The Adsorption Properties Of Carbon Coated Magnetic Nanocapsules

Carbon materials have been studied as adsorbents for wastewater treatment due to its high adsorption capacity, high specific surface area and adequate pore size distribution, including active carbon, carbon fiber, carbon nanotubes and graphene. However, they are difficult to regenerate with low recyclability. Therefore, to develop adsorbents with low cost, large adsorption capacity, simple desorption and circulation utilization is of great significance. Nowadays, magnetic adsorbents spark a new arena because of the effective recycling of adsorbents by magnetic force and easy separation of the adsorbed contaminants, especially the carbon coated magnetic nanoparticles with high saturation magnetization.In this paper, carbon coated iron nanocapsules (Fe@C NCs) and carbon coated nickel nanocapsules (Ni@C NCs) were fabricated in situ by DC electric arc discharge. Surface modification with hydrogen peroxide was to achieve the functionalization through forming oxygen-containing groups on the carbon, which could improve wettability and hydrophily. Transmission electron microscopy (TEM) indicated the obvious encapsulation structure, with the size of 20-50 nm and the carbon shell thickness in 5-7 nm for Fe@C NCs; the Ni@C NCs with size of 10-30 nm and carbon thickness in 2-5 nm. The BET surface area of Fe@C NCs and Ni@C NCs was 85.86 m2/g and 38.82 m2/g calculated according to N2 adsorption-desorption isotherm. Oxygen-containing groups (carboxyl and hydroxyl groups) were formed on the carbon shell certified by FT-IR test and zeta potential test also showed that surface treatment changed the surface charge characteristics.The surface modified Fe@C NCs and Ni@C NCs were applied as adsorbents to adsorb methylene blue (MB) and methyl orange (MO). We studied the effect of concentration, contact time, pH values, and temperature systematically. The kinetics was studied by pseudo-first-order and pseudo-second-order model and adsorption isotherms were fitted by Langmuir and Freundlich isotherms. The adsorption process obeyed the pseudo-second-order kinetics model and the Langmuir isotherm. The maximum adsorption capacity of MB on Fe@C NCs and Ni@C NCs were calculated as 46.5 mg/g and 20.6 mg/g, respectively. The thermodynamic process of adsorption was revealed as the endothermic and spontaneous physisorptionIn addition, the recycling experiment was carried out for 5 cycles, which showed good adsorption performance and high recovery. Fe@C NCs and Ni@C NCs are considered technically feasible, economically attractive and promising candidate as an adsorbent for removal of cationic dyes or contaminants from the wastewaters.