Electrochemical and photoelectrochemical studies were conducted on self-assembled multilayer films of titania nanosheets on a conductive ITO substrate. Cyclic voltammogram (CV) curves indicated that the titania nanosheet electrode underwent insertion/extraction of Li+ ions into/from the nanosheet galleries, associated with reduction/oxidation of Ti4+/Ti3+. These processes accompanied reversible changes in UV−vis absorption of the titania nanosheet electrodes. Applying a negative bias of −1.3 V (vs Ag/Ag+) and lower brought about absorption reduction where the wavelength is shorter than 323 nm, and vice versa, indicating a flat-band potential of (approximately) −1.3 V and a band gap energy of 3.84 eV. Photocurrents were generated from the titania nanosheet electrodes under a positive bias. The onset potential for photocurrent generation from the titania nanosheet electrodes was around −1.27 V, and the band gap energy estimated from the photocurrent action spectra was 3.82 eV, in excellent agreement with th...

Electronic band structure of titania semiconductor nanosheets revealed by Electrochemical and photoelectrochemical studies

Small particles of metals in solution often behave like electrodes although they are not connected to a battery which determines their potential. However, when a chemical reaction occurs in the solution of such particles intermediate free radicals may transfer electrons to them. The particles are thus charged chemically and are able to act as a metal electrode on cathodic potential. Electron transfer reactions become possible at these micro-electrodes which cannot be brought about by the radicals in the absence of the colloidal catalyst.

Mechanism of reactions on colloidal microelectrodes and size quantization effects

Shape and Phase Control of ZnS Nanocrystals: Template Fabrication of Wurtzite ZnS Single‐Crystal Nanosheets and ZnO Flake‐like Dendrites from a Lamellar Molecular Precursor ZnS·(NH2CH2CH2NH2)0.5

Understanding the dynamic properties of charge carriers at the liquid−semiconductor interface is critical to many applications including photocatalysis, solar energy conversion and photoelectrochemistry. Dynamic properties of charge carriers, including trapping, recombination, and transfer, in a number of semiconductor nanoparticle systems have been studied using powerful time-resolved laser techniques. Several interesting features have been identified, including exciton−exciton annihilation upon trap state saturation at high excitation intensities for CdS, CdSe, TiO2, ultrafast electron injection in dye sensitization of TiO2, increased transient absorption over transient bleach with increasing intensity for Ag2S and CuxS due to trap state saturation, surface dependence of electronic relaxation in PbI2 and BiI3, complex kinetics of the orange emission in Mn-doped ZnS, and surface-independent relaxation for Fe2O3 and PbS. These observations provide new insight into the interfacial charge carrier properties...

Interfacial Charge Carrier Dynamics of Colloidal Semiconductor Nanoparticles

We have studied the optical properties of novel semiconductor nanosheets of Ti1-δ□δO24δ- (δ ∼ 0.09; □, vacancy) which were obtained by delaminating a layered titanate into elementary host layers. A uniform thickness in subnanometer scale as well as high crystallinity resulted in a sharp absorption onset with a well-developed peak assignable to excitonic transition. The absorption was pronouncedly blue shifted (>1.4 eV) relative to the band edge for bulk TiO2, which is attributed to size quantization effects. Room-temperature photoluminescence spectra showed resonant emission and well-structured fluorescence extending into a lower energy region.

Semiconductor Nanosheet Crystallites of Quasi-TiO2 and Their Optical Properties

Microcrystallites of the layered semiconductor ${\mathrm{PbI}}_{2}$ were prepared in colloidal form and examined by transmission electron microscopy and optical absorption. The crystallites have lateral dimensions grouped around 12, 18, and 29 A\r{} corresponding to close-packed clusters with bulk ${\mathrm{PbI}}_{2}$ symmetry. Blue-shifted absorption features can be explained by carrier confinement in these differently sized crystallites, each a single layer (\ensuremath{\sim}7 A\r{}) thick.

W. M. Chung

Papers

Carrier confinement and special crystallite dimensions in layered semiconductor colloids.