Green Synthesis of Recyclable BaPbFe2O6 Nanoparticles for Photocatalytic Removal of Organic Dye Pollutant

Introduction

Human activities are the cause of pollution. Due to the excessive release of industrial wastes to the environment, water, soil and land are polluted. In order to overcome this problem, special attention should be paid to our natural resources. waste water is contaminated with many contaminants that are difficult to remove using conventional water treatment methods. ¹ The biggest challenge of the textile industry today is to create fabrics with long- lasting colors that do not fade in different weather conditions. It is estimated that textile production is responsible for about 20% of the world’s water pollution. Most of these fabrics are made from synthetic fibers and the current goal is to create new dyes that can bind materials well. Brilliant green is an arylmethane dye that is difficult to remove because these molecules are stable and do not break easily. It also has many other medicinal uses, so avoiding it is inevitable.It is also used as an antiseptic for the injured area after surgery and as an anti-inflammatory and antiseptic if diluted with alcohol. Many microscopic flora and fauna can be lost from the presence of a small amount of green color. Exposure to it in humans can cause digestive problems, stomach upset, eye irritation, and in some severe cases, blindness  ².

Few inorganic semiconductor nanomaterials for the photocatalytic degradation of organic pollutants in wastewater are promising catalyst as they are non-toxic, inexpensive, photostable, morphologically diverse and reusable ³. In recent years various nanomaterials have been used as photo-catalysts in photo-catalytic degradation. The performance of some photocatalytic oxides such as Fe(III) doped PbO₂ ⁴ , Fe₃O₄ ⁵ , strontium doped BaO⁶ became more attractive due to narrow band gap.

Due to their chemical stability, current wastewater treatment technologies cannot remove dyes from industrial wastewater. However, degradation by advanced oxidation process (AOP) using metal oxide semiconductors has proven beneficial due to its high efficiency, efficient degradation, non-toxicity and ease⁷. The AOPs involves the production of many reactive chemicals such as hydroxyl radicals , superoxide , hydrogen peroxide and molecular oxygen ( O₂), and almost all organic pollutants can be processed into non-toxic CO₂ and H₂O using light catalyst. During dye degradation using BaPbFe₂O₆, the dye is usually irradiated with BaPbFe₂O₆ nanoparticles under UV light.

Materials And Methods 

Nitrate salts of Barium, Lead nitrate and Iron nitrate are used of analytical grade (merck), NaOH is used for precipitation purpose. EDTA is used for scavenger test. Brilliant green dye is used in present investigation of degradation of dye.

Synthesis Of Nano-Sized BaPbFe₂O₆ Photocatalyst

The co-precipitation method was used to synthesize the BaPbFe₂O₆ nano particles. For this, 5N sodium hydroxide solution was added to a mixture of 0.1 M [Ba(NO₃)₂], 0.1M [Pb(NO₃)₂], 0.1M [Fe(NO₃)₃] solution and stirred at room temperature for 2 h. . The solution was then kept standstill for 8 h to obtain the precipitate. It was then washed by distilled water multiple times and dehumidified in oven at 80 °C. It was calcined at 500 °C for 5h to obtain BaPbFe₂O₆ nano-particles. A brown colored fine powder of semiconductor with yield 96.40% was obtained. The nano-particles were then stored in desiccators in the dark for further characterization.

Characterization

UV–Vis spectra show maximum absorbance at 199.2nm with an optical bandgap of ≈5.45 eV, respectively. The absorption coefficient (α) is calculated using⁸:

α=2.303A/t

Where,

A = absorbent;  t= sample thickness

The EDX spectrum of BaPbFe₂O₆ NPs, has strong band for Ba, Pb, Fe, and O bands with elemental weight percent of 4.83, 5.24, 12.91and 77.02, respectively, confirming the synthesis of BaPbFe₂O₆ NPs.

