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doi.org/10.1002/cctc.202100298
ChemCatChem
about 40 nm and a thickness of about 6 nm. More specific
structures of Au/TiO2 are revealed in high resolution trans-
mission electron microscopy (HRTEM) images (Figures 1b and
1c). The lattice spacing of metal particle in area �1 is 0.23 nm,
corresponding to the (111) plane of Au. Meanwhile, the lattice
(Figure 3d), there are two peaks at 83.33 eV and 86.91 eV,
corresponding to the binding energy of Au 4f7/2 and Au 4f5/2
,
respectively.[15] As for the high-resolution spectrum of Ti 2p in
Figure 3e, Ti 2p spectrum could be fitted into four peaks,
namely Ti3+2p3/2 (458.33 eV), Ti4+2p3/2 (458.65 eV), Ti3+2p1/2
(463.85 eV), Ti4+2p1/2 (464.67 eV), it can be proved that the
material is doped with Ti3+. Compared with pure titanium
dioxide material, the characteristic peak of Ti 2p shifts to the
low-energy region, which may be due to the loading of gold
nanoparticles causing electrons to move to titanium dioxide.
Besides, in O 1s spectrum, it is found that, like the pure titanium
dioxide material, in addition to the peak of O 1s (529.71 eV),
there is a wider peak at 530.99 eV. Compared with TiO2, it is
more in the direction of the low energy region, which may be
due to the decrease in the binding energy of TiÀ O.[16]
spacing of flake in area � is 0.35 nm, attributing to the (101)
2
plane of anatase TiO2, which is consistent with the XRD analysis
result. The lattice spacing in area �3 is 0.235 nm, which is
indexed to the (001) plane of TiO2.
The phase and crystal structure of TiO2 and Au/TiO2 photo-
catalytic material were investigated by the X-ray diffraction
(XRD) as shown in Figure 2. In Figure 2a, there are 5 strong
°
°
°
°
°
diffraction peaks located at 25.3 , 37.8 , 48.1 , 53.9 and 55.1 in
as-synthesized TiO2, corresponding to (101), (004), (200), (105)
and (211) planes of anatase TiO2 (JCPDS: 21-1272), respectively.
In Figure 2b, except for the peaks of gold (JCPDS: 4-784) and
anatase titanium dioxide, no other XRD diffraction peaks
appeared in Au/TiO2, indicating that the addition of gold did
not change the crystal form of titanium dioxide. Moreover, it
could be found that the peak of the gold element in Au/TiO2 is
weak, which may be caused by the low loading of gold. The
result of the ICP test shows that the loading amount of gold
element in the material is 4.98%. No new peak appears after
the noble metal Au is embedded, which suggests that the
synthesized composite catalyst material has no lattice distor-
tion.
Figure 4a is the UV-vis diffuse reflectance spectroscopy test
(DRS) of TiO2 and composite Au/TiO2 catalyst materials. It can
be seen from Figure 4a that compared with pure anatase TiO2
material, Au/TiO2 composite photocatalytic material has a more
obvious absorption broadening in the visible light region (400-
800 nm), and the absorption bandredshift. The results can prove
that the local surface plasma effect of Au nanoparticles can
increase the material‘s absorption of visible light and improve
the light absorption of the composite material, so that the
composite material has better photocatalytic activity. In
addition, through the formula Eg =1240/λ, it can be deduced
that the band gap of Au/TiO2 is 2.95 eV, which is significantly
shorter than the band gap of 3.2 eV of anatase TiO2.
Figure 3 shows the XPS analysis of the TiO2 material and Au/
TiO2 nanocomposite. For comparison, the Ti 2p and O 1s high-
resolution spectra of TiO2 are shown in Figure 3a and 3b. The Ti
2p spectrum could be deconvoluted into four peaks, namely
Ti3+2p3/2 (458.61 eV), Ti4+2p3/2 (459.01 eV), Ti3+2p1/2 (464.20 eV),
Ti4+2p1/2 (464.94 eV), which proves that Ti3+ is doped in the
material.[13] By fitting the O 1s spectrum, two peaks could be
obtained. In addition to the peak of O 1s (529.95 eV), there is a
wider peak located at 531.36 eV, which is caused by oxygen
vacancies. In order to maintain the electrical neutrality of the
material, whenever two Ti3+ appear, an oxygen vacancy will
appear. Ovac and Ti3+ in the material would also inhibit the
recombination of photogenerated carriers to a certain extent.[14]
To further illustrate the successful loading of Au nano-
particles on TiO2, XPS characterization was also performed on
Au/TiO2 composite samples. In the survey spectrum (Figure 3c),
in addition to the standard peak of C 1s, there are also peaks of
Au, Ti and O. In the high-resolution spectrum of Au 4f
According to the diffuse reflectance spectrum, the Tauc
plots of the two materials can be obtained, as shown in
Figure 4b. It can be seen in the figure that Au/TiO2 has a smaller
optical band gap.
Fluorescence analysis was performed on the prepared
anatase TiO2 and Au/TiO2 composite materials to characterize
the recombination efficiency of photogenerated carriers. The
experiment was performed at an excitation wavelength of
300 nm, and the results are summarized in Figure 5a. It can be
seen from Figure 5a that the fluorescence emission intensity of
the TiO2 material is greater, indicating that the recombination
efficiency of its photogenerated carriers is higher. The low
fluorescence emission intensity of Au/TiO2 composite material
proves the low recombination efficiency of photogenerated
carriers. This is due to the migration of Au nanoparticles to
photogenerated electrons, which strongly inhibits the recombi-
nation of photogenerated carriers. It might indicate that the
composites possessed higher photocatalytic activity under
visible light irradiation than TiO2.
Figure 5b is the Mott-Schottky curve of the two materials.
Knowing that C=1/ωZi, plot 1/C2 with potential to get the
Mott-Schottky curve. According to calculations, the correspond-
ing slopes of the two materials TiO2 and Au/TiO2 are 2.262 and
1.746 respectively. The slope is positive, which proves that the
two materials prepared are all n-type semiconductors. And the
slope of the Au/TiO2 material is the smallest, which means the
concentration of photogenerated carriers is the highest.
Figure 2. (a) XRD patterns of TiO2 and (b) Au/TiO2.
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