Research Article pubs.acs.org/journal/ascecg
Preparation and Characterization of Fe2O3 Nanoparticles by SolidPhase Method and Its Hydrogen Peroxide Sensing Properties Chen Hao,*,† Yuru Shen,† Zhiyuan Wang,† Xiaohong Wang,*,† Feng Feng,† Cunwang Ge,§ Yutao Zhao,‡ and Kun Wang† †
School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, China School of Material Science & Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, China § School of Chemistry and Chemical Engineering, Nantong University, Nantong, Jiangsu 226019, China ‡
ABSTRACT: Modified Fe2O3 nanoparticles were obtained by a conventional solid-phase method with different additions of sodium lignosulfonate (SLS) and calcining temperatures. The microstructures and morphologies of the synthesized Fe 2 O 3 samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric/differential scanning calorimetry (TG/DSC) analysis, Fourier transform infrared spectroscopy (FT-IR) and surface area and porosity analyzer (BET). The results indicate that the fine Fe2O3 particles with uniform morphology were gained (1.0 g SLS, calcined 400 °C). Then, the as-prepared Fe2O3 nanoparticle, along with graphene (G), was immobilized on the surface of glassy carbon electrode (GCE) by a bridge constituted of chitosan (CS) for further electrochemical measurement of cyclic voltammetry and chronoamperometry. The prepared G-Fe2O3CS/GCE with the above-mentioned fine Fe2O3 particles (1.0 g SLS, calcined 400 °C) displayed high sensitivity (84.32 μA mM−1 cm−2), wide detection range (0.001−6.0 mM) and low detection limit (1.1 μM) when applied to the electrochemical sensing of hydrogen peroxide. Moreover, the sensor was also confirmed to exhibit good anti-interference for ascorbic acid and uric acid, excellent repeatability, and long-term stability. KEYWORDS: Fe2O3, Hydrogen peroxide, Sodium lignosulfonate, Graphene, Solid phase
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INTRODUCTION Hydrogen peroxide (H2O2) is an important inorganic chemical raw materials and green products, which has attracted more and more researcher’s attention.1−5 It is not only as an strong oxidant widely used in the environmental, chemical, paper, electronics, textile, pharmaceutical and other industries; but also suitable for such fields as clinical, food, industrial and environmental analysis, etc. as a medium.6 Consequently, the determination of H2O2 is of important significance in industry, common life, environmental protection and many other fields.7,8 Many methods for the detection of H2O2, such as titrimetry,9 spectrophotometry,10 fluorescence,11 chemiluminescene12 and electrochemistry13−15 have been developed in recent years for its wide range of applications and distinguished performance. The above-mentioned first four detection methods have lots of obvious drawbacks, they all are, for example, complicated, time-consuming and expensive, etc.16 The electrochemical technique may be the most excellent and appropriate method for the detection of H2O2 because of its operational simplicity, low-cost, high sensitivity and selectivity.17,18 Up to now, a number of high-efficiency electrochemical sensors have been prepared.19−23 However, most of the above-mentioned electrochemical sensors were assembled based on proteins or enzymes, which © XXXX American Chemical Society
limited the application of the sensors in many aspects for their tenderness, instability, susceptibility to the environment and ease of inactivation.24,25 In comparison with the immobilized enzyme biosensors, enzyme-free sensors are intrinsically more stable because of their strong adaptability to environment, high durability and long lifetime.26 Recently, a series of enzyme-free sensors have been successfully constructed, and meanwhile they are also proved to be promising as the electrochemical sensors.27,28 On account of a low production cost, a narrow bandgap (∼2.1 eV) and good chemical