“…Ishikawa et al have found that the CaHap surface possesses three kinds of P-OH groups acting as the adsorption sites for CO 2 , CH 3 OH, CH 3 I, and H 2 O [5][6][7]. In addition, it has been found by TPD and Fourier transform infrared (FTIR) that pyridine, n-butylamine, and acetic acid are adsorbed on CaHap by hydrogen bonding to the surface P-OH groups of CaHap, and the number of surface P-OH groups on nonstoichiometric CaHap is 2.6 groups nm −2 [8][9][10]. Hence the regulation of surface P-OH groups may be expected to change various properties of CaHap, e.g., acidity and basicity, affinity and reactivity to molecules, and catalytic activity.…”