Effects of Different Biosynthesis Methods on the Structural and Optical Properties of Iron Oxide Nanoparticles and Photocatalytic Application

INTRODUCTION 
New nanomaterial developments in the physical, chemical, and biological sciences have gained a lot of interest because of their performance in the production of electronics such as microprocessors, lithium-ion batteries, transistors, emitting diodes, and sensors. In addition to cancer treatments, antimicrobial and antibacterial drugs are derived from them. Among the many vital applications that rely on their use are pollution control catalysts and gas detection systems. When it comes to polluted drinking water, nanomaterials will be able to remove heavy metals as well as organic and inorganic substances [1-6]. Recently, researchers have explored the nanometer-scale structures of metallic oxides in an effort to create ways to monitor those materials. [7]. Just a few examples of metallic oxides include titanium dioxide, zinc oxide, bismuth oxide, copper oxide, and iron oxide (Fe2O3)[2, 8]. Iron oxides are widespread natural substances found in both the earth’s crust (rocks, bedrock, and water) and living creatures (animals and plants)[9]. Stable Fe2O3 NPs are widespread in nature, even at room temperature and pressure. They have a low magnetic field strength [10] and in the majority of cases, do not respond to hand magnets [11]. “Green synthesis” is a new area of nanotechnology. Some of the species used in this process include plants, algae, and microbes [12-16]. Iron oxide nanoparticles (IONPs) and other metal oxide nanoparticles can be manufactured in a variety of ways to produce efficient and ecologically friendly metal NPs. Plants can be used in a number of green synthesis techniques for NPs to decrease or remove toxic compounds  [10]. NPs of iron oxide (Fe2O3) have good environmental and medical uses due to their narrow band gap, chemical stability, and magnetic characteristics [11-14]. Long-term stability is claimed for the ecologically beneficial Fe NP green synthesis. Antimicrobial and cytotoxic characteristics as well as photocatalytic activity in the breakdown of MB dyes, have been demonstrated by Fe NPs. [15]. Shahana B., etal [16] An extract of Cynometra ramiflora fruit is used in the production of IONPs (chemical way). The presence of a dark solution proved the synthesis of IONPs. To show that MB dye had been irradiated for 150 minutes, the absorption peak at 663 nm (a signature of the dye) gradually decreased. Recently, Chauhan etal[17] Lawsonia inermis Conocarpus extract was used to make chemically synthesized iron oxide NPs.. In (2019), Sammy I., etal [17],Preparation IONPs as a catalyst to degrade MB degradation by using Galinsoga parviflora, Conyza bonariensis, and Bidens pilosa extracts using (chemical way). Sol-gel is an example of a bottom-up approach for making NPs. Only a handful of investigations employing the Sol-gel have explored the idea of MB dye breakdown in typical light conditions. The chemical and sol-gel methods of IONP manufacture will be compared in this investigation. Toxic-free, environmentally friendly, and cost-effectively produced NPs with superior crystalline structures can be made with Sol-gel. These NPs have higher purity and are safer for the environment. A major advantage of green synthesis is that it can be easily scaled up for large-scale synthesis and does not require as much energy or hazardous substances as chemical or physical techniques .Green synthesis allows for greater control over crystal growth. Green nanoparticles produced (green NPs) in a factory are cheap and useful [10, 18, 19]. Conocarpus extract and iron (II+III) chloride (FeCl2+FeCl3) were used to make IONPs using simple chemical and sol-gel methods. Drop-casting was used to create these films, which were then characterized in terms of their structural and optical properties. It was decided to employ scanning electron microscopy and high-resolution X-ray diffraction to determine the crystallinity and morphology of the samples produced. UV-VIS spectrophotometers and photoluminescence (PL) measurements were used to investigate these characteristics. Our researchers also examined the disintegration of MB dye under typical lighting conditions.

MATERIALS AND METHODS
FeCl2+FeCl3 (iron (II+III) chloride) and fresh Conocarpus from Baghdad, Iraq, were procured from the local market in Iraq. Vitamins, amino acids, phenolic acid, glycosides, and minerals are all present in this plant. All of the experimental glassware was made with Borosil. Using water, the glass and substrates were sanitized and air-dried at room temperature to remove any contaminants or flaws.

