Synthesis and application of mixed manganese-iron oxide nanoparticles for adsorption of As(V) from aqueous solutions

KỶ YẾU HỘI NGHỊ KHOA HỌC THƯỜNG NIÊN TRƯỜNG ĐẠI HỌC ĐÀ LẠT NĂM 2018 53 SYNTHESIS AND APPLICATION OF MIXED MANGANESE-IRON OXIDE NANOPARTICLES FOR ADSORPTION OF As(V) FROM AQUEOUS SOLUTIONS Synthesis of adsorbent and its adsorption Le Ngoc Chunga*, Le Thanh Quoca aThe Faculty of Chemistry, Dalat University, Lamdong, Vietnam Correspoding author: Email: chungln@dlu.edu.vn Abstract A simple method has been used to synthesize nanoparticles of mixed manganese-iron oxide for the adsorption of As(V) metal ions from aqueous solutions. Transmission Electron Microscopy (TEM), X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), BET analysis were used to determine particle size and characterization of produced nanoparticles. The x-ray diffraction pattern indicated that the as-synthesized adsorbent is amorphous with 288.268 m2/g surface area; the amorphous synthesized products were aggregated with many nanosized particles. The crystallinity of the Mn2O3/Fe2O3 were obtained at 400°C and 600°C calcination temperature. The FTIR spectra confirmed the presence of -OH group and H-O-H group localized at 3200 - 3400 cm–1 and 1618-1653 cm−1; theses intense bands is weak (fade) at the high calcination temperature of the mixed manganese-iron oxide nanoparticles. In addition, when the calcination temperature of the mixed manganese-iron oxide nanoparticles was 400OC, the weak absorption bands at 630 cm−1 due to the vibrations of (Fe-O). The results showed that the mixed manganese-iron oxide nanoparticles has high selectivity for As(V). Keywords: Mixed manganese-iron oxide nanoparticles; Amorphous; As(V). KỶ YẾU HỘI NGHỊ KHOA HỌC THƯỜNG NIÊN TRƯỜNG ĐẠI HỌC ĐÀ LẠT NĂM 2018 54 TỔNG HỢP VÀ ỨNG DỤNG HỖN HỢP NANO OXID MANGAN- SẮT ĐỂ HẤP PHỤ As(V) TỪ DUNG DỊCH NƯỚC Tổng hợp chất hấp phụ và tính chất hấp phụ Lê Ngọc Chunga*, Lê Thành Quốca aKhoa Hóa học, Trường Đại học Đà Lạt, Lâm Đồng, Việt Nam *Tác giả liên hệ: Email: chungln@dlu.edu.vn Tóm tắt Một phương pháp đơn giản cho sự tổng hợp chất hấp phụ hỗn hợp nano oxid mangan-sắt để hấp phụ ion kim loại As(V) từ dung dịch nước. Phương pháp kính hiển vi điện tử truyền qua (TEM), nhiễu xạ tia X (XRD), kính hiển vi điện tử quét (SEM), phổ hồng ngoại (FTIR), phân tích BET được sử dụng để xác định kích thước hạt và đặc trưng của hỗn hợp nano oxid mangan-sắt. Nhiễu xạ tia X cho thấy chất hấp phụ tổng hợp là hỗn hợp nano oxid mangan- sắt có cấu trúc vô định định hình có diện tích bề mặt 288.268 m2/g và bị hiện tượng aggregation. Khi nung hỗn hợp nano oxid mangan-sắt ở nhiệt độ 400OC và 600OC sẽ xuất hiện cấu trúc của tinh thể Mn2O3/Fe2O3. Phổ hồng ngoại FTIR cũng xác nhận hỗn hợp nano oxid mangan-sắt được tổng hợp có sự hiện diện của nhóm –OH và nhóm H-O-H tại dải hấp thụ 3200 - 3400 cm–1 và 1618-1653 cm−1; cường độ của dải hấp thụ này sẽ yếu đi khi hỗn hợp nano oxid mangan-sắt nung ở nhiệt độ cao. Hơn nữa, khi hỗn hợp nano oxid mangan- sắt nung đến nhiệt độ 400OC thì xuất hiện peak hấp thụ yếu tại 630 cm−1 gây nên do nhóm Fe-O. Kết quả cũng chỉ rằng hỗn hợp nano oxid mangan-sắt có tính chọn lọc cao đối với As(V). Keywords: Mixed manganese-iron oxide nanoparticles, Amorphous , As(V). KỶ YẾU HỘI NGHỊ KHOA HỌC THƯỜNG NIÊN TRƯỜNG ĐẠI HỌC ĐÀ LẠT NĂM 2018 55 1. INTRODUCTION Water plays important roles in the natural environment, human activities, and social development. However, the presence of arsenic in natural waters has become a worldwide problem in the past decades [1,2]. Arsenic pollution has been reported recently in USA, China, Chile, Bangladesh, Taiwan, Mexico, Romania, United Kingdom, Argentina, Poland, Canada, Hungary, New Zealand, Vietnam, Cambodia, Japan and India [1-7]. Arsenic commonly exists as two inorganic forms of arsenite (AsO33−) and arsenate (AsO43−) which are the popular forms in water and referred to as As(III) and As(V). In general, As(V) is stable in aerobic environment and As(III) often exists in anaerobic environment. The toxicity of arsenic species is different, generally the toxicity of inorganic arsenic compounds is about 100 times higher than organic arsenic compounds, and the toxicity of inorganic As(III) compounds are approximately 60–80 times higher to humans than As(V) compounds [4-10]. They causes skin, lung, bladder and kidney cancer as well as pigmentation changes, skin thickening (hyperkeratosis), neurological disorders, muscular weakness, loss of appetite and nausea [5-12]. Therefore, it is really necessary to remove arsenic from water to make sure that our environment is safe. Adsorption has been recognized as a promising technique for removing arsenic from drinking water due to its high removal capacity and ease of operation. However, As(III) is less efficiently removed than As(V) from aqueous solutions by almost all of the arsenic removal technologies and pre-oxidation of As(III) to As(V) is required [4-17]. Recently, increasing attention has been focused on metal oxide sorbents such as iron, aluminum, titanium, manganese, and zirconium. Among these iron oxides were the mostly studied because of their high affinity to arsenic species, low cost and environmental friendliness [8-21]. Most recently, many researchers used metal composite materials (containing two or more metals) as adsorbents to remove As from contaminated water. The results showed that the composite metal oxides can not only inherit the advantages of parent oxides but also show a synergistic effect of higher adsorption capacity than that of individual metal oxides (Lata and Samadder 2016). For instances, Zhang et al. (2005) developed an Fe-Ce bimetal oxide sorbent, which has a much higher As(V) adsorption capacity than the individual Ce and Fe oxide. Zhang et al. (2007) prepared an Fe-Mn binary oxide sorbent, exhibiting a greater enhancement in both As(V) and As(III) removal [20-26]. Previously, we have synthesized the MnO2 nanoparticles via the reduction– oxidation between KMnO4 and C2H5OH at room temperature [27-29], in this paper we report a simple method to synthesize the mixed manganese-iron oxide nanoparticles and used it as selective adsorbent for adsorption of As(V) from aqueous solutions. KỶ YẾU HỘI NGHỊ KHOA HỌC THƯỜNG NIÊN TRƯỜNG ĐẠI HỌC ĐÀ LẠT NĂM 2018 56 2. EXPERIMENTS 2.1. Chemicals and Instruments 2.1.1. Chemicals Chemicals used included potassium permanganate (KMnO4), FeCl2.4H2O, ethyl alcohol (C2H5OH), HNO3 and NaOH. All chemical reagents used as starting materials are of analytical grade and purchased without any further purification. 2.1.2. Preparation of Adsorbate Solutions The solutions of As(V), Cd(II), Co(II), Cu(II), Zn(II) were used as adsorbates, the As(V), Cd(II), Co(II), Cu(II), Zn(II) solutions were prepared by the standard solutions (1000 ppm) of Merck production for AAS. Studied solutions have been diluted to concentration about 20, 50, 100, 150, 200, 250, 300,ppm (~mg/L), and used for a short period of time that not exceeding three days. 2.1.3. Instruments Atomic Absorption Spectrophotometer (Spectrometer Atomic Absorption AA – 7000 made in Japan by Shimadzu.). The pH measurements were done with a pH-meter (MARTINI Instruments Mi-150 Romania); the pH-meter was standardized using HANNA instruments buffer solutions with pH values of 4.01±0.01, 7.01±0.01, and 10.01±0.01. Temperature-controlled shaker (Model IKA R5) was used for equilibrium studies. 