INNOVATIVE SYSTEMS FOR THE MITIGATION OF RISKS: CATALYSTS AND SMART MATERIALS FOR DETECTION AND DECONTAMINATION OF HAZARDOUS CHEMICAL, BIOLOGICAL AND EXPLOSIVE SUBSTANCES

Incidents involving Chemical, Biological, Radiological, Nuclear and explosive agents (CBRNe), whether intentional or accidental, pose significant threats in the modern international scenario. The use of these substances, not only endangers human life, but also represents a threat to national defence, the economy and, above all, the environment due to their strong harmfulness, persistence and recalcitrance. Consequently, there is a critical need for the development of innovative systems to mitigate the risks associated with these hazardous agents. This research spans several areas related to the mitigation of chemical, and biological risks. The broad aim of this Ph.D. thesis was to overcome the problems and limitations currently present in some conventional decontamination and detection methods concerning these hazardous agents. Decontamination of Hazardous Biological Agents - In this field, it is a priority to focus on substances that are both environmentally and economically sustainable, as well as safe from a toxicity point of view, aiming to avoid the extensive use of chlorine-based solutions or to minimise the release of VOCs into the environment. In response to the COVID-19 pandemic, hydrogen peroxide has emerged as a sustainable alternative for inactivating SARS-CoV-2 in the liquid phase. A diluted 3% w/w H2O2 solution acidified to pH 2.5 by adding citric acid inactivated SARS-CoV-2 virus by more than 4 orders of magnitude in 5 min. Conversely, H2O2 solutions with no additives displayed a scarce virucidal activity, confirming that a pH-modifying ingredient is necessary to have a H2O2-based disinfectant active against this virus. Furthermore, recognizing that an acid and an oxidizing functionality are important for the inactivation of many pathogens, efforts were made to heterogenize and immobilize these functionalities within a system based on sulfonic acid cation exchange resins. After a simple contact treatment with an aqueous H2O2 solution, these resins demonstrated the ability to store oxidising species and release them over time. These systems exhibited potent biocidal efficacy against bacteria, resulting in a reduction of 9 and 5 orders of magnitude in Escherichia coli (Gram -) and Staphilococcus aureus (Gram +) viability, respectively, even after 1 min. Additionally, they showed effectiveness against viruses, with a complete absence of viral replication for SARS-CoV-2 (RNA virus), Herpes simplex (DNA virus), and Monkeypox (DNA virus) after 2 min. This drastic biocidal action is therefore attributable to the synergistic effect between the strong Brønsted acidity of the resins and the oxidising capacity due to the presence of H2O2 and in-situ formed peroxosulfonic species. Decontamination and abatement of hazardous chemicals - The transition from stoichiometric to catalytic methods is crucial for the effective and sustainable decontamination of hazardous chemicals. In this study, nanostructured porous materials, including commercial non-ordered aluminosilicates (SiO2-Al2O3), niobium oxide (Nb2O5), and modified synthetic saponites clays (NbSAP, Na-SAP, H-SAP), were selected and tested as heterogeneous catalysts for the liquid-phase degradation of two organophosphorus obsolete agrochemicals and CWAs simulants, namely paraoxon-ethyl and parathion-ethyl. Regarding synthetic saponite clays, they represent a class of hydrated smectite-type phyllosilicate materials, consisting of a 2:1 trioctahedral structure of alternating tetrahedral (T) and octahedral (O) sheets, typically composed of Si(IV), Al(III), Mg(II) and O2- sites, organised to form T-O-T layers alternating with an interlamellar space containing exchangeable cations and water molecules. Thanks to the ability to modulate the physico-chemical features of saponites at different levels: 1) by modifying the composition, structure, and morphology through varying the dilution of the synthesis gel in the hydrothermal synthesis; 2) by introducing metal ions into the lamellae framework in order to confer specific properties to the final materials; 3) by modifying the interlayer space of saponite through the intercalation of different chemical entities (e.g., ions, organic substances, metal chelates), it was possible to obtain the aforementioned materials NbSAP, Na-SAP, and H-SAP. The experiments were conducted under mild reaction conditions, both in anhydrous and aqueous media. In the case of paraoxon-ethyl degradation tests, the saponites, particularly NbSAP, exhibited high conversion rates in both media (up to 84% in water and 87% in EtOAc), attributed to a cooperative adsorption and acid-catalyzed hydrolytic reaction. NbSAP also showed good regenerability after three cycles. In catalytic tests on parathion-ethyl in anhydrous environment, saponites and aluminosilicates with a high Al2O3 content show a decrease of about 20% after 