produce the PAN-based ultra-fine activated carbon fiber (UFACF) adsorbent. According to the specific surface area, pore volume, pore size distribution and phenol adsorption value, the effects of different factors on the yield of activation and adsorption properties of UFACF were investigated through the orthogonal experiment. TG, field emission-scanning electron microscope, FTIR, XRD were employed to characterize the morphology and structure evolvement of UFACF during thermal treatment process. At the optimal conditions, the yield of activation of UFACF was from 37.2 to 58.5%, the maximal specific surface area 1075.1 m² g⁻¹, and the maximal phenol adsorption value 377.1 mg g⁻¹.     

Activation of ultra‐thin activated carbon fibers as electrodes for high performance electrochemical double layer capacitors

Activated carbon fibers (ACFs) contain pores with a weak resistance to electrolyte migration but with high electrical resistance between the fibers. The ACFs used herein were prepared from ultra‐thin polyacrylonitrile (PAN) fibers, to be used as electrodes in electrochemical double layer capacitors (EDLCs), by varying the activation temperatures and the holding times during steam activation. As the activation temperature and holding time were increased, the specific surface area increased along with the specific capacitance (F g^?1). A maximum specific capacitance as high as 283 F g^?1 can be obtained using the ultra‐thin ACFs fabricated at 1000°C for 10 min with a specific surface area of 1408 m² g^?1. This investigation demonstrates that the surface area, pore structure, and surface functional groups of ACFs were all significant factors in determining the capacitive characteristics of ACFs. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of activated carbons by utilizing solid wastes from palm oil processing mills

Feasibility of producing activated carbons by utilizing solid wastes (extracted flesh fibre and seed shell) from palm oil processing mills was investigated. The effects of activation conditions (CO₂ flow rate, activation temperature and retention time) on the characteristics of the activated carbons, i.e. density, porosity, BET surface area, pore size distribution and surface chemistry were studied. In this study, the optimum conditions for activation were an activation temperature of 800 °C and a retention time of 30 min for fiber or 50 min for shell, which gave the maximum BET surface area. Pore size distribution revealed that the shell-based activated carbons were predominantly microporous whilst fiber activated carbon had predominant mesopores and macropores, suggesting the application of shell and fiber activated carbon as adsorbents for gas-phase and liquid-phase adsorption, respectively. This was confirmed by further gas- and liquid-phase adsorption tests.