Researches of npfd group

The aim of Nanoparticles Functional Design Group is to make a contribution on the solution of various environmental or energy issues with "nanosystem" established by multi-scale design and development based on the nanoparticles and nanomaterials. Our core materials are porous coordination polymers such as Prussian blue analogues and metal organic frameworks. Our R&D is proceeded for adsorbents of molecules/ions and color-switchable devices with the structural optimization for each target application.

1. Multi-scale structural optimization  of porous coordination polymers.
 The core technology of our group is design and development of the materials. Materials, components, modules, devices, and systems are designed and developed concurrently in nanometer, micro-meter, milli-meter, and also meter scale. Our final goal is to utilize the "true performance" of the materials at the scale of human being, with a connection among different scales.

Concept of the multi-scale design from atomic to human being:
In the case of Cs-decontamination technology for example. 

The porous coordination polymers, our core materials, has a porous structure at atomic scale. For example, Prussian blue analogues has a crystal structure like jungle gym, suitable to adsorb small molecules and ions. This property can be used for adsorbent or electrochemical electrodes. In addition, by changing the metallic site or introducing vacancies, the appropriate structural optimization for each application is possible. 

Example of the optimization of the crystal structure of porous coordination polymers. Prussian blue analogues can be used as adsorbent both for radioactive Cs and for gaseous ammonia, but the detailed structures for each purpose are different with metal substitution and with the vacancy introduction.

Development of nanoparticles is one of the important structural design and development. With the preparation of the nanoparticles, it is possible to make a dispersion liquid, the "INK", resulting in that we can fabricate the thin films and patterned ones with coating or printing. The preparation of the nano-composite with other materials is also possible. In addition, the porosity design in nano-scale is possible, i.e. the aggregate of the nanoparticles has the porosity in the same scale as the nanoparticle size.
 To connect the functional design in atomic scale and the application in the human-scale, we need to prepare the large amount of nanoparticles with accurate structure control. To achieve the requirement, we use flow-synthesis method, e.g. micromixer synthesis. Because crystal of Prussian blue tend to be small, it is possible to prepare the Prussian blue nanoparticles just only mixing the two chemicals. However, with the simple mixing, the fluctuation of the chemical composition and that of  the size becomes larger, resulting in the difficulty in the derivation of the appropriate parameters to fabricate the best material. The flow synthesis would solve the problem by decreasing the fluctuation. 

Comparison of the Cu-substituted Prussian blue nanoparticles 
(Left) batch-synthesized and (Right) flow synthesized. 

Movie of the synthesis of Prussian blue nanoparticles with a micromixer.

Main achievement
  • Efficient synthesis of size-controlled open-framework nanoparticles fabricated with a micro-mixer: route to the improvement of Cs adsorption performance, Akira Takahashi, Tohru Kawamoto et al., Green Chemistry, 2015, 17, pp4228-4233. (04/06/2015), DOI:0.1039/C5GC00757G

2. trace molecule adsorption from atomsphere
 There are a various trace molecules in atmosphere, some of which often make a bad influence on human life. For example, ammonia is odor materials and an origin of low yield at semiconductor device facility. In museums, the concentration of ammonia must be controlled to avoid the degradation of historical arts. 
 We developed recyclable adsorbent for trace ammonia with the highest capacity. The adsorbent shows excellent adsorption even for the trace ammonia less than 0.1 ppm. 

Ammonia adsorbent and its crystal structure

 Our main project is the removal of ammonia at the pig farm. With this technology, we can maintain the condition in pig farm, temperature, humidity, and  the concentration of the toxic materials, resulting in that the production efficiency would be improved. 

