Characterization of Cr2O3 Nanoparticles Prepared Using Cauliflower Extract by Two Methods

Chromium oxide nanoparticles were synthesized using cauliflower extract by two methods: simple chemical method and the sol-gel method. These technologies are new, environmentally friendly and cheap. Cauliflower contains plant materials and biomolecules (chromium, phenols, alkalis, vitamins, amino acids, quinones, etc . (that convert chromium chloride hexahydrate (CrCl3.6H2O) into chromium nanoparticles. The plant extracts also act as diluents, stabilizers and anti-caking agents. X-ray diffraction (XRD) analysis showed that the size of the crystals decreased from (36.1 to 57.8) nm using the simple chemical method to (13.31 to 20.68) nm of Cr2O3 using sol-gel. The scanning electron microscopy (SEM) showed that Cr2O3 NPs of the simple chemical method were Nano layers with (130.3) nm, while the Cr2O3 NPs of the sol-gel method were spherical or semispherical in shape with a particle size of (14.89 to 39.08) nm. The results obtained have no matches in the reported literature.. Ultraviolet-visible (UV-Vis) showed that the band gap energy of Cr2O3 NPs of the simple chemical method was 2.5 eV, while it was 3.4 eV for Cr2O3 NPs of the sol gel method . Cr2O3 NPs of high purity , small particle size, and large energy gap were obtained from the sol-gel method This means that the NPs from the sol gel method were better than those of the simple chemical method. The study revealed that the Chromium oxide nanoparticles synthesized using cauliflower extracts could be used as antibacterial agent for human pathogenic bacteria


Introduction
The study of fine and ultrafine particles has received in-creasing interest due to the new properties that the material may show when the grain size is reduced [1]. During the past decades, considerable progress in the synthesis of nano-particles has been achieved. Nanomaterials, particularly transition-metal oxides play an important role in many areas of chemistry, physics and material science [2]. Nanotechnology is one of the most active areas of research in modern materials science; nanotechnology has become a form of the pioneering and exciting field in chemistry, physics, and biology. The study of nanoparticles has received increasing attention due to the material's novel qualities that may emerge as particle size is lowered .Nanotechnology can describe the fabrication and characterization of nanomaterials, (1-100) nanometers, for the development of science [2].Nanotechnology is an enormously powerful technology, which holds a huge promise for the design and development of many types of novel products with its potential medical applications on early disease detection, treatment, and prevention. Nanoparticles are shown new (improved) properties based on specific characteristics such as size, distribution, and morphology [3]. The nanoscale dimension is important because quantum mechanical properties of electronics, photons and atoms are shown at this scale. In addition, nanostructures allow controlling the correction of materials without changing the chemical state. In general, nanotechnology plays an important role in the specialized qualities of the most innovative scientific field. Nanotechnology. It is mainly involved in the manufacture of nuclear plants in various sizes, shapes, chemical compositions, chemical compositions [4,5]. The major benefits of NPs over larger particles are high surface-to-image ratio. In the last two decades, nanostructured materials have undergone extensive study due to their unique specialization and applications in the many fields [6]. Nanotechnologies involved in the fabrication of nano materials may be classified as top-down or bottom-up approaches. Top-down (physical methods) or bottom-up (chemical and biological methods) is a measure of the level of advancement of nanotechnology. The NPs which can be synthesized by both top-down (physical) and bottom-up (chemical methods and via a green pathway as in this research) [7]. In technological applications, conventional metal oxides are used in the manufacture of electronic circuits, motorcycles, fuel cells, and coatings to protect the surface from corrosion, and as a catalyst [8]. The development of nanomaterials has garnered great interest, especially in the physical, chemical and biological sciences for their performance in the manufacture of microelectronics, transistors, and light emitting diodes as well as in cancer treatment [9].

Materials
All the chemicals used were of highest purity available and were used as received without further purification or distillation: [CrCl 3 .6H 2 O] (99.5%, Sigma-Aldrich), sodium hydroxide (NaOH) (99%, Fluka), cauliflower extract; its source was from local market.

Preparation of Plant extracts
In a simple chemical method, small parts of the cauliflower plant were purified from impurities, and cut into small pieces and left in the sun for two days. After that it was grounded to fine powder with a solid metal electric mixer. The plant extracts were made from a mixture of 5 g of powder in 100 ml of deionized water. The solution was heated at 70 ° C for 30 min on a magnetic stirrer. The resulting aqueous solution was cooled at room temperature and purified during Whitman's filtration Figure 1 an explanation of the steps for converting a fresh plant into an extract. In the sol -gel method.

Preparation of chromium oxide NPs by the simple chemical method
Non-synthesized Cr 2 O 3 NPs (50 mL, 1 M) and chromium chloride hexahydrate (CrCl 3 .6H 2 O) were added to 100 mL of the prepared cauliflower extract.. This prepared solution was placed on a magnetic stirrer at 70 ° C for 30 min.After that, the solution was left to cool to room temperature. 25 mL of Cr 2 O 3 was placed in a ceramic oven at 200 ° C for two hours to obtain a nano-base. The Cr 2 O 3 NPs powder was stored in sealed labeling serum tubes. Figure 2 shows the stages to prepare NPs using cauliflower extracts.

