Abstract
This research aimed to assess the potential of Ethiopian coffee extracts in synthesizing nano zerovalent iron (nZVI) from ferric chloride hexahydrate (FeCl(3)·6H(2)O) and to explore their ability to adsorb hexavalent chromium (Cr (VI)) from solution. The resulting nano zerovalent iron (nZVI) was analyzed using transmission electron microscopy (TEM) and Fourier-transform infrared (FTIR) spectroscopy. The particle sizes of nZVI derived from Wenbera (W-nZVI) and Sidama (S-nZVI) coffee extracts were below 10 nm. Cr (VI) adsorption to W-nZVI and S-nZVI were 91 and 94%, respectively, achieved at a pH of 3, an initial Cr (VI) concentration of 10 mg/L, and a temperature of 30 °C. The results confirmed that both W-nZVI and S-nZVI adsorbed significant amounts of Cr (VI). Adsorption isotherm models indicate that favorable removal of Cr (VI) by W-nZVI followed the Langmuir equation (R (2) = 0.9913; 0 < R (L) < 1) better than the S-nZVI adsorption data (R (2) = 0.9795). However, adsorption behavior for S-nZVI fitted the Freundlich isotherm model better (R (2) = 0.9999; n = 2.029) compared with the W-nZVI adsorption data (R (2) = 0.999; n = 0.559). The maximum adsorption capacities for W-nZVI and S-nZVI were 35 and 38 mg/g, respectively. The adsorption of Cr (VI) from aqueous solutions was spontaneous, accompanied by a negative Gibbs energy and exothermic, accompanied by a negative enthalpy of adsorption. The adsorption kinetics were better described by the pseudo-second-order model for both adsorbents. Taken together, nZVI synthesized by using coffee extract may provide a sustainable approach to remove hexavalent chromium from solution.