Browsing by Author "Topuz, Fuat"
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Item Open Access Atomic layer deposition of palladium nanoparticles on a functional electrospun poly-cyclodextrin nanoweb as a flexible and reusable heterogeneous nanocatalyst for the reduction of nitroaromatic compounds(Royal Society of Chemistry, 2019-09) Topuz, Fuat; Uyar, TamerWe here show a rational approach for the fabrication of a flexible, insoluble catalytic electrospun nanoweb of cross-linked cyclodextrin (CD) for the reduction of nitroaromatics. CD nanofibers were produced by electrospinning an aqueous HP-β-CD solution containing a multifunctional cross-linker (i.e., 1,2,3,4-butanetetracarboxylic acid, BTCA) and were subsequently cross-linked by heat treatment, which led to an insoluble electrospun poly-CD nanoweb. The poly-CD nanoweb was decorated with Pd nanoparticles (Pd-NPs) by atomic layer deposition (ALD) technique over 20 cycles to give rise to a catalytic electrospun nanoweb (i.e., Pd@poly-CD). The formation of the Pd-NPs on the poly-CD nanofiber surface was clearly evidenced by TEM and STEM imaging, which displayed the homogeneously distributed Pd-NPs with a mean size of 4.34 nm. ICP-MS analysis revealed that the Pd content on the Pd@poly-CD nanoweb was 0.039 mg per mg of nanoweb. The catalytic performance of the Pd@poly-CD nanoweb was tested for the reduction of a nitroaromatic compound (i.e., 4-nitrophenol (4-NP)), and high catalytic performance of the Pd@poly-CD nanoweb was observed with a corresponding TOF value of 0.0316 min−1. XPS was used to explore the oxidation state of Pd atoms before and after the catalytic reduction of 4-NP, and no significant change was observed after catalytic reactions. In brief, the Pd@poly-CD nanoweb having handy, flexible, structural stability and reusability can be effectively used in environmental applications as a heterogeneous nanocatalyst for the reduction of toxic nitroaromatics.Item Open Access Catechin encapsulated antioxidant electrospun nanofibers: A comparative study between cyclodextrin complex nanofibers and poly(vinyl alcohol) nanofibers(American Chemical Society, 2023-05-31) Yıldız, Zehra İrem; Topuz, Fuat; Uyar, TamerCatechin is a plant polyphenol with a strong antioxidant effect. However, its use is limited due to its poor water solubility and sensitivity to light and oxygen. Here, catechin could be solubilized by inclusion complexation with cyclodextrin (CD) (CD-IC), and their solutions were electrospun into fibers in the presence and absence of poly(vinyl alcohol) (PVA) to compare the stabilization of catechin for its antioxidant activity. The antioxidant activity of catechin/CD IC nanofibers was also compared to that of the powder form. Scanning electron microscopy (SEM) analysis revealed the production of bead-free nanofibers. The successful incorporation of catechin into nanofibers was confirmed by Fourier-transform infrared spectroscopy (FTIR) analysis of catechin CC bond stretching. Likewise, 1H NMR spectroscopic analysis revealed the characteristic aromatic protons of catechin. The formation of inclusion complexes was confirmed by X-ray diffraction (XRD) and dissolution testing by the disappearance of crystalline peaks and rapid fiber dissolution, respectively. Finally, antioxidant testing demonstrated the higher antioxidant activity of polymer-free CD-IC nanofibers.Item Open Access Cyclodextrin-assisted synthesis of tailored mesoporous silica nanoparticles(Beilstein-Institut Zur Forderung der Chemischen Wissenschaften, 2018) Topuz, Fuat; Uyar, TamerMesoporous silica nanoparticles (MSNs) have sparked considerable interest in drug/gene delivery, catalysis, adsorption, separation, sensing, antireflection coatings and bioimaging because of their tunable structural properties. The shape, size and pore structure of MSNs are greatly influenced by the type of additives used, e.g., solvent and pore-templating agent. Here, we studied the influence of cyclodextrin (CD) molecules on the formation of MSNs. The nanoparticles over 100 nm in diameter were synthesized by surfactant- templated, hydrolysis-polycondensation reactions in the presence of pristine CD (β-CD) or hydroxypropyl-functionalized CDs (HP-γ-CD and HP-β-CD). Depending on the formulation conditions, differently shaped MSNs, such as bean-like, spherical, ellipsoid, aggregate and faceted were generated. The morphology and size of MSNs varied with the CD-type used. Generally, spherical particles were obtained with β-CD, while a faceted morphology was observed for the particles synthesized using HP-CDs. The particle size could be tuned