Elsevier

Applied Catalysis B: Environmental

Volume 241, February 2019, Pages 359-366
Applied Catalysis B: Environmental

High performance visible-light responsive Chl-Cu/ZnO catalysts for photodegradation of rhodamine B

https://doi.org/10.1016/j.apcatb.2018.09.048Get rights and content

Highlights

  • Chlorophyll as an electron donor helps improve photoactivity of ZnO nanoparticles.

  • Copper in the Cu2+ form could inhibit electron-hole pairs recombination reaction.

  • Chlorophyll and Cu loading increased visible-light response of ZnO nanoparticles.

  • Chlorophyll-Cu co-modified ZnO shows excellent performance in RhB photodegradation.

Abstract

The photocatalytic degradation of rhodamine B (RhB) over chlorophyll-Cu co-modified ZnO catalysts (Chl-Cu/ZnO) was studied under visible-light irradiation. It was found that chlorophyll as an electron donor and copper in Cu2+ form help inhibit the recombination of electron-hole pairs and improve photoactivity of the catalyst. The synergistic effect between chlorophyll and Cu was found to improve visible-light response of ZnO nanoparticles, resulting in excellent performance in photodegradation of RhB. The appropriate ratio of chlorophyll and Cu loadings over ZnO was 0.5Chl-0.10Cu/ZnO—at this ratio, under visible-light irradiation of 2 h, the degradation efficiency was approximately 99% (60 mg/l of RhB solution), of which 18% of RhB adsorption occurred in dark condition. Moreover, outstanding reusability of Chl-Cu/ZnO, for up to six cycles, was found, with more than 80% degradation efficiency.

Introduction

Organic dyes are one of the main pollutants in wastewater released from food, textile, plastic and cosmetic industries. Even though the residual dyes in wastewater are present in low concentrations, they are still harmful to plants, aquatic animals and humans due to their non-biodegradable properties and toxicity [[1], [2], [3]]. Therefore, removal of dyes from wastewater is an essential process to lessen this environmental concern. To find out an appropriate solution, various techniques, including photocatalytic degradation [4], Fenton process [5], bioremediation [6] and ozonation [7], have been proposed. Among these techniques, catalytic photodegradation is considered as a potential method as it can be operated without expensive oxidants at low pressure and temperature using stable and low-cost catalysts [[8], [9], [10]]. In order to examine the degradation on efficiencies of photocatalysts, rhodamine B (RhB) is generally used as a representative dye since it is important in reference to its harmful impacts for human health, such as cancer, skin irritation, and allergic dermatitis [[11], [12], [13]]

Among various kinds of photocatalysts, zinc oxide (ZnO) and titanium dioxide (TiO2) have been widely used for photodegradation [[14], [15], [16]] due to their non-toxicity, excellent thermal and chemical stability and high photocatalytic efficiency [17,18]. In comparison to TiO2, ZnO has received much attention because of its strong oxidation activity, low cost and high quantum efficiency [19,20]. However, due to the fact that the band-gap energy for visible-light activation is approximately 1.8–3.1 eV, ZnO, with its wide band-gap energy (3.3 eV), can be activated only under UV irradiation [[21], [22], [23]]. Taking inspiration from natural photosynthesis, chlorophyll, which plays a potential role as a photopigment, has been applied in the catalytic field to reduce the band-gap energy for photocatalytic applications under visible-light irradiation. Phongamwong et al. [24] used chlorophyll in Spirulina with N–doped TiO2 for CO2 reduction and found that chlorophyll could improve the photocatalytic activity under visible-light irradiation by acting as a sensitizer and electron donor, effectively giving an electron for promoting photoreaction. In addition, chlorophyll has also been found to promote the degradation of adsorbed dye molecules by facilitating the absorption of dye and thus leading to better photocatalytic ability [25,26]

In order to improve ZnO based catalysts in terms of the vital problems that are the recombination of electron-hole (e–h+) pairs and backward reaction [27,28], metals such as Fe, Ag, Ni and Cu have been doped onto ZnO [[29], [30], [31]]. Among these, Cu is promising in the prevention of the formation of recombination centers [[32], [33], [34]] as it can potentially substitute zinc atoms in ZnO lattice because of the similar size of ionic radius of Cu and Zn. Moreover, copper can improve photocatalytic activity of ZnO by providing electron capture to separate charges [35,36]. In addition, the strong coupling interaction between O 2p and Cu 3d plays an important role in narrowing the band-gap energy in Cu/ZnO system, resulting in visible-light activation ability [37].

In this work, a series of chlorophyll-Cu co-modified ZnO (Chl-Cu/ZnO) catalysts were synthesized and investigated for photocatalytic degradation of rhodamine B under visible-light irradiation. Outstanding performances of Chl-Cu/ZnO catalysts, particularly in terms of high catalytic activity under visible-light irradiation, were clearly observed due to the high capacity for dye adsorption and the inhibition potential of electron-hole pairs recombination.

