FTIR Study of Adsorption of CO₂ on Nonstoichiometric Calcium Hydroxyapatite

Abstract

The surfaces of calcium hydroxyapatite (CaHAP) particles with different Ca/P atomic ratios, synthesized by the precipitation method, were characterized and the adsorption mechanism of CO2 on CaHAP at 25 °C was elucidated mainly by FTIR. The number of surface P-OH groups was maximum at Ca/P ) 1.6 while the quantity of irreversibly adsorbed CO2 was minimum at the same Ca/P. This indicates that the surface P-OH groups not only are the reversible adsorption sites for CO2 but also interfere with the irreversible adsorption of CO2. IR bands due to H2O and CO3 2appeared on CO2 adsorption and were intensified by increasing the adsorbed amount. The physisorbed CO2 was converted into CO3 2ions with the course of time. These results demonstrated that the irreversible adsorption of CO2 progresses via the reaction of CO2 with surface OH -: 2OH -+ CO2 f CO3 2-+ H2O.

The importance of amino acid interactions in the crystallization of hydroxyapatite

“…In line with the XRD results, the FT-IR spectra for all samples recorded at the precipitation time and after 2 days of reaction matched the spectra recorded on carbonated HA (CHA) [43,44] (figure 8), and were very different from those obtained for other crystalline phases of calcium phosphates such as OCP [45]. However, the phosphate n 3 peaks on HA-Cont and AA-containing HA samples were sharper than in CHA, most likely indicating that the HA samples were more crystalline than the reference CHA [46], which is very rsif.royalsocietypublishing.org J R Soc Interface 10: 20120906…”

VAPOR-PHASE CATALYTIC CONVERSION OF ETHANOL INTO 1,3-BUTADIENE ON Cr-Ba/MCM-41 CATALYSTS

“…Regarding the measured CO 2 adsorption (Table 1), the CO 2 concentration per unit area increased with addition of barium and chromium in the following order: Al-MCM-41 < 16%Ba/Al-MCM-41 < 1.4%Cr-16%Ba/Al-MCM-41. In previous studies, it was reported that CO 2 can be absorbed irreversibly on OH -groups (basic sites) producing CO 3 2-and H 2 O species [Cheng et al, 1998]. Therefore, an increase of the catalyst basicity can be assigned to the alkali-earth properties of barium [Yang and Kim, 2010;Zhang and Singh, 2008] and to the tendency to form carbonates on the chromium surfaces [Seiferth et al, 1999;Kuhlenbeck et al, 1992].…”

Silicon and Phosphorus Linkage with Iron via Oxygen in the Amorphous Matrix of Gallionella ferruginea Stalks

“…5B, f), and 3,740 cm Ϫ1 (Fig. 5B, g) are assigned to the O-H stretching vibrations of OH groups attached to P (8,28), Fe (28), and Si (49,54,58,59), respectively. The band near 1,000 cm Ϫ1 is assigned to overlapped bands of Si-O-Fe (7,48,49) and P-O-Fe (10,22) stretching vibrations (Fig.…”