Experimental and Theoretical Studies of Green Synthesized Cu2O Nanoparticles Using Datura Metel L

In biomedical applications, Cu2O nanoparticles are of great interest. The bioengineered route is eco-friendly for the synthesis of nanoparticles. Therefore, in the present study, there is an attempt to synthesis Cu2O nanoparticles using Datura metel L. The synthesized nanoparticles were characterized by UV–Vis, XRD, and FT-IR. UV–Vis results suggest the presence of hyoscyamine, atropine in Datura metel L, and also, nanoparticles formation has been confirmed by the presence of absorption peak at 790 nm. The average crystallite size (19.56 nm) was obtained by XRD. FT-IR was also used to confirm the different functional groups. Fourier Power Spectrum was also employed to examine the synthesized nanomaterials spectrum data to emphasize the peak of the prominent frequencies. Density functional theory (DFT) was also utilized to assess the energy of the substance over time, which appears to indicate a stable molecule. Furthermore, calculated energies, thermodynamic properties (such as enthalpies, entropies, and Gibbs-free energies), modeled structures of complexes, crystals, and clusters, and predicted yields, rates, and regio- and stereospecificity of reactions were all in good agreement with experimental results. Overall, the results show that the successful production of Cu2O nanoparticles with Datura metel L. corresponds to theoretical research.


Introduction
Engineered nanoparticles and their technical implications are already generating breakthrough ideas in the industrial process by leveraging optical, electrical, magnetic and biological features [1][2][3][4][5]. Cu 2 O is an important promising candidate among the transition-metal oxides due to high abounded, nontoxic and cheap availability. Generally, it consists of + 1, + 2 oxidation states known as cuprous and cupric ions [6]. The nanoparticles of Cu 2 O is naturally P-type semiconductor material with a narrow bandgap of ̴ 1.2 and ̴ 2 eV, which could be favor of light absorption in several biomedical applications such as MRI-ultra sound dual imaging, microbial activity [7,8], and bandgap of 2.98 eV used as a photoelectrode for solar energy conversion [9]. The green path to the manufacture of copper oxide nanoparticles is a simple and environmentally benign technology [10]. Hence, green synthesis is the best adopted route for nanoparticles production when compared with the chemical method due to without requirement of any reducing and stabilizing agent. The plant metabolism like flavonoid, alkaloids, terpenoids, polyphenols, and proteins are a reservoir of plant tissue, it could be used as a reducing agent on various nanoparticles synthesis [11,12]. Datura metel L. is a Solanaceae family agriculture plant that is geographically spread over on gibbous world either as an origin or foreign plant in Asia, America, and Europe. The species of Datura metel L. have been used as classical Chinese medicine for the treatment of asthma, coughs and antitumor activities, etc. Particularly, the major constituent of this plant namely withanolides having plant steroids built on by ergostane skeleton in the side chain of δ-lactone and their predominant alkaloid content of hyoscyamine, atropine has given the medicinal properties on nanoparticles formulation [13]. Various experimental studies show that the size and morphology of Cu 2 O nanoparticles play an important role in the appearance of specific properties [14][15][16][17]. For example, nanocubic Cu 2 O particles can reduce CO 2 emissions in the gas phase through the possibility of performing heterogeneous photocatalytic hydrogenation [14]. Smaller cubic Cu 2 O nanoparticles exhibit the strongest gas-sensitive response [15]. It is known that the cabbage-like architecture of Cu 2 O makes it possible to form nanocomposites with various substances, in particular with graphene oxide [16]. The nanocomposites are used for photocatalysis to remove organic pollutants by exposure to sunlight [16,17]. It is also known that the use of organic substances, their combinations, and plants in the synthesis of nanoparticles makes it possible to create a structure of nanocomposites with a well-defined morphology [17]. In particular, the addition of glucose leads to an increase in the size of nanoparticles with a cabbage-like architecture [16,17]. By varying the choice of plant, the concentration of the extract for green synthesis of nanoparticles, it is possible to achieve the formation of nanoparticles of the required size and shape. For example, Ramesh et al. [18] obtained spherical and hemispherical Cu 2 O nanoparticles using the leaf extract of Arachis hypogea L. Abboud et al. [19] also synthesized spherical Cu 2 O nanoparticles using Bifurcaria bifurcate, a marine alga. Kerur et al. [20] received truncated octahedron, octahedral and spherical Cu 2 O nanoparticles, simply by varying the concentration of the Aloe vera leaf plant extracts. Thus, using new plants and varying the concentration of their extract, Cu 2 O nanoparticles with a specific structure and unique properties can be obtained. In this regard, it is necessary to study new ways of green synthesis of Cu 2 O nanoparticles.
DFT has been used for understanding and studying the stability of new compounds in previous documents [21,22]. Using a general approximation gradient (GGA) and the interpolation method [23], the electron exchange and correlation of geometry optimization, electronic structure, and optical properties were determined. The interaction between the electron and the ion is defined by an ultra-soft potential provided by the Vanderbilt optimization approach. The electronic valence wave properties are extended to a 16 eV power reduction on a plane wave basis. Fourier power values, in addition to DFT, can be utilized to determine the indigenous signature of any substance [24,25]. The four spectral selections are different for different compounds and the same for the same molecules. Studying the pureness, stability and other intrinsic characteristics of the compound, which can be directly seen at the peaks of Fourier, can benefit us. Therefore, there is an attempt to synthesize Cu 2 O nanoparticles using Datura metel L. in the current research. UV-Vis, XRD, and FT-IR were used to characterize the synthesized nanoparticles and further the compound stabilization has calculated by the DFT method. Calculated energies, thermodynamic properties (such as enthalpies, entropies, and Gibbs-free energies), modeled structures of complexes, crystals, and clusters, and anticipated yields, rates, and regio-and stereospecificity of reactions are also investigated.

