Journal of Fashion Technology & Textile EngineeringISSN: 2329-9568

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Research Article, J Fashion Technol Textile Eng Vol: 2 Issue: 3

Degradation of Textile Dye by UV Light Using Nano Zno/Bamboo Charcoal Photocatalysts

Ming-Shien Yen*, Mu-Cheng Kuo and Chien-Wen Chen
Department of Materials Engineering, Kun Shan University, Tainan, Taiwan 71003, Republic of China
Corresponding author : Dr. Ming-Shien Yen
Department of Materials Engineering, Kun Shan University, Tainan, Taiwan 71003, Republic of China
Tel: +88662050349; Fax: +88662050349
E-mail: [email protected]
Received: October 28, 2014 Accepted: November 05, 2014 Published: November 09, 2014
Citation: Yen MS, Kuo MC, Chen CW (2014) Degradation of Textile Dye by UV Light Using Nano Zno/Bamboo Charcoal Photocatalysts. J Fashion Technol Textile Eng 2:3. doi:10.4172/2329-9568.1000115

Abstract

Degradation of Textile Dye by UV Light Using Nano Zno/Bamboo Charcoal Photocatalysts

The purpose of this study is to fabricate a composite material made of nano zinc oxide and bamboo charcoal through calcination and to investigate the decolorization effect of this composite material on simulated textile wastewater containing the acidic dye C.I. Acid Red 266. The parameters contributing to the photocatalytic decolorization of Acid Red 266 are the concentration of the composite solution, the proportion of nano zinc oxide and bamboo charcoal in the composite, the change in the pH of the dye solution, and the reaction time under UV irradiation. The decolorization of C.I. Acid Red 266 by the composite materials is measured with an ultraviolet spectrometer. The experimental result shows that decolorization is optimal when the pH of the dye solution is 4 and the proportion of nano zinc oxide and bamboo charcoal in the composite material is 1:9.

