9 research outputs found
Photochemical Grafting of Organic Alkenes to Single-Crystal TiO<sub>2</sub> Surfaces: A Mechanistic Study
The UV-induced photochemical grafting of terminal alkenes
has emerged
as a versatile way to form molecular layers on semiconductor surfaces.
Recent studies have shown that grafting reactions can be initiated
by photoelectron emission into the reactant liquid as well as by excitation
across the semiconductor band gap, but the relative importance of
these two processes is expected to depend on the nature of the semiconductors,
the reactant alkene and the excitation wavelength. Here we report
a study of the wavelength-dependent photochemical grafting of alkenes
onto single-crystal TiO<sub>2</sub> samples. Trifluoroacetamide-protected
10-aminododec-1-ene (TFAAD), 10-<i>N</i>-BOC-aminodec-1-ene
(t-BOC), and 1-dodecene were used as model alkenes. On rutile (110),
photons with energy above the band gap but below the expected work
function are not effective at inducing grafting, while photons with
energy sufficient to induce electronic transitions from the TiO<sub>2</sub> Fermi level to electronic acceptor states of the reactant
molecules induce grafting. A comparison of rutile (110), rutile (001),
anatase (001), and anatase (101) samples shows slightly enhanced grafting
for rutile but no difference between crystal faces for a given crystal
phase. Hydroxylation of the surface increases the reaction rate by
lowering the work function and thereby facilitating photoelectron
ejection into the adjacent alkene. These results demonstrate that
photoelectron emission is the dominant mechanism responsible for grafting
when using short-wavelength (∼254 nm) light and suggest that
photoemission events beginning on mid-gap states may play a crucial
role
Covalent Attachment of Catalyst Molecules to Conductive Diamond: CO<sub>2</sub> Reduction Using “Smart” Electrodes
We report here covalent attachment of a catalytically
active cobalt
complex onto boron-doped, p-type conductive diamond. Peripheral acetylene
groups were appended on a cobalt porphyrin complex, and azide–alkyne
cycloaddition was used for covalent linking to a diamond surface decorated
with alkyl azides. The functionalized surface was characterized by
X-ray photoelectron spectroscopy and Fourier transform IR spectroscopy,
and the catalytic activity was characterized using cyclic voltammetry
and FTIR. The catalyst-modified diamond surfaces were used as “smart”
electrodes exhibiting good stability and electrocatalytic activity
for electrochemical reduction of CO<sub>2</sub> to CO in acetonitrile
solution