Due to the unique properties of nanomaterials compared to the bulk counterparts, nanotechnology has been of great interest. In recent years, CuO nanoparticles have attracted much attention in catalysis, all photovoltaic, sensor and environmental remediation due to their marvelous waturements of electrical, optical and catalytic [1,2]. CuO nanoparticles are also known for their antimicrobial properties [3,4] and hence would have applications in medical and environmental realm. Chemical methods traditionally used for the synthesis of CuO nanoparticles are usually based on toxic reagents that present environmental and health hazards. To overcome these issues, green synthesis by use of plant extracts are taking advantage of a sustainable and ecofriendly pathway [5,6]. Several researches have been aimed to develop of metal nanoparticles by plants. 

"Different parts of the plant like the fruits, seeds, leaves, stems, roots, flowers and bark can be used to extract plant extracts" [7]. The potential for exploration in the domain of plant-synthesized nanoparticle synthesis is substantial.  This method may be used to many plant components, including leaves, stems, roots, flowers and fruits.  As seen in Figure 1, a plant extract functions as both a reducing and a capping (stabilizing) agent in the production of nanoparticles, whereby a metallic precursor is combined with the plant extract [8].

Leaves of Urtica dioica (nettles) contain flavonoids, phenolic acids and alkaloids that can be used as natural reducing agents for nanoparticle synthesis [9,10]. Urtica dioica has largely unexplored potential in metal nanoparticle synthesis because of its anti-inflammatory and antioxidant qualities, which have been widely used in traditional medicine.; Urtica dioica Leaf extract was utilized for the green production of CuO nanoparticles, which were evaluated for their structural and optical characteristics in this study.

Fresh Urtica dioica leaves were collected, properly washed and dried and then used as reducing and stabilizing  agents,  while  copper (II) nitrate  trihydrate (Cu (NO₃) ₂·3H₂O) was used as a source of copper ions.

The fresh leaves of Urtica dioica (commonly known as stinging nettle, were collected from the banks of the Tigris River. The leaves were  rinsed  thoroughly  with  deionized

Figure 1: Reduction of ions mediated by plant extracts during nanoparticle formation [8].

Figure 2: Schematic illustration of the green manufacturing method for copper oxide (CuO) nanoparticles utilizing Urtica dioica leaf extract.

water and left to dry out completely in air. The leaves were once dried and then ground into a fine powder. I mixed  it  with  100 milliliters  of  distilled  water  and  put 10 grams of this powder into it. The mixture was then heated to 80°C and kept there for 30 min. Thus, a clear plant extract was obtained after heating and filtered using Whatman filter paper. In the nanoparticle synthesis process, this extract was also used further as a reducing agent to reduce metal ions and a stabilising agent to prevent nanoparticle aggregation.

Synthesis of Copper Oxide Nanoparticles (CuO NPs)

A 10 mM copper (II) nitrate trihydrate precursor was dissolved in 50 mL of deionized water while being magnetically stirred at 60°C to create a 50 mL aqueous solution.  Subsequently, 10 mL of the Urtica dioica extract was incrementally added to the precursor solution while maintaining continuous agitation. To proper nucleation and stability of the nanoparticles the pH was adjusted to 10 with 1 M NaOH. In order to prevent photodegradation the reaction was carried out with the assumption that it is dark and maintained at 60°C for 6 hours to allow complete reduction and formation of CuO nanoparticle. The schematic representation of the process of green synthesis of copper oxide (CuO) nanoparticles using leaf extract of Urtica dioica is represented in Figure 2. It has been confirmed that CuO NPs have formed as there was a distinct color change from blue to dark brown. Overall, the reaction can be simplified as [11]:

Cu²⁺+Phytochemicals (from Urtica dioica) + OH⁻→CuO (s)+H₂​O

To separate the nanoparticles, the solution was centrifuged for 30 minutes at 15,000 rpm followed by rinsing in deionized water twice to remove any unaccounted-for plant metabolites and any leftover residues. The precipitate was purified and dried at 50°C.

Structural Analysis

Figure 3 shows the X-ray diffraction pattern of CuO NSs, with the indication of the crystalline particles by the peak corresponding to standard Brag reflection (111) at an angle of 38.2. The Nano-Sized spheres were CuO and had a monoclinic crystal structure. The fact that the peak broadens at this angle is evidence of formation of monocrystalline copper oxide.

XRD examination validated the synthesis of CuO nanoparticles, with 2θ peak values aligning with conventional references CuO crystalline lines. Scherrer’s equation [12] was used to estimate the crystallite size:

Figure 3: The XRD pattern of CuO NSs

Figure 4: SEM images revealed that the synthesized CuO NPs

Figure 5: UV-VIS absorption spectrum of CuO NPs

Figure 6: (α h υ)² versus hv of CuO NPs

In such a specific equation, G is crystallite size parameter and K stands for a shape factor generally 0.9. It is indicated by λ or the x-ray wavelength and by β either the full width at half max of the diffracton peak or it also refers to the difracton angle θ. According to this equation, size of copper oxide synthesized nanoparticles (CuO NPs) was found to be around 40.33 nm. On top of that, using the equations indicated below, the microstrain (δ) and the dislocation density (η) of the nanoparticles can be inferred to gain more information about the structural characteristics of the synthesized material [13,14]:

(2)

(3)

Morphological Analysis

As shown in Figure 4, the SEM image of the CuO NPs synthesized through the green synthesis method utilizing Urtica dioica extracts and coated on a glass substrate reveals, that the resulting CuO NPs have a nonuniform distribution of different sizes that vary between approximately 10 nm to 50 nm. This is mostly spherical or quasi-spherical particles and some irregular shapes; these are probably due to the effect of biological reducing agents on the formation of particles. Parel   clustering   is   observed    in    some    areas    which indicate partial clustering. The morphology and size distribution may influence optical properties of the material.
 

Figure 5: UV-VIS absorption spectrum of CuO NPs

Figure 6: (α h υ)² versus hv of CuO NPs

Optical Analysis 

UV-Vis spectrophotometry was used to confirm optical characteristics of CuO NPS with an absorption peak around 300 nm.

In order to study a material's optical range gap in terms of its electrical nature, it is easier to study UV-VIS absorption spectroscopy. In Figure 5, the absorption spectra of CuO NPs are given. The process by which the near-ultraviolet absorption occurs is caused by related electron activities of the sample as indicated by the absorption edge at 316 nm. The strong absorption of the material in a UV range of 316 nm was concluded to make the material effective.

A mathematical model based on Tauc’s relation is used to plot the square of the energy band gap of CuO NPs as a function of (h υ). Figure 6 shows the energy gap value that was found by extrapolating a straight line to (α h υ) ² = 0. Because of direct band to band transition, the CuO NP optical band gap is around 3.6eV. SEM support the increase in energy gap by the formation of nanoparticles.

This study concludes based on this ecofriendly successfully demonstrated CuO nanoparticles synthesis using Urtica dioica leaf extract. Extraordinary structural and optical properties of the synthesized nanoparticles make them suitable candidates for use in the field of catalysis, sensor, solar cells and biomedicine. Since we are using plant-based reducing agents, this gives a sustainable alternative to conventional synthesis methods.

Acknowledgment

The author thanks Wasit University College of Science - Iraq for giving permission to the Physics department’s laboratories’ facilities and equipment as a necessity to finish this study.

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