*4.1.2 FT-IR spectroscopy*

**Figures 4** and **5** shows the FT-IR spectra of CaHAp, CaHAp-Alg and CaHAp- (Carr). In all IR spectra, the vibration bands of PO4 3− groups of the apatite structure are observed at (νs) 965 cm−1, (δs) 482 cm−1, (νas) 1041-1094 cm−1 and (δas), 567- 605 cm−1 [25]. Moreover, for characteristic bands of hydroxyl ions were observed towards (νs) 3572 cm−1 and (νL) 634 cm−1 [26].

The two broad bands located at 1403-1462 and 1640 cm−1 were assigned, respectively, to the carbonate ions and water adsorbed on the surface. Besides, the band located at 877 cm−1 was assigned to the (HPO4 2−) group [27].

After grafting, the intensity of the hydroxyls bands (υs and νL) decrease progressively with increasing Alg or (λ-Carr) amount. This can be explained by the low degree of crystallinity [28].

**171**

(Alg) [29, 30].

**Figure 4.**

**Figure 3.**

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents…*

The presence of biopolymers (Alg or carr) on the apatitic surface is confirmed by the appears of new vibrations bands at 1231 cm−1 and (1626, 1323 and 1428 cm−1)

On the other hand, the conservation in the band intensity of P-OH group at 870 cm−1 indicates that fixing process of (λ-Carr) or Alg is done only by the interaction

groups of

which are assigned respectively, to S-O groups of (λ-Carr) and COO<sup>−</sup>

*FTIR spectra of modified hydroxyapatites by sodium alginate.*

*Powder x-ray diffraction patterns of modified hydroxyapatites by lambda carrageenan.*

*DOI: http://dx.doi.org/10.5772/intechopen.95347*

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents… DOI: http://dx.doi.org/10.5772/intechopen.95347*

**Figure 3.** *Powder x-ray diffraction patterns of modified hydroxyapatites by lambda carrageenan.*

**Figure 4.** *FTIR spectra of modified hydroxyapatites by sodium alginate.*

The presence of biopolymers (Alg or carr) on the apatitic surface is confirmed by the appears of new vibrations bands at 1231 cm−1 and (1626, 1323 and 1428 cm−1) which are assigned respectively, to S-O groups of (λ-Carr) and COO<sup>−</sup> groups of (Alg) [29, 30].

On the other hand, the conservation in the band intensity of P-OH group at 870 cm−1 indicates that fixing process of (λ-Carr) or Alg is done only by the interaction

*Dyes and Pigments - Novel Applications and Waste Treatment*

X-ray diffractograms of hydroxyapatite-Alg and hydroxyapatite-(λ-Carr) are presented in **Figures 2** and **3**. For all compounds, the hydroxyapatite phase is conserved according to 00-024-0033 reference from the ICDD-PDF2 2003 database. However, in the case of CaHAp1-(Alg)20% new peaks appear at 2θ = 26.60° and 30.14°. These peaks are characteristic of monetite phase (CaHPO4) according to 01-077-0128 reference from the ICDD-PDF22003 database. The increase of the amount of biopolymer induced the broadening of peaks, which proves their

**Figures 4** and **5** shows the FT-IR spectra of CaHAp, CaHAp-Alg and CaHAp-

The two broad bands located at 1403-1462 and 1640 cm−1 were assigned, respectively, to the carbonate ions and water adsorbed on the surface. Besides, the band

After grafting, the intensity of the hydroxyls bands (υs and νL) decrease progressively with increasing Alg or (λ-Carr) amount. This can be explained by the low

2−) group [27].

are observed at (νs) 965 cm−1, (δs) 482 cm−1, (νas) 1041-1094 cm−1 and (δas), 567- 605 cm−1 [25]. Moreover, for characteristic bands of hydroxyl ions were observed

3− groups of the apatite structure

**4. Results and discussion**

*4.1.1 X-ray diffraction*

*4.1.2 FT-IR spectroscopy*

degree of crystallinity [28].

**4.1 Characterization of adsorbents**

incorporation on the apatitic surface.

(Carr). In all IR spectra, the vibration bands of PO4

towards (νs) 3572 cm−1 and (νL) 634 cm−1 [26].

located at 877 cm−1 was assigned to the (HPO4

*Powder x-ray diffraction patterns of modified hydroxyapatites by sodium alginate.*

**170**

**Figure 2.**

**Figure 5.**

*FTIR spectra of modified hydroxyapatites by lambda carrageenan.*

between ≡Ca-OH groups of apatitic surface and functional groups of each biopolymer.

The possible modes of interaction of (Alg) or (λ-Carr) with the CaHAp1 or CaHap2 surface have been gathered in **Figures 6** and **7**.

