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Preparation of
Fe<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub>/graphene oxide composite as visible light-driven photocatalytic in degradation of rhodamine B dyes
To cite this article before publication: Yudha Pratama Putra et al 2019 Mater. Res. Express in press https://doi.org/10.1088/2053-1591/ab56bc
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Preparation of Fe 2 O 3 /TiO 2 /Graphene oxide
composite as visible light-driven photocatalytic in degradation of rhodamine B dyes
Yudha Pratama Putra1, Sayekti Wahyuningsih1*, Ari Handono Ramelan1 and Rahmat Hidayat2
1 Inorganic Material Research Group, Faculty of Mathematic and Natural Sciences, Sebelas Maret University, Indonesia
2Chemistry Department, Graduate School, Sebelas Maret University, Surakarta, Indonesia
E-mail: [email protected]
Received xxxxxx
Accepted for publication xxxxxx Published xxxxxx
Abstract
Ternary Fe2O3/TiO2/Graphene oxide composite material has been synthesized. Fe2O3 was obtained from Glagah (Indonesia) iron sand by hydrometallurgy method. While, GO was obtained from graphite flakes by modified Hummer method. Fe2O3/TiO2/GO (FTG) composites were synthesized by sonochemical and hydrothermal method. The effect of GO addition into Fe2O3/TiO2 (FT) composites on the physical and chemical properties were investigated using FTIR, XRD, SEM and UV-Vis Spectrophotometer. The XRD pattern shows the appearance of anatase and hematite phase corresponds to TiO2 and Fe2O3 after calcinated at 600 °C. SEM image shows that Fe2O3/TiO2 particles spreads on GO layer. The interaction of Fe-O-C and Ti-O-C band (450 cm-1) can be known from FTIR spectra. Then, the performance and stability of FTG composite also have been investigated.
Keywords: composite, Fe2O3, TiO2, graphene oxide, photodegradation
1. Introduction
Environmental friendly becomes popular word due to of environmental destruction. This is caused by pollutions that can disturb the nature balance [1]. The environmental contamination, especially water, is the dangerous condition because of the essential thing for human in the world. There are many efforts that have been made to solve this condition.
The water contaminant can be treated by evaporation [2], ion selective membrane [3], complexation [4], adsorption [5], photocatalytic performance [6,7] and many others.
Indonesia, a country which has various natural resources.
Mining materials that commonly found in Indonesia are coal, gold, silver, nickel, copper, diamond, limestone and iron [8].
Iron is the most abundance metal on the earth crust, commonly found as iron sand deposits [9]. Indonesia has a large source of iron sand, Bengkulu iron sand has Fe2O3
79.96%, TiO2 10.53% and SiO2 3.66%, Glagah iron sand has Fe2O3 48.88%, SiO2 18.97% and CaO 7.71% [10,11]. The presence of Fe2O3 in iron sand can be used to modify TiO2 as a photocatalyst material. Modification of TiO2 with Fe2O3
showed high absorption of visible light (maximum wavelength is 550 nm) [12].
Hematite is an iron oxide element which is most abundance, stable photocatalyst and non-toxic [13]. Addition of Fe2O3 to TiO2 can enhance electron transfer and inhibit electron-hole recombination [14]. Furthermore, Fe2O3 only has narrow band gap energy (1.9-1.2 eV), so the electron- hole pairs in valence band are easier to be excited under 3
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visible light irradiation. In addition, the junction between TiO2 and Fe2O3 crystals can avoid the recombination, promote transfer electron and improve the photocatalytic performance [15]. However, modification of TiO2 with Fe2O3 still has short lifetime photocatalyst and low electron mobility [16].
The other attractive material, graphene, two-dimensional single layer of sp2 hybridized is arranged by carbon atoms.
