INTRODUCTION:

Nanoscience is one of the most important research and development frontiers in modern science. The use of nanoparticles [NPs] materials offers many advantages due to their unique size and physical properties[1]. Nanoparticle are submicron moieties [diameters ranging from 1 to 100 nm according to the used term, although there are examples of NPs several hundreds of nanometers in size] made of inorganic or organic materials, which have many novel properties compared with the bulk materials [2]. On this basis, magnetic NPs have many unique magnetic properties such as superparamagnetic, high coercivity, low Curie temperature, high magnetic susceptibility, etc.

Magnetic nanoparticles are attractive to many researchers because of their widespread applications in various areas of magnetic fluids, catalysis, biosciences biotechnology /biomedicine, magnetic resonance imaging, data storage, and environmental technology [3-11] Nanotechnology is an emerging science with wide applications in the remediation of environmental pollutants. In recent years, a great deal of attention has been focused on the synthesis and application of nanostructure materials as adsorbents or catalysts to remove toxic and harmful substances from water and air. The development of nanotechnology has been developed fastly in recent years. Nanosized magnetic particles possess high performance in the separation process due to the high specific surface area and the absence of internal diffusion resistance [12]. Nanosized magnetic iron oxide particles have a wide range of applications in ferrofluids, highdensity information storage, magnetic resonance imaging [MRI], biological cell labelling and sorting, separation of biochemicals, targeting, and drug delivery [13]. They can be easily recovered with an external magnetic field [14]. In recent years, many researchers and scientists has been interested in magnetic nanoparticles activated carbon. The main advantage of this technology consists in its capacity of treating large amount of wastewater within a short time and producing less contamination [15, 16]. Magnetic filtration is emerging as a water treatment technology, which can provide rapid, efficient contaminant removal from aqueous waste streams [17]. Inexpensive adsorbents could be developed that can bind to environmental contaminants and then be magnetically separated. Magnetic nanoparticles activated carbon adsorbents can easily be separated from a solution using a magnetic separator even if the solution contains a significant concentration of solids. In contrast, traditional adsorbents are removed by screening. Various magnetic adsorbents have been used to remove contaminants. These include magnetic ion exchange resins, magnetic solvent extracts, magnetic zeolites, magnetic activated carbon fibers, magnetic composites, magnetized Chitosan beads, magnetic nanoparticles, magnetic nanobowls, magnetic nanoparticles-impregnated tea waste, and magnetic polymer adsorbents. Magnetic nanoparticles activated carbons are not fully investigated, but some synthetic routes have been reported [18-25]. Recently, magnetic materials have gained special attention in water treatment [26-29], based on their advantage such as easy separation, simple manipulation process, kind operation conditions and easy specifically functional modifications. These unique properties in combination with appropriate magnetic activities can provide the basis of developing magnetic nanoparticles activated carbon. In this short review we will focus on some method for preparation of magnetic nanoparticles activated carbon, characterization and some application of magnetic nanoparticles activated carbon in biosciences, bioseparation, drug delivery hyperthermia catalysis and environmental applications.

Synthesis of Magnetic Nanoparticles Activated carbon:

In the last decades, much research has been developed to the synthesis of magnetic nanoparticles activated carbon, and many reports have described efficient synthesis approaches to produce the shape controlled, stable, biocompatible, and mono dispersed magnetic nanoparticles activated carbon. Magnetic nanoparticles Activated Carbon have been synthesized with a number of different compositions and phases, including iron oxides, such as Fe₃O₄ and g-Fe₂O₃, [30–32] pure metals, such as Fe and Co,[33-34] spinel-type ferromagnets, such as MgFe₂O₄, MnFe₂O₄, and CoFe₂O₄,[35-36] as well as alloys, such as CoPt3 and FePt [37-38]. The most common methods including co-precipitation, high temperature treatment method, encapsulation, thermal decomposition and hydrothermal synthesis. These routes can all be directed to the synthesis of high quality magnetic nanoparticles activated carbon. In addition, these NPs can also be prepared by the other methods such as electrochemical synthesis [39-40], laser pyrolysis techniques [41], microorganism [42, 43], sol gel process etc. However, the most common method for the production of magnetic nanoparticles activated carbon is the chemical coprecipitation technique of iron salts.[44–48] As one convenient and cheap method, chemical coprecipitation method has the potential to meet the increasing demand for the direct preparation of magnetic nanoparticles activated carbon. Developments of magnetic nanoparticles activated carbon are therefore a challenging area of research. Several chemical methods can be used to synthesize magnetic nanoparticles are as:

