Non-magnetic and magnetically responsive support materials immobilized peroxidases for biocatalytic degradation of emerging dye pollutants—A review

In recent years, the removal of hazardous pollutants from many industries has become a significant challenge for mankind as a growing number of contaminants, including a wide range of organic pollutants, synthetic dyes, and polycyclic aromatic hydrocarbons (PAHs), have inevitably led to an increased anthropogenic impact on the biosphere. Due to the complex aromatic structure, most synthetic dyes show resistance to degrade by the classical approaches, such as coagulation, flotation, adsorption, membrane process, and reverse osmosis. Enzyme-assisted biodegradation of pollutants offers an eco-friendlier and cost-effective alternative to remediate dyes, dyes-based effluents, other toxins, etc. Various plant and microbial oxidoreductase (Horseradish and manganese peroxidase) have recently received more attention for degrading and detoxifying a wide range of dyes either by opening the aromatic ring structure or by precipitation due to their high activity under milder conditions, high substrate specificity, and biodegradable nature. To enhance the efficiency, stability and recyclability, enzymes were immobilized on various support media such as sodium alginate, agarose, chitin/chitosan, polyvinyl alcohol, polyacrylamide, macroporous exchange resins, hydrophobic sol-gels, and nanoporous silica gel, including magnetically separatable media. Among various types of magnetic nanoparticles (MNPs), iron oxide magnetic nanoparticles, such as hematite, magnetite, and maghemite, have gained great attention due to their properties like small size, superparamagnetism, high surface area to volume ratio, and ease of separation for repeated cycles of uses. These carriers can be separated easily and rapidly from the reaction medium by an external magnetic field without being subjected to mechanical stress than centrifugation or filtration. Various methods have been employed for immobilizing oxidoreductase on different media, such as adsorption, covalent binding, entrapment, and encapsulation using different cross-linking agents. Compared to the free enzyme, insolubilized enzymes reduce production costs by enzyme reusability, tolerance to unfavorable environmental conditions, and high catalytic stability. Here, we review various immobilization methods and biocatalytic degradation of emerging dye pollutants, focusing on various non-magnetically and magnetically responsive supports to immobilize peroxidases. Conclusively, magnetically separatable peroxidases show more stability towards extreme temperature and pH conditions and can be used for repeated cycles than free and non-magnetically separatable peroxidase.