Solution Plasma Method Research Articles

Electrosynthesis of Ammonia Using Carbon Supported WO x /RuO y Nanoparticles

1. Introduction A hydrogen energy society is one of the solutions to overcome the problem of global warming and to build a sustainable society. If the electrochemically synthesis of highly efficient at low temperatures and atmospheric pressure, ammonia can be used as a hydrogen carrier using the electric energy generated by natural energies. However, there is no active nitrogen reduction catalyst at the conditions. In this study, electrochemical nitrogen reduction was performed under low temperature and atmospheric condition using carbon-supported WO x /RuO y nanoparticles prepared by a low-voltage low-frequency solution plasma method and a hydrogen reduction method. 2. Experimental 2.1 Synthesis of WO x/KB Ketjenblack (KB) supported WO x (denoted as WO x/KB) were prepared by two methods: the reduction of Na2WO4∙2H2O by H2 (denoted as -H2) and a low-voltage and low-frequency solution plasma method (denoted as -LVLFSP). RuO y loading on WO x /KB was performed as follows: each WO x /KB was suspended in RuCl3 aqueous solution, and was stirred at 80℃ for 24 h, followed by drying under vacuum to obtain each precursor. WO x /RuO y /KB-H2 and WO x /RuO y /KB-LVLFSP were obtained by the heat-treatment of the precursors at 250℃ for 24 h under 300 mL/min of H2 flow. 2.2 Electrochemical measurements 5 wt% Nafion®-2-PrOH solution and Milli-Q water was added to the prepared catalyst, and the planetary ball mill was stirred for 180 rpm and 30 min to obtain a catalyst suspension. The suspension was coated with a spray method on a carbon paper and dried. The carbon paper and Nafion® film (NRE-212) were thermally crimped at 130℃ and were incorporated into an electrolysis cell shown in Fig. 1(a). The gas flowing out of the cell was vented into two serially connected vials (4 mM methanesulfonic acid solution for NH3 collection and only gas phase for H2). The electrochemical reduction of nitrogen was carried out at 0.6 V vs. RHE for 1 h under 5 mLmin-1 N2 flow, followed by the electrolysis at –1.0 V vs. RHE. The amount of ammonia production was quantified by cation chromatography using an IC YS-50 (Shodex) column with 4 mM methanesulfonic acid as eluent at 40℃. 3. Results and Discussion SEM-EDX revealed that each metal is uniformly dispersed on the KB. The bulks of WO x /RuO y /KB -H2 and WO x /RuO y /KB-LVLFSP were amorphous and a WO3 crystal phase, respectively. Diffraction peaks derived from Ru element were not observed in both the samples. Fig. 1(b) shows the result of electrosynthesis of ammonia using WO x /RuO y /KB catalysts. The ammonia production rate of WO x /RuO y /KB-H2 was about 2 times as large as that of WO x /RuO y /KB-LVLFSP, suggesting that the amorphous tungsten oxide suppresses a competitive proton reduction reaction．Faraday efficiency and energy conversion efficiency of both the catalysts at –0.6 V vs. RHE were larger than those of –1.0 V vs. RHE, probably owing to the increasing rate of the competitive reaction. Figure 1

Modification of titanium dioxide by solution plasma

A solution plasma approach for modification of phase and morphology of titanium dioxide is explored as complementary to the standard sol-gel method. Titanium dioxide powders with different proportions of anatase and rutile phases were successfully synthesized by solution plasma treatment and the photocatalytic activities investigated by solar irradiation of methylene blue. The plasma can facilitate not only the phase transition from anatase to rutile structure but also decrease of particle size significantly through a thermal shocking effect, resulting in shifting of energy bandgap from 3.2 to 3.0 eV. Degradation of methylene blue in the titanium dioxide is evident and amounts up to 50% drop in absorbance. Therefore, the solution plasma method is a new promising economic method for titanium dioxide to facilitate the phase transition and decrease of grain size compared to the traditional sol-gel method.