1. Chemical co-precipitation method

2. High temperature treatment method

3. Encapsulation

4. Thermal Decomposition

6. Hydrothermal Synthesis

Chemical co-precipitation method:

The co precipitation is probably the simplest and most efficient chemical pathway to obtain magnetic nanoparticles activated carbon. Iron oxides [either Fe₃O₄ or γ-Fe2O3] are usually prepared by an aging stoichiometric mixture of ferrous and ferric salts [Fe2+ / Fe3+] in the presence of activated carbon in followed by heating of the aqueous medium. This is done by addition of a base under inert atmosphere at room temperature or at elevated temperature. The chemical reaction of Fe₃O₄ formation may be written as eq 1.

Fe₂++2Fe₃++8OH------------- Fe₃O₄+4H₂O ..... [1]

The complete precipitation of Fe3O4 should be expected at a pH between 8 and 14, with a stoichiometric ratio of 2:1 [Fe₃⁺/Fe₂⁺] in a non-oxidizing oxygen environment [49-50]. However, magnetite [Fe₃O₄] is not very stable and is sensitive to oxidation. Magnetite is transformed into maghemite [γ-Fe₂O₃] in the presence of oxygen.

Fe₃O₄+2H+---------------γ-Fe₂O₃+Fe₂⁺+H₂O ...... [2]

Oxidation in air is not the only way to transform magnetite [Fe₃O₄] into maghemite [γ-Fe₂O₃]. Various electron or ion transfers depending upon the pH of the suspension are involved, according to eq 2. Under acidic and anaerobic conditions, surface Fe₂⁺ ions are desorbed as hexa-aqua complexes in solution, whereas, under basic conditions, the oxidation of magnetite involves the oxidation-reduction of the surface of magnetite. Magnetite nanoparticles [Fe₃O₄] are not very stable under ambient conditions, and are easily oxidized to be a maghemite or dissolved in an acidic medium. Since maghemite [γ-Fe₂O₃] is ferrimagnet, making its oxidation is the lesser problem. Therefore, magnetite particles can be subjected to deliberate oxidation to convert them into a maghemite [51]. A wide variety of factors can be adjusted in the synthesis of magnetic nanoparticles activated carbon to control size, magnetic characteristics, or surface properties. A number of studies have dealt with the influence of these different factors [52–58]. The size and shape and composition of the magnetic nanoparticles can be controlled with relative success by adjusting pH, ionic strength, temperature and nature of the salts [perchlorates, chlorides, sulfates, and nitrates], or the FeII/FeIII concentration ratio [59-60]. Particles with sizes ranging from 5 to 100 nm have been obtained using this method. The addition of chelating organic anions, such as carboxylate ions [e.g. citric, gluconic, or oleic acid] or polymer surface complexing agents [e.g. dextran, carboxydextran, starch, or polyvinyl alcohol] during the formation of magnetite can help to control the size of the nanoparticles [61]. The influence of different parameters like media composition, FeII/FeIII ratio, injection fluxes, iron, temperature, and oxygen on magnetic properties and size has been studied in a basic coprecipitation process [62].

The main advantage of the chemical coprecipitation process is that a large amount of magnetic nanoparticles activated carbon can be synthesized. Some examples of described procedures for conversion of activated carbon [charcoal] into their Magnetic derivatives using chemical coprecipitation method.

1] NaOH in the presence of charcoal, followed by aging for 24 h and heating at 473 K [63]

2] Precipitation of iron oxides from FeSO₄ and FeCl₃ by NaOH in the presence of charcoal, followed by drying at 100°C for 3 h [64]

3] Precipitation of hydrated iron oxides from FeSO₄ by NaOH in the presence of charcoal, followed by heating to 100°C for 1 h [65]

4]Activated carbon was suspended in NaOH solution and heated to 100 °C; then a solution of Fe[NO₃]₃ and Co[NO₃]₂ was quickly poured into the AC suspension and refluxed at 100°C for 2 h [66]

5] Bamboo charcoal powder was suspended in Fe[NO₃]₃, Zn[NO₃]₂, Ni[NO₃]₂ and aqueous ammonia solution and then heated in an autoclave at 180°C for 2 h and air cooled to room temperature [67]

6] Activated carbon was suspended in CuCl₂ and FeCl₃ solution, followed by NaOH solution addition and heating to 98-100 °C for 2 h [68]

7] FeCl₃ and FeSO₄ solution was mixed with NaOH solution to keep pH value of 9.5, then activated carbon was added and the obtained material was dried in an oven at 100 °C for 3 h[69].

