Nanotechnology was defined as the manipulation of matter via a number of elements and/or real processes to produce components along with specific properties, which can be used in certain application . A new nanoparticle could be defined as a new tiny particle which includes a minimum of one sizing below 100 nanometers in proportions . Unlike bulk components, they have had exclusive optical, thermal, electro-mechanical, element, as well as real properties  , that’s why, many people uncover a number of applications in the actual areas of medicine, chemistry, environment, energy, agriculture, information, and communication, heavy industry, and consumer goods .Chemical synthesis strategies for nanoparticle synthesis (e. g., element lowering, sol serum approach, and so on.) include things like the use of harmful compounds, creation of hazardous byproducts, and also contamination through precursor compounds . And so, the benefit of acquiring fresh, nontoxic, and also environment-friendly procedures intended for nanoparticle functionality. Green chemistry synthesis methods for nanoparticles have possessed positive aspects over chemical methods, for example safe, eco-friendly, harmful compounds will not be employed, and also cheap . Examples of green synthesis were as follows, the active biological component such as enzyme itself have worked as a reducing and also capping agent, small nanoparticles could be generated even in the course of large-scale production , The Plant extracts also have reduced the metal ions in a shorter time, it was widely used due to the presence of reducing and stabilizing agent at its extract (10). An incredibly wide range of natural resources such as germs (bacteria, thrush, fungi, algae, and also viruses) and crops could be utilized intended for nanoparticle functionality . Iron oxide nanoparticles (FeNPs) with different polymorph structures were actually extensively studied due to their extensive app throughout contemporary science and technological innovation (R. Zboril et al. 2002). The most common iron oxide polymorphs were usually α-Fe2O3, γ-Fe2O3, Fe3O4 and FeO. The α-Fe2O3 type has provided purposes throughout catalysts, high-density permanent magnetic storage media, pigments, anticorrosive agents, water splitting, water purification, solar energy conversion and gas sensors (E.J. Shin et al. 2005; R. Prucek et al. 2009; F. Rettig and R. Moos, 2010; I. Cesar et al. 2006. ) The γ-Fe2O3 and Fe3O4 nanoparticles were widely-used throughout permanent magnetic resonance image resolution (MRI) form a contrast agencies, ferrofluids, targeting drug delivery, anticancer therapies, hyperthermia cell labelling and separation. Because of the biocompatibility and non-toxicity. (D. Amara et al. 2012; L. L. Breen et al. 2001; Ymca. Deng et al. 08; Farreneheit. Caruso et al. 1999).
2. Various types of green synthesis of nanoparticles
2.1. From plant extract
Many researchers discovered constituents of various herbs, spices and plants that act as a powerful antioxidant compounds such as amino acids, polyphenols, nitrogenous bases and reducing sugars .These compounds act as capping [16,18] and reducing agents for the synthesis of nanoparticles. Because of plant diversity, we can control the morphology and the size of the wanted nanoparticle by changing the source of the extract. (Malik et al. 2014). The plant leaf extract used for NPs synthesis can be scaled up and applied for larger scale production in addition of its economic advantages . The metal and metal oxide NPs produced from a plant extract are usually stable even after a month no visible changes were remarked.  .A research studied, the aqueous extracts of leaves, stem and flower of Euphorbia milli, Datura innoxia, Calotropis procera , Tinospora cordifolia , Tridax procumbens and leaves of Cymbopogon citratus to evaluate their potential in the synthesis FeNPs . And their methods of extraction were as follows , 20gm of leaves, 10 g of stem and 2 g flower were washed with running and then with distilled water to remove the dust particles . They were dried by the use of blotting paper, cut into fine pieces by the use of a sterilized blade and with pestle they were crushed in a mortar. After 5-10 min of boiling them with 100 ml distilled water at 800C then cooled and filtered by Whatman filter paper no.1, then the extract was ready. At a temperature of about 50-60 C a mixture of 5 ml 0,001 M ferric chloride and 5ml of the plant extract Pattanayak M and Nayak PL. a change in color occurs by a final appearance of dark blue indicates the formation of Fe NPs. Shah S.
2.2. Microorganism-based methods for NPs synthesis
These methods are based on microorganisms like bacteria [10–22], algae [26–28] and fungi [23–25], to produce nanoparticles. Metallic nanoparticles are produced by adding metallic ions to the medium of culture of these microorganisms in controlled conditions. Prokaryotic bacteria have had an easy way of manipulation that’s why it was the most investigated microorganisms among all of the mentioned ones for the synthesis of metallic nanoparticles .
