**5.1 Effect of pH**

The modified polysaccharide superabsorbent (MPSA) hydrogel was synthesized by Guilherme et al. [42] following free radical polymerization protocol by first treating KOH with AAc, followed by addition of known amount of AAm, modified gum arabic (MAG), and 84 mmol sodium persulfate (SPS) as an initiator. The synthesized SAHs were used as an ionic absorbent for the removal of two metal ions. It was found that the swelling of these SAHs is dependent on the pH of the medium. They studied the removal of Cu2+ and Pb2+ from aqueous medium, and it was found that the removal of heavy metals increases with the increase in pH value from 3 to 5. It is because of the deprotonation of carboxyl groups above the pKa value (4.0) present in hydrogel network. Thus the basic media generated anionic atmosphere which in turn established an ionic bond with positive metal ions in the medium and favor the process of removal. Another pH-sensitive hydrogels were reported by Peng et al., which were synthesized by grafting acrylic acid (AA) on hemicellulose having xylene. The samples were used for the removal of heavy metal ions like Pb2+, Cd2+, and Zn2+ from the medium. The maximum adsorption capacity of the sample for the heavy metal ions was reported by the authors as Pb2+ (859 mg/g), Cd2+ (495 mg/g), and Zn2+ (274 mg/g). It was also reported by the authors that the increase in the uptake capacity of the heavy metal ions from the solution by hydrogels was due to the increase in the pH value of the medium, which is due to the presence of ▬COOH group. The ▬COOH group deprotonated into ▬COO▬ at high pH value; thus more active sites are available on hydrogel network to remove the positive heavy metal ions and vice versa.

#### **Figure 5.**

*(a) Variation in the adsorption capacity as function of initial Cu(II) ion concentration using AAc/NaAlg/ SH SAHs with the different amount of SH. (b) Variation in the adsorption capacity as function of initial Pb(II) ion concentration using (AAc/NaAlg/SH) SAHs with the different amount of SH. (c) Variation in the adsorption capacity as function of initial Fe(II) ion concentration using (AAc/NaAlg/SH) SAHs with the different amount of SH [43].*

#### **5.2 Effect of initial concentration of heavy metal ions**

A novel synthesis of SAH consisting of acrylic acid (AA), sodium alginate (SA), and sodium humate (SH) (AAc/SA/SH) to produce poly (AAc-co-NaAlg-co-SH) superabsorbent hydrogels via copolymerization process in the presence of MBA at 70°C for 6 h was reported by Agnihotri and Singhal [43]. These SAHs were used as sorbent for adsorption of heavy metal ions (Cu2+, Pb2+, and Fe2+) and dyes (MB and CV) from aqueous solution. They observed that the adsorption capacity (mg/g) increased with the increasing initial concentration of heavy metal ions, which is

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*Superabsorbent Hydrogels for Heavy Metal Removal DOI: http://dx.doi.org/10.5772/intechopen.89350*

Mn2+ ions from contaminated wastewater.

**5.3 Effect of temperature on removal of heavy metal ions**

shown in **Figure 5**.

network.

**6. Conclusion**

this field.

**Acknowledgements**

**Abbreviations**

AcGGM acetyl-galacto glucomannan

PEDOT poly(3,4-ethylenedioxythiophene)

P(AA) poly acrylic acid PEG poly ethylene glycol

due to force established by the heavy metal ions as a mass transport from liquid to adsorbent surface. The increased trends observed in the adsorption capacity are

Zendehdel et al. [44] reported about the synthesis of SAH of poly acrylamideco-acrylic acid (p(AAm-co-AA/Na zeolite)) for the successive removal of heavy metal ions (Pb2+ and Cd2+) and studied the effect of temperature (ranging from 285 to 323 K) on the removal of these heavy metal ions from the aqueous solution. They reported that raising temperature from 285 to 303 K, the adsorption of heavy metal ions increased, which indicates that the process is endothermic. However, further increase in temperature up to 323 K, the adsorption of heavy metal ions was decreased, which is due to the desorption of heavy metal ions from the hydrogel

The synthesis of a copolymer composed of itaconic acid (IA) and acryl amide (AAm) [p(IA-co-AAm)] has been reported by Sharma and Tiwari [45]. The sample was successfully tested for the removal of Mn2+ ions from contaminated water at various environmental conditions. They studied and reported briefly about the effect of adsorbent dose on the removal of Mn2+ ions. It was observed that increasing the absorbent dose ranging from 0.04 to 0.10 g increases the % removal of the

The industrial growth for manufacturing of goods not only enhances the manufacturing process but also promotes the market for economic development. However, on the other hand, many industries severely contaminated the water bodies with toxic heavy metals and other pollutants. Therefore, the treatment and removal of toxic heavy metals from the wastewater is necessary before going into stream and rivers. The adsorption of heavy metal ions by superabsorbent hydrogels is more popular due to easy operation, low cost, more effectiveness, biodegradable, reusability, and recyclability. The removal of heavy metal ions by these superabsorbent hydrogels is more recent and attracts the interest of the scientists working in

L.A. Shah is highly grateful and acknowledges the financial support by the

Higher Education Commission of Pakistan under research grant no: 7309.

**5.4 Effect of dosage of adsorbent on the removal of heavy metal ions**

*Trace Metals in the Environment - New Approaches and Recent Advances*

**5.2 Effect of initial concentration of heavy metal ions**

A novel synthesis of SAH consisting of acrylic acid (AA), sodium alginate (SA), and sodium humate (SH) (AAc/SA/SH) to produce poly (AAc-co-NaAlg-co-SH) superabsorbent hydrogels via copolymerization process in the presence of MBA at 70°C for 6 h was reported by Agnihotri and Singhal [43]. These SAHs were used as sorbent for adsorption of heavy metal ions (Cu2+, Pb2+, and Fe2+) and dyes (MB and CV) from aqueous solution. They observed that the adsorption capacity (mg/g) increased with the increasing initial concentration of heavy metal ions, which is

*(a) Variation in the adsorption capacity as function of initial Cu(II) ion concentration using AAc/NaAlg/ SH SAHs with the different amount of SH. (b) Variation in the adsorption capacity as function of initial Pb(II) ion concentration using (AAc/NaAlg/SH) SAHs with the different amount of SH. (c) Variation in the adsorption capacity as function of initial Fe(II) ion concentration using (AAc/NaAlg/SH) SAHs with the* 

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**Figure 5.**

*different amount of SH [43].*

due to force established by the heavy metal ions as a mass transport from liquid to adsorbent surface. The increased trends observed in the adsorption capacity are shown in **Figure 5**.
