Degradation of aqueous and soil-sorbed estradiol using a new class of stabilized manganese oxide nanoparticles.

Manganese oxide (MnO₂) was reported to be effective for degrading aqueous pharmaceutical chemicals. However, little is known about its potential use for degrading soil-sorbed contaminants. To bridge this knowledge gap, we synthesized, for the first time, a class of stabilized MnO₂ nanoparticles using carboxymethyl celluloses (CMC) as a stabilizer, and tested their effectiveness for degrading aqueous and soil-sorbed estradiol. The most desired particles (highest reactivity and soil deliverability) were obtained at a CMC/MnO₂ molar ratio of 1.39 × 10(-3), which yielded a mean hydrodynamic size of 39.5 nm and a narrow size distribution (SD = 0.8 nm). While non-stabilized MnO₂ particles rapidly aggregated and were not transportable through a soil column, CMC-stabilized nanoparticles remained fully dispersed in water and were soil deliverable. At typical aquatic pH (6-7), CMC-stabilized MnO₂ exhibited faster degradation kinetics for oxidation of 17β-estradiol than non-stabilized MnO₂. The reactivity advantage becomes more evident when used for treating soil-sorbed estradiol owing to the ability of CMC to complex with metal ions and prevent the reactive sites from binding with inhibitive soil components. A retarded first-order rate model was able to interpret the oxidation kinetics for CMC-stabilized MnO₂. When used for degrading soil-sorbed estradiol, several factors may inhibit the oxidation effectiveness, including desorption rate, soil-MnO₂ interactions, and soil-released metals and reductants. CMC-stabilized MnO₂ nanoparticles hold the potential for facilitating in situ oxidative degradation of various emerging contaminants in soil and groundwater.