Amidoxime-derived rice husk as biocatalyst and scavenger for organophosphate neutralization and removal

Organophosphates are a worldwide threat because of their presence in agrochemicals and chemical warfare. Situations of misuse, apprehensions of prohibited chemicals (e.g. pesticides), undesired stockpiles and chemical attacks require effective measures for neutralization and removal. Herein, a green approach is shown by func-tionalizing the agricultural waste rice husk with amidoximes leading to heterogeneous catalysts that were applied in the degradation/scavenging of toxic organophosphates. In aqueous medium, the waste-derived catalyst was efficient in the catalytic neutralization of a phosphotriester (increments up to 1 x 104-fold), while allying important features: selective, recyclable and lead to less toxic products. Curiously, the amidoxi-mated rice husk behaved as a scavenger in the aprotic polar solvents MeCN and acetone by covalently bonding to the phosphoryl moiety. Upon addition of water, this bond is broken and the phosphoryl liberated (hydrolyzed) to the aqueous medium. Thus, the scavenging process is reversible and can be used to remove toxic organophos-phates. 31P nuclear magnetic resonance spectroscopy was crucial for confirming the overall mechanisms involved. In summary, a sustainable material was synthetized from a waste source and employed as catalyst and scavenger for eliminating threatening organophosphates. This is promising for assuring chemical security such as in chemical emergencies.

Automated summary

A green approach was demonstrated by functionalizing rice husk waste and using it as a catalyst and scavenger to remove toxic organophosphates. The waste-derived catalyst effectively neutralized phosphotriesters in aqueous medium with significant increases in efficiency. The amidoximated rice husk also acted as a scavenger in aprotic polar solvents, forming covalent bonds with the phosphoryl moiety, which could be reversed by adding water.