Browsing by Author "Patil, Bhushan"
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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 Electrospun cyclodextrin nanofibers as precursor for carbon nanofibers(Springer, 2020) Patil, Bhushan; Yıldız, Zehra İrem; Uyar, TamerThe carbon nanofibers (CNF) based on the electrospun polymer-free hydroxypropyl-β-cyclodextrin (HPβCD) nanofibers were obtained by the combination of chemical and thermal (pyrolysis) treatment. The thermal and chemical decomposition of HPβCD makes it challenging to obtain persistent CNF from HPβCD nanofibers. The chemical treatment of HPβCD nanofibers by using 0.6 mM H2SO4 partially dissolves nanofibers and resulted in fused CNF while direct pyrolysis of HPβCD nanofibers totally ruins the nanofiber structure and produces char. The partial chemical treatment of HPβCD nanofibers with 10 µM H2SO4 dehydrates the top layer of the nanofibers, and a shield-like structure is formed which helps to retain the fibrous morphology during the pyrolysis. The diameter of HPβCD nanofibers was reduced after carbonization process where CNF having average diameter of 380 ± 150 nm were obtained. The presence of typical D and G Raman bands and XRD peak at 2θ ~ 26° further validates CNF formation from HPβCD nanofibers. The oxygen content is decreased from 34.7 to 5.8%, and carbon content increased from 62.3% to 94.2% after transformation of HPβCD nanofibers into CNF. To the best of our knowledge, for the first time, this study reports the use of electrospun polymer-free HPβCD nanofibers as a precursor to produce CNF.Item 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 Hydrochromic carbon dots as smart sensors for water sensing in organic solvents(Royal Society of Chemistry, 2019-10) Senthamizhan, A.; Fragouli, D.; Balusamy, B.; Patil, Bhushan; Palei, M.; Sabella, S.; Uyar, Tamer; Athanassiou, A.Smart, stimuli-responsive, photoluminescent materials that undergo a visually perceptible emission color change in the presence of an external stimulus have long been attractive for use in sensor platforms. When the stimulus is the presence of water, the materials that undergo changes in their light emission properties are called hydrochromic and they can be used for the development of sensors to detect and quantify the water content in organic solvents, which is fundamental for laboratory safety and numerous industrial applications. Herein, we demonstrate the preparation of structurally different carbon dots with tunable emission wavelengths via a simple carbonization approach under controlled temperature and time, involving commercial brown sugar as a starting material. The detailed experimental analysis reveals the “structure-hydrochromic property” relationship of the carbon dots and assesses their capability as effective water sensors. The carbon dots that were proved most efficient for the specific application were then used to identify the presence of water in various aprotic and protic organic solvents via a sensing mechanism based either on the fluorescence wavelength shift or on the fluorescence intensity enhancement, respectively, attributed to the formation of intermolecular hydrogen bonds between carbon dots and water molecules. This is the first demonstration of structurally defined carbon dots in a specific application. The developed carbon dots, apart from being environmentally friendly, were proved to also be biocompatible, enabling this presented process to be a path to “green” sensors.Item Open Access Influence of various sol-gel parameters on the physico‐chemical properties of sulfuric acid chelated zirconia aerogels dried at ambient pressure(Wiley-VCH Verlag, 2020) Bangi, U. K. H.; Patil, Bhushan; Pawar, R. C.; Park, H.-H.This work represents the influence of various sol–gel parameters on the physico‐chemical properties of sulfuric acid chelated zirconia aerogels dried at ambient pressure. The sol–gel parameters such as concentrations of precursor, chelating agent and catalyst are found to be the dominant factors which influence the physical, chemical and textural properties of the aerogels. Therefore, the influence of concentration of Zr precursor, ZrPr:H2SO4 molar ratio and ZrPr:H2O molar ratio on these properties of zirconia aerogels is studied. Zirconia lacogels are formed by the hydrolysis and condensation of zirconium n‐propoxide in n‐propanol chelated with sulfuric acid (18.4 M) and catalyzed with deionized water. Aerogels are obtained by subsequent