Carbonaceous layer interfaced TiO2/RGO hybrids with enhanced visible-light photocatalytic performance

Article abstract of DOI:10.1039/c6ra02431a

A facile solvothermal method combined with heat treatment was introduced to obtain enhanced photocatalytic activity of TiO₂@C/RGO (reduced graphene oxide) photocatalyst under visible light. By adjusting the annealing temperature, the physical and chemical status of the interfacial carbonaceous layer could be successfully tuned. The carbonaceous layer with optimal thickness and degree of order obtained at 360 °C forms a good bridge between the TiO₂ particles and RGO sheet. The resulting TiO₂@C-360/RGO photocatalyst exhibited the best performance in the photodegradation of MO under visible light, benefiting from the ideal connection provided by the optimal carbonaceous layer and thus enhanced separation of activated electron-hole pairs at the interface. In addition, the photocatalytic activity was adjusted synchronously by controlling the thickness and degree of order of the carbonaceous layer in the TiO₂@C/RGO hybrids. This work indicates the importance of interface engineering to obtain TiO₂-based nanohybrids with high photocatalytic performance.

Full text of DOI:10.1039/c6ra02431a

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Paper
Carbonaceous layer interfaced TiO2/RGO hybrids with
enhanced visible-light photocatalytic performance
Received 00th January 20xx,
Accepted 00th January 20xx
Jianfeng Xu, Jiawei Tian, Yuewei Zhang, Ammara Riaz, Yi Liu, Mingjia Zhi, Zhanglian Hong,
Chunmei Zhou*
DOI: 10.1039/x0xx00000x
A facile solvothermal method combined with heat treatment was introduced to obtain enhanced photocatalytic activity of
TiO2@C/RGO (reduced graphene oxide) photocatalyst under the visible light. By adjusting the annealing temperature, the
physical and chemical status of interfacial carbonaceous layer could be successfully tuned. The carbonaceous layer with
optimal thickness and order degree obtained at 360 oC well bridges the TiO2 particles and RGO sheet. The resulted
TiO2@Cꢀ360/RGO photocatalyst obtained the best performance on the photo degradation of MO under visible light
benefiting from the ideal connection provided by the optimal carbonaeous layer and thus enhanced activated electron – hole
pairs separation at the interface. In addition, the photocatalytic activity was adjusted synchronously by controlling the
thickness and order degree of the carbonaceous layer in the TiO2@C/RGO hybrids. This work indicates the importance of
interface engineering to obtain TiO2ꢀbased nanohybrids with high photocatalytic performance.
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1
Introduction
In recent decades, TiO2ꢀbased nanohybrids have received photon activated electronꢀhole pairs is another main drawback
increasing interests from scientists for their great potential in seriously hindering its applications.7
the various industrial applications, such as photocatalysts, solar
To solve these two big problems and thus improve the
cells, and sensors.1ꢀ5 Under the concern to alleviate the photocatalytic performance of TiO2 hybrids, researchers have
deterioration of the environment pollutant and energy crisis and proposed a lot of methods and successfully obtained TiO2 based
8, 9
to insure sustainable global development, as one of the most photocatalysts with wellꢀimproved photocatalytic activity.
promising photocatalyst candidates, TiO2 hybrids are playing a Nonꢀmetal or metal element doping is one of the efficient ways.
more and more important role with their superior properties, Asahi et al prepared Nꢀdoped TiO2 film which had good
including chemical stability, nonꢀtoxicity, and low cost. visibleꢀlight activity.10 Kim et al obtained solar light responsive
However, the intrinsic band gap structure, 3.0~3.2 eV, which is TiO2 photocatalyst through coꢀdoping of Fe and N.11 However,
only corresponding to the UV light spectrum region, strictly a higher electronꢀhole pair recombination rate is usually
limits their practical use.6 Besides, highly recombination rate of followed by doping. Noble metal modification was another
powerful tool to extend light absorption spectrum and reduce
recombination rate of the electronꢀhole pairs.12ꢀ15 Nevertheless,
the high cost and relatively low stability of noble metal become
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new problems to be solved. Among a large amount of previous importance of interface engineering in hybrid photocatalysts to
studies, carbon materials modified photocatalysts exhibit its optimise the photocatalytic activity and provides a new design
superiority.16 Li et al using glycerol as the carbon source strategy to fabricate ideal interface.
