Next Article in Journal
Photoacoustics Waveform Design for Optimal Signal to Noise Ratio
Previous Article in Journal
Surface Terminations of MXene: Synthesis, Characterization, and Properties
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Symmetry
Volume 14
Issue 11
10.3390/sym14112231
symmetry-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

A Study of the Optical and Structural Properties of SnO2 Nanoparticles Synthesized with Tilia cordata Applied in Methylene Blue Degradation

by
Eduardo Quintero González
1,
Eder Lugo Medina
2,*,
Reina Vianey Quevedo Robles
1,
Horacio Edgardo Garrafa Gálvez
3,
Yolanda Angelica Baez Lopez
1,
Eunice Vargas Viveros
1,
Ferdinanda Aguilera Molina
1,
Alfredo Rafael Vilchis Nestor
4 and
Priscy Alfredo Luque Morales
1,*
1
Facultad de Ingeniería, Arquitectura y Diseño-Universidad Autónoma de Baja California, Ensenada C.P. 22860, Baja California, Mexico
2
Tecnológico Nacional de México-IT de Los Mochis, Los Mochis C.P. 81259, Sinaloa, Mexico
3
Departamento de Ingeniería y Tecnología, Universidad Autónoma de Occidente (UadeO), Guasave C.P. 81048, Sinaloa, Mexico
4
Centro Conjunto de Investigación en Química Sustentable, UAEM-UNAM, Toluca C.P. 50200, Estado de México, Mexico
*
Authors to whom correspondence should be addressed.
Symmetry 2022, 14(11), 2231; https://doi.org/10.3390/sym14112231
Submission received: 16 September 2022 / Revised: 9 October 2022 / Accepted: 18 October 2022 / Published: 24 October 2022
(This article belongs to the Section Chemistry: Symmetry/Asymmetry)
Browse Figures
Versions Notes

Abstract

:
Water contamination is one of the most worrisome problems in the world. Industrial dyes are discharged without previous treatment, promoting water pollution and affecting the environment. In this paper, semiconductor SnO2 nanoparticles (NPs) were synthesized using Tilia cordata extract, as a reducing agent, at different concentrations, 1%, 2%, and 4% (weight/volume; w/v). These NPs were used as photocatalysts characterize an alternative for degrading wastewater compounds. Nanoparticle symmetry is an important factor for understanding the properties that provide tools for further treatments. Additionally, the structural, morphological, and optical properties of the green-synthesized SnO2 NPs were studied. Fourier transform infrared spectroscopy (FTIR) showed the characteristic absorption band of Sn–O centered at 609 cm−1. Meanwhile, X-ray diffraction (XRD) confirmed a tetragonal rutile-type crystalline phase without impurities whose crystallite size increased from 15.96 nm and 16.38 nm to 21.51 nm for SnO2-1%, SnO2-2%, and SnO2-4%, respectively, as extract concentration was increased. NPs with a quasi-spherical morphology with agglomerations were observed through scanning electron microscopy (SEM). On the other hand, the bandgap remained at ~3.6 eV throughout all samples, even at variable extract concentrations. The NPs yielded great photocatalytic activity capable of degrading methylene blue (MB) dye under ultraviolet radiation and solar radiation, achieving degradation percentages of 90% and 83% of MB under UV and solar radiation at 90 and 180 min, respectively.

1. Introduction

Water pollution is one of the major problems worldwide, caused by industrial waste discharge such as organic dyes, which are considered pollutants in concentrations from 1 ppm [1]. Due to their chemical structure, dyes are resistant to solar radiation and to the action microorganisms [2], which makes them slow-degrading and nonbiodegradable contaminants. In humans, they are considered mutagenic and can cause malnutrition as a result of bioaccumulation. In addition, they cause skin and eye irritation, kidney, and respiratory problems [3,4,5,6]. Furthermore, dyes prevent reoxygenation and sunlight passage through bodies of water, causing adverse effects on aquatic life [7]. Throughout history, different physical or chemical methods have been developed to remove dyes, for instance, adsorption [8], coagulation–flocculation [9], ozonation [10], and biological methods [11], among others. These procedures are considered highly efficient; however, they require additional treatment since they generate byproducts, and even worse, some use toxic chemical agents. Alternatively, photocatalysis, reported in 1987 by Fujishima and Honda [12], has positioned itself as one of the most promising advanced oxidation chemical methods today [13] due to its ability to degrade organic dyes until their mineralization and to its working conditions, atmospheric temperature, and pressure and under solar or UV radiation [14]. SnO2 being photoexcited by irradiating it with an energy equal to its bandgap or greater, generating electron-hole pairs that interact with H2O and O2 molecules in the solution, giving rise to reactive species that act on the dye degrading it [15]. Semiconductor oxide nanoparticles, such as TiO2 [16], ZnO [17], Co/Co3O4 [18], Nb2O5 [19], BiVO4 [20], DyBa2Fe3O7.988/DyFeO3 [21] and SnO2 [22], whose high surface area allows greater interaction with dyes, have been widely used in photocatalysis. SnO2 has stood out for its high stability, high oxidation potential, corrosion resistance, and nontoxicity, as well as for its excellent photocatalytic activity [23]. Within the NPs, SnO2 semiconductor synthesis methods excel on the basis of using natural precursors like extracts from plants [24,25,26], algae [27], fungi [28], and bacteria [29] that contain primary metabolites and secondary polyphenols such as flavonoids and terpenes, which can reduce metal salts to metal ion NPs. In addition, they can stabilize NPs by avoiding contact between nuclei, preventing fusion and hence controlling their size. Using natural extracts decreases the inherent environmental impacts of chemical processes, making them safe, biocompatible, and eco-friendly [30]. Diverse research on SnO2 NP green synthesis using plant extracts has been reported in the literature. Suresh et al. [31] used Delonix elata for synthesizing NPs between 13 and 19 nm whose photocatalytic activity in the rhodamine B degradation was evaluated, rendering a maximum degradation of 92.8% after 150 min under UV radiation. Karthik et al. [32] obtained SnO2 NPs through microwave-assisted green synthesis using Andrographis paniculata extracts; the NPs were evaluated for their optical and photocatalytic properties in Congo red dye degradation. Rathinabala et al. [33] used Canna indica leaf extracts obtaining SnO2 NPs that were analyzed for rhodamine B degradation under UV and sun radiation; cytotoxicity was also evaluated. To the best of our knowledge, there are no reports within the literature on SnO2 NPs biosynthesized utilizing Tilia cordata extracts. Tilia cordata, also known as lime or linden, is a straight-stemmed tree with a smooth bark that can reach 18 m in height. Its leaves are heart-shaped, dark green on the upper side, and bluish green on the underside. Its flowers are yellowish in color, grouped in clusters of one to six flowers that mature into globose-looking fruits [34]. At least 24 water-soluble phenolic compounds have been detected in its extract with a flavonoids and antioxidants high content, in a 58.86 ± 21.51 y 82.99 ± 13.13 mg/g proportion, respectively [35]. These molecules can be used in NP semiconductor green synthesis. In the present work, semiconductor SnO2 NPs were synthesized through biosynthesis utilizing Tilia cordata extracts at different concentrations to evaluate their photocatalytic activity in MB degradation.

