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1. Creation of inorganic-organic composite materials (especially layered compounds)

Selective separation of metal ions (Li+, Cu2+, Ni2+, Cd2+, Pb2+, Sr2+, Sc3+, La3+, Y3+, Nd3+) and non-ionic organic compounds (bisphenol A, diethyl phthalate, benzenes, phenols, naphthalenes) in aqueous solutions using inorganic-organic composite materials in which layers of layered compounds (e.g. layered double hydroxides: LDH) are functionalized with organic ions.・We developed a capture technology (Fig.3, Fig.4). Specifically, we succeeded in selectively separating and capturing metal ions and nonionic organic compounds from aqueous solutions using the functions of the functional groups of organic anions (chelate complex-forming ability, hydrophobic interaction, and π-π stacking interaction). We also succeeded in utilizing the functions of the functional groups of organic cations. We aim to apply this technology to the recovery of valuable metals and valuable organic compounds in process solutions.

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2. Capture and concentration of heavy metals by creating

  inorganic materials with capture and reduction functions

Efficient removal of heavy metal oxoanions (Cr(VI), Se(VI), As(V), Sb(V)) in aqueous solutions was developed using inorganic materials with scavenging and reducing functions. Fe2+ ​​doped Mg-Al-Fe LDHs with reducing ability have better scavenging ability than Mg-Al LDHs for Cr(VI) scavenging. This is due to the formation of Cr(OH)3 accompanying the reduction of Cr(VI) to Cr(III) by doped Fe2+ in addition to the anion exchange reaction between Cl- and CrO42- between LDH layers (redox reaction) (Fig. 5). Se(VI) and As(V) removal showed similar functions. This technology is expected to be applied to the removal of heavy metal oxoanions in wastewater, which is difficult to treat.

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3. Removal of various harmful substances in aqueous solution

A new treatment process for mineral acids (phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid) was developed using Mg-Al oxide obtained by calcination of Mg-Al LDH. We have found that Mg-Al oxide functions as a neutralizing agent for acids and a fixing agent for anionic species. Mg-Al LDH generated after hydrochloric acid and nitric acid treatment can be calcined as it is to generate hydrochloric acid and nitric acid. In addition, it was found that Mg-Al LDH, Mg-Al oxide and MgO can be recycled for removing boron and fluorine in an aqueous solution. Mg-Al LDH and Mg-Al oxide are also effective in removing heavy metal oxoanions of As(V) and Sb(V). It can be said that Mg-Al LDH and Mg-Al oxide are particularly effective in removing boron and fluorine from waste water, for which treatment methods are still being sought.

4. Development of heavy metal treatment of mine wastewater and contaminated soil

  and sludge reduction process

Mine effluent is usually acidic and contains heavy metals, so it must be treated to meet wastewater standards. At present, the neutralization method using Ca(OH)2 is common, but the large amount of sediment generated causes an increase in the load on the disposal site. In this study, we found that Mg-Al LDH is effective in treating heavy metals (Fe, Zn, Cu, Pb, As, Mn, Cd) in mine wastewater, and has a higher sediment volume reduction effect than conventional Ca(OH)2 treatment. Furthermore, in the treatment of heavy metals in mine wastewater, we found that the treatment efficiency of Mg-Al LDH nanosheets is much higher than that of Mg-Al LDH powder. It is expected to be put into practical use for actual mine wastewater treatment. On the other hand, we are developing extraction and enrichment techniques for Pb in contaminated soil by chelate reaction.

5. Construction of gas purification process using layered compounds

We found that Mg-Al oxide slurry is effective for simultaneous treatment of HCl, SOx and NOx in waste incineration flue gas. Mg-Al oxide is obtained by calcination of CO3•Mg-Al LDH. If CO3 • Mg-Al LDH can be used to treat waste incineration exhaust gas, the cost of the treatment agent (the cost of calcining) can be greatly reduced. In addition, NOx is often reduced by selective catalytic reduction (SCR), but reheating with boiler steam is performed to improve SCR efficiency, which is a major factor in reducing the efficiency of waste power generation. Therefore, in this research, we developed a new treatment technology for waste incineration exhaust gas (HCl, SOx and NOx) using CO3•Mg-Al LDH (Fig.6). This technology can contribute to reducing acid gas processing costs and increasing power generation efficiency. There is no technology that can treat HCl, SOx, and NOx at the same time, and CO3 • Mg-Al LDH can be recovered and recycled, so it can be recycled.

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6. Development of adsorption process for waste products in cell culture medium

In recent years, in the fields of pharmaceutical manufacturing and regenerative medicine, it has become necessary to artificially and efficiently culture cells and microorganisms in large quantities. Cells for which mass culture is required include antibody-producing cells such as Chinese hamster ovary cells (CHO cells) and pluripotent stem cells such as embryonic stem cells (ES cells) and induced pluripotent stem cells (iPS cells). Floating agitation culture using a culture vessel such as a spinner flask is considered as a method for industrially culturing cells and other materials in large quantities. To reduce costs, it is effective to increase the culture density of cells. However, the concentration of waste products (metabolites) in the culture medium (liquid medium) increases as the density of cells increases, which decreases the growth activity of cells. Lactic acid and ammonia are known as typical waste products that affect cells. In order to stably grow cells in a high-density state, it is desirable to remove lactic acid and ammonia that accumulate in the culture medium. In this study, Mg-Al LDH, Cu-Al LDH, Ni-Al LDH, Mg-Al oxide, Cu-Al oxide, and anion exchange resin were found to be effective (Fig. 7). In addition, zeolite, Prussian blue, and cation exchange resin were found to be effective adsorbents for ammonia.

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7. Development of dilute CO2 removal, concentration, and utilization processes

  (DAC: Moonshot Project)

As a core member of Tohoku University's PJ (Professor Yasuhiro Fukushima, Graduate School of Environmental Science), we are working on the technology to synthesize inorganic compounds with high CO2 adsorption, develop the DAC process in the atmosphere, and convert CO2 into ethylene urea (EU) at the same time as adsorption. Specifically, we will study the synthesis of mesoporous TixZr(1-x)O2 with a very large specific surface area by a combination of sol-gel and solvothermal methods, and functionalization of TixZr(1-x)O2 as a CO2 supply source for a reaction system that adsorbs CO2 and converts CO2 into EU (Fig.8). Previous studies have reported that EU, which is used in agricultural chemicals, can be synthesized from CO2 gas and ethylenediamine (EDA). However, the solvent corresponding to the saturated vapor pressure of the blown CO2 gas evaporates, and the reaction efficiency decreases. Therefore, in order to suppress the evaporation of the solvent, we are researching the adsorption of CO2 on the surface basic sites and pores of TixZr(1-x)O2 to function as a CO2 supply source for the reaction system of EU synthesis.

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