Research target (2014-Present)
Human being recognizes that the orientation of science in the 21st century should be “science for human”, since the whole world confronts inevitable subjects relating to safe, secure, and healthy human life. On the other hand, in the second half of 20th century, nanotechnology and nanomaterials strikingly developed with deepening of science. Therefore, at present, those are key technology and materials, which overstride all sectional sciences. Thus we focus on the advanced nanotechnology and smart nanomaterials participating in and finding vent for the “science for human” and have to care for the strong correlation among them at the global view.
Pollutants have adverse effects on human health and environment, and their generation must be prevented, detected and deduced. Especially, CO2 is a typical greenhouse effect gas and a causal agent of global warming. In order to remove pollutant gases including air pollutants (CO2, NOx, and suspended particulate matter), endocrine disruptor (environmental hormone) and toxic gases (ex. dioxins), we must develop the advanced filters, which selectively adsorb pollutant gases. Then the filter may equip with the functionality to self-decompose pollutants, and we can accomplish “the pollutant gas self-treatment membrane”. Sick house/building syndrome is also serious for residents, especially, for children with atopic hypersensitivity. We began the development of the wall materials, which have the functions to decompose sick-house gases (ex. Building material-derived formaldehyde and preservative-derived volatile organic compounds) in “green science”.
In the past years, there is growing interest in renewable energy generations, which are alternative of biofuel and atomic energy. Especially, the development of materials with high efficiency on solar cells and fuel cells is especially growing concern. The hybrid materials, which we have developed so far, are available as materials for such cells, and we targeted our investigation to such directions. To be specific, the hybrids consisting of metal oxide + carbon material or metal oxide + organic sensitizer are valuable to solar cells and the hybrids of Pt-embedded minerals or carbon materials are utilizable for fuel cells in “energy science”.
Lastly we targeted “life science”, because human population is exactly becoming an aging society and in the meanwhile there are many people who are forced unhealthy life in poverty society. In detail, we developed our research in drug delivery systems and photo thermal therapy. Although we partially accomplished such investigation, it was hastened by means of the collaboration with Department of Pharmacology, University of Malaya, Malaysia, and Tokyo University of Science, Japan. We completed, almost, carbon-based drug delivery systems and phototherapy-applicable non-spherical gold nanoparticles.
Research project and its achievement
During two years of 2014 and 2015, we focused three projects.
Project 1. Architecting of advanced systems for pollutant removal and decomposition (green science) – Preparation of nanofiber films embedding catalysts and their applications to air pollution degradation
Project 2. Development of validated systems for energy production and storage (energy science) – Designing of architectures composed of carbon materials toward applications in energy production
Project 3. Fabrication of nanobiotechnological systems for inspection and therapy (life science) – Production of graphene-based drug delivery systems and their therapeutic applications –
The investigations for two years can be summarized in the following results.
1. Green science: Architecting of advanced systems for pollutant removal and decomposition
2. Energy science: Development of validated systems for energy storage
3. Life science: Fabrication of nanobiotechnological systems for medical therapy
- Green science (Architecting of advanced systems for pollutant removal and decomposition):
Dendrimers should be reservoirs of small molecules but their handling is not easy because of their small size. Then, we successfully exchanged the ionic dendrimers in/on ion-exchange clays [1-3]. These hybrid materials could selectively adsorb CO2 and NH3 gases. The selectivity depends on the combination of dendrimer and clay. Cation-exchange clays exchanged by amine-terminated dendrimer selectively can adsorb CO2 and anion-exchange clay exchanged by carboxylate-terminated dendrimer can select the adsorption of NH3.
Cellulose nanofibers are products from natural cellulose pulps and these eco-friendly materials can form transparent films rather than textile. As preliminary experiments for the application to textile, we chemically combined dendrimer/clay hybrid materials on the nanofibers and the films prepared from three component composites were applied to the adsorption of CO2 and NH3 gases . The behavior of gas adsorption was similar to it on dendrimer/cray hybrids without nanofibers for the case of cation-exchange clays. However, nanofiber films embedded dendrimer/anion-exchange clay hybrids behaved largest adsorption of both gases CO2 and NH3, although the desorption behavior was different between two gases. These results can be explained from the character of dendrimer/clay hybrids and their embedded situation in nanofibers.
