Screening catalysts for agrochemical neutralization: selective functionalization and effects of coverage, support, group and neighboring Elisa Orth, Yane H. Santos, André H. G. Martinez, Vinícius O. Costa, José G. L. Ferreira, Willian Takarada, Mariana H. Nazareno, Maria H. Verdan, Aldo J. G. Zarbin Federal University of Paraná, Brazil Agrochemicals and chemical warfare have a lot in common, since they constitute the class of organophosphates, known to be highly toxic. Abusive use, intoxication, terrorist attacks, civil war, unsafe food are some of the issues that concern regarding these compounds. Hence, it has been of great interest to develop efficient methods for alerting attacks, monitoring crops/food and overall neutralizing undesired stocks and warheads. Catalysts- by-design is a promising approach, since the reactions of organophosphates are extremely slow. Our group has been focused in combating organophosphates, mainly seeking: (i) milder conditions for the neutralization/ synthetic processes; (ii) catalysts derived from various materials (cellulosic and nano) and sustainable sources (rice husk and shrimp shell); (iii) colorimetric sensors. We pursued site-selective mono and bifunctionalization of various complex materials, such as graphene oxide, carbon nanotubes, gum arabic (commercial and industrial waste) and cellulosic wastes (rice husk and shrimp shell), with thiol, imidazole, amidoxime and hydroxamate groups (covalently linked) and applied as neutralizing agents. The catalysts were obtained as powder (for carbon nanotube with magnetic properties) and thin film, which facilitates separation and reuse. For the bifunctionalization, two different groups were anchored on specific sites of the material: (i) carboxylic acid for the cellulosic residues; and (ii) both carboxylic acid and epoxy sites for the graphene oxide. The catalysts are able to act as neutralizing agents for organophosphates, accelerating the process to less than 1 day, that otherwise could take millions of years. The process guarantees less toxic products and is selective and recyclable. The bifunctionalized catalysts showed an interesting relationship between coverage degree, group identity and neighboring effects. The materials with the highest degree of functionalization were not the best catalysts. This was attributed to cooperative effects between neighbouring groups that promote multiple catalyses (acid, basic and nucleophilic). In addition, a higher coverage by functional groups can disturb or even inhibit possible catalytic mechanisms, either by steric effect or non-ideal positioning of the groups. This finding was extremely important since it shows that the functionalization process pursued should be driven by the application wanted since not always what we expect as a better functionalization methodology will lead to the best response for a specific application. The catalysts also showed a dual function: could be used as sensors (surface enhanced Raman spectroscopy, electrochemical) and scavengers for these toxic agents. Finally, colorimetric sensors based on PVG glass and paper were developed for the detection of glyphosate, one of the most concerning agrochemicals (with a very challenging detection procedure). In summary, indeed the strategic design of various materials seeking optimal catalysts opens a myriad of possibilities for achieving prominent catalysis, especially for promoting worldwide chemical security by fighting agrochemicals and chemical warfare.
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© The Author(s), 2021
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