Intercalative Ion-Exchange Route to Amino Acid Layered Double Hydroxide Nanohybrids and Their Sorption Properties

A soft chemical route to amino acid layered double hydroxide (LDH) nanohybrids was demonstrated on the basis of an intercalative ion‐exchange reaction. Two different amino acids, phenylalanine and glutamic acid, were intercalated and stabilized in the interlayer space of a 2‐dimensional double hydroxide lattice by electrostatic interaction. An attempt was also made to understand the effect of the intracrystalline structure of the amino acid in the LDH on the specific surface area, porosity, and gas sorption properties of the hybrid. According to the X‐ray diffraction analysis, the basal spacings of LDH intercalated with phenylalanine and LDH intercalated with glutamic acid were expanded to 1.80 and 1.22 nm, respectively, relative to that of the pristine Mg2Al‐NO3‐LDH (0.88 nm), which indicates that amino acid molecules were successfully intercalated into the LDH. Fourier transform infrared spectra for both samples confirmed that the carboxylic acid group in the amino acid is anionic carboxylate under basic conditions and it eventually interacts with the positively charged LDH surface. From N2 adsorption/desorption analysis, the BET specific surface area of the LDH intercalated with phenylalanine was found to be twice as large as that for the LDH intercalated with glutamic acid. However, the CO2 adsorption capacity of the former was determined to be three times more enhanced than that of the latter, due to an enhanced specific surface area and effective amine sites to form carbamates. The CO2 uptake capacity in the present study is influenced not only by the specific surface area but also by the number of reactive amine sites in the pore, as the amine groups of amino acids interact with adsorbed CO2 molecules to form carbamates by a zwitterionic mechanism even at low temperature.