Dendrimers can encapsulate nanoparticles of metal and metal oxides in their interior. When this type of organic/inorganic hybrids is bound on nanofibers, we can prepare films encapsulating functional organic/inorganic hybrids. For the case of cupper metal, the hybrid films could be used for cupper-catalyzing chemical reactions. The hybrid films including Ag nanoparticles were useful for decoloration reaction and as an antibacterial film . Especially, such films were reusable and self-degradable. These procedures were extended to encapsulate Pt catalysts. This research is the extension of our previous investigation, where Pt particle-encapsulated dendrimer was embedded in porous hydroxyapatite particles . These types of organic/inorganic hybrid particles were valuable to decompose formaldehyde in water, as we have reported before .
The reaction system described above was applied for the decomposition of formaldehyde gas in air, which is known as sick building syndrome gas . In this time we used cellulose nanofibers as a scaffold of dendrimer-mediated Pt catalyst, because the produced film can be easy handled as an absorbent of gases and to decompose the adsorbed gases. Pt nanoparticles were chemically combined to nanofibers by mediating dendrimer, and hybrid films were prepared. The hybrid films were exposed on formaldehyde vapor and the formaldehyde-adsorbed films were analyzed using spectrophotometry. The analytical results indicated that the formaldehyde was adsorbed on whole area of films but formaldehyde molecules trapped only in or near Pt-encapsulating dendrimer were catalysis-decomposed. These results indicate that the catalyst-loaded textile will be successfully created even for CO2 decomposition, although this is the subject in the next year.
1) Selective capture of CO2 by poly(amido amine) dendrimer-loaded organoclays, Kinjal J. Shah, Atindra D. Shukla, and Toyoko Imae,* RSC Advances 5, 35985-35992 (2015).
2) Analytical investigation of specific adsorption kinetics of CO2 gas on dendrimer loaded in organoclays, Kinjal Shah and Toyoko Imae,* Chem. Eng. J., 283, 1366-1373 (2016).
3) Applicability of organoclays towards wettability and gas adsorption, Kinjal J. Shah, PhD thesis in National Taiwan University of Science and Technology (2015).
4) Ag nanoparticle-immobilized cellulose nanofibril firms for environmental conservation, Bendi Ramaraju, Toyoko Imae* and Addisu Getachew Destaye, Applied Catalysis A: General 492, 184-189 (2015).
5) pH-dependent loading of Pt nanoparticles protected by dendrimer in calcium phosphate matrices, Yakub Fam, Toyoko Imae,* Jonathan Miras, Maria Martinez, Jordi Esquena, Microporous and Mesoporous Materials, 198, 161-169 (2014).
6) Catalytic oxidation of formaldehyde in water by calcium phosphate-based Pt composites, Yakub Fam and Toyoko Imae,* RSC Advances 5, 15944-15953 (2015).
7) Decomposition of sick house gas by catalyst embedded in cellulose nanofiber film, MS thesis, 劉加毅, MS thesis in National Taiwan University of Science and Technology (2015).
Energy science (Development of validated systems for energy storage):
The increasing demand for regenerable energy resources with enhanced energy density encourages the race for finding new devices for energy–production and storage, including solar cells, fuel cells, rechargeable batteries and supercapacitors. Among such devices, supercapacitors are one of the most talented devices. They exhibit many advantages, including high energy density, fast charge/discharge rate and excellent durability. These features enable supercapacitors to be efficiently used in hybrid electric vehicles and electronic devices. Electrochemical capacitors are classified into two major categories of electric double layer capacitors (EDLC) and pesudocapacitors (PC). The non–faradic process occurring in EDLC is caused by the ion absorption on the active electrode materials at the electrode/electrolyte interface. On the other hand, the faradic process happening in PC is engaged with the redox reactions originated by the charge transfer reactions of metal/metal oxide electrodes. EDLC and PC with various nano-architectures and morphologies have extensively been investigated to achieve high–energy storage and effective capacitance activity.