2. Materials and Methods

2.1. Materials

Stems, leaves, and flowers of Tilia cordata were obtained at a local market. Tin chloride (SnCl2•2H2O, 98%), used as tin precursor salt, and Methylene blue, as model dye, were purchased at Sigma-Aldrich. Deionized water was used as environmentally friendly solvent. All reagents were used as received.

2.2. Tilia Cordata Extract Preparation

Tilia cordata extract was prepared using a thermal method in an aqueous solution. Briefly, to prepare Tilia cordata extract, the stems, leaves, and flowers were pulverized. Subsequently, 1%, 2%, and 4% (w/v) extract solutions were prepared in 50 mL deionized water. The solutions remained under magnetic stirring for 2 h. They were consecutively placed in a water bath at 60 °C for 1 h. Afterward, the extracts were vacuum filtered to separate them from the organic matter. The extracts were stored for further use.

2.3. Green Synthesis of SnO2 NPs

In a typical procedure: 2 g of SnCl2•2H2O were dissolved in 42 mL of the Tilia cordata extract, 1%, 2%, and 4% (w/v), labeled SnO2-1%, SnO2-2%, and SnO2-4%, respectively. The solutions were mechanically stirred for 1 h until the Sn precursor’s complete dissolution, then placed in a thermoregulated water bath at 60 °C for 12 h to complete the reaction until a pasty consistency was obtained. Finally, they were submitted to heat treatment at 400 °C for 1 h. The grayish-white products were ground and stored for later characterization and photocatalytic activity evaluation.

2.4. Characterization Techniques of the NPs

The SnO2-1%, SnO2-2%, and SnO2-4% NPs were characterized by different analytical techniques. The functional groups were analyzed by Fourier transform infrared spectroscopy (FTIR) with attenuated total reflectance (ATR), using a Perkin Elmer Spectrum Two Spectrophotometer; the spectra were taken in a 4500 cm−1 to 300 cm−1 range. The XRD diffraction patterns were obtained in a Buker X-ray D2 phase diffractometer with a 1.5406 Å (Cu Kα) irradiation wavelength. The scanning angle was measured in a 10° to 80° range at a 0.02° step. Morphology was determined utilizing a JEOL JSM-6310LV scanning electron microscope (SEM) operating at 200 kV. Sample purity was probed by elemental composition analysis using energy-dispersive X-ray spectroscopy (EDX). The optical properties analyses were carried out by visible-ultraviolet light (UV-Vis) and photoluminescence (PL) spectroscopies. The UV-Vis analysis was performed in a Perkin Elmer Lambda 365 equipment at a 600 nm/min scanning speed, in the 200 nm to 800 nm wavelength range. The PL analysis was performed on a Horiba Nanolog PL spectrophotometer over a 200 nm to 600 nm wavelength range and 350 nm excitation wavelength.

2.5. Photocatalytic Activity

The SnO2 NPs photocatalytic activity was evaluated for MB dye degradation at a 15 ppm concentration. Degradation studies were performed using UV and solar radiation. In the experiment under UV radiation, 10 W Polaris UV-1C lamps with an energy of 18 mJ/cm2 were used. In a typical experiment, 50 mg of SnO2-1%, SnO2-2%, and SnO2-4% NPs were added to 50 mL of MB dye solution. The obtained suspension was then mechanically shaken in the dark for 30 min to obtain the adsorption–desorption equilibrium. Subsequently, the suspensions were placed under UV radiation. During the experiment, aliquots were taken at progressive times for up to 180 min. Analogously, the experiment carried out under solar radiation followed a procedure similar to that described above. MB photodegradation was studied from 10:00 am to 1:00 pm on sunny days during October in Ensenada, Baja California, Mexico. The degraded samples’ absorbance measurements were provided by UV-Vis spectroscopy. Degradation calculations were performed according to Equation (1):
η = 1 − (Ct/C0)
where η is degradation efficiency, Ct is dye concentration at any given time, and C0 is the initial dye concentration.

3. Results and Discussion

3.1. Fourier Transform Infrared Spectroscopy Analysis

Figure 1 shows the FTIR spectra in ATR mode for the Tilia cordata extract and the SnO2-1%, SnO2-2%, and SnO2-4% NPs. The Tilia cordata spectrum in Figure 1a shows an absorption band centered at 3323 cm−1 that is attributed to the vibrations of the O–H bond; the signals located at 2925 and 2851 cm−1 can be attributed to the C–H bond vibrations of methyls and methylenes, respectively, whereas the absorption bands centered at 1731–1600 cm−1 are attributed to the C=O bond vibrational mode [36]. The SnO2 NPs with 1%, 2%, and 4% extract (Figure 1a,b) presented 2 characteristic signals centered at 605 and 480 cm−1, which are attributed to the asymmetric and symmetric Sn–O and Sn–O–Sn stretching, respectively [37,38]. Additionally, it is possible to observe the absorption bands corresponding to Tilia cordata located at 3400 cm−1, 2925 cm−1, 2851 cm−1, and 1636 cm−1, indicating the presence of extract molecules in the SnO2 synthesized products [39,40].

