Effects of Mn, Cu doping concentration to the properties of magnetic nanoparticles and arsenic adsorption capacity in wastewater

Applied Surface Science 340 (2015) 166–172 Contents lists available at ScienceDirect Applied Surface Science journa l h om epa ge: www.elsev ier .com/ locate /apsusc Effects pro nanopa in Tran Min Anh Faculty of Phys a r t i c l Article history: Received 14 Se Received in re Accepted 22 F Available onlin Keywords: Mn Cu doped Fe3O Magnetic nano Arsenic adsorption , Cu d prese show nm. T turati o 53. m 0. died ecific about of 100.2 m /g. The pore size distribution of about 15–20 nm calculated by the BJH (Barrett, Joyner, and Halendar) method at a relative pressure P/P0 of about 1. Although the saturation magnetic moments of samples decreased when the increase of doping concentration, but the arsenic adsorption capacity of Cu doped Fe3O4 nanoparticles is better than that of Fe3O4 and Mn doped Fe3O4 nanoparticles in a solution with pH = 7. In the solution with a pH > 14, the arsenic adsorption of magnetic nanoparticles is insignificant. 1. Introdu Arsenic lem that h human hea porous Al2O arsenic rem tion faces t and leaving ied magnet magnetic n convenient of an extern Ferrite m transition m erties whic application [5], wastew nanomateri ∗ Correspon E-mail add 0169-4332/Cr ( Copyright © 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( ction contamination in natural waters is a world-wide prob- as been concerned by the influence of arsenic to a lth. Various metal oxide heterostructures, such as meso- 3, TiO2, CuO, ZrO2, MnO2 [1], were investigated for the oval. However, using these oxides for arsenic absorp- o the difficulties in recovering from aqueous solutions residuals in the solution. Recently, researchers stud- ic nanoporous materials as an arsenic absorbent. These anoporous materials bearing adsorbed arsenic can be ly separated from aqueous solutions with the assistance al magnetic field. aterials and Fe3O4 magnetic nanomaterials doped etals [2–4] have unique electric and magnetic prop- h enable them to have a wide range of technological s in different field such as magnetic resonance imaging ater treatment [6–8]. Many groups have used Fe3O4 als for removing As, Cr, Cd ions [6–11] from pollution ding author. Tel.: +84 0437547797. ress: tranminhthi@hnue.edu.vn (T.M. Thi). water, or for applying in medicine [12–14]. It is believed that the nanosized ferrites can exhibit improved physical and chemical properties and hence can effectively be used for various appli- cations. More interestingly, both the electronic and magnetic properties of Fe3O4 can be adjusted with substitution of Fe ions by other transition metals such as Zn, Mg, Cu, Zn, Ni [15–19]. In terms of Fe3O4 crystal structure, the unit cell of spinel fer- rite (AB2O4) consists of cubic closed-packed arrays of oxygen ions which result in two kinds of interstitial sites denoted as tetrahe- dral A-site (Fe3+) and octahedral B-site (Fe2+:Fe3+ = 1:1) [15,17]. Since the A-site ions are trivalent for Fe3O4, different from the general spinel materials with divalent ions at A-sites, this com- pound is called an inverse spinel. These sites are occupied by metal cations depending on their radii, the electrostatic energies of the lattice and the matching of the electronic configuration with the surrounding oxygen ions. The cation distribution among the (A) and (B) sites play an important role in controlling the electric and magnetic properties of the ferrite materials. In work [18], the mag- netization of Ni1−xZnxFe2O4 samples (x = 0, 0.5 and 1) was changed by substitutions of Ni2+ and Zn2+ ions into A-sites and B-sites. The Ni0.5Zn0.5Fe2O4 sample [19] with the saturation magnetic moment of 46.1 emu/g and specific surface area of 49.0 m2/g achieved the arsenic equilibrium adsorption quantity of 7.2 mg/g when the