Hydrothermal synthesis of simonkolleite microplatelets on nickel foam-graphene for electrochemical supercapacitors

Nickel foam-graphene (NF-G) was synthesized by chemical vapour deposition followed by facial in situ aqueous chemical growth of simonkolleite (Zn5(OH)8Cl2·H2O) under hydrothermal conditions to form NF-G/simonkolleite composite. X-ray diffraction and Raman spectroscopy show the presence of simonkolleite on the NF-G, while scanning and transmission electron microscopies show simonkolleite micro-plates like structure evenly distributed on the NF-G. Electrochemical measurements of the composite electrode give a specific capacitance of 350 Fg−1 at current density of 0.7 Ag−1 for our device measured in three-electrode configuration. The composite also shows a rate capability of ~87% capacitance retention at a high current density of 5Ag−1,which makes it a promising candidate as an electrode material for supercapacitor applications.The University of Pretoria and the National Research Foundation (NRF) of South Africa.http://www.springer.com/chemistry/physical/journal/10008hb2013ai201

Functionalized graphene foam as electrode for improved electrochemical storage

We report on a non-covalent functionalization of graphene foam (GF) synthesized via chemical vapour deposition (CVD). The GF was treated with pyrene carboxylic acid (PCA) which acted as a source of oxygen and/or hydroxyl groups attached to the surface of the graphene foam for its electrochemical performance improvement. The modified graphene surface enabled a high pseudocapacitive effect on the GF. A specific capacitance of 133.3 F g−1, power density ∼ 145.3 kW kg−1 and energy density ∼ 4.7 W h kg−1 were achieved based on the functionalized foam in 6 M KOH aqueous electrolyte. The results suggest that non-covalent functionalization might be an effective approach to overcome the restacking problem associated with graphene electrodes and also signify the importance of surface functionalities in graphene-based electrode materials.South African Research Chairs Initiative of the Department of Science and Technology (SARCHi-DST), the National Research Foundation (NRF) and University of Pretoria.http://link.springer.com/journal/100082015-09-30hb201

Preparation and characterization of Poly(vinyl alcohol)/graphene nanofibers synthesized by electrospinning

We report on the synthesis and characterization of electrospun polyvinyl alcohol (PVA)/graphene nanofibers. The samples produced were characterized by Raman spectroscopy for structural and defect density analysis, scanning electron microscopy (SEM) for morphological analysis, and thermogravimetric (TGA) for thermal analysis. SEM measurements show uniform hollow PVA fibers formation and excellent graphene dispersion within the fibers, while TGA measurements show the improved thermal stability of PVA in the presence of graphene. The synthesized polymer reinforced nanofibers have potential to serve in many different applications such as thermal management, supercapacitor electrodes and biomedical materials for drug delivery.University of Pretoria and the NRF Doctorate Innovation Fund.http://www.elsevier.com/locate/jpcshj201

Growth of graphene underlayers by chemical vapor deposition

We present a simple and very convincing approach to visualizing that subsequent layers of graphene grow between the existing monolayer graphene and the copper catalyst in chemical vapor deposition (CVD). Graphene samples were grown by CVD and then transferred onto glass substrates by the bubbling method in two ways, either direct-transfer (DT) to yield poly (methyl methacrylate) (PMMA)/graphene/glass or (2) inverted transfer (IT) to yield graphene/PMMA/glass. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) were used to reveal surface features for both the DT and IT samples. The results from FE-SEM and AFM topographic analyses of the surfaces revealed the underlayer growth of subsequent layers. The subsequent layers in the IT samples are visualized as 3D structures, where the smaller graphene layers lie above the larger layers stacked in a concentric manner. The results support the formation of the so-called “inverted wedding cake” stacking in multilayer graphene growth.MF thanks the Government of Lesotho, the University of Pretoria and the NRF for financial support for his study. A.T.C.J acknowledges support from the LRSM, through the U.S. National Science Foundation MRSEC, Grant No. DMR-1120901.http://scitation.aip.org/content/aip/journal/advahb2014ai201