by adjusting the amount of CD used; increasing the CD concentration led to larger particles. MSNs synthesized in the presence of β-CD displayed a smaller particle size than those produced with HP-functional CDs. FTIR, TGA and solidstate 13C NMR demonstrated the adsorption of CDs on the particle surfaces. The proposed concept allows for the synthesis of silica nanoparticles with control over particle shape and size by adjusting the concentration of additives in a simple, one-pot reaction system for a wide range of applications.Item Open Access Efficient removal of polycyclic aromatic hydrocarbons and heavy metals from water by electrospun nanofibrous polycyclodextrin membranes(American Chemical Society, 2019) Çelebioğlu, Aslı; Topuz, Fuat; Yıldız, Zehra İrem; Uyar, TamerHere, a highly efficient membrane based on electrospun polycyclodextrin (poly-CD) nanofibers was prepared and exploited for the scavenging of various polycyclic aromatic hydrocarbons (PAHs) and heavy metals from water. The poly-CD nanofibers were produced by the electrospinning of CD molecules in the presence of a cross-linker (i.e., 1,2,3,4-butanetetracarboxylic acid), followed by heat treatment to obtain an insoluble poly-CD nanofibrous membrane. The membrane was used for the removal of several PAH compounds (i.e., acenaphthene, fluorene, fluoranthene, phenanthrene, and pyrene) and heavy metals (i.e., Pb2+, Ni2+, Mn2+, Cd2+, Zn2+, and Cu2+) from water over time. Experiments were made on the batch sorption of PAHs and heavy metals from contaminated water to explore the binding affinity of PAHs and heavy metals to the poly-CD membrane. The equilibrium sorption capacity (qe) of the poly-CD nanofibrous membrane was found to be 0.43 ± 0.045 mg/g for PAHs and 4.54 ± 0.063 mg/g for heavy metals, and the sorption kinetics fitted well with the pseudo-second-order model for both types of pollutants. The membrane could be recycled after treatment with acetonitrile or a 2% nitric acid solution and reused up to four times with similar performance. Further, dead-end filtration experiments showed that the PAH removal efficiencies were as high as 92.6 ± 1.6 and 89.9 ± 4.8% in 40 s for the solutions of 400 and 600 μg/L PAHs, respectively. On the other hand, the removal efficiencies for heavy metals during the filtration were 94.3 ± 5.3 and 72.4 ± 23.4% for 10 and 50 mg/L solutions, respectively, suggesting rapid and efficient filtration of heavy metals and PAHs by the nanofibrous poly-CD membrane.Item Open Access Electrospinning combined with atomic layer deposition to generate applied nanomaterials: A review(American Chemical Society, 2020) Vempati, S.; Ranjith, K. S.; Topuz, Fuat; Bıyıklı, Necmi; Uyar, TamerCombining different material processing techniques is one of the keys to obtain materials that depict synergistic properties. In this review, we have reviewed a combination of two highly potential techniques, namely, electrospinning and atomic layer deposition (ALD), in the view of various applications. Over the past 10 years, our research groups are involved in the exploration of employing this combination for a range of applications. We also include some basic information on both the processes and diversity of nanostructures as a result of their combination. Nonwoven nanofiber membranes are excellent candidates for a wide range of applications. Also, they can act as templates to produce various other kinds of nanostructures when combined with ALD in small/large scale production. These nanostructures could be used as such or further subjected to other processing techniques yielding hierarchical structures. In this review, we exclusively survey and highlight the unique capabilities of combined electrospinning and ALD for applications in catalysis, photocatalysis, solar cells, batteries and gas sensors.Item Open Access Electrospinning of cyclodextrin functional nanofibers for drug delivery applications(MDPI AG, 2019) Topuz, Fuat; Uyar, TamerElectrospun nanofibers have sparked tremendous attention in drug delivery since they can offer high specific surface area, tailored release of drugs, controlled surface chemistry for preferred protein adsorption, and tunable porosity. Several functional motifs were incorporated into electrospun nanofibers to greatly expand their drug loading capacity or to provide the sustained release of the embedded drug molecules. In this regard, cyclodextrins (CyD) are considered as ideal drug carrier molecules as they are natural, edible, and biocompatible compounds with a truncated cone-shape with a relatively hydrophobic cavity interior for complexation with hydrophobic