Visible-light-driven photocatalytic properties of simply synthesized α-Iron(III)oxide nanourchins

Journal of Colloid and Interface Science 451 (2015) 93–100

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Visible-light-driven photocatalytic properties of simply synthesized a-Iron(III)oxide nanourchins Yang Jiao a, Yang Liu a, Fengyu Qu a, Ahmad Umar b,c,⇑, Xiang Wu a,⇑ a Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education and College of Chemistry and Chemical Engineering, Harbin Normal University, Harbin 150025, PR China b Department of Chemistry, College of Science and Arts, Najran University, P.O. Box 1988, Najran 11001, Saudi Arabia c Promising Centre for Sensors and Electronic Devices (PCSED), Najran University, P.O. Box 1988, Najran 11001, Saudi Arabia

g r a p h i c a l a b s t r a c t

500 nm

a r t i c l e

i n f o

Article history: Received 4 February 2015 Accepted 28 March 2015 Available online 6 April 2015 Keywords: a-Fe2O3 nanourchins Visible light Photodegradation Hazardous dyes

a b s t r a c t Well-crystalline a-Fe2O3 nanourchins were successfully prepared via a facile hydrothermal method using dimethylsulfoxide (DMSO) as the growth template and characterized in detail in terms of their morphological, structural, compositional and photocatalytic properties. To understand the growth process for the formation of a-Fe2O3 nanourchins, several reaction time and DMSO amount dependant experiments were performed and it was found that reaction time and the amount of DMSO are critical parameters to obtain urchin-shaped morphologies. A plausible growth mechanism for the formation of a-Fe2O3 nanourchins was presented. The prepared a-Fe2O3 nanourchins were used as efficient photocatalyst for the photocatalytic degradation of three harmful organic dyes, i.e. Congo red (CR), Eosin red (ER) and methylene blue (MB) under visible light illumination. The order of degradation rate for all used dyes are MB (80%) < Eosin red (84%) < CR (98%). By comparing the photocatalytic performance towards Congo red dye with other photocatalysts such as dendrite-shaped a-Fe2O3 structures and commercially available TiO2 (P-25), it was observed that the prepared a-Fe2O3 nanourchins exhibited superior photocatalytic performance towards CR dye. Finally, the photocatalytic recycle tests were also performed which showed that the prepared a-Fe2O3 nanourchins were stable after even five cycles. The presented works demonstrates that aFe2O3 nanourchins are promising candidate for the photocatalytic degradation of various harmful organic dyes and pigments. Ó 2015 Elsevier Inc. All rights reserved.

⇑ Corresponding authors at: Department of Chemistry, College of Science and Arts, Najran University, P.O. Box 1988, Najran 11001, Saudi Arabia (A. Umar). E-mail addresses: [email protected] (A. Umar), [email protected] (X. Wu). http://dx.doi.org/10.1016/j.jcis.2015.03.055 0021-9797/Ó 2015 Elsevier Inc. All rights reserved.

