**Figure 11.** *Cont*.

**Figure 11.** Degradation products of **HD** tracked during the decontamination process (*y*-axis values correspond to the values obtained for the area of the specific peak (counts) of each analyte): (**a**) sulfur mustard, (**b**) 1,4—dithiane, (**c**) thiodiglycol, (**d**) ethanol.2-((2-chloroethyl)thio)1-acetate, (**e**) Bis((2-cloroethylthio)ethyl)sulfide, (**f**) Bis(2-chloroethyl) disulfide, (**g**) sesquimustard and (**h**) O-mustard.

> The achieved **HD** decontamination efficiency was 90.89% for SD11. This experiment demonstrates the functionality of the polymeric films used for the capture and removal of the toxic agent and also a small amount of waste generation. A comparative assessment between the result obtained and SD11 polymer films on **HD**-contaminated metallic surfaces (DF ≈ 90.89%) and conventional decontamination products, which are commercially available (bleach (full strength)- DF ≈ 86% or hydrogen peroxide- DF ≈ 71% for HD-contaminated metallic surfaces) [59], shows a clear improvement in terms of decontamination efficiency, afforded by the strippable coatings herein reported (SD11).

> An ideal achievement is a 100% efficient decontamination, but in the case of operational decontamination, this percentage is relatively difficult to obtain for yperite, as the decontamination process depends on a multitude of factors, such as decontamination time, ambient temperature, the contact time elapsed between the contaminated surface and toxic agent until the application of the decontamination solution, and last but not least, the type of material that has been contaminated. In this regard, the U.S. Environmental Protection Agency (EPA) conducted some studies covering aspects of mustard decontamination using commercial decontamination solutions, wherein it concluded that depending on the factors listed above, decontamination efficiency can vary in practice between 37% and max. 95%

when applying the decontamination product only once [59,60]. Thus, we can affirm that SD11 polymeric films present unique perspectives in their operational use for removing **HD** contaminant.

In general, **DMMP** is much easier to decontaminate because of the weaker interactions it establishes with the metallic surfaces on which it is deposited in decontamination tests. Even so, it still requires an adequate decontaminating agent. All the decontamination solutions managed to reach DF values greater than 99.96%. These high values of DF were obtained due to the remarkable adsorption capacity of the materials employed for decontamination and the compatibility of the components of the decontamination solutions with **DMMP** but also due to the weak interactions between **DMMP** and the metallic substrate.

The last step in the evaluation of chemical decontamination efficacy consisted of the investigation of the degradation products of sulfur mustard. The **HD** solution employed for controlled contamination had a purity of 95%. Thus, 5% of the solution contained by-products of the synthesis of **HD** and small amounts of degradation products (Table S5). The solution utilized for controlled contamination, together with the degradation products of **HD**, was also tracked during the decontamination process because part of these synthesis by-products from the **HD** initial solution is also part of the blister agent class, possessing a higher blistering action than neat **HD**. Thus, even if they are found in a small concentration in the initial solution, the higher toxicity of these compounds imposes the necessity of examining their degradation. The results are illustrated in Figure 11 and Table S5.

In Figure 11, it can be noticed that the decontamination solution does not just entrap the toxic, but it also actively decomposes **HD** (and the other initial components of the contaminating solution) into less toxic compounds. These results offer clear evidence of the ability of the decontamination solutions to efficiently neutralize the toxic agent. The decontamination is performed by two pathways: the chemical degradation of the toxins, which is possible with the aid of the active components, as well as the entrapment and sealing-off of the degradation products and the toxic compounds that were only partially degraded. As can be seen in Figure 11, **HD** was only partially degraded, as **HD** can still be detected on the surface and in the nanocomposite films after DCM extraction. sesquimustard and O–mustard, which are well-known for their higher toxicity, both present in the initial contaminating solution were also partially degraded. In comparison with **HD**, sesqui–mustard, and O-mustard, the compound 1,4—dithiane was not visible in the polymeric film after decontamination. Thiodiglycol, the hydrolysis product of **HD**, was found in significant quantities in the samples obtained from DCM extraction of the polymeric film after decontamination, thus offering evidence of the high capacity of these decontamination solutions to hydrolyze **HD**.

Based on the chemical decontamination tests, it can be concluded that these novel water-based decontamination solutions are a useful and versatile tool for the neutralization and removal of chemical warfare agents, ensuring high decontamination levels.

### **4. Conclusions**

This study proposes new decontamination solutions consisting of innovative, ecological, peelable active nanocomposite films specially designed for biological and chemical warfare agents. These film-forming decontamination solutions are water-based solutions obtained from eco-friendly materials. Bentonite-supported nanoparticles (Cu, TiO2, and Ag) were successfully synthesized in aqueous solution and were employed in the decontamination formulations as active agents facilitating the neutralization of the hazardous materials. The unicity of these formulations consists of their environmentally responsible composition and high capacity to entrap and neutralize BCWA contaminants.

