Figure 4 A) Scheme of the
potentials of hydrogen evolution and oxygen evolution, bandgap of CdS
semiconductor, and Fermi levels of each metal. B) Scheme of hole shuttle
mechanism for the photocatalytic evolution of H2, nickel
nanoparticles growth on the cysteine-stabilized CdS nanorods for
photocatalytiv hydrogen generation, the photoexcited holes oxidize
hydroxyl anions which act as a radical-carry away the positive charges,
and in turn oxidize ethanol to acetaldehyde. The blue and red arrows
show the movement of the species and a redox reaction respectively. TEM
images of C) Au-CdS (2.5±0.6 nm), and D) Pt-CdS (1.9±0.5 nm) hybrid
nanorods, respectively. The dimensions of CdS nanorods are 48±5
nm×3.3±0.5 nm. E) TEM images of Pd-CdS hybrids. F) TEM image of
Au@Alloy-CdS hybrid nanorods (insert: from left to right are
EDS elemental maps of Au, Pd, and an
overlay of Cd, S, Au, and Pd). G) TEM image of bimetallic tips
Au-Pt-CdSe@CdS hybrid nanorods (insert: EDS elemental maps of the
bimetallic tip). H) TEM images of Co-CdSe hybrids after 24 h reaction at
80℃. The scale bar of TEM images above are 20 nm. A) Reproduced with
permission.[10i] Copyright 2018, The Royal Society
of Chemistry. B) Reproduced with permission.[4d]Copyright 2014, Macmillan Publishers Limited. C-D) Reproduced with
permission.[11] Copyright 2018, Wiley-VCH. E-F)
Reproduced with permission.[13] Copyright 2016,
American Chemical Society. G) Reproduced with
permission.[15] Copyright 2015, The Royal Society
of Chemistry. H) Reproduced with permission.[16]Copyright 2009, Wiley-VCH.
3.2. Size of metal domain
As an important component to separate excitons, extract electrons and
undergo reduction reaction, the size of the metal domain is one of the
most important parameters for obtaining the optimal catalytic activity
in the metal-semiconductor hybrid structure. Early studies show the
Fermi level shifting of metal domain is caused by size decreasing which
could affect catalytic performance of hybrid materials directly, the
quantum size effect will also bring the adjustable semiconducting
properties when the size of metal tip becomes tiny clusters. On the
other hand, the undesired radiative recombination might occur on the
metal clusters as well as the non-radiatively exciton recombination need
to be considered in the hybrid structure. [17]