obtained TiO2/C photocatalyst which had promoted
2 Experimental
photocatalytic activity.17 Amorphous carbon layer coated CdS
2.1 Synthesis of TiO2@C samples
synthesized by Hu et al revealed the significance of the carbon
20 mL titanium tetraꢀnꢀbutoxide (TNB) (Sinopharm, CP) and 100
in reducing the electronꢀhole recombination rate.18 Recently,
mL acetone were mixed in a quartz beaker which was placed in a
TiO2/graphene hybrids have received great attention as
200 mL teflon liner in an autoclave. 5 mL deꢀionized water was then
graphene emerged as a new ideal 2ꢀD carbon material with
added to the gap between the quartz beaker and the inner wall of
excellent properties, especially the high carrier mobility and
teflon liner. TNB was hydrolyzed by the H2O evaporated from the
large surface area.19ꢀ21 Researchers have proved that the
gap when the autoclave was heated at 240 oC for 6 h. The
introduction of graphene in TiO2/graphene hybrids could
precipitation powders were collected and washed by acetone and DI
greatly enhance the photocatalytic activity in visible light,
water several times and dried at 70 oC (labeled as TiO2@Cꢀpristine).
which could be attributed to the large surface area, improved
o
It was then annealed at 180, 360 and 450 C for 2 h and named as
excited electron – hole separation and narrowed band gap of
TiO2@Cꢀ180, TiO2@Cꢀ360 and TiO2@Cꢀ450, respectively.
TiO2 hybrids.22ꢀ27
2.2 Synthesis of TiO2@C/RGO hybrids
In spite of the incredible features of these hybrids, the
10 mg homeꢀmade graphene oxide (GO) by modified Hummers
photocatalytic activity is not always much higher than bare
method and 200 mg asꢀprepared TiO2@C were dispersed in a
TiO2, because it’s not easy to obtain ideal interfacial contact for
mixture solution with 80 mL DI water and 40 mL ethanol under
TiO/graphene hybrids which may result in lower contact areas
sonication and stirring each for 2 h. The homogeneous suspension
and weaker bonding force between TiO2 and graphene. Thus
o
was kept at 120 C for 3 h in 200 mL autoclave. The precipitation
these poor and noticeable interfaces would become
was filtrated and washed by ethanol and DI water, respectively,
recombination sites. Consequently, only few photoꢀinduced
followed by drying process at 70 oC overnight. The collected hybrids
electrons could be transferred through the interface leading to a
were named as, TiO2@Cꢀpristine/RGO, TiO2@Cꢀ180/RGO,
relatively lower photocatalytic activity.
TiO2@Cꢀ360/RGO, and TiO2@Cꢀ450/RGO, respectively.
There were rare studies focusing on the interface
modification between TiO2 and graphene. In this work,
2.3 Photocatalysis test
carbonaceous layer was employed to interface TiO2 particles
20 mg photocatalyst was dispersed in 100 mL methyle orange (MO)
and RGO sheet, as an ideal charger carrier transmitter and
solution (20 mg/L). After stirred for 30 min in the dark, the
effective stretcher from TiO2 to RGO. The thickness and order
suspension solution was illuminated under a halogen lamp (HQIBT,
degree of carbonaceous layer was easily adjusted by postꢀ
400 W/D, OSRAM) by a filter with the cutꢀoff wavelength of 420
annealing process which results tunable photocatalytic activity
nm to start photocatalytic degradation. After each hour, 5 mL
for TiO2@C/RGO hybrids. This work exemplifies the
suspension was collected and centrifuged at 8000 rpm to remove the
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photocatalyst. The supernatant was taken out for UVꢀVis absorption The thermal stability of the asꢀprepared TiO2@Cꢀpristine sample
spectrum measurement. The relative concentration of residual MO (made by organic Ti precusor) was analysed by TGA, and compared
solution (C/C0) at each hour was determined by the ratio of intensity with commercial TiO2 (made by inorganic Ti precusor), as shown in
of the characteristic absorption peak at about 464 nm of sample MO Fig. 1. The TGA curve of TiO2@Cꢀpristine shows three weightꢀloss
o
to that of the initial MO solution.
