**Abstract**

In this study, we reported the synthesis of hydroxyapatite modified with biopolymers as λ-carrageenan and sodium alginate, which could be used as effective adsorbents of cationic dyes. Evidence of chemical modification was proved through chemical analysis, Fourier Trans-form Infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, and specific surface area. The adsorption process was studied using methylene blue as representative cationic dye. The adsorbed quantity reached, at equilibrium, 142.85 mg/g and 98.23 mg/g using hydroxyapatite-sodium alginate and hydroxyapatite-(λ-carrageenan), respectively. However, it does not exceed 58.8 mg/g in the case of the unmodified hydroxyapatite. The adsorption of methylene blue using hybrid materials complied well with the pseudo-second-order suggesting a chemi-sorption. Freundlich and Langmuir isotherm described well the adsorption mechanism of the hydroxyapatite-(λcarrageenan) and hydroxyapatite-sodium alginate, respectively. The high capacities of MB removal obtained in this study suggest the potential use of these materials in the treatment from wastewaters.

**Keywords:** hydroxyapatite, biopolymer alginate, dye, kinetic

### **1. Introduction**

Contaminated waters can be successfully treated using inexpensive adsorbents. In this sense, many biopolymers were proposed including cellulose [1–3], chitosan [4, 5], chitin [6, 7], etc. Hybrid materials have attracted a particular attention. The interaction between calcium hydroxyapatite and biopolymers has been the subject of many studies such as carboxymethyl cellulose [8], polygalacturonic acid [9], collagen [10], Agar-Agar [11], polycaprolactone [12], banana peel [13], chitosan [14], and gelatin [15]. Currently, the application of hydroxyapatite modified by biopolymers for immobilization of various pollutants has been considered as a promising pollution control technology [16–20]. For example, Huijuan and colleagues [21] have, recently, reported interesting results about the preparation of hydroxyapatite-Chitosan composite and its efficiency for the removal of Congo red dye from aqueous solution.

The results indicate that the kinetic and isotherm studies showed that pseudo-second-order model and Langmuir model could well describe the

adsorption behavior, while thermodynamic investigation of Congo red adsorption by hydroxyapatite-Chitosan composite confirmed a spontaneous adsorption. It has been demonstrated that this composite is an effective and low-cost adsorbent for the dye-polluted water purification [21].

In the same framework, the present work describes the synthesis of hybrid compounds CaHAp-Alginate and CaHAp-(Carrageenan) as an adsorbent using a facile method by varying the content of the bio-polymer. Evidence of interaction between hydroxyapatite and Alg or (λ-Carr) was confirmed using various techniques including FT-IR, SSA, DRX and SEM. The factors that influence the dye uptake by the prepared adsorbents were also investigated and discussed.

### **2. Experimental**

#### **2.1 Synthesis of hydroxyapatite (CaHAp1 and CaHAp2)**

Hydroxyapatite was synthesized via co-precipitation method [22, 23]. As starting reagents, analytical grade CaCl2, Na2HPO4, Ca(NO3)2.4H2O, (NH4)2HPO4 and NH4OH were used. The chemicals equations that describes the reactions is given as follow:

#### **CaHAp1**

$$\begin{aligned} \text{10Ca(NO}\_3\text{)}\_2\text{4H}\_2\text{O} &\star 6\text{(NH}\_4\text{)}\_2\text{HPO}\_4 \star 8\text{(NH}\_4\text{OH)} \rightarrow\\ \text{Ca}\_{10}\text{(PO}\_4\text{)}\_6\text{(OH)}\_2 &\star 20\text{(NH}\_4\text{)} + 20\text{(NO}\_3^-\text{)} \star 46\text{H}\_2\text{O} \end{aligned} \tag{1}$$

#### **CaHAp2**

$$\text{10\text{CaCl}\_2\text{+6Na}\_2\text{HPO}\_4\text{+2H}\_2\text{O} \rightarrow \text{Ca}\_{10}\text{(PO}\_4\text{)}\_6\text{(OH)}\_2\text{+12(Na\text{+},Cl\text{)}\_2\text{8(H}\_7,Cl}\text{)}\tag{2}$$

An aqueous solution of 250 mL of Ca(NO3)2.4H2O or CaCl2 (0.2 M) was added drop-wise to 150 mL of (NH4)2HPO4 or Na2HPO4 (0.2 M) solution under N2 bubbling with a stoichiometric ratio of Ca/P = 1.67.

