Carbon nanotubes impregnated with metallic nanoparticles and their application as an adsorbent for the glyphosate removal in an aqueous matrix

New insights into glyphosate adsorption on modified carbon nanotubes via green synthesis: Statistical physical modeling and steric and energetic interpretations

“…However, so far, there are no reports of analysis and modeling of the adsorption of this herbicide from the perspective of statistical physics. In this sense, the present contribution provided new insights into the equilibrium data obtained in Diel et al [44] for temperatures ranging from 298 to 328 K (pH = 4). For this, six models based on statistical physics were applied: Hill model with 1 energy for ideal fluid, Hill model with 2 energies for ideal fluid, Hill model with 1 energy for real fluid, Hill model with 2 energies for real fluid, double layer model with two energy, and multilayer model.…”

“…As described in Table 4, for the GLY-MWCNTs/MPNs-Fe system, the values of n ranged from 0.67 to 1.66, with 0.5 < n < 1 to 298 K and n ≥ 1 at temperatures 308, 318, and 328 K. Concerning case 0.5 < n < 1 (0.67 to 298 K), the process was identified as of mixed geometry (parallel and non-parallel orientation) on the surface of the adsorbent, with the corresponding anchor number (n ′ ) equal to 1.49, indicating the anchorage of the GLY molecules by only one of the receptor sites available in the material (MPNs-Fe or COOH groups), more precisely by the interaction of the herbicide molecules with the MPNs-Fe, as previously evaluated by Diel et al [44]. This trend is because the raw MWCNTs, with only COOH functionalization, showed almost insignificant removal and adsorptive capacity percentages.…”

“…Nutshells (Carya illinoinensis) were used as a natural reducing agent, and iron sulfate (FeSO 4 ⋅7H 2 O, CAS: 7782-63-0, 99.99%, Neon) was used as a metal salt for reduction. The preparation and characterization of the modified material, labeled MWCNT/MPNs-Fe, were described in detail in the reported reference [39,44].…”

“…The modified material MWCNT/MPNs-Fe was used as an adsorbent in the removal of GLY (C 3 H 8 NO 5 P, molecular weight: 169.073 g mol − 1 , CAS: 1071-83-6, purity: 98%, Sigma-Aldrich) in the aqueous matrix and the adsorption results obtained (pH study, kinetic and equilibrium modeling, thermodynamic behavior, simulated effluent, and material regeneration) are included in the same reference [39,44]. Ninhydrin (C 9 H 6 O 4 , CAS: 485-47-2, Sigma-Aldrich) and sodium molybdate (MoNa 2 O 4 , CAS: 7631-95-0, purity: 98%, Sigma-Aldrich) were used for colorimetric complexation reaction [45], allowing the quantification of the pesticide in a UV-Vis spectrophotometer (Shimadzu, model: UV-2600, Japan), at 570 nm.…”

“…Diel et al [44] classified the experimental curves in Fig. 2 as having a typical L2 isotherm shape associated with favorable adsorption.…”