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.

An energy band compactable B-rGO/PbTiO3 p-n junction: a highly dynamic and durable photocatalyst for enhanced photocatalytic H2 evolution

Reduced graphene oxide (rGO) intentionally doped with boron atoms is a promising tactic to extract bandgap energy and p-type semiconducting behavior from graphene-based materials. Moreover, the integration of p-type boron-doped rGO with an n-type material through a heterojunction interface exhibits complementary properties to restrict the fast recombination of charge carriers and enhance the photoreaction towards energy applications. Herein, we have prepared boron-doped rGO/PbTiO3 p-n heterojunctions via a hydrothermal method. The successful formation of an excellent p-n heterojunction was demonstrated by TEM, XPS and Raman analysis. The constructed boron-doped rGO/PbTiO3 p-n heterojunctions exhibit dramatic increases in photoelectrochemical and photocatalytic performance due to the presence of a space charge region at the interface of the two materials. The scenario also revealed the double-edge sword functions of B-rGO: the material itself (i) acts as a visible light active photocatalyst with a band gap energy of 2.7 eV and (ii) participates in enhanced charge transfer via the band edge alignment between B-rGO and PbTiO3, as elucidated from photoluminescence and electrochemical impedance studies. Furthermore, the optimal 2B-rGO/PT p-n heterojunction possesses outstanding repeatability and exhibited the highest rate of hydrogen evolution, i.e. 293.79 μmol h-1 under visible light irradiation. The results for these materials may provide advanced insight into the design of next-generation high-efficiency black graphene-based heterojunctions.

Pyrochlore Ce2Zr2O7 decorated over rGO: a photocatalyst that proves to be efficient towards the reduction of 4-nitrophenol and degradation of ciprofloxacin under visible light

The synergistic interaction between phase pure Ce₂Zr₂O₇ and rGO enhances the photoreduction of 4-nitrophenol under visible light.

Extremely rapid engineering of zinc oxide nanoaggregates with structure-dependent catalytic capability towards removal of ciprofloxacin antibiotic

ZnO nanoaggregates with structure-dependent catalytic capability of removal of ciprofloxacin antibiotics were engineered by an extremely rapid polyol-mediated synthesis approach.

Insights into the structure-induced catalysis dependence of simply engineered one-dimensional zinc oxide nanocrystals towards photocatalytic water purification

One-dimensional nanocrystalline semiconductors have been comprehensively studied because of their fascinating properties and practical applications in various fields.

Fabrication of WO2.72/RGO nano-composites for enhanced photocatalysis

WO_2.72/RGO nano-composites exhibit remarkable photocatalytic activity in both oxygen evolution from water splitting and selective oxidation of benzyl alcohol due to the synergetic effects between WO_2.72 and RGO.

Tunable design of yolk–shell ZnFe2O4@RGO@TiO2 microspheres for enhanced high-frequency microwave absorption

Yolk–shell ZnFe₂O₄@RGO@TiO₂ microspheres with a tunable void size and TiO₂ shell thickness possess enhanced high-frequency microwave absorption properties.