Polyglutamic acid and its derivatives as multi-functional biopolymers for the removal of heavy metals from water: A review

The surge in industrial revolution has tremendously increased heavy metal pollution in the environment. The use of biopolymers such as polyglutamic acid for the treatment of heavy metals has received immense interest due to their environmentally friendly nature, low carbon footprint, and their efficiency in the remediation of water bodies. This review critically analyses research work that has used polyglutamic acid-based materials to remove heavy metals from water bodies in the last few decades. The mechanisms of the removal process have been discussed in detail. The challenges associated with the use of polyglutamic acid-based materials have also been elucidated. According to the reviewed articles, polyglutamic acid-based materials can be synthesized using various techniques including crosslinking reactions, grafting, coprecipitation and immobilization techniques to prepare various types of materials such as adsorbents, resins, membranes, and flocculants. Adsorption was identified as the prevalent heavy metal removal technology and most studies could be applied to the Langmuir and Freundlich adsorption isotherm model and to the pseudo-second-order adsorption kinetic model. The availability of functional groups such as amino and carboxyl groups facilitated the removal of heavy metals. The leading mechanisms of removal were found to be ion–exchange, electrostatic attraction, and chelation reactions. The production cost of polyglutamic acid was identified as a major challenge and can be addressed by further exploring various types of biomass as low-cost nutrition medium that is required during the production process.