Development of magnetic activated carbon from almond shells for trinitrophenol removal from water

Magnetic and non-magnetic low cost activated carbons from almond shells were prepared, characterized, and used to remove 2,4,6-trinitrophenol (TNP) from water. The magnetic carbon was made by mixing aqueous suspensions of activated carbon with an aqueous Fe3+/Fe2+ solution followed by treatment with NaOH. The morphologies and surface chemistries of both magnetic and non-magnetic activated carbons were studied by FT-IR, X-ray, SEM, SEM-EDX, TEM, EDXRF, pHpzc, elemental analysis, surface area (SBET), density and magnetic moment determinations. The SBET areas of non-magnetic and magnetic activated carbons were 733 and 527 m2 g−1, respectively. Batch sorption studies were performed at different temperatures, pH values and solid-to-liquid ratios. Sorption isotherms were obtained over a concentration range from ∼23 to 228 mg/L (1.0 × 10−4 to 1.0 × 10−3 M). As temperature increased, TNP adsorption modestly decreased on non-magnetic activated carbon (ASAC) but slightly increased on magnetic activated carbon (MASAC). Sorption performances at different temperatures were evaluated using the Freundlich, Langmuir, and Sips adsorption models. First and second order kinetic models were tested, confirming second order behavior. Both ASAC and MASAC readily removed TNP in single and binary systems. MASAC and ASAC gave similar overall adsorption results with TNP, although the lower carbon content per gram of adsorbent and lower surface area of MASAC reduced its overall adsorption capacity per unit weight. MASAC is easily manipulated by low external magnetic fields, permitting its use for easy separation from aqueous-phase environmental applications. Almost complete (∼97%) desorption of TNP was readily achieved by methanol and hot water. Magnetic removal would allow convenient adsorbent separation, desorption and recycling or replacement from contaminated water.

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► Magnetic and non-magnetic activated carbons from almond shells were developed.
► Activated carbons were characterized and used for 2,4,6-trinitrophenol removal.
► At 25 °C, ∼73 mg/g TNP was removed by magnetic carbon.
► Almost complete (∼97%) desorption of TNP was readily achieved.
► Simple separation by a magnetic field was demonstrated.