3. Magnetic materials for water treatment

There has been increased interest in using magnetic materials in water treatment which are basically composed of magnetic core of iron oxides organic compounds, carbon materials, etc. Recently, nanomaterials in different shapes, morphologies, forms, e.g., metal-containing nanoparticles, carbonaceous nanomaterials, zeolites, dendrimers, carbon nanotubes, nanofibers have been used for water purification [20]. However, the difficulty arises in using these materials is the separation of solid materials from liquid and which is more difficult as the particle size decreases in nanoscale. On the other hand, the using of magnetic, particularly the magnetic nanoparticles (MNPs) materials have the advantage of magnetic filtration in separation of solid from liquid and are more efficient [21].

However solid/liquid (S/L) separation is more difficult as the particle size decreases. On the other side, in case of magnetic sorbents based on Fe oxides, the magnetic filtration may be applied for S/L separation. Furthermore, the removal of particles from solution with the use of magnetic fields is more selective and efficient (and often much faster) than centrifugation or filtration (Yauvuz et al.) [21]. Here are the advantages of using MNPs adsorbent for water treatment processes:


## 3.1. Different types of magnetic materials for water treatment

Different types of magnetic materials have been synthesized and designed for development of advanced materials and applied effectively in widespread uses such as biomedicine, magnetic resonance imaging (MRI), catalysis, spintronics, robotics, engineering, environmental remediation, etc. [22] There are different synthesizing methods viz. co-precipitation, solvothermal, hydrothermal, microemulsion, sonochemical, etc. which determine their particle size, distribution, morphology, surface functionality, and magnetic properties and in turn of their various application [22]. Magnetic materials are made from mixtures of metals of iron, cobalt, nickel, and alloys and their oxides (of the type MFe2O4, where M is a metal). Out of these materials, iron (zero valent iron) and its oxides, i.e., usually γ-Fe2O3 (maghemite) and Fe3O4 (magnetite) nanoparticles have attained significant interest in recent years and have been used for water treatment processes. The various composite magnetic materials such as Fe3O4@C [23, 24], Fe@SiO2 [25], Fe3O4@TiO2 [26], Fe3O4@PPO (poly(propylene oxide)), PEO (poly(ethylene oxide) [27], Fe3O4@PDA (polydopamine) [28], Fe3O4@PNIPAM (poly(N-isopropylacrylamide)) [29], Fe3O4@MIPs (molecularly imprinted polymer-encapsulated particles) [30], Fe3O4@CNTs (multiwalled carbon nanotubes) [31], Fe@CS (carbon spheres) [32], Fe/iron oxide-oxyhydroxide/rGO (grapheme) [33], etc. have been used for environmental applications. Singh and his co-workers synthesized a series of magnetic nanocomposites such as CoFe2O4–ZnS [34], Fe3O4@GTPs (green tea polyphenols) [35], Fe3O4–Cr2O3 [36], CoFe2O4-Cr2O3-SiO2 [37] and applied for wastewater treatment.

of Cu(II), Co(II), and Ni(II) ions [43]. The magnetic hydrogels based on 2-acrylamine-2-methyl-1-propansulfonic acid can be used for removal of many heavy metal ions such Cd(II), Co(II), Fe (II), Pb(II), Ni(II), Cu(II) and Cr(III) from water in repeated cycles [44]. The Cu(II) can also be effectively removed by functionalized mesostructured silica containing magnetite [45]. The acrylate-based polymer composites with magnetite can be used in selective removal of heavy metals from water (selectivity: Cu > Cr > Zn > Ni) [46]. Layered double hydroxide (LDH) prepared from Fe3+ and Ni2+ shows good adsorption of As and subsequent magnetic separation [47]. The magnetic zeolite composites are used for decontamination of heavy metals from water [48]. The composite materials of mesoporous magnetic MCM-41 with aminopropyls are

Study on Magnetic Materials for Removal of Water Pollutants

http://dx.doi.org/10.5772/intechopen.75700

67

Magnetic nanoparticles are used as an adsorbent for the removal of various dyes and dyes stuff from aqueous solution. Removal of dyes from waste water has become a serious issue of concern because of its harmful impact on human. Dyes basically can be classified in to two

