Degradation of phenol by heterogeneous Fenton reaction using multi-walled carbon nanotube supported Fe2O3 catalysts

doi:10.1016/j.colsurfa.2009.04.037

Colloids and Surfaces A: Physicochemical and Engineering Aspects

Volume 345, Issues 1–3, 5 August 2009, Pages 95-100

https://doi.org/10.1016/j.colsurfa.2009.04.037 Get rights and content

Abstract

Multi-walled carbon nanotube (MWCNT) supported Fe₂O₃ catalysts were prepared by impregnating acid treated MWCNTs in Fe(NO₃)₃ solutions and calcined at 200 °C. The catalysts were used to degrade phenol and phenolic contaminants (resorcinol and ortho-chlorophenol) with H₂O₂ by Fenton reaction. The experimental conditions such as reaction temperature, catalyst load and H₂O₂ dosage on the degradation of phenol have been investigated. More than 70% phenol has been degraded with Fe₂O₃/MWCNT catalysts after 200 min, 20% higher than with bare Fe₂O₃, suggesting that the reaction performance could be enhanced by the presence of MWCNTs. This demonstrates that MWCNTs are good and promising supporting materials and catalysts for advanced oxidant process and other catalytic reactions as well.

Introduction

Nowadays, the pollution of water resource has become a very serious problem attracting more and more concerns. Among all kinds of contaminants, phenol, widely used as industrial raw materials or intermediates, is one of the most toxic organics discharged by numerous manufactories. Therefore, wastewater treatments including adsorption [1], biodegradation [2] and advanced oxidation process [3] have been developed. Advanced oxidation process is based on the generation of hydroxyl radicals with high oxidizing potential (2.8 eV), second only to fluorine in its reactivity [4]. Fenton reaction producing hydroxyl radicals through the reaction between Fe²⁺ and H₂O₂ is effective in the complete destruction of organic contaminants into harmless compounds and thus removing pollutants from water [5]. However, homogeneous Fenton reaction needs 50–80 ppm of iron ions in solution, which is much higher than 2 ppm allowed by European Community Directives [6]. In addition, the separation and recovery of ions become another hindrance in the application of homogeneous reaction. To overcome these disadvantages, heterogeneous catalysts like clay [4], SBA-15 [7], silica [8], carbon [9] etc., supporting ferric ions have been developed. The mechanism of heterogeneous Fenton reaction is presented as:Fe³⁺ + H₂O₂ → Fe(OOH)²⁺ + H⁺Fe(OOH)²⁺ → Fe²⁺ + HO₂ radical dot Fe²⁺ + H₂O₂ → Fe³⁺ + HO⁻ + HOFe³⁺ + HO₂ → Fe²⁺ + H⁺ + O₂

Using carbon nanotubes (CNTs) as catalysts or supports is promising in the field of environmental remediation due to their large specific surface areas. Garcia et al. [10] reported that CNTs were efficient ruthenium supports for catalytic wet air oxidation of wastewater containing aniline. Zhang et al. [11] investigated the Pd cluster filled in multi-walled carbon nanotubes (MWCNTs) as catalysts applied in liquid phase benzene hydrogenation and found that they exhibited higher activity than other supports such as zeolite and activated carbon. Serp et al. [12] indicated that CNTs were attractive and competitive supports compared with other kind of carbon materials because of their stability and adsorption property. These studies inspire the idea of using MWCNTs as supports of Fe₂O₃ in Fenton reaction to degrade phenol and its derivatives in water. So far, MWCNTs have not been used for such purpose in wastewater treatment. In this study, MWCNT supported Fe₂O₃ catalysts have been prepared by impregnation and used to degrade phenol, resorcinol and ortho-chlorophenol (o-CP) by Fenton reaction. Their improved degradation performance indicates the potential application of MWCNTs in environment protection.

Section snippets

Sampling

Pristine MWCNTs commercially obtained from Chengdu Institute of Organic Chemistry have diameters ranging from 10 to 20 nm. The purity is about 95 wt% claimed by the provider. They were ultrasonicated in mixed acid (HNO₃/H₂SO₄ = 1/3, v/v) for 5 h. The mixture was filtered through 0.2 μm filter, washed with distilled water and anhydrous ethanol and then dried at 60 °C for 24 h. They were denoted as acid MWCNTs.

Analytical grade Fe(NO₃)₃·9H₂O was employed to prepare aqueous solution of Fe(NO₃)₃ with

Characterization

Fig. 1 shows the TEM images of pristine MWCNTs, acid MWCNTs and Fe₂O₃/MWCNTs. There is no significant difference between pristine MWCNTs and acid treated ones. Their lengths range from several to tens micrometers. Carboxyl groups produced in acid treatment make acid MWCNTs negatively charged. The ferric ions with positive charge adsorb onto acid MWCNTs through electrostatic attractions. After calcination, Fe₂O₃ has formed and coated on MWCNTs with particle size less than 10 nm as shown in Fig. 1

Conclusions

In conclusion, MWCNTs have been firstly used as supports for Fe₂O₃ in heterogeneous Fenton reaction to degrade phenol and other phenolic contaminants. The catalysts have been well characterized by TEM, XRD, TG–DSC and N₂ adsorption analysis. The experimental conditions such as reaction temperature, catalyst load and H₂O₂ dosage on phenol degradation have been investigated. About 80% phenol is degraded with 0.01 g Fe₂O₃/MWCNTs and 4.75 mmol H₂O₂ at 80 °C after 200 min reaction. Compared with bare Fe₂

Acknowledgments

Financial support from NSFC (50572114), National 973 project (2005CB623605) and Hundred Talents Program of Chinese Academy of Sciences is greatly acknowledged.

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Degradation of phenol by heterogeneous Fenton reaction using multi-walled carbon nanotube supported Fe2O3 catalysts

Abstract

Introduction

Section snippets

Sampling

Characterization

Conclusions

Acknowledgments

Microchem. J.

Ultrason. Sonochem.

J. Hazard. Mater.

Appl. Catal. B

Chem. Eng. J.

Appl. Catal. B

Chem. Eng. J.

Carbon

Catal. Today

Appl. Catal. A

Chem. Phys. Lett.

Chem. Phys. Lett.

Degradation of phenol by heterogeneous Fenton reaction using multi-walled carbon nanotube supported Fe₂O₃ catalysts