Preparation of the Conocarpus extract
To remove any impurities, the Conocarpus specimens used in this investigation were cleaned, diced, and air dried for 8–10 days. Dried herbs were ground into a fine powder using an industrial stainless steel blender. The extract was made by dissolving 10g of Conocarpus powder in 100 mL of water. The mixture was heated for two hours at 80 °C using a magnetic stirrer. The final product was ready for use after cooling to room temperature and filtering through Whatman paper.[20]. Fig.  1 depicts the process through which Conocarpus is made into an extract.

Preparation of iron oxide NPs by using Conocarpus extract (By simple chemical)
Conocarpus extract (100 ml) was added to (0.1 M + 0.2 M, 100 mL) of FeCl2+ FeCl3 to produce iron oxide NPs. Then, a magnetic stirrer was used to agitate the solution for 30 minutes at 80 °C. It was immediately apparent that β-Fe2O3 NPs had been formed during the manufacture of this substance by the rapid shift in hue from translucent yellow to black. It was then cooled to room temperature. It took two hours at 200 °C to dry out 25 mL of this solution in a ceramic dish in order to produce a fine powder from the solution. IONP solutions were eventually stored in sealed serum tubes for further study. [21]. Fig.  2 demonstrates the usage of iron (II+III) chloride in the preparation of IONPs from Conocarpus extract.

Preparation of IONPs from Conocarpus extract (By sol_gel)
It was done using the sol-gel method, with the addition of 100 mL of Conocarpus extract to FeCl2+FeCl3 (0.1 M+0.2 M,100mL) and constant stirring at 40 °C for one hour and 60 °C for half an hour. Centrifuged at 4000 rpm for 20 minutes, the solution became turbid (cloudy) due to dispersed particles. After the supernatant was collected and dried at 200°C for two hours, the precipitates were filtered.  Conocarpus extract with FeCl2 + FeCl3 was used to create IONPs, as shown in Fig.  3  [22].

Characterization of β-Fe2O3 NPs Prepared from Conocarpus extract
Analysts used data from the joint committee on powder diffraction standards (JCPDS) card to identify their specimen. Shimadzu’s step-by-step examination model (XRD-6000) was used to take XRD measurements across a temperature range of 20°–70°. (Jobin-Yvon HR800UV) employed a double-beam spectrophotometer to examine the power spectrum.

Photocatalytic activity of iron oxide NPs by using Conocarpus extract under normal light
A known amount of MB dye solution (1 mg, 3×10-5 M) was combined with 100 mL of deionized water to make a final MB dye solution concentration of 10 mg/L to test the photocatalytic activity of the IONPs. When 3 mg of iron oxide NP powder was added for the first time, the suspension was swirled for 5 minutes in total darkness using a magnetic stirring device to maintain equilibrium. After 5 minutes, the combination was subjected to a direct normal (115 mW/mm2 intensity, as measured by SM206 solar power meter). It is 0.15 meters from the source of light. In the end, 5 mL of the suspension was centrifuged for 20 minutes at 4000 rpm, and the absorbance was measured using a Shimadzu UV-1800 spectrophotometer. The greatest absorption rate may be observed at a wavelength of 664 nm.  Dye molecular interactions with adsorbed substances are principally influenced by surface modifications on both the dye molecular and the adsorbent material  [23].the experiment was repeated at 5 mg every 10 minutes.
The degradation efficiency of MB dye was calculated using the following equation :
According to this method, the MB dye degradation percentage was determined by Eq. 

Where: Cini = the original (MB) dye concentration, Cfin = the dye concentration at the end.
The kinetic constant rate (Kph) of the MB dye degradation was calculated using Eq. (2):

Where: Cini = the original (MB) dye concentration, Cfin= the dye concentration at the end,
 Kph= constant rate of MB dye, t = radiation time. 
The MB dye degradation efficiency can be calculated using the following equation:

Where: Cini = the original (MB) dye concentration, Cfin = the dye concentration at the end.