Preparation of chromium oxide
NPs by the sol-gel method 5 grams of (Cauliflower) powder was used in 100 ml of distilled water and putted on the magnetic stirrer for two hours at 70 °C, 13 grams of chromium sulfate is taken with 50 ml of distilled water for 10 minutes on the magnetic stirrer and then filtered using filter paper and then after filtering, a centrifuge is used at 15,000 cycles for 10 minutes Then, CrCl 3 is added over the plant extract for half an hour on the magnetic stirrer, and then it is placed on to turn it into a gel After that, and place on the magnetic stirrer. Then several drops of sodium hydroxide were add to the solution until it attained pH = 7. The temperature was increased to 90°C and left to turn into liquid (Gel). Thus it was allowed to stay for one and the half hour after which the temperature was increased to (120°C) and left to become dry gel (Xerogel) , then lifted and left to cool down. The powder was collected and placed in a container of porcelain and inserted into the oven 25 ml of the solution is taken and placed in a ceramic eyelid and placed in an oven at (200)°C for two hours. After turning off the oven, the sample is left inside for 24 hours to obtain a Nano powder.

X-ray Diffraction (XRD) of chromium oxide NPs prepared by the simple chemical method.
XRD is an important technique that is commonly used to investigate the structural properties to ascertain the crystalline nature and phase identification of chromium oxide nanocrystalline films.From Figure 4, it is noticed that the 012 and 104 peaks are the preferred orientations of prepared (Cr 2 O 3 ) NPs using cauliflower plant. Table (

(1)
Where k is called shape factor (0.9), λ is the wavelength (0.15418) β is full width at half maximum (FWHM), and θ is a diffraction angle.

X-ray Diffraction XRD for chromium oxide NPs by the sol-gel method.
It is noticed from Figure 5     SEM image measurements were performed to determine the surface morphology of chromium oxide NPs using cauliflower extract prepared by the simple chemical method. Figure 6 (A-D) shows the shape and average size of Cr 2 O 3 NPs. It is seen as e (Nano layers).  Figure 7 (A-D) are the SEM images of the (Cr 2 O 3 ) NPs prepared by the sol-gel method using cauliflower extract. It shows that the nanoparticles are spherical or semispherical in shape with a particle size of (14.89 to 39.08) nm.

UV-Vis properties of chromium oxide NPs prepared by the simple chemical method
The samples were examined by UV-Vis spectroscopy to determine the absorbance of the Cr 2 O 3 NPs cauliflower extract. Figure 8 shows the optical transmittance spectra of (Cr 2 O 3 ) NPs prepared by the simple chemical method(as shown in Figure 8. The spectrum, at the spectral range of (200-900) nm, shows a low transmittance at 400 nm resulting in strong absorption of (Cr 2 O 3 ) in this region.
The energy gap of the (Cr 2 O 3 ) NPs was estimated by plotting (αhυ) 2 against the photon energy (hυ). The intercept of the extrapolation of the linear part of the graph with the hυ axis gives the energy gap value. The gap depends on the energy band, the crystal structure of the film and the arrangement and distribution of the atoms in the crystal lattice. The optical band gap value of (Cr 2 O 3 )NPs was 2.5 V as shown in Figure 9.   Figure 10 shows a high transmittance percentage above 400 nm indicating the strong absorbance of Cr 2 O 3 in this region. All films showed increase in transmittance at the wavelengths longer than 400 nm.
The optical band gap of chromium oxide NPs was calculated by plotting (αhν) 2 versus hυ and by extrapolating the straight line of the curve to the hυ = 0 as shown in Figure 11. It was found that the Cr 2 O 3 NPs have direct transition type and the bandgap has increased from 2.5 eV to 3.4 eV with the sol-gel method. Increase of the optical energy gap of chromium NPs with the sol-gel method can be ascribed to the formation of smaller chromium oxide NPs.   It was noted that chromium oxide NPs prepared by the simple chemical method were less pure and were not completely good, but when the result using the sol-gel method was excellent. An increase in purity, a decrease in the particles size and an increase in the energy gap were noted. . Table (3) shows the results of chromium oxide NPs from the two methods.

Antibacterial Activity of Cr 2 O 3 NPs
The antimicrobial activity of Cr2O3 NPs synthesize have been examined against bacterial cultures Gram-positive (Bacillus subtilis), Gram-negative (Escherichia coli), and against fungal cultures (Candida albicans) using agar well diffusion method [11].

Conclusion
This work succeeded in the biosynthesis of chromium oxide nanoparticles using cauliflower extract by the simple chemical and sol-gel methods. The cauliflower extract has succeeded in converting CrCl 3 .6H 2 O into chromium oxide nanoparticles. Also, the cauliflower extract acted as a reducing, stabilizing and anti-agglomeration agent. It was noted that the results of the sol-gel method are better than those of the simple chemical method. This was noticed by an increase in purity, a decrease in the size of particles and an increase in the energy gap. The prepared powders were characterized using XRD, SEM, and UV-Visible spectroscopy.
No similar results was found in the literature on chromium oxide nanoparticles prepared using cauliflower extract.The study also revealed that chromium oxide nanoparticles repared using cauliflowerextract could be an antibacterial agent for human pathogenic bacteria.