Elsevier

Journal of Alloys and Compounds

Volume 553, 15 March 2013, Pages 19-29
Journal of Alloys and Compounds

Photocatalytic degradation of methylene blue dye using Fe2O3/TiO2 nanoparticles prepared by sol–gel method

https://doi.org/10.1016/j.jallcom.2012.10.038Get rights and content

Abstract

The photocatalytic degradation of methylene blue dye was successfully carried under UV irradiation over Fe2O3/TiO2 nanoparticles embedded various composition of Fe2O3 (0–20) wt.% synthesized by sol–gel process. Structural and textural features of the mixed oxide samples were investigated by X-ray diffraction [XRD], Fourier transformer infra-red [FTIR], Energy dispersive X-ray [EDX], Field emission electron microscope [FESEM] and transmission electron microscope [TEM]. However, the optical features were estimated using UV–Vis spectrophotometer. The results reveal that the incorporation of various Fe2O3 up to 7% is associated by remarkable increase in surface area, reduction of particle size, stabilization of anatase phase, shifting the photoexcitation response of the sample to visible region and exceptional degradation of methylene blue dye. On the other hand, increasing Fe2O3 contents up to 20 wt.% is associated by anatase–rutile transformation, increasing in particle size and remarkable decrease in surface area which are prime factors in reducing the degradation process. The experimental results indicate that Fe2O3/TiO2 nanoparticles having both the advantages of photodegradation–adsorption process which considered a promising new photocatalysts that involve in the abatement of various organic pollutants.

Graphical abstract

Photocatalytic degradation of methylene blue dye was successfully carried over Fe2O3/TiO2 nanorods embedded various proportion of Fe2O3 (0–20) wt.%.

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Highlights

► Fe2O3/TiO2 nano mixed oxide samples were successfully synthesized by sol–gel method. ► Manipulation of particle size and structure were achieved by micelle template approach. ► Both adsorption and photocatalytic reactivity are the main reasons for exceptional decolorization of methylene blue dye. ► A new mechanism for electronic transition between TiO2 and Fe2O3 was proposed.

Introduction

The discharge of several Hazardous dyes from many textiles industries in waste water is a main cause for serious environmental problems that concerned with human health and the aquatic medium due to the toxicity and the carcinogenic effect of these materials [1], [2]. Several approaches are devoted to remove these toxic dyes from water such as adsorption on high surface area supports, chemical precipitation, sedimentation, biological membranes and ion-exchange processes. However, these methods are slow, require expensive equipment and may lead to transfer of the main pollutant into a second one that requires further removal. Moreover, the majority of the textile dyes are photocatalytically stable and refractory towards chemical oxidation, and these characteristics render them resistant towards decolorization by conventional biochemical and physicochemical methods. A successful route for dye removal is concerned with utilizing nano semiconductors as TiO2, ZnO, Fe2O3 and CdS that exhibit high photocatalytic reactivity in removal several organic containments without transfer a primary pollutant into series of toxic materials. In the recent years, nano titanium oxide is considered the most suitable candidate photocatalyst that involved in degradation and removal of various toxic organic pollutants [3], [4] due to the stability of its chemical structure, biocompatibility, strong oxidizing power, non-toxicity and low cost [5], [6]. The crystalline and the textural features are considered the main causes that determine the photocatalytic features of the samples [7], [8], [9], [10]. The photocatalytic process is usually initiated by incident UV radiation on the oxide samples that leads to electron transfer from the filled valence band to the empty conduction band. This process is accompanied by generation of the negative electron (e) and the positive hole (h+) pairs on the surface of the photocatalyst [11], [12], [13], [14]. These charge carriers are either combine with each other or involve in mineralization of the organic pollutants on the catalyst surface through a series of redox reactions. Moreover, possible reactions between the positive hole and electrons with water and O2 lead to formation of peroxide and superoxide radicals which considered as active species in the degradation process [11], [12], [13], [14]. The fast recombination of charge carriers and the short wave length excitation are considered the main electronic obstacles that limit the photocatalytic applications and restrict its reactivity to UV region only. The incorporation of transition elements is a suitable way in enhancing the optical features of the titania by causing a batho-chromic shift of the absorption response and preventing the electron–hole recombination which increases the catalyst life time for the mineralization process [15], [16], [17], [18]. Fe3+ ion with narrow band gap energy (1.9 eV) is one of the promising candidates that can effectively enhance the photocatalytic features of titania due to its half-filled electronic configuration and the similarity of the ionic radius of Fe3+ (0.64 A) with that of coordinated Ti4+ (0.68 A). Several authors claim that the incorporation of Fe3+ on titania improves the photocatalytic features of the sample by reducing the band gap energy by about 2 eV and extending the photoexcitation response to visible region [19], [20], [21], [22], [23], [24], [25]. Many recent works have been devoted to study the influence of iron oxide on the physicochemical and optical features of titania in degradation of several organic pollutants. The results obtained indicate that the existence of an appropriate amount of iron (III) (less than 10%) shifts the photocatalytic reactivity toward a more favorable direction [26], [27], [28] as doped Fe3+ replaces Ti4+ in TiO2 lattice, forming localized bands near the bottom of conduction band and thereby decreasing the band gap energy. It is well established that the conduction and valence band of titania have potential of −0.2 to −0.65 and 2.6–3.0 eV, respectively [30], can provide electrons for the reductions of Fe3+ and Fe2+ (Fe3+ + e  Fe2+ E0 = 0.771 eV and Fe2+ + 2e  Fe0 E0 = −0.44 eV) [29], [30]. This arguments will allow the electrons generated on TiO2 by UV irradiation to be trapped by the two half reactions of Fe3+/Fe2+ and Fe2+/Fe0, that inhibit the electron–hole recombination. Elghniji et al. prepare Fe3+ doped titania by acid-catalyzed sol–gel process and they indicate that Fe3+ ions can be successfully inserted into the TiO2 crystal lattice by substituting Ti4+ which inducing a red shift of TiO2 absorption edge toward visible region [31]. Tada et al. prepare iron oxide modified anatase and anatase–rutile titania by ligand exchange method and they indicate that the existence of ferric oxide chemisorbed on titania surface improves the photocatalytic response of the samples under both the ultraviolet and visible light. Moreover, they indicate that the surface iron oxide species rapidly capture the excited electrons in the conduction band of TiO2 to suppress recombination via surface oxygen vacancy levels [32], [33]. In the recent year, Sun et al. indicate that the existence of bulk-Fe3+ can trap photogenerated electrons and transfer them to pre-adsorbed species to form active species, whereas incorporation of Fe3+ sites on the sample surface can trap holes. These different roles of Fe3+ increase the efficiency of charge separation and transfer of Fe–TiO2 and extend the photocatalytic oxidation of pollutants under visible light irradiation [21]. Jamalluddin and Abdullah indicate that the combination of 0.4 mol.% of Fe(III)/TiO2 with ultrasonic irradiation gave the highest sonocatalytic activity in the removal of RB4 from the aqueous solution. In addition, they indicate that the existence of too low of Fe(III) loading, the generation of OH radicals could not be sufficiently accelerated to consequently cause low removal of RB4. However, if the Fe(III) content was too high, it might inhibit the surface reaction of the TiO2 and decrease the production of OH radicals [26].