3. Synthesis of FeNps from plant extract
3.1. Commonly Used Plant Species (Tea extract)
First, in this method (Haung L et al. 2014.). A concentration of 60 g of Oolong tea extract per 1L of water was heated at 80 degrees Celsius for 1hour and a vacuum-filtered, then 0.1 mol/L of FeSO4 added to the extract at a ratio of 1:2 in volume. SEM (Scanning Electron Microscopy) image shows that the synthesized FeNPs has a spherical shape with a range of diameters from 40 to 50 nm. XRD (X-ray Diffraction) is another method showed that FeNPs was crystalline in nature. FeNPs could be used in the degradation of Malachite Green (MG), in aqueous solution where 12.3% of MG observed to be removed by effect of capping agents found in tea extract which are polyphenols and caffeine, which act also as reducing agents, where its removal efficiency using FeNPs observed to be 61.9% at 10 min and reached equilibrium at 75.5% within 60 min with a rate of0.045/ min. Degradation of MG caused due to cleavage of ─C═C─ and ═C═N─ bonds. The same method of extraction and synthesis was used with green tea[14,15]. And the same degradation and characterization results agreed with the green tea iron nanoparticles GT-FeNPs with a study of the effect of various parameters affecting this degradation as the solution temperature, FeNPs dosage, initial PH and the effect of H2O2 dosage . By the mention of dyes a study on the degradation of cationic and anionic dyes were established based on GT-FeNPs also. Iron nanoparticles were synthesized by extracts of green tea leaves (GT-Fe NPs). The extract was prepared by boiling 60.0 g/L green tea (Alwald Brand) and settling for 1h, then filtering by vacuum filtration method. Independently, an addition of 19.9 g of solid FeCl2•4H2O (Aldrich 22029-9) in 1.0 L of deionized water occur to form a 0.10 M FeCl2•4H2O solution. Following this a 2:3 volume ratio solution was formed by adding 0.10 M FeCl2•4H2O solution to 60.0 g/L green tea. Subsequently, the pH reached 6.0 by adding 1.0 M NaOH solution and the formation of intense black precipitate indicates the presence of ready GT-Fe NPs. The nanoparticles were separated by water evaporation from iron solution on a hot plate, then by letting it dry in a fume hood overnight. The characterization of the material using TEM (Transmission Electron Microscopy), SEM, XRD, and FTIR (Fourier Transform Infrared Spectroscopy) techniques showed that it contains mainly iron oxohydroxide and iron oxide. Then nanoparticles were used for decolorization of aqueous solutions having methyl orange (MO) dyes and methylene blue (MB) as a Fenton-like catalyst. The applicable experiments searched the effect of concentration for both MB and MO and the removal kinetics. GT-Fe NPs improved high capabilities of removal for both of MB and MO, in terms of the kinetics and the extent of removal. GT- Fe NPs showed faster kinetics and higher dye removal percentages when used as a Fenton-like catalyst comparing with sodium borohydride Fe NPs . As an application for arsenic removal tea waste was used, tea residue was sun dried after washing with water. 30g of dry tea residue was added to a solution of 150 ml distilled water and 15g of FeCl3.6H2O dissolved in it stirred for 4 h and left overnight. By filtration, FeCl3.6H2O treated tea residue was obtained and dried in an oven. Then in a muffle furnace, it was heated for 6 h at 450 degree Celsius and washed and dried. The resultant product was cuboid/pyramid shaped crystal structure of Fe3O4 (magnetite) with a size range from 5 to 25 nm that tend to cluster because they are magnetic in nature. This nanoparticles performed an excellent removal behavior for As(III) and As (V) arsenic ions in water. Magnetic iron nano oxide novel from tea (MINON-tea) has proved an efficient, high absorbent by making a comparison of adsorption capacity for arsenic removal. As it uses tea waste this is the most economical method . Finally, there was a study of biocompatibility of tea polyphenols based nanoparticles (Mallikarjuna et al., 2009). The Synthesis of Nanoscale Zero Valent Iron particles (NZVI) using tea polyphenols. Where the Caffeine/polyphenols were acting as reducing and capping agents as previously mentioned. Tow grams of tea powder (Red label from Tata, India Ltd. 99%) were extracted in 100 ml hot water and then used to carry out the reaction with 0.1 N Fe (NOɜ)ɜ. The different proportion of Fe (NOɜ)ɜ and tea extract were prepared at room temperature. The reaction is accompanied by a change in color from yellow to dark brown this indicates the synthesis of nanoparticles. TEM images show different structures of nanoparticles spherical, platelets and nanorods. This is due to the role of the concentration of tea extract as a key of size and the final structure of the iron nanoparticles. The increase in concentration of caffeine/polyphenol in the reaction mixture decreases the particle size. Biocompatibility of NZVIis examined using the human keratinocyte cell (HaCaT) line as a representative skin exposure model for time periods of 24 and 48 h. The appraisal of mitochondrial function (MTS) and membrane integrity (LDH) in human keratinocytes showed that these NZVI were nontoxic in the human keratinocytes exposed and induced a prolific response in the cellular function compared with samples synthesized using a sodium borohydride as reducing agent.
Tea extract is the most common method in the synthesis of FeNPs, there are other application of tea extract mentioned with other plant extracts mentioned below such as curcuma”مرجع الكركم “and eucalyptus”مرجع الايوكاليبتاس مع الشاي”.
3.2. Synthesis FeNPs from Other Plant Species
The synthesis of FeNPs from different plant species is studied and the results showed different size and morphology of FeNps which could be used in different application as follows.
First, iron nanoparticle as a dye removal. A successfully synthesized hematite (-Fe2O3) Nanoparticles was synthesized from curcuma and tea leaves (Alagiri et al., 2014). For synthesis from tea leaves,10 ml of the tea extract was added to the iron nitrate solution prepared by dissolving 1 mM of Fe(NO3)3•9H2O in 100 ml of distilled water with magnetic stirring around 6 h then two solution mixture was stirred by magnetic stirring at 50°C for 24 h. In case of synthesis by curcuma, 0.1 g of curcuma was added to 20 ml of distilled water with continued stirring for 6 h then 40 ml of Fe(NO3)3 • 9H2O (1 mM) was added with vigorous stirring at 50° C for 24 h. The two products were centrifuged at 15,000 rpm for 20 min and washed, then dried in a vacuum at 70°C. XRD results showed that α-Fe2O3 nanoparticles are well crystallinity with crystallite size 4 and 5 nm for α-Fe2O3 from curcuma and tea extract, respectively. SEM result showed that samples possess spherical-like shape. The photocatalytic activity of α-Fe2O3 nanoparticles was used to measure the photocatalytic degradation of methyl orange (MO) dye in distilled water under the illumination of visible light which is measured every 30 min irradiation time. The color of the MO solution turns into a colorless within 120 min of illumination time and the concentrations of MO solution changes as a function of illumination time.
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