regions. A dramatic loss of weight can be observed before 180 C,
and the weight loss is ca. 17%, which can be ascribed to the
dehydration and evaporation of volatile carbonaceous organic
species. The second stage was found from 180 oC to 360 oC with a ca.
7% weight loss. In this region, the weight decreases at a stable speed
which may be attributed to the combustion and carbonization of the
remaining organic species. The third stage is between 360 oC and
2.4 Analysis of hydroxyl radical
In a typical process, 20 mL NaOH solution (2mM) and 20 mL
terephthalic acid (0.5mM) were mixed in a quartz beaker and stirred
for 30 min to form a homogeneous suspension. Then 20 mg
TiO2@C/RGO sample was dispersed in the mixture with continually
stirring. The suspension was irradiated under the visible light and the
readings were taken every 30 min. After removal of the residual
photocatalyst by centrifugation at 8000 rpm for 10 min, the
suspension was tested by the PL spectra excited at 312 nm.
o
450 with a slight mass decrease, only ca. 2%, which is mainly
caused by the further oxidation of the carbonized amorphous carbon
layer under the air atmosphere. By comparing to the TGA curve of
commercial anatase TiO2 particles, more than 12% of weight loss for
TiO2@C sample can be observed which further confirms the organic
species existing around the TiO2 particles. Besides, the evolution of
the incorporated carbonaceous layer for TiO2 precursor is almost
completed after 450 oC because there is no obvious mass decrease.
Based on the TGA analysis, postꢀanneal was selected as the main
tool to modify the surface state of TiO2@C samples and TiO2@C
samples with various surface states were obtained by heat treatment
2.5 Characterization
All samples were measured by powder Xꢀray diffraction (XRD,
Rigaku, CuK=0.15406 nm). TGA curves were tested by SDTꢀQ600
at a heating rate of 10 oC / min. The morphology was analysized by
transmission electron microscopy (TEM, JEOLꢀ1230, 120 kV) and
hiꢀresolution transmission electron microscopy (HRTEM, Tecnai
G2ꢀF20ꢀSꢀTWIN, FEI, 200 kV). Diffuse reflectance absorption
spectra (DRS) were measured using HITACHI Uꢀ4100 UV–vis
spectrometer with an integrating spherical accessory and converted
by KubelkaꢀMunk function. Raman spectra were collected on a
Renishaw Invia Raman spectrometer (532 nm, 50 mW). The
photoluminescence (PL) emission spectra were recorded by
HITACHI Fꢀ4500 Fluorescence spectrophotometer. PL decay curves
were measured by Edinburgh FLS920 fluorescence spectrometer
with 375 nm and 980 nm pulse lasers.
o
at different temperatures (180, 360, and 450 C). Raman spectrum,
XRD and TEM were used to explore the quality and order degree of
carbonaceous layer, phase structure and crystallite sizes of the
TiO2@C samples.
