Preparation and photocatalytic performance of Fe (III)-amidoximated PAN fiber complex for oxidative degradation of azo dye under visible light irradiation

https://doi.org/10.1016/j.scitotenv.2010.01.020Get rights and content

Abstract

Polyacrylonitrile (PAN) fiber was modified with hydroxylamine hydrochloride to introduce amidoxime groups onto the fiber surface. These amidoxime groups were used to react with Fe (III) ions to prepare Fe (III)-amidoximated PAN fiber complex, which was characterized using SEM, XRD, FTIR, XPS, DMA, and DRS respectively. Then the photocatalytic activity of Fe–AO–PAN was evaluated in the degradation of a typical azo dye, C. I. Reactive Red 195 in the presence of H2O2 under visible light irradiation. Moreover, the effect of the Fe content of Fe–AO–PAN on dye degradation was also investigated. The results indicated that Fe (III) ions can crosslink between the modified PAN fiber chains by the coordination of Fe (III) ions with the amino nitrogen atoms and hydroxyl oxygen atoms of the amidoximation groups to form Fe (III)-amidoximated PAN fiber complex, and the Fe content of which is mainly determined by Fe (III) ions and amidoximation groups. Fe (III)-amidoximated PAN fiber complex is found to be activated in the visible light region. Moreover, Fe (III)-amidoximated PAN fiber complex shows the catalytic activity for dye degradation by H2O2 at pH = 6.0 in the dark, and can be significantly enhanced by increasing light irradiation and Fe content, therefore, it can be used as a new heterogeneous Fenton photocatalyst for the effective decomposition of the dye in water. In addition, ESR spectra confirm that Fe (III)-amidoximated PAN fiber complex can generate more radical dotOH radicals from H2O2 under visible light irradiation, leading to dye degradation. A possible mechanism of photocatalysis is proposed.

Introduction

Photoassisted Fenton technologies have been widely used in the degradation of water-soluble azo dyes in industrial wastewater. Ferrous salts react with H2O2 to produce hydroxyl free radicals during the Fenton reaction, which attack the unsaturated dye molecules, thus decolorizing the wastewater. But drawbacks in the use of Fenton reactions are (a) they are limited to the acidic pH < 4; (b) the Fe ions remain in aqueous solutions at the end of treatment and were discharged directly into the environment and produce a significant amount of Fe (III)-iron sludge, which requires further separation and disposal. To avoid these limitations, some attempts have been made to develop the heterogeneous photocatalysts for Fenton reactions by immobilized Fe ions on the polymer substrates. For example, Nafion membrane was often used for immobilizing Fe ions to form a Fe/Nafion catalyst for the decoloration of the dyes in water (Fernandez et al., 1998, Fernandez et al., 1999, Dhananjeyan et al., 2001). But, it is known that Nafion membrane is too expensive to be used as a catalyst support in an industrial scale (Feng et al., 2003). Hence, it is necessary to explore new heterogeneous catalysts for the photoassisted Fenton reactions by using lower-cost polymer materials. In addition to the granulated or membrane catalysts, fibrous catalysts are very promising. An important advantage is the developed outer surface, which facilitates access of the reacting substances to active sites during the reaction. Another advantage is the use of textile technology allowing the manufacture of inexpensive materials from synthetic complex in the form of woven cloth and bulky knit fabrics and creating designs of almost any geometric shape suitable for placing in equipment (Vitkovskaya et al., 2003).

Polyacrylonitrile (PAN) fiber is a kind of synthetic fiber used widely in modern textile process, and generally exhibits good resistance to mineral acids, and is unaffected by common oxidizing agents and sunlight (Choudhury, 2006). On the other hand, PAN fiber is easily modified with hydroxylamine at alkaline solution by partial conversion of its nitrile groups into amidoxime groups. There have been a number of works devoted to the modification of PAN fibers by hydroxylamine in aqueous and alcoholic media in order to produce effective sorption materials for the removal of heavy metal ions in water (Stefanova, 2001, Nicolae et al., 2004, Dedkova et al., 2006) and the recovery of uranium from seawater (Kavakli et al., 2004, Seko et al., 2005). Moreover, Ishtchenko et al., 2003a, Ishtchenko et al., 2003b found that PAN fiber modified with a mixture of hydrazine and hydroxylamine was used to fix Fe (III) ions to the fiber to produce a PAN fibrous catalyst, which had enormous potential for use as a heterogeneous Fenton catalyst in the degradation of organic pollutants in a range of industrial effluent. However, the detailed information on light adsorption properties of the PAN fibrous catalyst and its photocatalytic function on degradation of organic pollutants under visible light irradiation is very limited.

