Purification of Water by Ferrites - Mini Review - ACS Publications

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Purification of Water by Ferrites - Mini Review Vijayendra K. Garg,1,* Virender K Sharma,2 and Erno Kuzmann3 1Institute

of Physics, University of Brasília, 70919-970 Brasília, DF, Brazil of Environmental and Occupational Health, School of Public Health, Texas A&M University, College Station, 77843 Texas, United States 3Institute of Chemistry, Eötvös Loránd University, Pázmány Péter sétány, Budapest, H-1117, Hungary *E-mail: [email protected] 2Department

Ferrites are usually non-conductive ferrimagnetic ceramic compounds. A ferrimagnetic property of ferrites is derived from iron oxides (e.g., hematite (α-Fe2O3) and magnetite (Fe3O4)) and from oxides of other metals. Ferrites are hard and brittle, similar to most of the ceramics. Ferrites have remarkable physical properties and high chemical stability, which resulted in many applications in various fields. This chapter presents applications of ferrites in remediating water contaminated with heavy metals. Ferrites as photocatalysts to degrade organic contaminants are also presented.

Introduction Cubic spinel ferrites are designated as A[B2]O4 in which A is tetrahedral site with O4 coordination and B is octahedral site with O6 coordination (Figure 1). The square bracket around B defines that the site is present in the actual formulae. The octahedral site dominates the tetrahedral site by a ratio of 2:1.

© 2016 American Chemical Society Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 1. Structure of cubic spinel ferrites There are different terms used to define magnetism (Figure 2). Ferromagnetism refers to the moments that moments of individual atoms are aligned to the same direction (↑ ↑ ↑ ↑ ↑ ↑) (Figure 2b) while antiferromagentism does to moments that moments of alternating atom align to the opposite directions (↑ ↓ ↑ ↓ ↑ ↓). At ferrimagnetism unequal parallel moments of alternating atoms align to the opposite directions (↑↓ ↑↓↑↓↑) (Figure 2c). In the case of paramagnetism the atomic moments are not occupied parallel or antiparallel without applied magnetic field (Figure 2a). In the case of diamagnetism, no long ranger order and alignment are in the opposite field. From the magnetism point of interest, the cations occupying tetrahedral sites have their magnetic moments oppositely oriented with respect to the cations on octahedral sites. Ferrites, e.g. magnetite can show ferrimagnetic character, since the net magnetic moment of the A sublattice is directed to antiparallel to the net magnetic moment of the B sublattice, which may be useful in several applications including purification of water.

Synthesis of Ferrites Approaches to synthesis of ferrites include the thermal methods, the sol–gel and citrate based methods, co-precipitation, and solid-state reactions. A summary of these methods is given elsewhere (1). Different techniques are applied to characterize ferrites are X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning-electron microscopy (SEM), and transmission electron microscopy (TEM). Ferrites are used in electrical and electronic devises. Ferrites nanoparticles may have, ferrites may have superparamagnetic properties and are used in magnetic data storage, magnetic imaging, drug delivery, and microwave devices. Recent examples are of nanoferrites applications include gas sensing. The present chapter gives a few examples of the use of ferrites in remediation of water contaminated with metals and organics. 138 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 2. Simple schematic arrangements of magnetic moments of cubic spinel ferrites. (a) paramagnetic where all moments order randomly, (b) ferromagnetic when all moments are aligned parallel in one direction, (c) antiferromagnetic where the magnetic moments composed from two ferromagnetic sublattices aligned antiparallel are exactly equal and the net moment is zero and (d) ferrimagnetic where the magnetic moments composed from two ferromagnetic sublattices aligned antiparallel are not equal and result in a nonzero net moment.