stability, it is a right choice to use iron oxide nanoparticles as substrate of the enzyme-free sensor.29,30 However, there always goes with the agglomeration and forms the large particles in the synthesis process, which restricts application of iron oxide in sensors.31,32 Sodium lignosulfonate (SLS) is an abundant and unexpensive modified natural polymer with superb decentralization which is functionalized with lots of hydrophilic groups, such as sulfonic, carboxyl and hydroxyl groups.33 The aforementioned advantages make it to be a promising surfactant in modifying small particles.34 Received: September 23, 2015 Revised: December 11, 2015
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DOI: 10.1021/acssuschemeng.5b01150 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
ACS Sustainable Chemistry & Engineering
brown ink constituted of 3 mg of Fe2O3, 2 mg of graphene, and 0.4 mL of chitosan aqueous solution (0.2%, w/w), which was previously sonicated for 30 min to make it homogeneously mixed. All electrodes were stored at 4 °C in a refrigerator when they were not in use. Instrumentation. The morphologies of the obtained Fe2O3 nanoparticles were observed by using scanning electron microscopy (SEM, S4800, HI-9140-0006) at an accelerating voltage of 15.0 kV. The XRD patterns were recorded on a Bruker D8 Advance X-ray diffractometer operated at a voltage of 40 kV and current of 40 mA, using Cu Kα (λ = 0.154 06 nm) radiation. Thermogravimetricdifferential scanning calorimetry (TG/DSC) analysis was recorded using a integrated thermal analyzer (STA449C, NETZSCH) to characterize the thermal evolution of the α-FeOOH precursor at a heating rate of 5 °C·min−1 in the range of 25−1000 °C under a nitrogen atmosphere. FT-IR spectra of the powders (as pellets in KBr) were performed using Fourier transform infrared spectroscopy (FT-IR, Nicolet, AVATAR-370MCT) from 4000 to 400 cm−1. The specific surface area and pore size data were carried out on an automated surface area and porosity analyzer (NOVA-2000e). All electrochemical experiments were carried out by a computer-controlled CHI 660C electrochemical workstation (Chen Hua Instrumental Corporation, Shanghai, China). A conventional three-electrode arrangement consisted of Fe2O3 composite modified GCE as a working electrode, a platinum foil as the counter electrode, and a saturated calomel electrode (SCE) as the reference, respectively. All electrochemical experiments were repeated seven times to avoid random error.
Therefore, the researches of bringing SLS to guide the formation of nanomaterials have attracted more and more concern. The room temperature solid-phase method usually is used for preparing the metastable solid product that is not easy to be obtained by conventional solid-phase method at high temperature. Because of its good selectivity, simple process, no need of solvent and high temperature, high yield and low cost, the method has remained popular in the field of material preparation.35−38 In this paper, the Fe2O3 nanoparticles were synthesized through the traditional room temperature solid-phase method in the presence of SLS. A composite film modified electrode was then prepared for the electrochemical detection of hydrogen peroxide. Additionally, graphene was added into the composite and it was important to enhance the electron transfer rate in the H2O2 sensor for increasing the sensitivity and improving the response time.39 Cyclic voltammetry and chronoamperometry were utilized to characterize the electrochemical properties of the modified electrode and the effects of different preparation conditions on the composite were also discussed. Finally, the outstanding electrochemical sensor toward detection of H2O2 was obtained, and it exhibits high sensitivity, a rapid response, a wide linear range, a lower detection limit, a satisfactory anti-interference performance, and excellent storage stability.
