The objective of this work was to prepare a series of composite films (polysaccharides with LaFe0.8Cu0.2O3) for the degradation of methyl orange under ultraviolet irradiation. LaFe0.8Cu0.2O3 was prepared by a sol-gel method, and the composite films were obtained by cross-linking reactions between polysaccharides (xylan and chitosan) and LaFe0.8Cu0.2O3. Physical and chemical properties of the composite films were investigated by XRD, FTIR, SEM, and BET. Moreover, the influence of the weight ratio of polysaccharide to LaFe0.8Cu0.2O3 on the methyl orange degradation reaction was also studied. Results showed that 67% of the degradation efficiency was achieved within 480 min using chitosan/LaFe0.8Cu0.2O3 (2:1) as photocatalysts, while 58% was for xylan/LaFe0.8Cu0.2O3 (1:1). The difference was due to the variety in the structure of chitosan and xylan.
Photo-degradation of Methyl Orange by Polysaccharides/LaFe0.8Cu0.2O3 Composite Films
Aojie Deng,a, # Jianfeng Chen,a, # Huiling Li,a Junli Ren,a,* Runcang Sun,a,b and Lihong Zhao a,*
The objective of this work was to prepare a series of composite films (polysaccharides with LaFe0.8Cu0.2O3) for the degradation of methyl orange under ultraviolet irradiation. LaFe0.8Cu0.2O3was prepared by a sol-gel method, and the composite films were obtained by cross-linking reactions between polysaccharides (xylan and chitosan) and LaFe0.8Cu0.2O3. Physical and chemical properties of the composite films were investigated by XRD, FTIR, SEM, and BET. Moreover, the influence of the weight ratio of polysaccharide to LaFe0.8Cu0.2O3 on the methyl orange degradation reaction was also studied. Results showed that 67% of the degradation efficiency was achieved within 480 min using chitosan/LaFe0.8Cu0.2O3 (2:1) as photocatalysts, while 58% was for xylan/LaFe0.8Cu0.2O3(1:1). The difference was due to the variety in the structure of chitosan and xylan.
Keywords: Polysaccharides/LaFe0.8Cu0.2O3 composite films; Photocatalytic degradation; Methyl orange
Contact information: a: State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou, 510640, China; b: Institute of Biomass Chemistry and Utilization, Beijing Forestry University, Beijing, 100083, China; #: Equal contribution by the first two authors;
* Corresponding authors: firstname.lastname@example.org; email@example.com
Dyes are significant pollutants in the textile industry. About 10% of the total produced dyes used up during dyeing processes may be released as effluents, leading to environmental pollution (Vijayaraghavan and Yun 2008). Seeking for efficient treatments for industrial wastewater has attracted lots of attention in recent years.
It is difficult to handle wastewater from dyeing because of its high emission, high levels of organic pollutant, deep chroma, great variation of pH, dramatic changes in water quality, and difficulty in biodegradation. Organic dyes, one of the key pollutant sources, are widely used in light industries such as textiles, cosmetics, printing, and paper making (Aksu and Yener 2001; Hameed and Ahmad 2009; Shannon et al. 2008). Therefore, finding an efficient degradation approach for dyeing wastewater becomes an important issue in environmental protection.
Varies techniques have been applied to remove organic dyes in industrial effluents such as sedimentation, filtration, coagulation, oxidation, adsorption, ion exchange, and biological treatments (Gouvea et al. 2000; Neill et al. 2000; Swaminathan and Sandhya 2003.) One attractive approach is photo-degradation using photocatalysts (Linsebigle et al. 1995; Ejhieh and Khorsandi 2010a, 2010b; Ejhieh and Shamsabadi 2010; Ejhieh and Moazzeni 2013; Ejhieh and Hushmandrad 2010).
Among various photocatalysts, TiO2-based materials and other composite materials have been found to be efficient photocatalysts. (Yang et al. 2013) reported that up to 75% of degradation rate was achieved using TiO2 modified with 3 wt% alkali ions. (Zhu et al. 2012, 2013) used CdS/TiO2/chitosan and TiO2/ZnO/chitosan as catalysts to decolorize methyl orange solution under visible light. However, some drawbacks still exist, including high cost and limitations in photocatalytic activity, which greatly limits the industrial application of TiO2 for water treatment.