High temperature treatment method:

Another large group of methods for magnetic modifications is based on the treatment of activated carbon impregnated with iron or nickel salts by heating at high temperatures. Depending on the salt, heating conditions and atmosphere used various magnetic modifiers can be formed including magnetic iron oxides or nickel particles. Some examples of described procedures for conversion of activated carbon [charcoal] into their Magnetic derivatives using high temperature treatment method.

1] Activated carbon was impregnated with an aqueous solution of sucrose and Ni[NO₃]₂, followed by heating at 600°C under N₂ for 3 hours. Ni nanoparticles were formed within the porous AC matrix [70]

2] A solution of Ni[NO₃]₂ was dropped into NaOH solution, then ethanol solution of phenolic resin was added followed by solvent evaporation at 333 K and carbonization under argon atmosphere at 873 K [71]

3] Impregnation of activated carbon with Fe [NO₃]₃ solution followed by drying at 90°C and heated to 700°C under argon; then benzene vapour was introduced [72]

4] Activated carbon from rice husk was modified with HNO₃ for 3 h at 80°C followed by suspending in Fe[NO₃]₃ and drying. Thermal treatment was conducted at 750°C for 3 h in the presence of N₂ to enable formation of magnetite nanoparticles [73]

5] Dried chitosan microspheres were immersed in [NH₄]₃[Fe[C₂O₄]₃] solution followed by washing and drying, then the sample was carbonized under Ar atmosphere at 700-1000°C for 4 h [74]

6] Activated carbon was suspended in Fe[NO₃]₃ ; after drying it was heated to 800°C in N₂ atmosphere and after cooling heated at 850°C in CO₂ atmosphere for 1.5 h [75]

7] A mixture of the anthracite powder, coal tar, Ni[NO₃]₂ and water was mixed and extruded in the form of 1 cm cylinders. After drying the material was carbonized under a flow of N₂ at 600°C and then activated at 880°C under a flow of N₂ [76]

8] Activated carbon was impregnated with Fe[NO₃]₃ solution and then with ethylene glycol. The impregnated sample was subjected to heat treatment under N₂ atmosphere at a temperature 250-450°C for 2 h [77]

9] Activated carbon was filled with a Fe[NO₃]₃ solution in ethanol and then dried at 90°C for 2 h. Then the sample was impregnated with ethylene glycol followed by heat treatment under N2 atmosphere at a temperature 350 or 450°C for 2 h[78].

In alternative procedures magnetic nanoparticles activated carbon was prepared by mixing carbon powder with the suspension of magnetic iron oxides prepared by standard precipitation procedure; the mixture was stirred and then dried at 40°C [79]. Also magnetic fluid stabilized with triethanolamine oleate was used for rapid preparation of magnetic nanoparticles activated carbon by simple impregnation procedure followed by washing and drying at 90°C in air [80]. In another described procedure activated carbon was mixed with iron powder followed by treatment in a high-energy planetary ball mill [81].

Encapsulation:

Encapsulation of activated carbon together with magnetic particles in an appropriate biopolymer or synthetic polymer gel is another possibility for magnetic nanoparticles activated carbon formation. Some examples of described procedures for conversion of activated carbon [charcoal] into their magnetic derivatives using Encapsulation

1] Activated carbon was mixed with alginate solution and citrate stabilized ferrofluid and then the suspension was added dropwise into a CaCl2 solution [82]

2] Cellulose was dissolved in a cooled NaOH/urea solution followed by the addition of maghemite nanoparticles and activated carbon; the suspension was added dropwise into a NaCl solution. The formed beads were cross-linked with epichlorohydrin [83]

3] Charcoal and magnetisable ferric oxide were entrapped in a polyacrylamide gel followed by lyophilisation and micronisation [84]

4] Charcoal and barium ferrite microparticles were mixed with bovine serum albumin solution followed by emulsification in n-butanol – castor oil – glutaraldehyde continuous phase [85].

5] Charcoal and magnetisable ferric oxide were entrapped in a polyacrylamide gel followed by drying at 80°C overnight and milling to obtain particles of less then 50 μm in diameter[86].

