One-pot synthesis of S-doped Fe2O3/C magnetic nanocomposite as an adsorbent for anionic dye removal: equilibrium and kinetic studies
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Novel S-doped Fe2O3/C nanocomposite was synthesized via a one-pot hydrothermal method and was used for the first time as an efficient adsorbent for Congo red dye (CR) removal from water solution. The obtained catalyst was characterized by various methods including Fourier transform infrared spectroscopy, energy dispersive X-ray spectrometry, vibration sample magnetometry, X-ray diffraction and field emission scanning electron microscopy. To improve the adsorption performance, some important parameters affecting dye removal were optimized such as adsorbent dosage, contact time, solution pH, initial dye concentration and ionic strength. At the optimum conditions, the maximum capacity of adsorption for this nanocomposite was 270.2 mg g−1, which is better than other magnetic adsorbents for CR removal. The results of adsorption isotherm were matched with Langmuir model. Kinetic tests show that adsorption experimental data were best fitted by pseudo-first-order model.
KeywordsS-doped Fe2O3/C nanocomposite Congo red Adsorption Magnetic separation Kinetic study
Organic dyes are natural or synthetic compounds which have been widely applied in a number of processing industries such as leather, textile, cosmetics, packaging, food, and paper industries [1, 2]. There are more than 100,000 commercial dyes with an annual production of over 7 × 105 tons year−1 . The extensive application of dyes in industries brings about big amount of toxic dyes and pigments waste discharging to the environment, which subsequently causes serious environmental problems and threat to human’s health [4, 5]. The presence of organic dyes even in low concentrations has irreversible effects on human health from skin irritation, Heinz body formation, gastritis and tissue necrosis to the worst result of cancer . Therefore, removing dye pollutants from the environment is an important and necessary task.
A number of methods have been reported to remove the dye pollutions from water, for example, filtration by membrane and nanomaterials, coagulation, photocatalytic decomposition, aerobic and anaerobic microbial degradation, flocculation, advanced oxidation processes and treatment with ozone [11, 12]. Among these methods, adsorption is the most convenient and promising strategy due to the easy operation, high efficiency, low energy requirement, and easy recovery or reuse of the adsorbent [10, 13]. Compared to other adsorbents for dye removal, magnetic materials possessed many advantages such as chemical stability, nontoxic synthesis, environmentally friendly, low cost and facile separation from the water solution [14, 15].
Fe2O3 magnetic particles are frequently used as one of the suitable materials to remove the pollutants from environment For example, γ-Fe2O3 synthesized by metal etching approach was applied for the adsorption removal of methylene blue dye . Activated carbon/α-Fe2O3 nanocomposite was prepared by simple pyrolysis route and utilized to degrade the acid yellow 17 dye from water . In another work, S-doped α-Fe2O3 (α-Fe2O3/s) was synthesized with ferrous sulfate and Na2S2O3 via a hybrid hydrothermal–calcination treatment for the photogeneration of acid orange 7 and phenol . Similarly, γ-Fe2O3 and Fe3O4 nanoparticles loading on activated carbon were fabricated for the removal of cationic dye [19, 20] and Alizarin Red S . Mesoporous carbon nanocomposite was synthesized via a facile impregnation–carbonization method for dye and heavy metal adsorption , and other carbon derivatives (carbon nanotubes and graphene) for heavy metal removal [23, 24]. In previous studies, Dutta and coworkers used γ-Fe2O3 nanoparticles for photodegradation of methylene blue and rose Bengal dye . Wang et al.  used hydroxylated α-Fe2O3 for synergistic photocatalysis of Cr(VI) reduction and 4-chlorophenol degradation under visible light irradiation. Other reports about Fe2O3 magnetic composites for organic pollutant removal can be found in [27, 28, 29, 30, 31].
