Surface modification of calcium hydroxyapatite with pyrophosphoric acid

Structure of synthetic calcium hydroxyapatite particles modified with pyrophosphoric acid

“…However, to our knowledge, no study has been reported on the regulation of the number of surface P-OH groups except for our study [14]. Recently, we reported that pyrophosphoric acid (H 4 P 2 O 7 :PP) reacts with surface P-OH groups to form additional surface P-OH groups and suggested that the modified materials were more aggregated than unmodified one [14], though the detail aggregation process has not been fully established. To confirm this, the CaHap surface should be modified at higher PP concentrations rather than those used in the previous study.…”

“…The colloidal CaHap particles were synthesized from a wet method by aging the precipitates formed from the reaction of Ca(OH) 2 solutions with H 3 PO 4 in a sealed Teflon vessel under CO 2 -free conditions at 100 • C for 48 h [14]. The Ca/P molar ratio of CaHap thus prepared was 1.62, meaning that the material was Ca 2+ -deficient.…”

“…In spectrum b of the CaHap modified at [PP] = 2.0 mmol dm −3 , a new band is found at 3670 cm −1 . This band has been ascribed to the O-H stretching vibration modes of additional isolated surface P-OH groups formed by the reaction of surface P-OH groups of CaHap and PP as follow [14]:…”

“…[PP] (mmol dm −3 ): (a) 0, (b) 2.0, (c) 6.0, (d) 10.2, (e) 17.3, (f) 33.7, (g) 52.6, (h) 76.8. Before the measurements, the samples were outgassed at 300 • C for 2 h.Besides, the additional surface P-OH groups formed by reaction (1) also react with PP as follow[14]:P-O-PO(OH) 2 (surface) + H 4 P 2 O 7 →P-O-PO(OH)-O-PO(OH) 2 (surface) + H 3 PO 4 . (2)Note that the number of surface P-OH groups formed by reactions (1) and(2)corresponds to additional amounts of PO 4 of the materials, meaning that the number of surface P-OH groups of CaHap increases with increasing the additional amount of PO 4 .…”

Design and Synthesis of Hydroxyapatite with Organic Modifiers for Application to Environmental Remediation

“…This is accomplished by contacting the HAP with PPA in acetone. The higher the PPA concentration used in the contact, the greater the number of PO 4 groups in the resulting HAP, leading to a decreased Ca/P ratio, from 1.62 to 1.35 [36].…”