Recent progress in the application of pH-responsive polymers in separation science

Abstract

The present review aims to highlight the applications of pH-responsive polymers and their composites in separation science. Their physicochemical properties change in a controlled manner in response to pH alterations. Thus, pH-responsive polymers can be easily recovered by just adjusting the pH of the sample. As a result, they are recyclable and environmentally friendly. Due to these attributes, many researchers have applied pH-responsive polymers during the adsorptive removal of analytes in complex matrices. The various interactions and mechanisms involved during the adsorption of analytes using pH-responsive polymers are summarised in this review. The pH-responsive polymers have also found widespread applications in smart membrane systems. The presence of these smart polymers in membranes confer their nanopores with pH responsiveness and this facilitates the regulation of the flow of materials through it by pH adjustment. The applications of pH-responsive polymers during the fabrication of smart membrane systems are discussed in detail in this paper. The hydrophilicity of these smart polymers is pH-dependent. They can form homogeneous solutions in water due to the presence of a high density of charges in their structures. However, adjustment of pH to their isoelectric points make them to be hydrophobic causing phase separation to occur. Thus, pH-responsive polymers are important candidates for the construction of aqueous two-phase systems. This review also explores in detail the application of pH-responsive polymers in aqueous two-phase systems. In addition, the challenges and future prospects of pH-responsive polymer are discussed in detail in this review.