The pH was adjusted to 10 by adding NH4OH solution gradually. After the complete addition, the suspension was matured for 72 h at room temperature under magnetic stirring, the resultant precipitate was filtered, washed with distilled water, and dried overnight at 80°C.

#### **2.2 Synthesis of hydroxyapatite modified by sodium alginate CaHAp1-Alg**

A similar procedure of CaHAp1 was adopted to synthesize the modified hydroxyapatite by sodium alginate CaHAp1-(Alg), except for the fact that the (NH4)2HPO4was prepared with x mass of sodium alginate (5%, 10% or 20% of the total mass of Ca(NO3)2.4H2O in the starting solution).

#### **2.3 Synthesis of hydroxyapatite modified by sodium alginate CaHAp1-(**λ**-Carr)**

**169**

taken as a pHZPC.

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

In the text, Hydroxyapatite modified with (λ-Carr) is abbreviated as

MB (its structure is given in **Figure 1**) solution was prepared by dissolving the calculated powder dye in distilled water with different required concentrations. NaOH and acetic acid solutions were used for adjusting the p*H* of the dye solution. For the adsorption experiments, MB solution was mixed with modified hydroxyapatite. MB concentrations were measured before and after experiments using a double beam UV–vis spectrophotometer (UV-1601 Shimadzu, Japan) at 664 nm. The adsorbed amount of dye onto modified hydroxyapatite (q mg/g) was calculated

e Oe ( ) <sup>V</sup> q=C C x

Where Co and Ce are the initial and equilibrium dye concentration (mg/L), V is the solution volume (mL) and m is the weight of used modified hydroxyapatite

The FT-IR spectra were recorded on a Perkin Elmer model 597 using KBr pellet method in the 4000–400 cm−1 region. X-ray powder diffractograms were obtained at room temperature on a PANalytical X'Pert PRO MPD equipped with copper anticathode tube. The morphological observation of the synthesized samples was undertaken using a JEOL JSM-5400 scanning electron microscope. Specific surface area (SSA) measurements were performed by BET-method (adsorptive gas N2, carrier gas He, heating temperature 100°C) using an

Quantachrome Instruments, model: ASIM. LP2. The pH of the zero point charge (pHZPC) was determined by putting 0.15 g of adsorbent in a closed Erlenmeyer flask containing 50 mL of NaCl solutions (0.1 M). The initial pH of these solutions was adjusted by either adding NaOH (0.1 M) or HCl (0.1 M) and were then agitated for 48 h at 150 rpm at room temperature to reach equilibrium. The final pH of supernatant was, further, measured and the ΔpH = pH (final) − pH (initial) was plotted against the initial pH. The pH at which ΔpH was zero was

( ) 100.

*m Carr m calcium* <sup>×</sup>

<sup>m</sup> <sup>−</sup> (3)

(CaHAp-(Carr) n), where n represents the mass ratio ( )

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

**2.4 Adsorption experiments**

**Figure 1.**

*Structure of methylene blue.*

using the following equation [24]:

sample (g) for the adsorption.

**3. Characterization techniques**

CaHAp2-(Carr) was synthesized, following a similar procedure of CaHAp2, except for the calcium containing solutions that were prepared by mixing 0.05 moles of CaCl2 with x mol (x = 0.0025, 0.005 and 0.01) of (λ Carr).

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

**Figure 1.** *Structure of methylene blue.*

*Dyes and Pigments - Novel Applications and Waste Treatment*

prepared adsorbents were also investigated and discussed.

**2.1 Synthesis of hydroxyapatite (CaHAp1 and CaHAp2)**

bling with a stoichiometric ratio of Ca/P = 1.67.

total mass of Ca(NO3)2.4H2O in the starting solution).

and dried overnight at 80°C.

the dye-polluted water purification [21].

