Neighboring Effects on the Selective Bifunctionalization of Graphene Oxide for Nanocatalytic Organophosphate Neutralization

The bifunctionalization of graphene oxide (GO) has attracted attention as a promising tool for broadening applications, despite its many challenges, especially regarding site-specific reactions. Herein, we obtained mono- and bifunctionalized GO containing thiol and imidazole groups that were anchored on the carboxylic acid sites of GO via amidation reactions. We varied the bifunctionalization methodology and showed that consecutive addition of the reagents (containing imidazole and thiol groups) led to materials with higher degrees of functionalization, in contrast to their simultaneous addition. The functionalized materials were evaluated as nanocatalysts in the neutralization reaction of a toxic organophosphate. Also, it was evidenced that the effect of the mono- and bifunctionalized materials on the catalytic outcomes gives insight toward neighboring effects. All catalysts were effective in the reaction studied with the monofunctionalized materials (containing thiol or imidazole groups) showing similar activity. Among the bifunctionalized materials (with both thiol and imidazole moieties), the one with the lower degree of functionalization showed the best performance. This was attributed to a combination of mechanisms, strongly dependent on the neighboring groups: attraction on the GO surface, nucleophilic catalysis by thiol/imidazole groups, and bifunctional intramolecular catalysis, for example, by thiol and imidazole groups, assisting potential nucleophilic hydroxyl groups. Oddly, the bifunctionalized materials with the higher degree of functionalization did not show the most prominent activity; they were actually similar to the monofunctionalized ones. This can be attributed to the inhibition or hindering of some of the proposed mechanisms due to steric effects or a nonideal positioning of the groups. A lot remains to be clarified in this field, but one thing is clear: a higher degree of functionalization should not always be pursued because the application of the material is what should guide what characteristics should be determined. Several other applications should be impacted by neighboring effects, which are directly influenced by the functionalization procedure.

Automated summary

This study reports the synthesis of mono- and bifunctionalized graphene oxide (GO) materials containing thiol and imidazole groups via amidation reactions. The catalytic performance of these functionalized materials was evaluated in the neutralization reaction of a toxic organophosphate. The results showed that consecutive addition of reagents led to higher degrees of functionalization, and in the case of bifunctionalized materials, those with lower degrees of functionalization exhibited better catalytic performance. This study provides insights into neighboring effects and emphasizes the importance of considering the functionalization degree in determining the material's application.