Effective photocatalytic degradation of Rhodamine B using tin semiconductors over hydrotalcite-type materials under sunlight driven

doi:10.1016/j.cattod.2020.12.014

Catalysis Today

Volume 372, 15 July 2021, Pages 191-197

https://doi.org/10.1016/j.cattod.2020.12.014 Get rights and content

Highlights

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p-n-type semiconductors of tin species over hydrotalcite were successfully synthetized.
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The ratio p-n type depends of the content of tin.
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The meso/macroporosity plays a role essential in the degradation of Rhodamine B.
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75 % of degradation of Rhodamine B could be reached using a 10 wt% of tin on the hydrotalcite.

Abstract

In the current study, SnO₂(5, 10 and 15 wt%)/MgAl-HT hydrotalcite-type materials were synthesized by co-precipitation method. Besides, the photocatalytic activity of the materials was evaluated in the degradation of Rhodamine B under simulated sunlight. The characterization of the materials by X-ray diffraction (XRD), Raman spectroscopy, physisorption of nitrogen and X-ray photoelectron spectroscopy (XPS) showed the formation of the (003) and (110) characteristic plans of lamellar materials, vibrational modes typical of layered double hydroxides and tin, specific surface areas, pore size distribution and chemical composition, respectively. The photocatalytic activity showed that the SnO₂(10 %)/MgAl-HT catalyst has the best degradation of the dye reaching a 75 % of degradation after 210 min under simulated solar light irradiation. The route of action of charge carriers was evaluated using scavengers for photogenerated holes, hydroxyl and superoxide radicals, such as triethanolamine, isopropanol and benzoquinone, respectively, when benzoquinone was used it was confirmed that superoxide radicals play an important role in degradation of Rhodamine B.

Graphical abstract

Introduction

Wastewater from domestic and industrial sources contains a large amount of pollutants such as pesticides, detergents, drugs and dyes. These compounds can become harmful to the environmental and cause adverse health effects. Dyes are ionic salts solvated by water molecules making it difficult to separate them from water sources [1]. The Rhodamine B (RhB) is a dye that belong to the family of xanthenes that are often used in the staining industry and can also be used in biochemistry as a biology marker of viruses and diseases [2]. This highly stable molecule has been related with subcutaneous tissue sarcoma, irritation to eyes, skin and respiratory tract and suspected of being carcinogen and mutagenic for living organisms [3,4]. In addition, RhB can affect the photosynthesis of aquatic plants, since makes light absorption difficult [5]. Distinct techniques have been used for the treatment of pollutants such as dyes, which include different conventional treatment techniques as thermal degradation, biological treatment, adsorption and membrane separation treatment. However, biological treatments and adsorption require long operating times; thermal degradation consumes a large amount of energy. An alternative of treatment is the heterogeneous photocatalysis that is a radical-mediated oxidation process, capable of chemically modify the dyes, achieving a mineralization of the organic contaminants [6,7].

In this way, supported-semiconductor over mesoporous materials have demonstrated be adequate materials in the degradation of RhB [8], between those materials, the hydrotalcite- type materials or Layered Double Hydroxides (LDH) have emerged as promising photocatalysts due to their stable structure, high anion retention, charge separation and transfer efficiency, low-cost and facility of synthesis [9]. The hydrotalcite have a structure similar to brucite (Mg(OH)₂), where the magnesium atom is octahedrally coordinated to six hydroxyl groups [10]. When some divalent Mg atoms are isomorphically substituted by trivalent metals such as aluminum, a positive charge density is generated that is compensated by interlamellar anions such as carbonate anions [11]. The general formula of LDH is (M_1-x^IIM_x^III(OH)₂)Aⁿ⁻_x/n·mH₂O with M^II divalent metals, M^III trivalent metals and Aⁿ⁻ interlamellar anions, in the interlamellar regions there is also the presence of water molecules and hydroxyl ions [12].

However, the rate degradation of RhB in hydrotalcites is highly dependent of coordination of the active species of the semiconductor [13,14], as oxidant type used [[15], [16], [17]]. For example, Zn/M–NO₃-LDHs (M = Al, Fe, Ti, and Fe/Ti) displayed high to moderate activity under visible-light irradiation, being most active Ti⁴⁺ species than Fe³⁺ [14]. Additionally, it has been reported that Pt nanoparticles intercalated in ZnTi-layered double hydroxides favors the degradation of rhodamine due to high specific area, the negative shift in potentials and the easy of migration of photogenerated electrons that preventing recombination of the e⁻/h⁺ pair [18].

In particular, the use of hydrotalcite-type materials in the degradation of RhB result a catalyst depending of oxidant employed. For example, CoMgAl-LDHs is not as good photocatalyst in the degradation of this colorant using molecular oxygen [14], but, Cr-Zn layered hydroxide showed a degradation of rhodamine near to 100 %, employing H₂O₂. The formation HO₂· radicals resulting of the interaction between H₂O₂ and HO· is essential in the degradation of this colorant [17]. Thus same, cobalt phthalocyanine supported Mg–Al hydrotalcite using different H₂O₂ dosages reaches a degradation near to 90 % [19]. However, the effect of phtalocyanine was not discussed. Other efforts using this type of materials is the use of bicarbonate activated hydrogen peroxide to increase the degradation of Rhodamine [16].

