Researcher:
Balkan, Timuçin

Profile Picture
ORCID

Job Title

Other

First Name

Timuçin

Last Name

Balkan

Name

Name Variants

Balkan, Timuçin

Email Address

Birth Date

Filters

2020 - 202315

Advanced Search

Filter by

Settings

Researcher Of Publications: search.filters.isAuthorOfPublication.1dc1eb18-03f0-424c-95d1-c3faa8ddbf2c

Search Results

Now showing 1 - 10 of 15
  • Placeholder
    PublicationMetadata only
    Controlling oxygen reduction reaction activities of Ag@Pt core-shell nanoparticles via tuning of ag in the surface layer
    (Wiley-VCH, 2023) Savaci, Umut; Turan, Servet; N/A; N/A; N/A; Department of Chemistry; Department of Chemistry; Aksoy, Dilan; Karakaya, Cüneyt; Balkan, Timuçin; Metin, Önder; Kaya, Sarp; PhD Student; PhD Student; Other; Faculty Member; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; College of Sciences; College of Sciences; N/A; N/A; N/A; 46962; 116541
    Herein, the effect of Pt shell thickness and Ag content in the surface layer on the oxygen reduction reaction activities of Ag@Pt core@shell nanoparticles (NPs) is discussed. Ag@Pt NPs are synthesized via the seeded-growth method, where colloidal Ag NPs are first synthesized and used as seeds for the growth of Pt. Electrochemical activity measurements in alkaline media show a remarkable dependency between the Ag content in the shell and the oxygen reduction reaction (ORR) activity, where the overpotentials required for -1.0 mA cm(-2) drop gradually, that is, 0.72, 0.77, and 0.80 V-RHE for Ag@Pt-25, Ag@Pt-35, and Ag@Pt-45, respectively. Tafel analysis also confirms this dependency with 73.5 mV dec(-1) for Ag@Pt-25, 71.3 mV dec(-1) for Ag@Pt-35, and 68.8 mV dec(-1) for Ag@Pt-45. A combination of the high-resolution transmission electron microscope, X-ray photoelectron spectroscopy, and X-Ray diffraction analysis shows an increase of the Pt shell thickness. It is shown that the absence of Pt-H adsorption/desorption peaks in cyclic voltammetry of Ag@Pt NPs is correlated with Ag in the surface layer, which plays an important role in the ORR activity due to the blockage of Pt(111) terrace sites. Rate-limiting first-electron transfer to oxygen is facilitated by decreasing Ag amount at the surface.
  • Placeholder
    PublicationMetadata only
    Surfactant-free synthesis of CdS nanorods for efficient reduction of carcinogenic Cr(VI)
    (Taylor and Francis Ltd, 2021) Butler, Ian S.; Rehman, Zia Ur; N/A; N/A; Department of Chemistry; Ullah, Haseeb; Balkan, Timuçin; Kaya, Sarp; Researcher; Other; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); N/A; N/A; College of Sciences; N/A; N/A; 116541
    Hexavalent chromium, Cr(VI), is a toxic, mutagenic and carcinogenic species. We report here the semiconductor-based, photocatalytic reduction of Cr(VI) to trivalent chromium, Cr(III), using CdS nanorods (NRs) as the photocatalyst under visible light illumination. The CdS NRs were synthesized by a facile and scalable solvothermal method in which ethylenediamine acts as solvent and morphology controller. The CdS NRs produced were studied by PXRD, Raman, FESEM, EDX, XPS, PL, UV-visible DRS and BET techniques in order to investigate their structural, morphological and optical properties, as well as their porosity. The photoreduction of Cr(VI) to Cr(III) under visible light illumination was performed under a variety of conditions, i.e., varying the irradiation time, pH, substrate concentration, and the amount of photocatalyst. The maximum photoreduction of Cr(VI) to Cr(III) (99%) was achieved using 60 min of irradiation under acidic conditions (pH 4). The excellent photoreduction ability of the CdS NRs can be attributed to their rod-like structure together with their small particle size, large surface area, and clean surfaces. These properties enhanced separation of the photo-generated electron-hole pairs, which was confirmed by the XRD, BET, and PL measurements. In addition, the results of a kinetic study indicated that the photoreduction of Cr(VI) to Cr(III) follows a pseudo-first-order kinetic model. A possible mechanism for the photocatalytic reduction of Cr(VI) to Cr(III) is also proposed in this paper.
