Growing TiO₂nanowires 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.

Angiogenic Rg1/Sr-Doped TiO2Nanowire/Poly(Propylene Fumarate) Bone Cement Composites

“…X‐ray diffraction (XRD) analysis was used to investigate the effect of dopant on the phase structure of TiO 2 and Sr‐doped TiO 2 particles synthesized in scCO 2 (Figure S1, Supporting Information). For undoped TiO 2 particles (Figure S1a, Supporting Information) typical diffraction peaks in the range of 20° < 2 θ < 80° correspond to the 101, 004, 100, 200, 105, 211, 204, 116, 220, and 215 reflections of anatase crystal structure of TiO 2 . The as‐prepared materials were amorphous, while after calcination at 450 °C the material reorganized itself and anatase particles began to grow, resulting in crystalline material.…”

“…For undoped TiO 2 particles (Figure S1a, Supporting Information) typical diffraction peaks in the range of 20° < 2θ < 80° correspond to the 101, 004, 100, 200, 105, 211, 204, 116, 220, and 215 reflections of anatase crystal structure of TiO 2 . [38] The as-prepared materials were amorphous, while after calcination at 450 °C the material reorganized itself and anatase particles began to grow, resulting in crystalline material. In the XRD pattern of Sr-doped TiO 2 nanoparticles ( Figure S1b, Supporting Information), all peaks correspond to anatase phase, which indicates that the as-prepared materials transferred from amorphous to anatase phase during heat treatment.…”

Supercritical Fluid‐Facilitated Exfoliation and Processing of 2D Materials

“…[3,4] By using SCFs, the surfaces of graphene, rGO, or GO have been decorated with a variety of metal (such as Pt, [105,195] Ru, [105] Pd, [97,100,102,197] Ag, [84,198,216,217] Au, [100] Fe, [100] Ni, [100,105] PtRu, [199] PtFe, [107] and PtFeCo [200] ), metal oxide (such as ZnO, [99,101,218] Co 3 O 4 , [96] TiO 2 , [201,202,219] MoO 2 , [193] MnO 2 , [209] Al 2 O 3 , [215] and SnO 2 , [205] ), and metal sulfide (such as CdS [103] ) NPs with tunable sizes, loadings, and compositions. [3,4] By using SCFs, the surfaces of graphene, rGO, or GO have been decorated with a variety of metal (such as Pt, [105,195] Ru, [105] Pd, [97,100,102,197] Ag, [84,198,216,217] Au, …”

Graphene‐incorporated Photoelectrodes for Dye‐sensitized Solar Cells#

“…Commonly utilized TiO 2 nanoparticles with an average particle size of (1.5 × 10 -8 to 2 × 10 -8 m) do not exhibit any light scattering effect, as they are much smaller than the wavelength of visible light and the film is semitransparent with little light 45 In order to increase the light scattering effect, the TiO 2 nanosheets (TNS) (size ca. 1 × 10 -7 m) were produced by Fan et al using a hydrothermal method.…”