Green Synthesis of ZnO Nanoparticles Using Diverse Plant Extracts Sintesis Hijau Nanopartikel ZnO Menggunakan Ekstrak Tumbuhan yang Beragam Hamid Siti Nur Cholisa sitinur@gmail.com Muis Lidya Shery lidyasherymuis@umsida.ac.id Indonesia Indonesia 25 10 2024 <bold id="bold-1">Introduction </bold>

Nanotechnology refers to the precise manipulation, control, and fabrication of novel materials or devices at the nanometer scale (10-9m), exhibiting distinct properties from those of bulk materials. Nanoparticles are regarded as the fundamental building blocks of nanotechnology, serving as the essential foundation for various nanostructured technologies and materials. Nanomaterials can be acquired through natural means, such as viruses and proteins, or unintentionally, such as nanoparticles created from diesel combustion. They can also be intentionally manufactured using specific fabrication processes. Nanoparticles are particles that have one or more diameters between 1 and 100 nm. They can exist as individual particles, or they can be grouped together as aggregates or agglomerates [1–3]. The nanomaterials have exceptional properties against the bulk matter. First, the properties of material such as energy change at the nanometer level. Nanomaterials possess two notable characteristics. Firstly, they can be constructed atom by atom using two distinct production techniques (bottom-up and top-down). Secondly, nanomaterials exhibit the remarkable attribute of having a high surface-to-volume ratio in comparison to bulk materials [4,5]. These superior properties make the field of nanotechnology attractive to many researchers to synthesis and optimize new materials in nano scale range [5]. In addition, the preparation of nanoparticles is cost effective, facile, and simple and there is no need to large amount for an application. Thus, a clear enhancement has been obtained in fabricating nanoparticles with desired size and morphology for applications [6,7]. However for non-toxic, ecofriendly production of nanoparticles the green synthesis methods were employed by using different substrates including plants, bacteria, fungi, and algae for generating metal oxide particles at a large scale while ensuring their purity [8]. Thus , among verity of many metals and metal oxides and despite of their novel properties ,ZnO nanoparticles has been chosen because of high thermal stability , more cost effective production and the good antibacterial activity , also the wide range of applications such as electronics, communications, sensors, cosmetics and environmental protection [10-12] The present review primarily centers on the significance of ZnO nanoparticles and various synthesis methods, with a particular emphasis on biological approaches, characterization techniques employed, and factors influencing the properties and dimensions of biosynthesized ZnO nanoparticles.

 <bold id="bold-2">Approaches for producing ZnO NPs</bold>

Nanostructures can be created through the process of synthesis, and nanoparticles can be produced using various methods. These techniques involve synthesizing dry particles as well as dispersing nanoparticles in liquid. Nanostructures can be formed either by assembling atoms together or by reducing the size of micro particles to nanoparticles [13]. The synthesis of nano particles can be achieved through two distinct approaches, known as the top-down approach and the bottom-up approach [14]. The top-down technique entails the fragmentation of the bulk material into structures or particles at the Nano scale. Top-down synthesis techniques are an expansion of the methods used to create particles that are on the scale of microns. Top-down techniques are fundamentally more straightforward and rely on either removing or dividing bulk material or on shrinking bulk production procedures to create the desired structure with suitable attributes. The primary issue with the top-down strategy lies in the inherent flaws of the surface structure. For instance, nanowires produced using lithography exhibit surface roughness and can harbor a significant amount of contaminants and structural flaws. Aerosol spray, gas-phase condensation, atomic force manipulation, electron beam lithography, and high-energy wet ball milling are a few instances of these techniques [15]. The term "bottom-up approach" refers to the process of constructing material at the molecular, atomic, and cluster level by adding one molecule, atom, or cluster at a time. During the assembly process, physical forces are applied to the nanostructure to merge the particles into a bigger entity. Nanotechnologists mostly like the bottom-up method for making complex nanostructures because it lets them precisely control particle size, which improves optical, electrical, and other properties [16]. Additionally, the methods for synthesizing nanoparticles can be categorized into three classes: physical, chemical, and biological processes [17] as shown in Fig.(1). In comparison between the mentioned methods, the physical and chemical types have some drawbacks such as the difficulty to achieve the expected narrow size, having control over the surface chemistry and the structure of the nanoparticles, costly, non-eco-friendly as lead to the release of harmful by products. Moreover they caused energy consumption, environmental pollution and biological risk [18-22] While the biological method referred to the green chemistry and considered the best because its eco-friendly, biocompatible, facile technique, cheap and can deal with the limitations of nanoparticle synthesis. The biological system employed algae and plants [23], bacteria [24], yeast [25], fungi [26], and human cells [27, 28], and used the reductive and stabilizing agents of their proteins and metabolites to convert metal ions into their particular nanoparticles. Nanotechnology researchers are interested in green synthesis. Many studies have demonstrated that microorganisms and plant components can produce zinc oxide nanoparticles [29–31].

The synthesis and approaches of nanoparticles.