Keywords: Bamboo charcoal; Zinc oxide; Photocatalyst; Decolorization; Acid dyes

Keywords

Bamboo charcoal; Zinc oxide; Photocatalyst; Decolorization; Acid dyes

Introduction

Bamboo charcoal (BC) is regarded as a new environmentally friendly and functional material. It is produced as a residue from the pyrolysis of bamboo; BC has a high adsorption capacity, of 1 cm3 for a surface area of 350 m2. As bamboo can be grown readily, BC is considered a renewable resource; if BC is subjected to activation, it can be used as a suitable alternative to activated carbon (AC), which is a natural but depletable resource; for this reason, BC has attracted considerable attention for research and development in recent years. BC is produced from rapidly growing moso bamboo plants, which are abundant in China. BC is inexpensive, with its price approximately 1/3–1/5 of that of AC available in China [1]. Recently, BC has become a popular field of study in China [2]. Kimura et al. [3] and Mizuta et al. [4] found that the adsorption effectiveness of BC was greater than that of AC for removing nitrate–nitrogen from underground and surface water, and hence, the water treatment processes using BC are considered to be more efficient than the same processes using AC.
With rapid developments in chemical and other industries, numerous compounds and products are manufactured through processes that require the use of water; the chemical emissions from these processes is in the form of industrial wastewater, which requires treatment and recycling. The amount of water used in the dyeing and finishing industries is more than that used in other industries; the wastewater discharged from the processes in this industry contains dyes with high color and toxicity levels. This discharge results in extensive environmental pollution and can affect human health directly or indirectly through the food chain [5]. Some innovative approaches have been developed to eliminate the color of textile wastewater, which includes the ozonation method [6], the activated rice husk and activated coconut fibre system [7], TiO2 photodegradation system [8,9], UV/TiO2 photocatalytic system [10,11], ultrasound assisted system for textile wet processes [12] and waste bamboo scaffolding for wastewater treatment [13]. Various processes are used for physical wastewater treatment, such as dilution, sedimentation, filtration, adsorption, and centrifugation; on the other hand, chemical wastewater treatment methods include neutralization, coagulation, and oxidation. The most common physical treatment method is adsorption. In this method, activated carbon, clay, or other porous substances are ground into a powder or granular form and mixed with wastewater; the granular material possesses holes that adsorb the contaminants in wastewater and thus decontaminate the water [14-16].
At present, activated carbon is commonly used as an adsorption material and is very effective in adsorbing organic compounds from water, such as those present in ionic dyes, direct dyes, acid dyes, reactive dyes, and other water-soluble dyes. However, it is not very effective in removing colloidal material and hydrophobic dyes from wastewater; for these purposes, the use of BC can be considered as cheaper and more convenient potential alternative. Several studies have shown that BC has an excellent adsorption capacity for a wide variety of substances such as nitrate–nitrogen [4], heavy metals [17], dibenzothiophene [18], and harmful gases [19,20], and it can be used for the removal of impurities from both liquid solutions and air [21]. Therefore, as a new innovative and cost-effective adsorbent, BC may attract more attention as an alternative option for adsorption materials.
Further, zinc oxide (ZnO) is considered a low-cost photocatalyst with high photocatalytic activity, used for the complete degradation of organic pollutants in water without the formation of secondary pollutants. The photocatalytic properties of ZnO have been researched extensively, and it has been found that ZnO cannot be used for removing all pollutants perfectly. Hence, to achieve complete removal of pollutants, composite materials that have both the properties of adsorption and photocatalysts will be required [22-27].
