**3. Results and discussion**

#### **3.1. Carbon nanotube dispersed polarity**

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

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

#### **3.2. Particle Size Analysis**

Particle size analysis was conducted on A–series and B–series of carboxylated MWCNT. Figs. 3 and 4 show that as carboxylation reaction time increases the extent of carbon nano‐ tube shortening is increased; this is particularly true for the B–series, where the mixed-acid, hydrogen peroxide, and ultrasonic treatment times were all shortened. The B–series samples are much shorter than the A–series samples of MWCNT treated only with mixed-acid and ultrasonic treatment. This finding further corroborates the FT-IR results. With longer carbox‐ ylation reaction times the MWCNT is more severely damaged, inducing greater rupture on the C–C bond of the CNT. The higher activity at MWCNT ends facilitates bonding with free O and H from water or solution and the formation of carboxyl groups on the fracture site, increasing the functionalized carboxyl groups and the extent of MWCNT carboxylation.

**3.3. Adsorption property**

As shown in Figs. 5, 6, and 7, the absorption of MB increased with time. The decolorization of sample 1 (SA2MWCNT0) reached 40.16% after 120 h, meaning that SA itself has the ability to absorb MB. Compared with sample #1, the decolorizations of 2#, 3#, 4#, 5#, and 6# or‐ dered by increasing content of MWCNT, were 55.78, 66.62, 76.9, 82.06, and 83.46%, respec‐ tively, when tested under the same conditions. This trend of increased decolorization with increased MWCNT concentration is attributed to the fact that the surface of MWCNT has substantial amounts of carbonyl that reacted with MB (see Fig. 8). Another reason for this decolorization may be due to the large specific surface area of MWCNT that greatly affects adsorption ability. Voids present in the MWCNT may also favor of the adsorption of MB.

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

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**Figure 6.** Decolorization of MB by SA/MWCNT microsphere determined at 25°C.

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**Figure 5.** Absorbance of MB by SA/MWCNT microsphere, determined at 25°C.

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**Figure 3.** The A–series of MWCNT specimens on weight average particle size (white column) and surface volume par‐ ticle size (slash column) measured at 25°C.

**Figure 4.** The B–series of MWCNT specimens on weight average particle size (white column) and surface volume parti‐ cle size (slash column) measured at 25°C.

#### **3.3. Adsorption property**

**3.2. Particle Size Analysis**

Particle size analysis was conducted on A–series and B–series of carboxylated MWCNT. Figs. 3 and 4 show that as carboxylation reaction time increases the extent of carbon nano‐ tube shortening is increased; this is particularly true for the B–series, where the mixed-acid, hydrogen peroxide, and ultrasonic treatment times were all shortened. The B–series samples are much shorter than the A–series samples of MWCNT treated only with mixed-acid and ultrasonic treatment. This finding further corroborates the FT-IR results. With longer carbox‐ ylation reaction times the MWCNT is more severely damaged, inducing greater rupture on the C–C bond of the CNT. The higher activity at MWCNT ends facilitates bonding with free O and H from water or solution and the formation of carboxyl groups on the fracture site, increasing the functionalized carboxyl groups and the extent of MWCNT carboxylation.

A0 A1 A2 A3 A4 A5

B0 B1 B2 B3 B4 B5

**Figure 4.** The B–series of MWCNT specimens on weight average particle size (white column) and surface volume parti‐

**Figure 3.** The A–series of MWCNT specimens on weight average particle size (white column) and surface volume par‐

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ticle size (slash column) measured at 25°C.

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472 Syntheses and Applications of Carbon Nanotubes and Their Composites

As shown in Figs. 5, 6, and 7, the absorption of MB increased with time. The decolorization of sample 1 (SA2MWCNT0) reached 40.16% after 120 h, meaning that SA itself has the ability to absorb MB. Compared with sample #1, the decolorizations of 2#, 3#, 4#, 5#, and 6# or‐ dered by increasing content of MWCNT, were 55.78, 66.62, 76.9, 82.06, and 83.46%, respec‐ tively, when tested under the same conditions. This trend of increased decolorization with increased MWCNT concentration is attributed to the fact that the surface of MWCNT has substantial amounts of carbonyl that reacted with MB (see Fig. 8). Another reason for this decolorization may be due to the large specific surface area of MWCNT that greatly affects adsorption ability. Voids present in the MWCNT may also favor of the adsorption of MB.

**Figure 5.** Absorbance of MB by SA/MWCNT microsphere, determined at 25°C.

**Figure 6.** Decolorization of MB by SA/MWCNT microsphere determined at 25°C.

**Figure 9.** pH values of MB by SA/MWCNT microsphere determined at 25°C.

**Figure 10.** Electrical conductivity of MB by SA/MWCNT microsphere determined at 25°C.

The electrical conductivity was initially fixed at 79.3 µS/cm for the original sample, but in‐ creased considerably with increasing reaction time. The electrical conductivity of samples 5#, 6# increased sharply over the course of 120 h, but the electrical conductivity of the origi‐ nal sample (50 mL of MB solution) remained virtually unchanged, indicating that the origi‐

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**3.4. Electrical conductivity**

nal sample was stable.

**Figure 7.** The photograph of MB absorbtion by different amounts of MWCNT.

**Figure 8.** Reaction of MB by SA/MWCNT microsphere determined at 25°C.

The pH values decreased appreciably in samples 5# and 6# over the course of 120 h. The rea‐ son for this decrease may be the same as the reasons for decolorization previously men‐ tioned (see Fig. 9), but the pH value of the original sample (50 mL of MB solution) was virtually unchanged. The reaction generated much more HCl that decreased the pH values, but the reaction rate eventually diminished after 120 h because there was less HCl generated and the adsorption of MWCNT surfaces was also nearly complete.

**Figure 9.** pH values of MB by SA/MWCNT microsphere determined at 25°C.

#### **3.4. Electrical conductivity**

**Figure 7.** The photograph of MB absorbtion by different amounts of MWCNT.

474 Syntheses and Applications of Carbon Nanotubes and Their Composites

**Figure 8.** Reaction of MB by SA/MWCNT microsphere determined at 25°C.

and the adsorption of MWCNT surfaces was also nearly complete.

The pH values decreased appreciably in samples 5# and 6# over the course of 120 h. The rea‐ son for this decrease may be the same as the reasons for decolorization previously men‐ tioned (see Fig. 9), but the pH value of the original sample (50 mL of MB solution) was virtually unchanged. The reaction generated much more HCl that decreased the pH values, but the reaction rate eventually diminished after 120 h because there was less HCl generated

The electrical conductivity was initially fixed at 79.3 µS/cm for the original sample, but in‐ creased considerably with increasing reaction time. The electrical conductivity of samples 5#, 6# increased sharply over the course of 120 h, but the electrical conductivity of the origi‐ nal sample (50 mL of MB solution) remained virtually unchanged, indicating that the origi‐ nal sample was stable.

**Figure 10.** Electrical conductivity of MB by SA/MWCNT microsphere determined at 25°C.