In the present study, PAN fiber is firstly modified with hydroxylamine to generate the amidoximated PAN fiber as an effective ligand. And then these amidoxime groups of the ligand are used to coordinate with Fe (III) ions to prepare a new heterogeneous Fenton photocatalyst, Fe (III)-amidoximated PAN fiber complex. SEM, XRD, FTIR, BET, XPS, DMA (dynamic thermo-mechanical analysis) and UV–Vis DRS (UV–Vis diffuse reflectance spectroscopy) techniques are used to elucidate the nature of the photocatalyst specimens. Its photocatalytic properties were evaluated in the degradation of a typical azo dye, C. I. Reactive Red 195 in the presence of H2O2 under visible light irradiation. This dye was selected as the model pollutant, mainly because of its relatively high consumption rate in China for the dyeing of cotton fabrics. It has been produced by more than 10 chemical companies in China, but has been unable to meet the effluent color standard of China. Active hydroxyl radicals in the photocatalytic system are detected by ESR spectrum under visible light irradiation. The primary objective of this study is to explore the role of visible light radiation in Fe (III)-amidoximated PAN fiber complex for the dye degradation. A proposed mechanism of photocatalysis is also discussed.

Section snippets

Materials and reagents

PAN knitting bulky yarn (abbr. PAN yarn) that consisted of twisted PAN fibers were obtained from Shanghai Shilin Spinning Co. Its nitrogen, carbon and hydrogen contents were 22.97%, 66.31% and 5.51%, respectively. The contents of elements in PAN yarn were determined using Vario EL III Elemental analyzer (Elementar Analysensysteme GmbH, Germany). Hydroxylamine hydrochloride, hydrogen peroxide (30% aqueous solution), ferric chloride and N, N-Diethyl-p-phenylenediamine (DPD) were of laboratory

Preparation of Fe–AO–PAN

The preparation of Fe–AO–PAN began with the conversion of the nitrile groups on the surface of the PAN fiber to amidoxime groups in hydroxylamine solution. The amidoximated PAN fibers (AO–PAN) then were reacted with Fe (III) ions in solution to form Fe–AO–PAN. The two reactions are depicted by Eqs. (1) and (2).

To determine the dependence of CFe–PAN of Fe–AO–PAN during the preparation, Fe–AO–PAN was produced by the coordination of AO–PAN with different CP% values in the varied concentration of

Conclusions

Fe (III)-amidoximated PAN fiber complex (Fe–AO–PAN) can be prepared by the reaction between the amidoximated PAN fiber and Fe (III) ions. FTIR and XPS analysis suggests that the amino nitrogen atoms and the hydroxyl oxygen atoms of amidoxime groups of AO–PAN chains coordinate with Fe (III) ions to form Fe–AO–PAN. CFe–PAN of Fe–AO–PAN is dependent greatly on the concentration of Fe (III) ions in aqueous solution and CP% of AO–PAN. Fe–AO–PAN exhibits relatively high catalytic activity toward the

Acknowledgements

This work was kindly supported by a grant from the Natural Science Foundation of China (No. 20773093). The authors thank the support from the Ministry of Education of China through a grant from the Research Fund for the Doctoral Program of Higher Education of China (No. 20070058005). The research was also supported in part by “Open-Lab Grant (2005-01)” from the State Key Laboratory of Environmental Aquatic Chemistry, Research Center of Eco-Environmental Sciences, Chinese Academy of Sciences.

References (25)

  • M.R. Dhananjeyan et al.

    Photo-assisted immobilized Fenton degradation up to pH 8 of azo dye Orange II mediated by Fe3+/Nafion/glass fibers

    Helv Chem Acta

    (2001)
  • R. El-Shishtawy et al.

    Anionic coloration of acrylic fibre. Part 1: efficient pretreatment and dyeing with acid dyes, Color

    Technol

    (2005)
  • Cited by (126)

    • An efficient polymer supported Fenton type catalyst for photodegradation of organic dyes

      2024, Journal of Photochemistry and Photobiology A: Chemistry
    View all citing articles on Scopus
    View full text