**4. Polyaniline and its composites for wastewater treatment**

The application of PANI for wastewater treatment has been widely studied owing to its exceptional structure that comprises abundant amine and imine functional groups [50, 51]. The nitrogen atoms on these functional groups have lone pairs of electrons to facilitate chelation and adsorption of pollutants [28, 52]. However, PANI has disadvantages such as poor mechanical properties and processability as well

**153**

**treatment**

water purification.

**5.1 Adsorption of heavy metals**

*Polyaniline-Based Nanocomposites for Environmental Remediation*

and maximum adsorption capacity [35, 53, 65, 66].

**5. Application of polyaniline nanocomposites as adsorbents for water** 

In recent years, polyaniline nanocomposites have been used as adsorbents for the removal of various pollutants from wastewater [30]. More studies have been focussed on the adsorption of organic dyes and heavy metals ions due to their good interaction with PANI nanocomposites functional groups [52]. In the study of interaction between PANI nanocomposites and pollutants, various adsorption parameters such as pH, contact time, adsorbent dose, temperature, nature of the adsorbent and concentration of the pollutants are investigated [38]. From these parameters, the efficiency and adsorption capacity of nanocomposites can be determined to confirm the potential of the PANI nanocomposites as adsorbents for

The general sources of heavy metals are weathering of rocks due to their abundance in nature and mining industries as a result of mineral process of metal ores [61]. Various heavy metals known to pollute water include nickel, cadmium, lead, mercury, chromium, arsenic and copper. The water pollution by these toxic metals is a global concern owing to their acute toxicity and enduring accumulation [67].

as low solubility. These limitations emanate from its high conjugation and strong electrostatic interaction between chains, which decreases its performance and limit its commercial application [51, 53]. Composites formation offers potential in addressing the above shortfalls. Polyaniline composites can be regarded as a material consisting of PANI matrix and one or more components such as semiconductors, metal nanoparticles, organic compounds, inorganic compounds as well as biological and natural products in order to improve polymer backbone properties or extend its functionalities [51, 54]. In order to prepare the composite materials successfully, several methods like physical mixing, sol–gel technique, *in–situ* chemical polymerisation, emulsion technology, sonochemical process and irradiation technique are employed [55]. Since then, various PANI composites have been reported for the removal of pollutants from wastewater using membrane technology [56, 57], chemical reduction [50], photocatalytic degradation [58, 59] and adsorption technology [60, 61]. Among these methods, adsorption has been identified as a prestigious technology, due to its flexibility and simplicity of design, initial cost, ease operation and insensitivity to toxic pollutants [62]. Different polyaniline-based composites for adsorption of pollutants have been widely studied. Samani et al. [60] reported PANI/PEG (polyethylene glycol) composite for the removal of hexavalent chromium ions (Cr(VI)), which had the maximum adsorption capacity (qmax) of 68.97 mg/g. Debnath et al. [63] reported a PANI/lignocellulose composite with qmax of 1672.5 mg/g for Congo red (CR) removal. PANI/chitosan was studied by Janaki et al. [64] for the removal of dyes (CR, Coomassie Brilliant Blue (CBB), and Remazol Brilliant Blue R (RBBR)). They obtained the maximum capacities to be 322.58, 357.14 and 303.03 for CR, CBB and RBBR, respectively. PANI/silica (SiO2) gel was reported by Karthik et al. [52] with qmax = 63.41 mg/g for the removal of Cr(VI). However, most of these PANI composites have lower removal efficiency and adsorption capacity, owing to their irregular structure resulting from agglomeration, poor water dispersion and reduced surface area [35]. Numerous researches have been focussed on the development of nanostructured PANI composites with improved surface area