### *4.1.3 Scanning electron microscope (SEM)*

**Figure 8** shows the morphological variations of CaHAp1 or CaHAp1 before and after reaction with Alg or (λ-Carr). The CaHAp1 or caHap2 is composed of irregular particles with a strong tendency to aggregate (**Figure 8a, b**), whereas the modified hydroxyapatites showed that their shapes become relatively agglomerates

**173**

**Figure 8.**

**Figure 7.**

*4.1.4 Textural properties*

*(d) CaHAp2-(Carr)10.*

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents…*

*Proposed mechanism of the interaction between (*λ*-Carr) and CaHAp2 surface.*

of different sizes and poorly defined shape (**Figure 8**(**c**, **d**)). This change is due to the formation of new hybrid compounds CaHAp2–(λ-Carr) and CaHAp1-(Alg).

*SEM photomicrograph of modified hydroxyapatites: (a) CaHAp1, (b) CaHAp2, (c) CaHAp1-(Alg)10 and* 

The surface characteristics of the Hydroxyapatite samples obtained by the BET method, both before and after modification, are shown in **Table 1**. The treatment of hydroxyapatite with Alg biopolymer leads to the decreasing of specific surface area compared to that of ungrafted CaHAp1, covering the range from 20.52 to 3.39 m<sup>2</sup>

According to BET results, The fact that the surface area of CaHAp1-(Alg)5 and

/g.

*DOI: http://dx.doi.org/10.5772/intechopen.95347*

**Figure 6.** *Proposed mechanism of the interaction between Alg and CaHAp1 surface.*

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents… DOI: http://dx.doi.org/10.5772/intechopen.95347*

**Figure 8.**

*Dyes and Pigments - Novel Applications and Waste Treatment*

between ≡Ca-OH groups of apatitic surface and functional groups of each

CaHap2 surface have been gathered in **Figures 6** and **7**.

*Proposed mechanism of the interaction between Alg and CaHAp1 surface.*

*FTIR spectra of modified hydroxyapatites by lambda carrageenan.*

*4.1.3 Scanning electron microscope (SEM)*

The possible modes of interaction of (Alg) or (λ-Carr) with the CaHAp1 or

**Figure 8** shows the morphological variations of CaHAp1 or CaHAp1 before and after reaction with Alg or (λ-Carr). The CaHAp1 or caHap2 is composed of irregular particles with a strong tendency to aggregate (**Figure 8a, b**), whereas the modified hydroxyapatites showed that their shapes become relatively agglomerates

**172**

**Figure 6.**

biopolymer.

**Figure 5.**

*SEM photomicrograph of modified hydroxyapatites: (a) CaHAp1, (b) CaHAp2, (c) CaHAp1-(Alg)10 and (d) CaHAp2-(Carr)10.*

of different sizes and poorly defined shape (**Figure 8**(**c**, **d**)). This change is due to the formation of new hybrid compounds CaHAp2–(λ-Carr) and CaHAp1-(Alg).

#### *4.1.4 Textural properties*

The surface characteristics of the Hydroxyapatite samples obtained by the BET method, both before and after modification, are shown in **Table 1**. The treatment of hydroxyapatite with Alg biopolymer leads to the decreasing of specific surface area compared to that of ungrafted CaHAp1, covering the range from 20.52 to 3.39 m<sup>2</sup> /g. According to BET results, The fact that the surface area of CaHAp1-(Alg)5 and

#### *Dyes and Pigments - Novel Applications and Waste Treatment*


**Table 1.**

*Measurement of surface area of grafted hydroxyapatites.*

CaHAp1-(Alg)10 materials is lower than those in CaHAp1 can be explained with the filling of pores on the surface of hydroxyapatite by sodium alginate biopolymer. On the other hand, the specific surface of modified hydroxyapatite by lambda carrageenan increases with the increasing of grafting rate. The maximum value is obtained for CaHAp2-(λ-Carr) 20 (SSA = 260 m2 /g).

#### **4.2 Evaluation of the performance of the prepared compounds for the adsorption of MB**

#### *4.2.1 Effect of pH*

**Figures 9** and **10** represent the variation of the adsorption capacity of MB on the surface of CaHAp1, CaHAp2, CaHAp1-(Alg) and CaHAp2-(λ-Carr) at different pH values. According to these figures, the MB removal increases gradually up to a pH very close to 5, and after kept nearly constant with further pH increase. The effect

#### **Figure 9.**

*Effect of initial pH on the adsorption of MB (Adsorbent dosage = 1 g/L, initial MB concentration = 50 mg/L, solution volume = 50 mL, temperature = 25°C, contact time = 3h).*

**175**

(COO−

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents…*

of pH on adsorption depends on the point zero charge (pH pzc) of adsorbent. The value of pHpzc was found to be 6.2, 6.7 and 7.3 by CaHAp1, CaHAp2-(Carr)10 and CaHAp1-(Alg)10, respectively, in good agreement with literature data [31]. Indeed, for pH< pH pzc, the surface of hydroxyapatite is positively charged which causes