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1. Introduction Nanomaterials are considered as primary units of nanoscience and nanotechnology and developing nanomaterials with controlled morphologies using novel methods is extremely important not only for fundamental studies but also for high-technological applications [1–6]. From the last few decades, number of strategies have been applied to prepare controlled morphologies and dimensions of nanostructures and reported in the literature [7–19]. Among various semiconductor materials, it is considered that hematite (a-Fe2O3) is one of the most important n-type semiconductor materials due to its own properties and wide scientific and technological importance. Various fascinating and important properties of hematite make it an attractive material for various applications, to name a few, photocatalysis, pigments, magnetic storage media, gas, chemical and bio-sensors, and lithium-ion batteries and so on [20–26]. Thus, because of the several exotic properties and wide applications, various a-Fe2O3 nanostructures such as nanoparticles [27], nanocubes [28], nanowires [29] and nanotubes [30] were synthesized using several synthetic methods and reported in the literature. Recently, three-dimensional (3D) ordered a-Fe2O3 assembles with unique spatial construction have attracted much attention for their important applications in many fields [31,32]. Yu and co-workers have prepared cage-like a-Fe2O3 hollow spheres by a controlled hydrothermal precipitation reaction using urea as a precipitating agent and carbonaceous polysaccharide spheres as the templates in a mixed solvent of water and ethanol, and studied their photocatalytic properties [33]. Cao et al. have prepared single-crystal dendritic micro-pines of aFe2O3 by treating K3[Fe(CN)6] in aqueous solution [34]. Jiang’s group has synthesized cauliflower-like a-Fe2O3 microstructures constructed by nanoparticle based buds through one-step toluene-water biphasic interfacial reaction route [35]. In our previous work, we have prepared Fe2O3@NiO nanohybrids on carbon cloth using a hydrothermal process and studied their electrochemical properties [36]. Even though, a variety of a-Fe2O3 nanomaterials are developed and applied for various applications and reported in the literature, but still it is necessary to develop simple and reliable methods to prepare specific a-Fe2O3 nanoarchitectures for particular applications. In this work, we report a simple and facile method to prepare aFe2O3 nanourchins. The as-prepared nanourchins were characterized in detail and utilized as efficient photocatalysts for the photocatalytic degradation of three harmful organic dyes, i.e. Congo red, Eosin red and methylene blue, under visible light illumination. The detailed photocatalytic experiments revealed that the prepared a-Fe2O3 nanourchins are the excellent candidates for the photocatalytic degradation of organic dyes under visible light irradiation.

time, the autoclave was cooled to room temperature and finally yellow precipitate was obtained which was collected by centrifugation and washed for several times with ethanol and de-ionized water, sequentially and dried in an oven at 60 °C for 12 h. Finally, the obtained powder was annealed in air at 400 °C for 2 h. 2.2. Characterizations of a-Fe2O3 nanourchins The general and detail morphologies of the as-synthesized and calcined nanomaterials were examined by scanning electron microscopy (SEM, Hitachi-4800) and transmission electron microscopy (TEM, JEOL-2010EX). The crystallinity and crystal phases of the prepared powder were studied by X-ray diffractometer (XRD; Rigaku Dmax-rB), measured with Cu Ka radiation (k = 0.1542 nm, 40 kV, 150 mA). The specific surface area analyzer (NOVA2000E) was used to measure the N2-sorption isotherm and the Brunauer–Emmett–Teller (BET) formula was employed to calculate the specific surface area of the prepared nanourchins. 2.3. Visible-light driven photocatalytic degradation of harmful organic dyes using a-Fe2O3 nanourchins The photocatalytic degradation of harmful organic dyes were carried out in a doubled walled 500 mL reaction vessel with circulating water using a-Fe2O3 nanourchins as the photocatalysts under visible light illumination. For the photocatalytic degradation of organic dyes, 100 mg of a-Fe2O3 nanourchins was suspended in 200 mL dye solutions (40 mg L1) and the resultant solutions were continuously stirred for 60 min in the dark to ensure the establishment of an adsorption–desorption equilibrium between a-Fe2O3 nanourchins and organic dyes. After equilibrium, the solutions were exposed to visible light irradiation (from a 1000 W, Xe-Lamp) at room-temperature. The photocatalytic degradation was estimated by measuring the absorbance of dye solution in the presence of photocatalyst exposed under visible light at different time intervals. The absorbance was measured by UV–vis. spectrophotometer (Shimazu UV-2550) and the samples were collected at regular time interval to measure the organic dyes degradation. The aliquots were centrifuged and the absorbance of the obtained solution was examined. Finally, the degradation efficiency was calculated by using following equation:

Degradation Efficiency ¼ ð1  C=C 0 Þ  100% where C and C0 were the equilibrium concentration of dye after and before irradiation under visible light. 3. Results and discussion 3.1. Characterizations and properties of a-Fe2O3 nanourchins

2. Experimental details 2.1. Synthesis of a-Fe2O3 nanourchins For the synthesis of a-Fe2O3 nanourchins, all the used chemicals were analytical grade which were used as received without further purification. In a typical reaction process for the synthesis of aFe2O3 nanourchins, 0.05 M iron chloride hexahydrate (FeCl36H2O) and equal amount of sodium sulfate (Na2SO4) were thoroughly mixed under continuous stirring in 80 ml of distilled water. The resultant solution was stirred for 10 min and then 2 mL dimethylsulfoxide (DMSO; C2H6SO) was added into it. After stirring, the resultant mixture was transferred into a 100 mL autoclave with an inner lining of Telfon. The autoclave was sealed and kept at 120 °C for 8 h. After completing the reaction in desired

The general morphologies of the as-synthesized and calcined materials were examined by scanning electron microscopy. Fig. 1(a) and (b) demonstrate typical SEM images of the as-synthesized a-FeOOH materials. It is clear from the observed SEM images that the as-synthesized a-FeOOH materials posses urchin-like morphologies and grown in very high density. The urchin-like morphologies are made by the accumulation of several nanoneedles which are assembled at one single point in such a manner that they made beautiful urchin-like morphologies. All the nanoneedles were radially arranged at a central point and finally made urchinshaped morphologies. The typical size of each nanoneedle is in the range of 110 ± 30 nm while the full urchin size is in the range of 2 ± 0.5 lm. Fig. 1(c) and (d) exhibited typical SEM images of the samples calcined at 400 °C. Interestingly, it was observed that by calcination of the as-synthesized a-FeOOH nanourchins, it changes

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Fig. 1. Typical SEM images of (a and b) the as-synthesized a-FeOOH nanourchins and (c and d) calcined a-Fe2O3 nanourchins.

the phase to a-Fe2O3 nanourchins, without changing the basic morphologies, i.e. nanourchin morphologies. Thus, it is revealed that the calcination only affects the crystal phases but does not affect the morphologies of the as-synthesized products and after calcination, the shapes and sizes of the synthesized urchins was same. The typical sizes of the full a-Fe2O3 urchin structures are in the range of 2 ± 0.5 lm. The prepared a-Fe2O3 nanourchins were further characterized and used as the efficient photocatalysts for the photocatalytic degradation of harmful organic dyes. The detailed morphological and structural properties of the asprepared a-Fe2O3 nanourchins were examined by transmission electron microscopy (TEM) equipped with high-resolution TEM (HRTEM) and selected area electron diffraction (SAED) pattern. Fig. 2(a) and (b) exhibits the typical low-magnification TEM images of the prepared a-Fe2O3 nanourchins. The observed TEM images are fully consistent with the obtained FESEM results in terms of morphologies and dimensionality. It is clear evident from the observed TEM images that the nanourchins are made by the accumulation of several nanoneedles which are all originated radially through a single point and form special urchin-shaped morphologies (Fig. 2(a) and (b)). Fig. 2(c) exhibits the typical HRTEM image of corresponding nanoneedle shown in figure (b). The observed HRTEM image exhibited a well-defined lattice planes with the inter-planar lattice distance of 0.25 nm, correspond to the (1 1 0) plane of the rhombohedral hematite phase (Fig. 2(c)) and hence confirmed that the prepared material is a-Fe2O3. Fig. 2(d) shows the corresponding SAED pattern of a-Fe2O3 nanourchins and suggesting that the prepared material possess polycrystalline nature. To examine the crystallinity and crystal phases, the as-synthesized and calcined iron oxide nanomaterials were examined by X-ray diffraction pattern. Fig. 3(a) depicts the typical XRD pattern of the as-synthesized a-FeOOH nanourchins. Several well-defined diffraction reflections are seen in the observed XRD pattern. All the diffraction reflections are well matched with the standard values of goethite (a-FeOOH) and well consistent with the reported literature and Joint Committee on Powder Diffraction Standards (JCPDS) card number 29-0713. When the as-synthesized a-

FeOOH nanourchins were calcined at 400 °C for 2 h, it directly converts to a-Fe2O3. To check the conversion of a-FeOOH to a-Fe2O3, the calcined samples were also examined by X-ray diffraction. Fig. 3(b) shows the typical XRD pattern of calcined samples. Various well-defined diffraction reflections are seen in the pattern which is well matched with the hexagonal a-Fe2O3 phase and well consistent with the reported JCPDS card No: 33-0664. No other characteristic reflections related with other impurities were detected in the observed XRD patterns, revealed that the as-synthesized material is a-FeOOH while the calcined nanourchins are pure a-Fe2O3. The absorbance of the prepared photocatalysts were examined by UV–vis DRS spectroscopy and results are demonstrated in Fig. S1. It is clear from the observed UV–vis. DRS spectra that the urchin-like a-Fe2O3 and dendrite-like a-Fe2O3 nanostructures are exhibiting strong absorption in the visible range up to ca. 650 nm; however, the commercially available photocatalyst, i.e. P-25 is showing an ultraviolet region active absorption peak. This clearly revealed that the prepared iron oxide nanomaterials are efficient visible light active photocatalysts. To determine the surface area and pore size, the prepared aFe2O3 nanourchins were characterized by nitrogen adsorption– desorption measurements. The nitrogen adsorption/desorption isotherm and the corresponding BJH pore diameter distribution of the prepared a-Fe2O3 nanourchins are presented in Fig. S2. From the observed results, it is clear that the isotherm of the asprepared a-Fe2O3 nanourchins is a type III isotherm with H3-type hysteresis loops according to IUPAC. Quantitative calculation demonstrates that the BET surface area of the prepared a-Fe2O3 nanourchins is 76.703 m2 g1. 3.2. Growth process of a-Fe2O3 nanourchins To investigate the formation mechanism of the as-prepared hierarchical a-Fe2O3 nanourchins, a series of controlled experiments were conducted. First, time dependent experiments were carried out. Fig. 4 demonstrates the typical SEM images for time

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dependant growth of iron oxide nanomaterials synthesized at 120 °C at different reaction times. It is clear from the observed results that the urchin-shape morphologies are made at a particular reaction time, i.e. at 12 h. When reaction was carried out for 4 h, only random aggregates are seen in the micrograph (Fig. 4(a)). The aggregates vary in shapes and sizes and grown in high-density, hence exhibiting agglomeration. However, when the reaction time was increased to 8 h, the growth of small nanorods over the random aggregates was seen (Fig. 4(b)). The nanorods were grown almost in spherical shape and randomly grown in high density. Perfect urchin-shaped structures were obtained when the reaction time was increased to 12 h (Fig. 4(c)). The prepared structures exhibited the growth of large number of nanoneedles which were assembled in such a special fashion that they made urchin-shaped morphologies. Most of the urchin-shaped structures possess similar morphologies and dimensions (Fig. 4(c)). However, when the reaction time was increased to 16 h, breakages and over-growth on the urchin-shaped structures were seen (Fig. 4(d)). The observed results demonstrate that the reaction time has major impact on the growth of perfect urchinshaped structures. In addition to the reaction time, the roles of DMSO amount on the morphologies of the as-synthesized iron oxide nanomaterials were also examined. In this study, during the synthesis process, DMSO acts as a surfactant thus its amount also shows effects on the morphologies of as-synthesized nanomaterials. Fig. 5 depicts the typical SEM images of the as-synthesized iron oxide nanomaterials prepared with various amounts of DMSO. Fig. 5(a) exhibits the typical SEM image of the sample prepared at 120 °C for 12 h without DMSO. It is interesting to see that when DMSO was not used for the synthesis, high-density growth of nanoneedles are seen however, with adding, even 1 mL, DMSO in the synthesis process leads the assembly of these nanoneedles in irregular manner (Fig. 5(b)). Interestingly, when the concentration of DMSO was increased to 2 mL, perfect urchin-shaped morphologies are observed (Fig. 5(c)). Urchin-shaped structures were made by the fine accumulation of hundreds of nanoneedles, arranged radially

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Fig. 4. Typical SEM images for time dependant growth of iron oxide nanomaterials synthesized at 120 °C for different times: (a) 4 h, (b) 8 h, (c) 12 h, and (d) 16 h.

Fig. 5. Typical SEM images of iron oxide samples prepared with different amounts of DMSO at 120 °C for 12 h: (a) 0 mL, (b) 1 mL, (c) 2 mL and (d) 3 mL.

at one centre and form urchin shape morphologies. Further, by increasing the amount of DMSO up to 3 mL, the uniformity of urchin-shaped structures was deteriorated and nanoneedles were broken (Fig. 5(d)). The deterioration in the urchin-shaped structures with excessive DMSO was most probably due to the formation of inhomogeneous nuclei at initial growth stage.

Based on the above experimental results, a possible growth mechanism for the formation of a-Fe2O3 nanourchins can be proposed. Fig. 6 depicts the plausible schematic growth process for the formation of a-Fe2O3 nanourchins. Initially, during the reaction, small agglomerated particles are grown which act as base nuclei for the formation of urchin shaped structures. As the

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FeCl3·6H2O

DMSO

Na2SO4

Fig. 6. Plausible schematic growth process for the formation of a-Fe2O3 nanourchins.

reaction time increases, at particular reaction conditions, these small agglomerated particles get nucleated and lead the formation of nanoneedles/nanorods at their outer surfaces and finally urchinshaped morphologies were grown. The growth phenomenon can be understood as at the initial stage, primary a-FeOOH nanoparticles are formed through the hydrolyzation of Fe3+, which serve as the nuclei in the subsequent growth process [37–39]. It is well known that the aggregation process involves the formation of larger nanoparticles by reducing the interfacial energy of the smaller particles [40]. However, the interaction between unprotected building units is generally not suitable to form stable and uniform microstructures. The presence of DMSO provides strong surface protection to form the assembly of urchin-like structures. 3.3. Visible-light driven photocatalytic properties of a-Fe2O3 nanourchins towards Congo red, Eosin red and methylene blue The prepared a-Fe2O3 nanourchins were used as an efficient visible-light driven photocatalyst for the photocatalytic degradation of three highly harmful organic dyes, i.e. Congo red (CR),

Eosin red (ER) and Methylene blue (MB). The degradations of the organic dyes over the as-prepared a-Fe2O3 nanourchins were measured by observing the changes in the absorption spectra of centrifuged dye solution in every 5 min time interval under visible light illumination. Fig. 7(a) shows the adsorption spectra of CR solution in the presence of a-Fe2O3 nanourchins under visible light irradiation at different time intervals. For the degradation, the main absorption peak of CR centered at 495 nm was observed. Almost complete (98%) degradation of the CR dye was observed in 25 min under visible light illumination, when used a-Fe2O3 nanourchins as a photocatalyst. Fig. 7(b) demonstrate the adsorption spectra of Eosin red (ER) solution in the presence of a-Fe2O3 nanourchins under visible light irradiation at different time intervals. Almost 95% degradation of ER dye was observed, when dye solution was irradiated under visible light for 50 min. Like CR and ER dyes, similar trend for the photocatalytic degradation of methylene blue (MB) dye in presence of a-Fe2O3 nanourchins under visible light illumination was also seen. Fig. 7(c) exhibits typical adsorption spectra of methylene blue (MB) solution in the presence of

