Wastewater Treatment by Chemically Activated Carbons from Giant Reed: Effect of the Activation Atmosphere on Properties and Adsorptive Behavior

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Abstract
Uptake of nickel and benzene from dilute single‐solute solutions, mimicking wastewater with low concentrations of heavy metals or volatile organic compounds, was examined using activated carbons with similar good surface properties (BET surface area of ≈1100 m2/g). They were developed through H3PO4 acid activation of giant reed (Arundo donax L.) under flowing air or N2. The carbons obtained in air proved more effective to capture Ni(II) ions under pre‐established equilibrium conditions. Inversely, the N2‐derived carbons exhibited a better ability for benzene adsorption. The behavior was related to the smaller total content of acidic/polar surface oxygen functionalities of the carbons developed under N2 (1.9 meq/g), compared to that of the air‐derived ones (3.3 meq/g). Two‐, three‐parameter models described properly the isotherms, predicting similar maximum adsorption capacities (Xm ) for the investigated systems. The Xm parameter in the Langmuir's model was 0.44 mmol/g for the adsorption of Ni(II) ions on the air‐derived carbons, and 0.45 mmol/g for benzene adsorption on those obtained in N2. Present results highlight the relevance of the surface chemistry developed upon activation to optimize the performance of activated carbons for wastewater treatment according to the pollutants' nature.