In this study, we explore the use of conventionally produced composite material made of calcined nano ZnO and BC for decolorization of an acid solution. We also consider the effects of different treatment conditions on the decolorization of the acid dye solution. BC improves the surface area of ZnO, which helps in increasing the degradation of organic pollutants and, thus, increases the filtration of sludge. In this study, we aim to determine the optimal amount of composite material and the most suitable method for realizing the most efficient and cost-effective water treatment process.

Experimental Methods

Reagents and materials
Everacid Red 3RS (C.I. Acid Red 266) was purchased from Everlight Chemical Industrial Co. (Taiwan). Nano ZnO with an average diameter of 60–80 nm was obtained from Ming Yuh Scientific Instruments Co., Ltd. (Taiwan). Activated BC (Particle size: 60 μm) was obtained from Versicolor Sky Science & Technologies Co., Ltd.
Instruments and analysis
The instruments used for analysis are a micro-analytical balance (Precisa XS 360M), magnetic stirrer with heater (Globallab glhpsgs/ 50), UV-visible spectrometer (JASCO V-550), and a UV lamp T5- 8W (8W and 60 Hz). X-ray diffraction (XRD) analysis was performed using a RigakuD/MAX 2500V XRD instrument under the following conditions: Cu-Kα radiation, voltage 40 kV, current 80 mA, scanning speed 4°/min, scanning range 20–70°. The composition of the hybrid materials were measured with an energy dispersive spectrometer (EDS) equipped with a field-emission scanning electron microscope (FE-SEM, Philips XL40). The surface area of the hybrid materials were measured using a BET instruments (Micrometrics ASAP 2010). The changes in the spin number of the composite material of BC and ZnO were observed through electron paramagnetic resonance (EPR) detection using a spectrophotometer (BRUKER EIEXSYS E-580) at a microwave frequency of 9.743 GHz, a center field strength of 3473.9 G, and a scanning width of 100.0 G. From the spectrophotometer observations, it was determined that C.I. Acid Red 266 showed the maximum absorption wavelength at 524 nm The color removal percentage was calculated by the following equation:
R % = [(Ao – A)/Ao] × 100 %
where Ao and A are the absorbance values of textile wastewater before and after treatment.
Experimental procedure
Because the discharge color was evident at the ppm level (mg/l), the concentration of the dye in the textile wastewater was set at 50 ppm by mixing 0.0025 g C.I. Acid Red 266 in 500 ml water. The composite material was prepared through high-temperature calcination using different proportions of precisely weighed BC and ZnO nanoparticles at 300°C. Materials CM1–CM5 refer to the five doses of BC, at 100, 200, 300, 400, and 500 ppm, respectively, which were mixed with the 50 ppm dye solution having a pH of 4. The absorbance was measured every 5 min. Materials ZCC1–ZCC5 refer to the composite materials having a constant nano ZnO:BC proportion (1:9) under UV illumination, but with different concentrations (100, 200, 300, 400, and 500 ppm, respectively), mixed with a 50 ppm dye solution and having a pH of 4. The absorbance of the samples were measured every 5 min. Materials ZCR1–ZCR5 refer to the composite materials having a constant concentration of 500 ppm under UV illumination, but with different proportions of nano ZnO and BC (1:9, 2:8, 3:7, 4:6, 5:5, respectively), mixed with a 50 ppm dye solution and having a pH of 4. In this case too, the absorbance of the samples were measured every 5 min. In the case of the 50 ppm dye solution mixed with the composite material having a constant proportion (ZnO:BC=1:9) and concentration of 500 ppm under UV illumination, the pH conditions were varied to 2, 4, 6, 8, and 10and the absorbance was measured every 5 min. A single reaction was carried out for 30 min to obtain an operational parameter, and the absorbance was measured every 5 min for this reaction as well. The temperature of the textile wastewater was maintained at 25°C during the experiment.