    Main achievement
    • Historical pigment exhibiting ammonia capture beyond standard adsorbents with adsorption sites of two kindsAkira Takahashi, & Tohru Kawamoto, et al.,  Journal of the American Chemical Society2016, 138(20), pp6376-6379.  (05/05/2016), doi.org/10.1021/jacs.6b02721

     2. Ion-adsorbent from aqueous solution

      There are a lot of ions in environmental water or wastewater. Heavy metals often causes serious water pollution. Eutrophication is caused by nitrogen compounds such as ammonium anion. We are developing the adsorbent of radioactive cesium cation, ammonium anion, and arsenic to remove them from the water. The radioactive cesium adsorbent has been developed for the countermeasure of the accident of Fukushima Dai-ichi atomic power plant. Not only the adsorbent but also how to use them has been developed to achieve the speedy treatment for each issue. For example, the decontamination method of the ash and sediment of the pond has been developed.  The method for the pond sediment is published in the manual prepared by Ministry of Agriculture、Forestry and Fisheries, the Japan government. 

    Concept of radioactive cesium decontamination of ash
    Column filled with adsorbent for radioactive-Cs adsorption. It was used for the realistic decontamination of pond sediment. 5m3 of water per hour can be treated with the column.

    The radioactive-Cs adsorbent is also used for the analysis of trace Cs in environmental water. By the condensation of the radioactive Cs in the adsorbent, detection limit can be decreased.
    (Left)The crystal structure of the radioactive-cesium adsorbent. (Right) nonwoven cartridge for the condensation of radioactive-Cs in environmental water for the pretreatment of the Cs-analysis. 
    Adsorbent for ammonium cation is used for the removal from the wastewater but also for the recycle of the ammonium with desorption processes, the advantages against the conventional method. 

    Main achievement
    • Application of Prussian blue nanoparticles for the radioactive Cs decontamination in Fukushima region, Durga Parajuli, and Tohru Kawamoto et al., Journal of environmental radioactivity, 2016, 151(1), pp233-237, . (30/10/2015), DOI:10.1016/j.jenvrad.2015.10.014
    • Comparative study of the factors associated with the application of metal hexacyanoferrates for environmental Cs decontamination, Durga Parajuli, and Tohru Kawamoto et al., Chemical Engineering Journal, 2016, 283(1), pp1322-1328. (28/08/2015), DOI:10.1016/j.cej.2015.08.076
    • Radiocesium removal system for environmental water and drainage, Kimitaka Minami, and Tohru Kawamoto, et al., Water Research, 2016, 107(15), pp29-36. 18/10/2016), DOI:10.1016/j.watres.2016.10.043

    4. Electrochemical electrode and color-switchable devices
     The materials that adsorb and desorb ions electrochemically can be used as a electrochemical electrode. For example, in secondary batteries, the electrode adsorb the ions and electrons for the storage of electricity, and desorb them for discharge. This is called  a redox reaction.  Some of our materials change its color through the redox reaction, called electrochromism. With the phenomenon, we developed color-switchable devices. With using the nanoparticle ink, we can fabricate the devices with coating or printing, resulting in the drastic cost reduction. Similar reactions are also utilized for a recyclable adsorbent for radioactive cesium, where the adsorbent regenerated by electricity. 

    Artistic object consisting of 1000 pieces of our color-switchable devices fabricate 
    using coating with nanoparticle ink
    Front cover art of Journal of Materials Chemistry C
    Behavior of the color-switchable devices controlled by a smartphone

    Main achievement
    • Cobalt hexacyanoferrate nanoparticles for wet-processed brown–bleached electrochromic devices with hybridization of high-spin/low-spin phases, Elghool Kholoud, Tohru Kawamoto,  et al., Journal of Materials Chemistry C2017, 5, pp8921-8926(16/07/2017), DOI:10.1039/C7TC02576A
    • Accelerated coloration of electrochromic device with the counter electrode of nanoparticulate Prussian blue-type complexes, Kyoung-Moo Lee, Tohru Kawamoto, et al., Electrochimica Acta, 2015, 163(1), pp288-295. (16/02/2015), DOI:10.1016/j.electacta.2015.02.119.
    • Thermodynamics and mechanism studies on electrochemical removal of cesium ions from aqueous solution using a nanoparticle film of copper hexacyanoferrate, Rongzhi Chen, &Hisashi Tanaka et al., ACS applied materials & interfaces2013, 5(24), pp12984-12990. (02/12/2013), DOI:10.1021/am403748b