Synthesis of highly concentrated suspension of chemically converted graphene in organic solvents: Effect of temperature on the extent of reduction and dispersibility

We report the effect of temperature on the extent of graphene oxide reduction by hydrazine and the dispersibility of the resulting chemically converted graphene (CCG) in polar organic solvents. The extent of graphene oxide reduction at high temperatures was only slightly higher than at low temperatures (30–50 °C), while the dispersibility of the resulting CCG in organic solvents decreased markedly with increasing temperature. The low dispersibility of CCGs prepared at high temperatures was greatly affected by reduction and influenced by the formation of an irreversible agglomerate of CCG at high temperatures. The reduction of graphene oxide at low temperatures is necessary to prepare highly dispersible CCG in organic solvents. CCG prepared at 30 °C is dispersible in N-methyl-2-pyrrolidone concentrations as high as 0.71 mg/mL. The free-standing paper made of this CCG possessed an electrical conductivity of more than 22,000 S/m, one of the highest values ever reported.     

Effects of polymer properties on jetting performance of electrohydrodynamic printing

We perform systematic study on the jetting performance of electrohydrodynamic (EHD) with an insulating polymers such as polystyrene (PS) and poly(methyl methacrylate) (PMMA). EHD printing applies electrostatic field to ink droplet hang on nozzle tip, which causes the deformation of the meniscus to generate discrete droplets or continuous jet stream. Although EHD jetting mechanism has been frequently investigated with conducting or semiconducting materials, there still needs to elucidate EHD jetting of insulating polymer materials for producing controllable droplets. In the present study, we focused on how the physical/chemical properties (conductivity, dielectric constant, and molecular weight) of an insulating polymer affect jetting behavior of EHD printing (especially, the deformation of the meniscus and the corresponding morphology of the printed one). The relationship between the printing parameters and applied voltage is also investigated, thereby allowing the optimization of EHD printings for PS and PMMA. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45044.     

Synthesis and Self-assembling Properties of 2,2′:6′,2″-Terpyridine-Based Carbon Nanotube Coordination Polymers

A novel metallo-supramolecular polytopic ligand was synthesized from the attachment reaction involving an amino group-functionalized multi-wall carbon nanotube and 4-chloro-2,2′:6′,2″-terpyridine used for the preparation of metallo-supramolecular polymers with Co(II) or Ni(II) ions. Different colors were observed depending on either the ligands or the metal ions in this type of supramolecular assembly. The created supramolecular polymers were characterized by means of structure, morphology, and stimuli-responsive performance employing scanning electron microscopy, amperometric techniques, UV–Vis and Fourier transform infrared spectroscopy. UV–Vis spectroscopy and cyclic voltammetry studies confirmed that both the optical and electrochemical properties of metallo-supramolecular materials are affected by the substituent at the pyridine periphery.     

Combined adsorption and Chemical precipitation process for pretreatment or post-treatment of landfill leachate

Performances of combined adsorption and chemical precipitation were evaluated as one of the options for pretreatment or post-treatment of a municipal solid waste (MSW) landfill leachate and leachate from an industrial solid waste landfill. The COD and color removals of the leachate from a MSW landfill were 35% and 33% at an alum dose of 300 mg/L with preceding PAC (powdered activated carbon) dose of 200 mg/L, respectively. For MSW leachate, the combined adsorption and coagulation process showed 2.3 times higher COD removal at PAC dose of 200 mg/L and alum dose of 500 mg/L than the unit process of adsorption with poor settleability. The COD removal was accomplished mainly by adsorption, while coagulation was a key mechanism of color removal. The COD and color of the biologically treated leachate from an industrial solid waste landfill were removed up to 32% and 68%, respectively, at addition of 490 mgAlum/L and 1,000 mgPAC/L in adsorption-coagulation process with pH control. Combined adsorption and coagulation process with pH control showed better COD and color removal than the process without pH control. The color removal was influenced greatly by pH control, while COD removal was not. No difference in removal efficiency was observed between adsorption-coagulation and coagulation-adsorption. Maximum net increases in the COD and color removals by the adsorption-coagulation process were 40% and 46%, respectively, compared with the removals by sole chemical precipitation. The Freundlich isotherm exclusively described the adsorption of leachate components on the PAC. Thus, a combined adsorption and coagulation process was considered to be effective for pre-treatment or post-treatment of landfill leachate, and has distinct features of simple, flexible, stable and reliable operation against fluctuation of leachate quality and flowrate.     

