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

• A class of carboxymethyl cellulose stabilized MnO2 nanoparticles was synthesized.
• The nanoparticles effectively degrade aqueous and soil-sorbed 17β-estradiol.
• CMC-MnO2 is more effective than bare MnO2 for degrading soil-sorbed estradiol.
• A retarded first-order rate model adequately simulated the degradation kinetics.
• CMC-MnO2 can potentially be delivered and distributed in contaminated soil.

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.

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