Although several studies have been focused on Fe/TiO2 nanoparticles, all the previous works are not sufficient to investigate the influence of existence of various Fe2O3 contents on the structure, texture and the morphology of TiO2 nanoparticles system prepared by sol–gel method using an effective template as octadecylamine. This new system is expected to exhibit powerful influence on the photocatalytic degradation of several hazardous dyes.

In the present work, we make an attempt to synthesize Fe2O3/TiO2 nanoparticles by sol–gel method using octadecylamine template to fabricate nanoparticle with definite shape and size. The prepared samples are investigated using developed techniques as FTIR, XRD, BET, FESEM and TEM to assist the role of the existence of different composition of iron oxide on the structure, particle size, pore texture, morphology and optical features of the samples. Moreover, the photocatalytic performance of the samples in degrading methylene blue dye under UV irradiation dye was estimated using UV–Vis spectrophotometry.

Section snippets

Experimental

TiCl4, Fe(NO3)3·9H2O, ammonia solution and octadecylamine were all purchased from Aldrich Company were involved in preparation of pure titania and Fe2O3/TiO2 mixed oxide samples. An exact amount of about 6.79, 6.72, 6.5, 6.38, 6.17, 5.83 and 5.49 ml of TiCl4 solution is mixed with 0.25, 0.5, 1.25, 2.5, 3.75 and 5 g of Fe(NO3)3·9H2O dissolved in acetone in order to prepare mixed oxide samples embedded 1, 2, 5, 7, 10, 15 and 20 wt.% Fe2O3/TiO2, respectively. About 10.5 g of octadecylamine surfactant

X-ray diffraction

Fig. 1 depicts the X-ray diffraction pattern of TiO2, TiFe1, TiFe2, TiFe5, TiFe7, TiFe10, TiFe15 and TiFe20 samples. Several crystalline peaks are detected for pure titania sample at 2θ = 25.3°, 36.9°, 37.7°, 38.5°, 48°, 51.9°, 53.8°, 55.1°, 62.6°, 68.7° and 75° indicating the existence of predominant anatase phase, however, small peaks are detected at 2θ = 27.4°, 39°, 41°, and 44° owing to the existence of small proportion of rutile phase. The diffraction pattern for the samples embedded various

Conclusions

High surface area Fe2O3/TiO2 nanoparticles containing various proportion of Fe2O3 (0–20) wt.% were successfully synthesized using sol–gel and self assembly approach for photocatalytic degradation of methylene blue dye. The introduction of an appropriate amount of Fe2O3 (1–7 wt.%) is associated with shifting the physicochemical and optical features of samples toward more favorable state. XRD and FTIR results indicate the absence of crystalline ferric oxide phases reveling the dissolution in

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