3.2. X-ray Diffraction

The XRD patterns of the SnO2-1%, SnO2-2%, and SnO2-4% NPs are shown in Figure 2. The diffractograms display several well-defined peaks located at 26.53°, 33.82°, 37.95°, 51.75°, 54.5°, 57.85°, 61.88°, 64.75°, and 65.9° 2θ that correspond to planes (110), (101), (200), (211), (220), (002), (310), (112), and (301), respectively. The crystallographic planes are assigned to the SnO2, tetragonal rutile crystal phase, according to the crystallographic chart No.41-1445 from JCPDS database, confirming crystalline SnO2 achieved using 1%, 2%, and 4% (w/v) Tilia cordata extract [41,42]. Additionally, the absence of other peaks indicates only one phase without impurities.
The SnO2 NPs crystallite size was determined using the Debye–Scherrer model, Equation (2).
τ = (Kλ)/(βcos θ)
where τ is the average crystallite size, K is the dimensionless shape factor at ~0.9, λ is the X-ray wavelength, β is the full width at half maximum intensity (FWHM), and θ is the Bragg angle. According to Equation (2), the crystallite sizes of the SnO2-1%, SnO2-2%, and SnO2-4% synthesized NPs are 15.96 nm, 16.38 nm, and 21.51 nm, respectively, indicating an increase in crystallite size as extract concentration increases, denoting that the use of Tilia cordata extract facilitates SnO2 crystal growth [43].

3.3. Optical Properties

Figure 3 illustrates the UV-Vis absorption spectra of the SnO2-1%, SnO2-2%, and SnO2-4% NPs. In all the syntheses, an absorption edge centered ~300 nm was detected, which is characteristic of SnO2 semiconductors according to reports in the literature [44,45]. Bandgap calculation was performed using the Tauc model, Equation (3): [46]
α(v)hv = K(hv − Eg)n
where Eg corresponds to bandgap energy, hv is photon energy, K is a constant, α is the absorption coefficient, and ‘n’ is an index that can take on different values depending on the interband transition mechanism [47]. Figure 3b exhibits the (αhv)2 versus energy graphs over which the bandgap values were plotted and found to be 3.61 eV, 3.59 eV, and 3.64 eV for SnO2-1%, SnO2-2%, and SnO2-4% NPs, respectively. These values are similar to the 3.59 eV [48] y 3.6 Ev [49] reported in the literature for SnO2.

3.4. Photoluminescence

Photoluminescence studies are important for investigating structural defects in NPs such as oxygen vacancies. Figure 4 shows the PL spectra for the SnO2 NPs synthesized with different concentrations of Tilia cordata extract. The spectra were taken using a 350 nm excitation wavelength. SnO2-1%, SnO2-2%, and SnO2-4% NPs present different emission bands centered at 360 nm, 379 nm for UV region and bands located at 448 nm, 466 nm, 480 nm, 490 nm, 509 nm, 525 nm and 559 nm, which correspond to the visible region. UV bands are related to the direct combination of electrons (e−) from the conduction band (CB) to holes (h+) in the valence band (VB) [50]. On the other hand, the green emission centered at 509 nm is attributed to the oxygen vacancies that help reduce the recombination rate of the electron–hole pairs, increasing their lifetime [51].

3.5. Surface Morphology

The SEM micrographs in Figure 5 show the surface morphology changes of the synthesized SnO2 NPs with different Tilia cordata extract concentrations. Figure 5a depicts the SnO2-1% NPs, which present a quasi-spherical morphology with agglomerations. Figure 5b illustrates a similar SnO2-2% NP morphology to SnO2-1%, but scattered and uniform in size with a few larger particles. Moreover, the SnO2-4% NPs shown in Figure 5c present bumps supported on cluster-like particles and scattered, quasi-spherical particles; this could be due to the low nanoparticles nucleation caused by the high organic matter content [52,53], similar to those reported in the literature for SnO2 NPs biosynthesis using natural extracts [30]. The EDX analyses (Table 1) elucidated three main elements, C, O, and Sn. Carbon can be associated with organic matter from Tilia cordata extracts, as shown by FTIR, because the amount of carbon increases as the concentration of the extract increases [54]. The occurrence of Sn and O elements confirms that the NPs obtained are SnO2 [55].

3.6. Photocatalytic Activiy

The photocatalytic activity of the SnO2 NPs was evaluated for the MB dye photodegradation under UV and solar radiation. The results of MB degradation under UV radiation are shown in Figure 6a. It was observed that during the first hour, 73%, 90%, and 88% of dye was degraded by the SnO2-1%, SnO2-2%, and SnO2-4% NPs, respectively, proving to have a significant effect on dye degradation. Maximum MB degradation percentages of 94%, 99%, and 99% were reached at 180 min by the SnO2-1%, SnO2-2%, and SnO2-4% samples, respectively. The difference in MB-degradation percentage can be attributed to the SnO2 NPs size since the nanometric scale allows better dye, surface–adsorption, and provides higher availability of active sites to initiate degradation [56]. Additionally, the extract can function as a photosensitizer, thereby increasing the amount of extract increases photocatalytic activity [57]. Figure 6b shows the changes in the UV-Vis absorption spectrum of MB dye in the presence of SnO2-2% NPs, where absorbance decreases over time, indicating concentration reduction. Additionally, the photograph in Figure 6b shows the photocatalysis process, which is visible as the color changes gradually. Correspondingly, Figure 6c shows the MB degradation percentages under solar radiation, where 48%, 68%, and 83.5% of MB were degraded after 180 min with SnO2-1%, SnO2-2%, and SnO2-4% NPs, respectively, implying that under these study conditions there is a correlation between the amount of extract used in the synthesis of the NPs and the percentage of dye degradation.
These results confirm the successful synthesis of SnO2 NPs using Tilia cordata extract and their excellent photocatalytic activity towards MB degradation. Table 2 mentions several SnO2 NPs synthesis publications that evaluated MB photocatalysis in similar conditions. Certain stabilizing agents such as Brassica oleracea L. var. botrytis and Jujube extracts have similar effects on MB photocatalysis. However, the NPs synthesized with Tilia cordata transcend for their high efficiency, degrading up to 90% of the dye in just 60 min under UV radiation and 83.5% under solar radiation after 180 min.

