Among various methods to produce graphene sheets, electrochemical exfoliation has been regarded as an effective method for the mass production of high-quality graphene sheets because of its simplicity and environmental friendliness. However, conventional electrochemical exfoliation has a disadvantage of accumulating intercalating ions at graphite interlayers owing to the use of a constant voltage. In this study, we developed a DC switching technique to achieve more efficient intercalation of ions than that in the conventional method. In the DC switching method, positive and negative voltages are successively applied to release the accumulated intercalating ions. By testing various conditions, we found the optimum switching time to produce high-quality graphene sheets with the highest yield rate and the highest electrical conductivity. As a result, the graphene sheets using this DC switching technique showed 85% higher yield rate, 193% higher electrical conductivity, 160% larger area, and 25% thinner thickness than those obtained when using a constant DC method. We believe that this DC switching technique can be used for large-scale production of high-quality graphene sheets.

Tocopherol belongs to the Vitamin E class of lipid soluble antioxidants that are essential for human nutrition. Tocopherols consist of a chromanol ring and a 15-carbon tail derived from homogentisate (HGA) and phytyl diphosphate, respectively. Condensation of HGA and phytyl diphosphate, the committed step in tocopherol biosynthesis, is catalyzed by HGA phytyltransferase (HPT). To increase tocopherol level in cucumber fruit, we performed Agrobacterium-mediated transformation with mdhpt gene, encoding HPT, isolated from apple (Malus domestica). We obtained two independent T0 cucumber plants from transforming 2,142 explants. Southern blot analysis of T0 showed that mdhpt was inserted in the genome. In order to test the tocopherol level, T1 cucumber fruits were screened by GC analysis. From 39 T1 fruits tested, some fruits showed 1.5-2 fold in α- and β-tocopherol content comparing to control. However, most of fruits contained lower levels of γ- and δ- tocopherol indicating a partition of metabolites in tocopherol biosynthesis pathway. We selected these T1 line and made a self-cross to obtain T2 seeds.