Synthesis of graphene based materials and other applications as energy storage materials and Ni (II) ions adsorbant

Abstract

Today, with the increasing global concern regarding energy savings, CO2 emission and environmental protection, the development of low cost and environmentally friendly materials for electrodes in energy storage devices and adsorbent in wastewater treatment becomes important. Graphene, as a new materials, has attracted lots of attention due to its high current carrying capacity and high surface area. These properties give graphene the huge potential to be used as electrode materials for energy storage devices and adsorbant materials for heavy metal ions. However, the complicate synthesis methods and long reaction time limit its industrial scale up application. In this thesis, the research is focused on development of graphene based composite materials produced by fast, green and energy saving synthesis methods and study their usage as electrodes and for Ni (II) ions removal by analysing the electrochemical properties and Ni (II) ions absorb capacity. Beside graphene, bismuth has also been considered as safe and non-toxic material. In addition, a large amount of bismuth is produced as a by-product of the copper and tin refining industry. The long Fermi wavelength and high Hall coefficient give bismuth the possibility to reach high electronic conductivity with controlled structure. Therefore, bismuth compounds were selected to decorate graphene for the electrode materials. In this study, reduced graphene oxide bismuth composite (rGO/Bi, Bi2O3-GO, rGO/Bi2O2CO3) were synthesis at 60 C or room temperature with short reaction time of 3 hrs. These composite materials exhibit nano-structure and good electrochemical properties, such as high specific capacity and long cycling life. In the rGO/Bi composite materials, bismuth particles with size around 20 to 50 nm were wrapped and protected by graphene layers from oxidation. This composite materials achieves a specific capacity value of 773 C g-1, which is in the range of its theoretical value. In the Bi2O3-GO composite material, Bi2O3 shows a flower-like shape and linked by graphene oxide layer. This material reaches a specific capacity value as high as 559 C g-1. In the rGO/Bi2O2CO3 composite materials, nanosized bismuth subcarbonate were attached on the graphene layers. This composite material shows stable cycling performance even afi ter 4500 cycles. With the low cost of initial materials, simple synthesis methods, low reaction temperature, short reaction time, high specific capacity value and stable long cycling life, graphene bismuth compounds could be the promising candidates for the future electrodes used in electrochemical energy storage devices. The ability of Ni (II) ions removal by graphene oxide (GO) with sodium dodecyl sulphate (SDS) was also studied. Previous studies have proved that Ni is an excellent catalyst for carbon dioxide reforming. A robust Ni (II) ions removal absorbant is needed in order for this technology to become widely acceptable. SDS has been widely used as the industrial surfactant in toothpaste and shampoo. By adding SDS to decorate GO, it helps prevent graphene oxide sheets from stacking back together and then further enlarge the GO’s capacity of Ni (II) ions removal. In this work, SDS was added to modify graphene oxide surface by a one-step easy-to-handle method at room temperature. The effect of time on adsorption, initial concentration of Ni (II) ions and pH value of the Ni (II) ion solutions with GO and GO-SDS were analyzed. The driving force of the adsorption of Ni (II) ions on GO-SDS is proved to be by electrostatic attraction, Ni (II) ions are adsorbed on the GO surface chemically and by ion exchange. By using SDS modified GO, the Ni (II) ions adsorption capacity was increased dramatically from 20.19 mg g-1 to 55.16 mg g-1 in respect to pure GO.