6] Activated carbon was suspended in NaOH solution and heated to 100 °C; then a solution of Fe[NO₃]₃ and Co[NO₃]₂ was quickly poured into the AC suspension and refluxed at 100 °C for 2 h. This material was added to Na alginate solution followed by pouring dropwise into CaCl2 solution [87].

Thermal Decomposition:

Inspired by the synthesis of high-quality semiconductor nanocrystals and oxides in non-aqueous media by thermal decomposition [88-90] similar methods for the synthesis of magnetic particles with control over size and shape have been developed. Nanoparticles with a high level of monodispersity and size control can be obtained by high-temperature decomposition of organometallic precursors. Thermal decomposition of organometallic precursors which metal is the zerovalent in their composition [such as Fe[CO]₅] initially leads to a formation of metal NPs but if followed by oxidation can lead to a high in quality monodispersed metal oxides. Principally the ratios of the starting reagents including organ metallic compounds, surfactants, and solvents are the decisive parameters for controlling the size and morphology of magnetic nanoparticles. The reaction temperature and time, as well as the aging period may also be crucial for the precise control of size and morphology [91]. Chen et al. [92] prepared nickel NPs from the thermal decomposition of nickel[II] acetylacetonate in alkyl amines. The reaction temperature, heating rate and solvent type all played an important role in the control over the crystalline phase in their study. They found that by choosing an appropriate reaction temperature and solvent, nickel NPs that have the fcc or the hcp phase can be obtained. Monodisperse nickel NPs were also obtained by introducing surfactants. Also, the results of magnetic characterization showed that the magnetic properties of the hcp nickel NPs are quite different from those of the fcc nickel nanoparticles. Hyeon et al. [93] reported a synthesis of highly crystalline and monodispersed iron nanoparticles without size-selection process by the thermal decomposition of iron pentacarbonyl in the presence of oleic acid at 100⁰C. The resulting iron nanoparticles were transformed to monodispersed gamma-Fe2O3 nanocrystallites by controlled oxidation using trimethylamine oxide as a mild oxidant. Particle size can be varied from 4 to 16 nm by controlling the experimental parameters.

Thermal decomposition seems the best method developed to date for size and morphology control of nanoparticles. Although the thermal decomposition method has many advantages for producing highly monodispersed particles with a narrow size distribution, it has the disadvantage that the resulting nanoparticles are generally only dissolved in nonpolar solvents. Also, the yield of production is high and scalable. Thermal decomposition methods usually lead to complicated processes or require relatively high temperatures.

Hydrothermal Synthesis:

Magnetic nanoparticles activated carbon with controlled size and shape are technologically important due to strong correlation between these parameters and magnetic properties. Hydrothermal synthesis includes various wet chemical technologies of crystallizing substance in a sealed container from the high temperature aqueous solution at high vapour pressure. Several authors have reported the synthesis of iron oxide nanoparticles by hydrothermal method [94-98]. There are two major methods according to whether or not use the specific surfactants. For example, Wang et al. [99] have reported a one-step hydrothermal process to prepare highly crystalline Fe3O4 nanopowders without using the surfactants. The nanoscale Fe3O4 powder [40 nm] obtained at 140 _C for 6 h possessed a saturation magnetization of 85.8 emu_g-1, a little lower than that of the correspondent bulk Fe3O4 [92 emu_g-1]. It is suggested that the well-crystallized Fe₃O₄grains formed under appropriate hydrothermal conditions should be responsible for the increased saturation magnetization in nanosized Fe₃O₄. Moreover, hydrothermal treatment is one of the successful ways of growing crystals for magnetic nanoparticles activated carbon. Hydrothermal synthesis is conductive to prepare the unusual iron oxide nanostructures such as iron oxide nanocubes [100],iron oxide hollow spheres [101], etc.

Characterization:

The magnetic properties of nanoparticles depend upon their size, morphology, structure and the surface functional group of the prepared MNAC. Several physicochemical techniques are used to determine these parameters.

Size and Morphology:

Transmission electron microscopy [TEM]: Transmission electron microscopy reports the total particle size of the core [crystalline and amorphous parts] and gives access to a number-weighted mean value. Furthermore, it provides details on the size distribution and the shape. However, this technique needs an analysis by image treatment, and it has to be performed on a statistically significant large number of particles. Moreover, the sample preparation can induce aggregation of the colloids, and the TEM measurements may consequently not reflect the size and the distribution in solution. Aggregates of smaller particles can be discerned [102-109].

