Synthesis of Fe3O4@SiO2@α-Fe2O3/TiO2-rGO nanohybrids for heterogeneous photocatalytic transformation of lignocellulosic biomass.

This study explored mild and cost-effective conditions for the valorization of lignocellulosic biomass. Herein, reduced graphene oxide (rGO) supported magnetic core double-shell nanomaterials were successfully synthesized by an innovative four-step approach. Fe₃O₄ nanoparticles were first produced to act as cores without using any surfactants. The magnetite/silica core–shell structure was then prepared by hydrolysis of tetraethoxysilane in the presence of core particles under alkaline conditions. The outermost shell, the α-Fe₂O₃/TiO₂ layer, was grown over a magnetic core of Fe₃O₄@SiO₂ using a co-precipitation and calcination approach. Furthermore, nanohybrids were fabricated by loading Fe₃O₄@SiO₂@α-Fe₂O₃/TiO₂ nanoparticles on rGO using a hydrothermal method. Nanomaterial characterization by vibrating-sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) showed both nanomaterials with and without rGO support are soft ferromagnetic and the presence of Fe₃O₄, TiO₂, Fe₂O₃ and SiO₂ in both nanomaterials. The nanohybrids exhibited increasing photocurrent as a function of illumination by cool white fluorescent light, and their magnetic property enabled the particles to be magnetically separated for recycling and reuse. The efficient photoactivity of the Fe₃O₄@SiO₂@α-Fe₂O₃/TiO₂-rGO nanohybrids was confirmed for conversion of two lignocellulose model compounds: 83.9% for conversion of D-xylose, and production of 0.49 mol lactic acid for conversion of 1 kg of sodium lignosulfonate; these results represent an improvement compared to the core double-shell nanoparticle without rGO support. Increased productivities were also obtained for four other products in conversion of sodium lignosulfonate using the rGO-supported nanomaterials compared to the ones without rGO support. These findings indicate that the rGO support improved the properties of Fe₃O₄@SiO₂@α-Fe₂O₃/TiO₂, possibly by acting as an electron acceptor—thereby avoiding high recombination of electron–hole pairs and increasing the generation of hydroxyl radicals. Our primary results suggest that the approach exemplified by the produced photocatalysts may potentially lead to cost-effective and environment-friendly strategies for reducing lignocellulosic biomass and generating value-added chemicals in large scales. [ABSTRACT FROM AUTHOR]