In vitro cytotoxicity of carbon black nanoparticles synthesized from solution plasma on human lung fibroblast cells

Carbon black nanoparticles (CB-NPs) have been synthesized from liquid benzene by a solution plasma method at room temperature and atmospheric pressure. The morphological observation by scanning electron microscopy revealed the agglomeration of aggregated fine particles. The synthesized CB-NPs were predominantly amorphous as confirmed by X-ray diffraction. The in vitro cytotoxicity of CB-NPs on the human lung fibroblast (MRC-5) cell line was assessed by the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and systematically compared with those of two types of commercial carbon blacks (i.e., Vulcan XC-72 and Ketjenblack EC-600JD). Cell viabilities were studied at different concentrations of 32.5, 65, 125, and 250 µg/mL. It was found that the CB-NPs derived from solution plasma exhibited a lower cytotoxicity on the MRC-5 cells than the other two comparative carbon blacks. The viability of MRC-5 cells exposed to CB-NPs remained higher than 90% even at a high concentration of 250 µg/mL. This result preliminarily confirmed the biosafety and potential use of CB-NPs in the field of biological applications.

Accelerated formation of nanocarbons in solution plasma using benzene substituted with CF3 group

Nanocarbons were synthesized by a solution plasma method using benzene (C6H6) and benzotrifluoride (C5H5CF3) as precursors. The effects of the substituted CF3 group on the overall properties of synthesized nanocarbons were investigated and discussed. As determined from the characterization results, the nanocarbons obtained from both benzene and benzotrifluoride mainly exhibited an amorphous structure and their diameter was about 20–40 nm. There were no notable differences in morphology, surface area, and crystalline structure observed between them. Interestingly, the synthesis rate of nanocarbons from benzotrifluoride (20.3 mg/min) was almost three fold higher than that from benzene (7.6 mg/min). Moreover, a lower H/C ratio was observed in the case of nanocarbons from benzotrifluoride, indicating its more efficient H abstraction. The higher synthesis rate and lower H/C ratio of nanocarbons from benzotrifluoride were possibly attributed to the CF3 radicals generated in the reaction fields of solution plasma during synthesis.

Synthesis of Ag nanoparticles prepared by a solution plasma method and application as a cocatalyst for photocatalytic reduction of carbon dioxide with water

Silver nanoparticles (Ag NPs) were synthesized by a solution plasma method (SPM) in an aqueous solution of ammonia. Optical emission spectra of the plasma revealed that Ag NPs are fabricated with the sputtering of Ag rods as electrode by the produced energetic plasma particles such as H, OH and O radicals. In-situ optical absorption measurements of the solution during the discharge directly presented the concerted formation and aggregation processes of the Ag NPs, which controlled the size of Ag NPs. The synthesized Ag NPs were loaded on gallium oxide (Ga2O3) photocatalyst, and the photocatalytic activities of the obtained Ag loaded Ga2O3 (Ag/Ga2O3) samples were evaluated. Although the photocatalytic reaction proceeded over all the samples to produce CO, the CO production rates decreased with the reaction time. Measurements of DR UV–vis spectra and TEM images revealed that a part of the Ag NPs migrated and aggregated on the photocatalyst surface to become larger particles during the photocatalytic reaction, which would be related to the decrease of the photocatalytic activity. It was also found that the photoirradiation treatment on the prepared Ag/Ga2O3 sample before the use for the photocatalytic reaction improves the photocatalytic performance.

Au nanorods fabricated by means of solution plasma method

Au nanorods with a low toxicity are important in medical field. The nanorods are generally fabricated by using cetyltrimethylammonium bromide (CTAB), which has a high toxicity. We have attempted the fabrication of Au nanorods without CTAB reagent. In this study, Au nanoparticles as growth seeds of the nanorods have been fabricated by using Au rods and NaCl aqueous solution. Subsequently, Au3+ ions of HAuCl4 have been reduced in the mixing solution, which includes the Au nanoparticles and the NaCl aqueous solution, by means of the solution plasma between W rods. The amount of Au3+ ion has been directly monitored during the solution plasma process by using in‐situ UV–Vis‐NIR. The fabricated solution possesses the Au nanoparticles of shapes of rod, sphere, triangle plate and hexagonal plate, respectively. The Au nanorods may be fabricated by both aggregating the reduced Au3+ ion at the surfaces of the Au nanoparticles as the growth seeds and controlling the growth orientation of the Au nanorods by the adsorption of Cl− ions on Au{100} facets. To control the narrow dispersion relation between the short and the long axes lengths of the Au nanorods, the addition of HAuCl4 aqueous solution in small volume steps is a key point. Copyright © 2016 John Wiley & Sons, Ltd.

