A comprehensive review on photocatalytic removal of heavy metal ions by polyaniline-based nanocomposites

The primary goals of human civilization are sustainable growth and restoration of the ecosystem. Currently, the continuous release of effluents containing heavy metals from tanneries, and the mining, printing, and pharmaceutical industries into the aquatic environment has become a serious issue. Chromium (Cr) and mercury (Hg) pose a major threat to human beings. Several techniques have been employed to mitigate this threat, including adsorption, electrolysis, chemical precipitation, desalination, reverse osmosis, ion exchange, membrane filtration, and photocatalysis. However, photocatalysis is known for its cost-effectiveness and green aspects in the removal of heavy metal ions from solutions. Over the last few decades, there has been a growing interest among researchers worldwide to study this technique. Numerous materials, including conducting polymers (CPs), have been utilized for the removal of heavy metal ions from wastewater/aqueous solutions. Polyaniline (PANI)-based nanocomposites are effective photocatalysts for the removal of various types of heavy metal ions from wastewater/aqueous solutions. Despite its potential, several factors affect the removal efficiency, such as irradiation levels and the type of PANI-based nanocomposite used. Further research is needed to address these challenges and improve the stability and reusability of PANI-based photocatalysts. Given the available water resources in the real world, it is critical that in-depth research be conducted into PANI-based photocatalysts, and the stability and reusability of such catalysts and achieving the primary goals of human civilization, namely sustainable growth and ecosystem restoration.