Comprehensive study on Indian Plant extracts mediated biocompatible ZnO nanostructures: A Green Initiative

Abstract

Zinc oxide nanostructures (ZnO NSs) are extensively used in the biomedical, optical, sensing, and manufacturing sectors. It is due to their excellent physio-chemical properties, superior antimicrobial, anti-cancer, and enhanced photocatalytic activities. The unique antimicrobial and antiviral activities of ZnO NSs have raised their global demand in designing various diagnostic, preventive and treatment strategies to combat Coronavirus diseases (COVID-19).  ZnO NSs with distinct morphologies are conventionally fabricated through chemical and physical strategies like hydrothermal method, chemical reduction, ball milling, solid state route, and vapour/thermal deposition techniques. However, the inclusion and production of hazardous chemicals and requirement of extreme surroundings during their synthesis, and production of nano waste upon their use has been a serious global concern. In addition, various fabrication requirements such as the requirement of sophisticated equipment, elevated temperature and complex procedure in several physiochemical synthesis strategies limits their commercial viability due to increase in cost, complexity, toxicity and energy.

Contrary, green route synthesized ZnO NSs are eco-friendly, biocompatible, energy-efficient and cost-effective. The exclusion of harmful chemicals during fabrication results in prevention of environmental contamination and user safety. They are biocompatible resulting in combating the issues of production of nano waste. Green strategies are thus turned out revolutionary to synthesize ZnO NSs in terms of environmental sustainability. Various green strategies include use of bio-reducing agents extracted from plants, bacteria, fungi and algae. These strategies have been used to fabricate ZnO NSs with distinct morphologies such as orthorhombic, hexagonal rods, nanospheres, spherical, cylindrical, cubic, tetragonal crystalline, octahedral, sheets, flakes, and quai-spherical.

Among the present green routes, the plant extract-mediated technique is simple, readily available, cost-effective, and less time-consuming. The abundance of genetic variation in plants in terms of metabolites and biomolecules allows them to architect different nanostructured morphologies.  It involves the use of India-based plant extracts such as Azadirachta indica (Neem)/ Mangifera Indica (Mango)/Hibiscus subdariffa/Coriander sativum /Cassia Fistula /Aloe vera/Cinnamomum Verum  as precursors. These plant extracts includes various biological components and phytochemicals such as terpenoids flavonoids, alkaloids, aldehydes with different functional groups such as hydroxyl, carbonyl, and amines. These phytochemicals acts as solvent systems and reducing agents. They react with metal ions to bring their size to nano range through bio-reduction processes. Additionally, these compounds aid in the capping of nanostructures, which is essential for biocompatibility and stability.

This review focuses on applying various India-based plants for the fabrication of ZnO NSs with different morphologies. It will describe the various factors governing morphologies of plant-mediated ZnO NSs during the green synthesis. To the best of our knowledge, this review is the first comprehensive study on India-based plants to synthesize ZnO NSs and highlight their morphology governing parameters during the synthesis. This review will provide a general guide to fabricating these biocompatible and eco-friendly ZnO NSs and optimizing their morphologies. It also describes the associated challenges, their possible alternate solutions, and prospects in various environmental redemption applications. Hence, the biocompatible ZnO NSs opens new prospects in antiviral, antimicrobial, anti-cancer, removal of pollutant dyes, removal of heavy metal ions from polluted water, air contaminant monitoring and detection, catalytic activity and photocatalytic sectors.

Keywords: Green Nanotechnology, Indian Plant extract, Nanostructures, Zinc Oxide, Environmental sustainability

References

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