Green Preparation And Performance Of Eosin Y-Sensitization Graphene Photocatalytic Materials

The photocatalytic production of hydrogen by splitting water has attracted worldwide attention due to increasing energy demands.It is a challenge to establish stable,highly efficient and affordable heterogeneous photocatalytic systems for H₂production from water splitting today.Graphene,a 2-dimensional single sheet of sp²-hybrized carbon atoms,possesses huge specific surface area,excellent electron mobility,stable chemical performance and so on.Graphene itself acts as not only the carriers and sensitizers of other semconductors,but also the photocatalysts and cocatalyst for H₂ evolution.Hence,it has been the research topic in photocatalysis field.Graphene obtained by traditionally mechianical exfoliation of graphite or chemical vapor deposition?CVD?has the complete structure and excellent performances,however,which is not applicable in photocatalysis region.While graphene could be easily synthesized from reducing graphene oxide?GO?which is obtained by chemical oxidizing graphite via different reducing methods.It is a cheap,scalable and mass-scale preparation method.Moreover,the obtained reduced graphene oxide?RGO?not only retains the?-conjugated structure of graphite,but also contains some oxygen-containing functional groups on its surface.Therefore,RGO possesses good conductivity as well as high dispersity,which is beneficial to combination with other semconductors and cocatalysts.Recently,chemical reduction of GO has been one of the most important method to synthesize RGO and RGO based composites.However,the obtained RGO would restack seriously,be poor dispersity in water and low BET surface area.Moverover,the use of the toxic chemical reagents would harm to the human beings and the enviroment.In this thesis,RGO is firstly prepared by green and modified reducing GO for dye-sensitized photocatalytic hydrogen production under visible light irradiation.Secondly,in order to replace the noble metal Pt,layered and porous RGO/Ni composites are synthesized using GO and NiCl₂ as raw materials for electrocatalytic and dye-sensitized photocatalytic hydrogen evolution from water splitting under under visible light irradiation.The whole work is composed of the following four parts:???.Scalable RGO dispersion is synthesized by GO dispersion in a green method under a Xenon lamp irradiation.The obtained RGO possesses excellent dispersity and good conductivity.This RGO dispersion exhibits highly efficient dye-sensitization photocatalytic activity for hydrogen evolution with Eosin Y?EY?as a sensitizer and Pt as a co-catalyst.Under the optimum conditions,the maximal apparent quantum yield?AQY?of EY-RGO/Pt system for hydrogen evolution rises up to 12.9%under visible light irradiation???420 nm?,and 23.4%under monochromaticlight irradiation at 520 nm.???.To maintain graphene's properties and avoid restacking of RGO sheets in bulk,the preparation of 3-dimensional porous graphene sponge via 2-dimensional RGO sheets is considered a good strategy.RGO sponge is synthesized in a facile route of thermal treating GO powder at low temperature of 250 ^oC under N₂ atmosphere.The obtained sponge possesses macroporous structure?5-200 nm in size?with BET specific surface area 404 m² g^-1 and high conductivity.Using EY as a sensitizer of the RGO sponge and Pt as a co-catalyst,the photocatalytic activity for hydrogen evolution was investigated.The RGO sponge shows highly efficient dye-sensitized photocatalytic H₂ evolution activity using EY as a sensitizer and Pt as a co-catalyst.The maximum AQY reaches up to 75.0%at 420 nm,much higher than that of RGO obtained by chemical reduction,which is one of the most reported results.???.In order to replace the noble metal Pt,it is necessary to prepare the abundant and low-cost cocatalysts for electrocatalytic and photocatalytic H₂ evolution from water splitting.Reduced graphene oxide/Ni?GN?composites with various Ni contents as cocatalysts are synthesized by one-pot thermal reduction of GO/NiCl₂mixture in N₂+H₂ atmosphere at 500 ^oC.The GN composites show the sandwich layer structure and exhibit much better electrocatalytic and dye-sensitized hydrogen evolution reaction?HER?activities than RGO alone and Ni alone,namely synergetic effect.Under the optimal conditions,the maximum AQY of GN for dye-sensitization hydrogen evolution reaches 30.3%at 470 nm.???.In order to increase the diffuse of reactant H₂O,porous Ni/reduced graphene oxide composites?PNG?are synthesized using GO sol as a raw material.The PNG composites present sponge-like structure with hollow Ni NPs.The electrocatalytic and dye-sensitized photocatalytic activities for H₂ evolution of PNG exhibit excellent synergetic effect,much higher than those of GN composites,which are contributed to the presence of hollow Ni NPs.Under the optimal conditions,the highest AQY for dye-sensitized photocatalytic hydrogen evolution reachesup to 47.7%at 470 nm.This work provides a new approach for synthesis of various porous metal–RGO materials.