2.2. Synthesis of mixed manganese-iron oxide nanoparticles In our previous work, gamma-MnO2 nanostructure was synthesized via the reduction–oxidation between KMnO4 and C2H5OH by adding gradually KMnO4 saturated solution to the mixture of C2H5OH and H2O at room temperature. In the present work, the mixed manganese-iron oxide nanoparticles was prepared by adding gradually KMnO4 and FeCl2.4H2O solutions to the mixture of C2H5OH and H2O under stirring at the room temperature. Stirring continued for four hours. The effect of reaction time as well as the molar ratio between KMnO4 and FeCl2.4H2O also H2O and C2H5OH was studied. After the reaction was completed, the solid precipitate was washed with distilled water, and then dried at 1000C for 4h to get the product. The synthesized products are amorphous nanoparticles. The amorphous nanoparticles were crystallized using an annealing process at different temperatures (fig.1-2). 2.3. Batch adsorption study of metal ions Place 0.1 g mixed manganese-iron oxide nanoparticles to 50 mL metal ion solution in a 100 mL conical flask. Effect of pH (26), contact time (20240 minutes) and initial KỶ YẾU HỘI NGHỊ KHOA HỌC THƯỜNG NIÊN TRƯỜNG ĐẠI HỌC ĐÀ LẠT NĂM 2018 57 metal ion concentration (Co) (20500 mg/L) were examined. The obtained mixture was centrifugal at 5000 rpm within 10 minutes, then was purified by PTFE Syring Filters with 0.22 µm of pore size to get the filtrate. Atomic Absorption Spectrophotometer (Spectrometer Atomic Absorption AA – 7000) was used to analyze the concentrations of the different metal ions in the filtrate before and after adsorption process. Adsorption capacity was calculated by using the mass balance equation for the adsorbent[1-14].  .o eC C Vq m   (1) Here, q is the adsorption capacity (mg/g) at equilibrium, Co and Ce are the initial concentration and the equilibrium concentration (mg/L), respectively. V is the volume (L) of solution and m is the mass (g) of adsorbent used. 3. RESULTS AND DISCUSSION 3.1. Characterization of the mixed manganese-iron oxide nanoparticles. The crystal structure of mixed manganese-iron oxide nanoparticles was identified with X-ray powder diffraction analysis, as shown in Figure 1-2. The diffraction patterns were obtained in the 2θ range from 15-70O. Figure 1. X-ray powder diffraction of the Mn-Fe mixed sorbent Figure 1 reveal that the mixed manganese-iron oxide nanoparticle is amorphous. Absence of sharp peaks confirms the absence of ordered crystalline structure in the prepared sorbent nanoparticles. Figure 2(a,b,c) shows the XRD pattern of the mixed manganese-iron oxide nanoparticles (the synthesized products) after calcination at 200,400 and 600OC. Based on the XRD pattern, whereas the synthesized products calcined at 200°C proved to be amorphous (Fig. 2a). VatLieuNano_Mn_Fe_1_2 VatLieuNano_Mn_Fe_1_2 - File: VatLieuNano_Mn_Fe_1_2.raw - Type: 2Th/Th locked - Start: 15.000 ° - End: 84.990 ° - Step: 0.030 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 8 s - 2-Theta: 15.000 ° - T Li n (C ou nt s) 0 10 20 30 40 50 60 70 80 90 100 2-Theta - Scale 15 20 30 40 50 60 70 80 KỶ YẾU HỘI NGHỊ KHOA HỌC THƯỜNG NIÊN TRƯỜNG ĐẠI HỌC ĐÀ LẠT NĂM 2018 58 Figure 2a. X-ray powder diffraction of the Mn-Fe mixed sorbent after calcination at 200°C Figure 2b. X-ray powder diffraction of the Mn-Fe mixed sorbent after calcination at 400°C Figure 2c. X-ray powder diffraction of the Mn-Fe mixed sorbent after calcination at 600°C Figures 2b, the synthesized products calcined at 400°C, clearly revealed that the diffraction peaks presented in synthesized samples at 2θ values of 24.06O, 33.15O, 35.7O, 40.98O, 49.41O, 54.21O, 62.52O and 64.11O were due to Fe2O3, and these correlated with the reported data of hematite. However, the XRD data did not show any presence of Mn Nano_Mn_Fe_1_2_L2_200C Nano_Mn_Fe_1_2_L2_200C - File: Nano_Mn_Fe_1_2_L2_200C.raw - Type: 2Th/Th locked - Start: 15.000 ° - End: 84.990 ° - Step: 0.030 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 15 s - 2-Theta: 15.0 Li n (C ou nt s) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 2-Theta - Scale 15 20 30 40 50 60 70 80 Nano_Mn_Fe_1_2_L2_400C 00-033-0664 (*) - Hematite, syn - Fe2O3 - WL: 1.5406 - Rhombo.H.axes - a 5.03560 - b 5.03560 - c 13.74890 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - R-3c (167) - 6 - 301.926 - I/Ic PDF 2.4 - F30= Nano_Mn_Fe_1_2_L2_400C - File: Nano_Mn_Fe_1_2_L2_400C.raw - Type: 2Th/Th locked - Start: 15.000 ° - End: 84.990 ° - Step: 0.030 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 14 s - 2-Theta: 15.0 Li n (C ou nt s) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 2-Theta - Scale 15 20 30 40 50 60 70 80 d= 3. 67 00 9 d= 2. 69 68 8 d= 2. 51 28 8 d= 2. 19 92 0 d= 1. 83 86 0 d= 1. 69 30 7 d= 1. 48 45 5 d= 1. 45 17 7 Nano_Mn_Fe_1_2_L2_600C 00-041-1442 (*) - Bixbyite-C, syn - Mn2O3 - WL: 1.5406 - Cubic - a 9.40910 - b 9.40910 - c 9.40910 - alpha 90.000 - beta 90.000 - gamma 90.000 - Body-centered - Ia-3 (206) - 16 - 832.998 - I/Ic PDF 4.5 - S-Q 24.3 00-033-0664 (*) - Hematite, syn - Fe2O3 - WL: 1.5406 - Rhombo.H.axes - a 5.03560 - b 5.03560 - c 13.74890 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - R-3c (167) - 6 - 301.926 - I/Ic PDF 2.4 - S-Q 7 Nano_Mn_Fe_1_2_L2_600C - File: Nano_Mn_Fe_1_2_L2_600C.raw - Type: 2Th/Th locked - Start: 15.000 ° - End: 84.990 ° - Step: 0.030 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 14 s - 2-Theta: 15.0 Li n (C ou nt s) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 2-Theta - Scale 15 20 30 40 50 60 70 80 d= 3. 66 96 4 d= 2. 69 65 5 d= 2. 51 74 7 d= 2. 20 26 3 d= 1. 84 08 8 d= 1. 69 28 8 d= 1. 48 59 2 d= 1. 59 77 8 d= 3. 83 75 7 d= 2. 35 31 6 d= 1. 66 44 1 d= 1. 45 30 6 d= 1. 41 91 4 d= 1. 30 96 1 d= 1. 25 82 2 d= 1. 22 77 0 d= 1. 19 02 0 d= 1. 16 13 7 d= 2. 00 31 8 d= 1. 34 84 8 KỶ YẾU HỘI NGHỊ KHOA HỌC THƯỜNG NIÊN TRƯỜNG ĐẠI HỌC ĐÀ LẠT NĂM 2018 59 oxide particles in the Mn-Fe mixed oxide system which confirmed that Mn (III) enter into the Fe2O3 lattice substitution. In fact, ionic radius of Mn (III) of 58pm is similar to that of ionic radius (55pm) of Fe (III) thus the substitution in the matrix of Fe2O3 is a favorable process [30]. Nevertheless, when the calcination temperature of the synthesized products was 600OC, the peaks observed at 23.1O, 33.12O, 38.19O, 55.11O, 62.46O, 64.05O indicate the formation of Mn2O3 crystalline and the peaks at 24.21O, 33.12O, 35.64O, 40.89O, 49.5O, 54.12O, 62.46O and 64.05O are the characteristic peaks of Fe2O3. It was observed that after calcination at 600OC for 2h, the manganese iron mixed oxides change from amorphous structure to both Fe2O3 and Mn2O3 crystal structures (fig. 2c). Formation of the mixed manganese-iron oxide nanoparticle was further supported by FTIR analysis. Fig. 3. FTIR spectrum of the manganese-iron oxide nanocomposite particles Fig. 3 shows the FTIR spectrum of the mixed manganese-iron oxide nanoparticles before and after calcination at 200, 400 and 600OC. The intense band around 3200 - 3400 cm–1 may be due to the stretching modes of -OH group from adsorbed water in the sample. The bending vibration of H-O-H group also localized at 1618-1653 cm−1; theses intense bands is weak (fade) at the high calcination temperature of the mixed manganese-iron oxide nanoparticles. In addition, when the calcination temperature of the mixed manganese-iron oxide nanoparticles was 400OC, the weak absorption bands at 630 cm−1 may be the vibrations of (Fe-O), which are indicative of formation of mixed metal oxides. SEM and TEM Analysis The SEM images of the mixed manganese-iron oxide nanoparticles (the synthesized products) were obtained to observe the particle size and morphology (fig.4) KỶ YẾU HỘI NGHỊ KHOA HỌC THƯỜNG NIÊN TRƯỜNG ĐẠI HỌC ĐÀ LẠT NĂM 2018 60 Fig. 4. The SEM images of the manganese-iron oxide nanocomposite particles (the synthesized