Impact of Surface Chemistry on Microwave-Induced Degradation of Atrazine in Mineral Micropores

Abstract

Surface chemistry determines the interactions of sorbate and solvent molecules with the pore wall surfaces of microporous minerals, and affects the transmission and absorption of microwave radiation for a given solvent-sorbate-sorbent system. The sorption and microwave-induced degradation of atrazine in the micropores of nine Y zeolites with different densities (0.16-2.62 site/nm(2)) and types (Mg(2+), Ca(2+), H(+), Na(+), and NH(4)(+)) of surface cations were studied. The influence of the content of cosorbed water in the mineral micropores on atrazine degradation rate was also examined. The results indicate the presence of surface cations at around 0.23 site/nm(2) on the pore wall surface was optimal for atrazine degradation, probably due to formation of insufficient number of "hot spots" with too few cations but excessive competition for microwave energy with too many hydrated cations. Atrazine degraded faster in the presence of cations with lower hydration free energies, which could be attributed to less microwave energy consumption to desorb the bounded water molecules. Reducing the content of coadsorbed water in the micropores also increased atrazine degration rate because of less competition for microwave energy from water. Such mechanistic understanding can guide the design and selection of microporous minerals in the practical application of microwave-induced degradation.