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H-titanate NFs (0.05 g). The mixture was kept at 808C for 12 h.
ence of Au NPs. Both Au/TA-S12 and Au/P25 exhibited high
conversions for the nitrobenzene reduction at 50% and 76%,
respectively, in 5 h reaction time. The reaction on Au/TA-S12
and Au/P25 also proceeded in the dark, achieving conversions
of 25% and 55%, respectively. An interesting finding was that
azoxybenzene was the sole product if the photocatalyst of Au
NPs on TiO2 supports were used, whereas in our previous
study, the azoxybenzene was the intermediate product and
converted to azobenzene quickly on Au/ZrO2.[21] Evidently, the
support materials significantly affect the product selectivity in
the nitrobenzene reduction. Therefore, this finding can be uti-
lized to prepare intermediate compounds, which are unstable
to be obtained if catalysts at elevated temperatures are used.
The photocatalyst of H-titanate supported Au NPs exhibited
no activity for this reaction, also demonstrating the importance
of the support materials on the performance of the photocata-
lyst. The phenomenon has not been fully understood yet, and
further studies on the influence of the support materials is
underway.
After the reaction, the precipitate was collected and washed thor-
2À
oughly with deionized water to remove residual SO4 ions. Then
the washed white solid was dried at 808C for 12 h. The sample
was labeled as TA-S12. TiO2 NCs were also painted on other materi-
als such as laponite clay or fly ash by using the same approach. To
prepare the Au NPs photocatalysts (3 wt%) on the fibril supports,
H-titanate or TA-S12 (2.5 g) was dispersed into 3.8ꢁ10À3 m HAuCl4
solution (100 mL), followed by addition of 0.53m lysine (20 mL)
under magnetic stirring. The stirring was prolonged for 30 min. To
this suspension, 0.35m NaBH4 solution (10 mL) was added gradual-
ly, followed by addition of 0.3m hydrochloric acid (10 mL). Then
the mixture was aged for 12 h. Finally, the solid was separated,
washed with deionized water and ethanol, and dried at 808C (la-
beled as Au/TA-S12).
Characterization
TEM was used to study the detailed structure of anatase NC paint-
ed H-titanate NFs. TEM and high-resolution TEM (HRTEM) were
conducted on a Techni F20 transmission electron microscope oper-
ating at 200 kV. XRD patterns of the sample powders were record-
ed on a Philips PANalytical X’Pert PRO diffractometer using CuKa ra-
diation (l=1.5418 ꢂ) operating at 40 kV and 40 mA with a fixed
slit. Diffuse reflectance UV/Vis (DRUV/Vis) spectra of the samples
were measured on a Varian Cary 5000 spectrometer. The Raman
spectra of the samples were measured on a Spectra-Physics model
127 He-Ne laser (633 nm) at a resolution of 2 cmÀ1. Nitrogen sorp-
tion isotherms were measured by the volumetric method on an
automatic adsorption instrument (Micromeritics, Tristar 3000) at
liquid nitrogen temperature (77 K). Zeta potential measurements
were conducted on a Malvern nano-ZS zetasizer connected with
a MPT-2 multipurpose titrator.
Conclusions
In summary, painting anatase nanocrystals (NCs) on a substrate
is an efficient method that can be applied to various oxide
substrates. It allowed us to achieve large photocatalytic active
surfaces and solve the problems of particle aggregation and
photocatalyst recovery. These two problems have seriously im-
peded the practical applications of the photocatalysts. The
anatase NCs covered on H-titanate nanofibers (NFs) exhibited
high activities for the degradation of sulforhodamine B, and
high activities and selectivities (>99%) for the benzylamine
oxidation (to imine). The photocatalysts of Au NPs on the ana-
tase NC painted titanate NFs or on P25 could efficiently reduce
nitrobenzene to azoxybenzene. Given that on Au NPs on ZrO2
support under the same reaction conditions, the azoxybenzene
is the intermediate product and quickly converts to azoben-
zene, the support material significantly affects the product se-
lectivity of this reaction. Therefore, we can optimize the prod-
uct selectivity by choice of the support materials. The photoca-
talysts with the nanofibril morphology are feasible for practical
applications because they can be easily dispersed into a solu-
tion and separated from a liquid by filtration, sedimentation or
centrifugation, because of their fibril morphology. The results
of this study could be used for developing superior photocata-
lysts and other delicate functional nanostructures.
Photocatalytic degradation of sulforhodamine B
Six parallel Hg lamps (20W, NEC, FL20SBL) were used as the UV
light source, and the peak of the wavelength was at approximately
350 nm. The catalyst concentration was 0.5 gLÀ1, and the initial
concentration (C0) of the SRB was 1.8ꢁ10À5 m. At designed irradia-
tion time intervals, specimens were taken from the reaction disper-
sion, and filtered through a Millipore filter (400 nm, Teflon) to
remove the catalyst particles prior to the analysis. The filtrate was
analyzed by UV/Vis spectra (Varian Cary 100 spectrometer) for the
absorbance intensity by using the reading at 565 nm.
Photocatalytic oxidation of benzylamine
The UV source was a 100 W Hg lamp. Reactions were conducted in
an oxygen atmosphere at 408C. In a typical reaction, benzylamine
(0.2 mmol) was dissolved in acetonitrile (5 mL), to which the pho-
tocatalyst (50 mg) was added. The liquid products were analyzed
by using an Agilent HP-6890 GC and GC–MS with an HP-5 column.
Experimental Section
Photocatalyst preparation
All the chemicals used in this study were analytical grade from
Sigma–Aldrich unless otherwise stated and all the solutions were
prepared by using high-purity deionized water (Millipore Corp.,
18.2 MWcm). H-titanate was prepared by using the method pub-
lished previously.[50] TiOSO4 solution was obtained by dissolving
TiOSO4·xH2O (1.35 g, Fluka) in H2O (10 mL). An aliquot of 0.5 mL of
the above solution was diluted to 50 mL with H2O and mixed with
Photocatalytic reduction of nitrobenzene
The reduction of nitrobenzene was conducted in an argon atmos-
phere at 408C. In a typical reaction, nitrobenzene (1.5 mmol) was
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