XPS spectrum of composite nanomaterial synthesized shows two peaks of Pb 4f_7/2   136.7 and 138 eV;  711.87eV and 724.7eV that can be attributed to Fe 2p _3/2 and Fe 2p_1/2, 780.1 and 795.72 corresponding to Ba 3d_5/2 and 3d_5/2 and a broad peak at 531.23 eV to 533.27eV are attributed to  oxygen vacancies⁹.

 The XRD analysis results of BaPbFe₂O₆ NPs and diffraction peaks are located at 24.03°, 34.38°, 40.93°, 42.21°, 44.21° corresponding to  (101), (110),(111), (113) and (103) planes respectively^10,11. The average size of pure BaPbFe₂O₆ nanoparticle  is detected to be 12.31 nm.

The FTIR band of BaPbFe₂O₆ exhibits low intensity at 692.55 cm⁻¹ and high intensity peak at 856.06 cm⁻¹ this indicates the presence of BaO^12,13 and a strong band below 700 cm^-1 is attributed to Fe-O stretching.  Fe-O stretching mode of Fe₂O₃ ¹⁴ appears at 532 cm^-1  and 500–600 cm⁻¹ is attributed to the stretching band of Pb-O ¹⁵.

Thermal analysis (TGA) of nanomaterials  was carried out at a heating count of 15 °C/min, and major weight loss of nanomaterial occurred in the range of 350 °C to about 600 °C  this indicates loss of OH.

The Photoluminescence (PL) intensity reduction is evident, and the broad PL emission peak is located at 471.7, 627.5 and 548.2 nm,  resulting from direct excitation of BaPbFe₂O₆ at the 263.2 nm region¹⁶.

The decrease in PL intensity is shown in Figure 4. The decrease in PL intensity can be attributed to the stabilization of charge carriers¹⁷. As shown, direct excitation of  BaPbFe₂O₆ at 263.2nm results in PL emissions with peaks at 471.7, 627.5 and 548.2 nm.

Table 1: Percentage elements by EDS

Element	Weight %	Atomic %
O K	33.28	77.02
Fe K	19.47	12.91
Ba L	17.93	4.83
Pb M	29.32	5.24
Total	100.00

 

Figure 1: XRD patterns of Photocatalyst Click here to View Figure

Figure 2: FTIR spectra of photocatalyst Click here to View Figure

Figure 3: TGA spectra of photocatalyst Click here to View Figure

Figure 4: Photoluminescence spectrum. Click here to View Figure

Figure 5: UV-VIS-NIR absorbance Spectra of photocatalyst. Click here to View Figure

HR-TEM analysis

High-resolution transmission electron microscopy (HRTEM) is a type of imaging mode of the TEM that allows the imaging of the crystal structure at atomic scale¹⁸. It can be seen from the image that sample has irregular particles formed by the agglomeration of small spherical/cylindrical particles.  Nanoparticles have high unsaturated surface energy and therefore have a strong tendency to aggregate.

Figure 6: HRTEM images of photocatalyst Click here to View Figure

Photocatalytic Activity of BaPbFe₂O₆ Nanoparticles

The green hue of brilliant green dye degradation over the synthesized BaPbFe₂O₆ under UV irradiation was used to assess the photocatalytic activity of BaPbFe₂O₆. The graph of percentage degradation versus time under sunlight is shown in Figure 7. The findings showed that after 20 minutes in the presence of both BaPbFe₂O₆ and light, the percentage of dye degradation had reached 86.89%. The findings point to strong correlations, which support pseudo-first order kinetics for the process.

Figure 7: Photo Catalytic activity of BaPbFe2O6 for degradation of BG dye Click here to View Figure

Effect of pH

The effect of pH on the rate of dye degradation was examined in pH range 6.4-9.5 for BaPbFe₂O₆, keeping all other parameters the same. The graph of % degradation against time at various pH values under solar radiation is displayed in Figure 8. It was discovered that the rate of reaction rises as pH rises and that, once it reaches its maximum value at pH 9.5, it decreases with additional pH increase.

