Preparation, Application And Mechanism Of RGO/TiO₂and RGO/Fe₃O₄Nano-composites

When their sizes decrease into the nanoscale, the materials will display uniquedifferent properties, such as surface-dependent effect or quantum size effect.Nanomaterials have attracted continuous attention from their emergency. In2004,Geim and Novoselov firstly prepared the novel carbon materials, graphene, which is akind of single molecule plane material, which is made of two-dimensional hexagonalhoneycomb lattice of carbon. Development of nano materials will meet its newmilestone because of excellent properties of graphene. In this article, we mainlydiscussed the preparation, application and mechanism of RGO/TiO2and RGO/Fe3O4nano-composites which is based on the reduced grapheme oxide (RGO).1. By hydrothermal treating the precursors of TiO2hydrosol with incompletelycrystallized TiO2nanocrystalline and GO suspension obtained by a modified Hummers’method, we synthesized visible light responsive RGO/TiO2nanocomposites.Synthesized at the optimized condition of413K for24h, the sample G-TiO2-413, inwhich the sizes of TiO2nanoparticles were about4.7nm, displayed the best efficiency.More than99%methyl orange can be removed after2h visible light irradiation.Investigated by the control tests and the characterizations of FT-IR, ESR and Ramanspectra, the origin of the visible light activity of the RGO/TiO2nanocomposites wererevealed. The interaction between crystal oxygen and the adsorbed GO made it possibleto generate relatively stable oxygen vacancies during the growth of TiO2nanocrystalline, which is the main reason of visible light activity.The role of GO in thesynthesis of nanocomposites includes to increase the amount of alkoxy, induce crystaldisorder and create oxygen vacancy, which eventually lead to a significant increase ofcatalytic activity of G-TiO2-413under visible light. This study could provide newstrategy to develop visible light driven TiO2by surface modification on the molecularscale.2. Through an in situ coprecipitation approach, by dropwise adding ammonia into themixture solution of FeCl2, FeCl3and GO with various ratios, magnetic RGO/Fe3O4nanoadsorbent has been prepared. TEM images showed that Fe3O4nano-particles with sizes of10-20nm were uniformly dispersed on the surface of RGO.According tothe analyses of adsorption kinetics and isotherm, Fe3O4and RGO with a ratio of2:1hasthe highest adsorption capacity of142.86mg·g-1, which is3.7times higher than that ofAC, and has the relatively faster adsorption rate, about20min to reach an adsorptionequilibrium, which is30times faster than that of AC. The isothermal adsorption of thenanocomposites can be fitted better with the Langmuir model, indicating the adsorptionprocess is almost the monolayer adsorption. Employing Fe3O4nanoparticles as theheterogeneous Fenton catalyst, the adsorbed RhB can be removed efficiently byFenton-like reaction. The as-synthesized RGO/Fe3O4can be separated from aqueoussolution by weak magnetic field, and possess huge adsorption capacity and fastadsorption rate, which could be a promising novel efficient adsorbent. After saturatedby organics, the adsorbent can be regenerated by a Fenton-like reaction to remove theadsorbed organics, which could be a potential regeneration way with no generation ofsecondary pollution. Keywords: TiO2, Fe3O4, graphene oxide, photocatalysis, visiblelight, adsorbent, regeneration.