Abstract
Methyl orange dye-doped K2SO4 single crystal has been synthesized by a slow evaporation method, and its properties have been investigated. The powder X-ray diffraction (PXRD) studies on the single crystal confirmed the crystalline property, noncentrosymmetric system, and the space group P63/mmc (D64th) of crystal. The reaction involved in the functional group of the grown crystal has been confirmed from the FTIR analysis. The optical properties of absorbance and band gap were calculated from the UV-Vis analysis. The obtained materials were identified from the EDX analysis. The electron transformation and optical distortion were identified at 270 nm in the photoluminescence study. The transmission electron microscopy method analyzed the morphology of the grown crystal. The dielectrics of the grown crystal were studied. The effect of temperature on the grown crystal was studied using the TG/DTA analysis. The bacterial susceptibility of the grown crystal was evaluated from Gram-positive and Gram-negative bacteria. All the results demonstrated that the grown crystal is suitable for optical, electronic, and bacterial applications.
1. Introduction
Nonlinear optical compounds have recently attracted attention due to their potential applications in optical data storage, optical memory storage, frequency conversion, optoelectronics, light modulation, signal conversion, optical second harmonic generation, optical switching, and photonics [1–4]. Organic crystals such as 4‐nitro‐4′‐methyl benzylidene aniline (NMBA) and 40-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) were studied for optical devices such as optical modulators, optical switches, optical bistable devices, and electrooptical devices [5, 6]. However, crystals formed from pure organic compounds have poor mechanical and thermal properties since crystals are often bonded by weak van der Waals forces or hydrogen bonds [7]. To overcome these limitations, semiorganic crystals that comprise both organic and inorganic compounds have been investigated [8]. Unlike inorganic crystals, semiorganic nonlinear optical materials possess several advantages such as a wide transparency range, high damage threshold, less deliquescence, and high optical nonlinearity [2, 9]. Amino acids such as glycine [7, 9, 10], L-proline [4], and L-arginine [8] were studied as an organic part of semiorganic nonlinear optical materials. Moreover, inorganic salts such as potassium sulphate [7, 9] and strontium chloride [4] were studied as inorganic parts of semiorganic nonlinear optical materials. Organic compounds with high delocalized π-electrons have attracted attention for nonlinear optical material development [11].
In this work, the methyl orange dye-doped K2SO4 single crystal was synthesized by a slow evaporation method. The presence of azo moieties (-N=N-) conjugating polycyclic aromatic rings provides excess delocalized π-electrons making the methyl orange dye a potential candidate for nonlinear optical material [12–14]. Sulphate salts are one of the inorganic materials that are currently under investigation for nonlinear optical materials. For instance, Wei et al. [15] investigated antimony sulphates based on nonlinear optical (NLO) materials. Among sulphate salts, K2SO4 possesses a set of symmetry coordinates, and extraordinary contributions by improving their crystal growth, structural flexibility, and linear optical activity [16, 17]. Therefore, in the current work, the methyl orange dye-doped K2SO4 single crystal was grown, and their optical, electrical, structural morphological, and bacterial behaviors have been studied.
2. Materials and Methods
2.1. Materials
Both chemicals (K2SO4 and methyl orange- C14H14N3NaO3S) were obtained from the HiMeida AR grade. The chemicals were used without further purifications. For growing single crystals, double distilled water was used. Bacterial strains of Escherichia coli (MTCC.NO:443) and Staphylococcus aureus (MTCC.NO:97) were used for antibacterial activity.
2.2. Synthesis
The slow evaporation method was used to grow the methyl orange dye-doped K2SO4 single crystal. First, K2SO4 (0.1 g) was completely dissolved in 50 mL double distilled water. Then, methyl orange (0.01 M) was added to the potassium sulphate solution, and the solution was stirred for 24 h to attain a transparent solution. Finally, the combined solution was filtered with the Whatman No. 1 filter paper in order to obtain the purified solution from unwanted foreign particles. The filtered solution was kept in a beaker for a slow evaporation process, and the crystals were harvested after 15 days.
2.3. Characterization
The XRD spectra were obtained using a PANalytical X-ray diffractometer. The FTIR spectra were recorded using the Perkin Elmer FTIR spectrometer in the range 400–4000 cm−1 at 4 cm−1 resolution. The UV and PL spectra were recorded using UV-vis (ELICO) and a spectrofluorometer PC1 (ISS, USA), respectively. Morphological analyses were carried out using a transmission electron microscope (FEI Tecnai G2 20 TWIN) instrument. The elemental compositions were captured from energy dispersive X-ray (JEOL Model JED-2300). An impedance analyzer (HIOKI, Model-IM3570) was used to carry out the dielectric analysis at different frequencies and temperatures. The thermal characteristics were analyzed using a thermal analyzer (Perkin Elmer STA-6000). The photoconductivity was analyzed using a picoammeter (Keithley 480 picoammeter) in DC electric field.