3.7. Degradation Mechanism

The dye degradation mechanism through photocatalysis using SnO2 NPs is shown in Figure 7. The process is activated by the incidence of solar or UV radiation that promotes electrons from the valence band (VB) to the conduction band (CB), originating electron–hole pairs (e−/h+) in both [61]. The e−/h+ pairs can react directly with H2O and O2, generating highly reactive species such as hydrogen peroxide, hydroxyl radicals, and superoxide radicals. The radical species O2• and OH• interact with dye molecules, degrading them to mineralization [66,67]. The MB degradation process (Figure 8) by photocatalysis with SnO2 NPs can be set off by photogenerated holes as well as by OH• radicals, which attack the C–S+=C functional groups of MB, generating sulfoxide groups (C–S(=O)–C). Then, the OH• radicals attack the sulfoxide group causing ring dissociation; the byproducts react to generate intermediate byproducts until the dye is degraded to mineralization, as reported by Bhattacharjee et al. [68].

4. Conclusions

In summary, SnO2 NPs were successfully synthesized by a green and simple method, using Tilia cordata extract. The effects of extract concentration were evaluated, and it was determined that it had a significant influence on the nanoparticles’ optical and morphological properties, as well as crystallite size and photocatalytic activity. The morphology analyses revealed that all SnO2 NPs presented a quasi-spherical morphology and agglomerations, while the structural analyses of all synthesized materials revealed a rutile-type tetragonal crystalline structure, with crystallite sizes of 15.96 nm, 16.38 nm, and 21.51 nm for SnO2-1%, SnO2-2%, and SnO2-4%, respectively, whereas the bandgap values remained at ~3.6 eV. The SnO2 NPs presented excellent photocatalytic activity; UV radiation had a significant effect on the degradation of MB, resulting in 73%, 90%, and 88% degradation by SnO2-1%, SnO2-2%, and SnO2-4% during the first hour. Moreover, the degradation percentages reached under solar radiation after 180 min were 48%, 68%, and 83.5%, with SnO2-1%, SnO2-2%, and SnO2-4%, respectively. These studies presented similar and improved photocatalytic properties correspondingly to literature reports, demonstrating that Tilia cordata, used as a reducing agent, is a good candidate for the biosynthesis of semiconductor materials with application in the degradation of organic dyes by photocatalysis.

Author Contributions

E.Q.G. investigation, methodology, formal analysis, writing—original draft. E.L.M. investigation, methodology, formal analysis. R.V.Q.R. conceptualization, formal analysis, writing—review & editing. H.E.G.G. methodology, visualization. Y.A.B.L. investigation, visualization. E.V.V. investigation, visualization. F.A.M. investigation, visualization A.R.V.N. methodology, visualization P.A.L.M. conceptualization, investigation, writing—review & editing, supervision, validation. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

