Photocatalytic properties of hierarchical CuO nanosheets synthesized by a solution phase method

https://doi.org/10.1016/j.jes.2017.05.005Get rights and content

Abstract

CuO nanomaterials were synthesized by a simple solution phase method using cetyltrimethylammonium bromide (CTAB) as a surfactant and their photocatalytic property was determined towards the visible-light assisted degradation of Reactive Black-5 dye. A detailed mechanism for the formation of CuO nanostructures has been proposed. The effect of various experimental parameters such as catalyst amount, dye concentration, pH and oxidizing agent on the dye degradation efficiency was studied. About 87% dye was degraded at pH 2 in the presence of CuO nanosheets under visible light. The enhanced photocatalytic activity of CuO nanosheets can be ascribed to good crystallinity, grain size, surface morphology and a strong absorption in the visible region. CuO is found to be a promising catalyst for industrial waste water treatment.

Introduction

Various metal oxides such as CuO, ZnO, TiO2, Fe2O3, MnO2, and CdS have been used for the degradation of organic pollutants (Khataee et al., 2014, Liu et al., 2010, Liu et al., 2015, Shimizu et al., 2007, Sun et al., 2016, Yu et al., 2014, Zhang et al., 2006). Except CuO, remaining metal oxides have disadvantages like inactive in visible light, chemical instability, large bandgap, toxicity and a high cost of production. CuO is a p-type semiconductor with a band gap 1.2–1.5 eV and it can be prepared by simple methods using low cost starting materials and reagents. CuO was used in many applications such as anode material for Li-ion batteries (Gao et al., 2004), gas sensors (Chowdhuri et al., 2004), glucose sensors (Liu et al., 2012a), field emission emitters (Hsieh et al., 2003), photocurrent generation (Tian et al., 2012), solar cells (Anandan, 2007) and degradation of dyes (Liu et al., 2012b). Various methods have been proposed to synthesize CuO nanomaterials like hydrothermal (Mohamed et al., 2014), chemical precipitation (Zhu et al., 2004), solvothermal (Sun et al., 2013), thermal-decomposition (Bakhtiari and Darezereshki, 2011), reflux method (Xu et al., 2009), sonochemical (Sonia et al., 2014, Gusain and Khatri, 2013) and combination of these methods. The solution phase method is very simple and easy to carry out. The physical and chemical properties of nanomaterials depend on their size and morphology. Different CuO nanostructures were prepared such as nano urchin (Sun et al., 2013), nano dendrites (Zhang et al., 2008a, Zhang et al., 2008b), nanosheets (Zheng and Liu, 2007), dandelion (Zhang et al., 2012), nanoflower (Huang et al., 2012), cocoon (Kim et al., 2015a, Kim et al., 2015b) and spindle (Harish et al., 2015). Generally, surfactants and ionic liquids are used to get the desired morphology of nanomaterials (Zhang et al., 2008a, Zhang et al., 2008b).

Day by day, textile industries are introducing wastewater containing dyestuff into aquatic systems. These dyes cause environmental pollution, severe health problems for human beings as well as animals and ecosystem. Most of these dyes are carcinogenic and azo (single bondNdouble bondNsingle bond) bonded compounds are highly resistant to aerobic degradation. Biodegradation, adsorption, coagulation, and membrane methods were suggested for dye removal from wastewater. These methods can only transfer pollutants from one phase to another phase causing secondary pollution. So an efficient technique is required to complete degradation of organic dye molecules. Advanced oxidation processes are useful techniques due to the formation of highly reactive OH radicals. These hydroxyl radicals possess high oxidizing power and destruct the dye pollutants due to their high oxidation potentials (E0 = 2.8 V vs. normal hydrogen electrode (NHE)). CuO is a promising visible light photocatalyst for the degradation of dye molecules. It has been reported in the literature that catalytic property of CuO mostly depends on its morphology (Wang et al., 2016a, Wang et al., 2016b). The main aim of recent efforts on semiconductor materials was to prepare the photocatalyst which utilizes the visible light portion of the sunlight. Compared to other photocatalysts, CuO can effectively degrade the dye molecules by the generation of electrons and holes under visible light, which are powerful oxidants and reductants. The generated holes can form highly reactive hydroxyl radicals (·OH) by reacting with water molecules, which then oxidize the pollutants.

We have chosen Reactive Black-5 (RB-5) as a model dye pollutant for photocatalytic study because it has been widely used for dyeing cotton fabrics and released to the environment (Muruganandham et al., 2006). The structure of dye is very complex possessing two azo groups and vinyl sulphone groups. During dyeing process, the vinyl sulphone groups are hydrolysed giving 2-hydroxyethylsulphone groups which do not react with textile fibers resulting in a low efficiency dyeing process. Poulios and Tsachpinis (1999) used TiO2-P25 as a catalyst for degrading the RB-5 but TiO2-P25 catalyst was more effective in ultraviolet (UV). For the removal of dye pollutants many researchers used either 1D or 3D nanostructures, however the use of 2D materials may cause enhanced degradation rate due to its high surface area (Li et al., 2012). In the present work, we have synthesized CuO hierarchical nanosheets (2D) and photocatalytic decolourisation of RB-5 was carried out in the presence of visible light.

Section snippets

Materials

Copper sulfate pentahydrate (CuSO4·5H2O  99.0%) and cetyltrimethylammonium bromide (CTAB) were purchased from Sigma-Aldrich. Ammonium hydroxide (25 wt.% NH3·H2O) and sodium hydroxide (NaOH) were purchased from Merck India Pvt. Ltd. All other chemicals used were analytical grade and used as received without further purification. Deionized water was used for the synthesis and purification of CuO nanoparticles.