2.4. Antibacterial Activity
The bacterial activity was analyzed by applying the diffusion method. Mueller–Hinton agar was poured into Petri plates, and bacterial culture was spread through the Petri plates. Then, a well was made by applying the gel puncture method on each plate at 8 mm diameter. The bacterial samples were loaded by different concentrations of test samples to the Petri plates, and the well-occupied samples were incubated for 24 hours at room temperature. After that, the incubation period exhibited the zone of inhibition. The formed zone denoted bacterial death. The zones were compared with control gentamycin samples.
3. Results and Discussion
3.1. XRD Analysis
Figure 1 shows the powder XRD patterns of pure and methyl orange dye-doped potassium sulphate single crystals with indexed reflection peaks. The strong peaks in the XRD data indicate that the produced crystals are crystallinity rich. The use of the methyl orange dye causes a change in peak intensity but no significant change in the location of the XRD peaks. The presence of methyl orange dye molecules causes strain in the crystal lattice, resulting in a small shift in peak values [18, 19]. The pure and methyl orange dye-doped crystals correspond to the orthorhombic crystal system with space group Pmcn (62). The presence of dye molecules in the crystal lattice is therefore confirmed by XRD analysis [20]. The observed XRD patterns well matched with standard JCPDS card no: 83-0681. The peak intensity of doped samples differed significantly from that of pure, indicating that methyl orange has been incorporated into the pure crystal lattice.
3.2. FTIR Analysis
The mode of motion, bond strength, bond type, and molecular structure of the crystals are revealed by FTIR spectra. The strength, location, and shape of absorption bands in FTIR spectra also reveal the presence of various functional groups in the material. FTIR spectra of pure and methyl orange dye-doped crystals are shown in Figure 2, and Table 1 shows the FTIR vibrational band allocations of pure and methyl orange doped K2SO4 crystals. As a result, there were no discernible changes in the FTIR spectra of pure and methyl orange doped samples, which can be attributed to the low methyl orange dopant content in K2SO4. Furthermore, only slight variations in peak locations were seen in the spectra of methyl orange doped samples, but no secondary vibrational bands were detected, implying the presence of methyl orange additive in the pure lattice.
3.3. UV Analysis
The UV-visible absorbance spectra of methyl orange dye, K2SO4, and methyl orange dye-doped K2SO4 single crystal are displayed in Figure 3. The methyl orange dye exhibits the two major peaks at 228 nm and 440 nm. These peaks denote the organic substances in the associated dye molecules [24]. The pure K2SO4 single crystal emanates the peak at 231 nm which is characterized by the transfer of electrons from a lower energy state to a higher energy state in the UV region [25]. The incorporation of dye into the pure crystal modified the electronic configuration of the K2SO4 crystal. The modified K2SO4 single crystal increased the absorption nature, but their transparency level is higher (low amount of increment) than a pure single crystal. The dye-doped K2SO4 single crystal peak at 228 nm denoted the interaction of organic compounds and pure single crystal. The UV region absorbance spectrum exhibits low absorption and high transparency and blue emission shouldering. The band gap is calculated by the plotting of variation of (αhγ)2 versus hγ which is found to be 4.81 eV and 5.07 eV for pure and dye-doped single crystal, respectively [15, 26]. The formed energy gaps describe the transfer of electrons to the different energy levels (Figure 4). The wide band gap is suitable for NLO devices and optoelectronic applications.
3.4. Photoluminescence Analysis
The methyl orange doped K2SO4 single crystal luminescence properties were evaluated by photoluminescence (PL) spectroscopy. The excitation spectra of the methyl orange dye-doped K2SO4 single crystal were observed at 270 nm (Figure 5). The visible region excitation spectra denote the defects of the potassium sulphate crystals [27]. The shoulder peaks represent the transition between the dye and potassium crystals, revealing the optical applications and luminescence-oriented electrical applications [28].
3.5. TEM Analysis
The transmission electron microscopy method determined the shape, structure, texture, and size of the synthesized samples. The methyl orange doped K2SO4 single crystal TEM images are displayed in Figure 6. The TEM image shows a spherical shape with layer grains. The large grains show a hydrogen bond, which arises from the dye compounds. The dye and K2SO4 bonding enhanced the structural formations. The structural activity was re-ensured from the XRD analysis. The size and shape of the crystals serve an important candidate in electrical, optical, and biological activities.
3.6. EDX Analysis
The grown crystal of methyl orange dye-doped potassium sulphate single crystal elemental composition spectrum is shown in Figure 7. The material quantity and the ratio between the elements were displayed with material peaks. The incorporation of dye into the single crystal enhances the material crystallinity which very well coincides with XRD analysis.