High-resolution transmission electron microscopy [HRTEM]:

High-resolution transmission electron microscopy [HRTEM] gives access to the atomic arrangement. It can be used to study local microstructures [such as lattice vacancies and defects, lattice fringe, glide plane, or screw axes] and surface atomic arrangement of crystalline nanoparticles [110-112].

Scanning electron microscopy [SEM] :

SEM is a widely used technique for the determination of morphology and size distribution of prepared particles in the scales of micro to nanorange. SEM is not a good technique for characterization of core/shell NPs because this technique reports total particle size. Resolution of the SEM is lower than TEM and it is not efficient for NPs with particles size lower than 20 nm. PCS. Photon correlation spectroscopy [PCS], also called dynamic light scattering [DLS], or quasi-elastic light scattering [QELS], is a common technique to obtain nanoparticle size. size. The determination of the diffusion coefficient of the nanoparticles in solution gives access to the hydrodynamic radius of a corresponding sphere and the polydispersity of the colloidal solution [113]

Structure and Elemental Analysis XRD:

XRD can be performed to obtain the crystallographic structure of the particles. In a diffraction pattern, the intensity can be used to quantify the proportion of iron oxide formed in a mixture by comparing experimental peaks and reference peak intensities [114].

Extended X-ray absorption fine structure [EXAFS]:

Extended X-ray absorption fine structure [EXAFS] gives information on the particle size, especially for small sizes.[115-116]

Energy dispersive X-ray diffraction [EDXD]:

Energy dispersive X-ray diffraction [EDXD] provides the advantage of being carried out on the suspension and is used to improve the knowledge of fine structural details. EDXD can be used to provide an elemental analysis and determination of the chemical composition of prepared magnetic NPs. From EDXD data, the ratio of the elements in the nanoparticles structure can be estimated [117].

Surface Characterization:

X-Ray photoelectron spectroscopy [XPS].

XPS is a very useful technique for the study of the mechanisms of the reaction that occurs on the surface of magnetic nanoparticles. The XPS spectra are very useful in the determining of the characteristics in the bonding of the different elements involved. Also, it can be applied to confirm the structure as well as in the speciation of elements which are in the chemical composition magnetic nanoparticles.

Zetasizer Or PZC [point of zero charge]

The characterizing of a particle's surface properties is necessary in the understanding and for the predicting of properties under physiological conditions and also to optimize conjugation chemistry. Surface charge is characterized by zeta [ζ] potential analysis. The isoelectric point, also referred to as PZC [point of zero charge], is the pH at which the particles in suspension have a net charge of zero and no mobility in the electric field.

FT-IR:

FT-IR spectroscopy is a useful tool for the understanding of the functional group of any organic molecule. FT-IR has been widely used to confirm an attachment of different functional groups in each step of fictionalization.

Thermal gravimetric analysis [TGA]:

TGA has been performed to confirm the coating formation [especially surfactants or polymers] to estimate the binding efficiency on the surface of magnetic nanoparticles.

Magnetic Properties:

Vibrating sample magnetometry [VSM] [118] and SQUID magnetometry [119] are powerful tools to measure the sample’s net magnetization. These techniques are not element specific but they rather measure the whole magnetization.

VSM:

VSM is used to evaluate magnetization of the MNPs as a function of an applied external magnetic [H] generally between -3 and 3 Tesla. Based on the obtained VSM curve at low and room temperatures, magnetic behaviour of the MNPs can be identified. For example at room temperature, the zero magnetic remanence [when H is zero], and the an hysteretic loop feature indicates that the MNPs are super paramagnetic. Also, from the plateau part of the VSM curve, saturation magnetization [Ms] can be determined. On the other hand, it is most important that the core/shell materials should possess sufficient magnetic and superparamagnetism properties for use in practical applications; VSM is a good technique for estimating a shell's effect on MS.

SQUID:

SQUID magnetometry is routinely used to assess these magnetic properties. Monitoring magnetization as a function of temperature for particles cooled with or without an applied magnetic field followed by warming particles in the presence of a magnetic field allows the characteristic blocking temperature to be determined.