Particle-size control of the synthesized nanoparticles was accomplished by employing three different concentrations of bentonite nanoclay, which also served as adsorbent in the decontamination solutions, trapping the contaminants that diffuse in the polymeric composite network until the end of the drying process. Bentonite-supported silver nanopar-

ticles displayed high antimicrobial activity and had a positive effect on the degradation process of the chemical warfare agent sulfur mustard, as well as **DMMP**, a nerve agent simulant. TEM analyses confirmed the nanometric dimensions of the obtained metallic particles. The decontamination formulations were further prepared based on these active ingredients and a water-soluble polymer, APV. Their viscosity was evaluated, revealing only minor differences between them due to the low concentration of nanoparticles and nanoclay (up to 1.5%). Viscosity influences the application method (spraying vs. brushing), but it also influences the motion of the active ingredients towards the contaminants within the polymeric matrix. The evaporation rate of each decontamination solution was evaluated to assess the necessary time for obtaining the peelable nanocomposite films. Chemical, mechanical, and thermal characterizations of the polymeric nanocomposite films were performed using FT-IR, tensile tests, DTA, and DMA techniques, showing the influence of each component on the final properties of the polymeric nanocomposite designed for BCWA decontamination. The decontamination effectiveness was first evaluated by qualitative and quantitative approaches, employing specific analytic tools for each type of contaminant. The influence of the concentration of bentonite nanoclay, and subsequently, the influence of the nature and size of the synthesized nanoparticles over the decontamination efficiency were also emphasized. The presence of nanoparticles led to higher decontamination factors. The solutions containing Ag-NPs displayed more antimicrobial activity. Copper nanoparticles displayed less antimicrobial activity, but this aspect was improved by the addition of TiO2 nanoparticles. The efficacy of removal for the tested micro-organisms varies (93% < DF < 97%), thus confirming that these polymeric decontamination solutions represent a useful tool for biological decontamination of surfaces. The decontamination solution containing 1% bentonite nanoclay and Ag-NPs (**SD11**) displayed the best results for **HD** decontamination (DF ≥ 90.89%). In contrast, **DMMP** was almost completely removed from the contaminated surfaces, displaying a decontamination factor of DF ≈ 99.97% ± 0.01.

In conclusion, the eco-friendly, peelable active nanocomposite films designed for biological and chemical warfare agent decontamination can be successfully used on contaminated surfaces, reducing the risk of spreading bio-contaminants or chemical agents by neutralizing and entrapping the hazardous materials and their degradation products into the polymer nanocomposite matrix. In comparison with classical decontamination methods, employing ecological peelable coatings brings multiple advantages: significantly lower consumption of water and reagents, significantly lower amount of post-decontamination waste, ease of application, eco-friendly components, and high decontamination factors for both biological and chemical agents.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/polym13223999/s1, Table S1. Evaporation rate of the decontamination solutions; Figure S1. FT-IR spectra of the polymer nanocomposite films; Figure S2. Tensile tests results; Table S2. Tensile tests results; Figure S3. Cell population after 2 h in contact with the decontamination solutions for *E. coli; Table S3. Antimicrobial activity of the decontamination solutions against* E. coli; Figure S4. Cell population after 24 h in contact with the decontamination solutions for *E. coli; Table S4. Antimicrobial activity of the decontamination solutions against* S. aureus; Figure S5. Mass spectra of **HD** (up—from analysis; down—NIST database) RT—10.71 min; Figure S6. Chromatograms multigraph; Figure S7. Total Ions Chromatograms overlap for all samples, representing **HD** at the RT (retention time): 10.70; Figure S8. Chromatograms overlap for reference sample and samples extracted from the metallic surface after decontamination; Figure S9. Chromatograms overlap for reference sample and samples extracted from the nanocomposite film after decontamination; Table S5. Degradation products of **HD** monitorized during the decontamination process; Figure S10. Degradation products of Yperite; Figure S11. Mass spectra of **HD** (up—from analysis; down—NIST database) RT—5.93 min; Figure S12. Chromatograms overlap for all samples; Figure S13. Chromatograms overlap for all samples; Figure S14. Chromatograms overlap for reference sample and samples extracted from the metallic surface after decontamination; Figure S15. Chromatograms overlap for reference sample and samples extracted from the nanocomposite film after decontamination.

**Author Contributions:** Conceptualization, G.T., A.D., T.R., M.A., E.R. and R.E.G.; methodology, G.T., A.D., T.R. and M.A.; software, A.E.M., D.P., A.M.G. and R.S, .; validation, G.T., A.D., T.R., M.A., T.V.I. and E.R.; formal analysis, G.T., A.D., M.A., R.E.G., F.A., R.O., F.L.Z., A.P., A.E.M., D.P., A.M.G. and R.S, .; investigation, G.T., A.D., M.A., R.E.G., F.A., R.O., F.L.Z., A.P., A.E.M., D.P., T.V.I. and R.S, .; resources, G.T., T.R., M.A., A.D., T.V.I. and R.E.G.; data curation, G.T., A.D., M.A., F.A., R.O., F.L.Z., A.P., A.E.M., D.P. and R.S, .; writing—original draft preparation, G.T., A.D., T.R. and M.A.; writing review and editing, G.T., A.D., T.R., M.A., E.R., R.E.G., F.A., R.O., F.L.Z., A.P., A.E.M., D.P., A.M.G., T.V.I. and R.S, .; visualization, G.T., A.D., M.A., E.R., D.P.; supervision, G.T., A.D., T.R., M.A. and E.R.; project administration, G.T., A.E.M., R.E.G., A.D. and T.R.; funding acquisition, G.T., A.E.M., R.E.G., M.A., A.D. and T.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors are thankful for the financial support provided by the Executive Agency for Higher Education, Research, Development, and Innovation Funding (UEFISCDI), the Ministry of Education of Romania, through the National Projects PN-III-P2-2.1-PED-2019-4222 ctr. no. 427PED/2020 and PN-III-P2-2.1-PTE-2019-0400 ctr. no. 49PTE/2020.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** Aurel Diacon gratefully acknowledges financial support from the Competitiveness Operational Program 2014–2020, Action 1.1.3: Creating synergies with RDI actions of the EU's HORIZON 2020 framework program and other international RDI programs, MySMIS Code 108792, Acronym project "UPB4H", financed by contract: 250/11.05.2020.

**Conflicts of Interest:** The authors declare no conflict of interest.

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