RESULTS AND DISCUSSION
Synthesis and characterization of iron oxide NPs by using Conocarpus extract
Reaction conditions in the modern plant include a mixture of Conocarpus extract and iron extract. Nanoparticle generation, field, and stability can be controlled by the Conocarpus extract’s parameters. The phytochemicals in Conocarpus extract can lower the quantity of iron that has been used up in a short period of time. Conocarpus extract also has a key role in lowering and stabilizing a number of parameters in the simple manufacture of iron oxide NPs.
The XRD analysis of iron oxide NPs (β-Fe2O3) prepared by using Conocarpus extract with iron
It is possible to determine the material, structure, and orientation of materials using XRD analysis in this research. FeCl2+FeCl3 were dissolved in Conocarpus extract for 2 hours at 200 ◦C. The IONPs were made by utilizing a simple chemical and Sol-gel process, and the results were impressive. In a simple chemical method, the peaks of the crystalline (β-Fe2 O3) phase (wustite, space group Fm-3m, JCPDS no. (00-056-1302)) is (102) corresponding to (105),(113),(201),(207),(2010),(1115),(2016),(0217),(0024),and(226) millers indices   and   in  sol-gel method ( JCPDS no. (00-056-1302)) is (006) corresponding to (102),(105),(0012),(1011),(116),(119)and(1115) millers indices , as shown in Fig.  4[24, 25]. The results of IONPs (β - Fe2O3) phases, and crystallite size appear in table (1). The crystallite size (D) was determined. applied the following: Scherrer’s formula  [26, 27].

Where: λ is wavelength (0.15418) nm (CuKα),  k is shape factor (0.9), β is full width at half maximum (FWHM) and θ is diffraction angle[27]. 
The FE-SEM images of IONPs (β-Fe2O3) prepared from Conocarpus extract by FeCl2+FeCl3 extract
An FE-SEM imaging technique was employed at a temperature of 200 ◦C to examine the distribution of size and surface morphology of IONPs produced from Conocarpus extract and iron (II+III) chloride. Fig.  5 (A-B-C-D) shows the morphology of β-Fe2O3 NPs (wustite) in the chemical process, where the grain size ranges from 4.4 nm  to 205.7 nm, average grain size 47.2 nm and the morphology is (nanoparticles-like structure) [28].  And For β-Fe2O3 (wustite) NPs, the grain size ranges from 9.1 nm to 308 nm, average grain size 53 nm in the sol-gel process, and the morphology is a (Nano-assemblies due to high thermal energy) structure, as shown in Fig.  6. (A-B-C-D)  [29]. The difference in the amount of biomaterial between the extracts and the difference in the reaction mechanism of the two methods led to the appearance of different images in the FESEM examination of iron oxide NPs and the particle size range.

UV–Vis Spectrophotometer of Iron oxide NPs by sol-gel and simple chemical
As shown in Fig. 7, (A-B-C), conocarpus extract mixed with FeCl2 and FeCl3 salt is used to determine the optical transmittance spectra of Fe2O3 nanoparticles. [30] . Fig.  8 (A-B-C) appears the energy band gap for β-Fe2O3 NPs prepared by a sol-gel and simple chemical way by Conocarpus extract, estimated by plotting the square of (αhυ)2 vs the photon energy (hυ) with sol-gel and simple chemical methods. Using a straight line extrapolation to  (αhυ)2 , the energy band gap can be calculated. Because of the small size of NPs that reduce the potential attraction between the conduction electrons and metal ions of the particle that leads to the band energy gap increases for the smaller particles, or may be the concentration increase leads to the division of the level into secondary levels that called energy gap [31, 32]. According to the arrangement and distribution of atoms in the crystal lattice of a powder crystal, the energy band gap can vary in a variety of different ways. The values of the optical band gap for β-Fe2O3 NPs ranged from 1.94 to 3.16 eV in the sol-gel method Fig. 8 (A-C)[31]. The optical band gaps of β-Fe2O3 NPs measured by the simple chemical technique ranged from 1.94 to 3.3 eV. Fig. 8 (B-C)[32]. The energy band gap can be calculated by using the equation below [9, 33].

