Huang Nay Ming

Highly exposed {001} facets of titanium dioxide modified with reduced graphene oxide for dopamine sensing.

Titanium dioxide (TiO2) with highly exposed {001} facets was synthesized through a facile solvo-thermal method and its surface was decorated by using reduced graphene oxide (rGO) sheets. The morphology and chemical composition of the prepared rGO/TiO2 {001} nanocomposite were examined by using suitable characterization techniques. The rGO/TiO2 {001} nanocomposite was used to modify glassy carbon electrode (GCE), which showed higher electrocatalytic activity towards the oxidation of dopamine (DA) and ascorbic acid (AA), when compared to unmodified GCE. The differential pulse voltammetric studies revealed good sensitivity and selectivity nature of the rGO/TiO2 {001} nanocomposite modified GCE for the detection of DA in the presence of AA. The modified GCE exhibited a low electrochemical detection limit of 6 μM over the linear range of 2–60 μM. Overall, this work provides a simple platform for the development of GCE modified with rGO/TiO2 {001} nanocomposite with highly exposed {001} facets for potential electrochemical sensing applications.

Magnetically separable reduced graphene oxide/iron oxide nanocomposite materials for environmental remediation

Magnetically separable reduced graphene oxide/iron oxide (rGO/Fe3O4) nanocomposite materials were synthesized at room temperature through a facile, eco-friendly and cost-effective approach. The prepared nanocomposite materials were characterized by different techniques. X-ray diffraction analysis revealed the formation of the rGO/Fe3O4 nanocomposites, while transmission electron microscope images showed that the Fe3O4 nanoparticles with an average size of 10 nm were embedded uniformly on the surface of rGO sheets. The synthesized rGO/Fe3O4 nanocomposite materials were found to be super-paramagnetic in nature at room temperature. The photocatalytic performance of the rGO/Fe3O4 nanocomposite materials was investigated under natural sunlight irradiation using methylene blue (MB) as a model target organic pollutant. The rGO/Fe3O4 showed better adsorption behaviour and excellent photocatalytic activity towards the degradation of MB, when compared to other samples such as rGO and pristine Fe3O4 nanoparticles. This enhanced photocatalytic activity could be attributed to the synergistic effect that arises between the rGO and Fe3O4, which significantly reduces charge recombination. Moreover, the rGO/Fe3O4 nanocomposite materials exhibited good sustainability, which was evidenced by their consistent photocatalytic performance and the absence of any observable changes in morphology, even after eight cycles of operation during photocatalytic experiments. The overall results of the study indicate that these newly prepared photocatalytically stable and magnetically separable rGO/Fe3O4 nanocomposites could be potentially utilized for many environmental remediation applications.

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.

Investigation on the use of graphene oxide as novel surfactant to stabilize weakly charged graphene nanoplatelets

This paper presents a unique synergistic behavior between a graphene oxide (GO) and graphene nanoplatelet (GnP) composite in an aqueous medium. The results showed that GO stabilized GnP colloid near its isoelectric point and prevented rapid agglomeration and sedimentation. It was considered that a rarely encountered charge-dependent electrostatic interaction between the highly charged GO and weakly charged GnP particles kept GnP suspended at its rapid coagulation and phase separation pH. Sedimentation and transmission electron microscope (TEM) micrograph images revealed the evidence of highly stable colloidal mixtures while zeta potential measurement provided semi-quantitative explanation on the mechanism of stabilization. GnP suspension was confirmed via UV-vis spectral data while contact angle measurement elucidated the close resemblance to an aqueous solution indicating the ability of GO to mediate the flocculation prone GnP colloids. About a tenfold increase in viscosity was recorded at a low shear rate in comparison to an individual GO solution due to a strong interaction manifested between participating colloids. An optimum level of mixing ratio between the two constituents was also obtained. These new findings related to an interaction between charge-based graphitic carbon materials would open new avenues for further exploration on the enhancement of both GO and GnP functionalities particularly in mechanical and electrical domains.