Methods

The CuO nanostructures were synthesized by the following procedure: 1 g CuSO4·5H2O and 50 mg

Results and discussion

The synthesized CuO nanostructures (NSs) were analyzed by XRD to examine the crystallinity, crystal structure, and purity. Fig. 1 shows that all the diffraction peaks are sharp which indicates that the prepared CuO NSs are highly crystalline and pure. Calculated average crystal size of CuO nanostructures by using Debye–Scherrer's formula.D=0.891λ/βcosθwhere D is crystallite size, λ is the wavelength (1.5406 Å for Cu Kα), β is full-width at half-maximum (FWHM) of main intensity peak in radians

Conclusions

In this paper, hierarchical CuO nanosheets were successfully prepared by a simple solution phase method using CTAB as a surfactant and characterized by various characterization studies such as XRD, SEM, TEM, FTIR, Raman spectroscopy and UV-vis. Photocatalytic experiments were conducted for the degradation of RB-5 in the presence of visible light. It has been shown that CuO nanosheets are effective photocatalysts. In order to identify the optimum conditions for dye degradation rate, the effect

Acknowledgments

The research described herein was financially supported by the Department of Science and Technology, India under Water Technology Initiative scheme. Also, Sambandam Anandan thank the Department of Science & Technology (DST) for India-Taiwan joint project. Author Rao thanks the Ministry of Human Resource Development (MHRD), New Delhi for the junior research fellowship position.

References (52)

  • Y. Li et al.

    Ultralong Cu(OH)2 and CuO nanowire bundles: PEG200-directed crystal growth for enhanced photocatalytic performance

    J. Colloid Interface Sci.

    (2010)
  • J.A. Libra et al.

    Two stage biological treatment of a diazo reactive textile dye and the fate of the dye metabolites

    Chemosphere

    (2004)
  • T. Liu et al.

    Tartaric acid assisted hydrothermal synthesis of different flower-likeZnO hierarchical architectures with tunable optical and oxygenvacancy-induced photocatalytic properties

    Appl. Surf. Sci.

    (2015)
  • R.M. Mohamed et al.

    CuO nanobelts synthesized by a template free hydrothermal approach with optical and magnetic characteristics

    Ceram. Int.

    (2014)
  • M. Muruganandham et al.

    Solar assisted photocatalytic and photochemical degradation of Reactive Black 5

    J. Hazard. Mater.

    (2006)
  • V. Rajendran et al.

    Preparation and characterization of nanocrystalline CuO powders with the different surfactants and complexing agent mediated precipitation method

    Mater. Res. Bull.

    (2014)
  • A. Sadollahkhani et al.

    Photocatalytic properties of different morphologies of CuO for the degradation of Congo red organic dye

    Ceram. Int.

    (2014)
  • N. Shimizu et al.

    Sonocatalytic degradation of methylene blue with TiO2 pellets in water

    Ultrason. Sonochem.

    (2007)
  • S. Sonia et al.

    Effect of NaOH concentration on structural,surface and antibacterial activity of CuO nanorods synthesized by direct sonochemical method

    Superlattice. Microst.

    (2014)
  • T.W. Sun et al.

    α-Fe2O3 nanosheet-assembled hierarchical hollow mesoporous microspheres: microwave-assisted solvothermal synthesis and application in photocatalysis

    J. Colloid Interface Sci.

    (2016)
  • L.J. Wang et al.

    Size effect and enhanced photocatalytic activity of CuO sheet-like nanostructures prepared by a room temperature solution phase chemical method

    Appl. Surf. Sci.

    (2013)
  • X. Wang et al.

    Surfactant-free synthesis of CuO with controllable morphologies and enhanced photocatalytic property

    Nanoscale Res. Lett.

    (2016)
  • M. Yang et al.

    Fine tuning of the morphology of copper oxide nanostructures and their application in ambient degradation of methylene blue

    J. Colloid Interface Sci.

    (2011)
  • Z. Yu et al.

    Synthesis of self-assembled CdS nanospheres and their photocatalytic activities by photodegradation of organic dye molecules

    Chem. Eng. J.

    (2014)
  • S. Zaman et al.

    Efficient catalytic effect of CuO nanostructures on the degradation of organic dyes

    J. Phys. Chem. Solids

    (2012)
  • W. Zhang et al.

    Large-scale synthesis of β-MnO2 nanorods and their rapid and efficient catalytic oxidation of methylene blue dye

    Catal. Commun.

    (2006)
  • Cited by (44)

    • Synthesis, characterization and visible light-responsive photocatalysis properties of Ce doped CuO nanoparticles: A combined experimental and DFT+U study

      2021, Colloids and Surfaces A: Physicochemical and Engineering Aspects
      Citation Excerpt :

      In the case of photocatalytic applications, CuO preferred over Cu2O due to its superior stability and lower bandgap [13] which enable its optical bandgap to tune by suitable metal doping for utilizing a wide range of visible (solar/synthetic) radiations. The extreme reactivity of copper (Cu2+) together with the low bandgap of CuO makes it a promising photocatalyst for the decontamination of water [17]. For phase pure CuO, the electrons in the conductions band are unstable, most of the photo-generated electrons move to the valance band and recombine with the hole without taking part in the oxidation process [18].

    View all citing articles on Scopus
    View full text