Fig. 2 depicts the micro Raman spectra of TiO2@C samples
with D band at 1350 cmꢀ1 and G band at 1580 cmꢀ1 which are related
to the vibration of carbon atoms in disordered carbon structure or
defect sites and inꢀplane vibration of sp2ꢀbonded carbon atoms,
respectively.28 The ratio of intensities of two peaks (ID/IG) is
normally used as a measurement to represent the amount of defects
and the disorder degree inside carbon materials.29, 30 In this way, the
3 Results and discussion
3.1 Characterization of TiO2@C samples
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less defective order degree would be translated into a lower ratio of To extend the absorption spectrum and explore the effect of the
ID/IG in the Raman spectra. As shown in Fig. 2 and Table. 1, the interfacial carbonaceous layer on activated electronꢀhole separation,
results of ID/IG indicate that TiO2@Cꢀ180 and TiO2@Cꢀ360 have the asꢀprepared TiO2@C samples were composited with reduced
relatively ordered carbonaceous layer, 0.99 and 0.99, whereas those graphene oxides (RGO) by solvothermal process, named as
of TiO2@Cꢀpristine and TiO2@Cꢀ450 with higher disorder degree TiO2@Cꢀpristine/RGO, TiO2@Cꢀ180/RGO, TiO2@Cꢀ360/RGO and
are 3.98 and 1.12, respectively. This is also consistent with the TiO2@Cꢀ450/RGO. The whole synthesis flow diagram is illustrated
results of TGA analysis as more defects existing in the organic in scheme 1. For the reduction of GO, after the second solvothermal
species formed on the surface of TiO2@Cꢀpristine and no complete process, the GO was reduced to RGO which could be proved by
carbon layer is left on the surface of TiO2@Cꢀ450 sample suffering XRD patterns of GO and RGO shown in Fig. S2. The peak (001) of
from sufficient oxidation.
GO disappeared and the strong peak (002) of RGO formed at about
Powder XRD was used to investigate the phase structure and 25o.
crystallite sizes of the TiO2@C samples in Fig. S1. The XRD
The lowꢀresolution transmission electron microscopy (TEM)
patterns display analogical plots of anatase phase (JCPDs 21ꢀ1272) images in Fig. 3 (cꢀf) show the morphology of the TiO2@C/RGO
in which sharp peaks indicate the high crystallinity of TiO2. No hybrids. TiO2 nanocrystals less than 20 nm are well dispersed on the
remarkable variation of the fullꢀwaveꢀhalfꢀmaximum of TiO2 (101) twoꢀdimension RGO sheet and the average sizes of particles resulted
plane reveals no significant crystallinity growth of TiO2 during the from the TEM images of the four samples were calculated by Nano
postꢀannealing process which is consistent to the average sizes Measurer software shown in Table. 1 and Fig. S3. It is apparent to
shown in Table.1 calculated by Scherrer formula. This result means observe that the average sizes from TEM slightly decrease with
the particle size and crystallinity will have almost the same effect on temperature. The reason could be attributed that the amorphous
the photoactivity of the four typical TiO2@C/RGO samples. The carbonaceous layer was gradually removed by increasing
commercial TiO2 powders used in TGA analysis was also anatase as temperature. The HRTEM image of TiO2@Cꢀ360/RGO in Fig. 3 (b)
shown in Fig. S1. In addition, the HRTEM image of TiO2@Cꢀ360 in directly shows that the amorphous carbonaceous layer still exists on
Fig. 3 (a) directly displays the amorphous thin carbonaceous layer the surface of TiO2 and the particles are uniformly adhered to RGO.
uniformly formed on the surface of TiO2. And the lattice fringe of The lattice fringe of TiO2 is also the same as the TiO2@Cꢀ360. In
TiO2 is 0.35 nm for the nanoparticles matching well to the typical this way, TiO2@C/RGO hybrids with tunable carbonaceous layer
distance of anatase (101) plane.
were successfully obtained.
TiO2@C samples with an amorphous carbonaceous layer were
Fig. 5 shows the UVꢀvisible absorption properties of TiO2@C
successfully prepared by using organic Ti precursor. As a result of and TiO2@C/RGO samples. An obvious redꢀshift in absorption edge
postꢀanneal process at different temperatures, TiO2@C samples with and strong absorption in the visible range could be observed for
various surface chemical states and order degrees were obtained. TiO2@C/RGO hybrids in Fig. 4 (a) because of the introduction of
And the anneal process has little effect on the grain size and RGO. The photography of TiO2@C/RGO hybrids is shown in Fig.S4
crystallinity of TiO2.