24 h. Water tests, despite lower concentrations, show promising performance, with saponites and commercial aluminosilicates exhibiting good catalytic capabilities, as evidenced by liquid 31P-NMR analyses, where the signal associated with parathion disappears completely after 5 min. Solid-state 31P and 1H-NMR analyses on recovered catalysts reveal degradation products adsorbed on the surface and in the porous network of the materials. These results are particularly interesting, especially because they were obtained under mild environmental conditions, employing green solvents and cost-effective, durable materials. Likewise, cation-exchange resins with acid sulfonic groups were selected and studied as a cheap, versatile, and effective tool for the catalytic oxidative abatement of (2-chloroethyl)ethyl sulfide (CEES), a CWAs simulant of blistering sulfur mustard, in the presence of aqueous H2O2. Amberlyst® 15 showed excellent performance, reaching almost 89% conversion after 3 h, with gradual formation of the corresponding non-toxic sulfoxide (CEESO) and, only later, with further formation of the noxious sulfone (CEESO2). Extensive studies have revealed the factors influencing the distribution of products, suggesting a synergistic effect between Brønsted acid sites and oxidizing species. Excellent resin regenerability has been confirmed and up to 4 consecutive cycles were carried out. Sulfonic resins emerge as effective and cheap catalysts for chlorine-free oxidative abatement of hazardous organosulfur agents. The study is a remakable starting point for the implementation of efficient decontamination systems, suggesting applications in catalytic beds or as films for self-cleaning surfaces in chemical-contaminated environments. Detection of Explosives - With the aim of overcoming the limitations of traditional detection techniques, primarily associated with poor sensitivity and/or selectivity, two derivatives of cyclic triimidazole and pyrene, namely the blue emitting 3-(pyren-1-yl)triimidazo[1,2-a:1′,2′-c:1″,2″-e][1,3,5]triazine, TTPyr, and the yellow-orange-emitting 11-(pyren-1-yl)triimidazo[1,2-a:1′,2′-c:1″,2″-e][1,3,5]triazine-3,7-dicarbaldehyde, (CHO)2TTPyr, were here exploited for titration experiments with various nitroaromatic energetic hazardous materials and proposed as sensor species for the quantitative detection of explosives. The 565 nm fluorescence of (CHO)2TTPyr represents a valid alternative to the TTPyr 420 nm one for analytes absorbing in the blue region. (CHO)2TTPyr displays various fluorescence quenching values in the presence of different nitroaromatics. In particular, picric acid (PA) gave rise to the highest sensitive response with a Stern-Volmer quenching constant value equal to 1.25 × 104 M−1, with a calculated detection limit of 0.63 ppm. From time-resolved photoluminescence experiments, a static mechanism is recognized as responsible for the observed quenching. The hypothesis of a dark complex formation is supported through the isolation and characterization of a TTPyr/PA adduct with 2:1 stoichiometry. Nanostructured Inorganic Materials Functionalized with Bio-Active Principles for Sustainable Pest Control Methods – A series of nanostructured inorganic solids, including bentonite montmorillonite and zeolite clinoptilolite, were selected to find an alternative and sustainable approach against the olive fruit fly parasite, Bactrocera oleae, the most damaging pest of olive tree cultivations in the Mediterranean area. The implementation of sustainable pest control methods, alternative to conventional synthetic insecticides, have attracted increasing attention, especially after the ban of dimethoate by the European Union. These solids were functionalized with bio-active principles, particularly linear aliphatic aldehydes, or exchanged with copper(II), aiming to obtain materials with a slow release of these active ingredients. Extremely promising results were achieved in open-field trials, showcasing significant reductions in both fly infestation (up to a 98%) and damage to the olive fruit. In the same context, parallel studies were performed on synthetic saponite clay impregnated with either linear saturated or unsaturated aldehydes through an incipient-wetness deposition approach. To increase the aldehyde loading, saponite was also intercalated with positively charged cetyltrimethylammonium (CTA+) species, aiming to expand the clay gallery and to increase the hydrophobic character of the host solid. The analyses, conducted on the materials, revealed that the aldehydes are mainly adsorbed on the clay particles’ surface, with a small fraction inside the interlayer space. In CTA+-modified saponites, the concentration of aldehydes was higher than the one observed in the pure clay. These features are quite promising for the set-up of novel layered solids and hybrid materials containing bioactive molecules for environmentally friendly and economically sustainable applications, whose application is particularly relevant to agriculture.