The increase in reaction rate up to pH 9.5 may be due to the increase in  ^–OH ions formed as pH increases. The ^–OH ions react with the h⁺ (hole) to form more OH radicals that interact with and disrupt color molecules.  Increasing the pH causes the constant value of the catalyst activity to decrease, the catalyst to deteriorate and the color to become almost neutral because of the absorption of ^–OH ions on the catalyst surface.¹⁹ 

Figure 8: Photo-degradation of BG dye on BaPbFe2O6 on different pH Click here to View Figure

Effect of dye concentration

The degradation rate was shown to be affected by changes in brilliant green dye concentration 0.4 × 10⁻⁵ to 1.6 × 10⁻⁵ M while maintaining the same values for all other parameters. Figure 9 represents the graph of % degradation versus time in different dye concentration with sunlight exposure. As the dye concentration increases, the reaction  rate decreases as the number of dye molecules increases, and therefore the collision between the dye molecules  andOH radicals decreases. Therefore, rate of reaction decreases. ²⁰

Figure 9: Photo degradation of BG dye on BaPbFe2O6 on different Concentrations of Dye (in 10-5 M) Click here to View Figure

Effect of amount of catalyst

Other parameters remaining the same, various amount of catalyst changes the rate of dye discoloration in the range of 0.04g to 0.16 g. It is clear from aforementioned statistics that the degradation rate rises with the amount of catalyst as the catalyst concentration ranges from 0.04g to 0.120 g. The rate of reaction decreases with further increase in the catalyst concentration. This is due to the fact that  catalyst surface area increases as the amount of catalyst increases. However, when the amount of catalyst is increased above a limit, the catalyst entirely occupies bottom of the reaction vessel, now only the thickness of the catalyst layer is increased and not the exposed surface area of the catalyst ²¹. Figure 10 shows the  effect of change in catalyst dosage on the rate of dye degradation versus sun exposure time.

Figure 10: Photodegradation of BG dye on BaPbFe2O6 on different photocatalyst Dosage (in gm). Click here to View Figure

Effect of light intensity

All else being constant, the effect of change of  light intensity on the rate of color degradation was also examined for BaPbFe₂O₆. Figure 11 shows plot of percentage degradation compared to sunlight exposure time at different light intensities. The statistics show that the reaction rate of degradtion increases as the irradiation intensity increases, with the highest rate of degradation is observed at 1850 W m⁻² for catalyst. This can be elucidated by the fact that when the irradiation intensity increases, the number of photons/quanta  hitting per unit area of catalyst also increases, and this results in higher rate of dye molecule degradation ²².  Additionally, the use of higher light is avoided as the use of additional light may cause some thermal side reactions.

Figure 11: Photodegradation of BG dye on BaPbFe2O6 on different Intensities of Light (in W/m2). Click here to View Figure

Mechanism

On the basis of the experimental observations a tentative mechanism has been proposed for the degradation of brilliant green dye by heterogeneous photocatalyst²³.

Photocatalyst + hv  → photocatalyst ( e^– , h⁺)

H₂O₂ + 2h⁺  → O₂ + 2h⁺

OH^– + h⁺ → ^.OH

H₂O + h⁺  → H⁺ + ^.OH                         

Figure 12: Mechanism of Photocatalytic Dye Degradation Click here to View Figure

Effect of Scavenger on the Photocatalytic Degradation Efficiency of the BG Dye:

The photocatalytic dye degradation efficiency of all products depends on the separation competence of electron-hole pairs (e⁻─h⁺), leading to the formation of active species like superoxide and hydroxyl radicals (·O₂⁻ and ·OH⁻) ⁽²⁴⁾. The EDTA has been used as a scavenger for hydroxyl radicals. Degradation of BG dyes with the nanomaterial BaPbFe₂O₆ in the presence of 5 ml of 1N EDTA. After 45 minutes, degradation was complete and only 4.85% dyes was distorted.

