Efficient catalytic degradation of organic pollutants with cupric oxide nanomaterials in aqueous medium

https://doi.org/10.1016/j.jece.2021.106305Get rights and content

Highlights

  • Eco-friendly, facile and simple method was used to prepare CuO nanomaterials at room temperature.

  • The HR-XRD reveals great crystallinity of 95.94% and a crystallite size of ~38 nm.

  • The calculated crystal lattice strain of ~3.01 × 10-3 by Williamson-Hall analysis.

  • The band gap value is obtained 1.36 eV from Tauc plots.

  • The catalytic degradation efficiency ~90.54% has been achieved in 480 s for AR dye degradation under UV light.

Abstract

In this work, an eco-friendly, facile, and efficient method has been applied for CuO nanostructures (NSs) synthesis using ascorbic acid as capping agent. For surface morphology, FESEM analysis was applied to reveal nanostructure with ~100 nm length, and ~90 nm width morphology which was also supported by TEM images of CuO. Thus obtained CuO NSs resulted in an optical energy having ~1.36 eV band gap obtained from Tauc plots of UV–visible plots because of strong quantum confinement effect of nanoparticles. XRD reveals a monoclinic phase of CuO NSs for which follow the reference JCPDS No. 98–004–3179 (Space group of C 12/c 1) crystal structure with high crystallinity of ~95.94% and crystallite size of ~38 nm. In addition, Williamson-Hall analysis was applied to calculate crystal lattice strain of ~3.01 × 10-3 for CuO catalyst followed by 28.36 m2/g high BET surface area (0.9999 correlation coefficient) having ~14.38 nm average BJH pore size. Furthermore, CuO NSs exhibited ultrafast and high catalytic degradation efficiency of ~90.54% for Allura Red AC dye (AR dye) in 480 s under UV light. The photodegradation kinetics followed a pseudo first-order reaction with rate constant (k) of ~0.0046 s−1 having approximately ~150.65 s of half-life (t1/2) for AR dyes in the aquatic medium as per the Langmuir–Hinshelwood model. As synthesized catalyst, CuO NSs explored good leaf-like morphology with high recycling ability after five degradation cycles of AR dye in aqueous medium.

Introduction

The surface morphology of nanomaterials plays a key role for their potential applications which might be manipulated using various synthesis methods such as gas-phase oxidation techniques, sol–gel technique, and chemical bath [11], [18], [44]. Owing to low temperature, ease of handling, and cost-effective nature, the wet-chemical method is widely accepted compared to other synthetic techniques of nanomaterials [23], [46]. Due to their unparalleled dimensions, metal oxide nanostructures have received considerable attentions for various applications [3], [19], [44]. Among metal oxides nanomaterials, cupric oxide (CuO) as p-type, nontoxic, and highly stable semiconductor having energy band gap of ~1.2 eV, is widely studied with ease of synthesis methods and diverse applications [35], [36]. Based on synthesis protocols, CuO might acquire different morphologies as nanorods, nanosheets, nanodentrites, nanoribbons, nanoplatelets, nanosphere, dandelion-like, dumbbell-like, flower-like, honeycomb-like, urchin-like nanomaterials [21], [37], [46], [7]. As morphology and size of CuO nanomaterials are important characters to determine physical and chemical properties for different applications [17], [42].

In addition, CuO nanomaterials have been utilized in numerous applications for example heterogeneous catalysis, field emitter, lithium ion batteries, solar energy and sensors [22], [40], [45]. In synthesis techniques, nanomaterials have been grown with catalytic mechanism, solution, hydrolysis, hydrothermal, solvothermal, microwave irradiation to achieve different morphologies [22], [27], [28], [46], [9]. The hydrothermal reactions still creating a great buzz and interest for nanomaterials synthesis of various CuO NSs with a variety of capping agents due to its low temperature, safe, eco-friendly, cheap, and high yielding properties [25], [36], [39]. Cupric oxide (CuO) nanomaterials display promising properties in diverse field applications including solar cells, lithium ion batteries, chip-memory devices, as well as field effect transistors [31]. CuO exhibits monoclinic crystal system where every Cu atom bonded to 4 neighbor oxygen atoms, as well as exists at center of O atom and located at center of a distorted tetrahedron structure [20]. CuO nanomaterials reveal different size and shapes based on precursors used in synthesis which greatly affect their performance towards dye degradation [12], [24].