*Effect of initial pH on the adsorption of MB (Adsorbent dosage = 1 g/L, initial MB concentration = 10 mg/L,* 

tion of dye. In the case of modified hydroxyapatite, the amount of dye adsorbed is higher than unmodified because (Alg) or (λ-Carr) contains carboxylate (–COO<sup>−</sup>

The adsorptions of MB onto modified hydroxyapatites were studied with

in **Figures 11** and **12**, the adsorption amounts of MB on the modified hydroxyapatites increased rapidly with an increase in time and then became slower until the equilibrium was reached. Equilibrium is reached for all compounds prepared at low durations between 20 and 30 min. This may be due to the rapid saturation of the pores of ours prepared adsorbents. The maximum adsorption is obtained for hydroxyapatite synthetized in the presence of biopolymer with 10% content. Therefore, the increase of MB removal with the increasing of adsorbent dose is mainly due to the increasing of interaction forces between the carboxylate groups

−

groups. The possible modes of interaction between MB and either CaHAp1-(Alg) or

*4.2.3 Effect of temperature and initial dye concentration on the adsorption process*

**Figures 15** and **16** shows the effect of temperature on the adsorption of MB on the surface of the prepared supports CaHAp1, CaHAp2, CaHAp1-(Alg) and CaHAp2-(λ-Carr). As it is observed, the removal of MB by CaHAp2 increases with increasing the temperature of the solution from 25 to 60°C, indicating that

different biopolymer doses and at different periods of time. As shown

) groups, respectively, that increase the interaction with dye

), and hence low adsorp-

) of (λ-Carr) and MB molecules via N<sup>+</sup>

)

the repulsion of cationic groups of the MB molecule (=N+

−

*solution volume =25 mL, temperature = 25°C, contact time = 3h).*

*4.2.2 Effect of contact time and adsorbent dose*

) of (Alg) or sulphonate goups (OSO3

or CaHAp2-(λ-Carr) surface are given in **Figures 13** and **14**.

and sulphonate (OSO3

molecules.

**Figure 10.**

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*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents… DOI: http://dx.doi.org/10.5772/intechopen.95347*

#### **Figure 10.**

*Dyes and Pigments - Novel Applications and Waste Treatment*

obtained for CaHAp2-(λ-Carr) 20 (SSA = 260 m2

*Measurement of surface area of grafted hydroxyapatites.*

**adsorption of MB**

*4.2.1 Effect of pH*

**Table 1.**

**174**

**Figure 9.**

*Effect of initial pH on the adsorption of MB (Adsorbent dosage = 1 g/L, initial MB concentration = 50 mg/L,* 

CaHAp1-(Alg)10 materials is lower than those in CaHAp1 can be explained with the filling of pores on the surface of hydroxyapatite by sodium alginate biopolymer. On the other hand, the specific surface of modified hydroxyapatite by lambda carrageenan increases with the increasing of grafting rate. The maximum value is

**Samples Surface area (m2**

CaHAp1 21.64 CaHAp2 93.00 CaHAp1-(Alg)5 12.84 CaHAp1-(Alg)10 3.39 CaHAp2-(λ-Carr)5 168.00 CaHAp2-(λ-Carr)10 253.00 CaHAp2-(λ-Carr)20 260.00

**Figures 9** and **10** represent the variation of the adsorption capacity of MB on the surface of CaHAp1, CaHAp2, CaHAp1-(Alg) and CaHAp2-(λ-Carr) at different pH values. According to these figures, the MB removal increases gradually up to a pH very close to 5, and after kept nearly constant with further pH increase. The effect

**4.2 Evaluation of the performance of the prepared compounds for the** 

/g).

**/g)**

*solution volume = 50 mL, temperature = 25°C, contact time = 3h).*

*Effect of initial pH on the adsorption of MB (Adsorbent dosage = 1 g/L, initial MB concentration = 10 mg/L, solution volume =25 mL, temperature = 25°C, contact time = 3h).*

of pH on adsorption depends on the point zero charge (pH pzc) of adsorbent. The value of pHpzc was found to be 6.2, 6.7 and 7.3 by CaHAp1, CaHAp2-(Carr)10 and CaHAp1-(Alg)10, respectively, in good agreement with literature data [31]. Indeed, for pH< pH pzc, the surface of hydroxyapatite is positively charged which causes the repulsion of cationic groups of the MB molecule (=N+ ), and hence low adsorption of dye. In the case of modified hydroxyapatite, the amount of dye adsorbed is higher than unmodified because (Alg) or (λ-Carr) contains carboxylate (–COO<sup>−</sup> ) and sulphonate (OSO3 − ) groups, respectively, that increase the interaction with dye molecules.