  • Placeholder
    PublicationMetadata only
    Enhanced electron transport induced by a ferroelectric field in efficient halide perovskite solar cells
    (Elsevier, 2020) Askari, Masoud; Halali, Mohammad; Department of Chemistry; N/A; N/A; Department of Chemistry; Zarenezhad, Hamaneh; Solati, Navid; Balkan, Timuçin; Kaya, Sarp; Researcher; PhD Student; Other; Faculty Member; Department of Chemistry; N/A; N/A; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); N/A; College of Sciences; Graduate School of Sciences and Engineering; N/A; College of Sciences; N/A; N/A; N/A; 116541
    Perovskite solar cells have been appearing as a superior photovoltaic device owing to their high photovoltaic performance and low cost of fabrication. The formation of a compact and uniform perovskite layer with large crystal size is a significant factor to get the best device performance. In this work, polyvinylidene difluoride (PVDF) was used as a ferroelectric polymer additive to fabricate high-performance mesoporous CH3NH3PbI3-xClx mixed-halide perovskite solar cells in a sequential deposition method. Power conversion efficiency has been enhanced from 10.4 to 16.51% in an ambient atmosphere in the presence of an optimized amount of PVDF assuring continuous and smooth layers with large grain size. Besides morphological improvements, this progress in the photovoltaic performance is attributed to the dipole field exerted by PVDF that leads to enhanced charge separation. Further improvements in efficiency (18.60%) have been achieved by directing the dipoles under an external field.
  • Placeholder
    PublicationMetadata only
    Mesoporous molybdenum sulfide-oxide composite thin-film electrodes prepared by a soft templating method for the hydrogen evolution reaction
    (American Chemical Society (ACS), 2022) Savaç, Umut; Keleş, Emre; Turan, Servet; N/A; N/A; N/A; Department of Chemistry; Karakaya, Cüneyt; Solati, Navid; Balkan, Timuçin; Kaya, Sarp; PhD Student; PhD Student; Other; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; College of Sciences; N/A; N/A; N/A; 116541
    Electrode designs involving binder-free nanoparticles integrated within interconnected pore networks are critical in scaling up electrolyzers. MoS2 is the most promising electrocatalyst candidate that can show hydrogen evolution reaction (HER) activity comparable to platinum (Pt). Herein, a facile one-step soft templating method was developed to synthesize mesoporous molybdenum sulfide-oxide composite thin-film electrocatalysts directly on any substrate without using a binder or a template. Fabricated electrocatalysts contain amorphous MoS3 and small crystallite-sized MoS2 embedded into amorphous MoO3 with a large surface area (around 182 m(2)/g). The electrocatalyst layer undergoes in situ electrochemical activation in which amorphous MoS3 is reduced to MoS2 during the HER in acidic media. The electrocatalyst layer on the carbon fiber exhibits a low overpotential (similar to 189 mV at 10 mA/cm(2)) and Tafel slope (53 mV/dec) toward the HER after electrochemical activation.
  • Placeholder
    PublicationMetadata only
    Ag/AgCl clusters derived from AgCu alloy nanoparticles as electrocatalysts for the oxygen reduction reaction
    (Royal Society of Chemistry (RSC), 2022) Harfouche, Messaoud; N/A; N/A; N/A; Department of Chemistry; Department of Chemistry; Balkan, Timuçin; Küçükkeçeci, Hüseyin; Aksoy, Dilan; Metin, Önder; Kaya, Sarp; Other; Master Student; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; 46962; 116541
