Study of the Optical, Structural and Adsorption Properties of Tellurium Oxide Nanoparticles and Graphene Nanosheets Prepared by Q-Switched Nd-YAG Pulsed Laser

INTRODUCTION

Nanoscience and nanotechnology are concepts used to describe the universe of “extremely small materials” (10^–9 meters) that have a wide “range of applications in sorts like energy, chemistry, biomedicine, environmental engineering, material science, optoelectronics, and life science”[1]. Nanostructures do, in fact, exhibit unique capabilities (size-dependent optical, catalytic, electrical, and mechanical properties, for example [2]. Nanoscale materials can be used in a variety of applications due to their unique physical-chemical features (large surface energy, spatial confinement, and high surface to volume ratio). The building blocks of existing nanomaterials, nanoparticles (NPs), occur in a range of shapes. creation of a wide range of nanostructures [1]. Thin films and three-dimensional (3D) structures (super lattices) Tellurium (Te) is a p-type semiconductor with a band gap of (E_g= 0.35 eV) [3].It possesses a unique set of characteristics, including photoconductivity and catalytic activity in oxidation and hydration reactions[4], and nonlinear optical responses, thermoelectronic and high piezoelectronic[5]. Furthermore, solid tellurium combines with other elements to produce a variety of useful compounds, such as Bi₂Te₃, ZnTe, CdTe [6], However, the obtainability of low-dimensional tellurium (Te) nanostructures will almost certainly expose new applications or improve the performance of existing available devices in terms of the properties stated above [7]. As a result, the synthesis and characterization of tellurium nanoparticle fabrications piqued researchers’ curiosity. It is, nevertheless, one of the rarest materials on the planet. Because of its scarcity, there is a significant desire to shape it as a nanoparticle, nanowire, or nanotube so that it can be used just where it is needed. As a result, it is a material of particular interest for a variety of applications, including solar cells [8]. The advantages of PLAL include the purity of the surface, which is free of chemical contamination, and the ease with which the particles may be collected and stored after synthesis. TeO₂ is a high-index refractive material that transmits in the infrared range, making it particularly intriguing for optical applications. TeO₂ has an energy gap of approximately 4.05 eV. It has also been shown to have Raman gain up to 30 times that of silicon dioxide, making it particularly effective in fiber optic amplification [9]. TeO₂ crystals are useful in acousto-optic systems owing to their advantageous photo-elastic characteristics, as well as their low light absorption, excellent optical homogeneity, and high optical damage resistance [10]. TeO₂ is an important material in both its amorphous and crystalline forms such as α-TeO2, with applications including optical storage material, X-ray detectors, laser devices, optical storage material, and gas sensors [11] and propane oxidation catalysts [12]. For the fabrication of TeO₂ thin films, several procedures such as reactive dip-coating, sputtering [13], and laser ablation have been utilized [14]. This work illustrated the activity of TeO₂NPs toward the removal of methyl blue dye from water. We have successfully produced TeO₂NPs in distilled water via PLA method. The morphological and optical properties were calculated for TeO₂NPs. Graphene is a proposed 2D-carbon lattice in the field of material research because of its unique chemical and physical features”[15]. Graphene is a potential component in a variety of sectors, including solar cells [16], storage devices [17], sensors [18], energy conversion [19], and so on, due to its unique thermal and chemical stability, outstanding mechanical strength, superior electrical conductivity, large surface area. In recent years, a variety of techniques have been used to create graphene, including mechanical exfoliation of graphite [20], chemical vapor deposition            (CVD)[21], orchemical reduction of graphene oxide (GO) [22]. Chemical reduction of graphene oxide is the most efficient way for preparing graphene in comparison to the other methods due to its low cost and large manufacturing capacity, as GO can be produced.

MATERIALS AND METHOD

Preparation of Te and Graphite Disc

A hydraulic piston was used to press (6 gm) of Te and (10 gm) of graphite powder at a pressure of 2 MP. After that, they were annealed in the oven for 24 hours.

Pulsed Laser Ablation in Liquids Syntheses of TeNPs and Graphene Nanosheet (GNS)

Tellurium oxide nanoparticles (TeO₂NPs) and graphene nanosheets (GNS) were generated as colloidal solutions by Q-Switched Nd-YAG pulsed laser ablation of a solid target of Te and Graphite powder in distilled water, with the Te and Graphite disc located in a glass container full with (10 ml )of distilled water. After that, a Q-Switched Nd-YAG pulsed laser (energy per pulse 80 mJ, number of pulses 500, λ =1064 nm, frequency (PRR) of 6 Hz, and pulse duration 10 ns) was used to irradiate the target. The colloidal liquid was then distillated onto the glass plate, which had previously been cleaned with water and alcohol, to create a thin film. It is then dry in an electric oven at a temperature of 25 ⁰C. Finally, the thin film is ready to be measured using XRD, SEM, and EDX. The pulsed laser ablation method used to prepare the TeNPs and GNS is shown in Fig. 1.