#### *4.2.2 Effect of contact time and adsorbent dose*

The adsorptions of MB onto modified hydroxyapatites were studied with different biopolymer doses and at different periods of time. As shown in **Figures 11** and **12**, the adsorption amounts of MB on the modified hydroxyapatites increased rapidly with an increase in time and then became slower until the equilibrium was reached. Equilibrium is reached for all compounds prepared at low durations between 20 and 30 min. This may be due to the rapid saturation of the pores of ours prepared adsorbents. The maximum adsorption is obtained for hydroxyapatite synthetized in the presence of biopolymer with 10% content. Therefore, the increase of MB removal with the increasing of adsorbent dose is mainly due to the increasing of interaction forces between the carboxylate groups (COO− ) of (Alg) or sulphonate goups (OSO3 − ) of (λ-Carr) and MB molecules via N<sup>+</sup> groups. The possible modes of interaction between MB and either CaHAp1-(Alg) or or CaHAp2-(λ-Carr) surface are given in **Figures 13** and **14**.

#### *4.2.3 Effect of temperature and initial dye concentration on the adsorption process*

**Figures 15** and **16** shows the effect of temperature on the adsorption of MB on the surface of the prepared supports CaHAp1, CaHAp2, CaHAp1-(Alg) and CaHAp2-(λ-Carr). As it is observed, the removal of MB by CaHAp2 increases with increasing the temperature of the solution from 25 to 60°C, indicating that

**Figure 11.**

*Effect of contact time on MB adsorption by CaHAp1 and CaHAp1–Alg (adsorption conditions: 0.05 g of adsorbent, initial MB concentration = 50 mg/L, solution volume = 50 mL, 6 < pH< 7, rpn =110 tr/min and temperature = 25 °C).*

#### **Figure 12.**

*Effect of contact time on MB adsorption by CaHAp1 and CaHAp2–(*λ*-Carr) (adsorption conditions: 0.05 g of adsorbent, initial MB concentration = 50 mg/L, solution volume = 50 mL, 6 < pH< 7, rpn =110 tr/min and temperature = 25 °C).*

the process is endothermic. In the case for other absorbents, the decrease of the adsorption of MB with the increase of temperature indicates that the adsorption is exothermic in nature.

This phenomenon could be explained by the decrease of the interaction between the MB ions and active sites in hydroxyapatite surface and the weakening of adsorptive forces between the carboxylate (COO<sup>−</sup> ) groups of (Alg) or sulphate (OSO3 − ) groups of (λ-Carr) and cationic dye molecules. As also depicted from **Figures 15** and **16**, the adsorbed amounts increase with the initial dye concentration to a threshold concentration corresponding to the saturation of the adsorption sites.

**177**

**Figure 13.**

could be seen as a good adsorbent.

a favorable adsorbent for MB dye removal.

*4.2.4 Modeling and determination of kinetic parameters*

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents…*

According to these figures, the maximum adsorption capacity of CaHap1- (ALg)10 is more important than those of CaHAp2-(λ-Carr)10, CaHAp1 and CaHAp2. The adsorbed quantities are respectively 128.4, 98.23, 68.5 and 58.8 mg/g. Compared to other adsorbents gathered from the literature (**Table 2**), this registered amount of dye removal is so very interesting and thus our developed product

*The possible modes of interaction between MB and either (a) CaHAp1 or (b) CaHAp1-(Alg).*

In fact, this value is more important com-pared to garlic peel used as adsorbent (82.64 mg/g), Raw date pits (80.3 mg/g) and wood (84 mg/g). It is nearly twice higher compared to Wood ash (50 mg/g). It is five times more important than the Cotton waste (24 mg/g) and. It is six times important than modified pumice stone (15.87 mg/g) and Pure kaolin (15.55 mg/g). It is hundred times important than Fly ash (1.3 mg/g). Consequently, the above results confirmed that CaHAp-(Alg)10 was

In order to evaluate the kinetics involved in the process of the adsorption of MB dye onto CaHAp1, CaHAp2, CaHAp2-(Carr)10 and CaHAp1-(Alg)10 surface,

*DOI: http://dx.doi.org/10.5772/intechopen.95347*

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents… DOI: http://dx.doi.org/10.5772/intechopen.95347*

**Figure 13.**

*Dyes and Pigments - Novel Applications and Waste Treatment*

the process is endothermic. In the case for other absorbents, the decrease of the adsorption of MB with the increase of temperature indicates that the adsorption is

*Effect of contact time on MB adsorption by CaHAp1 and CaHAp2–(*λ*-Carr) (adsorption conditions: 0.05 g of adsorbent, initial MB concentration = 50 mg/L, solution volume = 50 mL, 6 < pH< 7, rpn =110 tr/min and* 

*Effect of contact time on MB adsorption by CaHAp1 and CaHAp1–Alg (adsorption conditions: 0.05 g of adsorbent, initial MB concentration = 50 mg/L, solution volume = 50 mL, 6 < pH< 7, rpn =110 tr/min and* 

This phenomenon could be explained by the decrease of the interaction between the MB ions and active sites in hydroxyapatite surface and the weakening

tion to a threshold concentration corresponding to the saturation of the

) groups of (λ-Carr) and cationic dye molecules. As also depicted from **Figures 15** and **16**, the adsorbed amounts increase with the initial dye concentra-

) groups of (Alg) or sulphate

of adsorptive forces between the carboxylate (COO<sup>−</sup>

**176**

(OSO3 −

**Figure 12.**

**Figure 11.**

*temperature = 25 °C).*

exothermic in nature.

