2.2.5. Evaluation of the Decontamination Efficacy through Atomic Absorption Spectrometry (AAS) Technique

For the controlled contamination with heavy metal, a standard solution of lead was employed. Standard solutions containing Sr and Co were also utilized for controlled contamination (as simulants for their analogous radionuclides). To obtain surfaces with similar contamination degrees, 1 mL from each metal standard solution (Pb, Sr, and Co) was placed in a distinct glass Petri dish (ϕ = 50 mm) and they were allowed to dry. Then, the decontamination solutions (8 mL) were applied on the contaminated surfaces. After being completely dried, they were easily peeled. Triplicate experiments were performed for a better accuracy. Decontamination efficacy was evaluated by comparing the remnant metal concentration from the surface with the initial concentration of contaminant. For this analysis, after removing the strippable coatings, the Petri dishes were washed three times with 5 mL of distilled water and the collected solutions (3 × 5 mL) constituted the sample that were subjected to AAS investigation, to assess the remnant metal concentration on the decontaminated surface. The decontamination factor was calculated with the following formula: DF = 100·(C0 − Cf)/C0 [4,30], where DF is the decontamination factor, C0 is the initial metal concentration, and Cf is the final concentration, reflecting the residual contamination.

In parallel, the concentration of "toxic metal" found in the polymeric nanocomposite film was also calculated using the AAS technique. For this purpose, each of the polymeric nanocomposite films obtained was dissolved in 50 mL of distilled water, sonicated, and then centrifugated and filtered to obtain a clear aqueous solution that was also subjected to AAS analysis. Since these samples required intermediary operations before being ready for AAS analysis, we can use the concentrations obtained only to demonstrate the presence of the "toxic metal" in the exfoliated film, and we can presume that the lacking amount of contaminant remained fixed in the bentonite eliminated after centrifugation and filtration steps. The differences between the values obtained for "toxic concentration" occur due to a certain degree of uncertainty evaluated internally, for the performance of sample preparation procedures for AAS analysis. This consists in a cumulative uncertainty regarding the measuring instruments, the human factor, and the analysis equipment. Losses also occur in the process of extraction, filtration, and dilution. To minimize the uncertainty, triplicate analyses were performed with the same sample, reporting the measured average value. The data collected from these decontamination tests are useful for a better understanding of the metallic contaminant removal process. As already mentioned above, these experiments were repeated three times and the average value was reported.