rg/10.1016/j.apsusc.2015.02.132 own Copyright © 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ecommons.org/licenses/by-nc-nd/4.0/). of Mn, Cu doping concentration to the rticles and arsenic adsorption capacity h Thi ∗, Nguyen Thi Huyen Trang, Nguyen Thi Van ics, Hanoi National University of Education, Viet Nam e i n f o ptember 2014 vised form 1 February 2015 ebruary 2015 e 27 February 2015 4 nanoparticles particles a b s t r a c t The research results of Fe3O4 and Mn for As(III) wastewater treatment are mission electron microscopy images sizes were varied from 9.4 nm to 18.1 at room temperature showed that sa samples decreased from 65.9 emu/g t increase of Cu, Mn concentrations fro typical Fe3O4 sample at 77 K was stu nanoparticles by BET method. The sp 2perties of magnetic wastewater oped Fe3O4 nanomaterials synthesized by a chemical method nted in this paper. The X-ray diffraction patterns and trans- ed that samples had the cubic spinel structure with the grain he results of vibrating sample magnetometer measurements on magnetic moments of Fe1−xCuxFe2O4 and Fe1−xMnxFe2O4 2 emu/g and 65.9 emu/g to 61.5 emu/g, respectively, with the 0 to 0.15. The nitrogen adsorption–desorption isotherm of a in order to investigate the surface and porous structure of surface area of Fe3O4 magnetic nanoparticles was calculated T.M. Thi et al. / Applied Surface Science 340 (2015) 166–172 167 initial arsenic concentration of 3 mg/L. Due to the nature of adsorp- tion process was attributed to the inelastic exchange interaction energy between the arsenic and the porous materials with high specific surface area of adsorption substance, these results were analyzed an then compa the Temkin the arsenic using Langm The nano in their surf ties signific At the same mum state o transforma grains and are interest urate magn in applicati doping effe tion in the a paper we p the magnet Cu doped F centrations pH. 2. Experim The hig company w (CH3COO)2 with concen arsenic con 10 times hig by the Wor (EC) and Un Besides, the pH of soluti The FeCl and Cu2+ w 0.10, and 0 solutions w the NH3 sol pH = 10. Thi netic mater through a fi conditions Fe0.90Cu0.10 Similarly Fe0.85Mn0.1 0.05, 0.10, a The obta an arsenic c level and st adsorption the solutio atomic abso The mic diffraction ( (TEM, JEOL ties were m The mesopo using TriSta ware. he ma 2 mo he Roentgen diffraction patterns of the Mn, Cu doped Fe3O4 samples. ults and discussion agnetic and microstructure properties and chemical lity of Fe3O4 sample t, the stability of magnetic, microstructure property of Fe3O4 vestigated by examining a sample right after synthesized at sample after 2 months. Fig. 1 showed that the saturate tic moment of Fe3O4 sample decreased from 65.9 emu/g to /g, corresponding to freshly synthesized sample and this measured after 2 months of synthesis. This decrease was ted that after formation, Fe3O4 material is easy to be oxi- nto -Fe2O3 due to the effects of oxygen in air as following on: + O2 + 18H2O → 6Fe2O3 + 12H2O appearance of -Fe2O3 phase can be seen in Raman spectra 4 sample freshly synthesized and after 2 months in (Fig. 3). Raman spectrum of the pristine sample (spectrum a), a peak ave number of 668 cm−1 can be observed corresponding to oscillation mode of Fe3O4. In addition, the peak at 360 cm−1 all intensity can also be detected which was attributed to sence of a -Fe2O3 phase with such a tiny amount that it not be detected by XRD measurement. The appearance ofd calculated by the pseudo-second-order kinetic model, ring with the two- and three-parameter models and and Redlich-Peterson model [19]. The parameters of adsorption isotherm process are studied and calculated uir isotherm equation [19,22,25]. particles show the special properties due to an increase ace area and mass. Then the electrical, magnetic proper- antly change due to the quantum