R.V.Q.R. acknowledgment CONACyT for postdoctoral scholarship.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Danish, M.S.S.; Estrella, L.L.; Alemaida, I.M.A.; Lisin, A.; Moiseev, N.; Ahmadi, M.; Nazari, M.; Wali, M.; Zaheb, H.; Senjyu, T. Photocatalytic Applications of Metal Oxides for Sustainable Environmental Remediation. Metals 2021, 11, 80. [Google Scholar] [CrossRef]
  2. Routoula, E.; Patwardhan, S. v Degradation of Anthraquinone Dyes from Effluents: A Review Focusing on Enzymatic Dye Degradation with Industrial Potential. Environ. Sci. Technol. 2020, 54, 647–664. [Google Scholar] [CrossRef] [PubMed]
  3. Al-Tohamy, R.; Ali, S.S.; Li, F.; Okasha, K.M.; Mahmoud, Y.A.-G.; Elsamahy, T.; Jiao, H.; Fu, Y.; Sun, J. A critical review on the treatment of dye-containing wastewater: Ecotoxicological and health concerns of textile dyes and possible remediation approaches for environmental safety. Ecotoxicol. Environ. Saf. 2022, 231, 113160. [Google Scholar] [CrossRef] [PubMed]
  4. Topaç, F.O.; Dindar, E.; Uçaroğlu, S.; Başkaya, H.S. Effect of a sulfonated azo dye and sulfanilic acid on nitrogen transformation processes in soil. J. Hazard. Mater. 2009, 170, 1006–1013. [Google Scholar] [CrossRef] [PubMed]
  5. Schneider, K.; Hafner, C.; Jäger, I. Mutagenicity of Textile Dye Products. J. Appl. Toxicol. Int. J. 2004, 24, 83–91. [Google Scholar] [CrossRef] [PubMed]
  6. Arshad, H.; Imran, M.; Ashraf, M. Toxic effects of Red-S3B dye on soil microbial activities, wheat yield, and their alleviation by pressmud application. Ecotoxicol. Environ. Saf. 2020, 204, 111030. [Google Scholar] [CrossRef]
  7. Kishor, R.; Bharagava, R.N.; Saxena, G. Industrial Wastewaters: The Major Sources of Dye Contamination in the Environment, Ecotoxicological Effects, and Bioremediation Approaches. In Recent Advances in Environmental Management; CRC Press: Boca Raton, FL, USA, 2018; pp. 1–25. ISBN 1351011251. [Google Scholar]
  8. Zhou, Y.; Lu, J.; Zhou, Y.; Liu, Y. Recent Advances for Dyes Removal Using Novel Adsorbents: A Review. Environ. Pollut. 2019, 252, 352–365. [Google Scholar] [CrossRef]
  9. Dotto, J.; Fagundes-Klen, M.R.; Veit, M.T.; Palácio, S.M.; Bergamasco, R. Performance of different coagulants in the coagulation/flocculation process of textile wastewater. J. Clean. Prod. 2018, 208, 656–665. [Google Scholar] [CrossRef]
  10. Le, T.M.H.; Nuisin, R.; Mongkolnavin, R.; Painmanakul, P.; Sairiam, S. Enhancing dye wastewater treatment efficiency in ozonation membrane contactors by chloro- and fluoro-organosilanes’ functionality on hydrophobic PVDF membrane modification. Sep. Purif. Technol. 2022, 288, 120711. [Google Scholar] [CrossRef]
  11. Shoukat, R.; Khan, S.J.; Jamal, Y. Hybrid anaerobic-aerobic biological treatment for real textile wastewater. J. Water Process Eng. 2019, 29, 100804. [Google Scholar] [CrossRef]
  12. Fujishima, A.; Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature 1972, 238, 37–38. [Google Scholar] [CrossRef] [PubMed]
  13. Saravanan, A.; Kumar, P.S.; Vo, D.-V.N.; Yaashikaa, P.R.; Karishma, S.; Jeevanantham, S.; Gayathri, B.; Bharathi, V.D. Photocatalysis for removal of environmental pollutants and fuel production: A review. Environ. Chem. Lett. 2020, 19, 441–463. [Google Scholar] [CrossRef]
  14. Malato, S.; Maldonado, I.M.; Fernández-Ibáñez, P.; Oller, I.; Polo, I.; Sánchez-Moreno, R. Decontamination and Disinfection of Water by Solar Photocatalysis: The Pilot Plants of the Plataforma Solar de Almeria. Mater Sci. Semicond. Process 2016, 42 Pt 1, 15–23. [Google Scholar] [CrossRef]
  15. Enesca, A. The Influence of Photocatalytic Reactors Design and Operating Parameters on the Wastewater Organic Pollutants Removal—A Mini-Review. Catalysts 2021, 11, 556. [Google Scholar] [CrossRef]
  16. Youssef, Z.; Colombeau, L.; Yesmurzayeva, N.; Baros, F.; Vanderesse, R.; Hamieh, T.; Toufaily, J.; Frochot, C.; Roques-Carmes, T.; Acherar, S. Dye-sensitized nanoparticles for heterogeneous photocatalysis: Cases studies with TiO2, ZnO, fullerene and graphene for water purification. Dye. Pigment. 2018, 159, 49–71. [Google Scholar] [CrossRef]
  17. El-Belely, E.F.; Farag, M.M.S.; Said, H.A.; Amin, A.S.; Azab, E.; Gobouri, A.A.; Fouda, A. Green Synthesis of Zinc Oxide Nanoparticles (ZnO-NPs) Using Arthrospira platensis (Class: Cyanophyceae) and Evaluation of their Biomedical Activities. Nanomaterials 2021, 11, 95. [Google Scholar] [CrossRef] [PubMed]
  18. Yousefi, S.R.; Alshamsi, H.A.; Amiri, O.; Salavati-Niasari, M. Synthesis, characterization and application of Co/Co3O4 nanocomposites as an effective photocatalyst for discoloration of organic dye contaminants in wastewater and antibacterial properties. J. Mol. Liq. 2021, 337, 116405. [Google Scholar] [CrossRef]
  19. Osman, N.S.; Sulaiman, S.N.; Muhamad, E.N.; Mukhair, H.; Tan, S.T.; Abdullah, A.H. Synthesis of an Ag3PO4/Nb2O5 Photocatalyst for the Degradation of Dye. Catalysts 2021, 11, 458. [Google Scholar] [CrossRef]
  20. Mallikarjunaswamy, C.; Pramila, S.; Nagaraju, G.; Ramu, R.; Ranganatha, V.L. Green Synthesis and Evaluation of Antiangiogenic, Photocatalytic, and Electrochemical Activities of BiVO4 Nanoparticles. J. Mater. Sci. Mater. Electron. 2021, 32, 14028–14046. [Google Scholar] [CrossRef]
  21. Mahdi, M.A.; Yousefi, S.R.; Jasim, L.S.; Salavati-Niasari, M. Green Synthesis of DyBa2Fe3O7.988/DyFeO3 Nanocomposites Using Almond Extract with Dual Eco-Friendly Applications: Photocatalytic and Antibacterial Activities. Int. J. Hydrogen Energy 2022, 47, 14319–14330. [Google Scholar] [CrossRef]
  22. Buniyamin, I.; Akhir, R.; Asli, N.A.; Khusaimi, Z.; Mahmood, M.R. Biosynthesis of SnO2 nanoparticles by aqueous leaves extract of Aquilaria malaccensis (agarwood). IOP Conf. Ser. Mater. Sci. Eng. 2021, 1092, 012070. [Google Scholar] [CrossRef]
  23. Maruthupandy, M.; Muneeswaran, T.; Chackaravarthi, G.; Vennila, T.; Anand, M.; Cho, W.-S.; Quero, F. Synthesis of chitosan/SnO2 nanocomposites by chemical precipitation for enhanced visible light photocatalytic degradation efficiency of congo red and rhodamine-B dye molecules. J. Photochem. Photobiol. A Chem. 2022, 430, 113972. [Google Scholar] [CrossRef]
  24. Gomathi, E.; Jayapriya, M.; Arulmozhi, M. Environmental benign synthesis of tin oxide (SnO2) nanoparticles using Actinidia deliciosa (Kiwi) peel extract with enhanced catalytic properties. Inorg. Chem. Commun. 2021, 130, 108670. [Google Scholar] [CrossRef]
  25. Luque, P.; Chinchillas-Chinchillas, M.; Nava, O.; Lugo-Medina, E.; Martínez-Rosas, M.; Carrillo-Castillo, A.; Vilchis-Nestor, A.; Madrigal-Muñoz, L.; Garrafa-Gálvez, H. Green synthesis of tin dioxide nanoparticles using Camellia sinensis and its application in photocatalytic degradation of textile dyes. Optik 2021, 229, 166259. [Google Scholar] [CrossRef]
  26. Garrafa-Galvez, H.; Nava, O.; Soto-Robles, C.; Vilchis-Nestor, A.; Castro-Beltrán, A.; Luque, P. Green synthesis of SnO2 nanoparticle using Lycopersicon esculentum peel extract. J. Mol. Struct. 2019, 1197, 354–360. [Google Scholar] [CrossRef]
