Novel synthesis, characterization and TDD-DFT computations for ZrO2-bromothymol blue nanocomposite thin film [ZrO2+BTB]C and its application


 A novel [ZrO2 + BTB]C nanocomposite was synthesized and prepared as a thin film using the Sol-Gel spin coating method. Different characterization techniques for [ZrO2 + BTB]C like FTIR, UV-Vis, and optical properties have been used. The resulted XRD and SEM data have been employed to study interface composites. The optimization was performed using DFT by DMol3 and CASTEP program. The chemical structure was confirmed by spectroscopic and structural properties for [ZrO2-BTB]C, XRD results showed the same crystal structure. Combined between experimental and TDD-DFT data, the average crystallite size and composite interface are 12.36 nm and orthorhombic symmetry (a = 7.38(5); b = 18.178(6); c = 26.10(3) Å and a = b = g = 90o) with space group (P61) for [ZrO2 + BTB]C, respectively. Furthermore. While the computed by DFT are 2.897 eV and 2.492 eV for as-isolated crystals of [BTB]TF and [ZrO2 + BTB]C, respectively. Both [BTB]TF and [ZrO2 + BTB]C thin films have direct allowed transitions. In addition, the optoelectrical parameters have been calculated for [BTB]TF and [ZrO2 + BTB]C films such as refractive index, extinction coefficient, dielectric constant, and optical conductivity. The simulated values obtained by CATSTEP for the optical parameters of [ZrO2 + BTB]C are in good agreement with the experimental values. The [ZrO2 + BTB]C presents a good candidate for optoelectronics and solar cell applications.


Introduction
The applications of dye composites in industries have been enhanced quickly due to their unique properties, such as light-in-weight, high stiffness, and high strength. [1][2]. Bromothymol blue (C27H28Br2O5S) (sometimes known as bromothymol sulfone phthalein, and BTB) is one of the promising candidates for state-of-the-art organic semiconductors, valid for various optoelectronic devices [3]. It is regularly used in applications that need measuring substances that would have a relatively neutral pH ≅ [4,5]. Sulfone phthalein dyes are an essential pH indicator class for some applications in modern sensors [6][7]. For this goal, the sol-gel process has been successfully employed due to its singular versatility and the following characteristics: optic transparency, mechanic stability, chemical resistance, and flexibility of sensor morphological configurations [8][9][10]. Therefore, these materials have potential applications in the pharmaceutical, food, and chemical industries [11,12]. Once again, the molecular chemical reactivity of the dye molecules was investigated using DFT-based reactivity descriptors, electrophilicity index (A), chemical potential (μ), and chemical hardness (A) values were approximated in terms of molecular orbital energy, HOMO and LUMO frontier values [13]. A TD-DFT investigation of ground and excited-state properties in indoline dyes used for dye-sensitized solar cells, the ground and excitedstate properties of three indoline dyes, namely D102, D131, and D149, specially designed for dyesensitized solar cell applications have been studied by the means of density functional theory (DFT) and time-dependent DFT (TD-DFT) and compared with experimental absorption and fluorescence spectra [14].
Sulfonphthaleine dyes are an essential pH indicator class for certain applications in new sensors.
A theoretical analysis to elucidate the impact of physical factors on the sulfonphthalein dyes halochromic behavior. Sulfonphthaleine dyes are phenol red, cresol red, bromophenol blue, and consideration are given to physical factors such as temperature, strain, solvent dielectric constant, and the form of constituent atoms isotope. Meanwhile, variations in pH of indicator color change, i.e. pH, are studied with the indicators' physical factors in the acid-base equilibrium. These findings show the significance of physical factors on the halochromic activity of colorants for further study and the production of pH sensors [15].
At the same time, environmentally friendly nano regime materials were developed for the past few years with the aim of low-cost production using simple green technologies. Nano zirconia [ZrO2] NPs are widely used in various photocatalytic, piezoelectric applications, as a catalyst in various organic reactions [16] and industries for ceramics, dental, and optical coatings [17,18]. The cytotoxic activity of nanoparticles mainly depends on its size and shape [19,20]. Various chemical methods such as the solvothermal method, hydrothermal method [21][22][23][24][25], aqueous precipitation method [26], sol-gel method [27][28][29], thermal decomposition methods [30][31][32] and pyrolysis of zirconium oxychloride salt organic precursors have been applied to prepare ZrO2 NPs [33]. These methods are more effective for controlling the shape and size of nanoparticles but often results in the formation of mixed crystal phases [34][35][36].
However, all these methods require high temperature, costly, and environmentally hazardous chemical precursors during synthesis processes [37][38].
In this work, a novel synthesizes [ZrO2+BTB] C to study the structural and optical properties of the fabricated nanocomposite thin films has been carried out. Also, study the molecular structure of [ZrO2+BTB] C using FTIR and molecular electrostatic potential (MEP) techniques. Also, the configuration and morphology description of the [ZrO2+BTB] C using XRD and SEM techniques will be studied. Finally, the optical properties of the fabricated film have been carried out. Simulated measurements of the optical properties were also conducted for [ZrO2+BTB] C as-deposited films by CATSTEP in the DFT method.

