Híbridos de nanotubos de carbono e hematita: síntese e caracterização

Abstract

Developing renewable and non-polluting energy sources is one of the major challenges of this century. Solar energy has many advantages: its renewable, abundant and generously distributed throughout the world. Solar radiation can be converted to heat or to electricity, or stored in chemical fuels, like hydrogen (H2). The solar hydrogen productionoccurs by the splitting of water molecules into O2 and H2. However a water molecule itself does not absorb light in the visible spectrum so it is essential to use a material to absorb the energy and carry the splitting reaction. In this work, the synthesis of carbon nanotubes/hematite hybrids was investigated aiming their application as photoanodes for H2generation. Hematite has several advantages as a semiconductor material for this end. However, it shows poor charge transport properties that limit its efficiency. The use of carbon nanotubes aims to minimize recombination losses by capturing the photo-generated electrons and transporting them to external circuit. The hybrids were produced by two different inexpensive and simple methods of growing: solvothermal method and method of physical impregnation. A systematic study was performed exploring different reaction parameters such as CNT functionalization, reaction duration, temperature and solvent. The hybrids were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive spectroscopy and UV-VIS absorption spectroscopy. Scanning and transmission electron microscopy results demonstrate that the CNTs were decorated with hematite nanoparticles (NPs). The size and concentration of the NPs varies with the reaction parameters. X-ray diffraction and energy dispersive analysis confirm that the NPs have the alfa-Fe2O3, hematite phase. Thin films of the hybrid material were deposited on indium-tin oxide substrates by electrophoretic deposition and filtration. Translucent and homogeneous films were produced. Finally, preliminary tests showing the photoelectrochemical response of the produced films demonstrate the potential of this hybrid material as an anode for the photolysis of water.