Novel efficient photocatalysts have been under development in recent years. Compared with TiO2, perovskite-type oxides are much more suitable for photocatalysis under various light sources and reaction conditions due to their multiple band energies and favorable stability in acidic and basic solutions (Tian et al. 2013). Perovskite-type LaCoO3 hollow spheres, nanosized perovskite-type oxides (LaCoO3), ultrafine perovskite-type LaCoO3, LaCoO3-x porous powder, and LaCoO3nanoparticles prepared by different methods have exhibited high photocatalytic activity under different light irradiation due to the high chemisorbed oxygen, and hence they could be promising candidate materials for photocatalytic application (Fu et al. 2013; Fu et al. 2011; Ha et al. 2013; Jung and Hong 2013; Sun et al. 2010a; ). The perovskite-type composite oxide La0.5Pb0.5MnO3 with specific surface area was successfully synthesized by the stearic acid method, and it showed excellent catalytic activity (Chen et al. 2013). La-loaded
Polysaccharides such as cellulose and chitosan (CS), as valuable and renewable resources, have been widely applied for the composite photocatalysts. (Zhao et al. 2011) used chitosan-TiO2 as catalysts to decolorize methyl orange solution under UV light. (Obeid et al. 2013) used chitosan/maghemite composites as catalysts to degrade methyl orange. Moreover, xylan belongs to the hemicellulose cell wall components of all plants, and it is the most abundant polysaccharide in nature after cellulose. However, there is no report on the application of xylan and CS as composite photocatalysts with perovskite-type oxides.
From perovskite-type oxides mentioned above, metal oxides (iron oxide) as well as the rare earth metals have the good photocatalysis performance. In this work, we prepared perovskite-type oxides LaFe0.8Cu0.2O3 by sol-gel method and synthesized two kinds of composite photocatalysts (xylan/LaFe0.8Cu0.2O3 and CS/LaFe0.8Cu0.2O3) by cross-linking reaction to form composite films. Physical and chemical properties of the composite films were investigated by X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM), ultraviolet visible spectra (UV-vis), and BET method. These two composite films were evaluated relative to photocatalytic degradation of methyl orange under ultraviolet irradiation (365 nm).
La(NO3)2.6H2O was purchased from Aladdin. Fe(NO3)2.9H2O, sodium hypophosphite (SHP), and methyl orange were obtained from Tianjin Damao Chemical Reagent CO., Ltd. Cu(NO3)2.3H2O was provided by Guangzhou Chemical Reagent Factory. NaOH, ethyl alcohol, and acetic acid were purchased from Guangdong Guanghua Sci-Tech Co., Ltd. Citric acid, ethylene glycol, and glutaric dialdehyde were bought from Shanghai Lingfeng Chemical Reagent CO., Ltd. Xylan was obtained from Sigma-aldrich CO., Ltd. Ultrapure water was used throughout the study.
Preparation of Perovskite-Type Oxides and Composite Films
LaFe0.8Cu0.2O3 was prepared by sol-gel method (Li et al. 2013). La(NO3)2.6H2O (0.1 mol), Fe(NO3)2.9H2O (0.08 mol), and Cu(NO3)2.3H2O (0.02 mol) were added into ultrapure water to form homogeneous solution. Then, citric acid (the molar ration of citric acid to La3+ of 1.5:1) and ethyl alcohol (the ethylene glycol/citric acid ratio of 1.5:4, mL/g) were added into the solution. After that, the mixture was dried at 110 oC overnight and calcined at 700 oC for 6 h. And then desired perovskite structures were obtained.
CS/LaFe0.8Cu0.2O3 composite films were prepared by the following cross-linking reaction. A certain weight ratio of chitosan and perovskite powder (1:2, 1:1 and 2:1, w/w) were added to 10-mL acetic acid solution (2%) and ultrasound for 2 h. After that, the mixture solution was poured into a glass plate to form film at 55 oC. The prepared film was congealed in the 0.2-mol/L NaOH solution and then soaked in 0.25% glutaric dialdehyde for 30 min. The composite films were washed with ethyl alcohol and water for several times and dried at 110 oC to get the target product.
Xylan/LaFe0.8Cu0.2O3 composite films were prepared by the cross-linking reaction. 0.6 g of xylan and 0.2 g of SHP were added into 8-mL ultrapure water at 60 oC. 2.4 g of citric acid was dissolved in 2-mL ultrapure water, and then perovskite powder (the Xylan/LaFe0.8Cu0.2O3 ratio of 1:2, 1:1, and, 2:1 w/w) was added. The above mixture was ultrasonicated for 20 min and then dried at 100 oC for 30 min. After that, temperature was elevated to 120 oC and kept for 5 h. Products were washed by 70% and 95% ethyl alcohol, respectively. Finally, the product was dried at 50 oC for 24 h.
