title: Growing TiO2 nanowires on the surface of graphene sheets in supercritical CO2: characterization and photoefficiency.
abstract: Tremendous interest exists towards synthesizing nanoassemblies for dye-sensitized solar cells (DSSCs) using earth-abundant and -friendly materials with green synthetic approaches. In this work, high surface area TiO(2) nanowire arrays were grown on the surface of functionalized graphene sheets (FGSs) containing -COOH functionalities acting as a template by using a sol-gel method in the green solvent, supercritical carbon dioxide (scCO(2)). The effect of scCO(2) pressure (1500, 3000 and 5000 psi), temperature (40, 60 and 80 °C), acetic acid/titanium isopropoxide monomer ratios (HAc/TIP = 2, 4 and 6), functionalized graphene sheets (FGSs)/TIP weight ratios (1:20, 1:40 and 1:60 w/w) and solvents (EtOH, hexane) were investigated. Increasing the HAc/TIPweight ratio from 4 to 6 in scCO(2) resulted in increasing the TiO(2) nanowire diameter from 10 to 40 nm. Raman and high resolution XPS showed the interaction of TiO(2) with the -COOH groups on the surface of the graphene sheets, indicating that graphene acted as a template for polycondensation growth. UV-vis diffuse reflectance and photoluminescence spectroscopy showed a reduction in titania's bandgap and also a significant reduction in electron-hole recombination compared to bare TiO(2) nanowires. Photocurrent measurements showed that the TiO(2)nanowire/graphene composites prepared in scCO(2) gave a 5× enhancement in photoefficiency compared to bare TiO(2) nanowires.
authors: Department of Chemical and Biochemical Engineering, University of Western Ontario, London, ON, N6A 5B9, Canada.
authors: Nasrin
authors: N
authors: Farhangi
authors: Yaocihuatl
authors: Y
authors: Medina-Gonzalez
authors: Rajib Roy
authors: RR
authors: Chowdhury
authors: Paul A
authors: PA
authors: Charpentier
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry; D004396:Coloring Agents / Q000737:chemistry*; D055664:Electrochemical Techniques; D006108:Graphite / Q000737:chemistry*; D055772:Green Chemistry Technology / Q000379:methods*; D049329:Nanostructures / Q000648:ultrastructure; D036103:Nanotechnology / Q000379:methods*; D053770:Nanowires / Q000737:chemistry* / Q000648:ultrastructure; D055668:Photochemical Processes; D016062:Porosity; D012993:Solar Energy; D014025:Titanium / Q000737:chemistry*
chemical_list: D004396:Coloring Agents; D002245:Carbon Dioxide; C009495:titanium dioxide; D006108:Graphite; D014025:Titanium