Organic dyes with azo (–Ndouble bondN–) groups covers about > 50% of industrial water pollutions. Allura Red AC (C18H14N2Na2O8S2 = Chemical Formula, 496.4 = Molecular Weight), a synthetic food dye with azo group, generally used in various food, bakery, dairy, cosmetic, meat and fish products [5]. In addition, AR dye reveals carcinogenic effects in body according to World Health Organization (WHO) data resulting in harmful and toxic issues on excess consumption [27], [28]. Various industrial sectors, as textile, lather, paper, cosmetics, paint and printing industries have produced various organic materials as major water pollution sources. The azo dyes explore anionic, cationic or non-ionic properties at various pH owing to presence of carboxyl, and amino groups. on addition of azo dyes, many food products become attractive as well as appealing with zero enhancement in nutritional values [10], [34]. Various industrial dyes comprise of organic compounds which produce different color in water and cause water pollution as well as loss of aquatic living organisms [35], [9].

In this manuscript, we report an eco-friendly, facile synthesis of cupric oxide (CuO) nanostructures with ascorbic acid as capping agent for application of AR dye degradation in water. As-grown CuO NSs reveals high energy band gap of ~1.36 eV compared to bulk CuO nanomaterials owing to quantum confinement effect. The catalytic degradation of Allura Red dye was investigated in presence of reducing agent using UV–vis absorption spectroscopy. CuO NSs attained ~90.54% degradation efficiency within 480 s under light at room temperature.

Section snippets

Materials and methods

Chemical compounds, CuCl2. 2H2O (Copper chloride dihydrate), NaOH (sodium hydroxide), and L-ascorbic acid, NaBH4 (sodium borohydride), have been purchased from Sigma Aldrich, Korea. During experiment, all chemicals and reagents have been used were of analytical grade and applied without further purification. Deionized (DI) water has been used in experiments to develop aqueous solution with different components and spectroscopic analysis.

Materials characterizations

UV–vis AR dye solutions spectra have been collected

Morphological properties

FESEM analysis (Fig. 2a-b) of CuO NSs were performed with corresponding elemental mapping at different magnifications. The surface morphology CuO powder might reveal leaf-like morphology along with nanorods having an average length of ~ 100–120 nm. While, CuO nanoleaves have display ~20 nm thickness and width ~85–100 nm range. For synthesis, accumulation of many CuO nanorods produce nanoleaves morphology by self-assembly property [26]. Furthermore, TEM image (Fig. 2c-d) of CuO exhibits nanorods

Conclusions

An eco-friendly and efficient synthetic route was adopted using ascorbic acid as capping agent for growth of CuO nanostructures at room temperature. For structure analysis, XRD reveals a monoclinic phase of CuO NSs (reference JCPDS No. 98–004–3179) in crystal space group of C 12/c 1 with great crystallinity of ~95.94%. Williamson-Hall analysis was applied to calculate the lattice strain of ~3.01 × 10-3 for CuO catalyst (crystallite size of ~38 nm.) followed by high 28.36 m2/g BET surface area

CRediT authorship contribution statement

Aftab Aslam Parwaz Khan: Writing – review & editing. Mohammed Nazim: Writing – original draft, Methodology, Investigation, Software, Validation. Abdullah M Asiri: Visualization, Supervision.

Supporting information

The Supporting Information is available free of charge which contains Williamson-Hall plots, XPS plots, BET surface area plots, reusability plots of ten cycles, and XRD, FESEM image of CuO nanostructures after ten degradation cycles of AR dye.

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

This project was funded by the Deanship of Scientific Research (DSR) at King Abdulaziz University, Jeddah, under grant no. G-1285-130-1440. The authors, therefore, acknowledge with thanks DSR for technical and financial support.

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