<bold id="bold-f560b50e67fc38c4146ba0c5a09b8f26">Plants-mediated synthesis of ZnO nanoparticles. </bold>

It has been proven that plants can be used to synthesis nanoparticles by eco-friendly, facile, simple and safe methods to use. Utilizing plant extracts is a straightforward and efficient method for synthesizing metal or metal oxide nanoparticles in large quantities. This method is simpler and easier compared to using bacteria or fungi, as plants contain abundant medicinal compounds that can reduce complex metallic ions into simple ions. The concept of utilizing metal reduction on nano-sized materials was derived from the observation of metallic ions accumulating in plant cells and tissues [32]. Plants are frequently chosen as the primary biological source for producing ZnO NPs due to their cost-effectiveness in production and handling, minimal environmental impact, simplicity in manufacturing, and their resilience against potential harm from microorganisms. Additionally, plant extracts are commonly prepared using distilled water as solvents, which present fewer health risks compared to microbial-assisted ZnO NPs synthesis [33]. A great number of leaves have been utilized in the production of ZnO nanoparticles. ZnO nanoparticles can be produced through biological processes.Successful Biosynthesis of zinc oxide nanoparticles using plant extract is presented in table (1).

Table 1

Summarized the synthesis of ZnO NPs using different plants.

Plant Zinc salt Molarity Tem (˚C) Reaction Time Size(nm) Morphology Application Ref.
Aloe barbadensis miller leaves Zinc nitrate _ 80 5-6 h. 35nm Spherical and hexagonal nanoparticles. _ [34]
Corriandrum sativum leaves Zinc acetate dehydrate 0.02 60 2h. 66nm Cubic _ [35]
Hibiscus rosa-sinensis leaves Zinc nitrate _ 400 _ 30-35nm spongy shape nanoparticle _ [36]
Olea europaea leaves Zinc sulfate heptahydrate, ZnSO4.7H2O 4mM 60 5 min. 20nm Nano sheet _ [37]
Hibiscus subdariffa leaves Zinc acetate dihydrate _ 30 ,60 and 100 30 min. 16-60 nm irregular surface (amorphous),spherical and a dumbbell anti-bacterial & anti-diabetic agent [38]
Olea europaea leaves zinc nitrate _ 400 1h. 20-60 nm Spherical - [39]
Couroupita guianensis leaves Zinc acetate dehydrate _ 60 10 min. _ Nanoflakes antibacterial agent [40]
Aloe vera (gel/leaves)and Hibiscus sabdariffa (leaves) Zinc nitrate 0.01 80 6h. 9-18 nm Rod Antibacterial, Antioxidant and Anti-proliferative agent [41]
Camellia Sinensis Zinc Nitrate _ 400 _ 8 nm Spherical Photocatalytic agent [42]
olive,guava,fig, and lemon(leaves) Zn (NO3)2.6H2O 0.2 500 _ 7.1-28nm Spherical , spongy and irregular shapes Phenol Decontamination [43]
Costus pictus D. Don leaves Zinc nitrate 0.1 450 4h. 29.11 xrd20-80nm hexagonal and rod Antibacterial agent & anticancer [44]
Olive leaves zinc sulphate heptahydrate 100mM 60 _ 20-50 nm spherical - [45]
Hibiscus sabdariffa flower zinc nitrate _ 400 _ 30-8 nm semicircular shape - [46]
Fresh leaves of L. nobilisL. (Family Lauraceae Zincacetat 0.02 60 2h. 21.49 small spherical structures and accumulate like bullets _ [47]
zinc nitrate 0.05 60 2h. 25.26 The spherical flower-shaped bundles.
Deverra tortuosa zinc nitrate hexahydrate _ 400 1 h. 9.26 to 31.18 nm. hexagonal Anticancer agent [48]
Olea europaea leaf zinc acetate dihydrate 0.01M 50 _ 11-60 nm spherical star-shaped antifungal agent [49]
Raphanus sativus var. Longipinnatus leaves Zinc acetate 0.1M 60 2 h. 66.43nm spherical anticancer agent [50]
aqueous seed extract of Caesalpinia crista zinc nitrate hexahydrate _ 400 _ 34.67 nm _ Antimicrobial , antioxidant & anticancer agent [51]
Olea europaea zinc sulfate heptahydrate 5mM 80 10 min. 50nm homogeneous shape antimicrobial and antibiofilm [52]
<bold id="_bold-32">Conclusion</bold>

In conclusion, the review underscores the significance of ZnO nanoparticles in nanotechnology and the promising role of green synthesis methods in addressing environmental concerns. The comprehensive discussion of various green synthesis methods using plant extracts, alongside a summary of successful ZnO NP synthesis experiments, demonstrates the feasibility and effectiveness of this approach. Factors influencing the synthesis process, such as molarity, temperature, pH value, and reaction time, have been explored, emphasizing the need for careful consideration during the synthesis and characterization phases. The ability to control these parameters contributes to tailoring the size and morphology of the ZnO nanoparticles for specific applications. As researchers continue to explore and optimize these methods, the potential for ZnO nanoparticles to contribute to advancements in various fields remains a subject of ongoing interest and investigation.