Cellulose Nanocrystals Assembled on the Fe3O4 Surface as Precursor to Prepare Interfaced C/Fe3O4 Composites for the Oxidation of Aqueous Sulfide

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 sulfide. The composites were prepared by assembling cellulose nanocrystals surrounding Fe3O4 followed by a controlled thermal decomposition at 400, 600 and 800 degrees C. Mossbauer, 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 degrees C the cellulose nanocrystals decompose to different carbon forms, i.e., films, filaments and particles attached to the Fe3O4 crystals. At higher temperature, i.e., 800 degrees C, this carbon on the magnetite surface further reacted to produce Fe-0. UV-Vis, Raman and electrospray ionization mass spectrometry (ESI-MS) measurements showed that these composites catalyze the oxidation of aqueous sulfide to convert S-aq(2-) to polysulfides S-n(2-) (where n = 2-9) and also oxygen containing polysulfides HOSn-. Simple kinetic experiments showed very low sulfide oxidation activities for pure Fe3O4 and pure carbon. On the other hand, the composites, especially with 10% C obtained at 600 degrees 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.