In this study, new magnetic nanocomposite S-doped Fe2O3/C was synthesized through a one-pot hydrothermal method. The preparation method was optimized by modifying several synthesis conditions and the physicochemical properties of prepared S-doped Fe2O3/C were studied by means of characterization methods. The synthesized S-doped Fe2O3/C was applied as an adsorbent for the first time for the removal of CR dye from water.
Cellulose powder, thiourea, FeCl3·6H2O, FeCl2·4H2O, NaOH, HCl, and CR were purchased from Merck. All chemicals were of analytical grade applied without further purification. Deionized (DI) water was used to prepare all solutions.
Synthesis of S-doped Fe2O3/C nanocomposites
The typical preparation procedure of S-doped Fe2O3/C was depicted as follows: 8 g NaOH and 1.2 g cellulose powder were dissolved in 80 mL DI water. The mixture was stirred for 3 h at room temperature and aged at − 15 °C for 12 h. After that, the mixture was stirred vigorously by a magnet stirrer at room temperature for 2 h to dissolve cellulose. 0.28 g FeCl3·6H2O and 0.15 g FeCl2·4H2O were then added to the solution simultaneously and stirred for 2 h. Afterward, 1 g thiourea was added to the mixture and stirred for a few minutes before transferring the mixture to a Teflon sealed autoclave at 160 °C for 10 h. After cooling to room temperature, S-doped Fe2O3/C nanocomposite was collected by a magnet and washed for several times with DI water and diluted HCl. The product was finally obtained after drying in a vacuum oven at 60 °C for 12 h.
The properties of the S-doped Fe2O3/C nanocomposite were determined by different techniques. Morphology of adsorbent was studied by FE-SEM model of TESCAN, Mira III LMU, the Czech Republic at 15 kV. FT-IR analysis was conducted by Shimadzu FTIR 8400S spectrophotometer (Japan). Field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FE-SEM/EDS, TESCAN, Mira II LMU, Czech Republic) was used for the elemental analysis. XRD pattern was obtained in 2θ between 10 and 80° with a Philips-pw 1800 diffractometer, which was equipped with Cu-Kα irradiation (λ = 0.1524 nm) source. Magnetic property was measured by VSM analysis (Lake Shore 7410, USA). UV–Vis spectra were obtained with a Shimadzu UV–Visible Spectrophotometer model UV-mini 1240 (Japan).
Results and discussion
FE-SEM images and EDS elemental analysis of S-doped Fe2O3/C nanocomposite
CR dye removal studies
Effect of adsorbent dosage
Effect of solution pH on CR dye adsorption
Effect of shaking time
Effect of initial dye concentration
Influence of ionic strength on adsorption efficiency
Adsorption isotherm constants for adsorption of CR on S-doped Fe2O3/C
Dye adsorption kinetic study
In this equation k 1 (min−1) is the rate constant for pseudo-first (Lagergren) order, q t (mg g−1) and q e (mg g−1) are adsorption capacities at time t (min) and the equilibrium condition, respectively. The values of the constants k 1 and q e were obtained from the linear plot of ln (q e–q t ) vs. t.
Comparison of q max for different magnetic adsorbents for removal of CR
q max (mg g−1)
CTAB-coated Fe3O4 NPs
Fe3O4/MgAl-layered double hydroxide composite
Silica coated Fe3O4 magnetic nanospheres
In summary, a novel adsorbent magnetically separable S-doped Fe2O3/C nanocomposite was prepared by a simple one-pot hydrothermal method. Nanocomposite properties were determined by FE-SEM, XRD, FT-IR, EDS and VSM methods and the removal performance of the CR dye from water solution was determined on the obtained materials. The effect of important parameters on dye removal performance including initial solution pH, adsorbent dosage, shaking time, initial dye concentration with ionic strength was optimized. The adsorption data were fitted well with the Langmuir isotherm and the kinetic results were well matched with the pseudo-first-order model. Owing to the low cost, ease of preparation and high adsorption capacity, the investigated magnetic nanocomposite can be a suitable adsorbent for anionic dye removal.
The authors gratefully acknowledge the Iran University of Science and Technology for supporting this research.
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