Masato Uehara

Synthesis of CuInS2 fluorescent nanocrystals and enhancement of fluorescence by controlling crystal defect

For this study, Cu-In-S nanocrystals were developed as a low toxic fluorescent. The stoichiometric CuInS(2) nanocrystals were synthesized facilely by heating a solution of metal complexes and dodecanethiol. The fluorescence would be originated from the crystal defect. We intentionally introduced the crystal defect in nanocrystal with the prospect that the fluorescence intensity would be increased. The defect structure of products was analyzed using Raman spectroscopy and other techniques. The nanocrystals have many defects without phase separation as observed in the bulk material. Consequently, the fluorescence quantum yield achieved approximately 5%. Moreover, the fluorescence quantum yield was increased up to 15% by the ZnS coating.

Continuous synthesis of CdSe-ZnS composite nanoparticles in a microfluidic reactor

ZnS-coated CdSe composite particles have been continuously synthesized in a microfluidic reactor. By using this system, CdSe particles and a ZnS coating can be produced in sequence, and the particle size and layer thickness can be directly adjusted by the residence time. It demonstrated that the continuous synthesis in the microreactor was a simple and efficient way to prepare composite particles with different structures and determine the optimized experimental conditions.

Preparation of titania particles utilizing the insoluble phase interface in a microchannel reactor

A stable interface between two insoluble currents in a microchannel reactor has been obtained by selecting the solvents and adjusting the flow rate; titania particles with a size of less than 10 nm could be prepared continuously on this interface; this new method shows great advantage for the control and measurement of particle sizes.

Preparation of CdSe nanocrystals in a micro-flow-reactor

A micro-reactor was utilized for continuous and controlled CdSe nanocrystal preparation. Effects of reaction conditions on optical properties of the nanocrystals were investigated; in this current system, rapid and exact temperature control of the micro-reactor was beneficial for controlling particle diameter and reproducible preparation of particles; additional effort was made towards narrower particle-size distributions.

Efficient Immobilization of Enzymes on Microchannel Surface Through His-Tag and Application for Microreactor

We developed a simple immobilisation method for His-tagged enzymes on a microchannel surface. It facilitates immobilisation of protein molecule on microchannel surface through Ni-complex, using crude or purified protein solutions. By this method, we could immobilize proteins on microcapillary constantly. This method might be useful for further development of microreactor with reversibly immobilized enzymes.

Synthesis of CdSe magic-sized nanocluster and its effect on nanocrystal preparation in a microfluidic reactor

CdSe magic-sized nanoclusters were synthesised at relatively low temperatures (90–150 °C) in the organometallic raw material solution by a very simple method. The variation process from nanoclusters to nanocrystals has been determined using the microreactor, and it was found that these nanoclusters could increase the CdSe nuclei number and product yield in the microfluidic reactor method. Meanwhile, the microreactor shows the advantage for studying the nanocrystal-growth process due to the precise time and temperature control and high reproducibility.

A simple method for surface modification of microchannels

We previously developed a simple surface modification procedure to form a nanostructure on a microcapillary surfaces. However, only one set of conditions was examined and further optimization appeared necessary. This paper presents a detailed examination of the surface modification procedure and the effects of the surface modification level on the immobilisation of lipase. We first performed the reaction using a microcapillary with a 320 μm i.d and a 20 cm length. The number of surface amino groups was increased by increasing the content of 3-aminopropyltriethoxysilane in the silylating reagent by 60%, but a much higher content did not further increase the number of amino groups on the surface. The number of immobilised amino groups did not influence the amount of immobilised lipase. The performance of the microcapillary reactors was evaluated using the 7-acetoxycoumarin hydrolysis reaction. The microcapillary reactors showed equal reaction efficiency to each other, implying that surface structure, rather than the number of amino groups, affect microreactor performance. In a comparison of efficiency with a batchwise system, microreactors showed higher efficiency. We also applied our surface modification method to a ceramic microreaction device, which has a square channel (400 μm × 400 μm × 20 cm). The resulting lipase-immobilized ceramic microreaction device retained the same reaction efficiency. These results demonstrate that this modification method is applicable for the further development of microreaction devices.

In situ extended x-ray absorption fine structure study of initial processes in CdSe nanocrystals formation using a microreactor

The nucleation process of CdSe nanocrystals is studied by fluorescence-detected extended x-ray absorption fine structure (EXAFS) using a microreactor and synchrotron radiation. Detailed analysis of in situ Se K-edge EXAFS data measured along a microreactor channel revealed a strong position-dependence which displays a rapid increase in the CdSe phase with time at the initial stage. The results indicate that the CdSe nucleation completes within several seconds starting from trioctylphosphine Se solution and dodecylamine surfactant at 240 °C. This shows the promising capability of in situ EXAFS combined with a microreactor to investigate the nucleation process of nanocrystals synthesized in a solvent.

Synthesis of mesoporous silica modified with titania and application to gas adsorbent

Abstract Three kinds of silica-based mesoporous materials were synthesized and subjected to adsorption study. Firstly is pure silica involving >1000 m 2 /g of specific surface area (PS; pure silica). Secondly, titania was deposited onto the surface of pure silica (TDS; titania-deposited silica). Thirdly, titania was incorporated into silica network by a partial hydrolysis method (STM; silica–titania mesoporous composite). Acidity and adsorbability for water were enhanced by the addition of titania, especially in STM.

Simple method for preparation of nanostructure on microchannel surface and its usage for enzyme-immobilization

We developed a novel preparation method of nanostructure on the microchannel surface formed by sol-gel like simple treatment with 3-aminopropyltriethoxysilane, which is suitable for a highly efficient enzyme-immobilized microchannel reactor.