Effect of hydrothermal and chemical treatment on the optical and electrical properties of reduced graphene oxide deposited on ITO glass

In this work, the effect of hydrothermal and chemical treatment on the optical and electrical properties of reduced graphene oxide (RGO) was investigated. Reduced graphene oxide was synthesized by both hydrothermal route using a locally fabricated Teflon lined autoclave and chemical method using hydrazine monohydrate. The thin film was obtained by depositing RGO on Indium Tin Oxide (ITO) glass via spray pyrolysis technique. In RGO hydrothermal, the Raman spectroscopy analysis showed greater restoration of the conjugated networks in graphene sheet. The optical transmittance of RGO hydrothermal and RGO hydrazine decreased after the reduction methods unlike in highly oxidized graphene oxide (HOGO) where eighty percent transmittance was observed at 600 nm and above. For RGO hydrothermal and RGO hydrazine; the optical analysis gave an energy band gap value of 2.1 eV and 2.4 eV respectively, while the resistivity were calculated to be 0.3 Ω m and 0.09 Ω m respectively. This research showed a correlation between the band gap value of RGO and the electrical conductivity. This finding can improve the functionality of RGO as sensing materials. The improved electrical and optical properties of RGO hydrothermal makes it suitable in fiber-optic and opto-electronic applications.http://iopscience.iop.org/2053-1591am2021Physic

Single solid source precursor route to the synthesis of MOCVD Cu-Cd-S thin films

Bis-(morpholinodithiato-s,s')-Cu-Cd was synthesized from appropriate reagents as a single solid source precursor and characterized using particle induced x-ray emission (PIXE), Fourier transform infrared (FTIR) spectroscopy and differential thermal analysis (DTA). Cu-Cd-S thin films were deposited on sodalime glass substrate using MOCVD technique at temperatures in the range 360 °C–450 °C. The films were further characterized using Rutherford backscattering spectroscopy (RBS), x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy and four-point probe technique. PIXE revealed that the synthesized precursor contained the expected elements which led to the successful deposition of the Cu-Cd-S thin films. FTIR ascertained that the organic ligand actually attached to the metals. DTA analysis showed that the synthesized precursor was thermally stable and could pyrolyzed around 300 and 500 °C. RBS of the deposited films showed that the stoichiometry and the thickness depended on deposition temperature. XRD analysis revealed that the films deposited at 360 and 380 °C are amorphous while those deposited at 400 °C to 450 °C showed peaks, which supported the possible co-existence of CuS and CdS as Cu-Cd-S, with an improvement in the crystallinity as substrate temperature increased. SEM showed that the films are uniform and crack-free, in which the morphology strongly depended on substrate temperature. Optical analysis revealed that the films have high absorbance in the UV region and high transmittance in the visible and near infrared region, in which direct band gap energy of 2.36 to 2.14 eV was obtained as deposition temperature increased. Other optical parameters such as Urbach energy, refractive index, extinction coefficient, dielectric constant also increased as the deposition temperature increased. Electrical analysis showed that resistivity is temperature dependent as it reduced as deposition temperature increased.http://iopscience.iop.org/journal/2053-15912020-09-13hj2020Physic

Synthesis and characterization of porous carbon derived from activated banana peels with hierarchical porosity for improved electrochemical performance

Banana peels, a common fruit waste was adopted as a material precursor in this study to synthesize highly porous activated carbon from banana peels (ABP) which serves as an electrode material for a symmetric supercapacitor device. The activation was done using KOH pellets at different carbonization temperatures ranging from 750 °C to 950 °C. The ABP sample obtained from the 900 °C carbonization temperature (ABP900) exhibited unique material properties such as hierarchical porous nano-architecture containing micropores, and mesopores with the highest specific surface area (1362 m2 g−1). Electrochemical performance investigation in different neutral aqueous electrolytes showed that the best response was obtained in NaNO3 for the ABP900 electrode. The symmetric device subsequently assembled using 1 M NaNO3 operated in a potential window of 1.8 V, exhibited a specific capacitance of 165 F g−1 with a corresponding energy density of 18.6 W h kg−1 at 0.5 A g−1. A 100% capacitance retention and columbic efficiency were obtained after 10000 continuous charge-discharge cycles at 5 A g−1. Remarkably, after subjecting the symmetric device to a voltage holding test for 60 h, the specific capacitance was observed to increase from 165 F g−1 to 328 F g−1 with a corresponding increased energy density to about 36.9 W h kg−1 at 0.5 A g−1, suggesting a 98% increase in device energy density from its initial value after voltage holding. Thus, the results reported showcase the ABP900 material as a potential nanostructured porous material useful in the design of high-performance electrodes for stable electrochemical capacitors.The South African Research Chairs Initiative (SARChI) of the Department of Science and Technology, the National Research Foundation (NRF) of South Africa (Grant No. 61056).http://www.elsevier.com/locate/electacta2019-02-01hj2018Physic

Preparation and physico-chemical investigation of anatase TiO2 nanotubes for a stable anode of lithium-ion battery

Please read abstract in the article.The South African Research Chairs Initiative (SARChI) of the Department of Science and Technology in conjunction with the National Research Foundation (NRF) of South Africa.http://www.elsevier.com/locate/egyrhj2021Physic