Removal of Metals Harmful environment contributes very significantly to cause serious health problems. Continuous consumption of metal- contaminated water may be responsible for chronic diseases such as renal failure, liver cirrhosis, hair loss, and chronic anemia. These diseases are apparently related to presence of heavy metals in water (e.g., lead, cadmium, copper, molybdenum, nickel, and chromium). Industrial wastes and agriculture activities released hazardous and toxic materials to the source water (i.e., groundwater) and thereby led to the contamination of drinking water. In the literature, many approaches have been taken to remove metals in water. Hegazi (2) showed that low cost adsorbents like rice husk can be effectively used for removing metals. Ju-Nam et al. (3) reported environmental applications of ferrite nanoparticles on river-natural organic matters. Sen (4) have discussed advanced and emerging technologies for removing heavy metals from waste and contaminated sites. Separation processes are critical for meeting regulations of priority pollutants, especially arsenic, mercury, and lead. Apart from explaining the chemistry of heavy metals and their transport in various media, the task of water purification offers a comprehensive analysis of strategies for separating 139 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


metals from groundwater, wastewater, contaminated soils, and industrial sludge. Both the fundamentals and the applications of the preparation and characterization techniques have been discussed for the current problems of water purification and for potential applications of environmental resource reuse. These include ion-exchange, specialized sorbents, novel membranes, advanced precipitates, and electro-kinetic processes. This section summarizes the applications of metal ferrites to remove heavy metals in water. Wassana et al. (5) reported studies on retrieval of heavy metals from water by magnetic ferrites. DingMing (6) reported removal of heavy metals from waste water by meso ferrite. Hu et al. (7) performed a comparative study of various magnetic nanoparticles for removing Cr(VI). MnFe2O4 was the most efficient magnetic adsorbent for the rapid removal of Cr(VI). However, Hu at al. (7) found that the MnFe2O4 had the lowest recovery efficiency compared to other ferrites. Song et al. (8) examined removal of Cr(VI) and Ni(II) by the ferrite process. In the ferrite process, the heavy metal ions are incorporated into the lattice of ferrites during the formation of spinel structure by the oxidation of the Fe(II) ions. Nojiri et al. (9) studied electrolytic ferrite formation system for removing heavy metals. Yang et al. (10) investigated the removal of heavy metals and dyes by applying nano zero-valent iron supported-barium ferrite microfibers. Tu et al. (11) reported a multi-staged ferrite process to treat wastewater containing Cd, Cu, Pb, Cr, Zn, Ag, Hg, Ni, Sn and Mn Demirel et al. (12) studied removal of Cu, Ni and Zn from wastewaters by the ferrite process. Qdais and Moussa (13) carried a comparative study of membrane processes for removing heavy metals from wastewater. Mikhailovsky (14) studied and found that the ferrite treatment was one of the most promising techniques to remove impurities from water and wastewater. Studies were performed at plants, for treating electroplating wastewater based on the ferrite technique, with capacities from 1 to 8 m3/h using surface waters from different industrial sites. In recent years, potassium ferrite (KFeO2) was synthesized (15) by a new simple thermal process from natural waste ferrihydrite and KNO3 precursors. The synthesized KFeO2 showed considerable instability when it was in contact with water and CO2 of the humid air. The decomposition of KFeO2 followed first-order kinetics with rate constants as 0.93 × 10–1h–1 and 1.86 × 10–1 h–1 at a relative humidity of 30–35% and 65–70%, respectively. The products of decomposition were crystalline KHCO3 and nanocrystalline iron(III) oxides in the molar ratio of 2:1. The products were characterized in detail by X-ray powder diffraction, lowtemperature and in-field 57Fe Mössbauer spectroscopy, magnetization (SQUID) measurements, thermal analysis, and TEM and SEM. Washing and subsequent air drying of the decomposed products of KFeO2 yielded monodisperse superparamagnetic maghemite (γ-Fe2O3) nanoparticles, which turned out to be efficient as magnetic sorbents for removing Cu2+ in water. A direct addition of solid KFeO2 to water containing Cu2+ yielded rapid coagulation of iron(III) oxyhydroxides, which subsequently removed Cu2+ more efficiently compared to its sorption on the pre-formed maghemite nanoparticles nanoparticles, as have been observed by Machala et al. (15) An effective removal of Cr(IV) was also achieved by MgFe2O4 nanoparticles loaded on activated charcoal and in the case of water purification by Kaur and coworkers (16–18). 140 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Remediation of Organics Sharma et al. (1, 15, 19, 20) have extensively studied the purification of water and have reported a series of publications on the waste water purification. The review on the synthesis and photo catalytic activity of ferrites under visible light, presenting the use of ferrites in photo catalytic conversion of visible solar energy to generate e-/h+, which in turn produce reactive oxygen species through redox processes, for the degradation of the contaminants. Spinel ferrites have a relatively narrow band gap (2.0 eV) making them capable of such processes (2). Ferrites have been applied as photocatalysts alone, in composites with other photocatalysts for bacteria and dyes, as well as with other oxidants such as H2O2. Ferrites are effective in each case, however when used as composite photo catalysts their degradation efficiencies are enhanced. Combination of ferrites with H2O2 either under light irradiation or dark conditions creates a Fenton-type system, which produces hydroxyl radicals to enhance the degradation processes (Figure 3). Examples of the applications of ferrites for the degradation and/or adsorption of a number of different contaminants for environmental purification including inorganics, bacteria, and large organic molecules such as dyes were discussed by Sharma et al. (1)

