In recent times, nanoparticles have gained attention and interest by researchers due to its characteristics such as physical properties (size, shape, crystal structure, surface characteristics etc.), physiochemical properties (large surface area, strength, magnetic and optical property), mechanical properties (elastic modulus, hardness, friction and adhesion), thermal properties (thermal conductivity, thermal stability and heat transfer nature) [1] and biological properties (antimicrobial, anticancer and drug delivery system) [2]. It is reported that important properties of nanoparticles are high surface area over volume ratio [3], reduced imperfection, high percentage of atoms on the surface and high surface energy. Nanoparticles are classified into six major categories based on their physical and chemical nature. It includes carbon –based, Metal based, ceramic, semi –conductor based, polymeric and lipid based NPs. In metal based NPs production, metal precursors are used in the synthesize process. Several metal-based nanoparticles have been synthesized and characterized such as Au, Ag, Cu, Fe, Zn etc., [4]. The applications of metal based nanoparticles have vast potential in many sectors. Nano scale structures are synthesized by two major approach i.e. bottom-up and Top-down. Bottom-up synthesis approach is a method in which metal atoms combines to form clusters in nano scale level. It includes atom by atom, molecule by molecule and cluster by cluster. Under bottom-up synthesis, there are several methods to synthesis nanoparticles such as spinning, template support, plasma/flame spraying, laser pyrolysis, CVD, atomic or molecular condensation and biological synthesis [5, 6]. The size of the nanoparticle plays significant role in many end uses. Reducing and capping agents are used to stabilize the nanoparticles at the time of synthesis. The shape and size of the NPs is controlled by involving reducing and capping agent in the process of synthesis [7]. Top-down synthesis method is an approach of forming nanoparticle by breaking down the bulk material in to small tiny material i.e. converting macro & microscale particle to nanoscale [8, 9]. The disadvantage of top down approach synthesis method is imperfection in NPs surface structure. Top-down synthesis approach includes mechanical milling, mechanical alloying, chemical etching, sputtering, laser ablation, electro explosion etc., Nanoparticles can be synthesized via three different routes: Physical, chemical and biological method. Chemical method for nanoparticle synthesis uses chemicals as a solvent and reducing agent. The process like sono chemical, electro chemical decomposition, thermal decomposition, co-precipitation, hydrothermal and micro emulsion is chemical method. Physical methods for nanoparticle synthesis includes aerosol, gas phase deposition, laser induced pyrolysis, ball milling, electron beam lithography, pulsed laser ablation. Plant, fungi, bacteria and protein mediated synthesis are biological method of nanoparticle preparation [10–12]. Physical method has less possibility to control the size of the NPs in nano range. This is considered as main disadvantage of physical method. Chemical method synthesis is commonly used among these methods due to its characteristics like more yield, efficient, simple methodology and low cost [13]. Now a days, iron oxide nanoparticles have extended its hand in many fields. Iron oxide nanoparticles have attracted many researchers, scientist and industry experts due to its unique characteristics such as superparamagnetism, surface to volume ratio, simple preparation process, low toxicity and easy separation steps. Superparamagnetism characteristics of iron oxide nanoparticle showed colossal potential in biomedical sector [14]. Iron oxide exists in three common form in nature i.e. magnetite (Fe3O4), maghemit (γ-Fe2O3) and hematite (α-Fe2O3). Iron oxide nanoparticle has wide range of application in the field of biomedical, catalyst, lithium ion battery, magnetic recording media and heavy metal removal. 90% of super paramagnetic iron oxide nanoparticles are synthesized via chemical method [15]. It also shows good results for antimicrobial and anti cancer activity [16]. Iron oxide nanoparticles are prepared using co-precipitation, hydrothermal, thermal decomposition, micro emulsion and sonochemical method [17]. Isobutanol and Iron (II) chloride tetrahydrate along with sodium hydroxide and ammonium hydroxide was used in synthesis of iron nanoparticle [18].
Several plant extract have been used for iron oxide nanoparticle synthesis. Many reports have been published related to plant mediated iron oxide nanoparticles (IONPs) production. Plant extracts acts as a capping and reducing agent. These iron oxide nanoparticles are highly reactive and unstable in nature due to its high surface energy. The capping of nanoparticle is essential to control the agglomeration and over growth. It also stabilizes the nanoparticles during synthesis [19]. Phytochemicals present in the plant extract helps in the formation of nanoparticle. Now a days, plant waste such as peels, seed, hulls bagasse and stem have been used in synthesis of nanoparticle for sustainable production. For some type of vegetable, certain parts are not consumed by consumer such as stem and leaves of cauliflower, broccoli and pumpkin. Vegetable and fruit waste is responsible for green house gas emission. 44% of global food waste comes from vegetable and fruit by products [20]. The plant waste contains valuable phytochemicals which plays vital role in nanoparticle synthesis [21].
Chemically prepared Fe3O4/OA magnetic nanoparticle has superhydrophobicity, superparamagnetism, thermal stability and superlipophilicity [22]. Iron oxide nanoparticles have also developed using reverse co-precipitation method because of its simple nature and high yield value [23] Rapid inducing heating method involved in production of iron nanoparticles. The synthesized iron oxide nanoparticle size ranges from 3 to 11 nm in diameter [24]. Tridax procumbens leaf extracts contains carbohydrates, proteins and lipids components which acts as reducing and capping agent in nanoparticle synthesis [25].The medicinal plant tridax procumbens leaf extract mediated IONPs showed good antibacterial activity against E-Coli [26]. Gold and silver nanoparticles were synthesized using aqueous fruit extract of chaenomeles sinensis and the developed nanoparticles were characterized for biomedical application [27]. α-Fe2O3 nanoparticles were chemically synthesized and modified with leaf extract of Ocimum Sanctum to attain enhanced antimicrobial activity [28].
High antibacterial activity has obtained by biologically synthesized iron oxide nanoparticle (Plectranthus amboinicus leaf extracts) compared to the chemically synthesized nanoparticle [29]. There are several reports for green synthesis of iron oxide nanoparticle such as Graptophyllum pictum [30], Solanum trilobatum, Ziziphora tenuior, Persia Americana, Grape proanthocyanidin, peel extract of plantain Abutilon indicum, Azadirachta indica, Camellia sinensis [31], Bauhinia tomentosa leaves [32] and Carica papaya. The green synthesized iron oxide nanoparticles using leaf extracts of carica papaya were used in photo catalytic degradation of remazol yellow RR dye [33]. Tea extract is most commonly used plant source for iron based nanoparticles [34]. Green route iron oxide nanoparticles have been used as catalyst in degradation of methylene blue and methylene orange dyes [35]. The leaf extract of Zanthoxylum armatum mediated iron oxide nanoparticle was used in efficient absorption of methylene blue [36]. Flower petal extract of Hibiscus Rosa-sinensis was used to synthesis IONPs for fortifying wheat biscuits [37]. MyrtuscommunisL. Leaves extract was used in nanoparticle preparation because of the presence of phytochemicals such as flavonoids, phenolic compounds, terpenoids etc., [38]. Chlorella K01 extract was taken for the synthesis process to obtain iron oxide nanoparticle for potential enhancement of plant growth stimulating and antifungal activity [39]. Iron oxide nanoparticles have been synthesized by modified polyol method [40]. In this work, iron oxide nanoparticles were synthesized through chemical and green method. The synthesis technique and characteristics features of the prepared nanoparticles were studied, analyzed and characterized. This study also compares the advantage and properties of green synthesized nanoparticle over chemically synthesized nanomaterials.