Applications

Biological Applications:

Magnetic nanoparticle activated carbons have been efficiently used for both biochemical assays and medical applications employing their ability to be selectively separated from the reaction mixture or targeted to the specific area. Two key factors size and surface functionality play an important role for in vivo applications. Even without targeting surface ligands, magnetic nanoparticle activated carbons diameters greatly affect in vivo bio distribution. Particles with diameters of 10-40 nm, including ultra-small magnetic nanoparticle activated carbons, are optimal for prolonged blood circulation; they can cross capillary walls, and are often phagocytised by macrophages which traffic to lymph nodes, and bone marrow [120]. Radioimmunoassay [RIA] is a very sensitive in vitro assay technique used to measure concentrations of different antigens [for example, hormone levels in the blood] by use of antibodies. Radioimmunoassay require a separation step prior to isotope counting because it is impossible to distinguish between the radioactivity in the antibody-bound and –free fractions. Magnetically responsive activated carbon has been successfully used in radioimmunoassay of important analytes, such as steroids and small polypeptide hormones [121], digoxin [122], vitamin B12 [123] or progesterone [124]. Similar approach was used for rapid, high-throughput transglutaminase assay where magnetic dextran coated charcoal has been used to capture the low-molecular weight reagent from the reaction mixture [125].

Bio separation:

In biomedical research, separation of specific biological entities [e.g., DNAs, proteins, and cells] from their native environment is often required for analysis. Magnetic nanoparticles are ideal for this application because of their on-off nature of magnetization with and without an external magnetic field, enabling the transportation of biomaterials with a magnetic field. In a typical procedure for separation, the biological entities are labelled by Magnetic nanoparticles and then subjected to separation by an external magnetic field [126]. Nanometer-sized magnetic particles, such as magnetic nanoparticles iron oxide activated carbon particles, have been extensively used for separation and purification of cells and biomolecules in bioprocesses [127-132]. Due to their small size and high surface area, magnetic nanoparticle activated carbons have many superior characteristics for these bio separation applications compared to those of the conventional micrometer-sized resins or beads, such as good dispersability, the fast and effective binding of bimolecular, and reversible and controllable flocculation. One of the possible techniques is the addition of appropriate adsorbent to adsorb the unbound analyte; both AC and MAC were successfully used for this purpose. Magnetic derivative enabled simple separation of the adsorbent with the bound free analyte using a magnetic separator [133]. Magnetite nanoparticles covered with activated carbon by using epoxy resin as an adhesive were used as a carrier for the immobilization of Saccharomyces cerevisiae cells. The immobilized cells were used in batch and continuous alcoholic fermentation. The adsorption of the yeast cells obeyed the Langmuir isotherm equation. Satisfactory results were obtained both in the case of simple adsorption and adsorption followed by glutaraldehyde cross-linking [134]. The same magnetic material was used to separate Saccharomyces cerevisiae cells from aqueous suspensions using magnetically stabilized fluidized beds [MSFB] that utilized a horizontal magnetic field; the effects of some parameters, such as bed porosity and height, liquid flow rate and inlet concentration on cell removal efficiency and breakthrough curves were studied [135]

Drug Delivery:

Magnetic Drug targeting has emerged as one of the modern technologies for drug delivery. The possibilities for the application of magnetic nanoparticle activated carbons in drug targeting have drastically increased. [136-138]. Magnetic drug delivery has been an active field of study for several decades. Proposed in the 1970s, the concept of magnetic drug targeting is to inject a magnetically responsive material containing bound, adsorbed or entrapped drug and then to use an externally placed magnet or an advanced high field gradient magnet [139] to guide the magnetic drug to the targeted site. Magnetic nanoparticle activated carbons in combination with an external magnetic field and magnetisable implants allow the delivery of particles to the desired target area and fix them at the local site while the medication is released and acts locally [140-142]. Ferrocarbon particles, in which the Fe core acts as the magnetically susceptible component and activated carbon as the drug carrier, represent one type of important materials for drug targeting because the susceptibility of metallic iron is many times higher than that of magnetite. Activated carbon is a good choice as a coating, due to its high surface area and known adsorption–desorption properties for many molecules including peptides, proteins and drugs. The molecular adsorption to activated carbon depends on the carbon surface, pore size and the source of the material [143].

