Improved Photo Degradation of Rhodamine B Dye using Iron Oxide/Carbon Nanocomposite by Photo-Fenton Reaction

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1 Carbon Letters Vol. 9, No. September 2008 pp Improved Photo Degradation of Rhodamine B Dye using Iron Oxide/Carbon Nanocomposite by Photo-Fenton Reaction Min Il Kim 1, Ji Sun Im 1, Se-Jin In 2, Hyuk Kim, Jong-Gyu Kim and Young-Seak Lee 1, 1 Dept. of Fine Chemical Engineering and Applied Chemistry, BK21-E 2 M, Chungnam National University, Daejeon 05-76, Korea 2 Dept. of Fire and Disaster Protection Engineering, Woosong University, Daejeon , Korea Hanil Green Tech Co., LTD, Chungnam, Korea youngslee@cnu.ac.kr (Received August 12, 2008; Accepted September 17, 2008) Abstract A nanocomposite consisting of Fe and MWCNT was produced via sol-gel technique using FeCl along with MWCNT by calcination at 00 o C. The degradation effect of rhodamine B dye has been investigated under UV illumination in a darkroom. The degradation reaction was studied by monitoring the discoloration of dye as a function of irradiation time using UV-visible spectrophotometeric technique. The Fe -MWCNT samples have continuous degradation ability under the UV illumination with the first order kinetics and the dye removal was better than in the pristine Fe. The resultant composite catalyst was found to be efficient for the photo-fenton reaction of the dye. Keywords : Iron oxide, Nano composite, Photo-Fenton reaction, Dye removal 1. Introduction Since azo dye compounds have versatile applications in various fields, they have been the most widely used class of organic dyes (such as textile and fibers, pulp and paper, dyeing, paint, laser, liquid crystalline displays, and ink-jet printer, etc). These dyes are commonly utilized as water pollutant and they may be frequently found in trace quantities in industrial wastewater. Azo dye compounds were difficult to degrade due to their complex aromatic structure and thus tend to persist in the environment, creating serious water quality and public health problems [1,2]. Therefore, it would be necessary to develop technologies to eliminate them. Advanced oxidation processes (AOPs) have been developed for the destruction of certain pollutants in water due to its high efficiency, using heterogeneous photocatalytic oxidation [-5]. Among these AOPs, Photo- Fenton reaction was one of the promising photocatalytic reactions because of low cost and excellent performance [6, 7]. The photo-fenton process, which was combined Fenton process (Fe 2+ / ) and light energy [8-10], consists of two reactions. The first reaction was a reaction of Fe 2+ with, which generates hydroxide radicals and oxidizes Fe 2+ to Fe +, as seen in equation (1). The hydroxide radicals having strong oxidation ability can completely degrade organic pollutants to C and O. Fe 2+ + Fe + + OH+OH (1) The second reaction of photo-fenton reaction was a reaction of Fe + with water under the irradiation of light having the wavelength in the range of 00 to 650 nm [11]. In this reaction, OH radicals were generated and Fe + is reduced to Fe 2+. Fe + + O+hv Fe 2+ + OH+H + (2) These two oxidation-reduction reactions in the photo- Fenton process occur repeatedly and produce the OH radicals attacking azo dye compounds. Multi-walled carbon nanotubes (MWCNT) have many promising applications due to their inherent high surface-tovolume ratio and unique structures [12,1]. Especially MWCNT can be an ideal support in composites, because they were chemically inert even at low temperature. Carbon nanocomposite materials have interesting applications in many fields due to their unique properties compared to bulk material and had been a subject of numerous studies [1-16]. The hybridized Fe -MWCNT nanomaterial will combine the photocatalytic activity of Fe with the high adsorptivity of MWCNT. In the present work, the degradation of rhodamine B dye in aqueous solution was investigated using a catalyst consisting Fe -MWCNT prepared by a sol-gel method from FeCl as a precursor with MWCNT. The characteristics of the nanocomposite and the photocatalytic activities under different conditions have been studied.