in which all the samples are black gray suggesting good sensitivity
to visible light. Fig. 4 (b) shows plots of the KubelkaꢀMunk
3.2 Characterization of TiO2@C/RGO photocatalysts
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remission function (relationship of [αhν]1/2 versus photon energy). contribute to the high efficient separation of activated electron – hole
The band gaps of TiO2@C/RGO hybrids are all significantly pairs.
reduced to 2.80 eV which means the existing of carbonaceous with 3.3 Photocatalytic performance of TiO2@C/RGO photocatalysts
different thickness and order degree has no effect on the band gap To evaluate the photocatalytic activity and explore the synergetic
for these hybrids.
effect of carbonaceous layer, the decomposition of methylene orange
The XPS measurements were carried out to check the chemical (MO) solution (20mg/L) under visible light (> 420 nm) with 20 mg
status of TiO2@C/RGO hybrids. The fine spectrum of C1s of photocatalysts was used as a probe. As shown in Fig. 6, the
TiO2@C/RGO is showed in Fig. 5. The peaks at around 284.7, 286.0 decomposition of MO followed the order: TiO2@Cꢀ450/RGO <
and 288.3 eV are corresponded to CꢀC, CꢀOꢀR and TiꢀOꢀC bonds.31 TiO2@Cꢀpristine/RGO < TiO2@Cꢀ180/RGO < TiO2@Cꢀ360/RGO
There is no peak found at 282 eV suggesting the absence of carbon with the amount of MO decomposed over the course of 4h: 18%,
doping during the annealing process.32 The CꢀC bonds for 23%, 59% and 66%, respectively. Obviously, the different statues of
TiO2@C/RGO hybrids are accumulated from three regions: (1) the interfaced carbonaceous layer modified by annealing greatly
surface carbon of TiO2, (2) the RGO and (3) the bond between influenced the photocatalytic activity.
surface carbon and RGO. The portion of CꢀC bond in TiO2@Cꢀ
PL spectra excited at 420 nm was used to analyse the real
pristine/RGO in Fig. 5 (a) and TiO2@Cꢀ180/RGO in Fig. 5 (b) is function of the amorphous carbonaceous layer on the optical
84.2% and 81.2%, respectively. As discussed in TG analysis and property of the photocatalysts in visible light. As shown in Fig. 7,
Raman spectra, thick carbonaceous layer with more organic species TiO2@Cꢀ360/RGO exhibits the weakest emission peak, followed by
exists in TiO2@Cꢀpristine/RGO hybrid. While the thinner TiO2@Cꢀ180/RGO, TiO2@Cꢀpristine/RGO and TiO2@Cꢀ450/RGO.
carbonaceous layer with lower disorder degree in TiO2@Cꢀ The emission peaks appear between 430nm and 460nm are arised
180/RGO contributes to lower portion of CꢀC bond which may from the continually excitonic eꢀ ꢀ h+ recombination.33, 34 It is worthy
induce lower recombination rate at the interface. The high portion of to note that the result is in good agreement with the order degree of
CꢀC bond for TiO2@Cꢀ360/RGO in Fig. 5 (c), 90.7%, is assumed to samples. TiO2@Cꢀ360/RGO and TiO2@Cꢀ180/RGO with
be resulted from the strong conjunction between surface carbon shell carbonaceous layer of high order degree and fewer defects obtain
around TiO2 and the RGO which is much higher than that of efficient transfer of photoꢀinduced electron to RGO. In addition, the
TiO2@Cꢀ450/RGO, 79.2%. This excellent bridging connection emission intensity is also closely related to thickness of the
induced by optimal carbonaceous layer in TiO2@Cꢀ360/RGO carbonaceous layer. TiO2@Cꢀ360/RGO has thinner carbonaceous
hybrids may provide more charge transfer path during the layer with optimized order degree than TiO2@Cꢀ180/RGO so that
photocatasis.