  27. Sagadevan, S.; Lett, J.A.; Fatimah, I.; Lokanathan, Y.; Léonard, E.; Oh, W.C.; Hossain, M.A.M.; Johan, M.R. Current Trends in the Green Syntheses of Tin Oxide Nanoparticles and Their Biomedical Applications. Mater. Res. Express 2021, 8, 082001. [Google Scholar] [CrossRef]
  28. Yadav, A.; Kon, K.; Kratošová, G.; Durán, N.; Ingle, A.P.; Rai, M. Fungi as an efficient mycosystem for the synthesis of metal nanoparticles: Progress and key aspects of research. Biotechnol. Lett. 2015, 37, 2099–2120. [Google Scholar] [CrossRef]
  29. Al-Enazi, N.M.; Alwakeel, S.; Alhomaidi, E. Photocatalytic and biological activities of green synthesized SnO2 nanoparticles using Chlorella vulgaris. J. Appl. Microbiol. 2022. [Google Scholar] [CrossRef]
  30. Gour, A.; Jain, N.K. Advances in green synthesis of nanoparticles. Artif. Cells Nanomed. Biotechnol. 2019, 47, 844–851. [Google Scholar] [CrossRef] [Green Version]
  31. Suresh, K.C.; Surendhiran, S.; Kumar, P.M.; Kumar, E.R.; Khadar, Y.A.S.; Balamurugan, A. Green synthesis of SnO2 nanoparticles using Delonix elata leaf extract: Evaluation of its structural, optical, morphological and photocatalytic properties. SN Appl. Sci. 2020, 2, 1735. [Google Scholar] [CrossRef]
  32. Karthik, K.; Revathi, V.; Tatarchuk, T. Microwave-assisted green synthesis of SnO2 nanoparticles and their optical and photocatalytic properties. Mol. Cryst. Liq. Cryst. 2018, 671, 17–23. [Google Scholar] [CrossRef]
  33. Rathinabala, R.; Thamizselvi, R.; Padmanabhan, D.; Alshahateet, S.F.; Fatimah, I.; Sibhatu, A.K.; Weldegebrieal, G.K.; Razak, S.I.A.; Sagadevan, S. Sun light-assisted enhanced photocatalytic activity and cytotoxicity of green synthesized SnO2 nanoparticles. Inorg. Chem. Commun. 2022, 143, 109783. [Google Scholar] [CrossRef]
  34. D’Ambrosio, U. Tilia Platyphyllos y Tilia Cordata; Pardo De Santayana, M., Morales, R., Tardío, J., Molina, M., Eds.; Inventario; Ministerio De Agricultura y Pesca, Alimentación y Medio Ambiente: Madrid, Spain, 2018. [Google Scholar]
  35. Cittan, M.; Altuntaş, E.; Çelik, A. Evaluation of Antioxidant Capacities and Phenolic Profiles in Tilia cordata Fruit Extracts: A Comparative Study to Determine the Efficiency of Traditional Hot Water Infusion Method. Ind. Crops Prod. 2018, 122, 553–558. [Google Scholar] [CrossRef]
  36. Saygi, K.O.; Cacan, E. Antioxidant and cytotoxic activities of silver nanoparticles synthesized using Tilia cordata flowers extract. Mater. Today Commun. 2021, 27, 102316. [Google Scholar] [CrossRef]
  37. Beevi, A.F.; Sreekala, G.; Beena, B. Synthesis, characterization and photocatalytic activity of SnO2, ZnO nanoparticles against congo red: A comparative study. Mater. Today Proc. 2021, 45, 4045–4051. [Google Scholar] [CrossRef]
  38. Van, K.N.; Huu, H.T.; Thi, V.N.N.; le Thi, T.L.; Truong, D.H.; Truong, T.T.; Dao, N.N.; Vo, V.; Vasseghian, Y. Facile Construction of S-Scheme SnO2/g-C3N4 Photocatalyst for Improved Photoactivity. Chemosphere 2022, 289, 133120. [Google Scholar] [CrossRef]
  39. Mahakal, M.; Kutumbale, A.; Mehta, D.; Mehta, B.K. Green synthesis of zno nanoparticles from the methanolic extract of embelia ribes and their characterization by uv-visible, ftir, xrd and sem analysis. Int. J. Pharm. Biol. Sci. 2018, 8, 402–409. [Google Scholar]
  40. Ramesh, P.; Saravanana, K.; Manogar, P.; Johnson, J.; Vinoth, E.; Mayakannan, M. Green synthesis and characterization of biocompatible zinc oxide nanoparticles and evaluation of its antibacterial potential. Sens. Bio-Sens. Res. 2021, 31, 100399. [Google Scholar] [CrossRef]
  41. Ben Soltan, W.; Ammar, S.; Olivier, C.; Toupance, T. Influence of zinc doping on the photocatalytic activity of nanocrystalline SnO2 particles synthesized by the polyol method for enhanced degradation of organic dyes. J. Alloys Compd. 2017, 729, 638–647. [Google Scholar] [CrossRef]
  42. Wan, W.; Li, Y.; Ren, X.; Zhao, Y.; Gao, F.; Zhao, H. 2D SnO2 Nanosheets: Synthesis, Characterization, Structures, and Excellent Sensing Performance to Ethylene Glycol. Nanomaterials 2018, 8, 112. [Google Scholar] [CrossRef] [Green Version]
  43. Mustapha, F.; Jalil, A.; Mohamed, M.; Triwahyono, S.; Hassan, N.; Khusnun, N.; Hitam, C.; Rahman, A.F.A.; Firmanshah, L.; Zolkifli, A. New insight into self-modified surfaces with defect-rich rutile TiO2 as a visible-light-driven photocatalyst. J. Clean. Prod. 2017, 168, 1150–1162. [Google Scholar] [CrossRef]
  44. Mahmood, H.; Khan, M.; Mohuddin, B.; Iqbal, T. Solution-phase growth of tin oxide (SnO2) nanostructures: Structural, optical and photocatalytic properties. Mater. Sci. Eng. B 2020, 258, 114568. [Google Scholar] [CrossRef]
  45. Bhuvaneswari, K.; Nguyen, B.-S.; Nguyen, V.-H.; Nguyen, V.-Q.; Nguyen, Q.-H.; Palanisamy, G.; Sivashanmugan, K.; Pazhanivel, T. Enhanced photocatalytic activity of ethylenediamine-assisted tin oxide (SnO2) nanorods for methylene blue dye degradation. Mater. Lett. 2020, 276, 128173. [Google Scholar] [CrossRef]
  46. Tauc, J. Optical properties and electronic structure of amorphous Ge and Si. Mater. Res. Bull. 1968, 3, 37–46. [Google Scholar] [CrossRef]
  47. Yubero, F.; Jiménez, V.; Gonzalez-Elipe, A. Optical properties and electronic transitions of SnO2 thin films by reflection electron energy loss spectroscopy. Surf. Sci. 1998, 400, 116–126. [Google Scholar] [CrossRef]
  48. Abdelkader, E.; Nadjia, L.; Naceur, B.; Noureddine, B. SnO2 foam grain-shaped nanoparticles: Synthesis, characterization and UVA light induced photocatalysis. J. Alloys Compd. 2016, 679, 408–419. [Google Scholar] [CrossRef]
  49. Sadeghzadeh-Attar, A. Efficient photocatalytic degradation of methylene blue dye by SnO2 nanotubes synthesized at different calcination temperatures. Sol. Energy Mater. Sol. Cells 2018, 183, 16–24. [Google Scholar] [CrossRef]
  50. Wenderich, K.; Mul, G. Methods, Mechanism, and Applications of Photodeposition in Photocatalysis: A Review. Chem. Rev. 2016, 116, 14587–14619. [Google Scholar] [CrossRef]
  51. Aly, B. Controlled optoelectronic properties and abrupt change in photosensitivity by suppressing density of oxygen vacancies in SnO2 nanocrystalline thin films prepared at various spray-deposition temperatures. Phys. Scr. 2020, 95, 065807. [Google Scholar] [CrossRef]
  52. Oskam, G. Metal oxide nanoparticles: Synthesis, characterization and application. J. Sol-Gel Sci. Technol. 2006, 37, 161–164. [Google Scholar] [CrossRef]
  53. Jolivet, J.-P.; Henry, M.; Livage, J. Metal Oxide Chemistry and Synthesis: From Solution to Solid State; Wiley-Blackwell: New York, NY, USA, 2000; ISBN 0471970565. [Google Scholar]
  54. Jadoun, S.; Arif, R.; Jangid, N.K.; Meena, R.K. Green synthesis of nanoparticles using plant extracts: A review. Environ. Chem. Lett. 2020, 19, 355–374. [Google Scholar] [CrossRef]
