Quantum Dots (QDs) have been used in life science study because of their higher emission and photostability. Although physicochemical and biological properties of QDs were varied dramatically by the surface modification of QDs, little is known about the reason why the photoluminescence intensity (PLI) of QDs was changed by surface modification. We report on the millisecond-span change of PLI of QD's collective fluorescence oscillation. QDs covered with carboxylic acid and hydroxyl groups show enhanced PLI by adding NaN3, whereas QDs with amine showed less. Removal of NaN3 from QD solution abrogated the enhanced PLI. In addition, observation on evanescent field revealed that addition of antioxidants induced enhanced oscillation of QDs. Furthermore, the blinking count at one millisecond was also increased by addition of antioxidants. However the oscillation enhancement is observed in both aqueous solution and polar organic solvents but not in nonpolar organic solvents, indicating that PLI of QD was varied by the interaction between QDs and their environmental solvents. These millisecond oscillation mechanism was independent of "on" and "off" events which were conventionally known as "blinking". Taken together, the fluorescent emission of colloidal QDs is affected by both surface-covered colloidal molecules and external solvents around at millisecond span interaction.
We have developed supercritical hydrothermal synthesis method of nanoparticles. In the method, metal salt aqueous solution is mixed with high temperature water to rapidly increase the temperature of the metal salt solution and thus reduce the reactions and crystallizations during the heating up period. By using this method, we succeeded in the continuous and rapid production of nanocrystals.
In this paper, we propose a new method to synthesize organic-inorganic fused materials based on the methods of supercritical hydrothermal synthesis. By introducing organic materials in a reaction atmosphere of supercritical hydrothermal synthesis, nanoparticles whose surface was modified with organic materials were synthesized. In supercritical state, water and organic materials form a homogeneous phase, which provides an excellent reaction atmosphere for the organic modification of nanoparticles. Modification with bio-materials including amino acids was also possible. By changing organic modifiers, particle morphology and crystal structure were changed. This organic surface modification provides a various unique characteristics for the nanoparticles: Dispersion of nanoparticles in aqueous solutions, organic solvents or in liquid polymers can be controlled by selecting hydrophilic or hydrophobic modifiers. Polymer-like materials can be formed for the amino acid modified nanoparticles probably by the self-assembly of amino acid.
Combinatorial chemistry is an efficient technique for the synthesis and screening of a large number of compounds. Recently, we introduced a concept of combinatorial chemistry to computational chemistry for catalyst design and proposed a new method called "combinatorial computational chemistry". In the present study, we have applied our combinatorial computational chemistry approach to the design of methanol synthesis catalysts. Experimentally, it is well known that Cu/ZnO/Al203 catalyst has high activity and several reaction mechanisms of the methanol synthesis process on that catalyst have been proposed. Among those mechanisms, the reaction mechanism through cu-formate and cu-methoxide was strongly supported by experiments. Hence, in the present study we investigated the formation energies of several intermediates during the above reaction mechanism on many catalysts, such as Co, Cu, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt and Au by using density functional calculations. The calculation results suggested that Cu is an active catalyst for the methanol synthesis, which is in good agreement with the previous experimental results. Moreover, Pd, Ag, Ir, Pt and Au are proposed to be effective candidates ofthe most active catalysts for the methanol synthesis.
The combinatorial computational chemistry approach was applied to design new types of Fe-based catalysts, which can be used for the production of ecologically high-quality transportation fuels by the Fischer-Tropsch (FT) synthesis. For this purpose, the density functional theory (DFT) was used to investigate the adsorption of 10 intermediate species for methylene formation on Fe-based multi-component catalysts. The energetic, electronic and structural properties of these species on the catalyst surfaces were calculated. The detailed analysis of possible reaction mechanisms was performed from the comprehensive set of binding energies and structures. It was found that Mn, Mo, and Zr could be used as additional elements in the Fe-based catalysts, since one cannot observe a degradation of the adsorption properties of the active sites as well as showing a high sulfur tolerance. The obtained results are in agreement with available experimental data, thus confirming the validity of combinatorial computational chemistry approach. This also illustrates the role in which combinatorial computational chemistry approach can be used to provide data for discovering and designing new catalysts.
Combinatorial chemistry is an efficient technique for the synthesis and screening of a large number of compounds. Recently, we introduced the combinatorial approach to computational chemistry for a catalyst design and proposed a new method called `a combinatorial computational chemistry'. In the present study, we have applied this `combinatorial computational chemistry approach' to the design of deNOx catalysts. Various ion-exchanged ZSM-5 are good candidates as catalysts for removal of nitrogen oxides (NOx) from the exhaust gases in the presence of excess oxygen. Here we described the screening of the exchange cations in ion- exchanged ZSM-5 which are strong against poisons. In the deNOx reaction NO2 molecules play an important role in the formation of reaction intermediates with reductants. Here, we estimated adsorption energies of NO2 on various ion-exchanged ZSM-5 catalysts. The difference in the adsorption energies of NO2 and poisons such as water and SOx molecules has been compared. Cu+, Ag+, Au+, Fe2+, Co2+ and Cr3+-ZSM-5 were found to have a high resistance to water and SOx molecules during the deNOx reaction.
Combinatorial chemistry has been developed as an experimental method where it is possible to synthesize hundreds of samples all at once and examine their properties. Recently, we introduced the concept of combinatorial approach to computational chemistry for material design and proposed a new method called `a combinatorial computational chemistry'. In this approach, the effects of large number of dopants, substrates, and buffer layers on the structures, electronic states, and properties of metal oxide electronics material is estimated systematically using computer simulations techniques, in order to predict the best dopant, substrate, and buffer layer for each metal oxide electronics materials.
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