Preparation And Photocatalytic Hydrogen Production Performance Of Graphene/TiO₂-Bi₂O₃/PMMA Coaxial Microtubules

The shortage of energy sources has become a threat to human survival and development.Hydrogen energy is considered to be a promising alternative energy sources due to it’s efficient,clean,safe and stable.Photocatalytic water splitting for hydrogen evolution can convert the inexhaustible solar energy to hydrogen energy,which has become one of the most ideal approaches to solve environmental and energy problems.Preparing highly efficient and stable photocatalytic materials is the key for developing the photocatalytic hydrogen production technologies.In this study,micrometer-scaled copper wires were employed as template to construct a new composite photocatalyst with three-dimensional structure——Graphene/TiO2-Bi2O3/PMMA coaxial microtubules.The as-prepared materials were characterized by several methods and their photocatalytic activity of H2 generation was evaluated.The main research contents as follows:Firstly,graphene was grown on copper wires by chemical vapor deposition using methane as the carbon source.The CVD-grown graphene samples were characterized by scanning electron microscope,Raman spectra and atomic force microscopy,respectively.The bi-layered or tri-layered graphene with good quality were obtained at the optimized preparing conditions.Secondly,TiO2-Bi2O3 layer was synthesized on the surface of copper wire/graphene and a thin PMMA film was coated on the surface prior to the removal of copper wire using an etching solution(NH4)2S2O8.The results showed that the prepared materials possessed a hollow microtubule structure.The formation of heterojunctions by coupling narrow band gap semiconductor(Bi2O3)with wide band gap semiconductor(TiO2)extended the range of spectral response,and suppressed the recombination of photogenerated electron-hole pairs.Graphene acted as a supporting layer,moreover,it also helps transferring photogenerated electrons to improve the quantum efficiency.Finally,the photocatalytic hydrogen production activity of the resultant graphene/TiO2-Bi2O3/PMMA coaxial microtubules were evaluated under irradiation of a 300 W Xenon lamp.Triethanolamine was employed as a scavenger.The composite materials exhibit an obvious enhancement in photocatalytic H2 evolution activity.H2 evolution of the composite materials achieved 607.30 μmol/5h when the content of Bi2O3/TiO2 is 2 wt%,which was 18.9 times than pure TiO2(32.13 μmol).The higher photocatalytic performance of the composite materials can be attributed to the increment of the visible light absorption,the enhancement of separation efficiency of photogenerated charge carriers,the high of stability and the special structure of the materials.