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RESULTS AND DISCUSSION TG-DSC results of precursor (α-FeOOH) containing SLS are shown in Figure 1. As can be clearly seen from the TGA curve,
EXPERIMENTAL SECTION
Materials. Without specific illustration, all chemicals were of analytical reagent grade and used as received without further purification, and all solutions throughout experiments were prepared with deionized water. Ferric chloride, flake graphite, sodium nitrate, and hydrazine hydrate were bought from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Concentrated sulfuric acid (98%, m/m)) were purchased from Yangzhou Hubao Chemical Reagent Co., Ltd. (Yangzhou, China). SLS of industrial grade was bought from Fei Wong Xinyi Chemical Co., Ltd. (Xuzhou, China). Preparation of Fe2O3 Nanoparticle and Graphene. Solid powders, 24.35 g of FeCl3·6H2O and 10.8 g of block NaOH (1:3, molar ratio), were separately grinded for 20 min and then mixed with a certain amount of SLS (0.5, 1.0, 1.5, 2.0, and 2.5 g, respectively) in an agate mortar. The mixture was pestled for another 35 min to make the reaction happen. The resultant was centrifuged, washed by absolute ethanol for several times until the pH of the supernatant was less than 8. After that, the flaxen intermediate FeOOH was transferred to an oven to be dried at 60 °C for 24 h. Then the Fe2O3 nanoparticles was obtained by calcining the intermediate in a muffle furnace for 2 h. The calcining temperature was set at 300, 400, 500, and 600 °C, respectively. Graphite oxide was prepared from flake graphite by an improved Hummer’s method.40 The exfoliation of graphite oxide (GO) was achieved by ultrasonication of 1 g of GO in 250 mL of water with 10 mL of ammonia hydroxide for 30 min. The resultant solution was transferred to a 500 mL round-bottom flask to reflux under 30 °C for 1 h. Afterward, 42 mL of hydrazine solution (2 mL of hydrazine in 40 mL of water) was slowly added into the flask dropwise and the reaction was maintained for another 12 h at 100 °C. The vigorous mechanical agitation was used throughout all processes. The resultant black powder was washed by centrifuge for several times and stored at 4 °C in a refrigerator. Preparation of the Modified Electrodes. Prior to modification, GCE of 3 mm diameter was carefully polished with 1.0, 0.5 μm alumina slurry in sequence, and sonicated in water, absolute ethanol, and water for 5 min, respectively. Then the bare GCE electrode was chemically cleaned and activated by repeated cyclic potential scanning within the potential range of +1.0 to −1.0 V in freshly prepared 1.0 M H2SO4.41 The pretreated GCE electrode was modified with 3 μL
Figure 1. DSC-TGA curve for α-FeOOH precursor containing SLS.
the weight loss of the sample undergoes three steps from 25 to 1000 °C. The first weight loss of 6.24% below 120 °C is attributed to the dehydration of the water absorbed on the surface of the sample. The second mass loss from 120 to 450 °C was about 13.93%, which is due to the decomposition of the α-FeOOH and SLS, and the corresponding exothermic peak was observed at 287.4 °C in the DSC curve. The another small exothermic peak was seen at 531.6 °C in the DSC curve, which is ascribed to the phase transformation from γ-Fe2O3 to αFe2O3,42 as is confirmed by XRD analysis. The third mass loss of 2.71% between 450 and 950 °C is mainly due to the continuous decomposition of SLS surrounded by Fe2O3. No obvious weight loss was observed at the corresponding temperature over 950 °C in the TG curve. The FT-IR spectra of SLS (blue), α-FeOOH (green), and Fe2O3(black) are shown in Figure 2. It is clear that the SLS shows a large number of functional groups. The peak appears at B
DOI: 10.1021/acssuschemeng.5b01150 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering
approaching to disappearing with the addition of 2.0 g SLS. It is found that there appear three new peaks (220), (400), and (440) in the curve d compared with curve a. It is concluded that the increasement of SLS leads to the Fe2O3 crystalline structure transformation from the rhombohedral symmetry (JCPDS No. 33-0664) to maghemite (JCPDS No. 39-1346). The XRD data in Figure 3B proves that the crystalline intensity and structure were also affected by calcining temperature. It is clearly seen that the diffraction intensities were improved with the calcining temperature going up, and the peaks (220), (400), and (440) disappeared in curve c, which certificates that γ-Fe2O3 was successfully transformed to α-Fe2O3.45 Meanwhile, the average crystallite dimension (ACD) of these samples is calculated through the full width at half-maximum (fwhm) using Scherrer formula D = 0.9λ/βcos θ (where D is the crystal size, λ is the wavelength of X-ray radiation, β is the full width at halfmaximum, and θ is the diffraction angle), the results are shown in Table 1. We can find that the particle size was also greatly affected by the addition of SLS and the calcining temperature. The cause of this phenomenon can be analyzed as follows: Typical SEM images of Fe2O3 with different additions of SLS show greatly different morphologies, which are shown in Figure 4. The pure Fe2O3 sample (Figure 4A) owns a big particle size with heavy agglomeration and small interspace among them; nevertheless, the interspace greatly improves with the increase of SLS, and at the same time the particle size of Fe2O3 decreases gradually. Interestingly, when further increasing the addition of SLS, the size of particles does not decrease. Conversely, the size of particles begins to increase with the space decreasing and the agglomeration increases just as Figure 4D shows. The diameters of Fe2O3 samples are figured out varying from 25 to 50 nm from Figure 4F, which agrees with XRD analysis results. We also investigated the effect of calcining temperature on the particle size, and the typical SEM image of Fe2O3 annealed at 600 °C is displayed in Figure 4E. It is seen that the high calcining temperature leads to the heavy agglomeration and the narrowing of the space between particles. On the basis of SEM and XRD analysis results, we reached the conclusion that the addition of SLS and calcining temperature have a great effect on the particle size and crystalline structure. The diameters of Fe2O3 nanoparticles reduce with the increment of addition of SLS. However, when the addition of SLS increase to a certain value, the diameters of nanoparticles begin to increase. As for the influence of SLS on the morphology of iron oxide in the process of synthesis, we
Figure 2. FT-IR spectra of SLS (blue), α-FeOOH (green), and Fe2O3(black).