Figure 3. Hypothetical scheme for the generation of •OH radical in H2O2–ZnFe2O4–visible light system. (Reproduced with permission from reference (19). Copyright 2012 Elsevier.) An example of the photocatalytic activity of ferrite is shown for the meso-zinc ferrite (meso-ZnFe2O4) (20). A hydrothermal process was applied to synthesize meso-ZnFe2O4. Significantly, a cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), played an important role in synthesizing meso-ZnFe2O4. Initially, nanoparticles with size of 5–10 nm are formed and agglomerate to yield meso-ZnFe2O4. Various analytical and surface techniques have been applied to 141 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


fully characterize meso-ZnFe2O4, which include energy dispersive spectroscopy, (XRD), Brunauer–Emmett–Teller (BET) surface area, SEM, TEM, and diffuse reflectance spectra (DRS). Significantly, the synthesized meso-ZnFe2O4 had a phtocatalytical activity under visible light (> 400 nm). This was shown for the degradation of Acid Orange II (AOII). The hypothesized scheme that causes the degradation of AOII is presented in Figure 3. Basically, the highly reactive species, hydroxyl radical (•OH) is produced by possibly three processes (A, B, and C, in Figure 3). The process A is the Fenton reaction, which was initiated by Fe(III) on the surface of meso-ZnFe2O4. The process B belongs to the generation of •OH through holes. Holes are produced when the light is irradiated on the surface of meso-ZnFe2O4. The other species, produced during the photocatalytic activation of meso-ZnFe2O4, is electron that reacted with H2O2 to give •OH (process C). The photo catalytic degradation of AOII was almost complete within 2 h in H2O2/visible light system. More details are given elsewhere (19). Numerous experiments were performed to demonstrate that the formation of •OH in the system presented in Figure 3. A parent molecule, AOII, degraded to several intermediates, identified by liquid chromatography-mass spectrometry (LC/MS) technique. These intermediate are finally oxidized by •OH. A repeated batch studies on the degradation of AOII indicated that a high effectiveness of meso-ZnFe2O4.

Conclusions Properties of ferrites and their characterization using analytical techniques are summarized. Ferrites are suitable to remove metals and organics in water. Ferrites have shown potential to treat water contaminated with Cd, Cu, Pb, Cr, Zn, Ag, Hg, Ni, Sn and Mn. Ferrites have demonstrated their capability to treat organics in water. Ferrites have ability to be photocatalysts in order to degrade pollutants like dye in water.

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Purification of Water by Ferrites - Mini Review - ACS Publications

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