RESULTS AND DISCUSSION  

XRD measurements of TeO₂NPs and GNS samples

The crystal structure, distance between planes, crystalline size, and full width at half maximum (FWHM) were all studied using X-Ray Diffraction (XRD). Fig. 2 displays the TeO₂NPs XRD pattern at     2θ = 26. 7°, 33. 2°, and 61.9 °, which correspond to miller indices (011), (111), and (113) planes, respectively. The formation of TeNPs is indicated by these peaks, which is in agreement with the reference [23]. There is no additional peak, indicating that the synthetic material was of excellent crystalline purity. The Debye Scherrer equation (Eq.1) can be used to compute the crystallite size (D).

D= 0.89 λ/ (β cos θ)

β,θ and λ are  the Full Width at Half Maximum (FWHM),the Bragg diffraction angle and  X-ray wavelength respectively. the crystallite size of TeO₂NPs had a value of 39.6 nm, which was calculated. Commercial graphite is liable for the reflection peak at 26.7°, which corresponds to 002, as seen in Fig. 3a. Fig. 3b indicates the presence of a smaller peak at 26.7°, corresponding to 002, which is very insignificant in comparison to the graphite peak, showing the production of graphene nanosheets (GNS).

Analyses of TeO₂NPs and GNS using Scanning Electron Microscopy (SEM) and EDX”

The morphological parameters of the produced materials were determined using SEM. The TeO₂NPs have a spherical shape, as seen in Figs. 4, a-d. There is some agglomeration of these particles at various locations. As indicated in Fig. 5, the average particle size is 65 nm. As demonstrated in Figs. 6 (a-d) graphite fragmentation with water using a pulse laser resulted in the formation of graphene nanosheets (GNS) and It is similar to what was mentioned in the reference [24, 25].

Fourier Transform Infrared Spectroscopy((FTIR)

The FTIR spectrum of TeO₂NPs and graphene nanosheets (GNS) powder was illustrated in Fig. 7 and (8), respectively. The absorption band at 561.5 cm^-1, 1048.2 cm^-1, 1642.1 cm^-1, and 3288.8cm^-1 return to the stretching vibration of Te-O-T linkages, ester (COO) stretching vibrations, C=O bonded, and O-H stretching vibrations, respectively   [26, 27]. 

The FTIR spectrum of prepared GNS was illustrated in Fig. 8. The appeared intense peaks at (3288.8 cm^–1 ) were corresponding to stretching vibrations of hydroxyl (O-H) for water. The peak at (1632.6 cm^–1 ) refer to C=C stretching vibrations bond ( skeletal vibrations from unoxidized graphitic domains). Stretching vibration peaks of C–O (alkoxy) are observed at 1044.4 cm^–1 and it’s close to the reference [28].                      

UV-Visible Absorption Spectroscopy:

The absorption peaks of TeO₂NPs and graphene nanosheet (GNS) are shown in Figs. 9a and b) respectively. Fig. 9a. At 292 nm, an absorption peak occurs as the valence band transitions to the conduction band. It returns to the production of TeO₂ nanoparticles [43]. According to the tauc plot, the energy gap for TeO₂ is 1.40 eV, as illustrated in Fig. 9. The transitions of the atomic C–C bonds cause the absorption peak at 265 nm, as illustrated in Fig. 9b, which agrees with the researcher’s result in the reference [29].

Removing the Methylene Blue dye (MB) from the water by using the prepared TeO₂NPs and graphene nanosheets (GNS)

Methylene blue dye, which is utilized in textile and leather coloring, was removed using the TeO₂ NPs and GNS that had been prepared. 0.1 ml Methylene blue dye (M) was dissolved in 7.9 ml distilled water, and then 2.0 ml TeNPs and GNS were added to the methylene blue (MB) dye separately, and then the absorbance was calculated for each of the TeO₂NPs+MB and GNS+MB mixtures at two times t=5 s and t=15 s. Fig. 10 shows that TeNPs enhanced the absorbance of the methylene blue dye in the visible range. It is noted that the longer the time, the greater the absorbance intensity. This result indicates that it is not possible to use TeO₂NPs to remove pollutants, but this TeO₂NPs+MB mixture can be used in the manufacture of the solar cell because it enhances the absorption in the visible range.

As for Fig. 11 for the GNS+MB mixture, it indicates a high adsorption of MO dye due to the presence of GNS, with an adsorption efficiency of up to 65.3% and 68.7% for t = 5 s and t = 15 s, respectively.

CONCLUSION

TeO₂NPs and graphene nanosheets (GNS) were successfully generated in liquid utilizing a Q-Switched Nd-YAG pulsed laser (PLAL-Method). As indicated in UV-Visible absorption spectroscopy and FTIR investigations, the PLAL method is regarded a simple and important physical method in the exfoliation of graphite in order to obtain graphene sheets. The prepared graphene nanosheet (GNS) has a high efficiency in the adsorption of MB dye, especially at time t = 15 s, with an adsorption efficiency of 68.7%. This is in contrast to the behavior of titanium nanoparticles (TeO₂NPs), as it enhances absorption in the visible range, and this behavior helps in the use of TeO₂NPs with MB dye in the manufacture of the solar cell better than using it in the adsorption process. 

CONFLICT OF INTEREST

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