# Arsenic Removal from Water by Adsorption onto Iron Oxide/Nano-Porous Carbon Magnetic Composite
## 1 Introduction
Conventional methods, such as ion exchange, reverse osmosis, and membrane filtration, are not feasible for large applications due to low efficiency, generation of secondary pollutants, and high cost. In developing countries, precipitation and adsorption methods are widely used for As removal. Precipitation method requires a large amount of chemicals and creates a volumetric sludge as Arsenic III sulfide, calcium arsenate, or ferric arsenate. So, the adsorption method is the method of choice. The method is simple, cost-effective, and efficient with minimum waste production and can be applied in water containing a trace amount of pollutants [17]. A wide variety of adsorbents has already been studied, including kaolinite, montmorillonite, activated alumina, titanium dioxide, iron hydroxide, zero-valent iron, chitosan, etc. [18; 19]. Among them, iron-based magnetic material, particularly iron oxide, is commonly used as adsorbent due to their higher magnetic character and lower cost [20; 21]. However, its widespread application for As removal is limited because it is very bulky, highly amorphous, and flocculant. To deal with the problem, research efforts are being focused on creating media supporting iron oxide. In this regard, different porous supports have been employed, such as activated carbon, clay, zeolite, polymer, and biopolymer [21]. Activated carbon (AC) has been proven ideal support because of its stable and variable pore structure. Use of iron oxide-loaded activated carbons (ACs) for As removal from contaminated water has shown the promising results [17; 22]. During adsorption, the aqueous oxyanions (such as H\({}_{2}\)AsO\({}_{4}\)- and HAsO\({}_{4}\)\({}^{2-}\)) undergo a ligand exchange reaction with iron speciation on the carbon surface and form an inner-sphere surface complex [23]. After adsorption, the AC composite can also be separated from the medium by a simple magnetic process [17]. The efficiency of As removal depends upon both the amount of iron loading and dispersion and surface accessibility of this iron oxide within the porous AC. Iron oxide/AC magnetic composite was fabricated for arsenic adsorption from aqueous solution by [PERSON] et al., 2014 [17]. [PERSON] et al. [24] synthesized sugarcane bagasse derived nanomagnetic adsorbent composite for the removal of Cu (II) from aqueous solution. [PERSON] et al. [25] studied the adsorption of Pb (II) onto Fe\({}_{3}\)O\({}_{4}\)/activated carbon composite. Removal of dye from aqueous solution using Fe\({}_{3}\)O\({}_{4}\)/activated carbon nanocomposite was studied by [PERSON] et al. [26]. Iron oxide/AC composite can remove boron and organics from wastewater [27]. Similarly, it has also been found that iron oxide/AC composite is useful in removing different kinds of contaminants like trinitrophenol, phosphate, atrazine, lead, arsenic, mercury, and methylene blue dye from aqueous solutions [28; 29; 30; 31; 32; 33]. The obtained results indicate that the prepared magnetic nanocomposite of iron oxide and AC is one of the efficient adsorbents for the removal of these pollutants from aqueous solution. The high efficiency of magnetized adsorbents is due to their easy control and fast separation by direct application of a magnetic field. For the synthesis of AC, the use of agricultural wastes is being considered as a good alternative source material because of their abundant supply at no or low costs. They are lignocellulosic materials and comprised of about 10-25% lignin, 20-30% hemicellulose, and 40-50% cellulose [34]. Several agricultural wastes, including sugarcane bagasse, cottonwood, and coconut shell, are considered for the production of carbon composites. Agricultural wastes, such as sugarcane bagasse [35], coconut shell, cottonwood [36], and rice husk [37], have been reported to produce carbon composites.