Characterizations of Photocatalysts
Fourier transform infrared (FTIR) spectra were recorded on a TENSOR27 spectrometer (Bruker, Germany) at room temperature. The X-ray power diffraction (XRD) pattern was measured with a D8 Advance (Bruker, Germany) device. Scanning electron microscope (SEM) images were taken on an S-3700N (Hitachi, Japan) instrument. UV-visible spectra were obtained with a UV2550 ultraviolet spectrophotometer (Shimadzu, Japan). Specific surface area was measured by Gemini VII 2390 (Micromeritics, USA). Surface area (SBET) of samples were measured by N2 adsorption using a Micromeritics ASAP 2010 instrument at 77 K and calculated from the adsorption data in the relative pressure range from 0.05 to 0.30.
Photocatalytic Degradation Experiments
Photocatalytic reactions were carried out in a XH-300UL instrument (Xianghu, Beijing). 100-mL methyl orange solution (15 mg/L) was placed in a 250 mL quartz flask, and then photocatalysts were added. The photocatalytic degradation experiments were carried out under ultraviolet irradiation (365 nm) at different intervals. After a required time, the filtrate was measured by ultraviolet spectrophotometer at 464 nm for 3 times to reduce standard errors. Concentration of methyl orange was calculated as follows:
Concentration of methyl orange (mg/L) = 13.49 × Abs – 0.071 (1)
And then, the degradation efficiency of methyl orange was calculated as follows:
Degradation efficiency of methyl orange (%) = (2)
RESULTS AND DISCUSSION
The FTIR spectra of CS and CS/LaFe0.8Cu0.2O3 composites are presented in Fig. 1a. An absorption band at 560 cm-1 corresponded to the band of Fe-O in LaFe0.8Cu0.2O3 (Gosavi and Biniwale 2010; Pecchi et al. 2008). Bands located at 1668 cm-1, 2873 cm-1, 3417 cm-1, and 1055 cm-1 were attributed to the N-H stretch, CH2 stretch, O-H stretch, and secondary alcohol C-O stretch of chitosan, respectively (Jiang et al. 2012). The spectra of composite films were similar to that of chitosan, and the band of Fe-O is present in CS/LaFe0.8Cu0.2O3 composite films. This indicated that the composites contained CS and LaFe0.8Cu0.2O3.
The FTIR spectra of xylan/LaFe0.8Cu0.2O3 are presented in Fig. 1b. Bands at 1051 cm-1, 1168 cm-1, 1400 cm-1, 2918 cm-1, and 3450 cm-1 correspond to the stretches of C-O, C-C, C-O-C, and C-H in methyl and methylene, as well as CH2 and O-H in xylan, respectively.
Fig. 1. FTIR spectra of composite films (a) CS/LaFe0.8Cu0.2O3 (a1:LaFe0.8Cu0.2O3; a2:CS; a3:CS/LaFe0.8Cu0.2O3=1:1; a4:CS/LaFe0.8Cu0.2O3=1:2; a5:CS/LaFe0.8Cu0.2O3=2:1). Composite films (b) xylan/LaFe0.8Cu0.2O3 (b1:LaFe0.8Cu0.2O3; b2:xylan; b3:xylan/LaFe0.8Cu0.2O3=1:1; b4:xylan/LaFe0.8Cu0.2O3=1:2; b5:xylan/LaFe0.8Cu0.2O3=2:1)
For spectra 3b-5b, the absorption band at 568 cm-1 in the spectra of xylan/ perovskite composites with different weight ratios. A new signal at 1603 cm-1 is ascribed to the COO– group produced by the cross-linking reaction of xylan with citric acid, and the new band around 1412 cm-1 is assigned to CO stretching on –COOH groups (Wang et al. 2013). The band at around 1730 cm-1 is indicative of ester groups (carbonyl groups) in spectra 3b-5b. So the composites were confirmed to have cross-linked xylan and LaFe0.8Cu0.2O3.
X-ray Diffraction Analysis
The XRD patterns of samples are shown in Fig. 2. Diffraction peaks at 22.74o, 32.41o, 39.88o, 46.88o, 57.38o, 67.50o, and 76.71o were attributed to the specific diffractions of LaFe0.8Cu0.2O3 (Mo et al.2013). Two peaks at 10.53o and 19.89o were ascribed to chitosan (Liu et al. 2013). Characteristic peaks of chitosan observed in CS/LaFe0.8Cu0.2O3 with different weight ratios (1:1, 1:2, and 2:1) indicated that the composite films were prepared successfully. From Fig. 2b, an obvious peak at 19.11owas attributable to xylan. For spectra 3b-5b, the diffraction peaks of LaFe0.8Cu0.2O3 were present, and the crystal peak at 19.11o disappeared, indicating that the structure of xylan changed after cross-linking reaction. Those meant that the LaFe0.8Cu0.2O3 had been inserted in the composite films.