Hyperthermia:

Another interesting application of magnetic nanoparticles is in hyperthermia treatment which is considered as a supplementary treatment to chemotherapy, radiotherapy, and surgery in cancer therapy [144-146]. Placing super paramagnetic magnetic nanoparticle activated carbons magnetic fields randomly flips the magnetization direction between parallel and ant parallel orientations, allowing the transfer of magnetic energy to the particles in the form of heat, a property that can be used in vivo to increase the temperature of tumor tissues to destroy the pathological cells by hyperthermia. Tumor cells are more sensitive to a temperature increase than healthy ones [147-148].Magnetite cationic liposomal nanoparticles [149-150] and dextran-coated magnetite [151], have been shown to effectively increase the temperature of tumor cells for hyperthermia treatment in cell irradiation. This has been proposed to be one of the key approaches to successful cancer therapy in the future. An antitumor drug paclitaxel was bound to ferrocarbon particles [0.5 – 2 μm in diameter] which could be localized quantitatively at capillary [0.2 cm s-1] to arteriole [28 cm s-1] flow rates under the effect of magnetic field. In blood serum, 38 % of adsorbed drug could be released from the carrier in 24 hours. Similar carbon-based magnetic carrier also enabled efficient binding of doxorubicin, mitomycin C, camptothecin, methotrexate and verapamil. With the aid of an externally positioned permanent dipole magnet, the drug-loaded carrier could be localized and retained within a tumor mass. A one-step radio labeling procedure of magnetic activated carbon particles with the therapeutic β-emitter rhenium-188 has been developed and the prepared material was subsequently targeted to solid tumors; it enabled to deliver therapeutically relevant doses of radiation to tumors while minimizing radiation exposure to surrounding tissues or organs.

Catalysis Applications:

The facile recovery and reuse of homogeneous catalyst via covalent tethering to a heterogeneous support while maintaining high catalytic activity has long been a goal in catalysis research [152]. Thus, during the past two decades, a great deal of attention has been paid to developing methods for heterogenizing homogeneous catalysts in order to combine the advantages of both homogeneous and heterogeneous catalysis [153-154]. Among these methods, the binding of catalysts to organic polymer solids [155-156] or inorganic solids [157] has become widely used. Although the heterogenized catalysts can be recycled and easily separated from the reaction mixtures, they are significantly less reactive and selective than their homogeneous counterparts. For this reason, there is a need to find new methods and strategies in order to overcome these limitations. In recent years, catalysts supported on magnetic nanoparticle activated carbons have been extensively used to improve limitation of heterogeneous catalysis. Magnetically driven separations make the recovery of catalysts in a liquid-phase reaction much easier than using cross flow filtration and centrifugation, especially when the catalysts are in the sub-micrometer size range. Such small and magnetically separable catalysts could combine the advantages of high dispersion and reactivity with easy separation. In terms of recycling expensive catalyst or ligands, immobilization of these active species on magnetic nanoparticle activated carbons leads to the easy separation of catalysts in a quasi-homogeneous system [158]. The various types of transition metal-catalyzed reactions using catalytic sites grafted onto magnetic nanoparticle activated carbons that have emerged recently include carbon-carbon cross-coupling reactions [159], hydroformylation [160], hydrogenation [161-162] and polymerization [163] reactions. Other reports on magnetic nanoparticle activated carbons supported catalysts include enzymes for carboxylate resolution [164], amino acids for ester hydrolysis [165] and organic amine catalysts promoting Knoevenagel and related reactions [166].

Environmental Applications:

Activated carbons have been often used as efficient adsorbents for many types of organic and inorganic xenobiotics, radionuclides, noble metals etc. Magnetically responsive carbon derivatives usually exhibit similar or sometimes even better adsorption of the target compounds as the native activated carbon and in addition, they can be easily separated. Recently, a large number of studies have appeared in the scientific literature describing the applications of various modifications of magnetic nanoparticle activated carbons for xenobiotics removal from contaminated water resources. Magnetic nanoparticle activated carbons are an additional material to magnetically responsive biocomposites used for the same purpose [167].Magnetic nanoparticle activated carbons is considered to be among the first generation of nanoscale environmental technologies [168-169]. This technology could provide cost-effective solutions to some of the most challenging environmental cleanup problems [170]. Over the past decade, permeable reactive barriers have been developed, as alternatives for the conventional pump-and-treat technology, used to treat groundwater contaminated by different pollutants [171].

