Water treatment using stimuli-responsive polymers

Abstract

Water treatment is a process used to eliminate or reduce chemical and biological contaminants that are potentially harmful to the water supply for human use. Stimuli-responsive polymers are a new category of smart materials used in water treatment via a stimuli-induced purification process and subsequent regeneration of the polymers. Stimuli-responsive polymers dynamically change their physico-chemical properties upon environmental changes. They can undergo shrinkage or expansion, alter their optical properties, and change their electrical characteristics depending on the applied stimuli. In this context, various stimuli-responsive polymer systems such as self-assembled nanostructures, supramolecular polymers, hydrogels, porous nanoparticles, membranes, and responsive coatings can be used in water treatment. As two main water pollution sources, heavy metals and dyes have raised considerable concerns among researchers. Current methods are inefficient at removing these contaminants from water, which may endanger the ecosystem. This review focuses on stimuli-responsive polymers that absorb heavy metal ions, aqueous anions, and dyes through their responsive characteristics. In particular, our objective is to evaluate the effectiveness of different smart polymer systems in water treatment processes. Recent advances in the field of pH-, CO₂-, temperature-, and light-responsive polymers in water purification are reported in detail, and other stimuli including magnetic fields, redox systems, and electrical fields are discussed. This review also highlights novel dual- and multi-responsive polymers as these can exhibit favorable synergistic properties. In addition, future directions in water purification through smart polymers, the use of different regeneration processes, and finally the selectivity and efficiency of the removal systems are discussed.