3427 cm−1 may be attributed to hydroxyl groups in phenolic and carboxylic acids, and the peaks at 1039 and 619 cm−1 are characteristic peaks of the sulfonic groups (SO and SO stretching vibration).43 Both of these functional groups play an important role in the preparation of Fe2O3. Some of the characteristic peaks of SLS were observed among FT-IR spectra of the as-prepared α-FeOOH sample, indicating that the SLS was successfully doped into the as-prepared α-FeOOH. The aromatic groups of SLS can be recognized by the peak appearing at 1597 cm−1. The peak at 1420 cm−1 can be attributed to CH deformation. These characteristic peaks almost disappear after the phase transformation from αFeOOH to γ-Fe2O3 by high-temperature calcination. At 560 and 452 cm−1, the two distinct absorption peaks may be due to the vibration of chemical bond (Fe3+O2−),44 which are basically in accordance with literature values. The strong and broad charactristic peak of the −OH group at 3427 cm−1 was caused by Fe2O3 nanoparticles having absorbed moisture from the air. The crystalline structure of the as-prepared Fe2O3 nanoparticles with different additions of SLS and calcination temperatures are shown in Figure 3. All samples show clean Fe2O3 structure without characteristic peaks of impurities and other phases. The curve a with the narrowest and sharpest peaks in Figure 3A indicates the sample is the best crystallized Fe2O3 of all the samples with the addition of no SLS. The diffraction peaks (012), (104), (113), (024), (214), (300), and (1010) die away with the increase of SLS until they are
Figure 3. (A) XRD patterns of Fe2O3 samples with different additions of SLS calcined at 400 °C: (a) 0 g, (b) 0.5 g, (c) 1.0 g, (d) 1.5 g, (e) 2.0 g, and (f) 2.5 g. (B) XRD patterns of Fe2O3 samples prepared with 1.5 g SLS calcined at (a) 300 °C, (b) 400 °C, (c) 500 °C, and (d) 600 °C. C
DOI: 10.1021/acssuschemeng.5b01150 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering Table 1. Particle Sizes of Different Fe2O3 Samples SLS (g)
T (°C)
ACD (nm)
BET (m2·g−1)
SLS (g)
T (°C)
ACD (nm)
BET (m2·g−1)
0.0 0.5 1.0 1.5 2.0
400 400 400 400 400
39.53 35.88 31.86 24.55 16.79
10.67 14.75 24.11 52.23 41.53
2.5 1.5 1.5 1.5
400 300 500 600
34.00 41.16 31.81 38.26
10.91 25.09 13.09
Figure 4. SEM images of Fe2O3 samples with different additions of SLS calcined at 400 °C: (A) 0 g, (B) 1.0 g, (C) 1.5 g, and (D) 2.0 g. (E) SEM images of Fe2O3 samples with an addition of 1.5 g SLS calcined at 600 °C. Panel F is the high magnification photomicrograph of panel C.
