Muhammad Mehmood Shahid

An electrochemical sensing platform based on a reduced graphene oxide–cobalt oxide nanocube@platinum nanocomposite for nitric oxide detection

We report a facile one-pot hydrothermal synthesis of a reduced graphene oxide–cobalt oxide nanocube@platinum (rGO–Co3O4@Pt) nanocomposite and its application toward the electrochemical detection of nitric oxide (NO). The rGO–Co3O4@Pt nanocomposite was characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) mapping, X-ray diffraction (XRD) and Raman analyses. The nanocomposite modified glassy carbon (GC) electrode was used for the electrochemical oxidation of nitric oxide (NO) and it showed better catalytic performance in terms of catalytic peak current and shift in overpotential when compared to those of rGO, Co3O4 nanocubes and rGO–Co3O4 nanocomposite modified electrodes. The rGO–Co3O4@Pt nanocomposite modified electrode showed a better sensing ability toward the in situ generated NO in NO2− containing phosphate buffer solution (PBS) than the other controlled modified electrodes. The Pt nanoparticles present in the nanocomposite could enhance the sensing performance and the limit of detection (LOD) was found to be 1.73 μM with a signal-to-noise (S/N) ratio of ∼3 using the amperometric i–t curve technique. Furthermore, the nanocomposite modified electrode showed selectivity toward the detection of NO in the presence of a 100-fold higher concentration of other physiologically important analytes. The proposed sensor was stable, reproducible and selective toward the detection of NO.

Facile synthesis of graphene oxide–silver nanocomposite and its modified electrode for enhanced electrochemical detection of nitrite ions

In this report, silver nanoparticles (Ag NPs) were successfully deposited on graphene oxide (GO) sheets to form GO-Ag nanocomposite using garlic extract and sunlight and the nanocomposite modified glassy carbon (GC) electrode was applied as an electrochemical sensor for the detection of nitrite ions. The formation of GO-Ag nanocomposite was confirmed by using UV-visible absorption spectroscopy, TEM, XRD and FTIR spectroscopy analyses. Further, TEM pictures showed a uniform distribution Ag on GO sheets with an average size of 19 nm. The nanocomposite modified electrode produced synergistic catalytic current in nitrite oxidation with a negative shift in overpotential. The limit of detection (LOD) values were found as 2.1 µM and 37 nM, respectively using linear sweep voltammetry (LSV) and amperometric i-t curve techniques. The proposed sensor was stable, reproducible, sensitive and selective toward the detection nitrite and could be applied for the detection of nitrite in real water sample.

Synthesis of chitosan grafted-polyaniline/Co3O4 nanocube nanocomposites and their photocatalytic activity toward methylene blue dye degradation

In the present investigation, chitosan-grafted-polyaniline copolymer (ChGP) and Co3O4 nanocube-doped ChGP nanocomposites have been successfully synthesised via oxidative-radical copolymerisation using ammonium persulfate in an acidic medium for the photocatalytic degradation of methylene blue dye. The prepared nanocomposites were characterised by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). FESEM and TEM images confirmed the formation of Co3O4 nanocubes and a crosslinked polymeric network. The photocatalytic activities of ChGP and Co3O4 nanocube-doped copolymers were evaluated by monitoring the degradation of methylene blue dye under UV illumination. The degradation efficiency of the copolymer photocatalysts that were doped with Co3O4 nanocubes was higher than that of the undoped copolymer. Furthermore, the nanocomposite with 2 wt% Co3O4 nanocubes with respect to aniline was an optimum photocatalyst, with an 88% degradation efficiency after 180 minutes of irradiation under UV light.

Enhanced electrocatalytic performance of cobalt oxide nanocubes incorporating reduced graphene oxide as a modified platinum electrode for methanol oxidation

Herein, we report a facile hydrothermal method for the preparation of cobalt oxide nanocubes incorporating reduced graphene oxide (rGO–Co3O4 nanocubes) for electrocatalytic oxidation of methanol. The synthesized rGO–Co3O4 nanocubes were characterized using transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Raman techniques. The electrochemical behavior of an rGO–Co3O4 nanocube modified electrode was studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The electrocatalytic performances of rGO–Co3O4 nanocube-modified electrodes with different wt% of GO were investigated in relation to methanol oxidation in an alkaline medium. The rGO–Co3O4 nanocube modified electrode showed enhanced current density due to oxidation of methanol when compared to the bare Pt, rGO, and Co3O4 nanocube modified electrodes. The optimal GO content for an rGO–Co3O4 nanocube-modified electrode to achieve a high electrocatalytic oxidation of methanol was 2 wt%, and it showed an anodic peak current density of 362 μA cm−2.

Significantly improved photovoltaic performance in polymer bulk heterojunction solar cells with graphene oxide /PEDOT:PSS double decked hole transport layer

This work demonstrates the high performance graphene oxide (GO)/PEDOT:PSS doubled decked hole transport layer (HTL) in the PCDTBT:PC71BM based bulk heterojunction organic photovoltaic device. The devices were tested on merits of their power conversion efficiency (PCE), reproducibility, stability and further compared with the devices with individual GO or PEDOT:PSS HTLs. Solar cells employing GO/PEDOT:PSS HTL yielded a PCE of 4.28% as compared to either of individual GO or PEDOT:PSS HTLs where they demonstrated PCEs of 2.77 and 3.57%, respectively. In case of single GO HTL, an inhomogeneous coating of ITO caused the poor performance whereas PEDOT:PSS is known to be hygroscopic and acidic which upon direct contact with ITO reduced the device performance. The improvement in the photovoltaic performance is mainly ascribed to the increased charge carriers mobility, short circuit current, open circuit voltage, fill factor, and decreased series resistance. The well matched work function of GO and PEDOT:PSS is likely to facilitate the charge transportation and an overall reduction in the series resistance. Moreover, GO could effectively block the electrons due to its large band-gap of ~3.6 eV, leading to an increased shunt resistance. In addition, we also observed the improvement in the reproducibility and stability.

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.

Fabrication of CuO–1.5ZrO2 composite thin film, from heteronuclear molecular complex and its electrocatalytic activity towards methanol oxidation

A heteronuclear coordination complex [Cu4Zr6(μ-O)8(dmap)4(OAc)12]·H2O (1), where dmap = N,N-dimethylaminopropanolato and −OAc = acetato, has been isolated in pure form by the chemical interaction of Zr(dmap)4 with Cu(OAc)2·H2O in THF. Complex (1) has been examined by melting point, elemental analysis, FT-IR spectroscopy and single crystal X-ray diffraction. The thermal decomposition behavior of the complex has been explored by thermogravimetric, derivative thermogravimetric and differential scanning calorimetric analyses which reveal that complete conversion of (1) into 1 : 1.5 composite oxides, CuO : ZrO2, treated at 500 °C. The ability of complex (1) to act as a single-source precursor for the formation of advanced composite oxides thin film has been investigated by aerosol assisted chemical vapor deposition at 550 °C in air ambient. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopic (XPS) analyses of the developed thin films suggest the formation of good quality crystalline microspherical-shaped CuO–1.5ZrO2 composite oxide with high purity. The electrocatalytic activity of CuO–1.5ZrO2 composite oxide film was studied toward methanol oxidation in an alkaline medium and it showed high oxidation peak current of 14 μA during a forward scan which is ∼3.5-fold higher than the bare Pt electrode. The ease and low cost fabrication and high electrocatalytic activity of composite oxide film could make it potential candidate for direct methanol fuel cells application.