Materials
The list of chemicals used in conducting the current experiments is presented in Table 1. All chemicals were utilized as received without supplementary refinement.

Characterization
Characterization methods and typical conditions are listed in Table 2.

Fourier Transform Infrared Spectroscopy (FT-IR)
FT-IR reveals chemical changes to the structure of the dye and nanocomposite. Fig.1 and Fig. 2  [ZrO2+BTB] C . Moreover, the bending vibration of the ether (glycosidic) linkage δ (S-O-C) was designated by a strong peak at 1040 cm −1 [46]. The [ZrO2+BTB] C spectrum (Blue color) presents besides the above bonds a peak that is not found in that of [BTB], particularly at 3480 cm -1 is due to Zr-OH2 rocking of water. And also, the spectrum of the ZrO2+BTB] C exhibit additional FTIR strong bands at 570 cm -1 , 543 cm -1 and 464 cm -1 assigned to ν (M-O) modes [47].  It has been concluded that when the comparison between FTIR experimental data for [BTB] and [ZrO2+BTB] C as thin films ( Fig. 1) and IR Gaussian simulation for [BTB] and [ZrO2+BTB] C as isolated state or gas state ( Fig. 2(a-b)) that has a good agreement [50]. These agreements in peak intensities and locations confirmed the formation of the predicted [ZrO2+BTB] C structure in Scheme 1.

XRD
The X-ray powder diffraction analysis (XRD) is used to identify atomic configurations of orientation and crystalline phases: structure, target direction, change in order-disorder, thermal expansions, and thickness measurements for thin films and multilayer [51][52]. In an XRD study, a diffractogram indicates the frequency according to the angle of diffraction. Fig. 3   shapes) or brush such as a uniform structure was grown. By using the image j software program, Fig. 5b shows a long-range uniformity of the nanowires with an average thickness of ≅ 0. 45
The active location of MEP is displayed by a 3D illustration in Fig. 6(a) and Fig. 6 6.523×10 -2 and -7.063×10 -2 ≥[P]≥ 7.063×10 -2 , respectively, while the increase follows the order: red < brown < blue [62]. The blue color is the largest attraction, whereas the red color is a powerful repudiation.
The diagram of the MEP reveals that nitrogen electronegative atoms reflect the regions of negative potential and hydrogen atoms have a positive potential [63]. The chemical and physical similarities of Also, Fig. 7 shows the UV-Vis absorption spectrum for the hybrid nanocomposite of

Optical Dispersion constants
Polymers, dyes, and organic/inorganic compounds are of great importance in the creation of nanomaterials and other equipment such as optoelectronic devices or solar cells. The refractive index n(λ) and extinction coefficient k(λ) values, which included both refraction and absorption based on the interaction between the material being studied and the light-incident. n(λ) has a phase velocity correlation with the dispersion, while k(λ) is linked to a mass reduction coefficient and permits the computation of the electromagnetic wave dissipation rate material. The spectroscopic reflectometry measurement of transmission and reflectance permits the n(λ) and k(λ) versus photon energy (hν) has been studied.

(b) (c)
The spectral properties of n(λ) and k(λ) versus (ℎ ) values for [BTB] TF , [ZrO2+BTB] C asdeposited thin films (thickness 150 nm) over a range 1.0-5.5 eV of (ℎ ) are given in Fig. 9(a-b). Where the mathematical formula of both n(λ) and k(λ) is given by Eqs. (2) and (3) [72] as follows: As observed from Fig. 9(a), both n(λ) and k(λ) show similar spectral behavior to each other in the photon energy range from 1.0 ≤ ℎ ≤ 5.5 . Since both n(λ) and k(λ) spectral behaviors depend on the type of material. We can classify the patterns into two parts: (i) the first part in 2.25 ≤ ℎ ≤  [73][74]. CASTEP method in DFT calculations of [BTB] TF and [ZrO2+BTB] C as-single crystal was utilized to predict n(λ) and k(λ) values ( Fig. 9-b). It is also important to note that the simulation curve presents an approximate similarity for n(λ) and k(λ) with a shift towards the highest energies with lower peak intensities. The maximum peaks obtained for n(λ) and k(λ) are obtained ℎ ≅ 4.15 − 4.50 .

Dielectric constants and optical conductivity
Complex dielectric function ( * ) is related to both n(λ) and k(λ) as [75,76]: Where the real and imaginary parts of * are 1 ( ) and 2 ( ), respectively. The real dielectric constant ( 1 ( )) generally relates to dispersion, while the imaginary dielectric constant ( 2 ( )) provides a measure to the dissipative rate of the wave in the medium [77]. Also, it indicates the loss of energy in a dielectric material through conduction slow polarization currents and other dissipative phenomena.
Where ( 1 ( )) is the real part and ( 2 ( )) is the imaginary part of the optical conductivity. The values of real and imaginary parts are given by the relations [80,81]: Where is the angular frequency, 0 ℎ permittivity of free space (free space dielectric constant). The dependence of the real and imaginary parts of the optical conductivity on the incident photon energy of our samples is shown in Fig.11 (a-c). Finally, Fig. 11 (b-c) show the spectral dependence of optical conductivity σ(ω) versus photon energy