products) with different magnification From the SEM photographs, it was understood that the grains are connected with each other. (It was found that the grains present jointly with each other). In few places, bigger grains are also seen. It is seen that the synthesized products consists of nanoparticles aggregated together to form large clusters. It is a common phenomenon when amorphous nanoparticles are annealed [31]. Fig. 5. The TEM image of the manganese-iron oxide nanocomposite The TEM analysis shows the particles size of the mixed manganese-iron oxide nanoparticles are in the range of 20-30nm (fig.5). The surface area of the mixed manganese-iron oxide nanoparticles were measured by a BET analyzer, and the surface area of the samples was calculated to be 288.268 m²/g. KỶ YẾU HỘI NGHỊ KHOA HỌC THƯỜNG NIÊN TRƯỜNG ĐẠI HỌC ĐÀ LẠT NĂM 2018 61 3.2. Adsorption of As (V) onto mixed manganese-iron oxide nanoparticles 3.2.1. Affecting Factors  Effect of pH Determination of optimum pH is very important since the pH value affects not only the surface charge of adsorbent, but also the degree of ionization and speciation of adsorbate during reaction. Adsorption experiments were carried out in the pH range of 2- 6 for the synthesized products by keeping all other parameters constant (As(V) concentration = mg/l; stirring speed = 240 rpm; contact time = 120 min, adsorbent dose = 0.1g, room temperature = 25°C). The result showed that more adsorption at acidic pH indicates that the lower pH results in an increase in H+ ions on the adsorbent surface that results is significantly strong electrostatic attraction between positively charged adsorbent surface and As(V) arsenate ions (divalent HAsO42- or monovalent H2AsO4-). Lesser adsorption of As(V) at pH values greater than 6.0 may be due the dual competition of both the anions (HAsO42- and OH-) to be adsorbed on the surface of the adsorbent of which OH- predominates. Figure 6. Effect of pH on the As(V) adsorption  Effect of contact time The effect of contact time was studied at optimum condition of dose, pH, and agitation speed. From Fig. 7, it is observed that the adsorption of As(V) increased as contact time increased. The adsorption percentage of metal ions approached equilibrium within 120 min. After this equilibrium period, the amount of adsorbed metal ions did not significantly change with time. 50 60 70 80 90 100 0 1 2 3 4 5 6 7 A ds or pt io n, (% ) pH 250 ppm 300 ppm KỶ YẾU HỘI NGHỊ KHOA HỌC THƯỜNG NIÊN TRƯỜNG ĐẠI HỌC ĐÀ LẠT NĂM 2018 62 Figure 7. Effect of contact time on the As(V) adsorption  Effect of initial As(V) concentration The adsorption of As(V) with synthesized products was studied by varying As(V) concentration (100ppm - 1000ppm) keeping other parameters (adsorbent dose, stirring speed, solution pH, temperature and contact time) constant. As illustrated in Fig. 8, As(V) uptake reduced from 99.89% to ~ 30%, as the As(V) concentration increased from 100ppm to 1000ppm. Figure 8. Effect of initial As(V) concentrations on the As(V) adsorption 3.2.2. Comparation of Bivalent Cationic Metals Adsorption Cd(II), Co(II), Cu(II), Zn(II) and As(V) on mixed manganese-iron oxide nanoparticles The results of Table 1 showed that the mixed manganese-iron oxide nanoparticles have not successfully used for the adsorption of Cd(II) , Cu(II), Co(II), Zn(II) ions from aqueous solution on concentration of 20ppm for each (or more), inversely strongly adsorption of As(V) on mixed manganese-iron oxide nanoparticles. This remarkable 0 10 20 30 40 50 60 70 80 90 0 20 40 60 80 100 120 140 160 180 200 A ds or pt io n, (% ) The contact time (min) 262,97ppm 304,41ppm 0 20 40 60 80 100 0 200 400 600 8001000A ds or pt io n, (% ) Co (ppm) 0.1 g KỶ YẾU HỘI NGHỊ KHOA HỌC THƯỜNG NIÊN TRƯỜNG ĐẠI HỌC ĐÀ LẠT NĂM 2018 63 difference is probably due to the