2 196 Min Il Kim et al. / Carbon Letters Vol. 9, No. (2008) Fig. 1. Chemical structure of dye rhodamine B. 2. Experimental 2.1. Materials All chemical reagents used in this study are of analytical grade. The MWCNT used in this work was purchased from NanoKarbon Co., Korea (hollow MWCNT, 75p). The hollow MWCNT powder used was 60 ~ 80 nm in outer diameter with the surface area of 60.5 m 2 /g. Rhodaime B dye was purchased from Acros Organics Co. and the chemical structure was presented in Fig. 1. Iron chloride (FeCl ) was purchased from SIGMA Preparation of iron oxide-mwcnt composite catalyst samples by sol-gel method The MWCNTs of 0.1 g were dispersed in solution containing 0.5 ~ g of FeCl in separate beakers as presented in Table 1. The solution of ph 1.2 ~ 1.7 was adjusted to ph 9 by adding NaOH solution (8 N) and finally mixed at h. After adjusting the ph of solution, the product was filtered and washed with distilled water. The product was placed in a furnace elevated to 00 o C with 60 o C/h and hold for 8 h in air. The temperature was ramped back down to room temperature. The sample was placed in a clean container and used for further studies. 2.. Characterization of samples Scanning electron microscope (SEM, JSM-600, JEOL Ltd, Japan) was used to investigate the morphology of the samples with a working distance of 16 mm under the specified conditions of 20 kev. Elemental analysis was carried out using Energy Dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) technique. The XRD patterns of samples were recorded in a RIGAKU (D/MAX- Fig. 2. XRD patterns of Fe /MWCNT composite Ultima/PC) diffractometer with Cu Kα radiation and were analyzed from 5 o to 80 o (2θ) with the step size of 0.02 o and the step time of s to assess the crystallinity of the catalysts. 2.. Photocatalytic degradation studies The rhodamine B dye solution (10 mg/l) was prepared by diluting it to 1000 mg/l. In order to prepare 200 ml solution of 10 mg/l of rhodamine B in a glass beaker, the solid catalyst of 0.5 g was added. The samples in the dye solution were illuminated for 2 h at 65 nm using a W UV lamp (SPECTROLINE SPECTRONICS Co., USA). At regular intervals of time, the small portion of the examined solution was filtered with a nylon syringe filter (0.5 µm) to remove the suspended particles. The absorbance of the clear solutions was measured using a spectrophotometer (Mecasys, Optizen 2120 UV) at 55 nm to find out the degradation efficiency.. Results and discussion.1. Elemental analysis Fig. 2 showed the XRD patterns of pristine Fe and the composite C-Fe1. The original carbon peak was observed at 002 due to the MWCNT. It could be seen that the crystalline Fe was formed from the Fe(OH) upon heating at 00 o C. The result of elemental analysis obtained from the EDX was also summarized in Table 1. The result demonstrated the Table 1. Composite Samples Preparation Details and EDX Results No. Sample Code Details EDX (%) FeCl CNT C O Fe Total 1 C - Fe1 0.5 g 0.1 g C - Fe2 1 g 0.1 g C - Fe 2 g 0.1 g C - Fe g 0.1 g