Results and discussion

Analysis of the composite properties
From the results of the XRD analysis, as shown in Figure 1, the diffraction peak is observed to be more distinct between 20° and 30° on the BC XRD spectrogram. The signals of the other diffraction peaks are not as distinct. Furthermore, it can be observed that ZnO in the composite has very strong diffraction peaks at (100), (002), (101), (102), (110), and (103), which are primary diffraction peaks. On comparing the overlays of the two diffraction diagrams, it can be observed that the diffraction peaks that do not occur in the original BC sample appear in the composite. Hence, it can be inferred that ZnO is sintered to the BC in the composite.
Figure 1: XRD diagram of material CM and hybrid materials ZnO/ZCR1.
The results of the EDS elemental analysis of the composite and the original BC sample are presented in Table 1. From these results, it can be observed that as the quantity of ZnO increases, the content of the elements Zn and O also increases. Table 1 shows the EDS analysis diagram of the ZnO/BC composite ZCR5. From the diagram, it can be observed that when the proportion of ZnO and BC in the composite is 5:5, the Zn content in the composite is higher than the C content to the extent that the Zn content is very high for BC to combine entirely with ZnO. This observation indicates that the BC holes in the composite may not be easily filled with more ZnO during the sintering process.
Table 1: EDS analysis of hybrid materials ZCR1-ZCR5.
The surface area analysis of the BET specific composite and the BC is listed in Table 2. The test results indicate that the specific surface area, pore volume, and aperture size of the composite are larger than those of BC. Hence, the adsorption rate of the composite is greater than that of BC.
Table 2: BET analysis of CM and ZC materials.
Figure 2 shows an electron paramagnetic resonance (EPR) spectrogram of the composite, from which the changes in the spin number of BC and the composite can be known. The fundamental method of producing free radicals from neutral molecules requires photolysis, pyrolysis, and an oxidation-reduction reaction. The BC spin is primarily due to the free radicals formed during the pyrolysis of raw materials, and the composite spin is primarily due to the nano ZnO under UV irradiation. The electrons (e-) on the valence band are stimulated to leap to the conduction band. Free radicals (∙OH) are formed by the reactions that occur between the electron holes (H+) left on the valence band and H2O in the air and by the reactions between the electrons and the O2 and H2O molecules adsorbed on the surface of BC. Therefore, the spin number of the composite clearly increases, and the combination of circumstances can be analyzed from the EPR spectroscopy.
Figure 2: EPR diagram of material CM and ZC: (a) CM and (b) ZC.
The adsorption efficiency of the composite sample ZCR1 and the pure BC sample CM can be determined from the EPR spectra. Figure 2a shows that the magnetic field strength of CM is between 3470 G and 3475 G, and Figure 2b shows that the magnetic field strength of ZC is between 3470 G and 3475 G. Comparing the strongest and weakest signals of the two spectra, we found that the signal response of ZC is nearly five times stronger than that of CM. Thus, it can be inferred that the spin number of the composite has significantly increased and that ZnO and BC in the composite are completely combined.
Figures 3a and 3b show the SEM images of CM and ZCR1, respectively. In both figures, a group of small white powder pellets can be observed attached to the BC surface. In Figures 3c, it can be observed that as the amount of BC increases in the composite sample, the white powder pellets on the BC surface also increases, until the pellets cover almost the entire BC surface for the ZnO: BC ratio of 5:5. Therefore, it is inferred that most of the adsorption ability in the composite is attributed to the BC. However, because the ZnO powder covers most of the holes of BC, the quantity of Zn increases and the ability of adsorption decreases.
Figure 3: SEM micrograph of material CM, ZCR1 and ZCR5: (a) CM, (b) ZCR1 and (c) ZCR5.
Influence of different pH values on dye decolorization
For the constant dye concentration of 50 ppm, the ZnO:BC proportion in composite ZCR1 is fixed at 1:9. The concentration of the composite is 500 ppm, and the dye pH values are varied to 2, 4, 6, 8, and 10 to observe the effect on decolorization of C.I. Acid Red 266. Figure 4 shows that the decolorization effect on the solution is optimum when the pH is 2. However, because the cost of C.I. Acid Red 266 at pH of 2 is very high in those of preparation process, an adjustment liquid is required to be added, which is not a cost-effective approach. However, the wastewater discharged by some dye factories has a weaker acidity. Therefore, a dye solution with pH 4 is chosen to serve as the optimal condition for further experiments in treating dye wastewater. The selection of a pH of 4 as the optimal condition is advisable because the difference in decolorization rates between the pH levels of 2 and 4 is not significant, as shown in Figure 4. Therefore, the decolorization rate is found to be better when the composite ZCR1 enters a solution with a pH of 2 or 4 than when it is put into a solution with a pH of 8 or 10.
Figure 4: Effect of pH value on color removal.
Influence of bamboo charcoal sample of different concentrations on dye decolorization