Materials & Methods
The homogeneous Datura metel L. leaves collected from farmland on Krishnankoil, Tamil Nadu, India and Copper nitrate (Cu(NO 3 ) 2 ) purchased from SRL chemicals Mumbai, India, used without any further purification for the synthesis of Cu 2 O nanoparticles. Datura metel L. leaves dried at room temperature up to brown after then grained by mortar and pestle. The prepared powder was consumed for all the characterization and double distilled (DD) water was used throughout the experiment.
Dust and organic moieties contain in leaves of Datura metel L. were cleaned through the process of washing in tap water followed by DD water after then leaves were cut into small pieces. 10 mg of leaves poured into the 100 ml of DD water boiled at 60 ℃ for 20 min in a magnetic stirrer with a speed of 70 rpm. After cooling, the prepared extract solution has filtered through the Whatman No.1 filter paper. This extract was used as a reducing agent in copper oxide nanoparticles (Cu 2 O NPs) synthesis.
In this experiment, 20 ml of extract was added drop by drop with 100 ml of 3 mM copper nitrate aqueous solution. The reaction mixture of copper nitrate and leaf extract stirrer for 20 min in this meantime the colour of the solution changed from blue to sea green, which indicates the formation the Cu 2 O NPs. The formed NPs are maintaining the room temperature up to 15 days after that start to obtain black precipitation. The prepared NPs are filtered and dried at 60 ℃ for 3 h.

Characterization
The UV-Vis absorption spectra are recorded on Shimadzu UV-1800 suited with 10 mm quartz cuvette. XRD measurements were carried out on Brucker Eco D8 Advance diffractometer with Cu-Kα radiation (λ = 1.54060 Å). FTIR analysis was performed at room temperature on IRTracer-100 Shimadzu.

