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

Abstract

Discrete alpha-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 alpha-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 degrees 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.