Oxadiazole-Functionalized Polyacrylonitrile Fiber as Selective Adsorbent for Mercury Ion

A new oxadiazole-functionalized polyacrylonitrile fiber(PANAOF)was successfully fabricated by immobilizing the organic molecule 2-chloromethyl-5-phenyl-1,3,4-oxadiazole on aminated fiber(PANAF).The fibers were characterized completely by Fourier-transform infrared spectroscopy,elemental analysis,X-ray diffraction,and X-ray photoelectron spectroscopy techniques.Compared with PANAF,PANAOF showed a higher adsorption capability for Hg^2+ions in aqueous solutions.The functionalized fiber PANAOF exhibited a highly selective adsorption for Hg^2+when coexisting with other metal ions viz.Pb^2+,Cd^2+,Cu^2+,Zn^2+,Ni^2+,Co^2+,Cr^3+,Ca^2+,and Mg^2+.The PANAOF presented the best adsorption capacity for Hg^2+at pH 5.Moreover,the adsorption experimental data fit well with the pseudo-second-order kinetic model and Langmuir isotherm.Notably,the PANAOF almost retained its original adsorption capacity(112 mg/g)after five cycles,indicating its excellent reusability in practical applications.

Phase and Structural Transformation of Polyacrylonitrile Fiber during Two-Stage Thermal Stabilization

The influence of two-stage isothermal treatment on the change in the linear dimensions of the fiber, the average sizes of the coherent scattering regions, the texture and phase composition of the polyacrylonitrile fiber in the process of isothermal thermal stabilization is considered by the methods of dilatometry and X-ray diffraction analysis. It is shown that preliminary short-term heat treatment at a lower temperature affects the process of structural transformations of the polyacrylonitrile fiber material and the formation of a new highly dispersed phase of the thermally stabilized fiber.

Nitrogen-doped porous carbons from polyacrylonitrile fiber as effective CO_(2) adsorbents

In this report, nitrogen-doped porous carbons were synthesized from polyacrylonitrile fiber by a facile two-step synthesis process i.e. carbonization followed by KOH activation. Activation temperature and KOH/carbon ratio are two parameters to tune the porosity and surface chemical properties of sorbents. The as-obtained sorbents were carefully characterized.Special attention was paid concerning the change of sorbents’ morphology with respect to synthesis conditions. Under the activation temperatures of this study, the sorbents can still retain their fibrous structure when the KOH/carbon mass ratio is 1. Further increasing the KOH amount will destroy the original morphology of polyacrylonitrile fiber. CO_(2)adsorption performance tests show that a sorbent retaining the fibrous shape possesses the highest CO_(2)uptake of 3.95 mmol/g at 25℃and 1 bar. Comprehensive investigation found that the mutual effect of narrow microporosity and doped N content govern the CO_(2)adsorption capacity of these adsorbents. Furthermore, these polyacrylonitrile fiber-derived carbons present multiple outstanding CO_(2)capture properties such as excellent recyclability, high CO_(2)/N_(2)selectivity, fast adsorption kinetics, suitable heat of adsorption, and good dynamic adsorption capacity. Hence, nitrogen-doped porous carbons with fibrous structure are promising in CO_(2)capture.

Heterogeneous Fenton degradation of azodyes catalyzed by modified polyacrylonitrile fiber Fe complexes: QSPR (quantitative structure peorperty relationship) study

The amidoximated polyacrylonitrile （PAN） fiber Fe complexeswere prepared and used as the heterogeneous Fenton catalysts for thedegradation of28 anionicwater soluble azodyes inwater under visible irradiation. The multiple linear regression （MLR） methodwas employed todevelop the quantitative structure property relationship （QSPR） model equations for thedecoloration and mineralization of azodyes. Moreover, the predictive ability of the QSPR model equationswas assessed using Leave-one-out （LOO） and cross-validation （CV） methods. Additionally, the effect of Fe content of catalyst and the sodium chloride inwater on QSPR model equationswere also investigated. The results indicated that the heterogeneous photo-Fentondegradation of the azodyeswithdifferent structureswas conducted in the presence of the amidoximated PAN fiber Fe complex. The QSPR model equations for thedyedecoloration and mineralizationwere successfullydeveloped using MLR technique. MW/S （molecularweightdivided by the number of sulphonate groups） and N N=N （the number of azo linkage） are considered as the most importantdetermining factor for thedyedegradation and mineralization, and there is a significant negative correlation between MW/S or N N=N anddegradation percentage or total organic carbon （TOC） removal. Moreover, LOO and CV analysis suggested that the obtained QSPR model equations have the better prediction ability. The variation in Fe content of catalyst and the addition of sodium chloridedid not alter the nature of the QSPR model equations.

