No abstract

Non-thermal helium atmospheric pressure plasma jet treatment is applied to the surface activation of porous TiO nanoparticle assemblies. Treatment conditions such as the working distance of the plasma discharge, helium gas flow rate, and treatment time are optimized for effective removal of contaminants from the assembly surface. Laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) is applied to detect trace amounts of contaminants on assembly surfaces. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations confirm that the nanoparticle assemblies retain their original perfect spherical structures as well as their ultra-fine convex-concave nano-surfaces even after the plasma jet treatment. N adsorption/desorption and X-ray diffraction (XRD) measurements show no significant changes in their BET specific surface areas and crystal structures, respectively. The plasma jet-treated TiO nanoparticle assemblies show a 3.8 fold improvement in their reaction rate constants for methylene blue degradation and a 2 fold enhancement of their photocurrents under UV irradiation when compared with untreated TiO.

We herein describe a novel use of spherical nanoparticle assemblies of TiO 2 with ultrafine surface concave-convex structure as a catalyst support to prevent the sintering of dispersed metal nanoparticles. Owing to the unique surface structure derived from their fine primary particles, the TiO 2 nanoparticle assemblies show excellent dispersion ability of Au nanoparticles on their rough surface. Extremely exothermic CO oxidation as a probe reaction confirmed the high catalytic activity and stability of Au nanoparticles on the TiO 2 support and sintering resistance even after several cycles of the heat stress reaction at high temperatures.Well-dispersed metal nanoparticles (NPs) have received much attention in many fields of chemistry, physics, materials science, and practical applications, including synthetic chemistry, energy conversion, and environmental issues. [1][2][3][4][5][6][7][8][9][10][11] To obtain good dispersibility of NPs, the surface of metal NPs are directly modified with organic materials or the NPs are mixed with dispersion media such as fatty acids and amines with long alkyl chains. [12][13][14] In the case of heterogeneous catalysts, the dispersion media are called "supports." [15][16][17][18][19][20][21] Metal oxides are the most commonly used supports, because they not only have high heat tolerance and mechanical strength required for very high temperatureÀhigh pressure reactions, but also provide a wide surface area for dilution effect to occur that releases reaction heat. It is also believed that the metal oxide surface affords electronic effect on their catalytic activity of supported metal NPs.In the case of exothermic catalytic reactions, the temperature of catalysts, especially that of the catalyst surface, becomes notably high. Under such high temperature condi-tions, one of the most serious problems is catalyst sintering, because of which several catalyst NPs agglomerate to form large particles. This reduces the activity of catalyst NPs because of the loss of the surface area. [22][23][24][25][26] Ablation of the NPs from the support surface, called leaching, is another common problem that shortens the catalyst life-time. Generally, once the catalyst NPs are sintered or leached, they do not reproduce the original size, morphology, surface area, and crystal structure. Thus, it is better to focus on the prevention of sintering and leaching rather than to regenerate the NPs.To prevent the sintering and leaching of metal NPs, several methods such as alloying, ligand-assisted pinning, fixing on defects, and encapsulating as core-shell/sheath structures by oxides or polymer have been reported. [27][28][29][30][31][32][33][34][35][36][37] These strategies mainly focus on the isolation of the individual nanocatalyst, resulting in low possibility of catalyst aggregation/growth. However, some of them reduce the accessibility of the reactant to the active sites of the catalyst NPs, which lead to a lowering in their reaction rate. Besides, most of their preparation methods are usually complicate...

The microstructure of the electrodes in lithium-ion batteries (LIBs) strongly affects their gravimetric and volumetric energy and power as well as their cycle life. Especially, the effect of the microstructure in the case of next-generation Ni-rich cathode materials has not yet been investigated. A comprehensive understanding of the calendering process is therefore necessary to find an optimal level of the electrode microstructure that can enhance lithium-ion transportation, minimize plastic deformation, and improve conductivity. This work therefore aims to investigate the effect of microstructure and wettability on the electrode kinetics of next-generation Ni-rich LiNi0.88Co0.09Al0.03O2-based 18650 cylindrical cells, which were produced at the semiautomation scale of the pilot plant. Thus, all materials, electrodes, and the battery production are in quality control as the same level of commercial LIBs. With the optimized microstructure and other properties including a finely tuned compaction degree of 17.54%, a thickness of 188 μm, a sheet resistivity of 36.47 mΩ cm–2, a crystallite size of 88.85 nm, a porosity of 26.03%, an electrode Brunauer–Emmett–Teller (BET) surface area of 1.090 m2 g–1, an electrode density of 2.529 g cm–3, and an electrolyte uptake capability of 47.8%, the optimized LiNi0.88Co0.09Al0.03O2 18650 cylindrical cells exhibit excellent high-rate capacity retention, fast Li-ion diffusion, and low internal resistance. The optimized electrode microstructure of next-generation Ni-rich cathode materials could be an effective strategy toward the real application of next-generation Ni-rich LIBs.

Nanofiber bundles of TiO 2 with a unique cheek-brush morphology were prepared by simple, rapid, one-pot, single-step, and template-free solvothermal treatment of a titanium alkoxide and aromatic ester in methanol. The solvothermal reaction was performed by heating a mixture of titanium tetraisopropoxide and dimethyl phthalate in methanol to 300 8C. The precursor solution had to be kept at room temperature for 20 min before heating the solution to obtain a cheek-brush morphology. The heating rate (5-6 8C/min), final reaction temperature (300 8C), and holding time at the final temperature (10 min) were also crucial for formation of the cheek-brush morphology. A systematic study of additives in the precursor solution showed that aromatic esters such as diethyl phthalate and methyl benzoate gave cheek-brush morphologies. The cheek-brush TiO 2 assemblies were used to crosslink a poly(N-isopropylacrylamide) hydrogel; the brushes enhanced the physical adhesion properties of the hydrogel. The hydrogel prepared from a 20wt% polymer containing 0.02wt% of the cheek-brush TiO 2 assemblies had an 11 % and 9.1 % higher ultimate tensile strength and elongation ability, respectively, compared with a prototype hydrogel without a crosslinker. A hydrogel prepared using TiO 2 spheres of a similar size had an 11 % and 18 % lower ultimate tensile strength and elongation ability, respectively, compared with the prototype hydrogels. Scheme 1. Solvothermal synthesis of spherical TiO 2 nanoassemblies.[a] F.