Graphene could play an important role as the charge transfer site, which decreases the recombination of photochemically generated electron-hole pairs, thus increases charge transfer rate of electron and chemical molecules that absorbed at the surface through π-π interaction [17]. The previous studies have shown that the semiconductor oxide introduced with graphene oxide (GO) can enhance the photocatalytic activity.
The enhancement of photocatalytic activity also correlates with the improvement adsorption ability [18].
Herein, we report the extraction of Fe2O3 from Glagah iron sand by hydrometallurgical method to assembly of Fe2O3 and TiO2 co-doped graphene oxide (FTG) composite via one-pot sonochemical assisted hydrothermal route combined with freeze-drying. Then, FTG composite, Fe2O3/TiO2 (FT) particles were loaded on the surface of GO nanosheets. FTG composite showed predominately adsorption capacity and excellent visible light-driven photocatalytic activity for elimination Rhodamine B (RhB) dyes. The photocatalytic result showed that the FTG composite have better performance than Fe2O3 and TiO2
without GO.
2. Experimental 2.1 Materials
Iron sand was obtained from Glagah beach, Yogyakarta, Indonesia. Graphite powder as graphene oxide (GO) precursor (≥99%), TiO2 anatase powder (≥99%), sulfuric acid (H2SO4, 98%), ammonium hydroxide (NH4OH, 25%) and hydrogen peroxide (H2O2, 30%) were obtained from Merck. Potassium permanganate (KMnO4, ≥99%), sodium nitrate (NaNO3, ≥99%) and rhodamine B dye (RhB, ≥95%) were obtained from Sigma-Aldrich. Then, distilled water was supplied by Laboratory of MIPA Terpadu UNS. All chemical reagents were analytically pure without further purification.
2.2 Synthesis of Fe2O3/TiO2 (FT) composite
FT composites were prepared from Glagah iron sand referred to Wahyuningsih’s work with slight modification [19]. Iron sand was separated from nonmagnetic phase using magnet rod. Magnetic phase iron sand was grinded using ball-milling (300 rpm, 3 h). 10 g of iron sand was refluxed for 5 h at 90 °C with sulfuric acid (9 M). Furthermore, the solution mixture was separated from the remaining sand
powder. The liquor of iron sand was hydrolyzed using NH4OH (6 M) until pH reach 8-10 and solid precipitate was appeared. The mixture was filtered, then the obtained precipitate was dried in the oven at 150 °C for 4 h. The 3 g of solid precipitate mixed with 0.5 g of TiO2 anatase in 100 mL of distilled water. The mixture was ultrasonicated for an hour and calcined at various temperature (400, 500 and 600 °C) under ambient atmosphere. The resulted composites were denoted as FTx (x referred to the temperature of calcination process).
2.3 Synthesis of Graphene Oxide (GO)
Graphene oxide was prepared from graphite powder using modified Hummer’s method [20]. Briefly, 2.5 g of graphite powder was added to 150 mL of sulfuric acid and stirred in an ice bath for an hour. Then, 4 g of NaNO3 was added to the mixture. After that, 8 g of KMnO4 was added slowly with stirring the mixture vigorously and temperature of the mixture was kept at under 10 °C. The mixture was stirred continuously for 20 h at room temperature. Then, 200 mL of distilled water was added to dilute the mixture and a brownish liquor was formed. Next, 20 mL of H2O2 was slowly added to stop the reaction and obtained a golden- brown solution. The suspension was washed using distilled water until the pH of the supernatant was 7. Finally, the precipitate product was ultrasonicated for an hour and dried using freeze-drying technique for 24 h.
2.4 Synthesis of Fe2O3/TiO2/GO (FTG) composite
Fe2O3/TiO2/GO (FTG) composite was obtained via hydrothermal method based on Li’s work with slight modification [21]. The 200 mg of GO was added into 75 mL of distilled water under ultrasonication for an hour to re- exfoliate GO thoroughly and then 0.8 g of the FT composites were added to the GO suspension. The mixture was ultrasonicated for 80 minutes until a homogeneous suspension was obtained. The suspension was poured into a Teflon-lined stainless-steel autoclave and heated at 120 °C for 3 h to simultaneously obtain hybrid structure of Fe2O3/TiO2/GO (FTG) composite and reduction of GO.
