Study on some factors of magnetic fluid chitosancoated fe3o4 nanoparticles fabrication via hydrothermal method

Journal of Science and Technology 54 (2C) (2016) 341-347 STUDY ON SOME FACTORS OF MAGNETIC FLUID CHITOSAN- COATED Fe3O4 NANOPARTICLES FABRICATION VIA HYDROTHERMAL METHOD Le The Tam1, Nguyen Hoa Du1, *, Tran Dai Lam2, Phan Thi Hong Tuyet1, Le Thi Nhan1 1Faculty of Chemistry, Vinh University, 182 Le Duan, Vinh, Nghe An 2Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Ha Noi *Email: hoadu.nguyen@gmail.com Received: 15 June 2016; Accepted for publication: 23 October 2016 ABSTRACT To optimize reaction conditions of hydrothermal preparation of crystalline magnetite (Fe3O4) nanoparticles, the influence of some experimental parameters (temperature, initial concentration of ferric and ferrous ions, and heating time), and their interactions on the magnetic nanoparticle formation was studied using response surface methodology (RSM), based on a statistical design of experiments (DOE). The variation in the particle diameter and crystallite size of obtained magnetic nanoparticles (MNPs) with the synthesis conditions was examined and transmission electron microscopy (TEM) and X-ray diffraction analysis. The results showed that crystallite size was greatly affected by temperature, ferric salt concentration and the heating time, whereas the particle diameter strongly depended on the heating time, and on the interaction between the initial ferrous/ferric ion molar ratio and the initial concentration of ferrous ions. The MNPs produced by this method were the objects to coat surface with chitosan solution. The chitosan coated MNPs are nearly spherical with a mean size from 10 to 20 nm depending on the experimental conditions. RSM analysis showed that under optimized conditions, the chitosan coated MNPs with smallest size 13.43 ± 1.5 nm and saturation magnetization 68.12 emu/g at room temperature were obtained under the hydrothermal temperature 165oC, heating time 2 h 55 minute and ferric salt concentration 0.21 M. Keywords: synthesis, MNPs, Fe3O4, chitosan, hydrothermal, optimization, design of experiments (DOE), response surface methodology (RSM). 1. INTRODUCTION Magnetic nanoparticles have been of interest for their typical physical and chemical properties as well as their potential applications in various fields such as information technology, environmental treatment, catalysis, biomedicine (extraction of biomolecules, targeted drug delivery, magnetic resonance imaging (MRI), contrast enhancement and thermal magnetic therapy) [1, 2]. Amongst a Le The Tam, Nguyen Hoa Du, Tran Dai Lam, Phan Thi Hong Tuyet, Le Thi Nhan 342 variety of magnetic nanomaterials developed, iron oxide (Fe3O4) nanoparticles have been the most favored for biomedical applications due to their chemical stability and simple synthesis. There are some common ways to synthesize Fe3O4 nanoparticles, including co-precipitation, sol-gel or hydrothermal methods [3 - 5]. The chitosan covering provides them hydrophillic amino and hydroxyl groups that enable the possibility to bind to a diversity of chemical groups and ions, leading to a number of applications such as protein and metal adsorption, targeted drug and gene delivery, magnetic resonance imaging, tissue engineering. But most of the synthesis studies were conducted using conventional methods, i.e. investigating a process by varying one factor whilst maintaining all other factors involved at constant levels; such methods are time consuming and of low efficiency in optimizing a given process. In addition, the conventional optimization process cannot give an indication of the interactive effects between any two factors in a multi variable system. One powerful tool for analysing the degree of the effect of each experimental parameter is response surface methodology (RSM) [6], based on a statistical design of experiments (DOE), which can lead to the optimization of synthesis conditions. In this paper, the influence of the experimental parameters such as the reaction time, temperature, and concentration of the reactants of a hydrothermal preparation of Fe3O4 nanoparticles on particle formation was studied using RSM. 2. MATERIALS AND METHODS 2.1. Chemicals and instruments Ferric chloride hexahydrate, ferrous chloride tetrahydrate and sodium hydroxide were all purchased from Merck chemical company, chitosan PCT0817 (degree of deacetylation >= 75.0 %, Himedia, India). Ultra-pure nitrogen gas (99.99 %) was used