Polarity Effects on Synthesis of Feroxyhite FeOOH Nanomaterials by DC Atmospheric Pressure Microplasma in Air

Our presentation deals with feroxyhite FeOOH nanomaterial production by an atmospheric pressure microplasma in the air under different polarities. A positive (negative) DC voltage was applied to a carbon rod facing an aqueous ferrous solution connected to a negative (positive) terminal of a high-voltage source via a carbon electrode. A four-time higher mass-production yielded under the positive polarity setup than under the negative polarity setup at 9.0 kV and 3.0 kV/mm. X-ray diffraction investigations showed that all products were the same phase with nanostructures. UV-vis spectra indicated that the negative polarities led to a fast synthesis of the nanomaterials in 5 min while the positive polarities produced the phase in 20 min, 4 times slower, under the same experimental conditions. The polarity effect was also confirmed at high voltages up to 25kV. Possible chemical reactions in solution are discussed in light of the different polarities of the discharge. Our results showed that the polarities can affect nanomaterial syntheses significantly in atmospheric pressure microplasma.