    The structural changes induced by the selective dealloying of bimetallic alloy electrocatalysts could have a significant impact on the kinetics of the oxygen reduction reaction (ORR). Herein, we show that the activity of bimetallic AgCu alloy nanoparticles (NPs) towards the ORR can be enhanced by dealloying Cu in an acidic medium. A combination of core-level X-ray spectroscopy and X-ray diffraction investigations with scanning electron microscopy reveals that dealloying in HCl performed on annealed AgCu alloy NPs leads to the formation of relatively large nanostructures composed of Ag/AgCl. The initial composition of AgCu alloy NPs and the extent of the AgCl formation on Ag surfaces have a significant effect on the ORR activity. Furthermore, the formation of the active surface structure strongly depends on the initial composition of alloy NPs. Ag decorated with AgCl formed after dealloying Ag7Cu3 alloy NPs presents a superb ORR activity with a high onset potential (E-0) of approximate to 0.97 V vs. RHE, comparable to commercial Pt/C catalysts and outperforms dealloyed Ag3Cu2 and pristine Ag electrocatalysts. We suggest that Ag+ stabilized in the presence of sub-stoichiometric Cl- plays a critical role in the superior activity of the catalyst.
  • Placeholder
    PublicationMetadata only
    Green synthesis of mesoporous MoS2 nanoflowers for efficient photocatalytic degradation of Congo red dye
    (Taylor & Francis, 2021) Khan, Zaibunisa; Nasir, Jamal Abdul; Butler, Ian S.; Rehman, Zia Ur; N/A; Department of Chemistry; N/A; Ullah, Haseeb; Kaya, Sarp; Balkan, Timuçin; N/A; Faculty Member; Other; Department of Chemistry; N/A; College of Sciences; N/A; N/A; 116541; N/A
    A one-step, facile and scalable hydrothermal route was employed to synthesize molybdenum disulfide (MoS2) nanoflowers (NFs) for use in the photodegradation of Congo red (CR) dye. The phase purity, morphology, and structural features of the produced mesoporous MoS2-NFs were examined using PXRD, FESEM, EDX, XPS, BET, Raman and UV-visible DRS techniques. The nitrogen adsorption-desorption isotherms display a clear H-3-type of hysteresis loop at P/P-o of 0.8-1.0, which affords an insight into the mesoporous nature of the MoS2 NFs with a pore diameter of 1.5 to 40 nm. The mesoporous MoS2 NFs showed excellent CR degradation activity under solar light irradiation with a K-app of 0.76 x 10(-2 )min(-1). Importantly, the results showed a notable impact of reaction media on the degradation of CR suggesting that pH 7 is a favorable medium for this particular catalytic reaction. A kinetic study has illustrated that photodegradation of CR follows pseudo-first order kinetics. This work illustrates that mesoporous MoS2 NFs can be used as an efficient photocatalyst for the degradation of highly toxic and hazardous organic dyes in environmental remediation.
  • Placeholder
    PublicationMetadata only
    One -pot synthesis of monodisperse copper -silver alloy nanoparticles and their composition -dependent electrocatalytic activity for oxygen reduction reaction
    (Elsevier Science Sa, 2020) N/A; N/A; Department of Chemistry; Department of Chemistry; Department of Chemistry; Balkan, Timuçin; Küçükkeçeci, Hüseyin; Zarenezhad, Hamaneh; Kaya, Sarp; Metin, Önder; Other; Researcher; Researcher; Faculty Member; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; N/A; 116541; 46962
  • Placeholder
    PublicationMetadata only
    Scaling-up photocatalytic activity of CdS from nanorods to nanowires for the MB degradation
    (Elsevier, 2021) Rehman, Zia ur; N/A; N/A; N/A; Department of Chemistry; Ullah, Haseeb; Barzgarvishlaghi, Mahsa; Balkan, Timuçin; Kaya, Sarp; Researcher; PhD Student; Other; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); N/A; Graduate School of Sciences and Engineering; N/A; College of Sciences; N/A; N/A; N/A; 116541
