The reduced graphene oxide (rGO) has attracted more and more attention in recent years. How to choose a suitable reduction method to prepare rGO is a critical problem in the preparation of graphene composites. In this work, the differences of rGO reduced by thermal, microwave, Ultraviolet (UV) and reducing agent were studied. The reduction degree and functional groups of rGO were compared by SEM, XPS, Raman, FTIR and TGA. Thermal can remove most of the oxygen-containing groups of graphene oxide (GO) and the thermal reduction is the most effective reduction method. UV light can directly act on the unstable oxygen-containing groups, and its reduction efficiency is second only to thermal reduction. The efficiency of chemical reduction is not as good as that of UV reduction, because the reducing agent only act on the surface of GO. Microwave reduction is a mild thermal reduction with the lowest efficiency, but the residual oxygen-containing groups increase the hydrophilicity of rGO. To sum up, this work studies that rGO prepared by different reduction methods has different characteristics, which provides a reference for selecting appropriate reduction methods to prepare graphene composites with better properties.

Silver/graphene core/shell nanocomposites were synthesized through a one-step electric explosion of wire method using only silver wires and ethanol. The morphology of the graphene shell structures can be easily formed by alternating the solvent from deionized water to ethanol. Transmission electron microscopy revealed that the size of the prepared silver/graphene core/ shell nanocomposites was in the 10–110 nm range. The Raman spectra showed the formation of graphene shells on silver. A possible formation mechanism of the silver/graphene core/shell nanocomposites is proposed in this study. The crystallinity of the nanoparticles was investigated via X-ray diffraction. The graphene on the surfaces of the nanocomposites containing functional groups was analyzed through Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses. Zeta potential and dynamic light scattering analyses were performed to determine the dispersion characteristics of the nanocomposites when redispersed in other solvents.

In decommissioning a nuclear power plant, numerous concrete structures need to be demolished and decontaminated. Although concrete decontamination technologies have been developed globally, concrete cutting remains problematic due to the secondary waste production and dispersion risk from concrete scabbling. To minimize workers’ radiation exposure and secondary waste in dismantling and decontaminating concrete structures, the following conceptual designs were developed. A micro-blast type scabbling technology using explosive materials and a multi-dimensional contamination measurement and artificial intelligence (AI) mapping technology capable of identifying the contamination status of concrete surfaces. Trials revealed that this technology has several merits, including nuclide identification of more than 5 nuclides, radioactivity measurement capability of 0.1–107 Bq·g−1, 1.5 kg robot weight for easy handling, 10 cm robot self-running capability, 100% detonator performance, decontamination factor (DF) of 100 and 8,000 cm2·hr−1 decontamination speed, better than that of TWI (7,500 cm2·hr−1). Hence, the micro-blast type scabbling technology is a suitable method for concrete decontamination. As the Korean explosives industry is well developed and robot and mapping systems are supported by government research and development, this scabbling technology can efficiently aid the Korean decommissioning industry.

In this study, the community structure of marine benthic invertebrates was examined to evaluate the differences between the west, south, and east coasts of Korea and to identify the indicator species representing each region. Acrylic attachment plate sets were installed in Jeongok, Mokpo, Tongyeong, Yangpo, and Gangreung, and the invertebrate fauna thus captured were identified. Monitoring was performed in each area from March 2017 to May 2018. Water depth, temperature, and salinity at each location were measured to determine the potential influence of abiotic factors on the community structure. As a result, the mean depth of plates installed and the water temperature were significantly different in each area. A total of 32 invertebrate species were identified in all localities, and the most significant difference in the species compositions was found between Mokpo and Gangreung. The community structure differed significantly with a change in the plate depth, and a larger number of indicator species appeared on shallower plates. Finally, we determined the community structure of benthic invertebrates in different geographical regions of the Korean ocean by characterizing the dominant invertebrate taxa and the indicator species at each site.

We conducted a field survey from 2018 to 2020 to analyze the spatial distribution of phytoplankton communities at 13 stations in the East Sea. The diatom Chaetoceros curvisetus appeared as the dominant species in winter, and small flagellates less than 20 μm prevailed in all seasons except winter. The seasonal average range of the micro (>20 μm), nano (20 μm≥Chl-a>3 μm), and picophytoplankton (≤3 μm) was 20.6-26.2%, 27.1-35.9%, and 40.8-49.0%, respectively. The composition ratio of nano and picophytoplankton was high at the surface mixed layer from spring to autumn when the water columns were strongly stratified. Especially, the stability of the water mass was increased when the summer surface water temperature was higher than that of the previous year. As a result, the nutrient inflow from the lower layer to the surface was reduced as the ocean stratification layer was strengthened. Therefore, the composition ratio of nano and picophytoplankton was the highest at 77.9% at the surface mixed layer. In conclusion, the structure of the phytoplankton community in the East Sea has been miniaturized, which is expected to form a complex microbial food web structure and lower the carbon transfer rate to the upper consumer stage.

Fish assemblage of total 325 of Korean peninsula estuaries were surveyed to analyze the characteristics of community structure and diversity by sea areas for three years from 2016 to 2018. The scale (stream width) of Korean estuaries were various (14~3,356 m), and 68.9% of all estuaries showed salinity of less than 2 psu. Total 149 species classified into 52 families of fish were identified, and the dominant and sub-dominant species were Tribolodon hakonensis (relative abundance, RA, 12.5%) and Mugil cephalus (RA, 9.5%), respectively. The estuary of the Korean Peninsula had different physical and chemical habitat environments depending on the sea area, and accordingly, fish community structure also showed statistically significant differences (PERMANOVA, Pseudo-F=26.69, P=0.001). In addition, the NMDS (nonmetric multidimensional scaling) results showed the patterns that indicating fish community difference by sea areas, even though low community similarity within sea area (SIMPER, 21.79~26.39%). The estuaries of east sea areas were distinguished from the others in the aspects of which, the higher importance of migratory fishes and endangered species, and that of brackish species were characterized at south sea estuaries. However, the estuaries of west sea showed higher importance of species that have a relation with freshwater (primary freshwater species, exotic species), which is the result that associating with the lower salinity of west sea estuaries because of the high ratio of closed estuaries (78.2%). The SIMPER analysis, scoring the contribution rates of species to community similarity, also showed results corresponding to the tendency of different fish community structures according to each sea area. So far, In Korea, most studies on fish communities in estuaries have been conducted in a single estuary unit, which made it difficult to understand the characteristics of estuaries at the national level, which are prerequisite for policy establishment. In present study, we are providing fish community structure characteristics of Korean estuaries in a national scale, including diversity index, habitat salinity ranges of major species, distribution of migratory species. We are expecting that our results could be utilized as baseline information for establishing management policies or further study of Korean estuaries.

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