Finally, the resulting composite was dried by freeze-drying technique. The resulting composites were denoted as FTGx (x referred to the temperature of calcination process).
2.5 Photocatalytic activity testing
The photocatalytic performances of synthesized photocatalysts were evaluated based on the degradation of RhB dye under visible-light illumination (light source: 300 W wolfram lamp). The photocatalyst (20 mg) was mixed with (10 mL, 10 mg L-1) solution in a glass vial. The mixture was stored in dark for an hour to reach adsorption-desorption 1
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equilibrium. Photocatalytic reaction was carried out for 80 minutes and fixed amount of the solution were taken out at 20 minutes interval. The degradation of RhB dyes was determined using UV-Vis spectrophotometer. The stability of the photocatalysts was determined after four consecutive cycles. The amount of photocatalyst that was used in each cycle was 20 mg.
2.6 Characterization
The composition of iron sand before and after hydrometallurgical process was observed by X-ray fluorescense (XRF) from Bruker S2 Ranger. Diffraction patterns of the samples were recorded on XRD (Bruker D8 Advanced and X-Pert PANalytical) using Cu Kα radiation.
Fourier Transform Infrared (FTIR) spectra of the samples were recorded on an FTIR spectrophotometer (Shimadzu IR Prestige-21) using a KBr pellet technique. The morphology of all samples was observed by using SEM (JEOL JSM 6510 LA). The UV-Vis spectra of the solutions were measured using UV-Vis Spectrophotometer (Perkin Elmer Lambda 25).
3. Result and Discussion
3.1 Synthesis and characterizations of Fe2O3/TiO2
Elemental analysis of Glagah iron sand after hydrometallurgical process shows that Fe2O3 content increases up to 81.44%. Table 1 shows the chemical content in the Glagah iron sand before and after hydrometallurgical process. Hydrometallurgical process could increase the Fe2O3 and TiO2 content due to the dissolution of metal components in H2SO4. The SiO2 content decreases due to low solubility in H2SO4. Figure 1 shows the XRD pattern of Fe2O3/TiO2 (FT composite) at the different calcination temperature (400, 500 and 600 °C). The diffraction patterns of the FT400, FT500 and FT600 composites show sharp peaks at 2θ= 25.31 °, 37.85 °, 48.07 °, 53.90 ° and 62.72 ° are correlated to anatase phase and peak at 2θ= 35.75 ° is attributed to magnetite and maghemite [22]. The peaks at 2θ= 33.20 °, 24.18 °, 33.20 °, 35.70 °, 54.14 ° and 62.55 ° are corresponded to hematite [16]. The intensity of peaks for hematite rise up with the increasing calcination temperature and the characteristic peaks for magnetite and maghemite disappear in the pattern for FTG600, which could be caused by the phase transformation of iron oxide due to increasing of the temperature [23]. This is correlated to previous work that hematite formed at 325 °C [24].
According to XRD analysis, the grains show a strong peak at 2θ= 25.31° [101] which the FWHM value decreases with increasing of the calcination temperature. The estimation of the crystallite size (D) is calculated using the main diffraction peak (2θ= 25.31 °) according to the Debyee-
Scherrer equation [25]. The crystallite size of Fe2O3/TiO2
composites are shown in Table 2.
Figure 1. Diffraction pattern of Fe2O3/TiO2
composites with various calcination temperature (A=Anatase, M=Maghemite and H=Hematite).
Table 1. Element analysis of Glagah iron sand before and after hydrometallurgical process.
