Metal-free N-doped ultrafine carbon fibers from electrospun Polymers of Intrinsic Microporosity (PIM-1) based fibers for oxygen reduction reaction

Synthesis of nitrogen-doped carbon fibers (CF) has been proved to be one of the most promising oxygen reduction reaction (ORR) catalysts which can replace the state-of-art Pt catalyst for non-noble metal-free light-weight devices. Polymers of Intrinsic Microporosity (PIM-1) is soluble in common organic solvents and can be tailored by functionalization owing to nitrile groups in the backbone. PIM-1 was functionalized to amide (hydrolyzed PIM-1), amine and amidoxime groups. The modified PIM-1s were electrospun into ultrafine fibers and pyrolyzed to obtain CF. The present article investigates the influence of different functional groups on the properties of PIM-1 based CF and their nitrogen-doping. Particularly, their ORR performance has been evaluated. Interestingly, CF from hydrolyzed PIM-1 have the highest pore volume with small pore size among the CF based on PIM-1, amine and amidoxime PIM-1. The amount of nitrogen-doping in these CF shows the trend according to the functional groups as PIM-1 > amine > amidoxime > amide. Among all these PIM-1 based CF; CF from hydrolyzed PIM-1 has the highest percentage of pyridinic and graphitic nitrogen, furthermore, electrocatalysis revealed that ORR processed through four-electron with the onset potential 985 mV vs. reversible hydrogen electrode (RHE) which is comparable with the standard Pt/C catalysts. © 2020 Elsevier B.V

The formation and characterization of cyclodextrin functionalized polystyrene nanofibers produced by electrospinning

Polystyrene (PS) nanofibers containing the inclusion complex forming beta-cyclodextrin (β-CD) were successfully produced by electrospinning aimed at developing functional fibrous nanowebs. By optimization of the electrospinning parameters, which included varying the relative concentration of PS and β-CD in the solutions, bead-free fibers were produced. Homogeneous solutions of β-CD and PS in dimethylformamide (DMF) were used with concentrations of PS varying from 10% to 25% (w/v, with respect to DMF), and β-CD concentrations of 1% to 50% (w/w, with respect to PS). The presence of β-CD facilitated the production of bead-free PS fibers even from lower polymer concentrations as a result of the higher conductivity of the PS/CD solutions. The morphology and the production of bead-free PS/CD fibers were highly dependent on the β-CD contents. Transmission electron microscope (TEM) and atomic force microscope (AFM) images showed that incorporation of β-CD yielded PS fibers with rougher surfaces. Thermogravimetric analysis (TGA) and direct insertion probe pyrolysis mass spectroscopy (DP-MS) results confirmed the presence of β-CD in the PS fibers. X-ray diffraction (XRD) spectra of the fibers indicated that the β-CD molecules are distributed within the PS matrix without any phase separated crystalline aggregates up to 40% (w/w) β-CD loading. Furthermore, chemical analyses by Fourier transform infrared (FTIR) spectroscopy studies confirm that β-CD molecules are located within the PS fiber matrix. Finally, preliminary investigations using x-ray photoelectron spectroscopy (XPS) and time-of-flight static secondary ion mass spectrometry (ToF-static-SIMS) show the presence of the cyclodextrin molecules in the outer molecular layers of the fiber surfaces. The XPS and ToF-SIMS findings indicate that cyclodextrin functionalized PS webs would have the potential to be used as molecular filters and/or nanofilters for the purposes of filtration/purification/separation owing to surface associated β-CD molecules which have inclusion complexation capability

Highly selective surface adsorption-induced efficient photodegradation of cationic dyes on hierarchical ZnO nanorod-decorated hydrolyzed PIM-1 nanofibrous webs