*temperature = 25 °C).*

adsorption sites.

*The possible modes of interaction between MB and either (a) CaHAp1 or (b) CaHAp1-(Alg).*

According to these figures, the maximum adsorption capacity of CaHap1- (ALg)10 is more important than those of CaHAp2-(λ-Carr)10, CaHAp1 and CaHAp2. The adsorbed quantities are respectively 128.4, 98.23, 68.5 and 58.8 mg/g. Compared to other adsorbents gathered from the literature (**Table 2**), this registered amount of dye removal is so very interesting and thus our developed product could be seen as a good adsorbent.

In fact, this value is more important com-pared to garlic peel used as adsorbent (82.64 mg/g), Raw date pits (80.3 mg/g) and wood (84 mg/g). It is nearly twice higher compared to Wood ash (50 mg/g). It is five times more important than the Cotton waste (24 mg/g) and. It is six times important than modified pumice stone (15.87 mg/g) and Pure kaolin (15.55 mg/g). It is hundred times important than Fly ash (1.3 mg/g). Consequently, the above results confirmed that CaHAp-(Alg)10 was a favorable adsorbent for MB dye removal.

#### *4.2.4 Modeling and determination of kinetic parameters*

In order to evaluate the kinetics involved in the process of the adsorption of MB dye onto CaHAp1, CaHAp2, CaHAp2-(Carr)10 and CaHAp1-(Alg)10 surface, *Dyes and Pigments - Novel Applications and Waste Treatment*

**Figure 15.**

*Effect of temperature (a) and initial concentration (b) on the removal of MB using CaHAp1 and CaHAp1-(Alg).*

pseudo-first-order, pseudo-second-order, Elovich, and intra-particle diffusion models were applied and results were discussed [42].

The results of the kinetic study, for hydroxyapatite synthesized in the presence of different amounts of Alg or (λ-Carr) are summarized in **Tables 3** and **4**. The best fit model was selected based on the linear regression correlation coefficient, R2 values. According to the regression coefficients (R<sup>2</sup> > 0.99), the pseudo-secondorder equation appears more suitable to describe the retention of MB on all prepared supports.

**179**

is favorable.

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents…*

*Effect of temperature on the removal of MB using: (a) CaHAp2 and (b) CaHAp2-(*λ*-Carr)10.*

**Samples qm (mg/g) References** CaHAp1-(Alg)10 128.40 In this work Garlic peel 82.64 [32] Wood ashes 50 [33] Cotton waste 24 [34] Modified pumice stone 15.87 [35] Natural phosphate 7.23 [36] natural zeolite 16.370 [37] Raw date pits 80.30 [38] Pure kaolin 15.55 [39] Fly ash 1.3 [40] Wood 84 [41]

Consequently, it can be confirmed that the adsorption is chemical and assumes

*Comparison of the maximum BM adsorption capacity of the adsorbents in this study with other adsorbents.*

In this study, Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich (D-R) isotherm models were used to describe the adsorption of MB onto ungrafted

than those of the other models for modified hydroxyapatite by sodium alginate. This indicates that the Langmuir model appears appropriate for modeling the adsorption isotherms of MB on CaHAp1 or CaHAp1-(Alg) surface. As seen in **Table 5**, the RL values [44] are situated within the range of 0< RL< 1, which means that prepared CaHAp or CaHAp-(Alg) is favorable for the adsorption of MB dye

For modified hydroxyapatite by lambda carrageenan, the analysis of regression coefficients shows better applicability of Freundlich model. Moreover, in all compounds, the values of calculated n are less than 1, indicating that the adsorption of MB

The obtained parameters of each model are given in **Tables 5** and **6**. According

), Langmuir model has the highest value

that the surface of our adsorbent is heterogeneous.

*4.2.5 Adsorption isotherm*

**Figure 16.**

**Table 2.**

and grafted hydroxyapatites [43].

to the analysis of regression coefficients (R2

under the experimental conditions conducted in this study.

*DOI: http://dx.doi.org/10.5772/intechopen.95347*

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents… DOI: http://dx.doi.org/10.5772/intechopen.95347*

**Figure 16.**

*Dyes and Pigments - Novel Applications and Waste Treatment*

pseudo-first-order, pseudo-second-order, Elovich, and intra-particle diffusion

*Effect of temperature (a) and initial concentration (b) on the removal of MB using CaHAp1 and* 

*The possible modes of interaction between MB and either (a) CaHAp2 or (b) CaHAp2-(*λ*-Carr).*

order equation appears more suitable to describe the retention of MB on all

The results of the kinetic study, for hydroxyapatite synthesized in the presence of different amounts of Alg or (λ-Carr) are summarized in **Tables 3** and **4**. The best fit model was selected based on the linear regression correlation coefficient,

> 0.99), the pseudo-second-

models were applied and results were discussed [42].

values. According to the regression coefficients (R<sup>2</sup>

**178**

R2

**Figure 15.**

*CaHAp1-(Alg).*

**Figure 14.**

prepared supports.

