Fatin Saiha Omar

Graphene and its nanocomposite material based electrochemical sensor platform for dopamine

Dopamine (DA) is an important catecholamine neurotransmitter in the mammalian central nervous system that influences several physiological functions. The impact of DA levels within the human body significantly affects the body functions. Maintaining DA level is essential and the electrochemical detection methods are often used to detect the DA level to regulate the body function. In this review, graphene (functionalized graphene and N-doped graphene) and its composites (metal, metal oxide, polymer, carbonaceous materials, clay, zeolite, and metal–organic framework based graphene composites) modified electrodes with their improved sensing performance towards DA along with several interfering species are described. Further, recent developments on the fabrication of various graphene based composite modified electrodes are also presented. Some important strategies to improve the selectivity and sensitivity towards DA with graphene based composite modified electrodes are also described.

Microwave Synthesis of Zinc Oxide/Reduced Graphene Oxide Hybrid for Adsorption-Photocatalysis Application

This work reports on synthesis of zinc oxide/reduced graphene oxide (ZnO/rGO) nanocomposites in the presence of diethylenetriamine (DETA) via a facile microwave method. The X-ray diffraction (XRD) patterns of the nanocomposites correspond to the ZnO hexagonal phase wurtzite structure. The high-resolution transmission electron microscopy (HRTEM) images revealed that the ZnO nanorods, with an average length : diameter ratio of 10, were successfully deposited on the rGO sheets. Under the irradiation of sunlight, the nanocomposites showed enhanced adsorption-photocatalysis by more than twofold and photocurrent response by sixfold compared to the ZnO. The excellent photoactivity performance of the nanocomposites is contributed by smaller ZnO nanorod and the presence of rGO that acts as a photosensitizer by transferring electrons to the conduction band of ZnO within the nanocomposite during sunlight illumination.

Improved Synthesis of Reduced Graphene Oxide-Titanium Dioxide Composite with Highly Exposed 001 Facets and Its Photoelectrochemical Response

Crystal facet engineering has attracted worldwide attention, particularly in facet manipulation of titanium dioxide (TiO2) surface properties. An improved synthesis by solvothermal route has been employed for the formation of TiO2 with highly exposed facets decorated on reduced graphene oxide (RGO) sheets. The RGO-TiO2 composite could be produced with high yield by following a stringently methodical yet simple approach. Field emission scanning electron microscope and high resolution transmission electron microscope imaging reveal that the structure consists of TiO2 nanoparticles covered with TiO2 nanosheets of exposed facets on a RGO sheet. The photocurrent response of the RGO-TiO2 composite was discovered to outperform that of pure TiO2, as a ~10-fold increase in photocurrent density was observed for the RGO-TiO2 electrodes. This may be attributed to rapid electron transport and the delayed recombination of electron-hole pairs due to improved ionic interaction between titanium and carbon.

Enhanced electrochemical performance of cobalt oxide nanocube intercalated reduced graphene oxide for supercapacitor application

We investigated different molar concentrations of cobalt precursor intercalated reduced graphene oxide (rGO) as possible electrode materials for supercapacitors. Cobalt oxide (Co3O4) nanocubes intercalated reduced graphene oxides (rGO) were synthesized via a facile hydrothermal method. It has been found that the Co3O4 particles with a cubical shape are decorated on rGO matrix with an average size of ∼45 nm. The structural crystallinity of rGO–Co3O4 composites was examined by X-ray diffraction (XRD). Raman spectroscopy confirmed the successful reduction of GO to rGO and effective interaction between Co3O4 and the rGO matrix. The electrochemical performances of rGO–Co3O4 electrodes were examined using cyclic voltammetry and charge–discharge techniques. The maximum specific capacitance (278 F g−1) is observed at current density of 200 mA g−1 in the C2 electrode resulting from effective ion transfer and less particle aggregation of Co3O4 on the rGO matrix than in the other electrodes. C2 exhibits good rate capability and excellent long-term cyclic stability of 91.6% for 2000 cycles. The enhanced electrochemical performance may result from uniform intercalation of cobalt oxide over the rGO. These results suggest that the Co3O4 intercalated rGO matrix could play a role in improved energy storage capability.

Conducting polymer and its composite materials based electrochemical sensor for Nicotinamide Adenine Dinucleotide (NADH).

Nicotinamide Adenine Dinucleotide (NADH) is an important coenzyme in the human body that participates in many metabolic reactions. The impact of abnormal concentrations of NADH significantly causes different diseases in human body. Electrochemical detection of NADH using bare electrode is a challenging task especially in the presence of main electroactive interferences such as ascorbic acid (AA), uric acid (UA) and dopamine (DA). Modified electrodes have been widely explored to overcome the problems of poor sensitivity and selectivity occurred from bare electrodes. This review gives an overview on the progress of using conducting polymers, polyelectrolyte and its composites (co-polymer, carbonaceous, metal, metal oxide and clay) based modified electrodes for the sensing of NADH. In addition, developments on the fabrication of numerous conducting polymer composites based modified electrodes are clearly described.