Spectral Characterization
The Born-Oppenheimer approximation describes an inhomogeneous electron gas as a collection of interacting point electrons traveling quantum-mechanically in the potential domain of a set of static atomic nuclei. The independent electron approximation, Hartree theory, and Hartree-Fock theory are the most common approximation schemes used to solve such models. However, over the last thirty years or so, another approach-DFT-has become increasingly popular for the solution of such problems. This approach has the advantage of being able to solve a wide variety of problems with high precision while still being computationally simple. The electronic structure of atoms, molecules, and solids can be measured using DFT. Its goal is to get a quantitative understanding of material properties by using quantum mechanics' fundamental laws.
The Schrödinger equation of N interacting electrons traveling in an external, electrostatic potential is solved using classic electronic structure methodologies (typically the Coulomb potential generated by the atomic nuclei). This approach, however, has two important drawbacks: (1) the problem is nontrivial even for small N, and the resulting wave functions are sophisticated objects; and (2) the computational effort grows exponentially with N, making the description of bigger systems unaffordable. DFT provides a distinct approach, focusing on the onebody density rather than the many-body wave function as the fundamental variable. Because the density n(r) is a function of only three spatial coordinates, DFT is computationally possible even for enormous systems (rather than the 3 N coordinates of the wave function). The numerical approach, known as the Fast Fourier Transformation, was refined by Cooley and Tukey in 1965, and this had a huge impact on spectral analysis methods. In spectrum analysis, the value of the Fourier process is shown by the power density or power range continuum. The autocorrelation function of a continuous signal also plays a significant role. The Dirichlet condition and zero means for the continuous operation will be provided by the Fourier transform of a finite continuous signal and their relationship to infinite, continuous signals. The compound's experimental measurements in our paper are just for a short period of time. The record duration can be reduced to a given period T by multiplying the infinite continuous recording by a data window as defined.
The window in fourier integral leads to the identity as.
The Fourier transform of this product is the transformation of the infinite record which is paired with transformations of the window when multiplying the infinite record. The Convolution Theorem establishes this relationship, which affirms that: Discrete-time Fourier transform (DTFT) helps calculate the diffracted wave information and the obtained peaks tell us all about the molecular design's properties without having to measure the molecular structure. The DTFT is in the direction of x, y, z for a given compound.
The (x, y, z) gives the density distribution of the crystalline state of the compound and (a,b,c) represents the edge length in the (x,y,z) directions. The DTFT biosynthesis analysis of Cu 2 O as shown (Fig. 1) reveals a distinct difference in the spectral density peak for the three experiments. DTFT peaks shown above indicate that the peak value of 1100 is unique to the synthesized compound and that of the previous compound, the lower peak of 200 is. The sharp rise in maximum value also indicates that the compound is more active and reactive than the other compound.

UV-Vis Analysis
The optical properties of biomolecules loaded Cu 2 O NPs were analyzed through UV-Vis absorbance spectra. Figure 2 shows the optical absorbance spectra of the Cu 2 O NPs. The formation of Cu 2 O NPs confirmed by the color change of copper nitrate aqueous solution from bluish green to sea green when adding Datura metel L. leaf extract shown (Fig. 3). The SPR absorbance peak was found at 790 nm by

XRD Analysis
Crystallinity, size, and phase of the biosynthesized Cu 2 O NPs were determined through XRD analysis, and their diffraction pattern shown (Fig. 4) In this case, k is the dimensionless shape factor taken as 0.9, λ known as X-ray wavelength, β is line broadening at half the maximum intensity (FWHM) and θ is the Bragg angle. This result illustrated biomolecules are well bound with Cu 2 O nanoparticles during synthesis and Datura metel L. extract is one of the promising candidates for reduction and stabilization of Cu 2 O NPs.

Fourier Transform Infrared Spectroscopy Analysis
The FTIR spectra analysis revealed the presence of phytochemicals in the plant extract as well as the production of Cu 2 O. The IR spectra of Cu 2 O NPs are exhibited in comparison to Datura metel L. (Fig. 5). The broad absorption band at 3406 cm −1 in the FTIR spectrum of Datura metel L. leaf extract (Fig. 5b) is attributable to the O-H stretching mode of phenol and alcohols. The peak at 2937 cm −1 indicates C-H stretching of alkyl groups and strong peaks 1651 cm −1 show the C = C stretching vibration of carboxylic groups. The peaks at 1546 cm −1 reveal that the C-N stretch of aliphatic amines and peaks at 1406, 1359, and 1317 cm −1 are representing the C-C stretch (in-ring) of aromatics, N = O bending vibration of nitro compounds, C-N stretch of aromatic amines, respectively. The peaks that appeared at 1105, and 1068 cm −1 are belonged to the C-N stretch of aliphatic amines. The peaks at 752, 621, and 526 cm −1 are shown the existence of C-Cl stretch alkyl halides, C-H bends alkanes, and C-I stretches aliphatic iodo compounds. The FTIR spectrum of Cu 2 O NPs showed again the presence   (Fig. 5a) [33]. Particularly aliphatic amines in Datura metel L. leaf extract are mainly responsible for the reduction of copper ions into Cu 2 O NPs. The tentative values of peak assignments are given in Table 1.