Where :A is constant, hυ is the energy of light, and, α is the absorption coefficient,  n: is a constant depending on the nature of the electron transition [33]. In comparing the iron oxide NPs prepared with a sol-gel and a simple chemical method from Conocarpus extracted by FeCl2 +FeCl3 salt,the energy band gap showed a distinct blue shift, from 1.94 eV to 3.16 and 3.3eV respectively for β-Fe2O3 NPs.  The decrease in the crystal size and the particle size causes an increase in the optical band gap according to the principle of quantum confinement.

The PL spectrum of iron oxideNPs (β-Fe2O3) prepared by using Conocarpus extract with FeCl2+FeCl3 extract
At the near-band edge of the PL spectrum, iron oxide NPs synthesized by simple chemical and sol-gel procedures from Conocarpus extract with FeCl2+FeCl3 at (200 ◦C) can be seen. As shown in Fig.  9, the excitation band of β-Fe2O3 NPs at 200 ◦C has an excitation wavelength of 325 nm (wustite, the near wavelength (455.56 nm), which is the near-band edge of (2.72) eV. Fig.  10 shows that the near band edge of β-Fe2O3 NPs (wustite, the near wavelength (450.83 nm) at 200 ◦C in the sol-gel process is (2.75) eV with the exaction band being 325 nm.
The difference in the type of extract, the amount of biomaterial it contains, and the method of preparing the nanomaterial had an effect on the value of the near band edge.

Photocatalytic activity of iron oxide NPs from Conocarpus extract under normal light
The photocatalytic reaction follows the following basic mechanism: when β-Fe2O3 NPs are exposed to normal light at room temperature, electron-hole pairs are generated, as shown in Eq.1, electrons can be excited from the valance band to the conduction band, and holes are formed in the valance band. These holes and electrons interact with H2O and O2 in the extract solution, respectively, as shown in Eq. 2 and Eq. 3 to yield the OH and OOH hydroxyl radicals, as shown in Eq. 4. These hydroxyl radicals, which are highly oxidizing in nature, can completely oxidize the dyes by abstracting electrons from dye molecules and by breaking the large organic materials into less harmful small organic materials, as shown in Eq. 5 [9].

IONPs + hν → e⁻ + h⁺                                                (1)
 
e⁻ + O₂ → · O₂⁻                                                           (2)

h⁺ + H₂O/OH⁻ → · OH                                                (3)

O^2-+ H₂O → · OOH + OH⁻                                         (4)

OH + MB → CO₂ + H₂O                                             (5)

From the above Photocatalytic activity patterns, it is noticed that the maximum Photocatalytic activity by IONPs with 5 mg is corresponding to the sol-gel method with using Conocarpus extracts because of a high surface area and aspect ratio.

CONCLUSION 
Chemical and sol-gel methods were used to synthesize IONPs (β-Fe2O3) from the Conocarpus extract and FeCl2+FeCl3 without the need for any catalytic chemical material. It was found that the crystalline size of β-Fe2O3 NPs with a chemical technique was approximately 10.910730 nm, whereas the crystalline size of NPs with the Sol-gel method was about 18.834940 nm at 200 ◦C using Conocarpus extract. For β-Fe2O3 NPs (wustite), the average grain size measured by FESEM at 200 ◦C using Conocarpus extract ranged from 4.4 nm  to 205.7 nm and average grain size 47.2 nm in chemical way and from 9.1 nm to 308 nm and average grain size 53 nm in sol-gel way. Using Conocarpus as a PL spectrum, the optical near band edge value was shifted to the blue by (2.72) eV in chemical and (2.75) eV in sol-gel. Iron oxide nanoparticles (NPs) were found to have photocatalytic activity in environmental treatments. According to the results, the synthesized material is of high quality β-Fe2O3 NPs, with greater degradation efficiency when made using the sol-gel technique, reaching 77.2% at 75 minutes for 3 mg and 88.6% at 150 minutes for 5 mg, with a higher level of photocatalytic efficacy than the β-Fe2O3 with a simple chemical method, whereas degradation efficiency was 43.1% at 75 minutes for 3 mg and 51.7 percent at 150 minutes for 5 mg.

CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.