*Effect of temperature on the removal of MB using: (a) CaHAp2 and (b) CaHAp2-(*λ*-Carr)10.*


#### **Table 2.**

*Comparison of the maximum BM adsorption capacity of the adsorbents in this study with other adsorbents.*

Consequently, it can be confirmed that the adsorption is chemical and assumes that the surface of our adsorbent is heterogeneous.

#### *4.2.5 Adsorption isotherm*

In this study, Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich (D-R) isotherm models were used to describe the adsorption of MB onto ungrafted and grafted hydroxyapatites [43].

The obtained parameters of each model are given in **Tables 5** and **6**. According to the analysis of regression coefficients (R2 ), Langmuir model has the highest value than those of the other models for modified hydroxyapatite by sodium alginate. This indicates that the Langmuir model appears appropriate for modeling the adsorption isotherms of MB on CaHAp1 or CaHAp1-(Alg) surface. As seen in **Table 5**, the RL values [44] are situated within the range of 0< RL< 1, which means that prepared CaHAp or CaHAp-(Alg) is favorable for the adsorption of MB dye under the experimental conditions conducted in this study.

For modified hydroxyapatite by lambda carrageenan, the analysis of regression coefficients shows better applicability of Freundlich model. Moreover, in all compounds, the values of calculated n are less than 1, indicating that the adsorption of MB is favorable.


**Table 3.**

**181**

chemical [42].

**Table 5.**

**Table 4.**

*pH = 5).*

**Isotherm model**

following equation [21].

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents…*

**Pseudo-first-order Pseudo-second-order Elovich Intra-particular** 

**K1 qe R2 K2 qe R2 α** β **R2 Ki R2**

*Kinetic constants for the adsorption of studied dyes on hydroxyapatite-Carrageenan (T = 25°C, C0 = 10 mg/L,* 

**Adsorption constant Adsorbent**

KL (l/mg) 0.038 0.041 0.062 RL 0.34-0.08 0.33-0.07 0.25-0.04 R2 0.994 0.974 0.992

KF (l/mg) 11.762 0.0028 0.0209 R2 0.864 0.827 0.685

KT 0.286 3.8 \*1019 4.6 \* 1013 R2 0.946 0.777 0.886

E (KJ/mol) 91.28 100 158.11 R2 0.97 0.95 0.94

) 6\*10−5 5\*10−5 2\*10−5

*) for MB adsorption on the surface of CaHAp1 and* 

Langmuir q max (mg/g) 77.51 117.64 142.85

Freundlich n 2.876 0.468 0.541

Tempkin B1 18.462 0.032 0.028

D-R q max (mg/g) 66.62 105.50 120.50

**diffusion**

18 10.41 0.670 0.317 0.488

57 27.24 0.457 0.344 0.476

10 5.17 0.378 0.361 0.498

15 7.62 0.349 0.361 0.489

**CaHAp1 CaHAp1-(Alg)5 CaHAp1-(Alg)10**

The values of E calculated from Dubinin-Redushkevich equation are greater than 40 KJ mol−1 for all samples, which confirms that the adsorption is

The standard Gibbs free energy change (ΔG°) has been determined from the

Where R is the universal gas constant (8.314 J mol−1 K−1), T is the temperature (K) and KL value is the Langmuir equilibrium constant. The enthalpy change ∆H°

∆ − G°= RT LnKL (4)

*4.2.6 Determination of the thermodynamic parameters*

KD-R (mol2

*Isotherm constants and correlation coefficients (R2*

*CaHAp1-(Alg) at different temperatures.*

/J2

*DOI: http://dx.doi.org/10.5772/intechopen.95347*

0% 0.0088 0.41 0.346 2.7 4.58 0.999 7.49E

5% 0.0085 0.29 0.271 5.51 5.02 1 1.33E

10% 0.0075 0.53 0.247 −20.86 5.162 0.999 1.31E

20% 0.0079 0.34 0.2 −1.18 5.184 0.999 3.67<sup>E</sup>

*Kinetic constants for the adsorption of studied dyes on hydroxyapatite-Alginate (T = 25°C, C0 = 100 mg/L, 6 < pH < 7).*

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents… DOI: http://dx.doi.org/10.5772/intechopen.95347*


**Table 4.**

*Dyes and Pigments - Novel Applications and Waste Treatment*

**Pseudo-first-order**

**K1**

> 0%

5% 10% **Table 3.**

0.0181

7.197

0.4388 *Kinetic constants for the adsorption of studied dyes on hydroxyapatite-Alginate (T = 25°C, C0 = 100 mg/L, 6 < pH < 7).*