*DOI: http://dx.doi.org/10.5772/intechopen.82384*

#### *Polyaniline-Based Nanocomposites for Environmental Remediation DOI: http://dx.doi.org/10.5772/intechopen.82384*

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

**4. Polyaniline and its composites for wastewater treatment**

*a = in-situ polymerisation, NaCMCNa = sodium carboxymethyl cellulose sodium.*

*Some of PANI nanocomposites and their reported structures.*

The application of PANI for wastewater treatment has been widely studied owing

PPy-PANI/Fe3O4 a, FeCl3 roughly spherical particles [3]

to its exceptional structure that comprises abundant amine and imine functional groups [50, 51]. The nitrogen atoms on these functional groups have lone pairs of electrons to facilitate chelation and adsorption of pollutants [28, 52]. However, PANI has disadvantages such as poor mechanical properties and processability as well

*TEM images of AuPANI nanocomposite with different magnifications (a, b, c) showing rod-like Au nanoparticles embedded in a PANI synthesised by interfacial polymerisation and (d) corresponding selected* 

**and/or other reagents**

Fe3O4/G/PANI a, APS Mixture of sheets and

PANI/zeolite a, APS Mixture of sheets and

PANI/MnO2/TiO2 a, KMnO2 Aggregated spherical

PANI-PPy a, FeCl3 Fibres [40] PANI nanoadsorbent a, APS, stabiliser Spherical particles [41]

PANI/Fe0 a, FeCl3 Fibrous structure [43] PANI/ZrO2 Direct mixing, APS Irregular rougher surface [44] PANI–ZnO a, APS Flaky structure [45] PANI/SiO2 a, APS, NaCMCNa Uniform spherical particles [46]

In-situ method Spherical particles [42]

spherical particles

tubular particles

particles

**Morphology Refs.**

[47]

[48]

[49]

**Adsorbent Synthesis method, oxidant** 

**152**

**Table 1.**

**Figure 6.**

PANI/tin(II) molybdophosphate

*area electron diffraction (SAED) [36].*

as low solubility. These limitations emanate from its high conjugation and strong electrostatic interaction between chains, which decreases its performance and limit its commercial application [51, 53]. Composites formation offers potential in addressing the above shortfalls. Polyaniline composites can be regarded as a material consisting of PANI matrix and one or more components such as semiconductors, metal nanoparticles, organic compounds, inorganic compounds as well as biological and natural products in order to improve polymer backbone properties or extend its functionalities [51, 54]. In order to prepare the composite materials successfully, several methods like physical mixing, sol–gel technique, *in–situ* chemical polymerisation, emulsion technology, sonochemical process and irradiation technique are employed [55]. Since then, various PANI composites have been reported for the removal of pollutants from wastewater using membrane technology [56, 57], chemical reduction [50], photocatalytic degradation [58, 59] and adsorption technology [60, 61]. Among these methods, adsorption has been identified as a prestigious technology, due to its flexibility and simplicity of design, initial cost, ease operation and insensitivity to toxic pollutants [62]. Different polyaniline-based composites for adsorption of pollutants have been widely studied. Samani et al. [60] reported PANI/PEG (polyethylene glycol) composite for the removal of hexavalent chromium ions (Cr(VI)), which had the maximum adsorption capacity (qmax) of 68.97 mg/g. Debnath et al. [63] reported a PANI/lignocellulose composite with qmax of 1672.5 mg/g for Congo red (CR) removal. PANI/chitosan was studied by Janaki et al. [64] for the removal of dyes (CR, Coomassie Brilliant Blue (CBB), and Remazol Brilliant Blue R (RBBR)). They obtained the maximum capacities to be 322.58, 357.14 and 303.03 for CR, CBB and RBBR, respectively. PANI/silica (SiO2) gel was reported by Karthik et al. [52] with qmax = 63.41 mg/g for the removal of Cr(VI). However, most of these PANI composites have lower removal efficiency and adsorption capacity, owing to their irregular structure resulting from agglomeration, poor water dispersion and reduced surface area [35]. Numerous researches have been focussed on the development of nanostructured PANI composites with improved surface area and maximum adsorption capacity [35, 53, 65, 66].