  55. Yang, L.; Huang, J.; Liu, H.; Li, S.; Han, Y.; Qi, G.; Lv, M.; Shang, Y.; Ye, J. SnO2−x/Sb2O3 composites synthesized by mechanical milling method with excellent photocatalytic properties for isopropyl alcohol oxidation. J. Mater. Sci. Mater. Electron. 2020, 31, 8564–8577. [Google Scholar] [CrossRef]
  56. Nakibli, Y.; Mazal, Y.; Dubi, Y.; Wächtler, M.; Amirav, L. Size Matters: Cocatalyst Size Effect on Charge Transfer and Photocatalytic Activity. Nano Lett. 2017, 18, 357–364. [Google Scholar] [CrossRef] [PubMed]
  57. Rodwihok, C.; Wongratanaphisan, D.; Ngo, Y.L.T.; Khandelwal, M.; Hur, S.H.; Chung, J.S. Effect of GO Additive in ZnO/rGO Nanocomposites with Enhanced Photosensitivity and Photocatalytic Activity. Nanomaterials 2019, 9, 1441. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  58. Osuntokun, J.; Onwudiwe, D.C.; Ebenso, E.E. Biosynthesis and Photocatalytic Properties of SnO2 Nanoparticles Prepared Using Aqueous Extract of Cauliflower. J. Clust. Sci. 2017, 28, 1883–1896. [Google Scholar] [CrossRef]
  59. Honarmand, M.; Golmohammadi, M.; Naeimi, A. Biosynthesis of tin oxide (SnO2) nanoparticles using jujube fruit for photocatalytic degradation of organic dyes. Adv. Powder Technol. 2019, 30, 1551–1557. [Google Scholar] [CrossRef]
  60. Elango, G.; Roopan, S.M. Efficacy of SnO2 nanoparticles toward photocatalytic degradation of methylene blue dye. J. Photochem. Photobiol. B Biol. 2016, 155, 34–38. [Google Scholar] [CrossRef]
  61. Ramamoorthy, M.; Ragupathy, S.; Sakthi, D.; Arun, V.; Kannadasan, N. Synthesis of SnO2 loaded on corn cob activated carbon for enhancing the photodegradation of methylene blue under sunlight irradiation. J. Environ. Chem. Eng. 2020, 8, 104331. [Google Scholar] [CrossRef]
  62. Bhattacharjee, A.; Ahmaruzzaman, M. A green and novel approach for the synthesis of SnO2 nanoparticles and its exploitation as a catalyst in the degradation of methylene blue under solar radiation. Mater. Lett. 2015, 145, 74–78. [Google Scholar] [CrossRef]
  63. Kim, S.P.; Choi, M.Y.; Choi, H.C. Photocatalytic activity of SnO2 nanoparticles in methylene blue degradation. Mater. Res. Bull. 2016, 74, 85–89. [Google Scholar] [CrossRef]
  64. Sujatha, K.; Seethalakshmi, T.; Sudha, A.; Shanmugasundaram, O. Photocatalytic activity of pure, Zn doped and surfactants assisted Zn doped SnO2 nanoparticles for degradation of cationic dye. Nano-Struct. Nano-Objects 2019, 18, 100305. [Google Scholar] [CrossRef]
  65. Sagadevan, S.; Lett, J.A.; Alshahateet, S.F.; Fatimah, I.; Weldegebrieal, G.K.; Le, M.-V.; Leonard, E.; Paiman, S.; Soga, T. Photocatalytic degradation of methylene blue dye under direct sunlight irradiation using SnO2 nanoparticles. Inorg. Chem. Commun. 2022, 141, 109547. [Google Scholar] [CrossRef]
  66. Yang, X.; Wang, D. Photocatalysis: From Fundamental Principles to Materials and Applications. ACS Appl. Energy Mater. 2018, 1, 6657–6693. [Google Scholar] [CrossRef]
  67. Rosaline, D.R.; Suganthi, A.; Vinodhkumar, G.; Inbanathan, S.S.R.; Umar, A.; Ameen, S.; Akhtar, M.S.; LuizFoletto, E. Enhanced Sunlight-Driven Photocatalytic Activity of SnO2-Sb2O3 Composite towards Emerging Contaminant Degradation in Water. J. Alloys Compd. 2022, 897, 162935. [Google Scholar] [CrossRef]
  68. Bhattacharjee, A.; Ahmaruzzaman, M.; Devi, T.B.; Nath, J. Photodegradation of Methyl Violet 6B and Methylene Blue Using Tin-Oxide Nanoparticles (Synthesized via a Green Route). J. Photochem. Photobiol. A Chem. 2016, 325, 116–124. [Google Scholar] [CrossRef]
Symmetry 14 02231 g001 550
Figure 1. FTIR-ATR spectra of (a) Tilia cordata extract and SnO2-1%, SnO2-2%, and SnO2-4% NPs and (b) insert: infrared region from 750 cm−1 to 450 cm−1.
Figure 1. FTIR-ATR spectra of (a) Tilia cordata extract and SnO2-1%, SnO2-2%, and SnO2-4% NPs and (b) insert: infrared region from 750 cm−1 to 450 cm−1.
Symmetry 14 02231 g001
Symmetry 14 02231 g002 550
Figure 2. XRD patterns of SnO2 NPs synthesized with different concentrations of Tilia cordata extract.
Figure 2. XRD patterns of SnO2 NPs synthesized with different concentrations of Tilia cordata extract.
Symmetry 14 02231 g002
Symmetry 14 02231 g003 550
Figure 3. (a) UV-Vis spectra of SnO2 NPs synthesized with Tilia cordata extract, and (b) Tauc model plot of SnO2-1%, SnO2-2%, and SnO2-4% NPs synthesized with Tilia cordata, where the x-axis intercept was used to determine the bandgap.
Figure 3. (a) UV-Vis spectra of SnO2 NPs synthesized with Tilia cordata extract, and (b) Tauc model plot of SnO2-1%, SnO2-2%, and SnO2-4% NPs synthesized with Tilia cordata, where the x-axis intercept was used to determine the bandgap.
Symmetry 14 02231 g003
Symmetry 14 02231 g004 550
Figure 4. PL spectra of SnO2 NPs synthesized with Tilia cordata extracts.
Figure 4. PL spectra of SnO2 NPs synthesized with Tilia cordata extracts.
Symmetry 14 02231 g004
Symmetry 14 02231 g005 550
Figure 5. SEM micrographs of (a) SnO2-1%, (b) SnO2-2%, and (c) SnO2-4% NPs.
Figure 5. SEM micrographs of (a) SnO2-1%, (b) SnO2-2%, and (c) SnO2-4% NPs.
Symmetry 14 02231 g005
Symmetry 14 02231 g006a 550Symmetry 14 02231 g006b 550
Figure 6. MB photocatalytic degradation (a) under UV radiation, (b) UV-Vis absorption spectra of the MB dye vs. time using SnO2-2% NPs as photocatalysts, and (c) photocatalytic MB degradation under solar radiation.
Figure 6. MB photocatalytic degradation (a) under UV radiation, (b) UV-Vis absorption spectra of the MB dye vs. time using SnO2-2% NPs as photocatalysts, and (c) photocatalytic MB degradation under solar radiation.
Symmetry 14 02231 g006aSymmetry 14 02231 g006b
Symmetry 14 02231 g007 550
Figure 7. MB degradation mechanism with SnO2 NPs synthesized utilizing Tilia cordata extract.
Figure 7. MB degradation mechanism with SnO2 NPs synthesized utilizing Tilia cordata extract.
Symmetry 14 02231 g007
Symmetry 14 02231 g008 550
Figure 8. Proposed MB degradation mechanism through photocatalysis; adapted from [68].
Figure 8. Proposed MB degradation mechanism through photocatalysis; adapted from [68].
Symmetry 14 02231 g008
Table
Table 1. EDX of SnO2 NPs synthesized with different concentrations of Tilia cordata extract.
Table 1. EDX of SnO2 NPs synthesized with different concentrations of Tilia cordata extract.
% C% O% Sn
SnO2-1%8.9626.2464.8
SnO2-2%10.6426.5862.78
SnO2-4%18.2128.9652.83
Table
Table 2. Comparison of MB photodegradation using SnO2 NPs synthesized by different methods.
Table 2. Comparison of MB photodegradation using SnO2 NPs synthesized by different methods.
Method of SynthesisReducing/
Stabilizing
Agent		RadiationNPs Dose
(mg)		Time (min)Degradation (%)Ref.
Plant extractBrassica oleracea L.
var. botrytis		UV2018088.23–91.89[58]
Plant extractJujubeSolar830090[59]
Plant extractCyphomandra
betacea		UV2570>99[60]
Plant extractZea Maiz activated
carbon		Solar2012071.92[61]
MicrowaveArginineSolar1024096.4[62]
PrecipitationH2O2, KOHUV418079[63]
CoprecipitationAmmonia, surfactantsUV10012053[64]
HydrotermalNaOH, etOHSolar20, 40, 6012083, 97, 95[65]
Plant extractTilia cordataUV—Solar506090This work
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

