Characterization of TiO2 Nanoparticles in Langmuir-Blodgett Films

Abstract

In this work we have synthesized TiO2 nanoparticles, using either a sol-gel base catalysed process in the interior of CTAB reversed micelles (TiO2 CTAB sol), or the neutralization of a TiO2/H2SO4 solution in the interior of AOT reversed micelles. From the absorption and emission data of the TiO2 nanoparticles it is possible to conclude that in the sol-gel route there remains alkoxide groups in the structure, originating transitions lower than the energy gap of TiO2 semiconductor. These transitions disappear in the neutralization procedure, where the alkoxide groups are absent in the structure. We have assigned the observed indirect and direct optical transitions according to the anatase band structure. TiO2 Langmuir-Blodgett (LB) films were prepared either by direct deposition of titanium isopropoxide or by deposition of the TiO2 CTAB sol. These films showed photoluminescence, which was attributed to band-gap emission and to surface recombination of defect states.

Photocatalytic Nanocomposite Films Fabricated by Layer‐by‐Layer Self‐assembly of TiO2 Nanoparticles and Lignosulfonates

“…[9,10] Several different strategies have been developed to prepare uniform and high-quality TiO 2 thin films, including chemical vapor deposition, [11] sputtering, [12] sol-gel process, [13] dip-coating techniques, [14] and Langmuir-Blodgett (LB) method. [15] However, there are several inherent limitations associated with these methods, such as expensive fabrication equipment, high temperature, film non-uniformity and low mechanical instability.…”

A new route for the fabrication of an ultrathin film of a PdO–TiO2 composite photocatalyst

“…5a. Bulk anatase TiO 2 is known to be an indirect gap semiconductor, 31 with a band gap energy E g = 3.20 eV. This band gap is attributed to the lowest energy allowed phonon assisted transition (Γ 3 → X 1b ).…”

Nanoparticle Thin Films for Gas Sensors Prepared by Matrix Assisted Pulsed Laser Evaporation

“…It is well known that anatase TiO 2 is an indirect gap semiconductor due to the lowest Γ 1 ←X 1,2 transitions. However, absorption thresholds in anatase TiO 2 nanoparticles were already found at higher energy, with respect to bandgap, and attributed to direct transitions in an otherwise indirect bandgap semiconductor, due to size effects [20, 21]. In our case, the optical energy gap resulted to be of about 3.6 eV, as compared to the bulk anatase TiO 2 value of 3.18 eV, and close to the value reported in literature for anatase TiO 2 nanoparticle Langmuir-Blodgett films [21].…”