Selectivity of catalysts toward harmful cationic pollutants in industrial wastewater remains challenging but is of crucial importance in environmental remediation processes. Here, we present a complex network of a hydrolyzed polymer of intrinsic microporosity (HPIM)-based electrospun nanofibrous web with surface functional decoration of ZnO nanorods (NRs) as a hierarchical platform for selective and rapid degradation of cationic dyes. Over a single species or binary mixtures, cationic dyes were selectively adsorbed by the HPIM surface, which then rapidly degraded under simultaneous photoirradiation through the ZnO NRs. Both HPIM and ZnO exhibited high electronegative surfaces, which induced the selectivity towards the cationic dyes and rapidly degraded the pollutants with the production of reactive oxygen species under photoirradiation. Further, as a free-standing web, the catalytic network could be easily separated and reused without any significant loss of catalytic activity after multiple cycles of use. The hierarchical platform of ZnO/HPIM-based heterostructures could be a promising catalytic template for selective degradation of synthetic dyes in mixed wastewater samples. (C) 2019 Elsevier Inc. All rights reserved

FIRTINA VADİSİ (ÇAMLIHEMŞİN, RİZE) Buxus sempervırens L. TOPLUMLARININ YAYILIŞ GÖSTERDİĞİ ALANLARIN KARAYOSUNU (MUSCI) FLORASI

Kaçkar Dağları’nın kuzey yamaçlarında yer alan Fırtına Vadisi’nde Buxus sempervirens L.’in saf veya diğer bazı odunsu taksonlarla oluşturduğu meşcerelerdeki karayosunu (musci) florası araştırılmıştır. 2005 yılı Haziran ve Ağustos aylarında toplanan karayosunu örneklerinin değerlendirilmesi sonucunda 18 familya ve 34 cinse ait 47 takson tespit edilmiştir. Araştırma alanında bulunan karayosunlarından 6 tanesi ( Tetraphis pellucida Hedw., Dicranoweisia crispula (Hedw.) Milde, Dicranodontium denudatum (Brid.) E.Britton var. denudatum, Oncophorus virens (Hedw.) Brid., Pseudoleskeella nervosa (Brid.) Nyholm, Eurhynchium schleicheri (R.Hedw.) Jur.) Henderson (1961) tarafından uygulanan Türkiye kareleme sistemine göre A4 karesi için yeni kayıttır. Araştırma alanında içerdiği takson sayısı en yüksek olan ilk 5 familya; Dicranaceae (7), Hypnaceae (6), Brachytheciaceae (5), Mniaceae (5), Polytrichaceae (4) dir. İçerdiği takson sayısı en yüksek olan cinsler ise Plagiomnium (4), Polytrichum (3), Hypnum (3) dur. Araştırma alanından toplanan karayosunu örneklerinin yaşam formları, tercih ettikleri substrat ve nemlilik gibi ekolojik özellikleri Dierßen (2001)’e göre ve yaşam formlarına ait bilgiler de Mägdefrau (1982)’ye göre düzenlenmiş olup, bu bilgilerin ışığında taksonların ekolojik tercihleri ele alınmıştır. Anahtar Kelimeler: Fırtına Vadisi, Buxus sempervirens, Karayosunu florası, Rize

Amine modified electrospun PIM-1 ultrafine fibers for an efficient removal of methyl orange from an aqueous system

WOS: 000436940800026Polymers of Intrinsic Microporosity (PIM-1) is a promising material for adsorption and separation applications. While PIM-1 displays high affinity for neutral species, it shows lack of interaction with charged molecules in an aqueous system due to non-polar nature of it. Functionalization of PIM-1 provides an advantage of tailoring the interaction ability as well as the adsorption performance of PIM-1 towards target pollutants. In this study, electrospun Polymer of Intrinsic Microporosity (PIM-1) fibrous membrane (PIM-FM) was reacted with borane dimethyl sulfide complex to obtain amine modified PIM-1 fibrous membrane (AM-PIM-FM). Furthermore, PIM-1 film, which is referred as PIM-1 dense membrane (PIM-DM), was also modified under the same conditions as a control material. Structural analyses have confirmed that nitrile groups of PIM-1 have been fully converted to amine group as a result of the reduction reaction. Average fiber diameter of parent PIM-1 fibers was found 2.3 +/- 0.3 mu m, and it remained almost the same after the amine modification. In addition, no physical damage has been observed on fiber structure based on the SEM analysis. Both amine modified PIM-1 dense and fibrous membranes became insoluble in common organic solvents. Before the modification, water contact angle of PIM-FM was 138 +/- 2 degrees which also remained almost the same after the modification, showing water contact angle of 131 +/- 8 degrees. The insolubility along with amine functionality make membranes promising materials for adsorption of anionic dyes from wastewater. Here, dye (i.e. Methyl Orange) removal ability of AM-PIM-FM from an aqueous system was investigated and compared with parent PIM-1 (PIM-FM) as well as dense membrane form (AM-PIMDM). AM-PIM-FM shows extremely higher adsorption capacity than that of PIM-FM and AM-PIM-DM. The maximum adsorption capacity of AM-PIM-FM was found 312.5 mg g(-1) for Methyl Orange. Langmuir isotherm model was found more favorable for the adsorption. AM-PIM-FM was employed effectively in continuous adsorption/desorption studies for several times without having any damage on fiber morphology using batch adsorption process. Furthermore, AM-PIM-FM was successfully used as a molecular filter for the removal of methyl orange from an aqueous system. The results indicate that AM-PIM-FM could be a promising adsorbent for removal of anionic molecules from an aqueous system