Before After
Compound Value (%) Compound Value (%)
Fe2O3 28.00 Fe2O3 81.44
SiO2 24.95 TiO2 9.08
Na2O 25.26 SO3 4.69
CaO 10.94 P2O5 1.19
Al2O3 6.68 Al2O3 0.96
MgO 4.24 V2O5 0.58
TiO2 2.22 Cl 0.44
K2O 1.98 Nd2O3 0.39
P2O5 1.56 Pr6O11 0.26
3.2 Synthesis and characterizations of GO
Figure 2 clearly shows the difference of XRD pattern of Graphite and GO. From the XRD graph of the graphite flake in Figure 2a, it shows an intense and sharp peak at 2θ= 26.42
°, the peak corresponds to diffraction of the [002] plane. The XRD pattern of GO (Figure 2b) shows a broader peak at 2θ=
10.77 °. The interlayer spacing (dspacing) of graphite and GO 3
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can be calculated according to the Bragg equation [26]. The dspacing value is 3.37 Å for graphite and 8.21 Å corresponds to the GO. The disappearance of graphitic peak ensures the complete oxidation of graphite flake into GO sheets [27].
The various functional groups present in the both graphite and GO were confirmed by using FTIR spectroscopy that is shown in Figure 3. The FTIR spectrum of graphite (Figure 3a) shows peaks at 3440 cm-1 and 1631 cm-1 correspond to vibration of O-H due to the presence of absorbed water [27].
FTIR spectrum of GO (Figure 3b) shows the characteristic absorption at 3418 cm-1 corresponds to stretching vibration of O-H bond. The small peaks at 2928 cm-1 and 2830 cm-1 correspond to the symmetric and asymmetric stretching vibrations of C-H. Peak at 1717 cm-1 corresponds to the stretching vibration of C=O bond, then the peak at 1617 cm-1 corresponds to O-H vibrations due to the keto-enol tautomerism [28]. The peak at 1053 cm-1 corresponds to the stretching vibration of C-O bond from epoxy or alkoxy functional groups. All these functional groups present in the GO cause hydrophilic properties while the graphite is hydrophobic in nature.
Table 2. The crystallite size of Fe2O3/TiO2 composites.
Calcination
temperature (°C) 2 (°) FWHM D (nm)
400 25.31 0.156 59.603
500 25.31 0.153 60.926
600 25.31 0.146 63.501
Figure 2. XRD patterns of (a) Graphite and (b) Graphene Oxide.
The morphology of graphite and GO was imaged using scanning electron microscope (SEM) that is shown in Figure 4. From that figure, can be seen that the morphological changes from graphite to GO. Figure 4a shows that graphite has a flake shape that spreads in varying and irregular sizes.
Figure 4b shows the layers of graphene oxide with wrinkled surface. The formation of wrinkled on the graphene oxide surface indicates that the graphite flakes are successfully oxidized, which may be due to the undulation of the sheets as an epoxy and hydroxyl site formation [29].
3.3 Synthesis and characterizations of Fe2O3/TiO2/GO (FTG)composites
The FTIR absorption spectra of GO, FT and FTG composite are compared in Figure 5. FTIR spectra shows stretching vibration of O-H band between 3600-3100 cm-1 that decreases in FTG due to the reduction during hydrothermal process. In addition, the peak around 1717 cm-1 may be attributed to the C=O band that indicates the skeletal vibration of graphene in the FTG. Therefore, it can be concluded that GO is successfully exfoliated and formed FTG composite. The broad absorption below 1000 cm-1 can be assigned to combination of Fe-O vibration, Ti-O-Ti bridging stretching and Ti-O-C vibration that is resulted the chemical interaction between FT composite and GO [14].
Furthermore, it indicates the co-existence of TiO2, Fe2O3 and GO in the composite.
Figure 3. FTIR spectra of (a) Graphite and (b) GO.
Then, band-gap energy (Eg) of the composite materials were estimated by Tauc’s plot equation using absorption data. The Eg has been determined by extrapolating the linear curve of the plots of (αhυ)2 against hυ to the energy axis.