Figure 13: Effect of Scavenger on Dye Degradation Click here to View Figure

Conclusion

It is concluded that the nano-particles BaPbFe₂O₆ were produced using co-precipitation method. The structure and morphology of nano-particles were examined using XRD, FE-SEM, EDS, XPS, HR-TEM and UV-VIS-NIR analysis. The average grain size of these particles is 12.31 nm, and there are regular particles formed by small spherical/cylindrical particles. It was found that the prepared photocatalyst was effective in the photo degradation of BG dyes in an aqueous environment. When light intensity is high the photo degradation rate increases as pH increases up to an optimal level, at a low initial concentration of dye. During heterogeneous photocatalytic process, OH radicals react with dye molecules and break down them into smaller particles such as H₂O, CO₂, NO₃⁻ ions etc.

Acknowledgment

I would like to acknowledge and give my warmest thanks to my supervisor Prof Shipra Bhardwaj who made this work possible. Her guidance and advice carried me through all the stages of writing my research paper. All authors contributed significantly to this manuscript, participated in reviewing/editing and approved the final draft for publication. The research profile of the authors can be verified from their ORCID ids, given below:

References

1. Perez-Cuapio, R., Alvarado, J. A., Juarez, H., & Sue, H. J. Sun irradiated high efficient photocatalyst ZnO nano-particles obtained by assisted microwave irradiation. Materials Science and Engineering: B, 289, 2023,116263.
   CrossRef
2. S. Santosh, G. Himanshu, D. Soniya, S.K. Nawal, Applied Water Science, 12, 2022 p. 61.  
3. S. Maddila, E.O. Oseghe, S.B. Jonnalagadda J. Chem. Tech. Biotech. 91,2016,1 pp. 385-393.
   CrossRef
4. El Aggadi, S., Ennouhi, M., Boutakiout, A., Ennoukh, F. E., & El Hourch, A. Iron (III)-doped PbO2 and its application as electrocatalyst for decomposition of phthalocyanine dye. Environmental Science and Pollution Research, 30(27), 2023 70183-70193.
   CrossRef
5.  Zhang, Y., Yang, Q., Yue, L., Liu, Q., Luo, Y., Wu, J., & Sun, X.. Biomass juncus derived carbon modified with Fe3O4 nano-particles toward activating peroxymonosulfate for efficient degradation of tetracycline. Journal of Water Process Engineering, 51, 2023, 103324
   CrossRef
6. Kamran, M. A., Siddique, S., Ullah, S., Alharbi, T., Raza, M., Usama, M., & Zou, B. Bifunctional strontium-doped barium oxide nanorods as promising photocatalysts and electrodes for energy storage applications. Journal of Energy Storage, 67, 2023, 107598.
   CrossRef
7. Priyadharsan, A., Ranjith, R., Karmegam, N., Thennarasu, G., Ragupathy, S., Oh, T. H., & Ramasundaram, S.  Effect of metal doping and non-metal loading on light energy driven degradation of organic dye using ZnO nanocatalysts. Chemosphere, 330, 2023, 138708.
   CrossRef
8. Sharma, G., Kumar, A., Sharma, S., Naushad, M., Dhiman, P., Vo, D. V. N., & Stadler, F. J. (2020). Fe3O4/ZnO/Si3N4 nano-composite based photocatalyst for the degradation of dyes from aqueous solution. Materials Letters, 278, 2020, 128359.
   CrossRef
9. Verhoeven, J. T., & Van Doveren, H. XPS studies on Ba, BaO and the oxidation of Ba. Applications of Surface Science, 5(4), 1980, 361-373.
   CrossRef
10. Naz, F., Saeed, K. Synthesis of barium oxide nanoparticles and its novel application as a catalyst for the photo degradation of malachite green dye. Appl Water Sci 12, 2022, 121.
    CrossRef