González, E.Q.; Medina, E.L.; Robles, R.V.Q.; Gálvez, H.E.G.; Lopez, Y.A.B.; Viveros, E.V.; Molina, F.A.; Nestor, A.R.V.; Morales, P.A.L. A Study of the Optical and Structural Properties of SnO2 Nanoparticles Synthesized with Tilia cordata Applied in Methylene Blue Degradation. Symmetry 2022, 14, 2231. https://doi.org/10.3390/sym14112231

AMA Style

González EQ, Medina EL, Robles RVQ, Gálvez HEG, Lopez YAB, Viveros EV, Molina FA, Nestor ARV, Morales PAL. A Study of the Optical and Structural Properties of SnO2 Nanoparticles Synthesized with Tilia cordata Applied in Methylene Blue Degradation. Symmetry. 2022; 14(11):2231. https://doi.org/10.3390/sym14112231

Chicago/Turabian Style

González, Eduardo Quintero, Eder Lugo Medina, Reina Vianey Quevedo Robles, Horacio Edgardo Garrafa Gálvez, Yolanda Angelica Baez Lopez, Eunice Vargas Viveros, Ferdinanda Aguilera Molina, Alfredo Rafael Vilchis Nestor, and Priscy Alfredo Luque Morales. 2022. "A Study of the Optical and Structural Properties of SnO2 Nanoparticles Synthesized with Tilia cordata Applied in Methylene Blue Degradation" Symmetry 14, no. 11: 2231. https://doi.org/10.3390/sym14112231

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop