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Ternary P25–graphene–Fe3O4 nanocomposite as a magnetically recyclable hybrid for photodegradation of dyes
Accepted Manuscript Title: Ternary P25-graphene-Fe3 O4 nanocomposite as a magnetically recyclable hybrid for photodegradation of dyes Author: Lingli Cheng Shaofeng Zhang Yujia Wang Guoji Ding Zheng Jiao PII: DOI: Reference:
S0025-5408(15)30017-9 http://dx.doi.org/doi:10.1016/j.materresbull.2015.06.047 MRB 8304
To appear in:
MRB
Received date: Revised date: Accepted date:
31-3-2015 23-5-2015 24-6-2015
Please cite this article as: Lingli Cheng, Shaofeng Zhang, Yujia Wang, Guoji Ding, Zheng Jiao, Ternary P25-graphene-Fe3O4 nanocomposite as a magnetically recyclable hybrid for photodegradation of dyes, Materials Research Bulletin http://dx.doi.org/10.1016/j.materresbull.2015.06.047 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Ternary P25-Graphene-Fe3O4 nanocomposite as a magnetically recyclable hybrid for photodegradation of dyes
Lingli Cheng, Shaofeng Zhang, Yujia Wang, Guoji Ding*, Zheng Jiao*
School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, PR China *
Corresponding author: Guoji Ding, Email: [email protected], Tel./fax: +86 21 66137749. Zheng Jiao, Email: [email protected], Tel./fax: +86 21 66135160.
Graphical abstract
Highlights
P25-Graphene-Fe3O4 (PGF) nanocomposite was synthesized by a facile and efficient approach.
PGF catalysts showed high efficiency in photodegradation of various dyes.
The catalyst showed superior magnetic separation and stable cycling performance.
ABSTRACT A ternary P25-Graphene-Fe3O4 (PGF) magnetic nanocomposite has been successfully synthesized by decorating P25 and Fe3O4 nanoparticles on the reduced graphene oxide (RGO) through a facile solvothermal reaction，and its ability to photodegrade organic dyes in aqueous solutions was investigated. The as-synthesized sample exhibits high photocatalytic activity towards various dyes, and can be easily recycled by normal magnet due to the existence of Fe3O4 nanoparticles. Furthermore, owing to the presence of RGO, the photo-dissolution behavior of Fe3O4 nanoparticles occurring in the TiO2-Fe3O4 binary nanocomposites can be suppressed effectively, which increase the durability of such a recollectable photocatalyst. In addition, the PGF nanocomposite can work well under the acid pH conditions, and also can photodegrade the mixtures of various dyes. These advantages make the PGF ternary composite an excellent photocatalyst use in practical wastewater treatment.
Keywords: D. photocatalyst; A. nanocomposite; A. P25; A. graphene; A. iron
1. Introduction Due to its high water solubility, dyes are possibly the most widespread industrial wastewater contaminant, causing severe environmental damage [1]. Various technologies, including adsorption, coagulation, extraction, and chemical oxidation have been developed for the removal of dye pollutants from industrial wastewater [2-5]. Unfortunately, most of the current strategies developed according to the
adsorption principle still retain several problems, such as low efficiency, nonrecyclability, or complex operations for recycling. The photocatalytic degradation of dye pollutants based on wide band gap semiconductors has attracted increasing attention during the past decades due to their capability of simultaneous harvesting solar energy and driving chemical reactions via photo-excited charge carriers and activated electronic states [6]. Among various semiconductor materials studied, TiO2 has been recognized as the most common candidate for widespread environmental applications because of its long-term stability, nontoxicity, controllable structure and morphology, and economical excellence [7, 8]. However, the free-standing nanostructured TiO2 were difficult to reuse in the aqueous solution, due to the complicated separating procedures. It is necessary to develop a facile way to recycle the photocatalytic materials, and a strategy to integrate TiO2 nanocrystal with magnetite to deal with the recycle problems was proposed. For this purpose, TiO2-based binary materials were developed to realize the recollection of photocatalysts, which involved titania-coated magnetite, TiO2-Fe3O4 hollow spheres, and TiO2-Fe3O4 nanocomposites [9-11]. However, these binary composites always suffered a serious decrease of photocatalytic efficiency after several uses, possibly due to the chemical instability of Fe3O4 induced by the photogenerated electrons transferred from TiO2 [12, 13]. Therefore, it is particularly important to increase the durability of such recollectable photocatalysts for practical use. The TiO2 based photocatalysts have been rapidly developed in the past decade, but the photocatalytic degradation efficiency is inhibited to a large degree by the
recombination of the photogenerated charge carriers, which has not yet fully overcome [14, 15]. Recently, the TiO2 and carbon (TiO2-C) composites have been proven to be potential photocatalysts in promoting charge separation, which includes TiO2-mounted activated carbon, carbon-doped TiO2, carbon-coated TiO2, and graphene-TiO2 nanocomposites [16-20]. Among these, graphene-TiO2 composites showed fantastic activity for the excellent mechanical, thermal, optical, and electronic properties of graphene [21-26]. In our previous work, graphene-TiO2 nanocomposites exhibited higher photocatalytic activity to methyl orange than pure TiO2. The possible mechanism is that graphene can serve as an efficient acceptor for the photogenerated electrons, thus significantly suppressing charge recombination and enhancing the photocatalytic rate of the nanocomposites [27]. However, for practical applications, graphene-TiO2 nanocomposites still suffer from difficult recollection. In this work, we demonstrated a facile and reproducible route to obtain a ternary, hybrid graphene-semiconductor-magnetic nanocomposite, specifically referring to P25-Graphene-Fe3O4 (PGF). In the as-prepared PGF photocatalyst, P25 and Fe3O4 nanoparticles were loaded on the platform of a graphene nanosheet. The nanocomposite simultaneously covered three excellent attributes as depicted in scheme 1: (i) P25 nanoparticles as good photocatalytic to degrade dyes, (ii) graphene as an effective electron pathway to suppress the charge recombination in TiO2, enhance its photocatalytic activity and prevent instability of Fe3O4, and (iii) Fe3O4 nanoparticles as a magnetic material for magnetic separation. A systematic study was performed to determine the degradation of Rhodamine B (RhB) for the photocatalytic
properties of PGF. Meanwhile, successive photocatalytic reactions exhibited an excellent durability for the PGF nanocomposite. Furthermore, PGF is capable of degrading a mixture of different dyes efficiently.
2. Experimental sections
2.1. Materials Graphite powder (purity 99.9995%) was obtained from Alpha Aesar. TiO2 powders (Degussa P25) were used as received. Anhydrous ethanol, sulfuric acid (95%-97%) was purchased from Sigma-Aldrich. Hydrogen peroxide (30%) ， Fe(NO3)3·9H2O ， and ethylene glycol (EG) were obtained from Chem-Supply. Potassium permanganate, ammonia solution (28%), Rhodamine B (RhB), Methyl orange (MO) and methylene blue (MB) were purchased from Ajax Finechem. Hydrochloric acid (32% analytical grade) was obtained from Biolab. All other reagents were analytical grade and used without any further purification. Distilled (DI) water was used for all the experiments. 2.2. Synthesis of P25-Graphene Hummers’ method was adopted to obtain graphene oxide (GO) [28]. The P25-graphene composite was synthesized by a one-step hydrothermal method [29]. Briefly, 0.005 g GO was dispersed into H2O (20 mL) and ethanol (10 mL) solution with stirring and ultrasonic treatment. Then, P25 was added into the above GO solution to mix for 2 h. The homogenous suspension was transferred to a Teflon-sealed autoclave and maintained at 120 °C for 3 h. During this process both
the reduction of GO and the loading of P25 on graphene sheets occurred. The P25-graphene was rinsed with DI water and dried at 60 °C, before using as the seeds for the growth of Fe3O4. 2.3. Synthesis of P25-Graphene-Fe3O4 P25-Graphene-Fe3O4 nanocomposite and Fe3O4 nanoparticles were prepared by a gas/liquid interfacial reaction [30]. In a 20mL beaker, 0.404 g Fe(NO3)3·9H2O was dissolved in 15 mL of ethylene glycol (EG), and different amount of P25-Graphene sheets were added and sonicated for 3h to yield a homogeneous suspension. The beaker was placed into an 80mL Teflon-lined autoclave that contained 15mL of ammonia solution. Then the autoclave was sealed and placed in a drying oven preheated to 180℃ and kept at that temperature for 12 h. During this process, the Fe3O4 nanoparticles were in situ deposited onto the graphene sheets. Briefly, at the elevated reaction temperature (180℃), evaporated ammonia reacted with Fe3+ at the gas/liquid interface to produce Fe(OH)3, which could be quickly decomposed to Fe2O3 and further reduced to Fe3O4 by EG [31]. After cooling and centrifugation, washing with ethanol for several times, then the black solid product was dried at 60℃ in vacuum to obtain the desired P25-Graphene-Fe3O4 nanocomposite. For easy understanding, the final P25-Graphene-Fe3O4 nanocomposites with mass ratios of P25-Graphene to Fe3O4 0.5:1, 1:1, 2:1, and 3:1 were denoted as PGF-0.5, PGF-1, PGF-2, and PGF-3, respectively. 2.4. Analysis Instruments The structure and phase composition of the resulted samples were characterized
by X-ray diffraction (XRD) which was on the Rigaku D/max-2550 instrument operating at 40 kV and 40 mA using CuKα radiation (λ = 0.154 nm), scanning range from 5° to 90° with a scan rate of 8º min-1. The structure property and morphologies of the samples were examined by transmission electron microscope (TEM, JEOL JEM-200CX) at 120 kV，and high-resolution transmission electron microscopy (HRTEM, JSM-2010F). The chemical composition and elemental chemical status of the samples were investigated by field emission scanning electron microscopy (FESEM, JEOL JSM-6700F) at 15 kV. Elemental qualitative analysis was conducted by the energy-dispersive X-ray spectroscopy (EDX, OXFORD INCA) which was mounted in the JSM-6700F. X-ray photoelectron spectroscopy (XPS) measurements were performed on an AXIS Ultra DLD (Kratos, USA) using monochromatic Al Kα X-ray source (anode HT = 15 kV) operating at a vacuum better than 10–7 Pa. Kratos Vision v. 2.2 software was utilized to analyze and deconvolute the XPS peaks. Specific surface areas of the PGF composites were measured and calculated by the Brunauer–Emmett–Teller (BET) method from nitrogen adsorption–desorption data with an automated adsorption apparatus (Micromeritics, ASAP 2020). Vibrating sample magnetometry (VSM) with a maximum magnetic field of 8kOe was carried out at room temperature to evaluate the magnetic properties of the samples. 2.5. Photocatalytic degradation of dye pollutants Photocatalytic performances of PGF nanocomposites were evaluated by the photodegradation of dyes under UV light irradiation in a SGY-IB photochemical reactor. The initial dyes (RhB, MO, MB) concentration was controlled at 5 mg/L.
Then, 10 mg catalyst was mixed with 50 mL RhB solution. The mixture was seated in ultrasonic water bath for 5 min to ensure good dispersion of the catalysts, followed by stirring
in
the
dark
at
ambient
temperature
for
30
min
to
achieve
adsorption-desorption equilibrium. Upon equilibrium, 3-5 mL of suspension was extracted out to determine the initial concentration of the solution, which was recorded as the base concentration C0. The remaining mixture was illuminated by a 300 W Hg lamp. Then, the suspension which was centrifuged immediately was extracted out every 5 min, and the solution was analyzed by using a Hitachi U-3010 UV-Vis spectrophotometer in a region of 200-800 nm. All experimental cases were the same condition.
3. Results and discussion
3.1. Characterization of theP25-Graphene- Fe3O4 nanocomposite Fig. 1 shows XRD patterns of the as-prepared PGF nanocomposites (PGF-0.5, PGF-1, PGF-2, and PGF-3) and pure P25. The PGF nanocomposites own similar diffraction peaks with P25, meaning that the crystal phase of P25 does not change after hydrothermal and gas/liquid interfacial reaction. The majority of the composite is anatase phase, and the peaks of 25.5º, 37.8º, 48.2º, 54.1º, and 55.8º
can be
indexed to (101), (004), (200), (105), and (211) crystal planes of anatase TiO2, respectively. The typical diffraction peak at around 2θ=10.68º for GO corresponds to the (001) crystal plane of GO, which cannot be found in the XRD patterns of PGF nanocomposites due to the reduction of GO to RGO. No diffraction patterns from
carbon species have been detected, which may result from the main characteristic (002) peak of graphene at 25.9º might be shielded by the main peak of anatase TiO2 at 25.5º [32,33]. It also proves the reduction of GO. According to the JCPDS file no.19-0629 for the magnetite, the (220), (311), (400), (511), (440) planes of Fe3O4 were observed at 2θ=29.1º, 35.5º, 43.2º, 57.1º, 62.6º, respectively, suggesting the presence of magnetic phase in the composites. The above results prove that P25 and Fe3O4 magnetic particles were decorated on RGO successfully. From the TEM and HRTEM images of the RGO and PGF-3 nanocomposite (Fig. 2 a-c), we can clearly observe the two-dimensional structure of RGO sheets with wrinkles, which are well anchored by the spherical or rectangular Fe3O4 and P25 nanoparticles with sizes of 20-40 nm. And the spherical or rectangular Fe3O4 and P25 nanoparticles tend to accumulate along the wrinkles and edges of the graphene sheets. Furthermore, from the HRTEM image of PGF-3 nanocomposite (Fig. 2d), it is obvious that a clear interface exists between the Fe3O4 and P25 nanoparticles, so there are not formation of heterojunction structure of P25 and Fe3O4. Therefore, it can be reasonably concluded that the graphene sheets would be good supports for the Fe3O4 and P25 nanoparticles. The chemical states of elements in PGF nanocomposites were characterized by XPS measurement, and the results were shown in Fig.3. The peaks of the C1s, Ti2p and Fe2p observed in Fig. 3a collectively indicate the Fe3O4 and TiO2 nanoparticles load on graphene successfully. In Fig. 3b, two peaks at around 458.6 and 464.7 eV are assigned to the Ti2p3/2 and Ti2p1/2, respectively, coinciding with the reported values
of TiO2 [26]. Fig. 3c shows binding energies of 710.8 eV and 724.3 eV, corresponding to Fe2p3/2 and Fe2p1/2, respectively, in good agreement with the values reported for Fe3O4 [34, 35]. The C1s XPS spectra of PGF-3 nanocomposite was shown in Fig. 3d, which could be deconvoluted into four peaks arising from C-C/C=C (284.9 eV) in the aromatic ring, C-O (286.3 eV) of epoxy and alkoxy, C=O (287.8 eV) and O-C=O (289.2 eV) groups [36]. It is noted that the intensity of oxygenated groups in PGF-3 nanocomposite are very low, indicating that GO was reduced in the synthesis of composites. The mass concentration of each contents (C, O, Ti and Fe) in PGF nanocomposites was calculated according to the XPS survey spectra (Fig. 3a) and the values were listed in Table 1, which were coincide with proportions of ingredients added in the synthesis process. Therefore, the XPS results can also further confirm the formations of PGF nanocomposites. For further determining the elemental chemical status and microstructure of the prepared samples, the EDS and elemental mapping of PGF-3 have been investigated, and the results were shown in Fig. S1, Supporting Information. The EDS data (Fig. S1a) reveals that the selected bulk part of PGF-3 comprises the elements of C, O, Ti and Fe. And the EDS elemental mappings of PGF-3 (Fig. S1 c-f) show that the strong Fe and Ti signals come from Fe3O4 nanoparticles and TiO2 nanoparticles, respectively, whereas the O signal occurs mainly in both Fe3O4 and TiO2 nanoparticles, which implies that a uniform distribution of Fe3O4 and TiO2 nanoparticles on graphene. To determine the specific surface area of the composite nanomaterial, N2 adsorption/desorption measurements and Brunauer-Emmett-Teller (BET) analysis
method were used.
Nitrogen adsorption-desorption isotherm of the PGF
nanocomposites are shown in Fig. 4. The overall shape of the PGF indicates a material with mesoporous and macroporous characteristics. The measured BET specific surface areas of PGF-0.5, PGF-1, PGF-2 and PGF-3 are 79.362, 86.740, 88.339 and 93.334 m2g-1, respectively. We can see the surface area of the PGF composite increased with the increasing of graphene ratio. The results shows that specific surface area of PGF is much larger than that of pure P25 (ca. 49.9 m2g-1) [37, 38], which is due to the presence of graphene. The magnetic hysteresis loops of all samples are shown in Fig. 5. Obviously, all samples show ferromagnetic behavior [39]. The saturation magnetizations of the composites (PGF-0.5, PGF-1, PGF-2, and PGF-3) are 36.519, 12.386, 7.037 and 5.276 emu/g respectively, which are decreased with the increasing of nonmagnetic composites. The saturation magnetization of PGF-3 (5.276 emu/g) ensures the magnetic collection from solution in the presence of an external magnetic field, as shown in the inset of Fig. 5.
3.2. photoactivity evaluation
The photocatalytic capability of PGF was evaluated by photodegradation of RhB in an aqueous solution irradiated by UV light. Fig. 6a shows the UV–vis absorption spectra of RhB solution before and after UV irradiation for different exposure time in the presence of PGF-3 composite. The absorption peak at 554 nm, corresponding to the RhB molecule, weakened gradually as the exposure time increased, and nearly
disappeared after 25 min. The color of the dye solution changed from dark to nearly colorless (inset of Fig. 6a). The degradation curves of RhB in the presence of pure P25 and PGFs are shown in Fig. 6b. In comparison with pure P25, PGFs exhibit improved photodegradation performance. Additionally, photodegradation rate increased with increasing P25-graphene ratio. However, further increase in the P25-graphene ratio leads to difficult magnetic separation of photocatalyst. As a recyclable photocatalyst, renewable photocatalytic activity is important. Among reported systems such as TiO2-Fe3O4 composite, the photocatalytic activity is always dramatically reduced after use for a few cycles [10, 11, 40], thus hindering its practical application severely. The PGF composites could be readily recycled by simple magnetic separation after reaction. The stability and reusability of the PGF composites were examined by repetitive use of the catalyst. As shown in Fig. 7, the catalyst did not exhibit a significant loss of activity after five photodegradation cycles of RhB. It is worth noting that there is no elemental Fe detected by inductive coupled plasma emission spectrometer (ICP) in the residual solution after photodegradation, further verifying the durability of PGF-3 in photocatalytic reactions. Considering the actual dye solution may not be neutral, we also investigated the photocatalytic degradation of RhB by PGF-3 at different pH values (4, 7, 9 and 12). As shown in Fig. S2, Supporting Information, compared to the neutral solution, the photocatalytic activity of PGF increased when pH was 4, whereas it decreased obviously when the pH was 9 and 12. Usually, during the photocatalysis, three factors are crucial, including the adsorption of contaminant molecules, the light absorption,
and the charge transportation and separation [29]. For PGF nanocomposites, P25 and Fe3O4 nanoparticles are dispersed on the graphene support, and the carbon platform plays an important role in absorbing RhB. Based on the structure of RhB and graphene, there could be hydrogen bonds, electrostatic interaction, and hydrophobic interaction (including - stack) between these two molecules, which all are pH dependent. At low pH value graphene sheets are more hydrophobic leading to stronger interaction with RhB than at higher pH [41]. Hydrogen bond aids deposition of RhB on graphene at low pH values, since when the pH value is lower than the pKa value (4.2), the -COOH group in RhB cannot be deprotonized. The -COOH can interact with some remaining -OH and -COOH groups on graphene at low pH values. Ramette and Sandell described that RhB commonly contains a negatively charged -COOH group and a positively charged N atom in polar solvents like water [42]. Thus, the electrostatic interaction of graphene and RhB is more complicated at different pH. At low pH value, graphene is less negatively charged, thus, the electrostatic interaction between graphene and RhB is weak. While at high pH value, graphene is more negatively charged, RhB is also more negatively charged. Thus, although a more negatively charged graphene has a more electrostatic affinity to the N+ atom, the electrostatic interaction might also be weak, since the total RhB charge is negative, leading to an electrostatic repulsion between graphene and RhB [43]. Furthermore, when the pH is lower than the point of zero charge of TiO2, more H+ ions arise in the solution and make the TiO2 surface positively charged. The positive modification of the TiO2 surface benefits the photogenerated electrons moving to the surface,
inhibiting the recombination of electron-hole. Thus, in our experiments, at low pH value, PGF can not only enhance the adsorption of RhB, but also improve the photocatalytic efficiency of it. In addition to degradation of RhB, the PGF could be used in photocatalytic degradation of other dyes, as shown in Fig. S3a, Supporting Information. MO and MB could be effectively decomposed under the same experimental conditions as those in the degradation of RhB. When PGF-3 composites were added into the solutions, the photodagradation ratios of all dyes could achieve near 100% in 25 min, and the order of their degradation rates is as following: MB > RhB > MIX > MO due to the physical and chemical properties of different dyes are not the same [20, 44, 45]. Furthermore, to simulate real polluted water, we mixed three kinds of dyes involving RhB, MO, and MB. The photocatalytic degradation of this mixture by PGF-3 (Fig. S3b) shows the universality of PGF as a photocatalyst, indicating the potential application in practical use.
3.3. Mechanism of photocatalytic activity enhancement
The PGF nanocomposites showed high photocatalytic activity for various dyes. The significant enhancement in photodegradation can be attributed to the remarkable synergistic effect of TiO2 (P25) and graphene, where the photogenerated carriers in TiO2 are efficiently separated [29, 46, 47]. The mechanism for the photocatalytic enhancement is proposed as follows:
(1) (2) (3) (4) (5) (6) (7)
Under the UV light irradiation, TiO2 nanoparticles undergo charge separation to yield electrons (eCB-) and holes (hVB+) (reaction 1). For a traditional semiconductor photocatalyst, both electrons and holes generated in the photocatalyst could decompose pollutants directly. Alternatively, electrons could also react with oxygen to produce superoxide anion radicals (reaction 2). Because graphene sheets are known as good electron acceptors, the electrons are quickly transferred to the graphene sheets [48] (reaction 3). The negatively charged graphene sheets can also react with the dissolved oxygen to produce superoxide anion radicals (reaction 4). Then the superoxide anion radicals react with hydrogen ions to make hydroxyl radicals (reaction 5), while the holes are scavenged by the adsorbed water to form hydroxyl radicals (reaction 6). Finally, the active species (holes, superoxide anion radicals, and hydroxyl radicals) oxidize the dye molecules adsorbed on these active sites of the PGF system through the stacking and/or electrostatic attraction (reaction 7) [49, 50].
4. Conclusion
In conclusion, a ternary, hybrid nanocomposite consisting of TiO2 (P25) and Fe3O4 nanoparticles supported on graphene has been successfully synthesized via a facile method. This PGF nanocomposite exhibited a higher photocatalytic activity with the degradation of RhB as compared to the pure P25 nanoparticles. Graphene can suppress the photodissolution of Fe3O4 insuring the stability of PGF in photocatalytic reactions. The degradation efficiency is almost unchanged after reusage during five cycles. The electron transfer between the P25 nanoparticles and RGO plays a key role in achieving the high durability of PGF. More importantly, the PGF can be easily recollected from water with a magnet and works well in acid pH environment. Due to its attractive features such as easy recollection and reusability, the PGF hybrid nanocomposite obtained in this work may find use in many applications, especially in wastewater treatment. Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 11105089, 21371116, 11275121), Science Foundation for the Excellent Youth Scholars of Higher Education of Shanghai (No. ZZSD13020), Innovation Project of Shanghai Municipal Education Commission (14YZ003) and Innovation Fund of Shanghai University (No. SDCX2013034).
Supporting Information Available
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115 (2001) 23718-23725. [47] J. Liu, H. Bai, Y. Wang, Z. Liu, X. Zhang, D.D. Sun, S Adv. Funct. Mater. 20 (2010) 4175-4181 [48] I.V. Lightcap, T.H. Kosel, P.V. Kamat, Nano Lett. 10 (2010) 577-583. [49] Y. Xu, H. Bai, G. Lu, C. Li, G. Shi, J. Am. Chem. Soc. 130 (2008) 5856-5857. [50] Y.H. Lu, W. Chen, Y.P. Feng, J. Phys. Chem. B 113 (2009) 2-5. Figure captions Scheme 1. Schematic illustration of the structure and electron transfer in PGF. The inset is a photograph indicating the photodegradation of RhB aqueous solution using PGF-3 as the catalyst. The RhB molecules were eliminated with the help of PGF-3 under UV light, and the PGF can be efficiently recollected with a small magnet. Fig. 1. XRD patterns of P25, PGF-0.5, PGF-1, PGF-2, PGF-3. Fig. 2. TEM images of pure RGO (a) and PGF-3 (b) 200nm. HRTEM images of PGF-3 (c) 20 nm, (d) 5 nm. Fig. 3. (a) XPS survey spectra, (b) Ti2p XPS, (c) Fe2p XPS and (d) C1s XPS of PGF-3 nanocomposite. Fig. 4. Nitrogen adsorption–desorption isotherms for PGF nanocomposites. Fig. 5. Magnetic hysteresis loop of PGF nanocomposites at room temperature. Inset shows the digital image of the response of PGF-3 in RhB solution to an external magnetic field. Fig. 6. (a) UV–vis spectra of RhB concentration against the PGF-3 composite under
UV irradiation. (b) Photocatalytic decolorization behaviors of RhB over PGF composites under UV irradiation. Fig. 7. The cyclic photocatalysis of PGF-3 in the degradation of RhB.
Table 1. Elemental composition of PGF nanocomposites Table 1 Samples
PGF-3 PGF-2 PGF-1 PGF-0.5
Scheme 1.
XPS Carbon content (%)
Oxygen content (%)
Titanium content (%)
Iron content (%)
34.72 28.69 27.49 26.92
48.40 53.17 54.60 56.59
14.63 12.99 9.85 6.89
2.25 5.15 8.06 9.60
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
S0025-5408(15)30017-9 http://dx.doi.org/doi:10.1016/j.materresbull.2015.06.047 MRB 8304
To appear in:
MRB
Received date: Revised date: Accepted date:
31-3-2015 23-5-2015 24-6-2015
Please cite this article as: Lingli Cheng, Shaofeng Zhang, Yujia Wang, Guoji Ding, Zheng Jiao, Ternary P25-graphene-Fe3O4 nanocomposite as a magnetically recyclable hybrid for photodegradation of dyes, Materials Research Bulletin http://dx.doi.org/10.1016/j.materresbull.2015.06.047 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Ternary P25-Graphene-Fe3O4 nanocomposite as a magnetically recyclable hybrid for photodegradation of dyes
Lingli Cheng, Shaofeng Zhang, Yujia Wang, Guoji Ding*, Zheng Jiao*
School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, PR China *
Corresponding author: Guoji Ding, Email: [email protected], Tel./fax: +86 21 66137749. Zheng Jiao, Email: [email protected], Tel./fax: +86 21 66135160.
Graphical abstract
Highlights
P25-Graphene-Fe3O4 (PGF) nanocomposite was synthesized by a facile and efficient approach.
PGF catalysts showed high efficiency in photodegradation of various dyes.
The catalyst showed superior magnetic separation and stable cycling performance.
ABSTRACT A ternary P25-Graphene-Fe3O4 (PGF) magnetic nanocomposite has been successfully synthesized by decorating P25 and Fe3O4 nanoparticles on the reduced graphene oxide (RGO) through a facile solvothermal reaction，and its ability to photodegrade organic dyes in aqueous solutions was investigated. The as-synthesized sample exhibits high photocatalytic activity towards various dyes, and can be easily recycled by normal magnet due to the existence of Fe3O4 nanoparticles. Furthermore, owing to the presence of RGO, the photo-dissolution behavior of Fe3O4 nanoparticles occurring in the TiO2-Fe3O4 binary nanocomposites can be suppressed effectively, which increase the durability of such a recollectable photocatalyst. In addition, the PGF nanocomposite can work well under the acid pH conditions, and also can photodegrade the mixtures of various dyes. These advantages make the PGF ternary composite an excellent photocatalyst use in practical wastewater treatment.
Keywords: D. photocatalyst; A. nanocomposite; A. P25; A. graphene; A. iron
1. Introduction Due to its high water solubility, dyes are possibly the most widespread industrial wastewater contaminant, causing severe environmental damage [1]. Various technologies, including adsorption, coagulation, extraction, and chemical oxidation have been developed for the removal of dye pollutants from industrial wastewater [2-5]. Unfortunately, most of the current strategies developed according to the
adsorption principle still retain several problems, such as low efficiency, nonrecyclability, or complex operations for recycling. The photocatalytic degradation of dye pollutants based on wide band gap semiconductors has attracted increasing attention during the past decades due to their capability of simultaneous harvesting solar energy and driving chemical reactions via photo-excited charge carriers and activated electronic states [6]. Among various semiconductor materials studied, TiO2 has been recognized as the most common candidate for widespread environmental applications because of its long-term stability, nontoxicity, controllable structure and morphology, and economical excellence [7, 8]. However, the free-standing nanostructured TiO2 were difficult to reuse in the aqueous solution, due to the complicated separating procedures. It is necessary to develop a facile way to recycle the photocatalytic materials, and a strategy to integrate TiO2 nanocrystal with magnetite to deal with the recycle problems was proposed. For this purpose, TiO2-based binary materials were developed to realize the recollection of photocatalysts, which involved titania-coated magnetite, TiO2-Fe3O4 hollow spheres, and TiO2-Fe3O4 nanocomposites [9-11]. However, these binary composites always suffered a serious decrease of photocatalytic efficiency after several uses, possibly due to the chemical instability of Fe3O4 induced by the photogenerated electrons transferred from TiO2 [12, 13]. Therefore, it is particularly important to increase the durability of such recollectable photocatalysts for practical use. The TiO2 based photocatalysts have been rapidly developed in the past decade, but the photocatalytic degradation efficiency is inhibited to a large degree by the
recombination of the photogenerated charge carriers, which has not yet fully overcome [14, 15]. Recently, the TiO2 and carbon (TiO2-C) composites have been proven to be potential photocatalysts in promoting charge separation, which includes TiO2-mounted activated carbon, carbon-doped TiO2, carbon-coated TiO2, and graphene-TiO2 nanocomposites [16-20]. Among these, graphene-TiO2 composites showed fantastic activity for the excellent mechanical, thermal, optical, and electronic properties of graphene [21-26]. In our previous work, graphene-TiO2 nanocomposites exhibited higher photocatalytic activity to methyl orange than pure TiO2. The possible mechanism is that graphene can serve as an efficient acceptor for the photogenerated electrons, thus significantly suppressing charge recombination and enhancing the photocatalytic rate of the nanocomposites [27]. However, for practical applications, graphene-TiO2 nanocomposites still suffer from difficult recollection. In this work, we demonstrated a facile and reproducible route to obtain a ternary, hybrid graphene-semiconductor-magnetic nanocomposite, specifically referring to P25-Graphene-Fe3O4 (PGF). In the as-prepared PGF photocatalyst, P25 and Fe3O4 nanoparticles were loaded on the platform of a graphene nanosheet. The nanocomposite simultaneously covered three excellent attributes as depicted in scheme 1: (i) P25 nanoparticles as good photocatalytic to degrade dyes, (ii) graphene as an effective electron pathway to suppress the charge recombination in TiO2, enhance its photocatalytic activity and prevent instability of Fe3O4, and (iii) Fe3O4 nanoparticles as a magnetic material for magnetic separation. A systematic study was performed to determine the degradation of Rhodamine B (RhB) for the photocatalytic
properties of PGF. Meanwhile, successive photocatalytic reactions exhibited an excellent durability for the PGF nanocomposite. Furthermore, PGF is capable of degrading a mixture of different dyes efficiently.
2. Experimental sections
2.1. Materials Graphite powder (purity 99.9995%) was obtained from Alpha Aesar. TiO2 powders (Degussa P25) were used as received. Anhydrous ethanol, sulfuric acid (95%-97%) was purchased from Sigma-Aldrich. Hydrogen peroxide (30%) ， Fe(NO3)3·9H2O ， and ethylene glycol (EG) were obtained from Chem-Supply. Potassium permanganate, ammonia solution (28%), Rhodamine B (RhB), Methyl orange (MO) and methylene blue (MB) were purchased from Ajax Finechem. Hydrochloric acid (32% analytical grade) was obtained from Biolab. All other reagents were analytical grade and used without any further purification. Distilled (DI) water was used for all the experiments. 2.2. Synthesis of P25-Graphene Hummers’ method was adopted to obtain graphene oxide (GO) [28]. The P25-graphene composite was synthesized by a one-step hydrothermal method [29]. Briefly, 0.005 g GO was dispersed into H2O (20 mL) and ethanol (10 mL) solution with stirring and ultrasonic treatment. Then, P25 was added into the above GO solution to mix for 2 h. The homogenous suspension was transferred to a Teflon-sealed autoclave and maintained at 120 °C for 3 h. During this process both
the reduction of GO and the loading of P25 on graphene sheets occurred. The P25-graphene was rinsed with DI water and dried at 60 °C, before using as the seeds for the growth of Fe3O4. 2.3. Synthesis of P25-Graphene-Fe3O4 P25-Graphene-Fe3O4 nanocomposite and Fe3O4 nanoparticles were prepared by a gas/liquid interfacial reaction [30]. In a 20mL beaker, 0.404 g Fe(NO3)3·9H2O was dissolved in 15 mL of ethylene glycol (EG), and different amount of P25-Graphene sheets were added and sonicated for 3h to yield a homogeneous suspension. The beaker was placed into an 80mL Teflon-lined autoclave that contained 15mL of ammonia solution. Then the autoclave was sealed and placed in a drying oven preheated to 180℃ and kept at that temperature for 12 h. During this process, the Fe3O4 nanoparticles were in situ deposited onto the graphene sheets. Briefly, at the elevated reaction temperature (180℃), evaporated ammonia reacted with Fe3+ at the gas/liquid interface to produce Fe(OH)3, which could be quickly decomposed to Fe2O3 and further reduced to Fe3O4 by EG [31]. After cooling and centrifugation, washing with ethanol for several times, then the black solid product was dried at 60℃ in vacuum to obtain the desired P25-Graphene-Fe3O4 nanocomposite. For easy understanding, the final P25-Graphene-Fe3O4 nanocomposites with mass ratios of P25-Graphene to Fe3O4 0.5:1, 1:1, 2:1, and 3:1 were denoted as PGF-0.5, PGF-1, PGF-2, and PGF-3, respectively. 2.4. Analysis Instruments The structure and phase composition of the resulted samples were characterized
by X-ray diffraction (XRD) which was on the Rigaku D/max-2550 instrument operating at 40 kV and 40 mA using CuKα radiation (λ = 0.154 nm), scanning range from 5° to 90° with a scan rate of 8º min-1. The structure property and morphologies of the samples were examined by transmission electron microscope (TEM, JEOL JEM-200CX) at 120 kV，and high-resolution transmission electron microscopy (HRTEM, JSM-2010F). The chemical composition and elemental chemical status of the samples were investigated by field emission scanning electron microscopy (FESEM, JEOL JSM-6700F) at 15 kV. Elemental qualitative analysis was conducted by the energy-dispersive X-ray spectroscopy (EDX, OXFORD INCA) which was mounted in the JSM-6700F. X-ray photoelectron spectroscopy (XPS) measurements were performed on an AXIS Ultra DLD (Kratos, USA) using monochromatic Al Kα X-ray source (anode HT = 15 kV) operating at a vacuum better than 10–7 Pa. Kratos Vision v. 2.2 software was utilized to analyze and deconvolute the XPS peaks. Specific surface areas of the PGF composites were measured and calculated by the Brunauer–Emmett–Teller (BET) method from nitrogen adsorption–desorption data with an automated adsorption apparatus (Micromeritics, ASAP 2020). Vibrating sample magnetometry (VSM) with a maximum magnetic field of 8kOe was carried out at room temperature to evaluate the magnetic properties of the samples. 2.5. Photocatalytic degradation of dye pollutants Photocatalytic performances of PGF nanocomposites were evaluated by the photodegradation of dyes under UV light irradiation in a SGY-IB photochemical reactor. The initial dyes (RhB, MO, MB) concentration was controlled at 5 mg/L.
Then, 10 mg catalyst was mixed with 50 mL RhB solution. The mixture was seated in ultrasonic water bath for 5 min to ensure good dispersion of the catalysts, followed by stirring
in
the
dark
at
ambient
temperature
for
30
min
to
achieve
adsorption-desorption equilibrium. Upon equilibrium, 3-5 mL of suspension was extracted out to determine the initial concentration of the solution, which was recorded as the base concentration C0. The remaining mixture was illuminated by a 300 W Hg lamp. Then, the suspension which was centrifuged immediately was extracted out every 5 min, and the solution was analyzed by using a Hitachi U-3010 UV-Vis spectrophotometer in a region of 200-800 nm. All experimental cases were the same condition.
3. Results and discussion
3.1. Characterization of theP25-Graphene- Fe3O4 nanocomposite Fig. 1 shows XRD patterns of the as-prepared PGF nanocomposites (PGF-0.5, PGF-1, PGF-2, and PGF-3) and pure P25. The PGF nanocomposites own similar diffraction peaks with P25, meaning that the crystal phase of P25 does not change after hydrothermal and gas/liquid interfacial reaction. The majority of the composite is anatase phase, and the peaks of 25.5º, 37.8º, 48.2º, 54.1º, and 55.8º
can be
indexed to (101), (004), (200), (105), and (211) crystal planes of anatase TiO2, respectively. The typical diffraction peak at around 2θ=10.68º for GO corresponds to the (001) crystal plane of GO, which cannot be found in the XRD patterns of PGF nanocomposites due to the reduction of GO to RGO. No diffraction patterns from
carbon species have been detected, which may result from the main characteristic (002) peak of graphene at 25.9º might be shielded by the main peak of anatase TiO2 at 25.5º [32,33]. It also proves the reduction of GO. According to the JCPDS file no.19-0629 for the magnetite, the (220), (311), (400), (511), (440) planes of Fe3O4 were observed at 2θ=29.1º, 35.5º, 43.2º, 57.1º, 62.6º, respectively, suggesting the presence of magnetic phase in the composites. The above results prove that P25 and Fe3O4 magnetic particles were decorated on RGO successfully. From the TEM and HRTEM images of the RGO and PGF-3 nanocomposite (Fig. 2 a-c), we can clearly observe the two-dimensional structure of RGO sheets with wrinkles, which are well anchored by the spherical or rectangular Fe3O4 and P25 nanoparticles with sizes of 20-40 nm. And the spherical or rectangular Fe3O4 and P25 nanoparticles tend to accumulate along the wrinkles and edges of the graphene sheets. Furthermore, from the HRTEM image of PGF-3 nanocomposite (Fig. 2d), it is obvious that a clear interface exists between the Fe3O4 and P25 nanoparticles, so there are not formation of heterojunction structure of P25 and Fe3O4. Therefore, it can be reasonably concluded that the graphene sheets would be good supports for the Fe3O4 and P25 nanoparticles. The chemical states of elements in PGF nanocomposites were characterized by XPS measurement, and the results were shown in Fig.3. The peaks of the C1s, Ti2p and Fe2p observed in Fig. 3a collectively indicate the Fe3O4 and TiO2 nanoparticles load on graphene successfully. In Fig. 3b, two peaks at around 458.6 and 464.7 eV are assigned to the Ti2p3/2 and Ti2p1/2, respectively, coinciding with the reported values
of TiO2 [26]. Fig. 3c shows binding energies of 710.8 eV and 724.3 eV, corresponding to Fe2p3/2 and Fe2p1/2, respectively, in good agreement with the values reported for Fe3O4 [34, 35]. The C1s XPS spectra of PGF-3 nanocomposite was shown in Fig. 3d, which could be deconvoluted into four peaks arising from C-C/C=C (284.9 eV) in the aromatic ring, C-O (286.3 eV) of epoxy and alkoxy, C=O (287.8 eV) and O-C=O (289.2 eV) groups [36]. It is noted that the intensity of oxygenated groups in PGF-3 nanocomposite are very low, indicating that GO was reduced in the synthesis of composites. The mass concentration of each contents (C, O, Ti and Fe) in PGF nanocomposites was calculated according to the XPS survey spectra (Fig. 3a) and the values were listed in Table 1, which were coincide with proportions of ingredients added in the synthesis process. Therefore, the XPS results can also further confirm the formations of PGF nanocomposites. For further determining the elemental chemical status and microstructure of the prepared samples, the EDS and elemental mapping of PGF-3 have been investigated, and the results were shown in Fig. S1, Supporting Information. The EDS data (Fig. S1a) reveals that the selected bulk part of PGF-3 comprises the elements of C, O, Ti and Fe. And the EDS elemental mappings of PGF-3 (Fig. S1 c-f) show that the strong Fe and Ti signals come from Fe3O4 nanoparticles and TiO2 nanoparticles, respectively, whereas the O signal occurs mainly in both Fe3O4 and TiO2 nanoparticles, which implies that a uniform distribution of Fe3O4 and TiO2 nanoparticles on graphene. To determine the specific surface area of the composite nanomaterial, N2 adsorption/desorption measurements and Brunauer-Emmett-Teller (BET) analysis
method were used.
Nitrogen adsorption-desorption isotherm of the PGF
nanocomposites are shown in Fig. 4. The overall shape of the PGF indicates a material with mesoporous and macroporous characteristics. The measured BET specific surface areas of PGF-0.5, PGF-1, PGF-2 and PGF-3 are 79.362, 86.740, 88.339 and 93.334 m2g-1, respectively. We can see the surface area of the PGF composite increased with the increasing of graphene ratio. The results shows that specific surface area of PGF is much larger than that of pure P25 (ca. 49.9 m2g-1) [37, 38], which is due to the presence of graphene. The magnetic hysteresis loops of all samples are shown in Fig. 5. Obviously, all samples show ferromagnetic behavior [39]. The saturation magnetizations of the composites (PGF-0.5, PGF-1, PGF-2, and PGF-3) are 36.519, 12.386, 7.037 and 5.276 emu/g respectively, which are decreased with the increasing of nonmagnetic composites. The saturation magnetization of PGF-3 (5.276 emu/g) ensures the magnetic collection from solution in the presence of an external magnetic field, as shown in the inset of Fig. 5.
