Orion star a222

The experiment was carried out in a forest in the ‘Ejido Santa Rita’, municipality of Arteaga Coahuila (25°14′ N, 100°29′ W). The soil is a sandy loam (92% sand, 6.0% silt, and 2.0% clay) of the Feozem series, with an electrolytic conductivity (EC) of 446.13 ìS cm⁻¹, pH in water of 7.5 (determined on a 1:2.5 soil/distilled water), pH in KCl 1N of 6.55 (determined on a 1:2.5 soil/KCl solution), delta pH of -0.65 (ΔpH = pH_KCl-pH_water), 3.06 % organic matter (determined by loss on ignition at 400 °C during 4 h).
The texture was determined following the protocols of the Official Mexican Standard (SEMARNAT, NOM 021-RECNAT-2000 ). The pH_water and pH_KCl values were obtained by a desktop pH detector (Thermo Scientific™, Orion Star A211, EUA). The delta pH was calculated as the difference between pH_KCl and pH_water. This parameter was determined to know the variation of the pH caused by the Fe NPs. Besides, the value indicates the predominance of positive, negative, or neutral charges in the soil (Mekaru and Uehara, 1972 ). The EC was determined by a portable EC detector (Thermo Scientific™, Orion Star A222, EUA). The OM was determined according to the methodology of Schulte and Hopkins (1996) . Soil temperature measured with a thermometer (ECO brand).

pH and F⁻ were measured in a pH/ion selective electrode (ISE) (Thermo Scientific Orion Star A214 pH/ISE). Conductivity was monitored using a benchtop conductivity meter (Thermo Scientific Orion Star A222, portable conductivity meter). The COD (substrate degradation efficiency) of anolyte was measured using the closed reflux method as described in the standard method (APHA, 2012). The substrate degradation and defluoridation efficiencies were determined using Eq. (1). $\mathrm{R}\mathrm{e}\mathrm{m}\mathrm{o}\mathrm{v}\mathrm{a}\mathrm{l}\mathrm{e}\mathrm{f}\mathrm{f}\mathrm{i}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{c}\mathrm{y}(\%)=\frac{A-B}{A}\times 100$ where, A and B are the initial and final concentration of contaminant, respectively.
Voltage (V) was monitored using a data logger (DAQ6510, Keithley). As per Ohm's law, current (I)V/fixed resistance. Corresponding to a particular external resistance, the current density (mA/m²) was estimated by dividing I and power density (mW/m²) by dividing VI by the effective area of anode (m²). Polarization study was conducted by manually varying the external resistance from 1 Ω to 10.2 MΩ.