An efficient removal of Indigo Carmine dye (IC) from aqueous medium using environmental friendly synthesized ZnAl2O4

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Abstract

In recent years, materials have not only shown significant application in human life but also have a very important role in various industries. Over the last few decades, metal oxide and mixed metal oxide (MMO) have been acknowledged as efficient and environment-friendly alternatives to present-day available materials for different chemical, food, dye, and pharmaceutical industries along with environmental treatments. In view of the significant use of MMO in different fields, in the current work, nanocrystalline zinc aluminate (ZnAl2O4) has been successfully synthesized by the eco-friendly, cost-effective solid-state Mechanochemical (MCh) method, and it is used for the photocatalytic degradation of Indigo Carmine (IC) pollutant present in the wastewater of different industries. Numerous appropriate techniques, like Fourier-transform infrared spectroscopy (FT-IR), Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UV-DRS), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM), were used for its characterization. It is revealed that ZnAl2O4 exhibits a pronounced photocatalytic activity under the influence of UV–visible light exposure. The present study also reveals a possible pathway for photocatalytic degradation of IC using liquid chromatography-mass spectrometry (LC-MS).

Introduction

Indefinitely raising the discharge of an ample amount of dyes by the dye and textile industries leads to a serious environmental threat. Most of the dyes are observed in suspension or dissolved state in an aqueous medium [1], [2]. A number of inadequate reports in the literature are available on the photocatalytic application of perovskite. This work tries to find the need for an effective MMO photocatalyst for cleaning the environment and to test the efficiency of the synthesized catalyst. It provides a large scope of inspection of the preparation of the catalyst under eco-friendly conditions. It is a worthwhile solution to cover a wider area of research in the presence of the perovskite catalyst (ZnAl2O4). Thus, for this study, the diversity and unique physiological and light-sensitive photocatalytic behaviour were considered, as well as a study of the preparation and characterization of significant environment-friendly solid state photocatalysts. It also focuses on its significance for the degradation of IC pollutants present in the waste discharge of the chemical industry under UV–visible light. The spinel ZnAl2O4 oxide possesses high chemical and thermal stability, high mechanical resistance, and low surface activity [3], [4], [5]. This property is appropriate for various uses such as optical coating, high temperature resistant ceramic materials, catalyst and, catalyst support material [6], [7]. Recently, this material has been used as a catalyst in various reactions such as degradation of gaseous toluene [8], ethanol steam reforming [9], hydrogenation [10], transesterification of vegetable oil [11], and isobutane combustion [12]. Surface topology is a significant characteristic of coatings and films and can substantially and consequently show a change in optical, electrical, and biological properties of materials. The properties of the material are controlled by proper surface topology.

Literature [13], [14] reveals that that ZnAl2O4 is used as an efficient catalyst for the photodegradation of dye [15], [16], [17], [18]. Owing to this valuable application of ZnAl2O4, various synthesis procedures have been developed using different precursors. Chen et al. [19] used ZnCl2 and AlCl3·6H2O as precursors during hydrothermal synthesis of nanocrystalline ZnAl2O4, The sol–gel method was employed by Phani et al. [20] using zinc acetate dehydrate and aluminium sec-butoxide organic materials as a precursor for the synthesis of ZnAl2O4. The above-mentioned methods suffer from some weaknesses due to costly raw materials and difficult handling processes.

In the present study, we have synthesized ZnAl2O4 to enhance the photo-physical property, and efforts are also being made to synthesize inexpensive and nontoxic photocatalysts. Hence, attention is paid to synthesizing ZnAl2O4 catalyst by the eco-friendly solid state MCh method [21], [22]. FT-IR, UV-DRS, SEM, and TEM were used for its characterization. Degradation of organic dye pollutants using the interaction between UV–visible radiation and semiconductor materials has great significance as it has been widely utilized in the present era [23]. The main part of the solar system is occupied by visible light-induced photocatalysts. The last few decades have witnessed studies on the light-induced degradation of organic pollutants using TiO2 catalysts [24], [25], [26]. Degradation of acid orange was performed by Alton and Ferry using SiW2O4 as a photocatalyst [27].

The possible pathway of photocatalytic degradation of IC was found by using liquid chromatography-mass spectrometry (LC-MS). This shows that ZnAl2O4 possesses remarkable photocatalytic behaviour under the influence of UV–visible light exposure. In the current study, industrial wastewater soluble IC (molar mass: 466.36 g/mol, C16H8N2Na2O8S2) was used. Acid dye gives a successful outcome for its application to new treads of silk; acid blue IC is cancer-causing and has a hazardous nature, thus care should be taken while removing IC methodically from an aqueous medium using ZnAl2O4 as a significant photocatalyst. In this connection, the main aim of this work is to synthesize ZnAl2O4 nanocrystalline material by the eco-friendly MCh method and to evaluate its potential application in the degradation of IC pollutants under UV–visible radiation.

Section snippets

Materials and methods

ZnO and Al2O3 (99.99 % pure, Sigma Aldrich) are used in their pure form during the synthesis of ZnAl2O4. The IC dye (Fig. 1) and other chemicals were purchased from Sigma Aldrich.

Synthesis of ZnAl2O4 photocatalyst

The ZnAl2O4 fine powder was obtained by grinding a 1:1 M ratio of ZnO and Al2O3 in a mortar and pestle for 20 min (MCh [28]). The obtained homogeneous powder was poured into an alumina crucible and heated at 900 °C for 3 h, and in the next cycle, it was further heated at 1230 °C for another 3 h. Finally, a white

Characterizations of ZnAl2O4 photocatalyst

The formation of the ZnAl2O4 photocatalyst was confirmed by the characteristic infrared spectrum (Fig. 2). The frequency band located at 486.06 cm−1 resolute the existence of Zn–O. The absorption bands between 555.50 cm−1 and 663.51 cm−1 correspond to the vibration of Zn-Al and Al-O-Zn stretching respectively. Fig. 3 depicts the UV–visible diffuse reflectance spectrum for ZnAl2O4 with an absorption edge cut off at 378 nm, which can be assigned to the band gap of 3.28 eV, which is smaller than the

Conclusions

The eco-friendly MCh method was successfully applied for the synthesis of nanocrystalline ZnAl2O4. ZnAl2O4′s catalytic action has been confirmed by average particle size, band gap energy, surface area, and surface shape. The degradation of IC contaminants using the synthesized ZnAl2O4 photocatalyst was found to be extremely successful. When 20 mg of IC dye was given to the reactor in the presence of UV light for 60 min, the photocatalytic degradation was shown to be more effective at slightly

CRediT authorship contribution statement

Ganesh Dabhade: Investigation, Methodology, Writing – original draft. Gaurav Daware: Conceptualization, Supervision. Yennam Rajesh: Visualization. Lakshmana Rao Jeeru: Validation.

Declaration of Competing Interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Ganesh Dabhade reports administrative support, article publishing charges, equipment, drugs, or supplies, statistical analysis, travel, and writing assistance were provided by KK Wagh Institute of Engineering Education and Research.

Acknowledgement

The authors are thankful to the Management and Dr. K. N. Nandurkar, Principal of K.K. Wagh Institute of Engineering Education and Research, Nashik (Affiliated to Savitribai Phule Pune University) for providing the laboratory and infrastructural facilities and support.

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