Nitrobenzene-adsorption capacity of NaOH-modified spent coffee ground from aqueous solution

Adsorption of nitrobenzene (NB) on the NaOH-modified spent coffee ground (NaOH-SCG) was examined and the effects of contact time and adsorbent dose were investigated. The adsorption isotherm of NB on NaOH-SCG was compared with that of untreated SCG. The results from our study showed that the removal efficiencies of NB (25 mg/L) on SCG and NaOH-SCG after 2 h were 91.8% and 98.2%, respectively. The adsorption rate was very quick with the equilibrium of adsorption being achieved within about 30 min. The values of parameters obtained for NB from the Langmuir isotherm saturated adsorption amount and adsorption equilibrium constant were 117.2 mg/g, 0.0753 L/mg for SCG and 169.4 mg/g, 0.1815 L/mg for NaOH-SCG. NaOH-SCG (0.44 mmol/g) has fewer acidic functional groups than SCG (1.49 mmol/g). Therefore, the surface polarity of NaOH-SCG is low, thus makes this material more hydrophobic. The strong hydrophobicity of the NaOH-SCG surface might explain the high adsorption capacity for NB. As a result, this study has found that the NaOH-modified spent coffee ground has high adsorption ability for NB. (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.