Effect of synergic cooperation on optical and photoelectrochemical properties of CeO2–MnO composite thin films

CeO2–MnO composite thin films have been deposited on glass substrates, which were coated with fluorine-doped tin oxide (FTO), by aerosol-assisted chemical vapor deposition (AACVD) using a 1 : 1 mixture of the cerium complex [Ce(OCOCF3)4]−[(CH3)2NHCH2CH2OH]+ (1) and acetatomanganese(II). X-ray diffraction (XRD), Raman spectroscopy and profilometry were used to investigate the phase purity, stoichiometry and thickness of the films. EDX results confirmed that the Ce : Mn ratio was 1 : 9 in the deposited composite thin films. FEG-SEM analysis illustrated that the morphology of the fabricated films was influenced by the deposition temperature and hence the optoelectronic properties. UV-vis studies of a composite thin film fabricated from methanol solution at 475 °C demonstrate a direct band gap of 2.5 eV. From its current–voltage characteristics it is evident that a CeO2–MnO composite semiconductor electrode exhibits n-type behavior and the photocurrent was strongly dependent on the deposition temperature. A CeO2–MnO photoanode deposited at 475 °C for 45 min from a 0.023 M solution of (1) and acetatomanganese(II) in methanol gave a maximum photocurrent density of 265 μA cm−2 at 0.65 V vs. Ag/AgCl/3 M KCl using a 0.5 M NaOH electrolyte.

Investigation on the Use of Graphene Oxide as Novel Surfactant for Stabilizing Carbon Based Materials

The present work reported on the use of graphene oxide (GO) as effective dispersant to isolate different carbon allotropes. The nature of its chemical structure which consists of hydrophobic and hydrophilic components enables GO to behave as surfactant, paving routes for dissolution of graphitic materials and achieving surfactant free all-carbon solutions. Two additional carboneous materials under the family of fullerene (carbon nanofiber—CNF) and graphite (graphene nanoplatelets—GnP) were introduced within the present study to form a new GO based hybrid complexes on top of the commonly investigated carbon nanotube (CNT) based GO hybrid. Investigation on GO stability with respect to particle size and zeta potential measurements showed that the strength of its dispersibility was highly dependent on its morphological size and less affected by the pH. Rheological study revealed that GO shear–strain relationship is highly sensitive to the particle size. The GO viscosity experienced dramatic changes from Newtonian toward shear thinning behaviors as the particle size increases. Thermal conductivity measurement highlighted as high as 8% increase in magnitude with the addition of CNT, CNF, and GnP carbon constituents, indicating that the enhancement may be attributed to the much efficient thermal transport along the conducting path of pristine carbon allotropes. GRAPHICAL ABSTRACT

Vysotskite structured photoactive palladium sulphide thin films from dithiocarbamate derivatives

A series of palladium(II) dithiocarbamate complexes [Pd(S2CNRR′)2]·n(py) [where py = pyridine; RR′ = Bz, n = 1 (1); Cy, n = 1 (2); nHex, n = 0 (3) and MeCy, n = 0 (4)] have been synthesized and characterized using various physicochemical techniques and their single crystal structures have been established. The decomposition modes and potential of the complexes as single source precursors (SSPs) for the development of palladium sulphide (PdS) thin films were investigated by thermogravimetric and derivative thermogravimetric (TGA/DTG) analyses. The PdS thin films were deposited on FTO conducting glass substrates at 400, 450 and 500 °C by the aerosol-assisted chemical vapour deposition (AACVD) technique and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) reveal that the deposit has a tetragonal structure with a 1 : 1 ratio of Pd : S. The shape and size of PdS crystallites and the texture of films depend on the deposition temperatures and the precursor type used. The direct band gap energy of 1.56 eV was estimated from UV-Vis spectroscopy of the PdS films fabricated from precursor (2) at 450 °C. The photoelectrochemical (PEC) properties of PdS films were studied by recording the current–voltage plots under alternating dark and illumination conditions. To the best of our knowledge, this is the first demonstration of PEC studies of photoactive PdS thin films fabricated using the AACVD technique using palladium(II) dithiocarbamate complexes as precursors.