the connection of TiO2 particles and RGO by CꢀC bond in TiO2@Cꢀ
In this way, TiO2@C/RGO photocatalysts with tunable 360/RGO photocatalyst is much better for the efficient separation of
carbonaceous layer were obtained. The existence of carbonaceous activated electron – hole pairs.35 TiO2@Cꢀpristine/RGO owns more
layer has little effect on the band gap of TiO2@C/RGO surface defects and carbonaceous organic species which will become
photocatalysts. However, the interfaced carbonaceous layer may numerous recombination sites and inhibit the well contact with
graphene. Similarly, as there is no efficient transmission path for
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TiO2@Cꢀ450/RGO to deliver the carriers to RGO timely attributed When TiO2 particles were composited by RGO, the band gap of
to the poor connection between TiO2 and RGO, the emission peak is obtained hybrid could be lowered to visible as reported study.23
much higher. These results indicate that an optimized thin and However, the charge separation at the interface between TiO2 and
ordered carbonaceous layer is very important to bridge the RGO is still a considerable factor affecting the photocatalytic
nanoparticles and graphene to enhance the charge transfer at the activity of the hybrid. When the photocatalyst was irradiated under
interface of the hybrids and thus improve the photocatalytic visible light, TiO2 could produce activated electron – hole pairs. The
performance.
modified carbonaceous layer of TiO2@Cꢀ360/RGO with optimal
More evidences are supported by the decay time of the samples order degree and thickness could provide efficient separation path
shown in Fig. 8 which give a direct view of the process about the for the electron – hole pairs. Thus the activated electron could be
electron diffusion under laser irradiation at 375 nm. The signal is transfer to RGO in time to form oxygen radicals and the remaining
collected at 440nm and reveals the lifetime of the samples in this hole could be used to form hydroxyl radicals. Fig 10 shows the PL
order: TiO2@Cꢀpristine/RGO < TiO2@Cꢀ450/RGO < TiO2@Cꢀ emission spectra of terephthalic acid with TiO2@C/RGO sample
180/RGO < TiO2@Cꢀ360/RGO.
under visible light irradiation. Clearly, a PL Peak at about 425 nm is
To evaluate the recycling ability of the photocatalyst with the observed when suspension illuminated by visible light and the
ꢀ
best performance, the sample was collected by centrifugation at 8000 intensity increases with time, indicating that OH produced during
rpm after first run of photo degradation test. The collection was photocatalytic reaction. Moreover, PL intensities for TiO2@Cꢀ
dispersed in water for desorption for 30 min and then centrifuged at 360/RGO in Fig. 10 (a) are much stronger than that for TiO2@Cꢀ
8000 rpm again. This operation was repeated 3 times. After weighed, 450/RGO in Fig. 10 (b) at the same time which means the amount of
the lost mass, a few milligrams, was made up and the photocatalysis ꢀOH radicals produced much more on TiO2@Cꢀ360/RGO than
test was the same as the previous description. As shown in Fig. 9 the TiO2@Cꢀ450/RGO.
The better interfacial structure induced by
TiO2@Cꢀ360/RGO photocatalyst owns stable recycling ability. After optimal carbonaceous layer improves the separation of activated
ꢀ
carried out for another two cycles, the degradation rate of TiO2@Cꢀ electron – hole pairs and promotes the formation OH radicals and
360/RGO photocatalyst maintains at 64% within 4h under visible ꢀO2ꢀ radicals contributing to enhanced photocatalytic activity. Finally,
light suggesting this photocatalyst is capable for longꢀterm runs.
the MO pollutant will be react with oxygen radicals and hydroxyl
Above all, the photocatalytic activity of TiO2@C/RGO could radicals to form water and carbon dioxide which can be illustrated in
be optimized by tuning the interfacial carbonaceous layer. TiO2@Cꢀ the mechanism scheme as show in Scheme 2.
360/RGO hybrid with relatively thin and ordered carbonaceous layer
Conclusions
exhibits the best charge transfer power and stable recycling ability
A novel TiO2@C/RGO photocatalyst was synthesized in this study.