On the other hand, the dispersion of n-type semiconductor in lamellar materials can favor the efficiency of the reaction of degradation of rhodamine. Tin oxide has been used in the dye degradation reactions, Babu and Antony employed SnO₂/bentonite nanocomposites in degradation of Methylene Blue (MB), in the photocatalytic mechanism suggest that electrons are excited to conduction band of SnO₂ and these electrons combined with oxygen lead to the formation of the superoxide radical (O₂^.−), in this reaction they added hydrogen peroxide (H₂O₂), which favors the formation of hydroxyl radicals (·OH), which are ultimately the species responsible for carrying out the degradation reaction [20]. Also, TiO₂ nanospheres over SnO₂ quantum dots composites were employed in the degradation of methyl orange, in this study SnO₂ quantum dots were dispersed over TiO₂ uniformly. In the discussion, Du and coworkers affirm that the efficiency in the photocatalytic activity using the composites is due to the synergistic effect between the two oxides [21].

If well, the role of semiconductor and the oxidant agent are indispensable in the degradation of RhB, the better results have been showed using typical semiconductors and H₂O₂ as a strong oxidant agent. In this work, we report the synthesis of materials of tin (IV) oxide over hydrotalcite-type materials used in the Rhodamine B photocatalytic degradation with simulated solar light. The advantage of this type of materials is the easy synthesis and the possibility of extend its use to scalable process using sunlight. It was also studied the role of some scavengers because of photogenerated charge carriers play an important role in the degradation of this type of colorants.

Section snippets

Synthesis of SnO₂/MgAl-HT

The solids SnO₂/MgAl with 5, 10 and 15 wt percent of tin oxide were synthetized by co-precipitation method. A mixture of the solutions of the precursor salts Mg(NO₃)₂.6H₂O (0.43 mol) and Al(NO₃)₃.9H₂O (0.14 mol) with a molar relation of 3 together with SnCl₄.5H₂O were added to a three mouth-ball while maintaining constant agitation and room temperature. Afterwards, 2.61 mol of urea was added to the solution mixture and hydrolyzed at 373 K under reflux for 10 h. Additionally, the pH was adjusted

Characterization of the materials

Fig. 1 shows the diffraction patterns of hydrotalcite-type materials and SnO₂. The characteristic peaks of lamellar solids (JCPDS 22−0700) corresponding to the basal plans (003), (006), (009), (015), (018) and (110) in angles 2θ at 11.59°, 23.32°, 34.77°, 39.37°, 46.8° and 64.64°, respectively [22], are present in MgAl-HT and SnO₂/MgAl-HT photocatalysts. The presence of the characteristic reflections in all the materials synthesized by co-precipitation method indicate that the formation of

Conclusion

The synthesis of the hydrotalcite-type materials by co-precipitation method were successfully development. The characterization of the photocatalysts by XRD allowed demonstrating the formation of the laminar structure and the segregation of the SnO₂ particles on MgAl-HT. The pore size distribution indicates that the solid SnO₂(10 %)/ MgAl-HT presents a meso/macroporosity, which makes it an interesting material for the degradation reaction. The evaluation of the photocatalytic activity in the

CRediT authorship contribution statement

Sonia Mancipe: Conceptualization, Methodology, Writing - original draft, Writing - review & editing, Project administration. José J. Martínez: Conceptualization, Methodology, Writing - original draft, Writing - review & editing, Supervision, Project administration. Cristian Pinzón: Writing - original draft, Writing - review & editing, Supervision, Methodology. Hugo Rojas: Writing - review & editing, Project administration. Dora Solis: Writing - original draft, Writing - review & editing,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We acknowledgements to the CCIQS research center of UAEM-UNAM by X ray photoelectron spectra and the Nuclear Science Institute of the UNAM for the Raman analysis.

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Effective photocatalytic degradation of Rhodamine B using tin semiconductors over hydrotalcite-type materials under sunlight driven

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of SnO2/MgAl-HT

Characterization of the materials

Conclusion

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgements

Environ. Dev.

Chin. Chem. Lett.

J. Environ. Manage.

Inorg. Chem. Commun.

J. Hazard. Mater.

Appl. Catal. B

Chem. Eng. J.

J. Photochem. Photobiol. A.

Appl. Clay Sci.

Appl. Catal. B

J. Colloid Interface Sci.

J. Sci. Adv. Mater. Devices

Appl. Surf. Sci.

Appl. Clay Sci.

Ceram. Int.

J. Colloid Interface Sci.

J. Energy Chem.

Appl. Clay Sci.

J. Phys. Chem. Solids

Chem. Phys. Lett.

Mater. Lett.

Appl. Surf. Sci.

Appl. Clay Sci.

J. Hazard. Mater.

Solid State Commun.

Appl. Surf. Sci.

J. Power Sources

Catal. Commun.

Energy Stor. Mater.

Synthesis of SnO₂/MgAl-HT