| Photocatalytic technology is considered to be a new and effective purification technology for the removal of various organic pollutants. TiO2 is one of the most well-known photocatalysts due to its low cost, chemical stability, and high photocatalytic performance. However, TiO2 photocatalytic materials still can't be widely used in practical applications due to its fast recombination of photogenerated electrons and holes in the surface and body of the TiO2, which results in a low quantum yield. Graphene nanosheet, as a new carbon material from a single layer of carbon atoms, shows excellent electrical conductivity and high specific surface area, which can be used as an effective mediator(electron-cocatalyst) for the TiO2 photocatalytic materials to enhance its photocatalytic performance. To further modify the graphene as electronic cocatalyst, this paper focuses on the surface functionalization of graphene:(1) the synergistic effect of Fe(III) and rGO for the improved TiO2 photocatalytic activity;(2) the amine-functionalized graphene-TiO2 composite materials for the photocatalytic selective degradation of methyl orange. The main results could be summarized as follows:Firstly, for a high-performance cocatalyst-modified photocatalyst, an effective interfacial separation of photogenerated electron from its corresponding holes and its following reduction reaction at the active sites are highly required. However, it is difficult for a single-component cocatalyst to simultaneously realize the crucial functions. In this study, an effective interfacial transfer of photogenerated electrons and its following rapid oxygen-reduction can be easily realized in a dual electron-cocatalyst modified Fe(III)/rGO-TiO2 photocatalyst, where the rGO nanosheets function as an electron-transfer mediator for the effective transfer of photogenerated electrons from the TiO2 surface while the Fe(III) cocatalyst serves as an electron-reduction active site to promote the following interfacial oxygen reduction. In this case, the rGO nanosheets were firstly loaded on the TiO2 nanoparticle surface by a hydrothermal method and then the Fe(III) cocatalyst was further modified on the rGO nanosheets by an impregnation method to prepare the Fe(III)/rGO-TiO2 photocatalyst. It was found that the dual electron-cocatalyst modified Fe(III)/rGO-TiO2 photocatalyst showed an obviously higher photocatalytic performance than the naked TiO2 and single-cocatalyst modified photocatalysts(such as Fe(III)/TiO2 and rGO-TiO2) owing to the synergistic effect of rGO and Fe(III) bi-cocatalysts. The present work can provide some new insights for the smart design of high-efficiency photocatalytic materials.Secondly, amine-functionalized graphene is mainly used in lithium-ion battery and supercapacitors, and has seldom been used in photocatalytic field. In this study, the amine-functionalized graphene-based TiO2 photocatalyst(namely PNH2–rGO /TiO2) was first prepared via a hydrothermal(160oC) method to prepare the rGO/TiO2 precursor, and then the aniline was loaded on the surface of rGO nanosheets in rGO/TiO2. The results showed that the PhNH2-rGO/TiO2(30:1) photocatalyst showed the highest photocatalytic activity for the degradation of methyl orange(MO), which is about 11.4 and 2.3 times of pure TiO2 and rGO/TiO2, respectively. In addition, only phenylamine(the mass ratio of phenylamine to graphene is 30: 1 to 50: 1) in PhNH2 –rGO/TiO2 can selectively degrade methyl orange, orange II and brilliant red X-3B. As a consequence, a selective photocatalytic mechanism was proposed to account for the selective photocatalytic activity. Compared with the phenylamine, other aliphatic amines(cyclohexylamine, n-butylamine), organic ammonium salts(ammonium iodide, CTAB) and inorganic ammonia(ammonia) as the modified substances showed no selective degradation performance in PNH2-rGO/TiO2, which may be caused by the destroy of coupling interface between the graphene and TiO2 nanoparticles. |
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