**2. Experimental**

**CaHAp1**

**CaHAp2**

adsorption behavior, while thermodynamic investigation of Congo red adsorption by hydroxyapatite-Chitosan composite confirmed a spontaneous adsorption. It has been demonstrated that this composite is an effective and low-cost adsorbent for

In the same framework, the present work describes the synthesis of hybrid compounds CaHAp-Alginate and CaHAp-(Carrageenan) as an adsorbent using a facile method by varying the content of the bio-polymer. Evidence of interaction between hydroxyapatite and Alg or (λ-Carr) was confirmed using various techniques including FT-IR, SSA, DRX and SEM. The factors that influence the dye uptake by the

Hydroxyapatite was synthesized via co-precipitation method [22, 23]. As starting reagents, analytical grade CaCl2, Na2HPO4, Ca(NO3)2.4H2O, (NH4)2HPO4 and NH4OH were used. The chemicals equations that describes the reactions is given as follow:

> ( ) ( ) ( ) ( ) ( ) ( ) ( ) 32 4 4 4 <sup>2</sup> <sup>2</sup>

10 4 6 2 4 3 2 10Ca NO .4H O+6 NH HPO +8 NH OH Ca PO OH +20 NH +20 NO +46 H O

2 2 42 10 4 6 2 10CaCl +6Na HPO +2H O Ca PO OH +12 Na+,Cl- +8 H+,Cl → (2)

An aqueous solution of 250 mL of Ca(NO3)2.4H2O or CaCl2 (0.2 M) was added drop-wise to 150 mL of (NH4)2HPO4 or Na2HPO4 (0.2 M) solution under N2 bub-

The pH was adjusted to 10 by adding NH4OH solution gradually. After the complete addition, the suspension was matured for 72 h at room temperature under magnetic stirring, the resultant precipitate was filtered, washed with distilled water,

**2.2 Synthesis of hydroxyapatite modified by sodium alginate CaHAp1-Alg**

A similar procedure of CaHAp1 was adopted to synthesize the modified hydroxyapatite by sodium alginate CaHAp1-(Alg), except for the fact that the (NH4)2HPO4was prepared with x mass of sodium alginate (5%, 10% or 20% of the

**2.3 Synthesis of hydroxyapatite modified by sodium alginate CaHAp1-(**λ**-Carr)**

CaHAp2-(Carr) was synthesized, following a similar procedure of CaHAp2, except for the calcium containing solutions that were prepared by mixing 0.05

moles of CaCl2 with x mol (x = 0.0025, 0.005 and 0.01) of (λ Carr).

+ -

→

( ) ( ) ( ) ( )-

(1)

**168**

In the text, Hydroxyapatite modified with (λ-Carr) is abbreviated as (CaHAp-(Carr) n), where n represents the mass ratio ( ) ( ) 100. *m Carr m calcium* <sup>×</sup>

#### **2.4 Adsorption experiments**

MB (its structure is given in **Figure 1**) solution was prepared by dissolving the calculated powder dye in distilled water with different required concentrations. NaOH and acetic acid solutions were used for adjusting the p*H* of the dye solution. For the adsorption experiments, MB solution was mixed with modified hydroxyapatite. MB concentrations were measured before and after experiments using a double beam UV–vis spectrophotometer (UV-1601 Shimadzu, Japan) at 664 nm. The adsorbed amount of dye onto modified hydroxyapatite (q mg/g) was calculated using the following equation [24]:

$$\mathbf{q}\_e = \left(\mathbf{C}\_0 - \mathbf{C}\_e\right) \mathbf{x} \frac{\mathbf{V}}{\mathbf{m}} \tag{3}$$

Where Co and Ce are the initial and equilibrium dye concentration (mg/L), V is the solution volume (mL) and m is the weight of used modified hydroxyapatite sample (g) for the adsorption.

#### **3. Characterization techniques**

The FT-IR spectra were recorded on a Perkin Elmer model 597 using KBr pellet method in the 4000–400 cm−1 region. X-ray powder diffractograms were obtained at room temperature on a PANalytical X'Pert PRO MPD equipped with copper anticathode tube. The morphological observation of the synthesized samples was undertaken using a JEOL JSM-5400 scanning electron microscope. Specific surface area (SSA) measurements were performed by BET-method (adsorptive gas N2, carrier gas He, heating temperature 100°C) using an Quantachrome Instruments, model: ASIM. LP2. The pH of the zero point charge (pHZPC) was determined by putting 0.15 g of adsorbent in a closed Erlenmeyer flask containing 50 mL of NaCl solutions (0.1 M). The initial pH of these solutions was adjusted by either adding NaOH (0.1 M) or HCl (0.1 M) and were then agitated for 48 h at 150 rpm at room temperature to reach equilibrium. The final pH of supernatant was, further, measured and the ΔpH = pH (final) − pH (initial) was plotted against the initial pH. The pH at which ΔpH was zero was taken as a pHZPC.
