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Science & Technology Development Journal, 23(2):555-563 Research Article Open Access Full Text Article Removal of methyl orange by heterogeneous fenton process using iron dispersed on alumina pillared bentonite pellet Ngo Thi Thuan1,* , Tran Tien Khoi1 , Nguyen Thi My Chi2 , Nguyen Ngoc Vinh1 ABSTRACT Use your smartphone to scan this QR code and download this article 1 Department of Environmental Engineering, International University, Vietnam National University Quarter 6, Linh Trung Ward, Thu Duc District, Ho Chi Minh City, Viet Nam Introduction: Heterogeneous Fenton is one of the Advanced Oxidation Processes (AOPs) and has been proven to be effective on azo dye degradation. However, a low-cost catalyst and factors affecting the processes of this system were further investigated. Methods: In this study, pellets of iron alumina pillared bentonite (PFeAPB) were prepared by dispersing iron ions on alumina pillared bentonite pellet. Catalyst activity and lifetime were investigated via efficiencies of Methyl Orange (MO) decolorization and Chemical Oxygen Demand (COD) removal, a typical dye type of textile wastewater. Characteristics of the PFeAPB catalyst were examined by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, and X-ray fluorescence (XRF). Results: Results of batch experiments showed that specific surface area of the PFeAPB catalyst was 111.22 m2 /g higher than its precursor by 2 times (57.79 m2 /g). Goethite, Hematite and Maghemite phases with approximately 11.5% of iron elements containing in the catalyst were detected via XRD and XRF. Experimental conditions of pH, initial MO solution, Hydrogen Peroxide concentration, reaction time and catalyst loading were 2.0 ± 0.1, 12.7 mmol/L, 150 min and 20 g/L, respectively, to achieve 88.68 ± 5.69% of MO decolorization and 50.27 ± 6.05% of COD removal while dissolved iron in this heterogeneous Fenton process was below standard limit (2 ppm). Catalyst activity decreased by 5.22% in decolorization efficiency after the two first reusages. Conclusion: These primary results showed the potential of applying PFeAPB catalyst in heterogeneous Fenton process with low iron leaching into water. Key words: Heterogeneous Fenton Catalyst, Alumina Pillared Bentonite, Pellet, Methyl Orange, Textile Wastewater 2 Faculty of Environment, University of Science, Vietnam National University 227, Nguyen Van Cu Street, 4th Ward, District 5, Ho Chi Minh City, Viet Nam Correspondence Ngo Thi Thuan, Department of Environmental Engineering, International University, Vietnam National University Quarter 6, Linh Trung Ward, Thu Duc District, Ho Chi Minh City, Viet Nam Email: ntthuan@hcmiu.edu.vn History • Received: 2020-04-16 • Accepted: 2020-06-12 • Published: 2020-06-30 DOI : 10.32508/stdj.v23i2.2139 Copyright © VNU-HCM Press. This is an openaccess article distributed under the terms of the Creative Commons Attribution 4.0 International license. INTRODUCTION Textile is a main export industry in Vietnam and its wastewater has been listed as difficult-to-degrade wastewater. Among several physical, chemical and biological processes, adsorption has been proven as a widely used, effective method to decolorize dye in textile effluent. However, pollutants in dye wastewater are adsor ed on the adsorbent and concentrated into a smaller volume but not degraded. Advanced Oxidation Processes (AOPs) have been proven worldwide as efficient methods in dye wastewater treatment due to high oxidation of active radicals and mineralization capability to persistent organic pollutants (such as azo dyes into CO2 and H2 O). Thus, homogeneous Fenton processes are commonly applied to treat textile wastewater. However, these processes still have some disadvantages of iron treatment, sludge, and strict operation under acidic condition. Heterogeneous Fenton processes have been introduced to overcome disadvantages of homogeneous Fenton processes. These processes apply iron catalysts which are immobilized on the surface of the adsor- bent and combined with hydrogen peroxide (H2 O2 ) to generate hydroxyl radicals (·OH) 1,2 , thus possibly minimizing iron leaching into water and operating under less acidic condition, enabling the catalyst to be reused and recycled. Bentonite clay has been used as an adsorbent and has gained much attention in environmental remediation due to iron content in clay, its low cost, its abundance, and ion-exchange capability, while still having low specific surface area 3,4 . Specific surface area of bentonite clay can be increased by intercalating inorganic/organic cations into expandable clay layers (so-called cation pillared bentonite). They are fabricated by cation exchange with polyoxycations of silica-alumina layers, then calcinated 5,6 . Among several cations to be pillared into clay, polycations of aluminum are preferred due to the well-known structure, synthesis conditions and stabilities 7 . In addition, alumina pillared clays give much higher surface Lewis acidity than their precursor 6,8 . Hence, alumina pillared bentonite may be used as a good supporter to be impregnated with irons which are active sites of heterogenous Fenton catalysts. Cite this article : Thuan N T, Khoi T T, Chi N T M, Vinh N N. Removal of methyl orange by heterogeneous fenton process using iron dispersed on alumina pillared bentonite pellet. Sci. Tech. Dev. J.; 23(2):555-563. 