High temperature corrosion behavior of Ni-based alloys

The high temperature corrosion behavior of N07263, N06600, and N06625 in LiCl-Li₂O molten salt was investigated at temperatures ranging from 650 to 850 °C in a glove box. The high temperature corrosion behavior was observed using measurements of the oxide morphology and thickness, the extent of internal corrosion, and the compositional changes in the scale and in the substrate. Corrosion tests were performed, and these demonstrated that the main corrosion products were Fe(Ni,Co)₃, FeNi₃, and LiCrO₂. The internal corrosion of N07263 was localized, while that of N06600 maintained intergranular corrosion throughout the test temperature range. N06625 exhibited uniform intergranular corrosion behaviors at low and high temperatures. N07263 exhibited superior corrosion resistance, as evidenced by its corrosion layer which was more continuous, dense, and adherent when compared with those of N06600 and N06625.     

Evaluation of coagulation and PAC adsorption pretreatments on membrane filtration for a surface water in Korea: A pilot study

Application of membrane filtration has been significantly expanded throughout the world in two decades. A project was launched to facilitate the application of membrane filtration in drinking water plants in Korea in 2004. Five pilot plants each with a capacity of 500 m³/d were installed in a Gueui Drinking Water Plant. The Han River water was a main raw water source for the plants. Key parameters of the raw water were examined. The raw water characteristics are tremendously varied with seasons and rain fall, especially in terms of turbidity and algae numbers. The operation of pretreatment was of substantial importance due to the variation of the raw water. Coagulation and powdered activated carbon adsorption were performed as pretreatment options of microfiltration. The coagulant doses were optimized with increasing turbidity compared to the conventionally used operational manual. PAC adsorption was applied to overcome fouling by high algae numbers. The addition of PAC relieved the aggravation of fouling. However, the PAC addition could not stop the undergoing fouling. A set of laboratory experiments showed that the removal of floc aggregates after coagulation and PAC was critical to maintain high water flux in the membrane system.     

Influence of nickel oxide nanolayer and doping in organic light-emitting devices

Here we report the effect of introducing nickel oxide (NiO) on the performance of organic light-emitting devices (OLEDs) based on small molecules. For the purpose of aligning the NiO deposition with the conventional OLED process, we employed a thermal evaporation method using the NiO powders. To understand the influence of the NiO introduction, we fabricated two types of devices: (1) OLED with the NiO nanolayer and (2) OLED with the NiO-doped hole transport layer. Results show that the NiO introduction improved the hole injection in both types of OLED. However, the device with the NiO nanolayer exhibited greatly improved efficiency, whereas the efficiency was significantly lowered for the device with the NiO-doped hole transport layer.     

Microstructures and transformation behavior of Ti-Ni-Cu shape memory alloy powders fabricated by ball milling method

Ti-Ni and Ti-Ni-Cu alloy powders have been fabricated by ball milling after which their microstructures and transformation behaviors were investigated by means of scanning electron microscopy, X-ray diffraction, energy dispersive X-ray analysis, transmission electron microscopy and differential scanning calorimetry. The powders of as-milled Ti-Ni-Cu alloys whose Cu-content is less than 5 at.% were mixtures of crystal and amorphous, whereas those alloy powders whose Cu-content is more than 10 at.% were crystalline. The B19’ martensite is formed in the Ti-Ni-Cu alloy powders whose Cu-content is less than 10 at.%, whereas the B19 and B19’ martensites coexist in those whose Cu-content is more than 10 at.%. The martensitic transformation range became wider with increasing rotating speed, and so endothermic and exothermic peaks obtained from differential scanning calorimetry were indiscernible.