Jan.  23,  2014  1  US  2014/0021404 Al  METHOD FOR PRODUCING  ANION-EXCHANGING LAYERED DOUBLE  HYDROXIDE AND METHOD FOR  SUBSTITUTING CARBONATE ION OF  LAYERED DOUBLE HYDROXIDE  TECHNICAL FIELD  BACKGROUND ART  CITATION LIST  Patent Literature  Non-Patent Literature  [0001]  The present invention relates to a method for pro› ducing an anion-exchanging layered double hydroxide hav› ing easily ion-exchangeable anions  (X-)  between layers.  More specifically, the present invention relates to a method  for producing an anion-exchanging layered double hydroxide  by substituting carbonate ions, using a layered double  hydroxide containing hardly ion-exchangeable carbonate  ions (CO$_{3 }$ 2 -) between layers as a starting material, and a  method for substituting carbonate ions of the carbonate-ion› containing layered double hydroxide.  [0002]  Many layered compounds have been developed by  using layered compounds such as clay minerals, and by  allowing various types of cations or cationic functional  organic substances to be included in such layered com› pounds. This method capitalizes on the fact that clay mineral  layers have negative charge, and that cations existing between  layers are easily ion-exchangeable. The layered double  hydroxide (hereinafter referred to as LDH) has, unlike clay  minerals, positively-charged layers, has anions between lay› ers, and has anion-exchanging property. Since there are only  a few types of inorganic anion-exchanging materials, LDHs  are attracting attention (Non-patent Literature 1).  [0003]  As a method for synthesizing a layered compound  having anions between LDH layers, some methods for sub› stituting carbonate ions by other anions using an LDH con› taining carbonate ions between layers (hereinafter referred to  as carbonate ion-type LDH) are known.  [0004]  Since the carbonate ion-type LDH can be synthe› sized easily and high-quality crystal having high crystallinity  can be obtained, most of the LDHs manufactured industrially  are this carbonate ion-type LDHs. However, the carbonate  ion-type LDHs have extremely low ion-exchangeability, and  therefore it is difficult to change them into LDHs containing  anions other than carbonate ions by ordinary anion exchange  (Non-patent Literature 2). If carbonate ion-type LDHs can be  converted into anion-exchanging LDHs containing easily  ion-exchangeable anions (such as perchlorate ions, nitrate  ions, and chlorine ions) by simpler chemical process, broad  application is expected both industrially and at research and  test levels. A method for converting carbonate ion-type LDHs  to anion-exchanging LDHs by simpler chemical process has  therefore been desired.  [0005]  The inventors have found that by allowing a mixed  solution of hydrochloric acid and sodium chloride (NaCl) to  react with a carbonate ion-type LDH at a room temperature,  decarbonation occurs, converting the carbonate ion-type  LDH into an LDH containing chlorine ions (Ci-) (Patent  Literature 1, Non-patent Literature 3).  [0006]  Decarbonation that uses a mixed chloric acid-NaCl  solution is simple. However, since the solution is highly  acidic, and in addition the LDH itself is easily soluble to an  aqueous solution of acid, it is necessary to cause decarbon› ation to occur under the condition where LDH does not dis› solve. Furthermore, in the decarbonation using a mixed chlo- ric acid-NaCl solution, complete conversion into an anion› exchanging LDH other than  c1- type (such as ClO$_{4}$ -- and  NO$_{3 }$ - -types) was difficult (Non-patent Literature 4). As  described above, the decarbonation using a mixed chloric  acid-NaCl solution is groundbreaking as a method for pro› ducing LDHs containing chlorine ions, namely easily anion› exchangeable anions without affecting particle size or unifor› mity. Due to problems described previously, however, further  improvement has been desired.  [0007]  The inventors found that by using a mildly acidic  acetic acid buffer solution and allowing a solution prepared  by adding neutral salt such as sodium chloride (NaCl),  sodium perchlorate, and sodium nitrate to this acetic acid  buffer solution to react with carbonate ion-type LDH at a  room temperature, decarbonation occurred, causing conver› sion into an LDH containing anions that had been added  (Patent Literature 2, Non-patent Literatures 5 and 6). This  method has also ensured conversion into an anion-exchang› ing LDH of a type other than  c1- type (such as ClO$_{4}$ - - and  NO$_{3 }$ - -types).  [0008]  With this reaction, however, since ion exchange  reaction due to chemical equilibrium also occurs, a largely  excessive amount of anions to be inserted in LDH layers must  exist in the reaction system. In particular, since perchlorate  ions and nitrate ions are low in affinity to LDHs, an excessive  amount of salt was needed to introduce these anions (Non› patent Literature 6). Furthermore, as a result of using acetic  acid buffer solution to adjust the acidity, anionic acetate ions  exist in the system. Consequently, depending on the type of  the LDH, there was a risk of entry of acetate ions between  layers. As described above, the method using an acetic acid  buffer solution has allowed decarbonation to occur under  stable pH conditions. However, many types of reagents must  be used in largely excessive amounts, and depending on the  type ofLDH, there was a risk of allowing entry of acetate ions  existing in the system. Solving these problems has been nec› essary.  [0012]  Non-patent Literature 1: Cavani, F., Trifiro, F., Vac› cari, A., Cata!. Today 11, 173-301 (1991)  [0013]  Non-patent Literature 2: Miyata, S., Clays Clay  Miner. 31, 305-311 (1983)  [0009]  Patent Literature 1: JP 4228077 B  [0010]  Patent Literature 2: WO 2009/072488  [0011]  Patent Literature 3: JP 2005 335965 A  [0014]  Non-patent Literature 3: Iyi, Nobuo, Matsumoto, T.,  Kaneko,  Y., Kitamura, K., Chem. Mater. 16, 2926-2932  (2004)  [0015]  Non-patent Literature 4: Iyi, Nobuo, Okamoto, K.,  Kaneko,  Y., Matsumoto, T., Chem. Lett. 34, 932-933  (2005)  [0016]  Non-patent Literature 5: Iyi, Nobuo, Sasaki, Takay› oshi, J. Colloid Interface Sci. 322, 237-245 (2008)  [0017]  Non-patent Literature 6: Iyi, Nobuo, Yamada, Hiro› hisa, Chem. Lett. 39, 591-593 (2010)  [0018]  Non-patent Literature 7: Iyi, N., Fujii, K., Okamoto,  K., Sasaki, Takayoshi,Appl. Clay Sci. 35, 218-227 (2007) 