Fig. 2. XRD spectra of composite films (a) CS/LaFe0.8Cu0.2O3 (a1: LaFe0.8Cu0.2O3; a2: CS; a3: CS/LaFe0.8Cu0.2O3=1:1; a4: CS/LaFe0.8Cu0.2O3=1:2; a5: CS/LaFe0.8Cu0.2O3=2:1). Composite films (b) xylan/LaFe0.8Cu0.2O3 (b1: LaFe0.8Cu0.2O3; b2: xylan; b3:xylan/LaFe0.8Cu0.2O3=1:1; b4: xylan/LaFe0.8Cu0.2O3=1:2; b5: xylan/LaFe0.8Cu0.2O3=2:1)
SEM and BET Analysis
Figure 3 shows the SEM images of the ground samples. Small particles of LaFe0.8Cu0.2O3 and compact morphology of chitosan were observed, which implied that the LaFe0.8Cu0.2O3 was likely to have had a larger surface area. Moreover, after the combination of polysaccharides (CS and xylan) with LaFe0.8Cu0.2O3, pore structure was formed, and many small particles were present at the surface of amorphous solids.
Fig. 3. SEM of prepared catalysts
The BET area of the prepared catalysts is presented in Table 1. LaFe0.8Cu0.2O3 showed the largest surface area (9.37 m2/g), which was consistent with the SEM results. When the weight ratio of polysaccharides to LaFe0.8Cu0.2O3 was 1:2, a higher specific surface area was obtained in composite films.
Table 1. BET of Composite Films
Photocatalytic Activities of Catalysts
The photo-degradation experiments were carried out under UV irradiation as shown in Fig. 4. 50 mg of catalysts were added into 100 mL methyl orange solution (15 mg/L). The degradation rate increased with the increasing irradiation time. In comparison with xylan/LaFe0.8Cu0.2O3 composite films, the chitosan/LaFe0.8Cu0.2O3 system showed better catalytic ability for the degradation of methyl orange. The rate of degradation increased dramatically with growth in photocatalytic reaction time. When the ratio of CS to LaFe0.8Cu0.2O3 was 2:1, the largest degradation rate of 67% was achieved in 480 min, and then it flattened out with prolonging irradiation time. For xylan/LaFe0.8Cu0.2O3, increasing irradiation time led to an increment of the degradation rate. When the weight ratio of xylan and LaFe0.8Cu0.2O3 was 1:1, the maximum degradation rate of 58% was obtained in 480 min. The difference in the methyl orange degradation rate for CS/ LaFe0.8Cu0.2O3 and xylan/LaFe0.8Cu0.2O3was due to the various structure of nature macromolecules. Chitosan is a natural resource with positive charge and high molecular weight (Cestari et al. 2004). –OH and –NH2 groups endow chitosan with the ability to adsorb and to engage in chelation. Compared with xylan, chitosan is a more suitable material for preparing the composite photocatalysts.
Fig. 4. Photo-degradation performance of different photocatalysts
The photocatalytic efficiency of a catalyst is based on three aspects: adsorption ability, quantum efficiency of the photo-generation of the electron-hole pair, and the separation speed of electron-hole pair. Under UV irradiation, electrons in Fe2O3 and CuO may transfer from valence band (VB) to conduction band (CB), which forms large number of active electrons and holes with high reducibility and oxidability. The co-operation of Fe2O3, CuO, and La2O3 benefits the transformation of electrons and holes so that they could shift to the surface of catalysts to react with methyl orange. Hence, the decomposition of methyl orange occurs.
- In summary, the two described polysaccharides/perovskite-type oxides composite films (CS/LaFe0.8Cu0.2O3 and xylan/LaFe0.8Cu0.2O3) were synthesized successfully via cross-linking reactions, and the photo-degradation ability of each for methyl orange was investigated under UV irradiation.
- Results showed that the addition of polysaccharides could greatly enhance the catalytic ability of LaFe0.8Cu0.2O3. When the weight ratio of CS to LaFe0.8Cu0.2O3 was 2:1, the highest degradation rate of 67% was obtained in 480 min. And the maximum degradation rate of 58% for xylan/ LaFe0.8Cu0.2O3 (1:1) was achieved in 480 min.
- This study provides an efficient strategy to solve dyeing pollution problems using new photocatalysts for industrial applications.
This work was supported by the grants from Guangdong Natural Science Funds for Distinguished Young Scholar (S20120011250), Program for New Century Excellent Talents in University (NCET-12-0194), and the Fundamental Research Funds for the Central Universities (2014ZG0003), SCUT. The authors are grateful to the kind support from the Committee of the 4th Conference on Biorefinery towards Bioenergy (ICBB2013) in Xiamen, China.
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Article submitted: January 15, 2014; Peer review completed: March 9, 2014; Revised version received and accepted: March 20, 2014; Published: March 31, 2014.