Large-scale production of Fe3O4 nanopowder using ferrous ions in a rotating packed bed with precipitation
Graphical abstract
Introduction
Over the past few years, Fe3O4 nanopowder has received increasing interest on account of its excellent physical and chemical properties [1,2]. Fe3O4 nanopowder is superparamagnetic when its particle size is lower than 15 nm [3]. It exhibits large saturation magnetization, good magnetic susceptibility, biocompatibility, chemical stability, and innocuousness [4]. Therefore, Fe3O4 nanopowder is widely used in the biomedical field, for targeted drug delivery [1], [2], [3], [4], magnetic resonance imaging [1], [2], [3], [4], hyperthermia [1], [2], [3], [4], biosensing [1,2,4], and tissue engineering [1,2]. In recent years, Fe3O4 nanopowder has been extensively utilized as an efficient adsorbent in the treatment of water [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], since it not only has a high adsorption capacity due to its large specific surface area but also outstanding reusability due to its prominent magnetic property [14,16]. Practical applications of Fe3O4 nanopowder depend on its average particle size, particle size distribution, shape, surface chemistry, and magnetic property [[17], [18]]. To control these characteristics, attention must be paid to its method and parameters of production [[17], [18]].
Among diverse methods for producing Fe3O4 nanopowder [1], [2], [3], [4], the controlled co-precipitation of ferrous and ferric ions with a stoichiometric molar ratio of 1:2 under alkaline conditions is the most common and simplest since Fe3O4 contains both ferrous and ferric ions in this molar ratio [17]. As proposed elsewhere [17,18], one parameter that significantly affects the generation of the crystal structure of Fe3O4 nanopowder is the species of iron salts that are used in its production. Iida et al. [17] used ferrous chloride as the iron salt to produce Fe3O4 nanopowder in a batch process. They found that an FeCl2 concentration of 0.05 mol/L produced Fe3O4 nanopowder with an average particle size of 37 nm [17]. Suppiah and Hamid [18] used ferrous sulfate as the iron salt to produce Fe3O4 nanopowder in a batch process. They proposed that an FeSO4 concentration of 0.1 mol/L produced Fe3O4 nanopowder with an average particle size of 44.6 nm [18]. However, present methods for producing Fe3O4 nanopowder using Fe2+ are performed in a batch reactor [17,18], making its large-scale production difficult. Accordingly, a new method for the large-scale production of Fe3O4 nanopowder using Fe2+ must be developed.
As proposed in our earlier investigations [19], [20], [21], [22], the rotating packed bed (RPB) is favorable for the large-scale production of Fe3O4 nanopowder using ferrous and ferric ions, as described by Eq. (1). During the operation of the RPB, high-gravity conditions are obtained on account of its large centrifugal acceleration, and tiny droplets and thin films are therefore generated as the aqueous reactants break apart [19], [20], [21], [22]. Furthermore, the RPB has been confirmed to cause excellent micromixing [23]. Thus, the aqueous reactants in an RPB can undergo uniform supersaturation and homogeneous nucleation. Hence, the RPB can support a large-scale, high-productivity process (about 23 kg/day) for the production of Fe3O4 nanopowder with a mean diameter of 8.4 nm [22]. This process was performed at a production temperature of 25 °C, an aging temperature of 25 °C, an FeSO4 concentration of 0.15 mol/L, an FeCl3 concentration of 0.3 mol/L, an NaOH concentration of 1.2 mol/L, a rotational speed of 1800 rpm, a flow rate of aqueous FeSO4/FeCl3 of 0.5 L/min, and a flow rate of aqueous NaOH of 0.5 L/min [22].Fe2++2Fe3++8OH–→Fe3O4+4H2O
Very few studies of the large-scale production of Fe3O4 nanopowder using only Fe2+ in an RPB with precipitation have been published. Accordingly, the main aim of this study is to produce Fe3O4 nanopowder on a large scale using FeCl2 as the Fe2+ source and NaOH as the precipitating agent in the RPB. The characteristics and adsorption capacity of the Fe3O4 nanopowder thus produced are also examined.
Section snippets
Experimental
Fig. 1 displays the continuous operation of an RPB for the large-scale production of Fe3O4 nanopowder. The inner radius, outer radius, and axial length of the packed bed were 2.1 cm, 3.9 cm, and 2.2 cm, respectively [[19], [20], [21], [22]]. Thus, the radial length of the packed bed was 1.8 cm [[19], [20], [21]]. Wire mesh that was made of stainless steel formed the structured packings. The structured packings in the packed bed had a specific surface area of 790 m2/m3 and a voidage of 0.95 [[19]
Results and discussion
XRD analysis was performed to identify the produced black powder. The prominent peaks in the XRD pattern in Fig. 3 were those of the standard pattern of magnetite Fe3O4 (JCPDS 19–0629). Therefore, the produced black powder contained the Fe3O4 phase. The XRD peaks were distinct and sharp, showing the high crystallinity and homogeneity of the produced black powder. The absence of other characteristic peaks that correspond to other iron oxides, such as FeO, Fe2O3, and FeOOH, confirmed the high
Conclusions
Fe3O4 nanopowder was successfully produced on a large scale using ferrous chloride and precipitation in an RPB in which the FeCl2 concentration was 0.15 mol/L, the NaOH concentration was 0.3 mol/L, the rotational speed was 1800 rpm, the flow rates of aqueous FeCl2 and NaOH were 0.5 L/min, and the temperature was 25 °C. The Fe3O4 nanopowder that was produced in this manner exhibited a mean crystallite size of 28.4 nm, an average particle size of 34.5 nm, and a BET specific surface area of 32.5 m2
CRediT authorship contribution statement
Chia-Chang Lin: Conceptualization, Methodology, Validation, Resources, Writing – original draft, Writing – review & editing, Supervision, Project administration, Funding acquisition. Jun-Hong Lin: Methodology, Validation, Investigation, Writing – review & editing. Kuan-Yi Wu: Validation, Writing – review & editing, Funding acquisition. Yin-Ping Wu: Validation, Investigation.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors would like to thank the Ministry of Science and Technology of the Republic of China, Taiwan, for financially supporting this research (MOST 104–2628-E-182–001-MY3, MOST 107–2221-E-182–003).
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2023, Ceramics InternationalCitation Excerpt :The maximum adsorption capacity of nanostructured goethite for Reactive Red 2 was 29.1 mg/g, which was lower than that of Fe3O4 nanoparticles that were prepared using Fe2+ and Fe+3 in the rotating packed bed with the chemical co-precipitation approach [36]. However, the maximum adsorption capacity of nanostructured goethite for Orange G was 24.5 mg/g, which was higher than that Fe3O4 nanoparticles that were prepared using Fe2+ in the rotating packed bed with the chemical precipitation approach [37]. Nanostructured goethite that was prepared using Fe3+ in the rotating packed bed with the chemical precipitation approach exhibited a potential for removing dyes from water.