8th Micropol & Ecohazard
IWA-11772: Optimization Removal of Sulfonated Diazo Dye from Water by Nanotitania Based Ceramic 1,
1
1
Masoud. Rastegar *, Kamran. Rahmati Shadbad , Reza. Pourrajab and AliReza. Khataee 1 2
2
Water and Wastewater Company of East Azerbaijan, Tabriz, Iran, Department of Applied Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran,
*corresponding author’s email address:
[email protected]
Abstract. photocatalytic mineralization of C.I. Reactive Green 19 (RG19) under UV light irradiation using ceramic coated TiO2 nanoparticles was studied and optimized. The investigated TiO2 was Millennium PC–500 (crystallites mean size 8 nm) immobilized on ceramic plates. Optimization results that were achieved from Central composite design (CCD) showed that maximum decolorization efficiency was predicted at the optimum conditions: initial dye concentration 10 mg/L, UV light intensity 47.2 W/m2, flow rate 150 mL/min and reaction time 240 min. Photocatalytic mineralization of RG19 was monitored by chemical oxygen demand (COD) decrease and changes in UV–Vis spectrum. Introduction. Heterogeneous photocatalysis for water-treatment technologies has attracted the attention of many research groups around the world. The fixation of TiO 2 nanoparticles on the different substrates led to decreasing of difficulties due to separation of photocatalyst and treated phases. Therefore, the key to the problem of industrializing the technology seems to be immobilization of TiO2 nano-particles, as the most successful photocatalyst reported [1– 3]. But, deposition of photocatalyst nanostructure on the different surfaces redounded to reduction of photocatlysis efficiency in organic dye pollutant. Therefore, we needed to the support materials with high surface areas have been applied to immobilize photocatalysts. In this work, ceramic plates were used as a support of TiO 2 nanoparticles. Methods. The investigated photocatalyst was Millennium TiO2 PC–500 (anatase>99%, crystallites mean size 8 nm) immobilized on ceramic plates. These characteristics were proved by our XRD and SEM analyses. The dye, C.I. Reactive Green 19, was obtained from Alvan Sabet Company, Iran. Its chemical structure and characteristics are given in Table 1. Methanol, methyltrimethoxysilane (MTMOS) and HCl were obtained from Merck Co., Germany. Table 1. Structure and characteristics of RG19. Colour index name
C.I. Reactive Green 19 (RG19)
Chemical structure
Molecular formula
C40H23Cl2N15O19S6.6Na
CAS no.
68110-31-6
λmax (nm)
630
TiO2 nanoparticles were fixed on ceramic plates by sol-gel dip-coating method. The experimental set-up is based on a continuous circulation rectangular photocatalytic reactor, with a workable of area 15 cm × 90 cm, made out of stainless steel. 2000 mL solutions of RG19 were degraded in all cases. Artificial irradiation was provided by three 30 W UV–C lamps (Philips, The Netherlands) with peak intensity at 254 nm, positioned above the reactor. The lamps were turned on at the beginning of each experiment. The distance between the solution and the UV source was adjusted according to the experimental conditions. On the surface of the solution, the radiation intensity was measured by a UV radiometer purchased from Cassy Lab Company, Germany. At different reaction times obtained with experimental design, 2 mL sample were taken and the remaining RG19 was determined using a spectrophotometer at λmax= 630 nm and calibration curve. The photocatalytic reactions were monitored by UV–Vis spectrophotometer (WPA lightwave S2000, England). Scanning electron microscopy (SEM) was carried out on a Hitachi SEM (Model S–4160, USA) device after gold–plating of the samples. Results and discussion. Figure 1 shows the scanning electron microscopy (SEM) images of the ceramic plate before and after immobilization of TiO2 nanoparticles on it. As shown in Figure 1, the entire surface of the ceramic plate was been coated with TiO2 nanoparticles.
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Figure 1. Scanning electron microscopy images of TiO2 nanoparticles (a) before and (b) after deposition on ceramic plates.
In the present study central composite design was employed for optimization of photocatalytic decolorization process. In order to evaluate the influence of operating parameters on the photocatalytic decolorization efficiency of RG19, four main factors were chosen: initial dye concentration (mg/L), UV light intensity (W/m2), flow rate (mL/min) and reaction time (min). A total of 31 experiments were employed in this work, including 24=16 cube points, 7 replications at the center point and 8 axial points. Experimental data were analysed using Minitab 15 software and the optimum values of the process variables for the maximum decolorization efficiency were 10 mg/L, 47.2 W/m2, 150 mL/min and 240 min for initial dye concentration, UV light intensity, flow rate and reaction time, respectively. Photocatalytic mineralization of the dye in UV/TiO2 process studied with 20 mg/L of RG19 solution at the achieved optimum conditions. Mineralization was monitored by COD and changes in UV−Vis spectrum. COD is the measurement of the amount of oxygen in water consumed for chemical oxidation total concentration of organics in the solution and the decrease of COD reflects the degree of mineralization at the end of the photocatalytic process. COD disappearance of RG19 has been depicted in Figure 2. The results indicated that more than 92% COD removal was achieved under optimized conditions at the irradiation time of 9 h. It implies that the strategy to optimize the decolorization conditions and to obtain the maximal degradation efficiency by RSM for photocatalytic decolorization of RG19 in this study is successful. The changes in the UV–Vis spectra of RG19 during the photocatalytic process at different irradiation times are shown in Figure 3. The dye carries two azo groups as the chromophoric moiety and two chlorotriazine groups as reactive groups in different sites on the molecule. The colour of RG19 is the result of chromospheres such as azo functional group and the two substituted aromatic species. The decrease of the absorption peak of the dye at the maximum absorption wavelength (630 nm) in Figure 3 indicates photocatalytic destruction of RG19. The decrease is also meaningful with respect to the nitrogen-to-nitrogen double bond (–N=N–) in RG19, as the most active site for oxidative attack. Decrease in absorption intensity of the band at λmax during the irradiation also expresses the loss of conjugation, especially the cleavage near the azo bond of the organic molecule. 0.8
450 0.7
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Absorbance
COD (mg/L)
400
250 200 150 100
0.4 0h
0.3 0.2
50 0.1
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180
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540
Time (min)
Figure 2. COD changes during photocatalytic degradation of RG19 at the optimized conditions.
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Wavelength (nm)
Figure 3. The changes in the absorption spectra of RG19 during the photocatalytic process at different irradiation times under the optimized conditions.
References [1] N. R. C. F. Machado, V. S. Santana, Catal. Today 107 (2005) 595. [2] X. Hong, Z. Wang, W. Cai, F. Lu, J. Zhang, Y. Yang, N. Ma, Y. Liu, Chem. Mater. 17 (2005) 1548. [3] H. Liu, L. Gao, J. Am. Ceram. Soc. 87 (2004) 1582.
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