Figure 6 shows the approximation of band gap for TiO2, 1
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FT600 and FTG600 were respectively 3.30, 3.10 and 3.05 eV.
The SEM micrograph of graphene oxide and FTG600 composite are shown in Figure 7. The wrinkled sheets were clearly visible in SEM image of GO. The FTG600 image indicates that the GO surface is clearly modified with Fe2O3
and TiO2 particles, that is consistent with the previous studies [22]. Table 3 shows a list of elemental contents (wt%) of GO and FTG600 composite. The results confirm that there are C (66.02%) and O (33.43%) elements in the GO, while C (31.17%), O (42.68%), Ti (8,43%) and Fe (16.88%) elements in the FTG600 composite.
3.4 Photocatalytic degradation performances
The photocatalytic activities of synthesized materials, namely Fe2O3, FT400, FT500, FT600, FTG400, FTG500 and FTG600 were evaluated by degradation of RhB under visible light irradiation. Here, these materials were prepared by varying calcined temperature and the GO addition. Hence, the degradation efficiency is calculated based on the decreasing amount of the constituents and thereby its effect on the catalytic activity. Total concentrations of RhB were determined from the maximum absorption (λ=554 nm) that was measured by UV-Vis spectrophotometer. The initial RhB absorption is regarded as Ao. The A/Ao is used to determine the degradation that represented for the absorption ratio before and after a certain reaction time.
Figure 4. SEM images of (a) Graphite and (b) GO.
The results for the photocatalytic degradation of RhB are shown in Figure 8. It is clearly observed that the FTG600 showed the highest photocatalytic activity among tested photocatalysts: 92.98% of RhB was degraded by FTG600 within 80 minutes of irradiation. In contrast, the photocatalytic activity of Fe2O3 is low, only 5.34% of RhB was degraded after 80 minutes of irradiation. This result indicates that addition of graphene oxide has the most significant influence on the photocatalytic activity of the composites. The degradation efficiency of the synthesized photocatalyst materials can be explained by understanding of the synergistic interplay between adsorption capability and photocatalytic activity of the materials. Increasing of adsorption capability causes the degradation of RhB is higher because of the interaction enhancement between RhB and photocatalyst.
Figure 5. FTIR spectra of (a) FTG, (b) FT and (c) GO.
Figure 6. Tauc Plot of TiO2, FT600 and FTG600.
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In order to investigate the stability and recyclability of the resulting photocatalyst materials, the repetitive test in removal of RhB dye were performed over FTG400, FTG500 and FTG600 under visible light irradiation. After each reaction run, the composites were separated from the reaction system and washed with distilled water, dried at 90 °C and reused again. As shown in Figure 9, the removal efficiency of RhB is still 83.4% after four cycle runs, indicates the activity of recovered FTG600 is stable enough for recycling than FTG400 and FTG500.
In this work, the FTG composite showed excellent photocatalytic activity toward the degradation of RhB dye.
We can observe that graphene oxide plays important roles in enhancing the photocatalytic activity.
Figure 7. SEM images of (a) GO and (b) FTG.
Therefore, FTG composites are expected to be promising in environmental remediation due to their adsorptivity, photocatalytic activity and stability.
Figure 8. Photodegradation of RhB dye by Fe2O3, FT400, FT500, FT600, FTG400, FTG500 and FTG600.
Figure 9. Stability of the various FTG composites in the removal of RhB dye.
4. Conclusion
In this study, FT composites were collected from Glagah iron sand and FTG composites were prepared by hydrothermal method and their activities during RhB dye removal was evaluated. The FTG composite showed highly enhancement of photocatalytic activity under visible light irradiation than TiO2 and FT composite. This composite material also has a good stability from recycle test that is still more than 83% after it is used for four cycles..
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Acknowledgements
This research was funded by Sebelas Maret University through the Hibah Pascasarjana PNBP 2019 program (No.
368/UN27/HK/2019).
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