to provide anaerobic condition in solution. Distilled deionized water was used to prepare all the solutions. Predetermined amounts of ferrous chloride (FeCl2) and ferric chloride (FeCl3) were dissolved in 30 ml of deionized and deoxygenated water at 75 oC under N2 with stirring at 400 rpm for 15 minutes. The obtained solution was added by dropwise into 17 ml sodium hydroxide (NaOH 2 M) solution with rate of 3 ml/min, under vigorous stirring with a magnetic stirrer in an N2 atmosphere, after which the color of the mixture turned to black and the pH value was higher than 13. The resulting suspension was transferred into a teflon-lined stainless steel autoclave with a capacity of 50 ml and was introduced in an oven at 120 - 180 oC for 2-4 h. The synthesized Fe3O4 particles were washed several times with deionized distilled water until neutralization, and were separated using a super magnet and decanting. The prepared MNPs were dispersed in to chitosan solution at temperature 70 oC under N2 with ultrasonic vibration for 30 minutes, after that filtered off the product of chitosan coated MNPs, washed with deionized water, acetone and freeze dryed under a vacuum at -86 oC. The experiments were performed in the laboratory of inorganic chemistry, Vinh University. The crystal structures of the samples were characterized by XRD using diffractometer SIEMENS D5000 with Cu-Kα radiation (λ = 1.5406 Å) (Faculty of Chemistry, Vietnam National University, Hanoi). The binding of chitosan to the surface of Fe3O4 particles was analyzed in wavenumber range 4000 – 400 cm-1 by FT-IR spectroscopy (Bruker) (Faculty of Chemistry, Vinh University). Morphology (size and shape) of the particles was obtained by transmission electron microscopy TEM (JEM 1010) (National Institute of Hygiene and Epidemiology) and hysteresis loops were measured at room temperature to the highest field of 11 kOe using a vibrating sample magnetometer (VSM) (Institute of Materials Science, Vietnam Academy of Science and Technology). Study on some factors of magnetic fluid chitosan-Fe3O4 nanoparticles fabrication via hydrothermal 343 2.2. Experimental design All statistical analysis, modeling and numerical optimization was performed using Design- Expert software 7.1. The experiments were designed using a response surface methodology (RSM) - Central Composite Designs (CCD) was used as an optimization method in our synthetic procedure, which consisted of eight corners, and one centre point of the cubic region, and two repetitions. Table 1 summarizes the levels and ranges of independent variables. Table1. Levels of independent variables and experimental conditions. Factor Low level (-1) Medium level (0) High level (+1) Alpha level * (+/- 1.414) Temperature synthesized, oC (A) 120 150 180 192.426 107.574 Heating time, hours (B) 2 3 4 4.41 1.59 Initial concentration of Fe3+ ions (mol/l) (C) 0.1 0.17 0.25 0.28 0.17 * axial points 3. RESULTS AND DISCUSSION In this study, the initial Fe2+/Fe3+ ion molar ratio of 0.5 is constant as stoichiometrically required for Fe3O4, and hydrothermal time, ferric salt concentration and temperature of the reaction were varied to alter the crystal growth of Fe3O4. After the air in the hydrothermal reactor was replaced with N2 to prevent oxidation, the sealed reactor was maintained at 120°C - 180°C in an oven for a given heating time. The product was washed with deionized and deoxygenated water, before chitosan coating on nanoparticles and freeze drying under a vacuum at -86 °C. Table 3. ANOVA results for the magnetic properties of products. Source F-Value p-value (Prob > F) Model 35.75 0,0068a significant A 10.64 0.0038a B 7.31 0.0457b C 30.64 0.0116b AB 9.27 0.0308b AC 5.83 0.0346b BC 76.96 0.0031a A2 33.46 0.0103b B2 21.85 0.0185b C2 107.69 0.0019a a Significant at 1 % level b Significant at 5 % level R-Squared = 0.9908 Table 2. Magnetic properties of products. Run No Conditions Saturation magnetization [emu/g] A[0C] B[h] C [mol/l] M1 180 4 0.10 34.73 M2 180 2 0.25 53.22 M3 120 4 0.25 61.89 M4 120 2 0.10 57.26 M5 107.57 3 0.17 55.38 M6 192.43 3 0.17 63.21 M7 150 1.59 0.17 61.41 M8 150 4.41 0.17 60.07 M9 150 3 0.07 46.67 M10 150 3 0.28 59.96 M11 150 3 0.17 66.67 M12 150 3 0.17 65.32 Le The Tam, Nguyen Hoa Du, Tran Dai Lam, Phan Thi Hong Tuyet, Le Thi Nhan 344 The XRD patterns of Fe3O4 nanoparticles samples is presented in Figure1 a. All the characteristic peaks are consistent with the standard database peaks, revealing the cubic inverse spinel