solvent exchange, silylation, washing and ambient pressure drying. The physico‐chemical properties of as synthesized zirconia aerogels are carried out using FESEM, EDS, BET analysis and FTIR spectroscopy. The good quality zirconia aerogels are obtained using the molar ratio of ZrPr:PrOH:H2SO4:H2O:HMDZ::1:2.93:1.18:1.77:0.59. They possess the density of 0.54 g cm‐3, BET surface area of 328 m2 g‐1 and micropore volume of 0.028 cm3 g‐1. These aerogels can be applied as heterogeneous catalysts in many fields.Item Open Access Metal-free N-doped ultrafine carbon fibers from electrospun Polymers of Intrinsic microporosity (PIM-1) based fibers for oxygen reduction reaction(Elsevier, 2020) Patil, Bhushan; Satılmış, Bekir; Uyar, TamerSynthesis 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.Item Open Access Novel supramolecular photocatalyst based on conjugation of cucurbit[7]uril to non-metallated porphyrin for electrophotocatalytic hydrogen generation from water splitting(WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Kumar, Yogesh; Patil, Bhushan; Khaligh, Aisan; Hadi, Seyed E.; Uyar, Tamer; Tuncel, DönüşVisible‐light triggerable, stable, organic material‐based photocatalysts that can function in alkaline media without the necessity of sacrificial agent for hydrogen production are highly sought after. Here, we report a novel supramolecular photocatalyst that confers the aforementioned features. This supramolecular photocatalyst (TPP‐4CB7) is synthesized through the conjugation of monohydroxylated cucurbit(7)uril (CB7) hosts to a suitably substituted tetraphenyl porphyrin. Although TPP‐4CB7 by its own preforms as an efficient visible light triggered photocatalyst, the hydrogen production efficiency is significantly enhanced upon mixing with TiO2. The resulting nanocomposite (TPP‐CB‐TiO2@Pt) is observed to exhibit remarkable electrophotocatalytic activity under visible light and produces hydrogen (onset potential −10 mV, turn over frequency (TOF) 0.202 s−1, 24.5 mmol h−1 g−1) from water splitting without any significant degradation during four runs (5 h each) in alkaline media and in the absence of sacrificial agent.Item Open Access Novel supramolecular photocatalyst based on conjugation of cucurbit[7]uril to non-metallated porphyrin for electrophotocatalytic hydrogen generation from water splitting (WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Kumar, Yogesh; Patil, Bhushan; Khaligh, Aisan; Hadi, Seyed E.; Uyar, Tamer; Tuncel, DönüşThe front cover artwork for Issue 13/2019 is provided by Tuncel and co‐workers at UNAM and the Chemistry Department of Bilkent University (Turkey). The image shows solar energy promoted photoelectrocatalytic water splitting for hydrogen generation using a supramolecular photocatalyst. See the Communication itself at https://doi.org/10.1002/cctc.201900144.Item Open Access Structural, optical, electrical and electrocatalytic activity properties of luminescent organic carbon quantum dots(Wiley-Blackwell, 2018) Karatutlu, Ali; Patil, Bhushan; Şeker, İ.; İstengir, S.; Bolat, A.; Yıldırım, O.; Sevgen, Y. N.; Bakış, Y.; Ortaç, Bülend; Yılmaz, Eda; Sapelkin, A.Carbon is an essential element in human life and recently becoming technologically prominent due to the emerging field of “Carbononics”. We demonstrate organic carbon quantum dots (qdots) containing nitrile bonded (C≡N bond) d-glucose-like traces in various sizes obtained from wheat flour to be promising for imaging applications and to possess a relaxor ferroelectric property and an enhanced electrocatalytic activity that could reduce the cost of energy devices and simple to scale up for the commercialization. The secondary electron microscopy (SEM) imaging shows that the particle size of carbon qdots can be controlled via the sonication exposure time. Elemental analysis and vibrational spectroscopy results show that carbon qdots are sensitive to N2 gas in the atmosphere and could weaken its “carbogenic” property by making a stable C≡N bond at ambient atmosphere. Rietveld analysis and HR-TEM studies demonstrate that the structure of the C qdots was found to fit best with an acentric primitive orthorhombic lattice. The laser scanning confocal microscopy (LSCM) images show enhancement of the light emission when reducing the size and characteristic excitation wavelength-dependent light emission of C qdots. The photoluminescence and UV-Vis absorption spectroscopy techniques show surface dominant emission and absorption upon the nitrile bonding.