Ersan Harputlu

High-Capacitance Hybrid Supercapacitor Based on Multi-Colored Fluorescent Carbon-Dots

Multi-colored, water soluble fluorescent carbon nanodots (C-Dots) with quantum yield changing from 4.6 to 18.3% were synthesized in multi-gram using dated cola beverage through a simple thermal synthesis method and implemented as conductive and ion donating supercapacitor component. Various properties of C-Dots, including size, crystal structure, morphology and surface properties along with their Raman and electron paramagnetic resonance spectra were analyzed and compared by means of their fluorescence and electronic properties. α-Manganese Oxide-Polypyrrole (PPy) nanorods decorated with C-Dots were further conducted as anode materials in a supercapacitor. Reduced graphene oxide was used as cathode along with the dicationic bis-imidazolium based ionic liquid in order to enhance the charge transfer and wetting capacity of electrode surfaces. For this purpose, we used octyl-bis(3-methylimidazolium)diiodide (C8H16BImI) synthesized by N-alkylation reaction as liquid ionic membrane electrolyte. Paramagnetic resonance and impedance spectroscopy have been undertaken in order to understand the origin of the performance of hybrid capacitor in more depth. In particular, we obtained high capacitance value (C = 17.3 μF/cm2) which is exceptionally related not only the quality of synthesis but also the choice of electrode and electrolyte materials. Moreover, each component used in the construction of the hybrid supercapacitor is also played a key role to achieve high capacitance value.

Controlling the charge transfer flow at the graphene/pyrene–nitrilotriacetic acid interface

The fabrication of highly efficient bio-organic nanoelectronic devices is still a challenge due to the difficulty in interfacing the biomolecular component to the organic counterparts. One of the ways to overcome this bottleneck is to add a self-assembled monolayer (SAM) in between the electrode and the biological material. The addition of a pyrene–nitrilotriacetic acid layer to a graphene metal electrode enhances the charge transfer within the device. Our theoretical calculations and electrochemical results show that the formation of a pyrene–nitrilotriacetic acid SAM enforces a direct electron transfer from graphene to the SAM, while the addition of the Ni2+ cation and imidazole reverses the charge transfer direction, allowing an atomic control of the electron flow, which is essential for a true working device.

Orientation of photosystem I on graphene through cytochrome c553 leads to improvement in photocurrent generation

We report the fabrication of an oriented bioelectrode of photosystem I (PSI) on single-layer graphene (SLG). This bioelectrode demonstrates improved photocurrent generation, which can be directly attributed to the molecular conductive interface formed by cytochrome c553 (cyt c553) promoting the uniform orientation of PSI with its donor side towards the electrode. The conductive interface between PSI-cyt c553 and SLG is facilitated by a monolayer composed of π–π-stacked pyrene functionalized with the Ni-NTA moiety, which binds the His6-tagged cyt c553. The surface uniformity of the PSI protein orientation in the electrode structure is evidenced by cross-sectional scanning electron microscopy and fluorescence microscopy, with the latter also proving the efficient electronic coupling between majority of the PSI complexes and graphene. With the uniform organization of the biological photoactive layer, photocurrents are generated at the open circuit potential, which can be further increased when a negative potential is applied. Indeed, at the highest applied negative potential (−0.3 V), over 5-fold increase in the cathodic photocurrent for the PSI complexes conjugated via cyt c553 to the SLG substrate is observed compared with that obtained for the randomly oriented structure where PSI is physisorbed on graphene. These results indicate the key role of a strictly defined orientation of photoactive proteins on electrodes for proper electron transfer and substantial improvement in photocurrent generation in the present or similar bioelectrode architectures.

Preparation and evaluation of effect on Escherichia coli and Staphylococcus aureus of radiolabeled ampicillin-loaded graphene oxide nanoflakes

Ampicillin is a one of effective antibiotics against Gram‐positive and Gram‐negative bacteria. This study aimed to label ampicillin‐loaded graphene oxide nanoflake (AMP‐GO) with 99mTc and evaluate of its in vitro binding to Staphylococcus aureus and Escherichia coli. Firstly, ampicillin was loaded into graphene oxide nanoflake prepared. AMP‐GO was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) techniques, and the amount of loaded ampicillin onto GO was determined by UV‐Vis absorption spectroscopy. AMP and AMP‐GO were labeled with 99mTc using stannous chloride reducing agent. Labeling efficiency of 99mTc‐AMP‐GO was found to be 97.66 ± 2.06%. 99mTc‐AMP‐GO has higher binding efficiencies to both S. aureus and E. coli than 99mTc‐AMP. 99mTc‐AMP‐GO could be promising candidate as agent infection nuclear imaging. Furthermore, in vivo studies of 99mTc‐AMP‐GO with infected rats are planned to be performed.

Synthesis and performance of antifouling and self-cleaning polyethersulfone/graphene oxide composite membrane functionalized with photoactive semiconductor catalyst

This study was performed to synthesize membranes of polyethersulfone (PES) blended with graphene oxide (GO) and PES blended with GO functionalized with photoactive semiconductor catalyst (TiO2 and ZnO). The antifouling and self-cleaning properties of composite membranes were also investigated. The GO was prepared from natural graphite powder by oxidation method at low temperature. TiO2 and ZnO nanopowders were synthesized by anhydrous sol-gel method. The surface of TiO2 and ZnO nanopowders was modified by a surfactant (myristic acid) to obtain a homogeneously dispersed mixture in a solvent, and then GO was functionalized by loading with these metal oxide nanopowders. The PES membranes blended with GO and functionalized GO into the casting solution were prepared via phase inversion method and tested for their antifouling as well as self-cleaning properties. The composite membranes were synthesized as 14%wt. of PES polymer with three different concentrations (0.5, 1.0, and 2.0%wt.) of GO, GO-TiO2, and GO-ZnO. The functionalization of membranes improved hydrophilicity property of membranes as compared to neat PES membrane. However, the lowest flux was obtained by functionalized membranes with GO-TiO2. The results showed that functionalized membranes demonstrated better self-cleaning property than neat PES membrane. Moreover, the flux recovery rate of functionalized membranes over five cycles was higher than that of neat membrane.