3 197 Improved Photo Degradation of Rhodamine B Dye using Iron Oxide/Carbon Nanocomposite by Photo-Fenton Reaction Removal of rhodamine B in darkroom with the composite catalyst. Fig.. SEM images of samples; (a): C-Fe1, (b): C-Fe2, (c): CFe (d): C-Fe and (e): MWCNT. Fig.. influence of the mixing ratio. As expected, the Fe O content was increased with increasing the amount of precursor while the carbon content was decreased from 7 to 7% in the composites..2. Morphology of samples The SEM images of the samples prepared with the pristine Fe O and the MWCNT were shown in Fig.. Through the SEM observations, homogeneous distribution of Fe O to the MWCNT was found in the composite samples. As the Fe O content increased, the MWCNT were not seen due to the aggregate of Fe O particles. It was believed that the observed morphology was desirable for a photocatalytic application of the sample. Removal of rhodamine B by photodegradation with different catalyst. Fig. 5. illumination. When UV illumination was turned on to the reactor, photo-degradation of dye was occurred by Fe O, whereas in a darkroom the adsorption of dye was mainly occurred by the MWCNT. Fig. depicted the result of dye removal in the Fe O MWCNT composite, which was made at different mixing ratios of FeCl and MWCNT without UV illumination. It was clear from the figure that the adsorption amount of dye was increased with decreasing the FeCl mixing ratio in the composite. This may be due to the increase of Fe O coverage on the surfaces of MWCNT with the increase of FeCl content in the composite. During initial 20 minutes, rhodamine B dye was rapidly removed in all the cases due to a synergetic effect of the solid nano-hybrid. However, after 20 minutes the adsorption was not continued due to an adsorption capacity limit. The efficiency of rhodamine B dye removal using Fe O MWCNT composites was examined with and without UV.. Photocatalytic degradation studies

4 198 Min Il Kim et al. / Carbon Letters Vol. 9, No. (2008) effect studies In highly toxic wastewater where the degradation of organic pollutants was a major concern, the addition of electron acceptors to enhance the degradation rate may often be justified. With this viewpoint, the effect of electron acceptors using the on the degradation of dye rhodamine B was studied. It has been observed that the amount of to the rhodamine B dye solution very slightly improves the degradation efficiency only due to the formation of hydroxide radicals [17,18]. OH + O+H () + hv 2OH (if λ < 00 nm) () Fig. 6. amount effect under UV illumination with C-Fe1 in p. It should be noted that the reaction without passing air also conducted in open condition. With increasing the addition of, the rate of degradation was improved showing a catalytic effect of. But in the case of adding of 5 ml, there was no significant change comparing with the case adding of ml. It seemed that of about ml for the catalytic effect was needed. The efficiency of degradation was improved up to about 0% by the catalytic effect of..5. ph effect studies In order to investigate the effect of ph, the photodegradation was carried out in various conditions with acid and basic solutions. Fig. 7 showed the effect of ph. In the basic condition, the significant effect was not observed. But in the acid condition, the rate of degradation was increased. The result agreed with the work reported earlier [19]. Fig. 7. Effect of ph under UV illumination with C-Fe1 for dye removal. Fig. 5 showed the result of rhodamine B dye degradation values (subtracted from the adsorption value) under UV light. Initially the concentration of dye was decreased rapidly because of the adsorption of dye by the MWCNT. So, the C- Fe1 sample with much higher MWCNT contents showed the better removal ability than the C-Fe sample reacted for 10 min. The photo-degradation ability of sample improved with increasing a dosing amount of FeCl. It was clear from the result that the prepared nanocomposite catalyst possessed good photocatalytic activity, though there was reasonable adsorption of dye in the Fe -MWCNT composite in the dark environment due to MWCNT. This leads to the increased degradation of dye on prolonged exposure to UV light and to the completely disappeared color of the sample. Conclusions The surface modification of MWCNT with a photocatalyst Fe may be useful in order to treat colored dye efficiently, as found in the present study. The rhodamine B dye was rapidly removed in about 10 minutes by the adsorption of MWCNT in the composite. The adsorption of dye was decreased with increasing the amount of Fe. The color in the UV exposed samples was more efficiently removed than the sample in the darkroom. The Fe -MWCNT samples have continuous degradation ability under the UV illumination with the first order kinetics and the dye removal was better than in the pristine Fe. The positive effect of adding and the acid condition was also observed for the improved degradation. References [1] G unseli, T.; Mustafa, O. Dyes Pigments 2006, 70, 117.

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