In these barriers, zero-valent iron can be used as a reactive material due to its great ability to reduce and stabilise different types of compounds, when zero-valent iron is synthesised on the nanoscale, the uptake capacity increases largely due to the enlargement in surface area and the density of reactive sites [172]. An equally important property of nanoscale iron particles is their enormous flexibility for in situ applications. Modified iron nanoparticles, such as catalysed and supported nanoparticles, have been synthesised to further enhance their speed and efficiency of remediation [173]. Activated carbon modified with zero-valent iron deposits exhibited dehalogenation activity for chlorinated and brominated C1 and C2 hydrocarbons in aqueous solutions. The pollutants were collected and enriched at the magnetic nanoparticle activated carbons surface and destructed at the Fe clusters by reductive dechlorination. Lifetimes of the material in the order of several weeks have already been achieved in laboratory studies [174].

A novel magnetically separable composite photocatalyst, titania-coated magnetic nanoparticle activated carbon, was prepared by depositing of anatase titania onto the surface of magnetic nanoparticle activated carbons. The photocatalytic activity of the samples was determined by degradation of reactive brilliant red X-3B under either UV or visible irradiation; this activity was high and the composite photocatalyst could be reused with a little reduction of its photocatalytic activity [175]. Regeneration of magnetic nanoparticle activated carbons after finishing an adsorption process is important in order to keep the process expenses as low as possible. Recently magnetic CuFe2O4-activated carbon composite adsorbent has been prepared using a chemical co- precipitation method. After adsorption of acid orange II the composite regeneration was performed by heating in an inert atmosphere. The results indicated that the CuFe2O4 particles could effectively catalyze the thermal pyrolysis of the adsorbed dye. The results of regeneration tests suggested that almost all adsorption capacity of the composite adsorbent was re-established after thermal treatment and it could be reused for several cycles [176]. An alternative regeneration procedure was based on the use of hydrogen peroxide; the presence of the Fe3O4 nanoparticles in magnetic nanoparticle activated carbons was beneficial for achieving high regeneration efficiency [177].

Dyes are present in the wastewater streams of many industrial sectors such as, dyeing, textile factories, tanneries, and in the paint industry. Therefore, the replacing of magnetic nanoparticle activated carbons with expensive or low efficient adsorbent for treatment of textile effluent can be a good platform which need to more detailed investigations. Magnetic nanoparticle activated carbon has been used as a dyes adsorbent during the development of “magnetic solidphase extraction” [MSPE]; in this procedure magnetic adsorbent is added to a solution or suspension containing the target analyte. The analyte is adsorbed onto the magnetic adsorbent and then the adsorbent with adsorbed analyte is recovered from the suspension using an appropriate magnetic separator. The analyte is consequently eluted from the recovered adsorbent and analyzed. Up to 460-fold enrichment of analytes was observed using magnetic nanoparticle activated carbons as an adsorbent and water soluble dyes as analytes [178].

Solid phase extraction [SPE] is a routine extraction method for determining trace level contaminants in environmental samples. Recently, nanoparticles, have gained rapid and substantial progress, and have significantly an impact on sample extraction [179-189]. Nanomaterial can offer several advantages over traditional SPE sorbents such as having very high surface areas and a short diffusion route, which result in their high extraction capacity, rapid extraction dynamics and high extraction efficiencies [190-191]. Another advantage of nanoparticle is that nanoparticles surface functionality can be easily modified to achieve selective sample extraction [192-193]. However, the use of nanomaterial with a sub-100 nm size range has some inherent limitations, especially when applied in the adsorption and separation of contaminations from large volumes of environment samples. When column dynamic extraction mode is used, the nanosized particles packed SPE column exhibits a high backpressure, making it very difficult to adopt high flow rates; when the static batch mode is used, the nanosized SPE adsorbents often lead to a very low filtration rate. Among different kinds of nanoparticles, magnetic nanoparticles, mainly Fe₃O₄ nanoparticles, appears as an interesting advanced composite material. It has received increasing attention in the past decades due to its unique physical and chemical properties which can easily couple with magnetic carrier technology [MCT] which was first reported by Robinson in 1973 [194]. By applying this technology, magnetic nanoparticle activated carbons with adsorbed samples can be easily collected by using an external magnetic field placed outside of the extraction container without additional centrifugation or filtration of the sample, which makes sampling and collection easier and faster. Moreover, the magnetic nanoparticle activated carbons may be reused or recycled.

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Received on 13.11.2015 Modified on 27.11.2015

Asian J. Research Chem. 8(12): December 2015; Page 757-768

DOI: 10.5958/0974-4150.2015.00122.4