Synthesis of reverse micelle α-FeOOH nanoparticles in ionic liquid as an only electrolyte: Inhibition of electron–hole pair recombination for efficient photoactivity

• Discrete α-FeOOH nanoparticles with 5–10 nm in size were synthesized.
• Reverse micelle formation was found to stabilize and miniaturize the nanoparticles.
• The reverse micelle bound on the catalyst trapped the photogenerated electron.
• This Fenton-like system was optimized at pH 5, instead of highly acidic condition.
• H2O2 molar concentration was reduced by 10-fold compared to typical 2-CP degradation.

Discrete α-FeOOH nanoparticles (5–10 nm) were synthesized by a simple electrochemical method using an ionic liquid (IL), dodecyltrimethylammonium bromide (IL − FeOOH). IL that acts as an only electrolyte is capable of producing IL − FeOOH nanoparticles without any agglomeration. Its crystallinity, morphology, functional characteristics, and surface area were analyzed using an X-ray diffractometer, a transmission electron microscope, a Fourier-transform infrared spectrometer, and the Brunnauer–Emmett–Teller (BET) method, respectively. The characterization results verified that reverse micelle formation of IL plays an important role in the stabilization and miniaturization of the α-FeOOH nanoparticles. The activity of IL-FeOOH was tested on a photo-Fenton-like degradation of 2-chlorophenol (2-CP). Results showed that a nearly neutral condition of pH 5 was able to completely degrade 2-CP within 180 min of reaction at 50 °C, using 0.03 g L−1 of catalyst dosage and 50 mg L−1 of 2-CP initial concentration, with only a small amount of H2O2 (0.156 mM). It was found that the reverse micelle formed around the catalyst surface could trap the photogenerated electron to inhibit the recombination of photo-induced electron–hole pairs thus enhancing its catalytic activity. Kinetic studies using the Langmuir–Hinshelwood model illustrated that a surface reaction was the controlling step of the process. A reusability study showed that the catalyst was still stable after four subsequent reactions as shown by infrared spectroscopy. The results provide strong evidence to support the potential use of using IL as an alternative electrolyte to synthesize photo-Fenton-like nanocatalyst that can be used to treat organic pollutants such as 2-CP.

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