drugs and a hydrophilic exterior to increase the water-solubility of drugs. Further, the formation of CyD-drug inclusion complexes can protect drug molecules from physiological degradation, or elimination and thus increases the stability and bioavailability of drugs, of which the release takes place with time, accompanied by fiber degradation. In this review, we summarize studies related to CyD-functional electrospun nanofibers for drug delivery applications. The review begins with an introductory description of electrospinning; the structure, properties, and toxicology of CyD; and CyD-drug complexation. Thereafter, the release of various drug molecules from CyD-functional electrospun nanofibers is provided in subsequent sections. The review concludes with a summary and outlook on material strategiesItem Open Access Electrospinning of cyclodextrin nanofibers: the effect of process parameters(Hindawi Limited, 2020) Topuz, Fuat; Uyar, TamerCyclodextrin (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.Item Open Access Electrospinning of nanocomposite nanofibers from cyclodextrin and laponite(Elsevier, 2018) Topuz, Fuat; Uyar, TamerHerein, the electrospinning of nanocomposite nanofibers from a non-polymeric system using cyclodextrin (CD)and Laponite was reported. Laponite, a hectorite-type synthetic clay, was used as an additive in the aqueoussolutions of CD molecules, and its influence on the polymer-free electrospinning of CD was investigated. Flowtests showed that the viscosity of CD solutions increased with a Laponite content rise at low shear rates and anunequalled degree of shear thinning at high shear rates. The morphology of the CD/Laponite nanofibers wasexplored by SEM, which revealed the formation of smooth nanofibers at low Laponite content (0.62 wt%) andnon-smooth nanofibers at Laponite content over 1.56 wt% due to enhanced electrostatic interactions betweenthe charged surface of Laponite and hydroxyl groups of CD. Further increasing Laponite content to 12.5 wt% ledto only micro-sized beads instead offibers due to electrospraying, suggesting that the embedded Laponite sig-nificantly disturbed hydrogen bonds among CD molecules. The presence of Laponite in the nanofibers wasconfirmed over chemical analysis by EDX and XPS. TEM analysis displayed homogeneous distribution of theexfoliated Laponite in the CD nanofibers, as supported by the disappearance of the diffraction patterns ofLaponite by WAXS. The nanocomposite CD/Laponite mats with Laponite content of≤1.56 wt% maintained theirself-standing andflexible structure to some extent, as revealed by tensile tests. In brief, this study reports thepolymer-free electrospinning of nanocomposite nanofibers based on CD and Laponite and investigates the impactof the incorporated clay on the polymer-free electrospinning of CD molecules.Item Open Access Electrospinning of uniform nanofibers of polymers of intrinsic microporosity (PIM-1): the influence of solution conductivity and relative humidity(Elsevier, 2019) Topuz, Fuat; Satılmış, Bekir; Uyar, TamerPolymers of Intrinsic Microporosity (PIMs) are ultra-permeable macromolecules, which can be cast as a dense membrane and exploited in a wide spectrum of applications, particularly for gas separation owing to their extremely large inner surface area, free volume and high gas permeability. While they are mostly intended to serve as membranes for gas separation, in recent years, they have been also employed in water treatment applications owing to their solution processability, which enables the production of fibrous membranes by electrospinning. The fibrous form provides an increase in sorption performance, water permeability and flux for their application in water treatment. However, owing to the low conductivity of PIM-1 solutions in 1,1,2,2-tetrachloroethane (TeCA) that is the ideal solvent for the electrospinning of PIM-1 solutions, a higher polymer concentration is required to produce bead-free fibers. Furthermore, the electrospinning of highly concentrated PIM-1 solutions leads to the formation of microfibers. To tackle these problems, we herein incorporated an ammonium salt (i.e., tetraethylammonium bromide, TEAB) to increase the conductivity of PIM-1 solutions and study the impact of solution conductivity on the electrospinning of PIM-1 solutions. In parallel to the conductivity study, the influence of relative humidity on the electrospinning and morphology of PIM-1 fibers was explored. The addition of TEAB significantly increased the solution conductivity and drastically enhanced the electrospinnability of PIM-1. The electrospinning of PIM-1 solutions (10% (w/v)) in the presence 7.5 wt% TEAB (with respect to PIM-1) led to bead-free fibers, while at the same concentration, electrosprayed beads and droplet splashing were observed in the absence of TEAB. On the other hand, increasing humidity did not influence the electrospinnability of PIM-1 and the fiber texture, however, less fibers were formed in a given time at very high humidity conditions (~80%). Overall, the experimental findings revealed that the addition of the salt drastically enhanced the electrospinnability of PIM-1 solutions owing to the enhanced conductivity and could lead to the formation of very thin PIM-1 fibers with 160 nm in diameter while no significant effect of relative humidity on the electrospinnability of PIM-1 solutions was observed.Item Open Access Encapsulation of antioxidant beta-carotene by cyclodextrin complex electrospun nanofibers: solubilization and stabilization of beta-carotene by cyclodextrins(Elsevier BV, 2023-04-29) Yıldız, Zehra İrem; Topuz, Fuat; Kılıç, Mehmet Emin; Durgun, Engin; Uyar, TamerCarotenoids act as effective antioxidant defense systems in humans as they scavenge molecular oxygen and peroxyl radicals. However, their poor water solubility and being susceptible to degradation driven by light and oxygen hinder their bioactivity, therefore, they should be stabilized by host matrices against oxidation. Here, β-carotene was encapsulated in electrospun cyclodextrin (CD) nanofibers to increase its water-solubility and photostability to enhance its antioxidant bioactivity. β-carotene/CD complex aqueous solutions were electrospun into nanofibers. The bead-free morphology of the β-carotene/CD nanofibers was confirmed by SEM. The formation of β-carotene/CD complexes was explored through computational modeling and experimentally by FTIR, XRD and solubility tests. The antioxidant activity of the fibers exposed to UV irradiation was demonstrated via a free radical scavenger assay, where β-carotene/CD nanofibers revealed protection against UV radiation. Overall, this work reports the water-borne electrospinning of antioxidant β-carotene/CD inclusion complex nanofibers, which stabilize the encapsulated β-carotene against UV-mediated oxidation.Item Open Access Facile and green synthesis of palladium nanoparticles loaded into cyclodextrin nanofibers and their catalytic application in nitroarene hydrogenation(Royal Society of Chemistry, 2019-01) Çelebioğlu, Aslı; Topuz, Fuat; Uyar, TamerHerein, catalytically active cyclodextrin (CD) nanofibers loaded with in situ formed Pd nanoparticles (Pd-NPs) were prepared by solution electrospinning. Cyclodextrin (CD) acted as a reducing agent and catalyzed the formation of noble metal nanoparticles, e.g., palladium (Pd) over the reduction from Pd2+ to metallic Pd0, without requiring any other reducing agent. Nanofibers were produced by the electrospinning of CD molecules from aqueous and DMF solutions containing two different Pd loadings (1 and 2 wt% with respect to CD). The electrospinning of these solutions could give rise to bead-free CD nanofibers whose diameters showed variations depending on the solvent-type and the Pd content used: the nanofibers electrospun from DMF solutions were smaller in diameter than those produced from aqueous solutions. Furthermore, increasing Pd loading decreased the nanofiber diameter. TEM, HRTEM, STEM and SAED analyses confirmed the presence of homogeneously distributed polycrystalline Pd-NPs in the size range of 3–5 nm throughout the nanofiber matrix. XPS experiments demonstrated the presence of a higher proportion of metallic Pd0 atoms owing to the efficient reduction of Pd2+ by CD molecules. Lastly, the catalytic activity of the nanocomposite nanofibers was explored by the reduction of a nitroarene compound, p-nitrophenol (PNP), to p-aminophenol (PAP), and high catalytic activity of the nanofibers was observedItem Open Access Green one-pot synthesis of bimetallic Pd–Pt nanosponges using biomolecules with enhanced catalytic activity for hydrogen evolution reactions(Royal Society of Chemistry, 2023-03-14) Topuz, Fuat; Patil, Bhushan; Uyar, TamerGreen one-pot synthesis of bimetallic nanoparticles of Pd and Pt using RNA molecules as the capping/stabilizing agent and ascorbic acid as the reducing agent was described. Bimetallic nanoparticles have been used for hydrogen evolution reactions, which demonstrated improved catalytic performance than pure Pd nanoparticles and Pd/C materials.Item Open Access One-step green synthesis of antibacterial silver nanoparticles embedded in electrospun cyclodextrin nanofibers(Elsevier, 2019) Çelebioğlu, Aslı; Topuz, Fuat; Yıldız, Zehra İrem; Uyar, TamerAntibacterial electrospun nanofibers based on cyclodextrin (CD) and silver nanoparticles (Ag-NPs) were produced by solution electrospinning from aqueous and DMF solutions using different Ag contents. CD molecules acted as the reducing agent and catalyzed the formation of Ag-NPs. The nanofibers with smaller diameters were observed for the fibers generated from DMF solutions than those produced from aqueous solutions. TEM and STEM analyses revealed the Ag-NPs (∼2–5 nm depending on solvent-type and Ag loading) in nanofibers, while FTIR and surface enhanced Raman scattering (SERS) analyses showed the apparent frequency shift of OH stretching band and the enhancement of Raman bands of CD molecules with the incorporation of the Ag-NPs. The polycrystalline structure of the Ag-NPs was shown by XRD and SAED analyses over {111}, {200}, {220} and {311} planes. The nanofibers showed significant inhibition against the growth of Escherichia coli and Staphylococcus aureus owing to the antibacterial activity of the Ag-NPs.Item Open Access RNA-mediated, green synthesis of palladium nanodendrites for catalytic reduction of nitroarenes(Elsevier, 2019) Topuz, Fuat; Uyar, TamerPalladium (Pd)-catalyzed reactions mostly show structure sensitivity: i.e., the selectivity and activity of the reactions are highly dependent on the arrangement of Pd atoms. In this regard, branched Pd nanoparticles show enhanced catalytic performance owing to the presence of low coordinated Pd atoms. In this paper, a novel solution-phase synthesis of flower-like Pd nanodendrites using ribonucleic acid (RNA) as a capping agent and ascorbic acid as a reducing agent was described. On the other hand, the co-use of polyvinylpyrrolidone (PVP) and potassium bromide (KBr) instead of RNA at the same synthesis conditions led to cuboid nanoparticles, while the sole use of ascorbic acid resulted in faceted nanoparticles. The formation of nanodendritic morphology was attributed to the RNA-assisted growth through particle attachment. This scenario was supported by TEM analysis that demonstrated the aggregation of small particles to form larger nanoparticles at the onset of the reaction. The shape and size of the nanoparticles could be readily tuned by the RNA content used. XPS confirmed the formation of metallic Pd nanoparticles. The presence of crystalline planes of {1 1 1}, {2 0 0}, {2 2 0}, {3 1 1} and {2 2 2} was demonstrated by XRD and SAED analyses. The Pd nanodendrites were used for the reduction of p-nitrophenol (PNP) and 2,4,6-trinitrotoluene (TNT), and reduction rate constants (k) were calculated as 1.078 min−1 (normalized rate constant, knor = 59.66 mmol−1 s−1) for PNP and 0.3181 min−1 (knor = 17.6 mmol−1 s−1) for TNT with the corresponding turnover frequencies (TOFs) as 16.06 and 40.80 h−1, respectively.Item Open Access Water-insoluble polymer-free uniform nanofibers of peracetylated cyclodextrin by electrospinning(Springer, 2020) Topuz, Fuat; Shaikh, Ashif Y.; Mustafa O., Güler; Uyar, TamerHydrophobic cyclodextrin (CD) nanofibers were produced by the electrospinning of peracetylated β-CD without requiring any polymer as a carrier matrix. Native β-CD was peracetylated through the reaction with acetic anhydride, and the conversion of all hydroxyl groups into acetyl was confirmed by NMR, XPS, and TGA analyses. The peracetyl modification drastically boosted the thermal stability of the β-CD molecules. The electrospinning of the peracetylated β-CD from its highly concentrated solutions (180% (w/v)) in DMF led to bead-free nanofibers, while electrospinning at the concentrations of 140 and 160% (w/v) CDs resulted in beads and beaded nanofibers, respectively. The electrospinning process parameters such as applied voltage, flow rate, and tip-to-collector distances were systematically altered to produce a uniform nanofiber structure. The flow rate had the most drastic effect on the diameter and morphology of the resultant nanofibers: A threefold rise in the fiber diameter was observed with increasing the flow rate from 0.1 to 2 mL h−1. Similarly, higher electrical field increased the fiber diameter due to higher mass flow, while boosting the tip-to-collector distance did not reveal any significant change on the fiber diameter. The stability of the peracetylated β-CD nanofibers was observed in water for 24 h without any significant morphological change; however, the dissolution of the nanofiber mat was observed with a long-time exposure to water. We demonstrated production of hydrophobic uniform CD nanofibers without using any carrier polymer.