Section snippets

Synthesis of ZnO nanoparticles

ZnO nanoparticles were synthesized through a low-temperature precipitation technique modified from the work reported by Akir et al. [38]. In this work, zinc acetate dihydrate (Zn(CH3COO)2·2H2O: Loba) was used as a ZnO precursor, and deionized water was used as a solvent. A certain amount of sodium hydroxide (NaOH: PanReac AppliChem) was dissolved in deionized water and added dropwise into zinc acetate dehydrate solution at 60 °C; then the mixture was vigorously stirred for 2 h. After that, the

Performance of chlorophyll-modified ZnO catalysts

As shown in Fig. 1, dye adsorption capacities over Chl/ZnO catalysts were significantly higher than that on the ZnO catalyst. The degradation of RhB was found to increase with increased loading of chlorophyll, such that the optimum chlorophyll loading, giving the best degradation efficiency among all Chl/ZnO catalysts was found to be 0.5 wt.% Chl a. At loading amounts higher than 0.5 wt.% Chl a, the degradation activity tended to decrease due to significant decreases in the specific surface

Conclusion

Chlorophyll-Cu co-modified ZnO (Chl-Cu/ZnO) photocatalyst was successfully prepared and played a significant role in photodegradation of RhB under visible-light irradiation. Among all catalysts studied, chlorophyll-Cu co-modified ZnO catalyst gave the most outstanding degradation of RhB, attaining almost 99% within 2 h. The photocatalytic activities over ZnO catalysts were significantly improved by loadings of copper and the extracted chlorophyll on the ZnO surface. As an electron acceptor,

Acknowledgments

This work was financially supported by the Kasetsart University Research and Development Institute (KURDI), the Center of Excellence on Petrochemical and Materials Technology (PETROMAT), and the Institutional Research Grant (grant no. IRG5980004). The authors would like to thank the Synchrotron Light Research Institute (BL8: XAS and BL5.3: Nanotec-XPS) for their support regarding XAS and XPS measurements.

References (61)

  • D.R. Sulistina et al.

    Rhodamine B increases hypothalamic cell apoptosis and disrupts hormonal balance in rats

    Asian Pac. J. Reprod.

    (2014)
  • H. Lee et al.

    Rapid destruction of the rhodamine B using TiO2 photocatalyst in the liquid phase plasma

    Chem. Cent. J.

    (2013)
  • M. Ptaszkowska–Koniarz et al.

    Removal of rhodamine B from water by modified carbon xerogels

    Colloids Surf. A Physicochem. Eng. Asp.

    (2018)
  • H. Abdullah et al.

    Modified TiO2photocatalyst for CO2 photocatalytic reduction: An overview

    J. CO2 Util.

    (2017)
  • C.B. Ong et al.

    A review of ZnO nanoparticles as solar photocatalysts: Synthesis, mechanisms and applications

    Renew. Sust. Energ. Rev.

    (2018)
  • D. Štrbac et al.

    Photocatalytic degradation of Naproxen and methylene blue: Comparison between ZnO, TiO2 and their mixture

    Process Saf. Environ. Prot.

    (2018)
  • S. Liang et al.

    A novel ZnO nanoparticle blended polyvinylidene fluoride membrane for anti-irreversible fouling

    J. Membr. Sci.

    (2012)
  • B. Dindar et al.

    Unusual photoreactivity of zinc oxide irradiated by concentrated sunlight

    J. Photochem. Photobio. A Chem.

    (2001)
  • B. Pal et al.

    Enhanced photocatalytic activity of highly porous ZnO thin films prepared by sol–gel process

    Mater. Chem. Phys.

    (2002)
  • K.M. Lee et al.

    Recent developments of zinc oxide based photocatalyst in water treatment technology: a review

    Water Resea.

    (2016)
  • T. Phongamwong et al.

    Role of chlorophyll in Spirulina on photocatalytic activity of CO2 reduction under visible light over modified N-doped TiO2 photocatalysts

    Appl. Catal. B. Environ.

    (2015)
  • T. Phongamwong et al.

    Novel visible-light-sensitized Chl-Mg/P25 catalysts for photocatalyticdegradation of rhodamine B

    Appl. Catal. B. Environ.

    (2017)
  • M. Joshi et al.

    Chlorophyll-based photocatalysts and their evaluations for methyl orange photoreduction

    J. Photochem. Photobio. A Chem.

    (2009)
  • P. Kumbhakar et al.

    Observation of high photocatalytic activity bytuning of defects in chemically synthesized ethylene glycol capped ZnO nanorods

    Optik

    (2018)
  • L. Wang et al.

    Photocatalytic enhancement of Mg-doped ZnO nanocrystals hybridized with reduced graphene oxide sheets

    Prog. Nat. Sci. Mater. Int.

    (2014)
  • Ş.Ş. Türkyilmaz et al.

    Photocatalytic efficiencies of Ni, Mn, Fe and Ag doped ZnO nanostructures synthesized by hydrothermal method: The synergistic/ antagonistic effect between ZnO and metals

    J. Photochem. Photobio. A Chem.

    (2017)
  • S.P. Meshram et al.

    Cu doped ZnO microballs as effective sunlight driven photocatalyst

    Ceram. Int.

    (2016)
  • A.N. Kadam et al.

    Morphological evolution of Cu doped ZnO for enhancement of photocatalytic activity

    J. Alloys. Compd.

    (2017)
  • S.-H. Hsieh et al.

    Characterization and photocatalytic performance of ternary Cu-doped ZnO/Graphene materials

    Appl. Surf. Sci.

    (2018)
  • C.-M. Chou et al.

    Cu-doped ZnO nanowires as highly efficient continuous-flow photocatalysts for dynamic degradation of organic pollutants

    J. Photochem. Photobiol. A Chem.

    (2017)
  • Cited by (72)

    View all citing articles on Scopus
    View full text