No abstract

Attempts were made to synthesize high quality graphite oxide (GO) and reduced graphene oxide (rGO) by using successive oxidation-reduction process of high quality vein graphite from Sri Lanka. We report the lowest optimum reduction temperature for converting GO to rGO which has been systematically studied using X-ray diffraction spectroscope (XRD) with the high temperature heating attachment (HTA) for the first time. The effect of particle size of graphite on properties of GO and rGO is also compared using commercially available graphite of particle size of ~111 mm and ball-milled graphite of particle size ~37 mm. The GO and rGO were characterized using XRD, UV-Visible spectroscopy, Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The GO and rGO synthesized from ball-milled graphite showed higher oxidation and reduction properties as verified through the UV-Vis and FTIR analysis. The SEM analysis revealed that the splitting of graphene layers is efficiently taken place in GO from ball-milled graphite. The lowest optimum temperature for thermal reduction of GO to rGO was found to be at 475 °C. FTIR confirmed the removal of most of the functional groups in rGO and according to the BET surface area analysis few layers, supposed to be 2-6 is formed. The efficient oxidation and reduction process of smaller particle size graphite has led to yield highly oxidized GO and high quality rGO which can be used to prepare high quality graphene for future applications.

Embedding nanoparticles into an inert material like graphene is a viable option since hybrid materials are more capable than those based on pure nanoparticulates for the removal of toxic pollutants. This study reports for the first time on Cr(VI) removal capacity of novel starch stabilized nanozero valent iron-graphene composite (NZVI-Gn) under different pHs, contact time, and initial concentrations. Starch coated NZVI-Gn composite was developed through borohydrate reduction method. The structure and surface of the composite were characterized by scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), and point of zero charge (pHpzc). The surface area and pHpzc of NZVI-Gn composite were reported as 525 m2 g−1 and 8.5, respectively. Highest Cr(VI) removal was achieved at pH 3, whereas 67.3% was removed within first few minutes and reached its equilibrium within 20 min obeying pseudo-second-order kinetic model, suggesting chemisorption as the rate limiting process. The partitioning of Cr(VI) at equilibrium is perfectly matched with Langmuir isotherm and maximum adsorption capacity of the NZVI-Gn composite is 143.28 mg g−1. Overall, these findings indicated that NZVI-Gn composite could be utilized as an efficient and magnetically separable adsorbent for removal of Cr(VI).

High performing sensor consisting of SnO2/Gn nanocomposite was fabricated using a novel one-step in-situ sonochemical method. The reducing properties of SnCl2 was used to reduce graphite oxide (GO) so that SnCl2 could be transformed to SnO2 on the basal plane of graphene. The combined characterizations including X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier Transformed Infra-Red spectroscopic data (FTIR) indicated the successful formation of SnO2/Gn composites. Current-voltage (I-V) characteristics of the gas sensor showed ideal ohmic behavior having low resistance. To demonstrate the product on sensing application, gas sensors were fabricated using SnO2/Gn composites and used in detecting ethanol vapor at room temperature (27°C).The results indicate that the SnO2/Gn composite exhibits a considerably high sensing performance of 17.54% response at 150 ppm ethanol vapor, rapid response and reproducibility. Furthermore, the performance of the gas sensor based on SnO2/Gn is very stable for a long period of time under normal operating conditions. Therefore, it is suggested that SnO2/Gn can be considered as an excellent sensing material which also has a potential for wider range of applications on sensors.

A novel symmetric supercapacitor electrode material, rGO-SnO2-polyaniline nanocomposite,was synthesized using graphite oxide, SnCl2.2H2O, and pure Aniline as precursors in a scalable and straightforward one-pot process. Analysis revealed that the rGO-SnO2-polyaniline composite had been successfully synthesized. When the two-electrode supercapacitor was assembled using 1M H2SO4, it showed an outstanding specific gravimetric capacitance of 524.2 F/g at a 5 mV/s scan rate. To the best of our knowledge, such a higher value for a two-electrode specific capacitance for a supercapacitor was never reported.Furthermore, even at a high current density of 1 A/g, the material disclosed an outstanding charge-discharge characteristic. Thus, the rGO-SnO2-polyaniline nanocomposite couldalso be used as an electrode for commercial supercapacitors.