The dye solution has a fixed concentration of 50 ppm and a pH of 4. Composite samples with different BC concentrations are used for the decolorization of C.I. Acid Red 266. BC concentrations of CM1–CM5 can be observed from Figure 5. 30 min after the reaction is complete, the decolorization rate of CM1 and CM5 reaches 31% and 72%, respectively. These values confirm that adsorption strength increases as the BC concentration increases. However, the dye solution after treatment still has light coloration. A sample with a very high BC concentration is relatively expensive. Therefore, this study combines ZnO with BC, with the logic that the ZnO photocatalytic effect can facilitate an increase in the decolorization effect of BC. It is anticipated that this will increase the ability of BC in treating dye wastewater, while maintaining cost effectiveness.
Figure 5: Effects of bamboo charcoal concentration CM1-CM5 on color removal.
Influence of composite sample with varying proportions of ZnO and BC on dye decolorization
The dye solution has a fixed concentration of 50 ppm and a pH of 4. The composite concentration is fixed at 500 ppm. Composites ZCR1 to ZCR5 are made to react with the dye solution for 30 min. The decolorization effect is shown in Figure 6. After a 30 min reaction time, the decolorization rates for composites ZCR1 and ZCR5 reach 96 % and 87 %, respectively. Under the same conditions, as the quantity of BC in the composite decreases while that of ZnO increases; the decolorization rate decreases. Therefore, it is inferred that after the quantity of ZnO increases to a certain limit, the quantity of ZnO that the BC can load decreases. This may be attributed to the fact that the decolorization effect of ZnO on acidic dyes is not evident. The optimal proportion of ZnO and BC in the composite is experimentally found to be 1:9.
Figure 6: Effects of various proportion hybrid materials ZCR1-ZCR5 on color removal.
Comparison between dye decolorization rates of bamboo charcoal and composites of different concentrations
The dye solution has a fixed concentration of 50 ppm and a pH of 4. The decolorization effects of BC samples with different concentrations (CM1–CM5) and those of composite samples with different concentrations (ZCC1–ZCC5) on C.I. Acid Red 266 are observed. Figure 7 shows that as the concentrations of the BC samples increase from CM1 to CM5 and those of the composite samples increase from ZCC1 to ZCC5, the decolorization effect also increases. From the Figure 7, it can be observed that the decolorization effect of the composite samples is superior to that of the pure BC samples. The decolorization rate of CM1 after treatment only reaches 31%, whereas that of composite ZCC1 can reach 52%. The difference in the decolorization abilities of these two samples is significant. ZCC3 can achieve a decolorization rate of up to 70%. However, the decolorization rate of ZCC5 can be as high as 96%, while that of CM5 (i.e., the BC sample at the same concentration of 500 ppm) can reach 52%. These values indicate that when the concentration increases, the decolorization ability improves; therefore, the composite samples have greater decolorization ability than pure BC samples. Hence, composites can be employed to improve the effect of BC on dye wastewater treatment as well as the cost-effectiveness of the treatment process.
Figure 7: Effects of various concentration hybrid materials ZCC1-ZCC5 on color removal.
Comparison between decolorization rates of BC CM5 and composite ZCC5 at different treatment times
For a dye with a fixed concentration of 50 ppm and a pH of 4 and a composite sample with a fixed concentration of 500 ppm (ZCC5) and a ZnO:BC proportion of 1:9, the reaction times are varied to observe the change in the adsorption of dye wastewater by the composite; the changes in the reaction time are found to affect the adsorption rate. Figure 8 shows that at a reaction time of 30 min, the adsorption rate approaches 100% and the decolorization rate can reach 96%. In comparison, the effect of the reaction time on the dye absorption rate significantly differs in the case of the pure BC sample. On comparing the decolorization effects of CM5 and composite ZCC5 on the dye for a reaction time of 30 min, it is found that the decolorization rate of CM5 only reaches 71% whereas that of ZCC5 reaches 96%, a difference of approximately 25%. This explains the reason for the decolorization ability of the pure BC not being significant at the beginning of the reaction but increasing with the reaction time and for the decolorization ability of the composite to be strong at the beginning of the reaction; ZnO in the composite induces a photocatalytic reaction with the dye, adding to the effect attained by the decolorization ability of BC.
Figure 8: Effects of time for material CM5 and ZCC5 on color removal.

Conclusion

When composites of ZnO and bamboo charcoal (BC) that are sintered together are used to perform decolorization treatment on the acidic dye C.I. Acid Red 266, changes in the composite concentration, proportion of ZnO and BC, and reaction time influence the decolorization. The experimental results show that for a reaction time of 30 min, BC at a concentration of 500 ppm and a pH of 4 has a decolorization rate of only 72% on acidic dye solution. Under the same conditions, the composite can reach a decolorization rate of 96%. The decolorization effect can reach 96% when the composite treats acidic dye solutions with a pH of 4. Optimal decolorization effect was attained for composites with a ZnO:BC proportion of 1:9. The specific surface area, pore volume, and aperture size of the composite are all greater than those of pure BC. Hence, the decolorization rate of the composite is optimal. that the decolorization rate of the composite is always better than that of the pure BC When the composite concentration is 300 ppm, the decolorization effect can reach 70%, and when the composite concentration reaches 500 ppm, the decolorization effect can reach 96%.

Acknowledgments

The authors would like to thank the National Science Council of the Republic of China, Taiwan, for financially supporting this research under Grant NSC 99- 2622-E-168- 001-CC3.

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