Ultrahigh capacitance of amorphous nickel phosphate for asymmetric supercapacitor applications

This article presents the effect of different calcination temperatures on the structural, morphological and capacitance of nickel phosphate (Ni3(PO4)2) as an electrode material for supercapacitor applications. Ni3(PO4)2 was synthesized via a sonochemical method followed by calcination at different temperatures (300, 600 and 900 °C, denoted as N300, N600 and N900, respectively). The phase structure and purity of Ni3(PO4)2 were confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The surface morphologies showed that the particle size increased with increasing the calcination temperatures. The electrochemical performance of N300, N600 and N900 were investigated using cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) in a 1 M KOH electrolyte. It was found that N300 exhibited the maximum specific capacity of 620 C g−1 at 0.4 A g−1, which was significantly higher than N600 (46 C g−1) and N900 (14 C g−1). Here, the enhanced electrochemical performance was obtained due to the amorphous structure and augmentation of the redox active sites of the N300 particles. Additionally, the fabricated N300//activated carbon based asymmetric supercapacitor can be cycled reversibly at a cell voltage of 1.45 V. The device exhibited an energy density of 76 W h kg−1 and a power density of 599 W kg−1 with life cycles of 88.5% capacitance retention after 3000 cycles.

Binary nanocomposite based on Co3O4 nanocubes and multiwalled carbon nanotubes as an ultrasensitive platform for amperometric determination of dopamine

AbstractComposites containing cobalt oxide (Co3O4) nanocubes integrated with multiwall carbon nanotubes (MWCNT) were synthesized by a hydrothermal route. The fractions of MWCNTs in the composite were varied from 4, 8, 12, 16 and 20 wt.%, and the resulting materials are denoted as C1, C2, C3, C4 and C5, respectively. The formation of products with high structural crystallinity was confirmed by X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray diffraction. A morphological study by field emission scanning electron microscopy and high resolution transmission electron microscopy showed the successful integration of Co3O4 nanocubes to the MWCNTs with an average particle size of ∼32 nm. The surface of a glassy carbon electrode (GCE) was modified with the nanocomposites in order to evaluate the electrochemical performance of the nanocomposites. Cyclic voltammetry showed that the C4-modified GCE displays best performance in terms of oxidation potential and peak current in comparison to that of a bare GCE, Co3O4 nanocubes, or GCEs modified with C1, C2, C3 or C5. The detection limit (at an S/N ratio of 3) is 0.176 nM by using chronoamperometry, and the linear range is between 1 and 20 μM. Graphical abstractMWCNT-Co3O4 nanocubes were synthesized by one pot hydrothermal route. The nanocomposite is used for electrochemical detection of dopamine. The limit of detection is found to be 176 nM by chronoamperometry at a constant potential of + 0.13 V.

Hierarchical Si/ZnO trunk-branch nanostructure for photocurrent enhancement

Hierarchical Si/ZnO trunk-branch nanostructures (NSs) have been synthesized by hot wire assisted chemical vapor deposition method for trunk Si nanowires (NWs) on indium tin oxide (ITO) substrate and followed by the vapor transport condensation (VTC) method for zinc oxide (ZnO) nanorods (NRs) which was laterally grown from each Si nanowires (NWs). A spin coating method has been used for zinc oxide (ZnO) seeding. This method is better compared with other group where they used sputtering method for the same process. The sputtering method only results in the growth of ZnO NRs on top of the Si trunk. Our method shows improvement by having the growth evenly distributed on the lateral sides and caps of the Si trunks, resulting in pine-leave-like NSs. Field emission scanning electron microscope image shows the hierarchical nanostructures resembling the shape of the leaves of pine trees. Single crystalline structure for the ZnO branch grown laterally from the crystalline Si trunk has been identified by using a lattice-resolved transmission electron microscope. A preliminary photoelectrochemical (PEC) cell testing has been setup to characterize the photocurrent of sole array of ZnO NR growth by both hydrothermal-grown (HTG) method and VTC method on ITO substrates. VTC-grown ZnO NRs showed greater photocurrent effect due to its better structural properties. The measured photocurrent was also compared with the array of hierarchical Si/ZnO trunk-branch NSs. The cell with the array of Si/ZnO trunk-branch NSs revealed four-fold magnitude enhancement in photocurrent density compared with the sole array of ZnO NRs obtain from VTC processes.

The Effect of Incorporation of Multi-Walled Carbon Nanotube into Poly(Ethylene Oxide) Gel Electrolyte on the Photovoltaic Performance of Dye-Sensitized Solar Cell

ABSTRACT Gel polymer electrolytes (GPEs) consist of poly(ethylene oxide) (PEO), sodium iodide (NaI) and different amount of multi-walled carbon nanotubes (MWCNT) were prepared. The conductivity study revealed that the highest ionic conductivity of GPE was 7.02 × 10−3 S cm−1. The structural and complexation between the materials are authenticated via X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Under the exposure of AM 1.5, the fabricated DSSCs exhibited the highest photoenergy conversion efficiency of 7.23% with a short circuit current density (JSC) of 18.64 mA cm−2, open circuit voltage (VOC) of 0.590 mV and fill factor (FF) of 65.7%. GRAPHICAL ABSTRACT GRAPHICAL ABSTRACT

CoCl2-doped polyaniline composites as electrode materials with enhanced electrochemical performance for supercapacitor application

HCl-doped polyaniline (PANI) and polymeric composites of polyaniline–cobalt chloride (PANI–CoCl2) were synthesized in the laboratory via an in situ oxidative polymerization technique. Their chemical, structural and morphological properties were examined through FESEM, XRD, EDX and FTIR spectroscopic techniques. The electrochemical performance of the as-prepared composites was examined through cyclic voltammogram, electrochemical impedance spectroscopy and galvanostatic charge/discharge measurement techniques. The thermal properties of the as-prepared composites were examined through thermal gravimetric analysis technique. The results obtained were found satisfactory and well suitable for its use as hybrid electrode materials for supercapacitor application.