Kinetic study on removal of copper(II) using goethite and hematite nano-photocatalysts

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Abstract

Goethite and hematite nanomaterials (nano-goethite and nano-hematite) can be synthesized using a coprecipitation method. Nano-hematite is synthesized via the reaction of HCl and FeCl3 solution at 100 °C for 2 days, while nano-goethite is prepared by adding Fe2(SO4)3 into the 2.5 M NaOH solution for 4 h, and then heated at 40 °C for 2 days. Afterward the photocatalytic decomposition of methylene blue solution is performed by UV-light irradiation, and the adsorption procedure is carried out by batch experiments. It is observed that both nano-hematite and nano-goethite exhibit some photocatalytic activity and possess a high adsorption capacity for copper ions. The maximum Cu(II) adsorption capacity is 149.25 and 84.46 mg/g for nano-goethite and nano-hematite, respectively. Further, the experimental data are well fitted to the pseudo-second-order equation. It also suggests that the Langmuir isotherm is more adequate than the Freundlich isotherm in simulating the adsorption isotherm of Cu2+, and the Cu2+ adsorption onto nanomaterials is a spontaneous process. Therefore, these findings indicate that nano-goethite and nano-hematite are effective materials for Cu2+ removal and, together with its photocatalytic activity, may be applied in the removal of heavy metal ions from aqueous streams.

Graphical abstract

The synthesized nano-goethite and nano-hematite are effective materials for Cu2+ removal and, together with their photocatalytic activity, may be applied to alleviate environmental contaminations.

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Introduction

The pollution of heavy metals may cause a risk to the environment [1], [2] as well as threaten human health through the food chain. Therefore, it is very important to determine an effective way to remediate heavy metal contaminations. Numerous treatment technologies to eliminate or reduce environmental problems have been developed, such as biodegradation, adsorption, and photocatalysis [3], [4]. Photocatalysis is an environmentally friendly process that utilizes irradiation energy for catalytic reactions. Thus, the photocatalysis technology has been widely investigated for pollutant eradication [5], [6], [7], and nano-photocatalysts including nano-TiO2 [8], [9], nano-SrTiO3 [10], [11], and nano-Fe2O3 [12], [13] have been intensively studied. Adsorption also is an environmental treatment technology, and the adsorption process has been extensively examined for the elimination of organic substances or heavy metal ions from water and wastewater [14], [15], [16]. The most common absorbents are porous materials, such as activated carbon, quartz sand, activated alumina, and zeolite. The porous property of adsorbents can typically provide a large specific surface area.

The development of nanotechnology at the end of the 20th century has widened the variety of adsorbents. The removal of heavy metals by nanoparticles has shown promising results with nanocrystalline titanium dioxide [17], nanoscale zero-valent iron [18], and so on. Recently, it has been discovered in the United States that it is possible to remove As species with magnetite (Fe3O4) nanoparticles, and the adsorption capacity is very high [19], [20], [21]. Moreover, nano-maghemite (γ-Fe2O3) has been found to be very effective in Cr(VI) removal [22]. The main advantages of using nanoparticles as adsorbents are: (a) they can be easily synthesized at a lower cost, (b) the amount of nanoparticles used is much less, and (c) their adsorption capacity is large due to their large surface area. Since nanomaterials exhibit unique properties as compared to conventional materials (zeolite, goethite, hematite, quartz sand, and activated carbon), research on nanomaterials has gradually become increasingly important and popular.

Iron oxides, such as goethite (α-FeOOH) and hematite (α-Fe2O3), can effectively adsorb heavy metals [23]. There have been a number of studies about the goethite or hematite adsorption systems, and these studies are related to the adsorption modeling of the surface reactions [24], [25], [26], [27]. Although there have been some studies on nano-goethite and nano-hematite, reports on Cu2+ adsorption using nano-goethite or nano-hematite are not available. In this study, Cu(II) batch adsorption experiments are performed with nano-goethite and nano-hematite, which are synthesized by employing a coprecipitation method. Then, the photocatalytic properties and the adsorption characteristics of these two nanomaterials with special emphasis on adsorption are investigated, and it is found that owing to these properties and characteristics, nano-goethite and nano-hematite are potential candidates for applications in heavy metal removal from aqueous streams.

Section snippets

Preparation and characterization of nanomaterials

In this study, nano-goethite and nano-hematite were synthesized by using the coprecipitation method. The synthesized procedure of nano-hematite was as follows. Deionized water (DI water, 500 ml) was taken in a beaker and heated at 90 °C and then HCl (∼0.05 ml) and FeCl3 (∼2.7 g) were added into the preheated DI water. The mixture was put in an oven at 100 °C for 2 days and then hematite nanoparticles were obtained. As for the synthesis of nano-goethite, Fe2(SO4)3 (∼2.5 g) was added to the 1 M NaOH

Characterization of nano-goethite and nano-hematite

The morphology and particle size of nano-goethite and nano-hematite, investigated by TEM, are shown in Fig. 1. The crystal shape of nano-goethite is acicular, and they are aggregated. The average particle size is 10–15 nm in width and ∼500 nm in length; it is classified according to the nanowire. As for nano-hematite, it has a granular shape with a crystal size about 75 nm, which is regarded as the nanoparticle. The specific surface area of nano-goethite and nano-hematite is listed in Table 1. The

Conclusion

Goethite and hematite nanomaterials exhibit some photocatalytic activity and possess a high adsorption capacity for copper ions. The adsorption efficiency of Cu2+ is time dependent, and the adsorption capacity increases with time. The photocatalytic and adsorption properties of nano-goethite and nano-hematite are quite attractive and indicative of its high potential. On the basis of the results in this study, we believe that synthetic goethite and hematite nano-photocatalysts can be used for

Acknowledgments

The author thanks Prof. Li Hong-Chun of the Department of Earth Sciences, National Cheng Kung University, for his help with the ICP-AES analysis. I also thank the National Science Council for financial support.

References (37)

  • I.K. Konstantinou et al.

    Appl. Catal. B

    (2004)
  • S. Ahuja et al.

    J. Photochem. Photobiol. A: Chem.

    (1996)
  • D.L. Liao et al.

    J. Photochem. Photobiol. A: Chem.

    (2007)
  • H.S. Hafez

    Mater. Lett.

    (2009)
  • C.T. Hsieh et al.

    Sep. Purif. Technol.

    (2009)
  • C.H. Chang et al.

    Mater. Lett.

    (2006)
  • T. Puangpetch et al.

    J. Mol. Catal. A: Chem.

    (2008)
  • J.M. Gu et al.

    J. Solid State Chem.

    (2009)
  • M.H. Khedr et al.

    Mater. Lett.

    (2009)
  • C.F. Chang et al.

    Water Res.

    (2004)
  • M.E. Pena et al.

    Water Res.

    (2005)
  • J.T. Mayo et al.

    Sci. Technol. Adv. Mater.

    (2007)
  • P. Wang et al.

    Water Res.

    (2009)
  • R. Weerasooriya et al.

    Colloids Surf. A

    (2000)
  • B.H. Jeon et al.

    Water Res.

    (2004)
  • N. Xu et al.

    Chemosphere

    (2006)
  • Y.S. Hwang et al.

    J. Colloid Interface Sci.

    (2009)
  • S.J. Allen et al.

    J. Colloid Interface Sci.

    (2004)
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