0.01556

79.365

0.9999

28.931

8.903

0.6240

3.9032

0.4046

0.149

4.769

0.3244

0.02641

74.074

0.9999

28.701

11.128

0.5838

3.505

0.3675

0.0234

16.764

0.8305

0.00648

52.910

0.9991

12.946

12.210

0.8131

3.0578

0.6086

**qe**

**R2**

**K2**

**qe**

**R2**

**α**

**β**

**R2**

**Ki**

**R2**

**Pseudo-second-order**

**Elovich**

**Intra-particular diffusion**

**180**

*Kinetic constants for the adsorption of studied dyes on hydroxyapatite-Carrageenan (T = 25°C, C0 = 10 mg/L, pH = 5).*


#### **Table 5.**

*Isotherm constants and correlation coefficients (R2 ) for MB adsorption on the surface of CaHAp1 and CaHAp1-(Alg) at different temperatures.*

The values of E calculated from Dubinin-Redushkevich equation are greater than 40 KJ mol−1 for all samples, which confirms that the adsorption is chemical [42].

#### *4.2.6 Determination of the thermodynamic parameters*

The standard Gibbs free energy change (ΔG°) has been determined from the following equation [21].

$$
\Delta \mathbf{G}^{\circ} = -\mathbf{R} \mathbf{T} \, \text{Ln} \mathbf{K}\_{\text{L}} \tag{4}
$$

Where R is the universal gas constant (8.314 J mol−1 K−1), T is the temperature (K) and KL value is the Langmuir equilibrium constant. The enthalpy change ∆H°


 *Isotherm constants and thermodynamic parameters for dye adsorption on the surface of CaHAp2 and CaHAp2-(Carr)10 at different temperatures.*

**183**

removal.

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents…*

Δ**S° (KJ/mol)**

CaHAp1 −27.96 −0.094 0.218 1.163 2.109 3.055 CaHAp1-Alg(10) −20.432 −0.059 −2.789 −2.197 −1.605 −1.013

and entropy change ∆S° of the adsorption were estimated from the following

*Values of thermodynamic parameters for MB dye removal with CaHAp1 and CaHAp1-Alg.*

L H S LnK = +

(Alg)10) and positive for (CaHAp1, CaHAp2-(λ-Carr)10).

solid–solution interface during adsorption.

0 0

∆ ∆ <sup>−</sup> (5)

Δ**G° (KJ/mol) 298°K 308°K 318°K 328°K**

RT R

The values of ∆H° and ∆S° were determined from the slopes and intercept of the linear plot of Ln KL versus (1/T). The calculated thermodynamic parameters are

The values of the enthalpy ∆H° indicates that the adsorption process is endothermic for CaHAp2 (∆H° > 0), and exothermic for (CaHAp1, CaHap2-(λ-Carr)10, CaHAp1-(Alg)10) (∆H° < 0). The ΔG° values were negative for (CaHap2, CaHAp1-

The positive ΔG° values indicates that the instability activation complex of the adsorption reaction increases with increasing temperature, The negative values of ΔG° means that the process is feasible and adsorption is spontaneous thermody-

The negative value of entropy ΔS° confirms the decreased randomness at the

In this study, the results of characterization techniques IR, XRD, SSA and SEM analysis showed that the sodium alginate or lambda carrageenan were successfully grafted on the hydroxyapatite surface. The modified hydroxyapatite could be potentially applied for the removal of methylene blue dye from aqueous solution. The determination of the amount of dye adsorbed on the various apatitic phase CaHAp1, CaHAp2, CaHAp1-(Alg) and CaHAp2-(λ-Carr) allowed us to build the adsorption isotherms which give information on the adsorption mechanism. The Modeling of the isotherms proved that the adsorption of MB on modified hydroxyapatite is described by the Freundlich equation for CaHAp2-(λ-Carr) and Langmuir for CaHAp1-(Alg). The calculated adsorption capacities of CaHAp1, CaHAp2, CaHAp1-Alg10 and CaHAp2-(λ-Carr)10 for MB, at 25°C, were 68.5, 58.8 128.40, and 98.23 mg/g, respectively. The results gave a clear indication that the modified hydroxyapatite has a great capacity than pure hydroxyapatite for dye

Thermodynamic studies indicated that the physic-sorption is the dominating mechanism for the dye adsorption process onto CaHAp1-(Alg)10 or CaHAp2- (λ-Carr)10, spontaneous and exothermic in nature. The results indicate that the modified hydroxyapatite CaHAp2-(λ Carr) or CaHAp1-(Alg) possessed good adsorption ability towards MB dye and can be used as a low cost adsorbent for other

*DOI: http://dx.doi.org/10.5772/intechopen.95347*

Δ**H° (KJ/mol)**

equation:

**Table 7.**

namically [45].