Long et al. [50] synthesized Fe3O4@catechol/polyethylenimine (PEI) nanoparticles and tested for adsorption of three different kind of anionic dyes, i.e., methyl blue, orange G and amaranth and found the maximum adsorption capacities of 344.8, 192.3 and 146.2 mg/g, respectively. Saksornchai et al. [51] synthesized magnetite (Fe3O4) coated with cetyltrimethylammonium bromide (CTAB) and tested for the adsorption of anionic dye Congo red (CR) removal. They found maximum adsorption capacity for CR dye to be 93.46 mg/g. Faraji et al. [52] synthesized triazine-based nitrogen-rich network-modified magnetic nanoparticles were synthesized for the adsorption of methyl orange. Sahraei et al. [53] reported the synthesis of magnetic bio-sorbent hydrogel beads based on modified gum tragacanth/graphene oxide for the removal of heavy metals and dyes from water. They found the adsorption capacity of 101.7 mg/g for Congo red dye. Ge et al. [54] fabricated Fe@MgO magnetic nanocomposites for the removal of heavy metal ions and dye from water. They found that the synthesized nanocomposite showed excellent adsorption capacity of 6947.9 mg/g for methylene orange. Wu et al. [55] fabricated multifunctional magnetic nanoparticle core covered with polyethylenimine (PEI) derived quaternary ammonium compounds (QAC) corona through electrostatic attraction for the removal of dyes and metal ion adsorption. The adsorption results corresponding to synthesized nanoparticle showed the maximum adsorption capacity of 653 mg/g for AF as a representative of dyes. Konicki et al. [56] synthesized Fe@graphite core shell nanocomposite for the removal of anionic dyes from aqueous solution. The synthesized nanoparticles were tested for the adsorption of two anionic dyes namely acid red 88 (AR88) and direct orange 26 (DO26) and the maximum adsorption capacity was found to be 63.7 mg/g and 42.7 for AR88 and DO26, respectively. Zhang et al. [57] synthesized the Fe3O4 nanoparticle modified with 3-glycidoxypropyltrimethoxysilane (GPTMS) and poly-lysine (P-Lys). They found that the synthesized MNPs could effectively remove anionic dyes including methyl blue (MB), orange I (OR-I), amaranth (AM) and acid red

used for selective removal of As(V), and Cr(VI) in presence of Cu(II) [49].

3.2.2. MNPs for removal of organic contaminants

categories, i.e., anionic dyes and cationic dyes.

3.2.3. MNPs for the removal of anionic dyes

18 (AR-18) from water solution.

In addition to their suitable magnetic properties, i.e., ferrimagnetic, ferromagnetic and superparamagnetic (nanoparticle size less than 10 nm), their synthesis procedure is simple and costeffective and they can be easily functionalized as desired for many applications. The size and shape and magnetism of these magnetic materials can be easily controlled based on their application and thus they can be easily dispersed in liquid medium and their stability can be retained for multiple uses. Moreover, these materials are non-toxic or less toxic, chemically inert, thermally stable as well as biocompatible.

#### 3.2. Use of magnetic materials for clean water technology

Appearance of water pollution as a global threat demands the development of low-cost and reliable materials for effective waste water remediation. The magnetic materials have been used for clean water technology for both in laboratory as well as field scale [38, 39]. In recent years, iron oxide nanomaterials have been used as adsorbent or immobilizing agent and photocatalyst or the both depending on nature of contaminants in water [40].

#### 3.2.1. MNPs for the removal of metals

Heavy metal contamination in water such as cadmium, zinc, lead, chromium, nickel, copper, vanadium, platinum, silver and titanium due to industrial activities is significantly increasing which is detrimental to human beings and animals. Magnetic nanomaterial adsorbents have been potentially used for removal of metallic ions such as Cr(VI), Cu(II), Co(II),Cd(II), As(V), As(III) and Hg(II) in water [41, 42] which are more effective as compared to micron size particles. The magnetic chelating resin based materials have been used for effective removal

of Cu(II), Co(II), and Ni(II) ions [43]. The magnetic hydrogels based on 2-acrylamine-2-methyl-1-propansulfonic acid can be used for removal of many heavy metal ions such Cd(II), Co(II), Fe (II), Pb(II), Ni(II), Cu(II) and Cr(III) from water in repeated cycles [44]. The Cu(II) can also be effectively removed by functionalized mesostructured silica containing magnetite [45]. The acrylate-based polymer composites with magnetite can be used in selective removal of heavy metals from water (selectivity: Cu > Cr > Zn > Ni) [46]. Layered double hydroxide (LDH) prepared from Fe3+ and Ni2+ shows good adsorption of As and subsequent magnetic separation [47]. The magnetic zeolite composites are used for decontamination of heavy metals from water [48]. The composite materials of mesoporous magnetic MCM-41 with aminopropyls are used for selective removal of As(V), and Cr(VI) in presence of Cu(II) [49].
