Utilization of red clay brick waste in the green preparation of an efficient porous nanocomposite for phenol adsorption: Characterization, experiments and statistical physics treatment

Abstract

Red clay brick waste was utilized, for the first time, in the green preparation of nanoscale zero-valent iron (nZVI) to impregnate with activated charcoal (ACh). The as-synthesized nZVI@ACh composite was characterized via X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, thermogravimetric analysis (TG) and its derivative thermogravimetry (DTG), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). This novel material was employed for phenol remediation at 25, 35, and 45 °C and pH 7. The results indicated that the prepared ZVI nanoparticles could be either trapped or distributed on the ACh structure. Experimental studies and their modeling with statistical physics theory were applied to analyze the phenol adsorption performance and mechanism using the nZVI@ACh. The phenol adsorption data fitted well to the Langmuir model, with maximum adsorption capacities of 122.85, 137.46, and 152.22 mg/g at 25°, 35°, and 45 °C, respectively. Theoretical calculations via statistical physics indicated that phenol molecules were removed on the nZVI@ACh following the hypothesis of the advanced monolayer model. The number of molecules adsorbed per site (n) ranged from 1.13 to 1.26 suggesting the involvement of vertical geometry and multi-molecular mechanism at all temperatures. The increment of the receptor sites density (NM) from 83.47 to 121.40 mg/g and the adsorption capacity at saturation (Qsat) from 104.75 to 137.19 mg/g with increasing temperature suggested the endothermic behavior of this removal process. Energetically, the phenol adsorption was directed by physical forces with adsorption energies (ΔE) ranging from 13.85 to 16.45 kJ/mol. Macroscopically, phenol adsorption onto nZVI@ACh was spontaneous according to the calculated thermodynamic functions. The developed nZVI@ACh adsorbent can be easily regenerated and reused preserving its competitive adsorption performance. Overall, these results offer a new approach that takes the Fe-rich solid wastes to the next standard in the design of outstanding and low-cost adsorbents for wastewater remediation. Also, the experimental study supported by the theoretical analysis generated new insights of the adsorption system at the micro- and macroscopic scales.