Aldol Reactions Catalyzed by Proline Functionalized Polyacrylonitrile Fiber

A proline functionalized fiber catalyst was employed for aldol reactions in water. In the presence of the fiber catalyst, the aldol reactions proceeded smoothly at 40 ℃ and the products were obtained in excellent yields which were higher than those obtained for the reactions catalyzed by L-proline or trans-4-hydroxy-L-proline. This newly developed fiber catalyst is applicable to the reactions of a wide range of aromatic aldehydes and exhibits ex- cellent reusability（up to 6 times） without any additional treatment.

DSC Study on the Polyacrylonitrile Precursors for Carbon Fibers

Different polyacrylonitrile （PAN） precursor fibers that displayed various thermal properties were studied by using differential scanning calorimetry （DSC）. Results showed that some commercial PAN precursor fibers displayed double separated peaks and these fibers were of high quality because of their process stability during their conversion to carbon fibers of high performance. Some fabrication processes, such as spinning, drawing, could not apparently change the DSC features of a PAN precursor fiber. It was concluded that the thermal properties of a PAN precursor fiber was mainly determined from its comonomer content type and compositions.

Investigation of Voids in Polyacrylonitrile Fibers by USAXS and SAXS

The void structure of polyacrylonitrile(PAN)fibers was investigated using ultra-small angle X-ray scat-tering(USAXS)and small angle X-ray scattering(SAXS).A quantitative method was developed to analyze connected USAXS/SAXS data and thus determine the void parameters of PAN fibers.The results showed that voids affected the mechanical performance of PAN fibers and were present throughout the entire wet-spinning process.When the abso-lute quantity and size of voids decreased,the tensile strength and modulus of PAN fibers increased.The void para-meters were optimized by controlling the production process,and thus the tensile strength and modulus of PAN fibers were increased.The method for analyzing the void structure developed in this study is useful for analyzing voids over with larger size range,as well as the effect of the void structure on the mechanical performance of fibers.

Comparison of Structure and Properties among Various PAN Fibers for Carbon Fibers

To find out the high-quality polyacrylonitrile (PAN) fibers, some differences are sought by comparing domestic PAN fibers with the foreign ones. X-ray diffractometer (XRD), transmission electron microscope (TEM), Fourier transform infrared (FT-IR) spectrometer, elemental analyzer, tensile-testing machine and high-temperature differential scanning calorimeter (DSC) are used to characterize the individual microstructure, chemical structure, elemental content, mechanical properties and thermal properties. It is found that high-quality PAN fibers have high density, lower titre, higher or adequate tensile strength, and they also have better conglomeration structure, smaller crystal dimension with dispersive distribution, less microvoids and flaws.

Research on the Dynamic Performance of Polyacrylonitrile Muscles

The dynamic property of polyacrylonitrile (PAN) muscles was tested. The test results can help us to master PAN muscles' mechanical and chemical behaviors, which are indispensable for us to build dynamic model for the artificial muscle. Furthermore, here we provide an important experimental way to study gel muscles.

New Evaluation on the Preoxidation Extent of Different PAN Precursors

Structural changes in carbon fibers at each stage of, especially, preoxidation process are well known to play a great role in achieving the ultimate product quality. Differential scanning calorimetry (DSC), scanning electron microscope (SEM), density method and optical microscope were used to characterize the preoxidation extent. A conventional approach, e.g., density aim, to evaluate the extent of preoxidation is not very exact. A DSC curve of a PAN precursor only can provide general information, major in the temperature regime of preoxidation reaction. However, the evaluation of a preoxidation extent, especially from conventional preoxidation temperature with a great span regime of 200~400癈, is put forward in this paper, in which the evolution of core/shell morphological structure is a kind of straightforward evidence.