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Adsorption of citrate ions on hydroxyapatite synthetized by various methods.

Skwarek E, Janusz W, Sternik D - J Radioanal Nucl Chem (2013)

Bottom Line: The physical properties of the resulting powder were characterized by DTA/TG, XRD, AFM and SEM microscopy.The point of zero charge and the isoelectric point of samples were determined.The points pHpzc and pHIEP for sample 1 are pHpzc 7.5 and pHIEP 3; for sample 2 pHpzc 7.05 and pHIEP 3, for smaple 3 pHpzc 6.7 and pHIEP 3.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Chemistry, Maria Curie-Sklodowska University, Maria Curie-Sklodowska Sq. 5, 20-031 Lublin, Poland.

ABSTRACT

The specific adsorption of citric acid ions at hydroxyapatite interface was investigated by the means of radioisotope method ((14)C) as a function of citric acid ions concentration, NaCl concentration and pH. Application of the hydroxyapatite has become wide in the biomaterial field as the Ca10(OH)2(PO4)6 possess biocompatibility with human hard tissue. Hydroxyapatite was synthesized using three different methods. The physical properties of the resulting powder were characterized by DTA/TG, XRD, AFM and SEM microscopy. Physicochemical qualities characterizing the electrical double layer of the hydroxyapatite/NaCl solution interface were determined. The zeta potential and the adsorption of citric acid molecule were studied as a function of pH. The point of zero charge and the isoelectric point of samples were determined. Electrical double layer parameters of hydroxyapatite/NaCl interface are influenced by a synthesis method. The points pHpzc and pHIEP for sample 1 are pHpzc 7.5 and pHIEP 3; for sample 2 pHpzc 7.05 and pHIEP 3, for smaple 3 pHpzc 6.7 and pHIEP 3. Temperature has weak influence both on pure substance and with citric acid adsorbed, as derivatographic analysis has shown, and characterization of hydroxyapatite structure may be carried out by this thermal analysis. Two phenomena are responsible for citric acid adsorption: phosphate group's replacement at hydroxyapatite surface by citric ions parallel to intraspherical complexes formation.

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Adsorption of citric acid samples 1 (a), 2(b), 3(c)
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Fig6: Adsorption of citric acid samples 1 (a), 2(b), 3(c)

Mentions: Figure 6 presents dependence of citrate ions adsorption on hydroxyapatite/0.001 mol/dm3 NaCl solution. As it can be seen the citrate adsorption does not reach 100 % of pH in any of the initial concentrations. In lowest concentrations it reaches only 85 % and that is why it is hard to establish parameters of the adsorption rim such as pH50 % or pH10–90 %, because in the examined structure there is no adsorption envelope typical for specific anion adsorption. The proposed mechanism of citric acid adsorption on hydroxyapatite consists in replacing the phosphate ions with citrate ions. Dissociation constants of phosphoric acid pKa1 = 2.83, pKa2 = 7.2 pKa3 = 11.9 and citric acid pKa1 = 3.13, pKa2 = 4.76 pKa3 = 6.40, except for the first step are lower than the respective dissociation constants of citric acid. Therefore replacing the phosphate groups on the surface with the citrate groups will lead to the increase of the density of negatively charged groups on the hydroxyapatite surface. The mechanism of exchanging ions must be excluded because it should lead to a significant increase of negative charge as a result of the increase of citrate adsorption. The citrate ions definitely change the character of the surface of hydroxyapatite-they change its acidic character. Probably it is caused by the creation of the intraspherical complexes as a result of citrate adsorption.Fig. 6


Adsorption of citrate ions on hydroxyapatite synthetized by various methods.

Skwarek E, Janusz W, Sternik D - J Radioanal Nucl Chem (2013)

Adsorption of citric acid samples 1 (a), 2(b), 3(c)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4514589&req=5

Fig6: Adsorption of citric acid samples 1 (a), 2(b), 3(c)
Mentions: Figure 6 presents dependence of citrate ions adsorption on hydroxyapatite/0.001 mol/dm3 NaCl solution. As it can be seen the citrate adsorption does not reach 100 % of pH in any of the initial concentrations. In lowest concentrations it reaches only 85 % and that is why it is hard to establish parameters of the adsorption rim such as pH50 % or pH10–90 %, because in the examined structure there is no adsorption envelope typical for specific anion adsorption. The proposed mechanism of citric acid adsorption on hydroxyapatite consists in replacing the phosphate ions with citrate ions. Dissociation constants of phosphoric acid pKa1 = 2.83, pKa2 = 7.2 pKa3 = 11.9 and citric acid pKa1 = 3.13, pKa2 = 4.76 pKa3 = 6.40, except for the first step are lower than the respective dissociation constants of citric acid. Therefore replacing the phosphate groups on the surface with the citrate groups will lead to the increase of the density of negatively charged groups on the hydroxyapatite surface. The mechanism of exchanging ions must be excluded because it should lead to a significant increase of negative charge as a result of the increase of citrate adsorption. The citrate ions definitely change the character of the surface of hydroxyapatite-they change its acidic character. Probably it is caused by the creation of the intraspherical complexes as a result of citrate adsorption.Fig. 6

Bottom Line: The physical properties of the resulting powder were characterized by DTA/TG, XRD, AFM and SEM microscopy.The point of zero charge and the isoelectric point of samples were determined.The points pHpzc and pHIEP for sample 1 are pHpzc 7.5 and pHIEP 3; for sample 2 pHpzc 7.05 and pHIEP 3, for smaple 3 pHpzc 6.7 and pHIEP 3.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Chemistry, Maria Curie-Sklodowska University, Maria Curie-Sklodowska Sq. 5, 20-031 Lublin, Poland.

ABSTRACT

The specific adsorption of citric acid ions at hydroxyapatite interface was investigated by the means of radioisotope method ((14)C) as a function of citric acid ions concentration, NaCl concentration and pH. Application of the hydroxyapatite has become wide in the biomaterial field as the Ca10(OH)2(PO4)6 possess biocompatibility with human hard tissue. Hydroxyapatite was synthesized using three different methods. The physical properties of the resulting powder were characterized by DTA/TG, XRD, AFM and SEM microscopy. Physicochemical qualities characterizing the electrical double layer of the hydroxyapatite/NaCl solution interface were determined. The zeta potential and the adsorption of citric acid molecule were studied as a function of pH. The point of zero charge and the isoelectric point of samples were determined. Electrical double layer parameters of hydroxyapatite/NaCl interface are influenced by a synthesis method. The points pHpzc and pHIEP for sample 1 are pHpzc 7.5 and pHIEP 3; for sample 2 pHpzc 7.05 and pHIEP 3, for smaple 3 pHpzc 6.7 and pHIEP 3. Temperature has weak influence both on pure substance and with citric acid adsorbed, as derivatographic analysis has shown, and characterization of hydroxyapatite structure may be carried out by this thermal analysis. Two phenomena are responsible for citric acid adsorption: phosphate group's replacement at hydroxyapatite surface by citric ions parallel to intraspherical complexes formation.

No MeSH data available.


Related in: MedlinePlus