Effects of surface charges and surface states of chemically modified cadmium sulfide nanoparticles immobilized to gold electrode substrate on photoinduced charge transfers
M. Miyake et al., Effects of surface charges and surface states of chemically modified cadmium sulfide nanoparticles immobilized to gold electrode substrate on photoinduced charge transfers, LANGMUIR, 15(8), 1999, pp. 2714-2718
Cadmium sulfide nanoparticles (Q-CdS) modified with 2-mercaptoethanesulfona
te and 2-amiaoethanethiol in a molar ratio of 2:1 were covalently immobiliz
ed onto-an Au surface covered with a self-assembled monolayer of 3,3'-dithi
obis(succinimidylpropionate), and the resulting electrodes were further imm
obilized with Q-CdS using glutaraldehyde as a binding agent. The degree:of
anodic photocurrents was greatly influenced by charged conditions of hole s
cavengers used because of the presence of sulfonate groups on the Q-CdS sur
faces; triethylamine having positive charges gave large photocurrents, trie
thanolamine medium photocurrents, and formate small photocurrents. If Q-CdS
having a large emission from their surface trap states was used, anodic ph
otocurrents were depressed with increasing anodic polarization from the ons
et potentials which were ca. -1.1 V vs SCE for the use of any kinds of hole
scavengers, and the greatest depression appeared at -0.25 V, beyond which
a steep increase in anodic photocurrents was seen. In contrast, no signific
ant depression in photocurrents was observed and anodic photocurrents were
monotonically increased, in the case of using Q-CdS having an intense band-
gap emission. When the energetic position at the emission maximum is correl
ated to the potential at which the greatest photocurrent depression appeare
d, photocurrent-potential characteristics are discussed in terms of involve
ments of surface states in the photoelectrode reactions.