Cellulose nanocrystals assembled on the Fe3O4 surface as precursor to prepare interfaced C/Fe3O4 composites for the oxidation of aqueous sulfde

Abstract

In this work, composites based on carbon (1, 10 and 20 wt.%) interfaced with Fe3O4 (magnetite) have been studied as catalysts for the oxidation of aqueous sulfde. The composites were prepared by assembling cellulose nanocrystals surrounding Fe3O4 followed by a controlled thermal decomposition at 400, 600 and 800 °C. Mössbauer, X-ray diffractometry (XRD), Raman, thermogravimetry (TG), elemental analysis CHN, scanning electron microscopy (SEM/EDS), Fourier transform infrared spectroscopy (FTIR) and potentiometric titration indicated that at 400 and 600 °C the cellulose nanocrystals decompose to different carbon forms, i.e., flms, flaments and particles attached to the Fe3O4 crystals. At higher temperature, i.e., 800 °C, this carbon on the magnetite surface further reacted to produce Fe0. UV-Vis, Raman and electrospray ionization mass spectrometry (ESI-MS) measurements showed that these composites catalyze the oxidation of aqueous sulfde to convert S2- aq to polysulfdes Sn 2- (where n = 2-9) and also oxygen containing polysulfdes HOSn -. Simple kinetic experiments showed very low sulfde oxidation activities for pure Fe3O4 and pure carbon. On the other hand, the composites, especially with 10% C obtained at 600 °C, were remarkably active. These results are discussed in terms of a possible participation of oxygen based redox groups present on the carbon surface and an electron transfer from the carbon to the Fe3O4 phase.