DFT Analysis
A molecule's or crystal's optical qualities are one of the most useful types of parameters for predicting different traits. These can be used to locate wavelengths of optical radiation in the absorption or emission spectrum based on their electronic structure. DFT lets us calculate these properties, related to electron motion evolution under electric field control. DFT is the theory of differential and functional functions. The spectrum data are shown (Fig. 6). NUM is first standardized with [01] which Gaussian has reoriented to speed up the two calculations of electron energy models. Spectral data measurements were used to determine the internal nuclear energy. The Hamiltonian Fock matrix is then used to measure each electron transaction. Once, we know the propagation of the electron, we measure the angular momentum of the electrons that are then used to detect an electron's energy gap.
The energy of the synthesized compound stabilized over some time to a constant value of 16.6378 eV and remained the same indicating compound stability. As seen in Fig. 6. the first fluctuation is caused by the electron's excitation, which eventually returns the electron to its normal state. The oscillation reaction indicates that the compound is irregular, yet the proposed molecule's behaviour is extremely stable.
The MOPS algorithm has been used to model oxyhydrate gel formation [34,39,43], crystal structures of triosmium clusters [35,37,38,42,44,47,49,50], organic molecule  complexation during chemical reactions [45], protein affinity [48], and crystal structures and interaction energies of gas hydrates [40,51]. Calculated energies, thermodynamic properties (such as enthalpies, entropies, and Gibbs-free energies), modeled structures of complexes, crystals, and clusters, and predicted yields, rates, and regio-and stereospecificity of reactions were all in good agreement with experimental results which previously stated in publications as mentioned above. DFT B3LYP 6-311G (d,p) level of theory, the structures of hyoscyamine and atropine were optimized. The UV-Vis spectra were then estimated using TD DFT B3LYP 6-311G (d,p), which revealed that the absorption band is 253.3 nm, which matches the experimental data well.
The initial structure for the computer modeling of Cu 2 O nanoparticles was cuprite [52]  The initial structure of atropine and hyoscyamine in an aqueous solution (they are similar since atropine is a racemate and hyoscyamine is an L-isomer of the same compound) modeled within the MOPS software [34,39,43] with the continual account of the solvent influence shown (Fig. 7a). The structure contains the intramolecular hydrogen bond = O…H-O with a length of 2.22 Å.
Following that, a model of this nanoparticle's combination with hyoscyamine and atropine was created. The complex formation's computed Gibbs free energy is -179.4 kJ/ mol. During the formation of the complex, the structure and conformation of atropine (hyoscyamine) are nearly constant. Three short contacts make up the complex (Fig. 7b). Two of them (2.16 Å and 2.19 Å) are carried out by carbonyl oxygen with two copper atoms in nanoparticles. These bifurcate interactions are made possible by a flaw on the nanoparticles' surface, which occurs when two copper atoms lose their valence at the same time. The third point of contact is the hydroxyl hydrogen of atropine forming a hydrogen bond Fig. 6 Energy (eV) versus DFT iterations show the compound's stability after 10 iterations, since the energy levels obtain a constant value and remain the same Fig. 7 The structure of a) atropine and b) its complex with the fragment of Cu 2 O NPs with the oxygen on the nanoparticle surface (2.09 Å). The intramolecular hydrogen bond = O…H-O is preserved, but it is slightly lengthened to 2.37 Å.

Conclusions
A simple and cost-effective technique for the manufacture of Cu 2 O nanoparticles at room temperature within 30 min has been proposed, with plentiful, underappreciated plant extract (Datura metel L.) being used as a reducing and stabilizing agent. The UV-Vis analysis shows Cu 2 O NPs formation at 790 nm through the making of Cu 2+ ions transition in d-orbital. The result of the XRD pattern reveals that biomolecules of Datura metel L. encapsulation on synthesized Cu 2 O NPs and found in crystalline nature with an average crystallite size of 19.56 nm. This biomolecules encapsulation is validated by FTIR characterization, the aliphatic amines in Datura metel L. responsible for the reduction of Cu 2 O NPs, and their Phytochemicals are effectively utilized as a bio-capping agent and it has been bound along around the Cu 2 O NPs. The energy band stability and spectral fingerprints of the synthesized molecule were investigated using DFT and Fourier power spectrum. We were able to calculate the stability and distinctive spectral signature of the proposed Cu 2 O compounds using these two computational analyses. For the first time, we successfully used Fourier transform spectral characterization to biosynthesized Cu 2 O NPs and emphasized their spectrum. The high frequency of spectrum characterization shows that produced Cu 2 O NPs are more active and reactive than other compounds, yet oscillation reactions are unpredictable, and their behavior is extremely stable even after ten iterations of density functional theory analysis. Furthermore, the current data is being used to research nanoparticles stability in solar cells, wastewater treatment, and biological applications.