11. Ikram, M., Haider, A., Imran, M., Haider, J., Naz, S., Ul-Hamid, A. & Ali, S. Assessment of catalytic, antimicrobial and molecular docking analysis of starch-grafted polyacrylic acid doped BaO nanostructures. International Journal of Biological Macromolecules, 230, 2023, 123190.
    CrossRef
12. Ansari, M. A., & Jahan, N., Structural and optical properties of BaO nano-particles synthesized by facile Co-precipitation method. Materials Highlights, 2(1-2),2021, 23-28
    CrossRef
13. Bazeera, A. Zeenath, and M. Irfana Amrin. “Synthesis and characterization of barium oxide nano-particles.” IOSR J. Appl. Phys 1, 2017, 76-80.
    CrossRef
14. Farahmandjou, M., & Soflaee, F. Synthesis and characterization of α-Fe2O3 nanoparticles by simple co-precipitation method. Physical Chemistry Research, 3(3), 2015, 191-196.
15. Arulmozhi, K. T., & Mythili, N.. Studies on the chemical synthesis and characterization of lead oxide nanoparticles with different organic capping agents. American Institute of Physics advances, 2013,3(12).
    CrossRef
16. Raza, Junaid & Hamid, Abdul & Khan, Muhammad & Hussain, Fakhar & Tiehu, Li & Fazil, Perveen & Wahab, Zainul & Ali, Amjad. Spectroscopic characterization of biosynthesized lead oxide (PbO) nanoparticles and their applications in PVC/graphite-PbO nanocomposites. Zeitschrift für Physikalische Chemie, 2022.
    CrossRef
17. Borja-Urby, R., Díaz-Torres, L. A., Salas, P., Moctezuma, E., Vega, M., & Ángeles-Chávez, C. Structural study, photoluminescence, and photocatalytic activity of semiconducting BaZrO3: Bi nanocrystals. Materials Science and Engineering: B, 176(17), 2011, 1382-1387.
    CrossRef
18. Lone, I. H., Aslam, J., & Akhter, A. Characterization of advanced green materials. In Advanced green materials .2021, (pp. 31-41)
    CrossRef
19. Dao, T. T., Vo, T. L. N., Duong, A. T., Tran, D. T., Nguyen, D. L., Das, R., & Nguyen, H. T. Highly photocatalytic activity of pH-controlled ZnO nanoflakes. Optical Materials, 140, 2023, 113865.
    CrossRef
20. Dalal, C., Garg, A. K., Jain, N., Naziruddin, A. R., Prajapati, R. K., Choudhary, S. K., & Sonkar, S. K., Sunlight-assisted photocatalytic degradation of azo-dye using zinc-sulfide embedded reduced graphene oxide. Solar Energy, 251, 2023, 315-324.
    CrossRef
21. Pandey, A., Kalal, S., Ameta, C., Ameta, R., Kumar, S., & Punjabi, P. B.. Synthesis, characterization and application of naïve and nano-sized titanium dioxide as a photocatalyst for degradation of methylene blue. Journal of Saudi Chemical Society, 19(5), 2015, 528-536.
    CrossRef
22. Soltani-Nezhad, F., Saljooqi, A., Mostafavi, A., & Shamspur, T., Synthesis of Fe3O4/CdS–ZnS nanostructure and its application for photocatalytic degradation of chlorpyrifos pesticide and brilliant green dye from aqueous solutions. Ecotoxicology and Environmental Safety, 189, 2020, 109886.
    CrossRef
23. Ajmal, A., Majeed, I., Malik, R. N., Idriss, H., & Nadeem, M. A., Principles and mechanisms of photocatalytic dye degradation on TiO 2 based photocatalysts: a comparative overview. Royal society of chemistry Advances, 4(70), 2014, 37003-37026.
    CrossRef
24. Ahmadi, S., & Ganjidoust, H. (2021). Using banana peel waste to synthesize BPAC/ZnO nanocomposite for photocatalytic degradation of Acid Blue 25: Influential parameters, mineralization, biodegradability studies. Journal of Environmental Chemical Engineering, 9(5), 2021,106010.
    CrossRef

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