Browsing by Author "Khalily, Mohammad Aref"
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Item Open Access Atomic layer deposition of Co3O4 nanocrystals on N-doped electrospun carbon nanofibers for oxygen reduction and oxygen evolution reactions(Royal Society of Chemistry, 2019) Khalily, Mohammad Aref; Patil, Bhushan; Yılmaz, Eda; Uyar, TamerThe oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are considered as the two crucial reactions in key renewable-energy technologies including fuel cells and water splitting. Despite promising research progress in the preparation of various non-noble metal based electrocatalysts, it is still highly challenging but desirable to develop novel fabrication strategies to synthesize highly active and cost-effective ORR/OER bifunctional electrocatalysts in a precisely controlled manner. Herein, we report atomic layer deposition (ALD) of highly monodisperse Co3O4 nanocrystals of different sizes on N-doped electrospun carbon nanofibers (nCNFs) as high performance bifunctional catalysts (Co@nCNFs) for the ORR and OER. Co@nCNFs (with an average Co3O4 particle size of ∼3 nm) show high ORR performance exhibiting an onset potential of 0.87 V with a low Tafel slope of 119 mV dec−1 approaching that of commercial Pt/C. Similarly, the Co@nCNF electrocatalyst showed remarkable catalytic activity in the OER. The turnover frequency (TOF) value determined at an overpotential of 550 mV for the Co@nCNFs is ∼0.14 s−1 which is ca. 3 and ca. 15-fold higher than those of bulk Co (∼0.05 s−1) and the standard state-of-the-art IrOx (0.0089 s−1) catalyst, respectively. This work will open new possibilities for fabrication of inexpensive non-noble metal materials in highly controlled manner for applications as bifunctional ORR/OER electrocatalysis.Item Open Access Atomic layer deposition of NiOOH/Ni(OH) 2 on PIM-1-based N-Doped carbon nanofibers for electrochemical water splitting in alkaline medium(Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Patil, Bhushan; Satılmış, Bekir; Khalily, Mohammad Aref; Uyar, TamerPortable and flexible energy devices demand lightweight and highly efficient catalytic materials for use in energy devices. An efficient water splitting electrocatalyst is considered an ideal future energy source. Well‐aligned high‐surface‐area electrospun polymers of intrinsic microporosity (PIM‐1)‐based nitrogen‐doped carbon nanofibers were prepared as a free‐standing flexible electrode. A non‐noble‐metal catalyst NiOOH/Ni(OH)2 was precisely deposited over flexible free‐standing carbon nanofibers by using atomic layer deposition (ALD). The morphology, high surface area, nitrogen doping, and Ni states synergistically showed a low onset potential (ηHER=−40 and ηOER=290 mV vs. reversible hydrogen electrode), small overpotential at η10 [oxygen evolution reaction (OER)=390.5 mV and hydrogen evolution reaction (HER)=−147 mV], excellent kinetics (Tafel slopes for OER=50 mV dec−1 and HER=41 mV dec−1), and high stability (>16 h) towards water splitting in an alkaline medium (0.1 m KOH). The performance was comparable with that of state‐of‐the‐art noble‐metal catalysts (e.g., Ir/C, Ru/C for OER, and Pt/C for HER). Post‐catalytic characterization with X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy further proved the durability of the electrode. This study provides insight into the design of 1D‐aligned N‐doped PIM‐1 electrospun carbon nanofibers as a flexible and free‐standing NiOOH/Ni(OH)2 decorated electrode as a highly stable nanocatalyst for water splitting in an alkaline medium.Item Open Access Atomic layer deposition of Pd nanoparticles on N-Doped electrospun carbon nanofibers: optimization of ORR activity of Pd-Based nanocatalysts by tuning their nanoparticle size and loading(Wiley-VCHVerlagGmbH& Co. KGaA,Weinheim, 2019) Khalily, Mohammad Aref; Patil, Bhushan; Yılmaz, Eda; Uyar, TamerOptimization of size, loading and chemical composition of catalytic nanoparticles is a crucial step to achieve cost‐effective and efficient (electro) catalysts. This report elaborates optimization of palladium (Pd) nanoparticle size and loading on the electrospun based N‐doped carbon nanofibers (nCNF) towards oxygen reduction reaction (ORR) for the energy devices like fuel cell, metal air batteries. Electrospinning was utilized to produce one‐dimensional (1D) polyacrylonitrile nanofibers followed by a two‐step carbonization process obtaining well‐defined conductive nCNF having diameters in the range of 200–350 nm. As‐synthesized nCNF was decorated with discrete Pd nanoparticles ranging from 2.6±0.4 nm to 4.7±0.5 nm via thermal atomic layer deposition (ALD) technique. We found that nCNF deposited Pd nanoparticles having 3.9±0.6 nm size (Pd20/nCNF) showed the best ORR activity with the smallest Tafel slope of 58 mV dec−1 along with four electrons involved in the ORR. In addition, high value at half wave potential (E1/2=806 mV vs. RHE) and exchange current densities (i0=6.998 mA cm−2) at Pd20/nCNF makes it efficient catalyst among other Pd decorated nCNF. Moreover, we found that electrocatalyst with lower loading/density of Pd nanoparticles showed enhanced ORR activity.Item Open Access Atomic layer deposition of ruthenium nanoparticles on electrospun carbon nanofibers: a highly efficient nanocatalyst for the hydrolytic dehydrogenation of methylamine borane(American Chemical Society, 2018) Khalily, Mohammad Aref; Yurderi, M.; Haider, Ali; Bulut, A.; Patil, Bhushan; Zahmakiran, M.; Uyar, TamerWe report the fabrication of a novel and highly active nanocatalyst system comprising electrospun carbon nanofiber (CNF)-supported ruthenium nanoparticles (NPs) (Ru@CNF), which can reproducibly be prepared by the ozone-assisted atomic layer deposition (ALD) of Ru NPs on electrospun CNFs. Polyacrylonitrile (PAN) was electropsun into bead-free one-dimensional (1D) nanofibers by electrospinning. The electrospun PAN nanofibers were converted into well-defined 1D CNFs by a two-step carbonization process. We took advantage of an ozone-assisted ALD technique to uniformly decorate the CNF support by highly monodisperse Ru NPs of 3.4 ± 0.4 nm size. The Ru@CNF nanocatalyst system catalyzes the hydrolytic dehydrogenation of methylamine borane (CH3NH2BH3), which has been considered as one of the attractive materials for the efficient chemical hydrogen storage, with a record turnover frequency of 563 mol H2/mol Ru × min and an excellent conversion (>99%) under air at room temperature with the activation energy (Ea) of 30.1 kJ/mol. Moreover, Ru@CNF demonstrated remarkable reusability performance and conserved 72% of its inherent catalytic activity even at the fifth recycle.Item Open Access Biotin functionalized self‐assembled peptide nanofiber as an adjuvant for immunomodulatory response(Wiley-VCH Verlag, 2020-12) Demircan, Muhammed Burak; Tohumeken, Sehmus; Gündüz, Nuray; Khalily, Mohammad Aref; Tekinay, T.; Güler, M. O.; Tekinay, Ayşe B.Biotinylated peptide amphiphile (Biotin‐PA) nanofibers, are designed as a noncovalent binding location for antigens, which are adjuvants to enhance, accelerate, and prolong the immune response triggered by antigens. Presenting antigens on synthetic Biotin‐PA nanofibers generated a higher immune response than the free antigens delivered with a cytosine‐phosphate‐guanine oligodeoxynucleotides (CpG ODN) (TLR9 agonist) adjuvant. Antigen attached Biotin‐PA nanofibers trigger splenocytes to produce high levels of cytokines (IFN‐γ, IL‐12, TNF‐α, and IL‐6) and to exhibit a superior cross‐presentation of the antigen. Both Biotin‐PA nanofibers and CpG ODN induce a Th‐1‐biased IgG subclass response; however, delivering the antigen with Biotin‐PA nanofibers induce significantly greater production of total IgG and subclasses of IgG compared to delivering the antigen with CpG ODN. Contrary to CpG ODN, Biotin‐PA nanofibers also enhance antigen‐specific splenocyte proliferation and increase the proportion of the antigen‐specific CD8(+) T cells. Given their biodegradability and biocompatibility, Biotin‐PA nanofibers have a significant potential in immunoengineering applications as a biomaterial for the delivery of a diverse set of antigens derived from intracellular pathogens, emerging viral diseases such as COVID‐19, or cancer cells to induce humoral and cellular immune responses against the antigens.Item Open Access Design and synthesis of self-assembling peptides for fabrication of functional nanomaterials(Bilkent University, 2016-12) Khalily, Mohammad ArefSelf-assembling peptides are a class of supramolecular polymers, which exploit noncovalent interactions such as hydrogen bonding, hydrophobic, electrostatic, charge-transfer complex, π-π, and van der Waals interactions to generate well-defined supramolecular nanostructures including nanospheres, nanosheets, nanotubes, and nanofibers. These versatile peptide-based supramolecular nanomaterials have been utilized in variety of applications including catalysis, sensing, light harvesting, optoelectronic, bioelectronic and tissue engineering. In this thesis, use of supramolecular peptide nanofibers formed by specially designed short peptide sequences that can form sheet-like hydrogen bonded structures for controlled synthesis of nanometer scale functional materials were explored. Specifically, n-type and p-type β-sheet forming short peptide sequences were synthesized, which assemble separately into well-ordered nanofibers in aqueous media. These p-type and n-type nanofibers coassemble via hydrogen bonding and electrostatic interactions to generate highly uniform supramolecular n/p-coassembled 1D nanowires. This smart molecular design ensures alternating arrangement of D and A chromophores within n/p-coassembled supramolecular nanowires. Supramolecular n/p- coassembled nanowires were found to be formed by alternating A-D-A unit cells having an association constant of (KA) of 5 x 105 M-1. Moreover, I designed and synthesized β-sheet forming peptide nanofibers to fabricate different metal and metal oxide nanostructures in highly controlled manner using wet chemistry and atomic layer deposition techniques. These hybrid organic-inorganic nanostructures were employed in model Suzuki coupling, alkyne-azide cycloaddition and hydrolysis of ammonia borane reactions.Item Embargo Membrane based electrospun poly cyclodextrin nanofibers coated with ZnO nanograins by ALD Ultrafiltration blended photocatalysis for degradation of organic micropollutants(Elsevier, 2023-11-15) Ranjith, Kugalur Shanmugam; Yıldız, Zehra İrem; Khalily, Mohammad Aref; Huh, Y. S.; Han, Y.; Uyar, TamerMembranes with simultaneous selective adsorption functionality and excellent photocatalytic response have been proposed for water remediation, especially for treating textile and industrial wastewater. However, state-of-the-art membranes are easily fouled by pollutant adsorption that impacts their reusability. Here we report the development of a crosslinked electrospun poly-cyclodextrin (Poly-CD) nanofiber (NF) membrane coated by atomic layer deposition (ALD) with ZnO nanograins for the removal of pollutants from wastewater. The inherent high affinity of poly-CD NFs favored the selective adsorption of cationic impurities, and the reactive oxygen species produced by photoirradiation of the ZnO surface effectively degraded adsorbed contaminants. The NFMs has signifies that, even under the dark, they have a removal efficiency of around 80% which may be due to the high adsorption nature. Further, these NFM are highly reusable while decorating the ZnO nanograins on the NFM, which degraded the adsorbed pollutant and opened up the active site to further adsorb the dye molecule on the poly-CD surface. Under the static mode, the ZnO(100)@poly-CD NFM achieved the highest MB removal efficiency of 94.3%, followed by ZnO(25)@poly-CD, ZnO(200)@poly-CD, and poly-CD, which had removal rates of 91.3%, 87.7%, and 83.1%, respectively in 120 min of photoirradiation. Modulating the photocatalytic reaction in a flow channel, ZnO(100)@poly-CD nanofibrous membranes (NFMs) achieved 2.19-fold higher removal efficiencies (98.6% in 60 min) in a flow-through filtration system than under static conditions (a non-filtration method). Furthermore, the flow-through mode promoted the mass transfer of pollutants through NFMs, which increased reactive oxygen species production by inhibiting electron-hole recombination. Furthermore, the inherent self-cleaning function conferred by the photocatalytic activity of surface ZnO increased membrane structural stability and provided a faster removal rate.