A polypyrrole/modified poly (styrene-alt-maleic anhydride) conducting nanocomposite
Conducting polymers have recently attracted considerable interest on account of their desirable physical and chemical properties.1 The conducting polymer polypyrrole (PPy) is one of the most commonly used in commercial applications because of the long-term stability of its conductivity properties. However, PPy suffers from a number of disadvantages, including poor processability and insolubility.2, 3 Many studies have focused on improving the preparation of PPy-based composite materials in an attempt to overcome these limitations.2,4,5
One of the more promising methods that has emerged for alternative preparations of PPy-based nanocomposites is emulsion polymerization. The advantages of this method include the formation of high molecular weight polymers, uncomplicated control of the polymerization procedure, and suitable heat and mass transfer.6 Another strategy to arrive at more favorable physical and chemical properties is to develop composites of conducting polymers and synthetic polymers. We have explored the copolymer poly(styrene-alt-maleic anhydride) (PSMA) as a candidate for the synthetic polymer component, since it is inexpensive and possesses reactive groups within the main structure that allow for additional functionalization.7
In continuation of our previous work on conductive composites,8 we synthesized conducting nanocomposites of pyrrole (Py) and a modified PSMA in different weight ratios via emulsion polymerization (see Scheme 1). PSMA was first prepared by radical polymerization of styrene and maleic anhydride, with benzoyl peroxide acting as the initiator. PSMA was then modified via chemical grafting with 4-aminobenzenesulfonic acid (4ABSA) to produce the PSMA-g-4ABSA modified copolymer for PPy. PSMA-g-4ABSA is often used as an external dopant for conductivity enhancement. The production of PPy occurs during emulsion polymerization of pyrrole in the presence of PSMA-g-4ABSA. We collected field emission scanning electron microscopy images of the final PPy/PSMA-g-4ABSA nanocomposite to examine its structural properties and found an irregular aggregation of granular nanoparticles (see Figure 1).
With PPy/PSMA-g-4ABSA in hand, we characterized how the PSMA-g-4ABSA copolymer content affects the nanocomposite's electrical conductivity, antioxidant activity, and ability to remove heavy metal ions. We found that the conductivity of the nanocomposite improved with increasing PSMA-g-4ABSA content, most likely due to an increasing proportion of carboxylic and sulfonic acid groups that are contributed by the backbone of the PSMA-g-4ABSA copolymer (see Figure 2).
Meanwhile, we found that the antioxidant activity of the PPy/PSMA-g-4ABSA nanocomposite increased by up to 60% as the amount of PSMA-g-4ABSA increased. Our explanation for this observation is that the labile hydrogen atoms within the nanocomposite are increasingly consumed over the time of the experiment (120min), thereby reducing the amount of active hydrogen atoms that would have been available to eliminate diphenylpicrylhydrazyl free radicals (see Figure 3).
We believe that conducting nanocomposites that are capable of removing heavy metal ions can be used as novel sorbent materials where the permanent conductivity of the sorbent is enhanced by the doping effect of the heavy metal ions. The effect of different types of metal cations in wastewater on the conductivity of polypyrroles and polyanilines is currently under study in our laboratory. To continue these investigations, we characterized the ability of the PPy/PSMA-g-4ABSA nanocomposite to remove the heavy metals ions copper II, cadmium II, and lead II from aqueous solution (50ppm). After a contact time of 130min, adsorption of these heavy metal ions onto the PPy/PSMA-g-4ABSA nanocomposite had reached levels of 60, 26, and 55%, respectively (see Figure 4).
In summary, we prepared PPy/PSMA-g-4ABSA conducting polymer nanocomposites via emulsion polymerization and showed that an increase in PSMA-g-4ABSA content leads to an increase in conductivity and a decrease in antioxidant activity. Moreover, the PPy/PSMA-g-4ABSA nanocomposites demonstrated a good ability to remove heavy metals. Our future work will focus on the development of new biocompatible nanocomposites, with an emphasis on nanocomposites that remove heavy metal ions, show anticorrosion properties, or act as biosensors.
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