    The development of a scalable and facile method for the synthesis of visible light driven photocatalytic materials to degrade toxic organic dyes is highly challenging and essential. In this regards, cadmium sulfide (CdS) nanorods and nanowires with controlled aspect ratio, grain size, surface area, and bandgap were synthesized by a simple solvothermal method, and their photocatalytic performances were exploited for the photo-degradation of methylene blue (MB) under simulated solar light. Extensive structural characterizations to identify the origin of the activities were performed. The photocatalytic activity measurements showed that the degradation of MB was 94.41%, 97.24%, 97.88%, and 99.82% for CdS prepared by following four different synthesis routes and increasing trend showed a correlation with the nanostructure morphology changing from nanorod and nanowires with increasing aspect ratio. It has been found that CdS nanowires show more pronounced photocatalytic activity due to the efficient separation of photo-generated electron-hole pairs induced by increased the aspect ratio and higher active surface area.
  • Placeholder
    PublicationMetadata only
    Voriconazole incorporated nanofiber formulations for topical application: preparation, characterization and antifungal activity studies against candida species
    (Taylor & Francis, 2020) Esenturk, Imren; Ozhan, Guel; Doesler, Sibel; Gungor, Sevgi; Erdal, M. Sedef; Sarac, Abdulkadir Sezai; N/A; Balkan, Timuçin; Other; N/A; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); N/A
    In this study, voriconazole (VCZ) incorporated polyvinyl alcohol/sodium alginate electrospun nanofibers were produced and, then crosslinked with glutaraldehyde for topical antifungal treatment. The nanofibers were characterized in terms of fiber size, surface morphology, and compatibility between drug-polymer and polymer-polymer using scanning electron microscopy, atomic force microscopy, attenuated total reflection-Fourier transform infrared spectroscopy, and high pressure liquid chromatography. After optimization studies, in vitro drug release, skin penetration, and deposition studies were performed using Franz diffusion cells. Antifungal activities of the nanofiber formulations against Candida albicans, Candida tropicalis, and Candida parapysilosis strains were evaluated using susceptibility test and subsequently time-kill study was performed against C. albicans. The cytotoxicity study was performed using 4-succinate dehydrogenase viability assay on mouse fibroblast cell line. The release rate of VCZ from crosslinked nanofibers was slower than that of non-crosslinked nanofibers and Higuchi kinetic model best fitted to the in vitro release data of both of formulations. VCZ deposited in deeper skin layers from nanofiber formulations was higher than that of the control formulation (VCZ solution in propylene glycol (1% (w/v)). According to the susceptibility and time-kill studies, all of the nanofiber formulations showed antifungal activity against C. albicans with confirming no cytotoxicity on mouse fibroblast cells.
  • Placeholder
    PublicationMetadata only
    Efficient carrier utilization induced by conductive polypyrrole additives in organic-inorganic halide perovskite solar cells
    (Pergamon-Elsevier Science Ltd, 2020) Halali, Mohammad; Askari, Masoud; N/A; N/A; N/A; Department of Chemistry; Zarenezhad, Hamaneh; Balkan, Timuçin; Solati, Navid; Kaya, Sarp; Other; Other; Other; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A; N/A; N/A; College of Sciences; N/A; N/A; N/A; 116541
    The morphology of the perovskite layer, the effective extraction of the charge carriers, and their transport are the main factors determining the power conversion efficiency (PCE) of the perovskite solar cells (PSCs). In this work, we demonstrated that the geometric and electronic structures of the PSCs could be modified by using a conductive polymer additive in the lead (Pb) halide layer prepared by a two-step deposition method. Polypyrrole (PPy) as a conductive polymer is used in the perovskite layers which could increase the PCE of CH3NH3PbI3-xClx mixed-halide PSCs. By adding an optimized amount of PPy, PCE has been raised from 10.4 to 13.2%. PPy acts as a conductive channel facilitating the extraction of the charge carriers and easing their transport in the perovskite layer. The crystallization is also affected by PPy which is advantageous to form smooth perovskite layers with fewer voids.