Electrospinning of Cyclodextrin Nanofibers: The Effect of Process Parameters

Cyclodextrin (CD) nanofibers have recently emerged as high-performance materials owing to their large surface area-to-volume ratio, along with the presence of high active CD content for their applications in drug delivery and water treatment. Even though there are several studies on the polymer-free electrospinning of CD molecules of different types, the effects of electrospinning process parameters on the morphology and diameter of the resultant fibers have not addressed yet. In this study, the influence of electrospinning process variables on the morphology and diameter of the resultant CD nanofibers is systematically studied using two different solvent systems, i.e., water and N, N-dimethylformamide (DMF). On adjusting the electrospinning process parameters (i.e., electrical field, flow rate, tip-to-collector distance (TCD), and needle diameter), uniform CD nanofibers could be produced from aqueous and DMF solutions. Generally, the electrospinning of thicker fibers was observed by increasing the applied voltage and flow rate due to higher mass flow. Increasing TCD boosted the fiber diameter. Likewise, the use of needles with larger diameters resulted in the electrospinning of thicker fibers from DMF solutions, which might be attributed to higher viscosity due to reduced shear rate

Influence of Hydrogen-Bonding Additives on Electrospinning of Cyclodextrin Nanofibers

The electrospinning of highly concentrated solutions of cyclodextrin (CD) leads to bead-free nanofibers without the need of a polymeric carrier. The occurrence of numerous hydrogen bonds among CD molecules is the main driving force for their electrospinning, and hence, additives with hydrogen-bonding potential can disturb the aggregation of CD molecules and affect their electrospinning. In this study, we systematically investigated the influence of five different hydrogen-bonding additives, i.e., methylamine (MA), ethylenediamine (ED), urea, 2,2,2-trifluoroethanol (TFE), and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), on the solution behavior of hydroxypropyl-β-CD (HP-β-CD) by rheology, conductivity, and NMR analyses, and the morphology of the electrospun HP-β-CD nanofibers by scanning electron microscopy. The 1H NMR chemical shifts of the HP-β-CD protons in D2O were observed with the incorporation of hydrogen-bonding molecules due to the occurrence of intermolecular associations between HP-β-CD and additives. Dynamic light scattering measurements revealed a clear decrease in the aggregate size with the introduction of additives. Unlike other additives, which showed a general decreasing trend in viscosity with increasing additive content, the addition of MA led to a significant increase in the viscosity with increasing concentration and gave rise to HP-β-CD nanofibers at lower concentrations. The addition of low concentrations of ED, urea, TFE, and HFIP led to thinner nanofibers due to the lower viscosity of the respective solutions. Increasing additive content deteriorated the electrospinnability of HP-β-CD solutions, resulting in beaded fibers. A systematic relationship was found between the solution viscosity and morphology of the respective electrospun fibers. Overall, this study, for the first time, reports the influence of hydrogen bonding on the polymer-free electrospinning of CD molecules and shows a correlation between solution properties and morphology of their electrospun nanofibers