Synthesis of SnO2 nanoparticles using a solution plasma and their gas-sensing properties

A simple solution plasma method was applied to the synthesis of SnO2 nanoparticles directly from tin(II) chloride solution, without adding any precipitant, stabilizer, or other agents at atmospheric pressure, because solution plasma provides a reaction field with a highly excited energy state. The results of X-ray power diffraction (XRD) analysis and transmission electron microscopy (TEM) verified that well-crystallized SnO2 nanoparticles in the size range of 2–5 nm were synthesized. SnO2 nanoparticles show satisfactory sensitivities to acetaldehyde and ethanol.

Spectroscopic and morphological studies on interaction between gold nanoparticle and liposome constructed with phosphatidylcholine

The gold nanoparticles (Au NPs) colloidal solution and the phosphatidylcholine (PC) liposome aqueous solution are fabricated by the solution plasma method and the extrusion procedure, respectively. When the Au NPs colloidal solution and the PC liposome aqueous solution are mixed, considering the TEM image, we think that the Au NPs firstly are covered with the PC molecules, which do not contribute to form the PC liposome, and subsequently the Au NPs covered with the PC adsorb on the PC liposome surface. We propose that the PC molecule adsorbs on the Au sheet surface at the methyl group of N-CH3 and the oxygen atoms of P-O, P=O, C-O and C=O bonds, because each peak intensity of N, O and P K-edges NEXAFS spectra for the PC/Au sheet is reduced in comparison with that for the PC multilayer. Furthermore, the Au NPs covered with PC seem to be aggregated each other through the hydrophobic groups of PC on Au NPs.

Preparation of gold nanoparticles included in anatase‐phase titania by solution plasma method

The gold nanoparticles on titania support (AuNP/TiO2) has been paid attention as a catalyst and a photocatalyst. We perform the preparation of AuNP/TiO2, which is the combination of the sol–gel method and solution plasma method. In this method, we generate the plasma in the gelatinous peroxotitanic acid solution by the discharge between the gold electrodes, and then we synthesize the peroxotitanium gel containing gold nanoparticles. After drying and calcination process, we obtain the AuNP/TiO2 samples. The X‐ray diffraction results show that the AuNP/TiO2 is constituted by the nanocrystalline gold and anatase‐phase TiO2, and the lattice constant decreases by the embedded gold nanoparticles in the TiO2 matrix. Ultraviolet–Visible absorption spectroscopy shows that the AuNP/TiO2 samples absorb the visible light at about 630 nm based on the localized surface plasmon resonance of gold nanoparticles embedded in the TiO2 matrix. The surface chemical states of the AuNP/TiO2 samples are analyzed by the X‐ray photoelectron spectroscopy. The surface of AuNP/TiO2 is composed with the majority of oxidized gold and minority of metallic gold which interacted with the TiO2 surface. The Au L3‐edge near edge X‐ray absorption fine structure spectra indicate that the gold nanoparticles embedded in TiO2 have metallic chemical states. We successfully prepare the gold nanoparticles on the surface and in the matrix of anatase‐phase TiO2. Copyright © 2014 John Wiley & Sons, Ltd.

Adsorption behavior of l-cysteine on Ag nanoparticles under water environment studied by S K-edge NEXAFS

We have focused on the biocompatibility of the Ag nanoparticles. In this paper, we have fabricated the Ag nanoparticles by means of the solution plasma method. Since this method does not need to use the surfactant molecule, such as the water soluble polymer, the fabricated nanoparticle might possess the clean surface. The average diameter of the Ag nanoparticles is estimated to be 5.0±1.1nm. NEXAFS spectra show l-cysteine thiolate adsorbs on the Ag nanoparticle surface and l-cystine is synthesized. Though this reaction behavior is similar to the result of Rh(PVP, polyvinylpyrrolidone) system, in our previous study, the reaction speed for the Ag nanoparticle is much faster than that for the Rh(PVP) nanoparticle.