**2. Experimental**

in this class are synthetic and usually composed of aromatic rings, which makes them carci‐ nogenic and mutagenic [Ghosh & Bhattacharyya, 2002. Chen et. al., 2003]; they are inert and non-biodegradable when discharged into waste streams [Mittal & Gupta, 1996, Seshadri et. al., 1994]. With the social and economic development, the environmental consciousness of citizens and governing agencies was enhanced. Environmental pollution issues have gar‐ nered a considerable amount of attention throughout the world [Renmin et. al., 2005]. MB is a good representative of organic dyes that are difficult to degrade and substantially damage

Since carbon nanotube (CNT) was first discovered by S. Ijima in 1991, it has become an aca‐ demic research subject of great interest [Olson, 1994]. CNT is the thinnest tubular structure humans can presently fabricate. It is lightweight and has high strength, high toughness, flex‐ ibility, high surface area, high thermal conductivity, and good electric conductivity and is chemically stable [Baughman et. al., 2002, Thostenson et. al., 2001, Banerjee et. al., 2005]. To fully exploit the superior mechanical, electrical and optical properties of multi-walled car‐ bon nanotube (MWCNT), dispersion and adhesion to a polymeric matrix is a key issue [Iiji‐ ma, 1991]. Both the dispersibility and matrix adhesion of MWCNT can be improved either by covalent or noncovalent functionalization. For covalent functionalization, several ap‐ proaches studied, each having its advantages and drawbacks; examples of such methods in‐ clude wet chemical methods with typical treatment times of up to 24 h [Sahoo et. al., 2010, Liu et. al., 1998, Chen et. al., 1998], treatment in air at elevated temperatures [Tsai et. al., 2010, Ajayan et. al., 1993], by ozone oxidation [Ago et. al., 1999, Mawhinney et. al., 2000] and treatment with low-pressure plasmas [Simmons et. al., 2006, Tseng et. al., 2006, Chen et. al.,

Alginate is a collective term for a family of exopolysaccharides produced mainly by brown seaweeds. It has been widely used in the food, biomedical, pharmaceutical, and sewage-treat‐ ment industries, preferentially as sodium alginate due to its solubility in cold water. In mo‐ lecular terms, alginate is composed of (1–4)-linked b-D-mannuronic acid (M) unbranched binary copolymer and a-L-guluronic acid (G) monomer residue, constituting M-, G-, and MG sequential block structures [Chen et. al., 2009]. Most applications that use alginate are based on its gel-forming ability through cation binding: the transition from water-soluble sodium alginate (SA) to water insoluble calcium alginate, for example. Divalent cations preferential‐ ly bind toward the G-block rather than the M-block [Moe et. al., 1995, Braccini et. al., 1999]. The composition of monomers and their sequential character (i.e., blackness) affects the gel‐ atin behavior of alginate. In the presence of Ca2+, G-rich samples generally form hard and brit‐ tle gels while M-rich samples from soft and elastic gels [Braccini & Perez, 2001, Courtois et. al., 1993, Thakur et. al., 1997, Pe´rez et. al., 1996]. The ''egg-box'' model has been accepted as a general model to describe gel formation [Morris et. al., 1978, Thom et. al., 1985]. Alginate is

an excellent polymer flocculant and has been widely used in wastewater treatment.

composite, for the sorption of MB dyes from an aqueous solution were investigated.

This study reports for the first time the effect of the carboxylation method on CNT structure and property. The results can be used as reference for selecting the carboxylation method. Furthermore, the applicability of a new adsorbent, SA and MWCNT and the SA/MWCNT

the environment due to their toxicity and dark color [Ho et. al., 2005].

468 Syntheses and Applications of Carbon Nanotubes and Their Composites

2010, Zschoerper et. al., 2009].

#### **2.1. Materials and methods**

The SA, MB, and MWCNT were used as received from Fuchen Chemical Reagents Factory, Tianjin, China and Nanotechnologies Port Co., Ltd., Shenzhen, China. The MWCNTs was treated with a mixture of sulfuric and nitric acid under ultrasonic vibration, as seen in Table 1. According to the series reaction time in Table 1, the optimized ratio of the MWCNT to acid mixture is 3:1 by volume. Ultrasonic treatment was applied for the duration of varying reaction times. Filtration was conducted with a micropore filter and sand core filter. Pure de–ionized water (pure DI water) was used to rinse the filtrate until the pH of the aqueous solution was neutral. The compositions of the SA, MWCNT, and SA/MWCNT series speci‐ mens prepared in this study are summarized in Table 2. Ten milliliters of an aqueous solu‐ tion of SA/MWCNT was added drop-wise to 50 mL of calcium chloride (10%, w/v) aqueous solution for 20 min, followed by the sampling of supernatant at the specified time intervals. The gel particles were pre-consolidated under a pressure of 8–30 kPa in a consolidation cell with an inner diameter of 2.0–3.0 mm to produce a packed gel bed to determine their ex‐ pression characteristics. The schematic evolution of the SA and MWCNT in the microsphere, as a function of the calcium chloride, is shown in Figure 1. Other supplementary agents were of analytical grade (purity > 99.8 mass%) and all solutions were prepared with double distilled water.

**Figure 1.** The preparation process of the SA/MWCNT composite gel beads.


**2.4. Adsorption property**

ed sample.

**2.5. Electrical conductivity**

**3. Results and discussion**

**3.1. Carbon nanotube dispersed polarity**

week, it still maintained the state seen in Fig. 2.

**Figure 2.** Photograph depicting the polarity of pure MWCNT specimens.

ry, DDS-12A, China).