structure of the sample. The 2θ value of peaks with significant intensity at 30.208, 35.448, 37.128, 43.368, 53.808, 57.048 and 62.438, respectively, were in accordance with the dhkl crystal planes of Fe3O4 at (220), (311), (222), (400), (422), (511), and (440) which agree well with the standard peak values of XRD pattern of Fe3O4 (JCPDS: 19-0629). The successful formation of Fe3O4 nanoparticles can further be confirmed from the dark color of the resulting products. (a) (b) Figure 1. XRD patterns of MNPs and MNPs/CS (a); FTIR spectra for MNPs/CS and CS (b). Figure 1b shows the FTIR spectra of pure chitosan (CS), and MNPs/CS. The characteristic absorption bands for chitosan in Fig.1b appear at 3395 (O–H and N–H stretching vibrations), 2915 (C–H stretching vibrations), 1638 (N–H bending vibrations), 1408 (C–N stretching vibrations) and a group of bands from 1091 to 1058 cm-1 (C–O–C and C–O stretching vibrations). The spectrum of the products obtained using chitosan showed the characteristic absorption bands for this polymer, with a noticeable decrease the bands of C–O–C and C–O stretch around 1050 cm-1. Figure 1b showed the band at 605 cm-1 corresponds to Fe-O, has been shifted to 588 cm-1 due to interaction between Fe3O4 and CS in CS/MNPs. Table 2 lists the magnetic properties of Fe3O4 nanoparticles obtained under each synthesis condition. To analyse the degree of the effect of each experimental parameter and their interactions on the magnetic properties, an analysis of variance (ANOVA), based on a linear statistical model, was applied. First, the sum of squares was calculated from the experimental results, using commercially available software (Design-Expert, version 7.1, StatEase). Then, the p-value was determined using the sum of squares and the degrees of freedom. The p-value indicates the probability used to determine statistically significant effects in the model. P-value close to zero indicates that the effect of the experimental parameter is significant. The significant factors affecting the magnetic properties can be determined based on a comparison between the p-values. According to Table 3, A showed the lowest p-value and C the second lowest. However, the interactions between A and B, B and C was relatively small, and the effect of A, C and AC were the smallest among the factors. This result implies that A and C are the most important factor in obtaining Fe3O4 nanoparticles with high magnetic properties. By multiple regression analysis on the experimental data, the terms found to be significant were combined into the following fitted quadratic polynomial equation to predict the saturation magnetization [emu/g]: Y = 66.06 + 2.77A - 0.47B + 4.70C - 1.17AB + 2.90AC + 10.53BC - 3.77A2 - 3.04B2 - 6.76C2 (1) The Model F-value of 35.75 implies the model is significant. The goodness of the model fit was checked by determination coefficient (R2). In this case, the value of R2 is 99.08 % and the value of R2Adj (96.30 %) is also high to advocate that only 0.92 % of the synthesis of magnetic nanoparticles was not explained by the model. It indicated that the fitted quadratic model accounted for more than 96.30 % (R2Adj) of the variations in the experimental data, which were found to be highly significant Study on some factors of magnetic fluid chitosan-Fe3O4 nanoparticles fabrication via hydrothermal 345 (p < 0.001). An F-value test was also conducted to evaluate the goodness of the model. The F-ratio of quadratic regression model was 20.534. On this basis, it can be concluded that the model is well accurate for predicting the yield. The results of analysis showed that the experimental values were significantly in agreement with the predicted values and also suggested that the model of (1) was satisfactory and accurate. It was considered reasonable to use the regression model to analyze trends in the responses. Figure 2. 