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Fig. 7. Absorbance spectra of various organic dyes at various time intervals under visible light irradiation; (a) Congo red dye; (b) Eosin Red dye and (c) Methylene blue dye. (d) Extent of photocatalytic degradation of various organic dyes; Congo red (j), Eosin red ( ) and Methylene blue ( ) in presence of visible light irradiation. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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a-Fe2O3 nanourchins under visible light irradiation at different

3.4. Visible-light driven photocatalytic properties of a-Fe2O3 nanourchins, dendrite a-Fe2O3 structures and commercial TiO2 (P-25) towards Congo red dyes

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time intervals. It was observed that with increasing the illumination time, the intensity of absorption spectra, at 667 nm, 97% degradation of MB dye was observed in 45 min under visible light irradiation. Fig. 7(d) depicts the extent of photo-degradation of three organic dyes, i.e. CR, ER, and MB in presence of a-Fe2O3 nanourchins under visible light illumination in 25 min. Interestingly, it was observed that the Congo red dye in presence of a-Fe2O3 nanourchins exhibited best photocatalytic performance and almost complete degradation (98%) of this dye was observed in 25 min under visible light illumination. The order of degradation rate for all used dyes were as follows: MB (80%) < Eosin red (84%) < CR (98%). From the observed photocatalytic results, it is clear that the as-prepared a-Fe2O3 nanourchins are promising photocatalyst for the effective photocatalytic degradation of various harmful organic dyes and pigments.

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Time (min) Fig. 8. Extent of photocatalytic degradation of various photocatalysts towards Congo red dye in presence of visible light irradiation: (j) a-Fe2O3 nanourchins, ( ) dendrite-like a-Fe2O3 structures and ( ) commercial TiO2 (P-25). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

The photocatalytic degradation performance of the as-prepared

a-Fe2O3 nanourchins towards Congo red dye under visible light illumination was also compared with dendritic a-Fe2O3 structures

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[31] and commercially available TiO2 (P-25). Fig. S3 demonstrates the absorbance spectra of Congo red dye in presence of a-Fe2O3 nanourchins, dendritic a-Fe2O3 structures and TiO2 (P-25) under visible light irradiation. Fig. S3(a) exhibits the typical absorption spectra for Congo red dye at various time intervals under visible light irradiation. The obtained absorption spectra revealed that with increasing the irradiation time, the intensity of absorption spectra decreases and 98% photocatalytic degradation of Congo red dye was observed in 25 min under visible light illumination. Similar results are also observed for the photocatalytic degradation of Congo red dye towards dendritic a-Fe2O3 structure (Fig. S3(b)) and commercial TiO2 (P-25) (Fig. S3(c)), i.e. intensities of absorption band decreases with increasing the irradiation time. Fig. 8 exhibits the typical plot for the change in the absorption intensity for the Congo red dye as a function of irradiation time, under visible light, in presence of various photocatalysts, i.e. a-Fe2O3 nanourchins, dendritic a-Fe2O3 structure and TiO2 (P-25). The observed order of decomposition rate of Congo red dye in the presence of used catalysts was as follows: a-Fe2O3 nanourchins (98%) > dendritic a-Fe2O3 nanostructures (77%) > P-25 (75%). The results demonstrates that the prepared a-Fe2O3 nanourchins exhibited very good photocatalytic performance, even better than the commercially available TiO2 (P-25) and other iron oxide morphologies which revealed that the prepared a-Fe2O3 nanourchins is highly efficient photocatalyst for the photocatalytic degradation of various toxic and harmful dyes. The superior photocatalytic properties of a-Fe2O3 nanourchins are mainly due to the specific morphology and large surface area of the prepared nanomaterial. Furthermore, the multiple reflections of visible light between the urchin-like structures could also offer enhancement of light absorbance and thus the photocatalytic activity [41–43]. In order to further clarify the photocatalytic mechanism of a-Fe2O3 nanourchins, several trapping experiments to determine the main active species in the photocatalytic process were also conducted and presented in Fig. S4. As can be observed from the obtained results that the degradation efficiency of CR was decreased slightly with the addition of tert-butyl alcohol (TBA, 0.5 mM, a hydroxyl radicals scavenger) [44]. This phenomena suggests that the hydroxyl radicals OH are the main active species for the degradation of CR. Additionally, it is also noted that once the benzoquinone (BQ, 0.5 mM) which is a scavenger for superoxide