Figure 5. TEM images of G (A) and G-Fe2O3-CS (B).
results in the final size of iron oxide nanoparticles becoming larger. After crystal growth reaching stability, the interfacial energy between the crystals may be less than the interfacial energy between the crystal and the gel, which makes the crystal prefer to combine with crystal rather than disperse in the gel.46
can make the following conjecture: First, at the beginning of the Fe3+ and OH− crystallization nucleation, because crystal nucleus are small, the grain has a highly specific surface, which leads to a high surface energy. To reduce surface energy and improve stability, the crystal nuclei will continue to grow, which D
DOI: 10.1021/acssuschemeng.5b01150 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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Figure 6. (A) CVs of bare GCE (a) and G-Fe2O3-CS/GCE (b) in 5 mM [Fe(CN)6]3−/4− solution (1:1, molar ratio) with 0.1 mM KCl. (B) CVs of bare GCE (a and b) and G-Fe2O3−CS/GCE (c and d) in the absence (a and c) and presence (b and d) of 1 mM H2O2 in 0.25 M phosphate buffered saline (PBS). Scan rate: 50 mV s−1.
Figure 7. Response mechanism for the reduction of H2O2.
area and ultrathin film thickness of graphene. It is beneficial to the electron transfer of the G-Fe2O3-CS/GCE sensor that the Fe2O3 is adsorbed on the folded surface of graphene by chitosan. To make sure the Fe2O3 and graphene were successfully modified on the surface of the GCE, cyclic voltammetry in the potential range of −0.2 to +0.8 V was performed, and the Fe2O3 used in this experiment was prepared with the addition of 1.5 g SLS and calcined at 400 °C. The test was carried out in 5 mM [Fe(CN)6]3−/4− solution (1:1, molar ratio) with 0.1 mM KCl and the results were displayed in Figure 6A. We can see that the redox peaks were clearly shown for bare GCE. The anodic peak current ia = 1.774 × 10−4 A and the cathodic peak current ic = −1.808 × 10−4 A, the ia/ic ratio was 0.98, which means a preferably reversible system was acquired. Whereas for G-Fe2O3-CS/GCE, ia = 1.271 × 10−4 A, ic = −1.496 × 10−4 A, the ia/ic ratio was 0.85.48 It is clear that the G-Fe2O3-CS/GCE exhibits lower redox peaks than the bare GCE, suggesting the Fe2O3 and graphene have been successfully modified on the GCE surface. Although chitosan displays an excellent filmforming ability and good adhension on the electrode surface, the organic film also has an inhibition effect on the electron transfer between GCE and Fe2O3.49,24
Finally, the iron oxide with a high degree of agglomeration was thus obtained, as shown in Figure 4A. After adding surfactant SLS, sodium sulfonate produces the negatively charged sulfonic acid and carboxyl groups34 that can be drawn on the crystal nucleus surface by electrostatic interactions. When the quantity of SLS is appropriate, carboxyl, sulfonic acid groups and crystal nucleus will form a stable structure. Ultimately, the growth and agglomeration of the crystal nucleus as Figure 4C are suppressed. However, when the addition of SLS is enough, because of the characteristics of polymer itself, it will polymerize itself and lose the function to restrain the growth and agglomeration of the crystal nucleus, as is shown in Figure 4D. When it comes to the influence of temperature, we can speculate that the high temperature may accelerate the decomposition of FeOOH and promote the growth of iron oxide crystals. As shown in Figure 4D, the high-speed crystal growth easily leads to the formation of larger particles, while the aggregation of the particles will also increase.47 TEM images of G and G-Fe2O3 are shown in Figure 5. The conclusions can be drawn from the gray spots in Figure 5B, that the iron oxide nanoparticles have been adhered to the surface of graphene by chitosan. According to Figure 5A, it can be found that the graphene shows the typical translucent sheets and somecrumpled shape, which is due to the large specific surface E
DOI: 10.1021/acssuschemeng.5b01150 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering
Figure 8. CVs of G-Fe2O3-CS/GCE in 0.25 M PBS of pH 6.8 with 1 mM H2O2. (A) Fe2O3 used in this experiment was calcined at 400 °C with the addition of SLS (a) 0 g, (b) 0.5 g, (c) 1.0 g, (d) 1.5 g, (e) 2.0 g, (f) 2.5 g. (B) Fe2O3 used in this experiment was with the addition of 1.5 g of SLS and calcined at (a) 400 °C, (b) 500 °C, (c) 600 °C, and (d) 300 °C. Scan rate: 50 mV s−1.