3.7. Photoconductivity Analysis
The photoconductivity of pure and methyl orange dye-doped K2SO4 single crystal is shown in Figure 8. The pure single crystal produces the linear response to the current and applied field. The light illumination generated the charge carriers. The generated charge carrier was captured from the conductivity measurements [29, 30]. The methyl orange dye-doped K2SO4 single crystal exhibits enhanced photoconduction when compared to pure K2SO4 single crystal. The high value of photocurrent captured from dye-doped single crystals is due to their intrinsic center filled by dye molecules and the trapping of carriers in the crystals. The dye attachment increases the band gap and photon capture which can be applied in optical and telecommunication systems over long distances [31].
3.8. Dielectric Analysis
The electrical properties of the methyl orange dye-doped K2SO4 single crystal are derived from the dielectric constant and the dielectric loss, which are depicted in Figures 9 and 10. The temperature-dependent dielectric constant with applied frequency denotes the formation of the double nature of the crystals [32]. In the spectrum of the dielectric constant, the temperature with the applied frequency gradually increased due to its space charge polarization with the heat and its electric and ionic dipolar nature. The lower frequency produced a higher dielectric constant in a particular temperature than in other temperatures [33] because of their space charge and macroscopic distortion between the charge carriers. At the same time, the high frequency produced the lower dielectric constant at certain temperatures due to their ionic and electronic polarization. These polarizations are active in high temperatures and high frequencies. The dielectric loss [21] values represent the polarization parameters and frequency modification within the temperature limits (Figure 10). In high temperature, losses are low compared to their temperatures. The lower loss value suggested that the MO dye-doped K2SO4 single crystals can be used in optical, electrical, and telecommunications system due to their low loss in the high frequency and high-temperature range.
3.9. Thermal Analysis
The thermal property of crystals is crucial for the dealings of nonlinear optical devices. TG-DTA examination provides evidence about thermal stability, decomposition stages, and the melting point of the materials. TG-DTA curves of accumulated crystals are indicated in Figure 11. The accumulation of K2SO4 improves the thermal stability of the crystals. The accumulated crystals have good thermal stability, and there is decomposition from 100°C to 175°C, 175°C to 250°C, and 250°C to 275°C for 34.16, 3.47, and 4.84 weight loss percentages, respectively. The small boosts in temperature and weight loss percentage are reductions. The shape of the TG curve for K2SO4 exhibited that the ultimate weight loss happened in the range of 100°C to 175°C. Carbon molecules decompose at the endothermic stage. The endothermic investigation of K2SO4 generally differs when calculating water contents at each endothermic step. The endothermic process of K2SO4 begins at ambient temperature and is completed at 100°C [27]. Hence, the accumulated dye-doped K2SO4 single crystal is a better thermodynamically stable material, which is suitable for laser and NLO applications [15, 22–28].
3.10. Antibacterial Activity
The antibacterial activity was performed against the organisms of E.coli and S.aureus using the MO dye-doped K2SO4 single crystal. The test organism’s activity has been displayed in Figure 12. The activity of the crystals was compared with the control disc. The antibacterial activity of E.coli is higher than that of S.aureus due to their sensitivity against single crystals. The bacterial system was delocalized by the actions of penetration of crystal materials to the cells, inhibiting the permeability and restricting the electron mobilization. These parameters stopped cell growth and leads to cell death. The dye-doped single crystal against the organisms was noticed by a zone of inhibition, which is tabulated in Table 2. The observed results suggested that the dye-doped single crystal can be a strong advocate for biomedical applications.
4. Conclusion
A single crystal of methyl orange doped K2SO4 was grown by the solution growth slow evaporation method. XRD analysis confirmed the structural factor, symmetric system, and their space group. The title compound involved functional groups which were elucidated from FTIR analysis. The optical distinctiveness of the grown crystal was identified from pure and dye-doped single crystal. The dye incorporation increases the band gap at 5.07 eV and decreases the wavelength on the blue shift side. The photoluminescence peaks at 270 nm confirmed the blue emission, and thermal stability and material degradation described the thermo-electric behavior. The low value of dielectric constant and loss in various frequencies of the dye-doped single crystal is suitable for NLO and optoelectronic device fabrications. The Gram-negative bacterial sensitivity possesses more enhanced activity than Gram-positive bacteria. The grown dye-doped single crystal exhibited excellent optical, dielectric, antibacterial, and thermal stability in various applications.
Data Availability
The data are available from the corresponding author upon request.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
Acknowledgments
The authors are thankful to Nanjil Catholic College and Manonmaniam Sundaranar University, Tirunelveli, Tamil Nadu, India. The project was also supported by the Researchers Supporting Project, number (RSP-2021/143), King Saud University, Riyadh, Saudi Arabia.