effects of particle size. time, the particles show a tendency to shift to a mini- f free energy through some of forms such as: the phase tion, the change of surface structure, the agglomerate of surface absorption [20,21]. At present, the researchers ing to the chemical instability and the decrease of sat- etic moment of Fe3O4 over time and their effectiveness on [22–25]. However the complete investigation of the cts in Mn, Cu doped Fe3O4, and their potential applica- rsenic treatment of wastewater are still limited. In this resent the studying results of the synthesize process, ic properties, microstructure, surface properties of Mn, e3O4 nanomaterials and the influence of Mn, Cu con- on the arsenic adsorption process in water at different ent h purity initial chemicals from Merck chemical ere used: FeCl3·6H2O; Na2SO3; (CH3COO)2Cu·4H2O; Mn·4H2O acetone with 99% purity; the solutions: NH3 tration of 25% mol, the original AsO3 solution with the centrations of 1 g/L. (1 g/L = 106 ppb corresponding to her than that allowed arsenic levels (10 ppb) regulated ld Health Organization (WHO), European Commission ited States Environmental Protection Agency (US EPA). NaOH and HCl solutions also were used to adjust the on. 3·6H2O, (CH3COO)2Cu·4H2O solutions containing Fe3+ ith different doping nominal concentrations of 0, 0.05, .15 were mixed with a Na2SO3 solution. These mixed ere stirred until they turned to yellow in color. Then ution was added dripping slowly, drop by drop, until the s mixed solution was then stirred for 30 min. The mag- ials were obtained by using magnets, and then passed lter. These powders were dried at 50 ◦C in low-pressure for 48 h. They were called Fe3O4, Fe0.95Cu0.05Fe2O4, Fe2O4 and Fe0.85Cu0.15Fe2O4, respectively. , samples of Fe0.95Mn0.05Fe2O4, Fe0.90Mn0.10Fe2O4 and 5Fe2O4 with different doping nominal concentrations of nd 0.15 also were synthesized using above method. ined powders were mixed into an As (III) solution with oncentration of about 10 times higher than the allowed irred for 20 min. In order to determine the saturated capacity of the material, the arsenic concentrations in n before and after stirring were measured using the rption spectrophotometer (AAS 6300 Shimadzu). rostructure of the samples was measured by X-ray XRD, D5005, Bruker), transmission electron microscopy 5410 TEM NV) measurements. Their magnetic proper- easured using a vibrating sample magnetometer (VSM). res structure of samples was measured by BET method r 3000 V6.07A instrument with TriStar 3000 V6.08 soft- Fig. 1. T thesized Fig. 2. T 3. Res 3.1. M instabi Firs was in and th magne 56 emu sample attribu dized i equati 4Fe3O4 The of Fe3O In the with w the A1g with sm the pre could gnetic moment of Fe3O4. (a) New synthesized Fe3O4; (b) Fe3O4 syn- nths old. 168 T.M. Thi et al. / Applied Surface Science 340 (2015) 166–172 Fig. 3. The Ra thesized 2 mo the -Fe2O3 synthesis pr because the other hand, ple, the pea A1g oscillat at the 668 c two peaks a peaks sugge The change Fe3O4 samp to their app netic prope spinel lattic 3.2. The mi Fe3O4 nanop 3.2.1. The m Fe1−xMnxFe In orde microstruct with half m be selectiv [15,17,26,2 ture in whic (B) sites. On invokes a d at the (B) s magnetic in the Mn, Cu in the mate [17,18,26,2 In case doped Fe3O observed th ing Cu dopi increased m of the dope been previo hedral and migrates to such a way increases a imbalance o Table 1 The values of the lattice constant and particle size of samples. Sample Particle size (nm) Lattice constant (A˚) Fe O n0.10 n0.15 u0.10F u0.15F et m nside dope A sit rk at 2 nxFe oinc tter struc show ed. T ller t + ion uxFe ak in at of the lat nxFe ions the d –Sch Cu K e dif Fe1− tice c le 1 s ggest he in s wi ehav s (14 nd 0 4 p n0.1 of pman spectra of samples. (a) New synthesized Fe3O4; (b) Fe3O4 syn- nths old. phase in the pristine sample might