**5. Conclusion**

summarized in **Tables 6** and **7**.

*Preparation of Functionalized Hydroxyapatite with Biopolymers as Efficient Adsorbents… DOI: http://dx.doi.org/10.5772/intechopen.95347*


**Table 7.**

*Dyes and Pigments - Novel Applications and Waste Treatment*

**Langmuir constants**

**T (°C)**

25 40 60 25 40 60 **Table 6.**

0.004

500

0.181

0.87

0.955 *Isotherm constants and thermodynamic parameters for dye adsorption on the surface of CaHAp2 and CaHAp2-(Carr)10 at different temperatures.*

69.32

0.286

0.905

4.77

70.71

0.486

0.314

0.005

526.3

0.189

0.89

0.953

70.52

0.288

0.909

4.85

70.71

0.481

0.323

0.005

588.2

0.161

0.894

0.951

71.75

0.289

0.909

4.9

70.71

0.483

0.328

−3.1

−29.2

8.69

9.13

9.7

0.026

125

0.944

0.73

1.21

0.993

37.52

0.31 **CaHAp2-(**λ**-Carr)10**

0.928

4.1

79.05

0.572

0.025

156.2

0.851

0.62

1.12

0.991

37.1

0.30

0.925

3.98

70.71

0.588

0.017

285.7

0.407

0.51

1.03

0.990

36.85

0.29

0.916

3.84

70.71

0.596

42.3

0.25

−32.2

−26.95

−40.95

**KL**

**qm.L**

**R2**

**KF**

**nF**

**R2**

**BT**

**AT**

**R2**

**Q m.DR**

**E**

**R2**

**∆H°**

**∆S°**

**∆G°**

**Freundlich constants**

**Temkin constants**

**CaHAp2**

**Dubinin-redushkevich** 

**Thermodynamic parameters**

**constants**

**182**

*Values of thermodynamic parameters for MB dye removal with CaHAp1 and CaHAp1-Alg.*

and entropy change ∆S° of the adsorption were estimated from the following equation:

$$\mathbf{L}\mathbf{n}\mathbf{K}\_{\mathsf{L}} = -\frac{\Delta\mathbf{H}^{0}}{\mathbf{R}\mathbf{T}} + \frac{\Delta\mathbf{S}^{0}}{\mathbf{R}} \tag{5}$$

The values of ∆H° and ∆S° were determined from the slopes and intercept of the linear plot of Ln KL versus (1/T). The calculated thermodynamic parameters are summarized in **Tables 6** and **7**.

The values of the enthalpy ∆H° indicates that the adsorption process is endothermic for CaHAp2 (∆H° > 0), and exothermic for (CaHAp1, CaHap2-(λ-Carr)10, CaHAp1-(Alg)10) (∆H° < 0). The ΔG° values were negative for (CaHap2, CaHAp1- (Alg)10) and positive for (CaHAp1, CaHAp2-(λ-Carr)10).

The positive ΔG° values indicates that the instability activation complex of the adsorption reaction increases with increasing temperature, The negative values of ΔG° means that the process is feasible and adsorption is spontaneous thermodynamically [45].

The negative value of entropy ΔS° confirms the decreased randomness at the solid–solution interface during adsorption.

#### **5. Conclusion**

In this study, the results of characterization techniques IR, XRD, SSA and SEM analysis showed that the sodium alginate or lambda carrageenan were successfully grafted on the hydroxyapatite surface. The modified hydroxyapatite could be potentially applied for the removal of methylene blue dye from aqueous solution. The determination of the amount of dye adsorbed on the various apatitic phase CaHAp1, CaHAp2, CaHAp1-(Alg) and CaHAp2-(λ-Carr) allowed us to build the adsorption isotherms which give information on the adsorption mechanism. The Modeling of the isotherms proved that the adsorption of MB on modified hydroxyapatite is described by the Freundlich equation for CaHAp2-(λ-Carr) and Langmuir for CaHAp1-(Alg). The calculated adsorption capacities of CaHAp1, CaHAp2, CaHAp1-Alg10 and CaHAp2-(λ-Carr)10 for MB, at 25°C, were 68.5, 58.8 128.40, and 98.23 mg/g, respectively. The results gave a clear indication that the modified hydroxyapatite has a great capacity than pure hydroxyapatite for dye removal.

Thermodynamic studies indicated that the physic-sorption is the dominating mechanism for the dye adsorption process onto CaHAp1-(Alg)10 or CaHAp2- (λ-Carr)10, spontaneous and exothermic in nature. The results indicate that the modified hydroxyapatite CaHAp2-(λ Carr) or CaHAp1-(Alg) possessed good adsorption ability towards MB dye and can be used as a low cost adsorbent for other environmental applications as retention of heavy metal and pesticides from wastewater. Further works will be extended for the functionalization of hydroxyapatite materials with surfactants and cationic reagents for the removal of organic pollutants from contaminated waters.