Figure 9. (A) Amperometric response obtained under the increasing H2O2 concentration at −0.35 V with 0.3 mM for each step for G-Fe2O3-CS/ GCE. (B) Corresponding linear fit plots of current vs concentration of H2O2.
electrochemical abilities of these electrodes for the same concentration of H2O2 varied a lot. For pure Fe2O3, an obvious reduction peak around −0.35 V appears, indicating the fine electrocatalytic activity for H2O2. The peak current rises as the increasement of SLS until the maximum response appears for the Fe2O3 with 1.5 g of SLS, then the current drops as the successive addition of SLS. Interestingly, when comparing the results of cyclic voltammetry analysis with different SLS additions to Fe2O3 nanoparticles which the sizes have been figured out by SEM analysis, we can find the prepared sensors’ sensitivity to hydrogen peroxide has much to do with Fe2O3 size. As the particle size decreases gradually, the sensitivity to hydrogen peroxide increases. Figure 8B shows the cyclic voltammograms of different GFe2O3-CS/GCEs with Fe2O3 calcined at various temperatures. We can see from these curves that the peak current falls as the rising of the calcining temperature, indicating the reduction of the sensing ability of these electrodes. The current at −0.35 V of Fe2O3 at 600 °C drops more than quarter to be −6.381 × 10−5A compared that of Fe2O3 at 400 °C to be −8.774 × 10−5A. Therefore, we get the conclusion that the sensing ability of the Fe2O3 for hydrogen peroxide owns the positive correlation with its particle size. We speculate that this may be due to the intense surface force field, lacking of particle
All these evidence indicate that the GCE was successfully modified. To have a preliminary understanding of the modified electrode aimed to the determination of H2O2, we also performed the CVs to check their behavior in the potential range from −0.8 to +0.8 V in 0.25 M PBS in absence and presence of 1 mM H2O2. In Figure 6B, the bare GCE in the absence (a) and presence (b) of H2O2 both own a particularly weak current response. Different from the bare GCE, it can be seen that the current response for G-Fe2O3−CS/GCE is much larger than that of bare GCE, which reveals a greatly improved sensing ability. The response mechanism for the reduction of H2O2 is illustrated in Figure 7: Fe(III) was first electrochemically reduced to Fe(II) on the surface of the electrode, and then Fe(II) reacted with H2O2, which resulted in the conversion of H2O2 to H2O and at the same time the regeneration of the initial Fe(III).50 To investigate the effect of different additions of SLS and calcining temperatures on the electrochemical properties of Fe2O3 for the detection of hydrogen peroxide, we prepared some G-Fe2O3-CS/GCEs with different hybrid films and checked their performance by cyclic voltammetry. Figure 8A depicts the current responses of various electrodes with Fe2O3 prepared with different additions of SLS. It is sure that the F
DOI: 10.1021/acssuschemeng.5b01150 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering
Table 2. Comparison of the Linear Range (LR), Sensitivity, Detection Limit (DL), and Response Time (RT) of Hydrogen Peroxide Sensors electrode materials
LR (μM)
carbon paste/Fe2O3 Hb/CIN-chitosan/GCE Fe3O4 MNPs Fe3O4-Fe2O3/Nafion/GCE α-Fe2O3 nanorods Au/graphene/HRP/CS/GCE CTAB-SAMN/CPE G-Fe2O3-CS/GCE
0−8500 3.1−4000 5.0−100 200−1800 40−4660 5.0−5130 10−1500 1.0−6000
sensitivity (μA mM−1 cm−2)
20.325 30
DL (μM)
RT (s)
reference
20 1.2 3.0 200