Simonkolleite nano-platelets : synthesis and temperature effect on hydrogen gas sensing properties

Please read abstract in article.The African Laser Centre “ALC”-Pretoria, the Abdus Salam ICTP-Trieste, the Nanosciences African Network “NANOAFNET”-Cape Town, iThemba LABS-National Research Foundation of South Africa and the French-South Africa as well as the Japan-South Africa bilateral cooperation programmes.http://www.elsevier.com/locate/apsuscnf201

Competitive growth texture of pulse laser deposited VO2 nanostructures on a glass substrate

We report on the crystal structure and morphology of vanadium dioxide (VO2) nanostructures synthesized by pulsed laser deposition on soda-lime glass substrates. The VO2 nanostructures exhibit sharp a-axis diffraction peaks, characteristic of the VO2 monoclinic phase, which implies that highly a-axis textured VO2 was formed. A detailed description of the growth mechanisms and the substrate–film interaction is given, and the characteristics of the electronic transition and hysteresis of the phase transition are described in terms of the morphology and grain boundary structure. The sharpness of the transition and the hysteresis upon heating and cooling are found to be strong functions of the crystal structure and microstructure (grain size and shape).UNESCO-UNISA Africa Chair in Nanosciences-Nanotechnology, INRS (Canada), the ICTP-Trieste and the NANOAFNET.http://www.elsevier.com/locate/actamathb2014ai201

Effect of substrate temperature on the structure and the metal insulator transition in pulsed laser deposed V02\ films on soda lime glass

In this paper, we report the effect of soda lime substrate deposition temperature (Ts) on the crystal structure and the metal insulator transition of VO2 thin films. Samples were deposited at substrate deposition temperature ranging from 450 to 600 0C by pulsed-laser deposition and characterized by x-ray diffraction and UV-VIS spectrophotometer. At a substrate temperature of 550°C, the VO2 (100) reflection dominate the spectrum showing a change in crystalline grains orientation. The highest transition temperatures of 74 oC with the lowest hysteresis width of 11 oC were obtained on the same sample grown at a substrate deposition temperature of 500 oC and also corresponding to the largest grains size of a value of 350 nm.http://link.springer.com/journal/125962016-03-31hb201

Enhanced photoelectrochemical performance of TiO

In this paper, we report the photoelectrochemical performances of CdS nanoparticles (NPs) decorated TiO2 photoanodes. The TiO2 nanofiber arrays (NFAs) were fabricated into Titanium substrate by a hydrothermal method. Afterwards, the deposited TiO2 NFAs were decorated with CdS NPs by employing a successive ionic layer adsorption and reaction (SILAR) method. The obtained samples of CdS covered and uncovered TiO2 NFAs were characterized by X-ray diffraction, Scanning Electron Microscopy and UV-visible Diffuse Reflectance Spectroscopy. The size of the CdS nanoparticles increases with the number of SILAR cycles and leads to an additional broad absorption peak in the visible part of the spectrum. Consequently, the photo-electrochemical performance of the CdS decorated TiO2 was enhanced substantially resulting in a better electron-hole separation and transport. This enhancement has been discussed and assigned to a better sun light harvesting and an efficient charge transfer between the CdS nanoparticles and the TiO2 NFAs

Growth of graphene underlayers by chemical vapor deposition

We present a simple and very convincing approach to visualizing that subsequent layers of graphene grow between the existing monolayer graphene and the copper catalyst in chemical vapor deposition (CVD). Graphene samples were grown by CVD and then transferred onto glass substrates by the bubbling method in two ways, either direct-transfer (DT) to yield poly (methyl methacrylate) (PMMA)/graphene/glass or (2) inverted transfer (IT) to yield graphene/PMMA/glass. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) were used to reveal surface features for both the DT and IT samples. The results from FE-SEM and AFM topographic analyses of the surfaces revealed the underlayer growth of subsequent layers. The subsequent layers in the IT samples are visualized as 3D structures, where the smaller graphene layers lie above the larger layers stacked in a concentric manner. The results support the formation of the so-called “inverted wedding cake” stacking in multilayer graphene growth