3D response surface plot and contour diagram of A and C effects on the magnetic properties of Fe3O4 nanoparticles. Figure 3. Magnetic hysteresis loop M(H) of MNPs-CS obtained at different synthesis conditions. To visualize the effect of the independent variables on the dependent variable, surface response and contour plots of the quadric polynomial model were generated by varying two of the independent variables within the experimental range while holding the other constant at the centre point using the Design-Expert software (Figure 2). These response surface plots and their respective contour plots provide a visual interpretation of the interaction between two variables and are used to obtain the optimum conditions for the production of the complex. The shapes of the contour plots provide a measure of the significance of the mutual interactions between the variables. An elliptical contour plot indicates a significant interaction between variables. The optimum values of the selected variables were obtained by solving the regression equation (1). The optimum values of the test variables were: temperature synthesized (A) = 165 oC, heating time (B) = 2 h 55 minute, and initial concentration of Fe3+ ions (C) = 0.21 M, with the predicted yield of the saturation magnetization of 67.91 emu/g. In order to verify the prediction of the model, the optimum process conditions were applied to three independent replicates for the synthesis magnetic nanoparticles. The average yield is 68.12 emu/g (M_opt) (Figure 3), which is in good agreement with the predicted value (67.91 emu/g). The increasing of synthesis temperature and initial concentration leads to increasing of saturation magnetization and reaches to highest value of 68.12 emu/g. This may be explained by the increasing crystal growth of nanoparticles at high temperature. This indicates that the model can be considered quite reliable for predicting the effect of each factor on the magnetic properties of Fe3O4 nanoparticles. Figure 4 shows the most of magnetic nanoparticles, the spherical particles are relatively uniform with mean size 13.43 ± 1.5 nm. Figure 4. TEM image of MNPs-CS, particle size distribution pattern and MNPs-CS dispersed in water, which can be attracted by a magnet. Le The Tam, Nguyen Hoa Du, Tran Dai Lam, Phan Thi Hong Tuyet, Le Thi Nhan 346 4. CONCLUSIONS The synthesis of the magnetic nanoparticles (MNPs) and chitosan coated magnetic nanoparticles (MNPs/CS) was successfully optimized using RSM, whereas a satisfactory quadratic polynomial model was derived and demonstrated. The predicted model fits well with the experimental results, which is sufficient to describe and predict the responses. Temperature synthesized (A) = 165oC, heating time (B) = 2 h 55 minute, and initial concentration of Fe3+ ions (C) = 0.21 mol/l, were found to be the optimum conditions for achieving the maximum saturation magnetization. Under the optimum conditions, the maximum saturation magnetization of product reached 69.72 emu/g, which is in good agreement with the predicted yield. REFERENCES 1. Meng X., Seton H. C., Lu T. L., Prior I. A., Thanh N. T., Song B. - Magnetic CoPt nanoparticles as MRI contrast agent for transplanted neural stem cells detection, Nanoscale 3 (2011) 977-984. 2. Le T. L., Le D. T., James L., David G. F., Nguyen T. K. T. - Facile synthesis of stable, water- soluble magnetic CoPt hollow nanostructures assisted by multi-thiol ligands, J. Mater. Chem. 19 (2009) 6023-6028. 3. Thi K. O. V., Dai L. T., Trong L. L., Hung M. D., Xuan P. 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TÓM TẮT NGHIÊN CỨU CÁC YẾU TỐ ẢNH HƯỞNG ĐẾN QUÁ TRÌNH CHẾ TẠO CHẤT LỎNG TỪ NANO Fe3O4 BỌC CHITOSAN BẰNG PHƯƠNG PHÁP THỦY NHIỆT Lê Thế Tâm1, Nguyễn Hoa Du1, *, Trần Đại Lâm2, Phan Thị Hồng Tuyết1, Lê Thị Nhàn3 1Khoa Hóa học, Trường Đại học Vinh, Vinh University, 182 Lê Duẩn, Vinh, Nghệ An 2Học viện và Khoa học Công nghệ, Viện Hàn lâm Khoa học và Công nghệ Việt Nam, 18 Hoàng Quốc Việt, Hà Nội *Email: hoadu.nguyen@gmail.com Study on some factors of magnetic fluid chitosan-Fe3O4 nanoparticles fabrication via hydrothermal 347 Trong nghiên cứu này của chúng tôi, các hạt nano Fe3O4 bọc chitosan có từ độ bão hòa khá cao được tổng hợp bằng phương pháp thủy nhiệt ở các điều kiện phản ứng được tối ưu hóa bằng việc thiết kế ma trận thực nghiệm dùng phương pháp đáp ứng bề mặt (RSM) với phương án cấu trúc có tâm (CCD). Cấu trúc, hình thái và tính chất từ của mẫu phụ thuộc vào sự thay đổi nhiệt độ của phản ứng, thời gian phản ứng và nồng độ các chất tham gia. Các kết quả XRD và TEM cho thấy rằng tất cả các mẫu vật liệu thu được có cấu trúc đơn pha magnetite, với kích thước tinh thể trung bình khoảng 10 - 20 nm tùy thuộc vào điều kiện tổng hợp. Trong điều kiện tối ưu ở nhiệt độ thủy nhiệt 165 oC, thời gian ủ mẫu 2 h 55 phút và nồng độ muối sắt là 0,21 M, các hạt nano sắt từ điều chế được có kích thước trung bình 13,43 ± 1,5 nm, từ độ bão hòa 68,12 emu/g. Từ khóa: thủy nhiệt, nano từ Fe3O4, chitosan, thiết kế thực nghiệm, tối ưu hóa, phương pháp đáp ứng bề mặt (RSM), phương án cấu trúc có tâm (CCD).