555 Science & Technology Development Journal, 23(2):555-563 So far there are very few investigations of iron dispersed on alumina pillared bentonite used as heterogeneous Fenton catalyst for environmental remediation. Some studies focus on iron pillared bentonite as Fenton catalysts for degradation of cinnamic acid 9 , or dyestuff with UV light assistance 10 . However, researchers focus on powder type which cannot be used in a continuous system due to system clogging iron leaching into water of this catalyst as well as dye removal have not been investigated. Iron phases of this Fenton catalyst can leach into water possibly due to a poor supporter, especially in relatively acidic conditions. Therefore, a heterogeneous Fenton catalyst based on alumina pillared bentonite pellet was examined. The objective of this study was to investigate the reactivity of the PFeAPB catalyst during heterogeneous Fenton process for Methyl Orange (MO) removal from water. Experimental procedure The Fenton reactor was a 250 mL beaker filled with 100 mL of MO solution and placed in a magnetic stirring machine. The initial pH, H2 O2 concentration, MO concentration and catalyst loading were as follows: 3.0±0.1, 12.7 mmol/L, 100 ppm and 20 g/L, respectively; the reaction mixture was constantly stirred at 200 rpm for 120 min. Samples of the reaction mixture were taken with syringe at selected time intervals and then increased to pH~10 with NaOH 2N, and finally filtered through a 0.45 mm membrane for analysis. Each experiment was repeated 3 times. The mean value and standard deviation (± SD) of three replicated results in each experiment were calculated and presented. The used PFeAPB catalyst was washed with distilled water and dried at 105o C in an oven for 5 h. These regenerated pellets were used to investigate catalyst reusability and stability. MATERIALS-METHODS Materials A commercial clay product, bentonite powder, was purchased from a local company in Vietnam (Minh Ha Bentonite Mineral Joint Stock Company, Phan Thiet Province, Viet Nam); iron catalyst was prepared from ferric nitrate nonahydrate (Fe(NO3 )3 .9H2O; alumina pillared in clay was prepared from aluminum nitrate nonahydrate (Al(NO3 )3 .9H2 O); sodium hydroxide was purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA), hydrogen peroxide (>30 wt.%) and hydrochloric acid (37%) were purchased from Fisher Scientific (UK). Catalyst preparation Inorganic pillaring technique has been reported previously 5,6,11,12 and was adapted as follows: the bentonite powder was sieved with 2 mm to remove all big contaminants, then added into Al3+ solution to become alum-bentonite slurry. The slurry was stirred vigorously in 1 hour and left to age for 24 hours under ambient conditions. The alum-bentonite after aging was centrifuged and compacted into pellet shape (3 mm of diameter, 2-3 cm of length). This pellet was dried at 105o C for 12 hours and calcinated at 600o C to form the so-called pellet of alumina pillared bentonite (PAPB). Fe(NO3 )3 .9H2 O 1M with 10% of HNO3 solution was impregnated on the surface of PAPB for 4 hours and dried at 105o C for 15 hours, and finally baked at 350o C for 4 hours. The final product after iron impregnation was referred to as the pellet of iron alumina pillared bentonite (PFeAPB) (Figure 1). 556 Analytical methods The UV-VIS spectra of MO were recorded from 200 to 700 nm using a UV-VIS spectrophotometer with a spectrophotometric quartz cell and its concentration was measured at the maximum wavelength. Chemical Oxygen Demand (COD) and total ferrous ions were determined by bichromate and 1,10-phenanthroline methods, respectively, according to the Standard Methods for the examination of water and wastewater 13 . Degradation of MO was investigated via MO decolorization (MO removal) and COD removal efficiency: [ ] C0 −Ct MO(%) = × 100 C0 Where Co (ppm) is the MO initial concentration and initial COD, and Ct (ppm) is the MO concentration and COD at time of withdrawal. The catalysts were characterized by X-ray diffraction spectroscopy (XRD), X-ray fluorescence (XRF) and nitrogen adsorption/desorption isotherm by Brunauer–Emmett–Teller (BET) surface area. RESULTS Active phases of Fenton catalysts were examined with XRD and XFR analysis. Figure 2 shows X-ray diffraction spectra of 5% iron dispersed on the alumina pillared bentonite catalyst; there were Goethite (α FeOOH), Hematite (α -Fe2 O3 ) and Maghemite (γ Fe3 O4 ) found in the PFeAPB catalyst. Element compositions of the catalyst and its precursor were obtained by XRF analysis and are shown in Table 1. Notably, Si, Al, Fe, Ca and Mn were five elements found Science & Technology Development Journal, 23(2):555-563 Figure 1: Configuration of (a) PAPB and (b) PFeAPB catalysts. in both PFeAPB catalyst and its precursor in the range of 0.09 to 51.0%. Si, Al and Fe contents in the PFeAPB catalyst accounted for 49.1%, 21.1% and 11.5% of the total content, while their presence in its catalyst precursor accounted for 51.0%, 12.2% and 6.95%, respectively. Performance of PFeAPB catalyst in the heterogeneous Fenton system was evaluated by comparing removal efficiencies among H2 O2 , PAPB, PAPB + H2 O2 , and PFeAPB + H2 O2 systems with time; the data are presented in Figure 3. The results showed that increasing time from 15 to 180 minutes led to enhanced decolorization efficiency of MO from 2.09±0.66% to 75.23±5.35%, respectively, and in a sequence of H2 O2

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