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radicals O 2 was added to the reaction system, the degradation efficiency of CR was significantly decreased [45]. Thus, the observed results clearly demonstrate that the OH and O 2 are the main active species for the photodegradation of organic dyes and pigments. 3.5. Degradation kinetics study and recyclability It is well-known that the photocatalytic oxidation of organic pollutants obeys Langmuir–Hinshelwood kinetics [46]. This kind of pseudo-first-order kinetics can be represented as follows: 0

r ¼ dC=dt ¼ k KC=1 þ KC

ð1Þ

where r is the rate of dye mineralization, k0 is the rate constant, C is the dye concentration, and K is the adsorption coefficient. By integration, Eq. (1) can be arranged into the following:

ln C=C 0 ¼ kt

ð2Þ

where C0 is the initial concentration of Congo red dye solution and k is a rate constant. According to Eq. (2), rate constant k can be given by the slope of fitting curves, when plotting ln(C/C0). The degradation data with the linear fitting curves are plotted in Fig. 9. The reaction rate constants for a-Fe2O3 nanourchins, dendrite-like a-Fe2O3

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structures and TiO2 (P-25) were 0.0951 min1, 0.0515 min1 and 0.0362 min1, respectively. The results illustrate that a-Fe2O3 nanourchins possess excellent photocatalytic properties compared with other two photocatalysts (dendrite-like a-Fe2O3 structures and TiO2 (P-25)) under visible light irradiation. In addition, to promote recycle efficiency in practical industrial applications, the photocatalyst is expected to be reclaimable by a simple method. Therefore, it is necessary to investigate the stability and reusability of the catalyst. As shown in Fig. S5, under the identical reaction conditions, the catalyst can be reused with nearly constant photo-degradation ratio after 5 cycles. The slight reduction in the photocatalytic efficiency in the 5th cycle may be related to deactivation of the photocatalyst [47].

[9] [10]

4. Conclusions

[16] [17] [18]

In summary, well-crystalline a-Fe2O3 nanourchins were prepared by a facile hydrothermal route using DMSO as the growth template. The prepared nanourchins were characterized using several analytical techniques which revealed that the prepared materials are well crystalline and pure a-Fe2O3. After several time and DMSO amount dependant experimental findings, a plausible growth mechanism for the formation of a-Fe2O3 nanourchins was also proposed. The prepared a-Fe2O3 nanourchins were used as efficient photocatalyst for the photocatalytic degradation of three harmful organic dyes under visible light irradiation. The detailed photocatalytic experiments revealed that the prepared a-Fe2O3 nanourchins exhibited better photocatalytic degradation performance, under visible light, for Congo red dye compared to dendrite-like a-Fe2O3 structures and commercially available TiO2 (P-25) photocatalysts. These studies revealed that simply prepared a-Fe2O3 nanourchins can efficiently be utilized for the effective photocatalytic degradation of organic dyes and toxic chemicals under visible light irradiation.

[3] [4] [5] [6] [7] [8]

[11] [12] [13] [14] [15]

[19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32]

Acknowledgments

[33] [34]

This work was supported by the Scientific Research Fund of Heilongjiang Provincial Education Department (12531179). Ahmad Umar would like to acknowledge the support of the Ministry of Higher Education, Kingdom of Saudi Arabia for research grant (PCSED-021-13) under the Promising Centre for Sensors and Electronic Devices (PCSED) at Najran University, Kingdom of Saudi Arabia.

[35] [36] [37] [38] [39]

Appendix A. Supplementary material

[40] [41]

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jcis.2015.03.055.

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