Efficient removal of aqueous organic pollutants by well-ordered layered manganese oxide nanocomposites: Impacts of interlayer spacing and nanoconfinement

Although manganese oxide is able to spontaneously oxidize organic contaminants in nature, the slow kinetics limit its application in engineered water treatment processes. Herein, we prepared well-ordered layered manganese oxides (LMOs) with adjustable interlayer distances using cetyltrimethylammonium bromine as a guest molecule, which were applied to degrade 3-chlorophenol as an example of organic pollutants. The ordering of the layered structure was found to be highly dependent on the molar ratio of cetyltrimethylammonium ion (CTA+) to Mn in the solutions (range 0–1.2). The maximum interlayer spacing (11.27 Å) was obtained at a molar ratio was 1.0 (LMO-1.0), which reduces the steric hindrance for 3-chlorophenol entering the interlayers. Additionally, the surface of the LMOs becomes more hydrophobic as their molar ratio increased, further favors adsorption of 3-chlorophenol on the LMO-1.0. The LMO-1.0 provides a constrained reaction environment, which increases the probability of 3-chlorophenol interacting with the active species as well as promotes the production and enrichment of superoxide radical (O2•−). Consequently, the degradation rate constant of 3-chlorophenol (0.446 min−1) is two orders of magnitude higher compared to the unconfined bulk phase (0.004 min−1). These findings provide useful insights into the development of Mn-based layered materials for water purification.