All sorption measurements were performed by batch type with 50 mL of MB solution in a shaking incubator to form a final concentration of 50 mg/L (*A* 665 nm = 2.9966) at room temper‐ ature for 3 h. The equilibrium MB concentration was measured by means of double beam ultraviolet–visible spectroscopy (Shanghai Precision & Scientific Instrument Co., Ltd, UV762, China), and the pH values of the solution were measured using a pH meter (Shang‐ hai Yulong Instrument Co., Ltd., PHS-3 C, China) with a calomel and glass electrode

where A0 is the dye absorbance of the control specimen, A is the dye absorbance of the react‐

To understand the electrical conductivity properties of MWCNT in SA specimens dispersed in MB solution, the electrical conductivity of the SA and SA/MWCNT solutions were meas‐ ured at 25°C and 50% relative humidity using a conductivity meter (LIDA Instrument Facto‐

A typical photograph of the polarity of MWCNT and modified MWCNT specimens is shown in Fig. 2. Fig. 2 shows the dispersion of the modified MWCNT in aqueous and organ‐ ic solvent solutions after being exposed to the treatments highlighted in Table 1 and then left undisturbed for 12 h. The figure shows that in the six groups of MWCNT, except the un‐ modified carbon nanotube, there always exists an interface of two phases that cannot be dis‐ solved in one another. All five of the other groups show different extents of dispersion. MWCNTb3 shows the most stable dispersion in aqueous phase; even after being aged for a

Decoloration percentage(%) =(*A*<sup>0</sup> − *A*)/ *A*<sup>0</sup> ×100*%* (1)

Adsorption of Methylene Blue on Multi-Walled Carbon Nanotubes in Sodium Alginate Gel Beads

http://dx.doi.org/10.5772/50714

471

(E201-9). The dye decolorization percentage was defined as follows:

**Table 1.** Formulation for CNT carboxylation.


#### **2.2. MWCNT dispersed polarity**

Six small reagent bottles were filled with 6 mL pure DI water, 4 mL toluene and a small amount of MWCNT derived as shown in Table 1. They were ultrasonically treated for 0.5 h, and then, after the solution was stored for 12 h, they were recovered and observed.

#### **2.3. Particle size analysis**

The particle size analysis measurements of MWCNT and modified MWCNT series speci‐ mens were recorded using a Dandong Bettersize Instruments Ltd. BT-9300H at 25°C and 50% relative humidity, wherein six scans with a size range of 0.1–340 µm were collected during each data measurement. Particle size analysis samples of powder specimens were collected using approximately 15 mL pure DI water and a small amount of MWCNT de‐ rived as shown in Table 1.

#### **2.4. Adsorption property**

**A–series reaction group**

**Sample**

**Mixed-acid treatment time (h)**

470 Syntheses and Applications of Carbon Nanotubes and Their Composites

**Table 1.** Formulation for CNT carboxylation.

**Table 2.** The composites of SA/MWCNT series samples.

**2.2. MWCNT dispersed polarity**

**2.3. Particle size analysis**

rived as shown in Table 1.

**Hydrogen peroxide treatment time (h)**

A0 0 0 B0 0 0 A1 1 0 B1 1 0.5 A2 2 0 B2 2 1 A3 4 0 B3 4 2 A4 6 0 B4 6 3 A5 8 0 B5 8 4

> **SA (%, w/v)**

0# SA0MWCNT0 0 0 0 1# SA2MWCNT0 2 0 10 2# SA2MWCNT0.03 2 0.03 10 3# SA2MWCNT0.06 2 0.06 10 4# SA2MWCNT0.09 2 0.09 10 5# SA2MWCNT0.12 2 0.12 10 6# SA2MWCNT0.15 2 0.15 10

Six small reagent bottles were filled with 6 mL pure DI water, 4 mL toluene and a small amount of MWCNT derived as shown in Table 1. They were ultrasonically treated for 0.5 h,

The particle size analysis measurements of MWCNT and modified MWCNT series speci‐ mens were recorded using a Dandong Bettersize Instruments Ltd. BT-9300H at 25°C and 50% relative humidity, wherein six scans with a size range of 0.1–340 µm were collected during each data measurement. Particle size analysis samples of powder specimens were collected using approximately 15 mL pure DI water and a small amount of MWCNT de‐

and then, after the solution was stored for 12 h, they were recovered and observed.

**B–series reaction group**

**Mixed-acid treatment time (h)**

**MWCNT (%, w/v)** **Hydrogen peroxide treatment time (h)**

> **CaCl2 (%, w/w)**

All sorption measurements were performed by batch type with 50 mL of MB solution in a shaking incubator to form a final concentration of 50 mg/L (*A* 665 nm = 2.9966) at room temper‐ ature for 3 h. The equilibrium MB concentration was measured by means of double beam ultraviolet–visible spectroscopy (Shanghai Precision & Scientific Instrument Co., Ltd, UV762, China), and the pH values of the solution were measured using a pH meter (Shang‐ hai Yulong Instrument Co., Ltd., PHS-3 C, China) with a calomel and glass electrode (E201-9). The dye decolorization percentage was defined as follows:

$$\text{Decoloration percentage(\%)} = \left(A\_0 - A\right) / A\_0 \times 100\% \tag{1}$$

where A0 is the dye absorbance of the control specimen, A is the dye absorbance of the react‐ ed sample.

#### **2.5. Electrical conductivity**

To understand the electrical conductivity properties of MWCNT in SA specimens dispersed in MB solution, the electrical conductivity of the SA and SA/MWCNT solutions were meas‐ ured at 25°C and 50% relative humidity using a conductivity meter (LIDA Instrument Facto‐ ry, DDS-12A, China).
