Polyaniline-based adsorbents for water treatment: Roles of low-cost materials and 2D materials

Access to clean water and sanitization is crucial to all life on Earth, and has been listed among the United Nations Sustainable Development Goals. Adsorption is a simple and economical technology for water purification. However, conventional adsorbents, such as zeolites, biochar, activated carbon and clay minerals, have some limitations, particularly their unsatisfactory adsorption efficiencies. Polyaniline (PANI), a stable conducting polymer with facile synthesis, nitrogen-rich functional groups, and tuneable morphology, is a promising candidate for adsorbing various pollutants. This review attempts to critically assess PANI-based adsorbents in terms of their advantages, disadvantages, and separation mechanisms in pollutant removal. Low-cost natural and waste materials, and emerging ultrathin 2D nanosheets can also be promising adsorbents. We highlight the significant roles of low-cost materials as well as emerging 2D nanosheets in enhancing the performance of PANI-based adsorbents. Combining PANI-based adsorbents and low-cost materials or 2D nanosheets can not only address the challenges of PANI-based adsorbents (e.g., low surface areas and thus low adsorption efficiencies), but also employ the synergistic effects of these adsorptive materials. As a result, the PANI-based hybrid adsorbents have enhanced functionality, and improved pollutant removal performance. Finally, we offer insightful perspectives and future research directions in developing PANI-based adsorbents with low-cost and 2D materials.