originate from the ocess in which the oxidation of Fe2+ into Fe3+ happened samples were synthesized in the atmosphere. On the for the Raman spectrum of the 2-month-old Fe3O4 sam- ks at 360 cm−1, 486 cm−1, 1360 cm−1 corresponding to ion modes of -Fe2O3 were observed. Also, the peak m−1 position in Fig. 3 showed signs of splitting into t 666 cm−1 and 710 cm−1. The appearance of additional sted that Fe3O4 is easy to be oxidized to form -Fe2O3. of magnetic moment and the chemical instability of the le might lead to the unexpected phenomena affecting lication ability. So the technique to stabilize the mag- rty in Fe3O4 is to dope some transition metals into the e of Fe3O4 [15,17,26,27]. crostructure and magnetic properties of Mn, Cu doped articles icrostructure properties of Fe1−xCuxFe2O4 and 2O4 nanoparticles r to create stable materials while preserving the ure and interactive mechanism via the B site network etallicity, some of divalent transition metal need to ely substituted into the A sites, and not the B sites 7]. Fe3O4 possesses a cubic inverse spinel ferrite struc- h Fe cations occupy the tetrahedral (A) and octahedral e explanation for the observed ferrimagnetism in Fe3O4 ouble exchange interaction through Fe2+ and Fe3+ ions 3 4 Fe0.90M Fe0.85M Fe0.90C Fe0.85C in the n it is co of Mn at the netwo Fig. Fe1−xM peaks c tion pa cubic Fe3O4 increas is sma of Cu2 Fe1−xC tion pe than th due to [30]. The Fe1−xM condit where Debye of line  is th Fe3O4, the lat Tab was bi with t sample tion b sample of 0.1 a Fig. Fe0.90M erationite, while the (A) site magnetic ions form antiferro- teractions with (B) site Fe ions. To minimize oxidation, elements with concentrations below 0.15 were doped rial to reduce the oxidized possibility of Fe2+ to Fe3+ 7]. of high Cu concentration from 0.17 to 0.35, the Cu 4 films were prepared by sputtering method [27], it was at the saturation magnetization increases with increas- ng concentration. This behavior is expected due to the agnetic anisotropy and modifications in microstructure d films with increasing Cu doping concentration. It has usly suggested that Cu2+ ions can occupy both tetra- octahedral sites in the spinel structure. If a Cu2+ ion the tetrahedral site, the structural formula changes in that the number of Fe3+ ions at the octahedral sites t the cost of same ions on the tetrahedral sites. The f spins on the two sublattices will result in an increase calculated terns are q synthesize and Fe1−xM 3.2.2. Magn The ma doped Fe3O perature. T (Fig. 5) and paramagne Fe3O4 at in from 0.0 t from 65.9 e reduced fro ples. Oppos to 0.35 [27]14.49 8.3760 Fe2O4 14.09 8.3825 Fe2O4 14.08 8.3802 e2O4 12.37 8.3688 e2O4 11.78 8.3601 agnetization [27]. For case of Mn doping from 0.1 to 0.5, red that a changing magnetization and low resistivity d Fe3O4 were realized by the substitution of Mn2+ ions es without effect to the conduction path of the Fe ion the B sites [26]. showed the XRD pattern of Fe1−xCuxFe2O4 and 2O4 (x = 0, 0.10, 0.15) samples in which diffraction ide with the standard spectrum in the Roentgen diffrac- n. Therefore, these samples are single-phase with the ture of centered face. The XRD curves for Cu doped ed the increase of diffraction peaks when Cu content his increment is because the Cu2+ atomic radii (73 pm) han that of Fe2+ (78 pm) [29], and thus the substitution s for Fe2+ leads to the reduction of lattice constant in 2O4 samples (in Table 1). On the contrary, the diffrac- tensity of Fe1−xMnxFe2O4 samples seems to be smaller Fe3O4, but the diffraction peaks seems to be un-shifted atomic radii of Mn2+ is approximate to that of Fe2+ ion tice constant of the Fe3O4, Fe1−xCuxFe2O4 and 2O4 samples were calculated from the Bragg diffraction 2dsin = n by the equation: a = dhkl √ h2 + k2 + l2; h k l is the distance between the lattice planes. Using the errer formula D = 0.9/ ˇ cos  (here,  is the wavelength ˛ (1.5416 A˚); ˇ is the full width at haft maximum and fraction angle) the particle sizes were calculated for xCuxFe2O4 and Fe1−xMnxFe2O4 samples. The values of onstant and particle size were present in Table 1. hows that the particle size (14.49 nm) of Fe3O4 sample . The particle sizes of Cu doped Fe3O4 samples decreased crease of Cu content (12.37 nm and 11.78 nm for the th Cu content of 0.1 and 0.15, respectively). This reduc- ior is stronger than those observed Mn doped Fe3O4 .09 nm and 14.08 nm for the samples with Mn content .15, respectively). resented the TEM image of Fe3O4 and SEM image of 0Fe2O4 sample. TEM images (Fig. 4a) shows the agglom- articles with their size about 9.4–18.1 nm. Thus, the results of particle size from Roentgen diffraction pat- uite consistent with the TEM image. Hence, we could the single-phase and nanometer-scaled Fe1−xCuxFe2O4 nxFe2O4 samples using the chemical method. etic moment of Mn, Cu doped Fe3O4 gnetic properties of Fe3O4, Cu doped Fe3O4 and Mn 4 materials were measured by VSM at room tem- he magnetization curves of Fe3O4, Cu doped Fe3O4 Mn doped Fe3O4 samples (Fig. 6) expressed the super- tic properties with Hc value of about 3 Oe (sample set of Fig. 5). With the increase of x concentration o 0.15, the saturation magnetic moments decreased mu/g to 53.2 emu/g for Fe1−xCuxFe2O4 samples and m 65.9 emu/g to 61.5 emu/g for Fe1−xMnxFe2O4 sam- ite to this, in case of high Cu concentration from 0.17 , the saturation magnetization of Cu doped Fe3O4 films T.M. Thi et al. / Applied Surface Science 340 (2015) 166–172 169 Fig. 4. (a) T increases w ions can occ structure. T anisotropy with increa for these do lic cations w a spinel str B suffixes h tively, and x Thus, for x and for 0 < of XRD ana doping of lo be attribute structure [1 Fighe TEM image of Fe3O4. (b) The SEM image of Fe0.90Mn0.10 Fe2O4. ith increasing Cu doping concentration because Cu2+ upy both tetrahedral and octahedral sites in the spinel his behavior is attributed to the increased magnetic and modifications in microstructure of the doped films sing Cu doping concentration [27]. The empiric formula ped compounds is MY2O4 where M and Y are metal- ith different oxidation state. The general formula for ucture is [ M2+1−x Y 3+ x ] A [ M2+x Y 2+ 1−x Y 3+] B O4 where A and old for the tetrahedral and octahedral sites, respec- is a parameter usually ascribed to the inversion grade. = 0 the spinel is termed as normal, for x = 1 inverse x < 1 mixed spinel [17,18,27]. Thus, from the results lyses and above decrease of magnetic moment, the w concentration of Mn2+ and Cu2+ (x = 0.10, 0.15) can d by their substitution for Fe2+ at (A) sites in spinel 7,26]. Fig 3.3. Investi Fe1−xMnxFe 3.3.1. Inves arsenic adso In order doped Fe3O carried out surement, t fixed at 106 WHO). Each putted into 0.6, 0.8, 1.0 the mixtur these adsor tions befor absorption magnetic n reduce arse Figs. 7 a concentrati trations aft the arsenic 0.01 mg/L) the 1.6 g/L . 5. The magnetic moment of Cu doped Fe3O4 materials.. 6. The magnetic moment of Mn doped Fe3O4 materials. gation of arsenic adsorption of Fe1−xCuxFe2O4 and 2O4 nanoparticles tigation of the effects of the Mn, Cu doping on the rption to evaluate the arsenic adsorption capacity of Mn, Cu 4 nanoparticles, all the adsorption experiments were at room temperature of 25 ◦C and pH = 7. For each mea- he concentration of the original As (III) solution was ppb (10 times higher than the permitted level by the adsorbent of Fe1−xMnxFe2O4 and Fe1−xCuxFe2O4 were the original arsenic solution with concentrations of , 1.2, 1.4, 1.6, 1.8, 2.0 and 2.2 g/L, respectively. Then e solutions were stirred for 20 min for all samples. In ption isotherms, the arsenic concentrations in the solu- e and after adsorption were measured by the atomic spectroscope. The Fe1−xMnxFe2O