Carbon-based materials including graphene are unique sources of EDLC due to their unique physical, chemical, electrical and mechanical properties, and conductive polymers or metal oxides are main components of PC owing to their strong electroconductivity. However, the energy density of carbon-based capacitors is not enough high in comparison with PC, and PC is not enough stable at stronger electrochemical conditions. Then the hybrids with different materials including other carbon materials, metal oxides and polymers will provide the preferably appropriate platform for hybrid capacitors. Especially, the conjugation of conductive polymers e.g. polyaniline (PANI), polypyrrole (ppy) and polythiophene with carbon materials can play an crucial role in capacitance enhancement due to the increase in the conductivity and the addition of faradic capacitance to the EDLC. Among different conductive polymers used, PANI has given an exceptional attention due to its mild synthesis procedures. In situ polymerization and electrodeposition are two main methods studied to bind the conductive polymers with graphene oxide (GO) and reduced graphene oxide (rGO), and the implantation of the conductive polymers on the graphenized functional groups is the main way for polymerization. However, GO or rGO provides the defective structure and thus the strong internal resistance drop in the charge and discharge process.
In order to avoid the internal resistance drop, a non-destructive exfoliation and polymerization processes are required. In our previous research, we have successfully prepared the defect-free graphene with remaining iron oxide nanoparticles to exfoliate graphene sheets via a mild amine treatment . Herein, this material was further exfoliated through the thermal procedure, and PANI and ppy were conjugated (hybridized) with the thermally exfoliated, non–defected graphene. The as-prepared graphenes and their hybrids were applied to the investigation of capacitance, one of the important electrochemical parameters on energy storage devices, since this material was expected to be able to achieve the typical supercapacitor behaviour with favourable efficiency. Structural characterizations were performed to scope the optimum condition that provides the excellent capacitance. Hybrids of graphene (EDLC materials) with electroconductive polymer (PC materials) should become new generation capacitors.
1) Massive-Exfoliation of Magnetic Graphene from Acceptor–Type GIC by Long-Chain Alkyl Amine, Masaki Ujihara,* Mahmoud Mohamed Mahmoud Ahmed, Toyoko Imae* and Yusuke Yamauchi, J. Mater. Chem. A, 2 (12), 4244 – 4250 (2014). SCI
- Life science (Fabrication of nanobiotechnological systems for medical therapy):
Targetable drug nanocarriers have been developed to achieve highly selective delivery of anticancer drugs to tumor cells in a controlled-release fashion. Graphene oxide (GO) is an oxidized graphene composed of a graphitic sheet, which is chemically functionalized with oxygen-including groups such as hydroxyl, carboxyl, carbonyl and epoxide . Due to its biocompatibility, many researchers have focused on the potential of using GO and its derivatives as a promising new material for biomedical applications. In particular, GO has been considered to be a potential carrier for drug delivery system, because the 2D sheet of GO has a large surface area. As a result, drugs can be loaded onto both sides of the graphene sheet through π–π stacking, covalent binding, and hydrophobic or electrostatic interaction. Folic acid (FA)–conjugated nano–GO (FA–nano–GO) has been shown to specifically target human MCF–7 breast cancer cells that express the folate receptor. Furthermore, the successively controlled loading of two anticancer drugs, doxorubicin (DOX) and camptothecin (CPT), onto FA–nano–GO has been achieved via π–π stacking and hydrophobic interactions.
In addition to these properties, the functionalization of GO with biodegradable, biocompatible, nonimmunogenic and water-soluble polymers, such as poly(amido amine) (PAMAM) dendrimers , could further enhance the utility of GO nanohybrid materials as nanocarriers in drug delivery systems. Because low-generation (G1-G4) PAMAM dendrimers can be electrostatically associated with lipid membranes and amphiphilic bilayers, the immobilization of PAMAM dendrimers onto GO may help GO hybrids to bind tightly on cell membranes. In addition, the cellular uptake of dendrimer–based drug delivery systems has been proven to be significantly higher than the linear polymeric carriers, which can be attributed to the nanosize and the compact, spherical geometry of dendrimers. Thus, it is imperative to modify GO with dendrimers to achieve effective drug loading ability and, consequently, efficient drug delivery.
In the present study, the advanced nanocarriers for drug delivery systems were developed by protecting GO with water-soluble PAMAM dendrimers [3,4]. Hydroxyl–terminated PAMAM dendrimers (DEN–OH) were selected, because compounds with amine-terminals are rather toxic. FA was also bound onto GO to target the nanocarriers to specific cells including HeLa cells. Then, in addition to a comparative study of the size dependence of the GO/DEN–OH/FA carriers, the carriers were assessed their ability to load and release doses of DOX and were also evaluated their effects on the viability and the intracellular uptake efficiency by HeLa cells.