Surfactant-free single-layer graphene in water

Dispersing graphite in water to obtain true (single-layer) graphene in bulk quantity in a liquid has been an unreachablegoal for materials scientists in the past decade. Similarly, a diagnostic tool to identify solubilized graphene in situ has beenlong awaited. Here we show that homogeneous stable dispersions of single-layer graphene (SLG) in water can be obtainedby mixing graphenide (negatively charged graphene) solutions in tetrahydrofuran with degassed water and evaporatingthe organic solvent. In situ Raman spectroscopy of these aqueous dispersions shows all the expected characteristics ofSLG. Transmission electron and atomic force microscopies on deposits confirm the single-layer character. The resultingadditive-free stable water dispersions contain 400 m2 l–1 of developed graphene surface. Films prepared from thesedispersions exhibit a conductivity of up to 32 kS m–1

Activated carbon derived from tree bark biomass with promising material properties for supercapacitors

Activated carbon from tree bark (ACB) has been synthesized by a facile and environmentally friendly activation and carbonization process at different temperatures (600, 700 and 800 °C) using potassium hydroxide (KOH) pellets as an activation agent with different mass loading. The physicochemical and microstructural characteristics of the as-obtained material revealed interconnected microporous/mesoporous architecture with increasing trend in specific surface area (SSA) as carbonization temperatures rises. The SSA values of up to 1018 m2 g−1 and a high pore volume of 0.67 cm3 g−1 were obtained. The potential of the ACB material as suitable supercapacitor electrode was investigated in both a three and two-electrode configuration in different neutral aqueous electrolytes. The electrodes exhibited electric double-layer capacitor (EDLC) behaviour in all electrolytes with the Na2SO4 electrolyte working reversibly in both the negative (−0.80 V to −0.20 V) and positive (0.0 V to 0.6 V) operating potentials. A specific capacitance (Cs) of up to 191 F g−1 at a current density of 1 A g−1 was obtained for the optimized ACB electrode material in 1 M Na2SO4 electrolyte. A symmetric device fabricated exhibited specific Cs of 114 F g−1 at 0.3 A g−1 and excellent stability with a coulombic efficiency of a 100 % after 5000 constant charge–discharge cycles at 5.0 A g−1 and a low capacitance loss for a floating time of 70 h.The South African Research Chairs Initiative of the Department of Science and Technology, Republic of South Africa and National Research Foundation of South Africa (Grant no. 97994).http://link.springer.com/journal/100082018-03-30hb2016Physic