3.2. photoactivity evaluation
The photocatalytic capability of PGF was evaluated by photodegradation of RhB in an aqueous solution irradiated by UV light. Fig. 6a shows the UV–vis absorption spectra of RhB solution before and after UV irradiation for different exposure time in the presence of PGF-3 composite. The absorption peak at 554 nm, corresponding to the RhB molecule, weakened gradually as the exposure time increased, and nearly
disappeared after 25 min. The color of the dye solution changed from dark to nearly colorless (inset of Fig. 6a). The degradation curves of RhB in the presence of pure P25 and PGFs are shown in Fig. 6b. In comparison with pure P25, PGFs exhibit improved photodegradation performance. Additionally, photodegradation rate increased with increasing P25-graphene ratio. However, further increase in the P25-graphene ratio leads to difficult magnetic separation of photocatalyst. As a recyclable photocatalyst, renewable photocatalytic activity is important. Among reported systems such as TiO2-Fe3O4 composite, the photocatalytic activity is always dramatically reduced after use for a few cycles [10, 11, 40], thus hindering its practical application severely. The PGF composites could be readily recycled by simple magnetic separation after reaction. The stability and reusability of the PGF composites were examined by repetitive use of the catalyst. As shown in Fig. 7, the catalyst did not exhibit a significant loss of activity after five photodegradation cycles of RhB. It is worth noting that there is no elemental Fe detected by inductive coupled plasma emission spectrometer (ICP) in the residual solution after photodegradation, further verifying the durability of PGF-3 in photocatalytic reactions. Considering the actual dye solution may not be neutral, we also investigated the photocatalytic degradation of RhB by PGF-3 at different pH values (4, 7, 9 and 12). As shown in Fig. S2, Supporting Information, compared to the neutral solution, the photocatalytic activity of PGF increased when pH was 4, whereas it decreased obviously when the pH was 9 and 12. Usually, during the photocatalysis, three factors are crucial, including the adsorption of contaminant molecules, the light absorption,
and the charge transportation and separation [29]. For PGF nanocomposites, P25 and Fe3O4 nanoparticles are dispersed on the graphene support, and the carbon platform plays an important role in absorbing RhB. Based on the structure of RhB and graphene, there could be hydrogen bonds, electrostatic interaction, and hydrophobic interaction (including - stack) between these two molecules, which all are pH dependent. At low pH value graphene sheets are more hydrophobic leading to stronger interaction with RhB than at higher pH [41]. Hydrogen bond aids deposition of RhB on graphene at low pH values, since when the pH value is lower than the pKa value (4.2), the -COOH group in RhB cannot be deprotonized. The -COOH can interact with some remaining -OH and -COOH groups on graphene at low pH values. Ramette and Sandell described that RhB commonly contains a negatively charged -COOH group and a positively charged N atom in polar solvents like water [42]. Thus, the electrostatic interaction of graphene and RhB is more complicated at different pH. At low pH value, graphene is less negatively charged, thus, the electrostatic interaction between graphene and RhB is weak. While at high pH value, graphene is more negatively charged, RhB is also more negatively charged. Thus, although a more negatively charged graphene has a more electrostatic affinity to the N+ atom, the electrostatic interaction might also be weak, since the total RhB charge is negative, leading to an electrostatic repulsion between graphene and RhB [43]. Furthermore, when the pH is lower than the point of zero charge of TiO2, more H+ ions arise in the solution and make the TiO2 surface positively charged. The positive modification of the TiO2 surface benefits the photogenerated electrons moving to the surface,
inhibiting the recombination of electron-hole. Thus, in our experiments, at low pH value, PGF can not only enhance the adsorption of RhB, but also improve the photocatalytic efficiency of it. In addition to degradation of RhB, the PGF could be used in photocatalytic degradation of other dyes, as shown in Fig. S3a, Supporting Information. MO and MB could be effectively decomposed under the same experimental conditions as those in the degradation of RhB. When PGF-3 composites were added into the solutions, the photodagradation ratios of all dyes could achieve near 100% in 25 min, and the order of their degradation rates is as following: MB > RhB > MIX > MO due to the physical and chemical properties of different dyes are not the same [20, 44, 45]. Furthermore, to simulate real polluted water, we mixed three kinds of dyes involving RhB, MO, and MB. The photocatalytic degradation of this mixture by PGF-3 (Fig. S3b) shows the universality of PGF as a photocatalyst, indicating the potential application in practical use.
3.3. Mechanism of photocatalytic activity enhancement
The PGF nanocomposites showed high photocatalytic activity for various dyes. The significant enhancement in photodegradation can be attributed to the remarkable synergistic effect of TiO2 (P25) and graphene, where the photogenerated carriers in TiO2 are efficiently separated [29, 46, 47]. The mechanism for the photocatalytic enhancement is proposed as follows:
(1) (2) (3) (4) (5) (6) (7)
Under the UV light irradiation, TiO2 nanoparticles undergo charge separation to yield electrons (eCB-) and holes (hVB+) (reaction 1). For a traditional semiconductor photocatalyst, both electrons and holes generated in the photocatalyst could decompose pollutants directly. Alternatively, electrons could also react with oxygen to produce superoxide anion radicals (reaction 2). Because graphene sheets are known as good electron acceptors, the electrons are quickly transferred to the graphene sheets [48] (reaction 3). The negatively charged graphene sheets can also react with the dissolved oxygen to produce superoxide anion radicals (reaction 4). Then the superoxide anion radicals react with hydrogen ions to make hydroxyl radicals (reaction 5), while the holes are scavenged by the adsorbed water to form hydroxyl radicals (reaction 6). Finally, the active species (holes, superoxide anion radicals, and hydroxyl radicals) oxidize the dye molecules adsorbed on these active sites of the PGF system through the stacking and/or electrostatic attraction (reaction 7) [49, 50].
4. Conclusion
In conclusion, a ternary, hybrid nanocomposite consisting of TiO2 (P25) and Fe3O4 nanoparticles supported on graphene has been successfully synthesized via a facile method. This PGF nanocomposite exhibited a higher photocatalytic activity with the degradation of RhB as compared to the pure P25 nanoparticles. Graphene can suppress the photodissolution of Fe3O4 insuring the stability of PGF in photocatalytic reactions. The degradation efficiency is almost unchanged after reusage during five cycles. The electron transfer between the P25 nanoparticles and RGO plays a key role in achieving the high durability of PGF. More importantly, the PGF can be easily recollected from water with a magnet and works well in acid pH environment. Due to its attractive features such as easy recollection and reusability, the PGF hybrid nanocomposite obtained in this work may find use in many applications, especially in wastewater treatment. Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 11105089, 21371116, 11275121), Science Foundation for the Excellent Youth Scholars of Higher Education of Shanghai (No. ZZSD13020), Innovation Project of Shanghai Municipal Education Commission (14YZ003) and Innovation Fund of Shanghai University (No. SDCX2013034).
Supporting Information Available
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UV irradiation. (b) Photocatalytic decolorization behaviors of RhB over PGF composites under UV irradiation. Fig. 7. The cyclic photocatalysis of PGF-3 in the degradation of RhB.
Table 1. Elemental composition of PGF nanocomposites Table 1 Samples
PGF-3 PGF-2 PGF-1 PGF-0.5
Scheme 1.
XPS Carbon content (%)
Oxygen content (%)
Titanium content (%)
Iron content (%)
34.72 28.69 27.49 26.92
48.40 53.17 54.60 56.59
14.63 12.99 9.85 6.89
2.25 5.15 8.06 9.60
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7