The carbonaceous layer modified TiO2 nanoparticles were anchored
on RGO sheets by solvothermal process. The hybrid with moderate
which is in good agreement with the photocatalytic decomposition
result. Besides, TiO2@Cꢀ360/RGO photocatalyst also exhibits much
higher photocatalytic activity than P25/RGO prepared at the same
condition as shown in Fig. S5.
o
postꢀannealing, heatꢀtreatment at 360 C, exhibited the best visibleꢀ
light photocatalytic activity, due to the sufficient contact and
3.4 Photocatalysis mechanism
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[10] R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki and Y. Taga,
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enhanced charger transfer caused by the thin and ordered
carbonaceous layer at the interface between TiO2 and RGO. The
modification of interfaced carbonaceous layer in these hybrids has
been proved to be powerful on improving the photocatalytic activity.
This result of our study indicates the importance of interface
engineering to achieve highly active photocatalysts and better
understand the photoactivity mechanism of semiconductor/graphene
hybrids.
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Acknowledgements
This work was supported partially by National Natural Science
Foundation of China (21301153 and 21503187).
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Figure/Table Captions
Table 1 Information about the test results of TiO2@C and TiO2@C/RGO samples.
Fig. 1 TGA curve of TiO2 samples derived from hydrothermal synthesis and commercial TiO2.
Fig. 2 Raman spectra of TiO2@C samples using 532 nm laser with a power of 50 Mw.
Fig. 3 HRTEM images of TiO2@C-360 (a) and TiO2@C-360/RGO (b) and TEM images of TiO2@C/RGO hybrids
c-f
（
）.
Fig. 4 UV-Vis absorption spectra of TiO2@C and TiO2@C/RGO samples.
Fig. 5 XPS of C1s in TiO2@C/RGO sample: TiO2@C-pristine/RGO, TiO2@C-180/RGO, TiO2@C-360/RGO and
TiO2@C-450/RGO.
Fig. 6 Photocatalytic degradation curves of MO with the presence of TiO2@C/RGO photocatalysts under visible
light (> 420 nm).
Fig. 7 PL emission peaks excited at 420 nm for TiO2@C/RGO photocatalysts.
Fig. 8 PL decay curves of TiO2@C/RGO photocatalysts.
Fig. 9 Recycling test of TiO2@C-360/RGO for photocatalytic degradation of MO under visible light.
Fig. 10 PL emission spectra of terephthalic acid with TiO2@C/RGO sample under visible light irradiation excited
at 312nm: a, TiO2@C-360/RGO; b, TiO2@C-450/RGO.
Scheme 1 Experimental scheme of the synthesis of TiO2@C/RGO photocatalyst.
Scheme 2 The mechanism of photocatalytic process on TiO2@C/RGO photocatalyst.
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Table 1
Samples
Particle Size a
15.1
Id/Igb
3.98
0.99
0.99
1.12
ꢀꢀ
Band gap (eV)c
Degradationd
3.20
3.20
3.25
3.20
2.8
~0
~0
TiO2@C-pristine
TiO2@C-180
15.2
15.2
~0
TiO2@C-360
15.6
~0
TiO2@C-450
16.3
23%
59%
66%
18%
TiO2@C-pristine/RGO
TiO2@C-180/RGO
TiO2@C-360/RGO
TiO2@C-450/RGO
16.1
ꢀꢀ
2.8
16.0
ꢀꢀ
2.8
15.8
ꢀꢀ
2.8
aThe average particle sizes of TiO2@C samples were calculated by Scherrer formula based on the XRD patterns
(Fig. 3) and these of TiO2@C /RGO were calculated based on TEM images (Fig. 4).
bIntensity ratio of peak D and peak G in Raman spectrum (Fig. 2) .
cThe band gap was obtained based on the UVꢀvis absorption spectra (Fig. 5).
dThe photo decomposition was carried out with 20 mg photocatalyst and 20 mg/L MO under visible light (>420
nm) for 4h.
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Fig. 1
Fig. 2
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Fig. 3
(a)
(b)
Fig. 4
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Fig. 5
Fig. 6
Fig. 7
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Fig. 8
Fig. 9
Fig. 10
Scheme 1
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Scheme 2
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The amorphous carbon layer with optimized thickness and order degree well bridges a close
connection between TiO2 particle and RGO contributing to improved interface charge transfer
efficiency.