One-step fabrication of a new outstanding rutile TiO2 nanoparticles/anthracite adsorbent: Modeling and physicochemical interpretations for malachite green removal

Abstract

In this study, a facile method was developed to synthesize a new composite via the impregnation of rutile (TiO2) nanoparticles (Rt) into H2O2–modified anthracite (MAn). This new rutile(TiO2)/modified anthracite (Rt/MAn) adsorbent was characterized and employed as an outstanding and cost–effective material to remove malachite green (MG) dye at 25–55 °C. This adsorbent displayed the highest removal efficiency (96.2 %) as compared to its individual components MAn (49.8 %) and Rt (71.4 %) at pH 8.0. The experimental adsorption of MG onto Rt/MAn at equilibrium were satisfactorily fitted to the Freundlich equation and a multilayer statistical physics model at all tested temperatures. The physicochemical parameters (steric and energetic) related to a multilayer adsorption were calculated and interpreted to understand the adsorption mechanism. The theoretical number of adsorbed MG dye molecules per functional group (n) varied from 0.94 to 1.60 indicating a multi-docking adsorption mechanism. The adsorption capacity of MG at saturation (Qsat) increased from 513 to 740 mg/g at 25 and 55 °C and was primarily caused by the density of Rt/MAn functional groups (i.e., the DM parameter). MG adsorption energy with Rt/MAn varied from 13.87 to 29. 96 kJ/mol and was governed by physical interactions. The tested adsorbent was easily reactivated by the dye desorption and reused up to five cycles where it retained>80 % of MG adsorption capacity even after the 5th adsorption–desorption cycle. These results demonstrated that Rt/MAn is an effective adsorbent to remove MG, thus offering outstanding adsorption capacities largely beyond the current state of the art (up to 740 mg/g) and its application could be extended for the adsorption of other organic pollutants from wastewaters.