Cr(VI) uptake by a new adsorbent of CTAB-modified carbonized coal: Experimental and advanced statistical physics studies

The interaction between cetyltrimethylammonium bromide (CTAB) and carbonized coal (CC) resulted in the fabrication of a novel adsorbent (CTAB/CC). The new composite was characterized and applied for hexavalent chromium Cr(VI) uptake at three temperatures (25, 35, and 45 degrees C) and solution pH 2.0. Based on the correlation coefficient (R-2) and Chi-squared (chi(2)) values, Langmuir with maximum removal capacities of 78.67, 81.74, and 82.58 mg g(-1), described adequately the attained experimental data at 25, 35, and 45 degrees C, respectively. Advanced statistical physics models were applied to better understand the interaction between Cr(VI) ions and CTAB/CC active sites. Steric, energetic and thermodynamics parameters for the satisfactory model (monolayer with two energies) were deeply interpreted. The active sites number (n) was in the range of 0.76 to 1.8 reflecting the presence of multi-docking and multi-ionic mechanisms in Cr(VI) adsorption onto CTAB/CC composite. By increasing temperature from 25 to 45 degrees C, the receptor sites density (N-M) reduced from 45.83 to 22.76 mg g(-1) for N-1M , but improved from 22.23 to 55.01 mg g(-1) for N-2M (i.e., discordant behaviors). Energetically, the Cr(VI) adsorption onto the CTAB/CC adsorbent was endothermic and related to physical forces (i.e. <40 kJ mol(-1)). Adsorption capacities (Q(sat1) and Q(sat2)) were enhanced with temperature, which confirmed the endothermic character of the removal processes. Steric and energetic parameters were involved in controlling the adsorption of Cr(VI) on CTAB/CC product. Thermodynamic parameters revealed the spontaneous nature and viability of Cr(VI) adsorption onto the CTAB/CC composite. (C) 2019 Elsevier B.V. All rights reserved.