A TiO2/C catalyst having biomimetic channels and extremely low Pt loading for formaldehyde oxidation

Article abstract of DOI:10.1039/c8ra10314c

This study presents a TiO₂/C hybrid material with biomimetic channels fabricated using a wood template. Repeated impregnations of pretreated wood chips in a Ti precursor were conducted, followed by calcination at 400-600 °C for 4 hours under a nitrogen atmosphere. The generated TiO₂ nanocrystals were homogenously distributed inside a porous carbon framework. With an extremely low Pt catalyst loading (0.04-0.1 wt%), the obtained porous catalyst could effectively oxidize formaldehyde to CO₂ and H₂O even under room temperature (conv. ～100%). Wood acted as both a structural template and reduction agent for Pt catalyst generation in sintering. Therefore, no post H₂ reduction treatment for catalyst activation was required. The hierarchal channel structures, including 2-10 nm mesopores and 20 μm diameter channels, could be controlled by calcination temperature and atmosphere, which was confirmed by SEM and BET characterizations. Based on the abundant availability of wood templates and reduced cost for low Pt loading, this preparation method shows great potential for large-scale applications.

Full text of DOI:10.1039/c8ra10314c

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A TiO2/C catalyst having biomimetic channels and
extremely low Pt loading for formaldehyde
oxidation†
Cite this: RSC Adv., 2019, 9, 3965
Wei Liu,ab Yutao Gong,b Xueping Li,a Cai-wu Luo,a Congmin Liud
ac
*
and Zi-sheng Chao
This study presents a TiO2/C hybrid material with biomimetic channels fabricated using a wood template.
Repeated impregnations of pretreated wood chips in a Ti precursor were conducted, followed by
calcination at 400–600 ꢀC for 4 hours under a nitrogen atmosphere. The generated TiO2 nanocrystals
were homogenously distributed inside a porous carbon framework. With an extremely low Pt catalyst
loading (0.04–0.1 wt%), the obtained porous catalyst could effectively oxidize formaldehyde to CO2 and
H2O even under room temperature (conv. ꢁ100%). Wood acted as both a structural template and
reduction agent for Pt catalyst generation in sintering. Therefore, no post H2 reduction treatment for
catalyst activation was required. The hierarchal channel structures, including 2–10 nm mesopores and
20 mm diameter channels, could be controlled by calcination temperature and atmosphere, which was
confirmed by SEM and BET characterizations. Based on the abundant availability of wood templates and
reduced cost for low Pt loading, this preparation method shows great potential for large-scale applications.
Received 16th December 2018
Accepted 16th January 2019
DOI: 10.1039/c8ra10314c
rsc.li/rsc-advances
Formaldehyde (HCHO) is an important chemical feedstock that material-based formaldehyde absorbents, such as active
is widely used in the production of industrial resins, polymers carbon,4 porous Al2O3 (ref. 5) and zeolite,6 have been investi-
and coating materials. However, formaldehyde is highly toxic gated. For example, different porous Al2O3 materials were
and volatile, and it has been listed as a human carcinogen prepared by using the template method, which showed broad
group I by the International Agency for Research on Cancer pore size distribution and good formaldehyde adsorption–
(IARC).1 Formaldehyde is slowly emitted from building and desorption behavior.7,8 However, the porous inorganic adsor-
furnishing materials, which can cause serious health problems. bents have limited adsorption capacities, resulting in only
Developing an efficient and feasible catalyst for the removal of a short effective time.
formaldehyde pollutant from indoor environment has received
a growing concern recently.
Formaldehyde oxidation over porous material-supported
catalysts is a promising technology because formaldehyde can
Inorganic porous materials are good candidates for appli- be continuously oxidized to CO2 and H2O.9–11 The porous
cation in the removal of formaldehyde either by physical structure can facilitate fast diffusion and mass transport of
absorption or chemical catalytic oxidation.2,3 Inorganic porous formaldehyde and products. Furthermore, the high surface area
materials have multi-shapes of pore structures and large surface of the porous material provides a large number of active sites for
areas, which allow formaldehyde molecules access into holes. formaldehyde adsorption and catalyst loading. Many catalyst-
Moreover, the inorganic framework of the material has high loaded porous materials or porous transition metal oxides
thermal stability, suggesting that the material can be thermally were prepared and displayed excellent formaldehyde oxidation
regenerated and reused for many times. Many inorganic porous performance; some examples include Pt on ZSM-5 and NaY
zeolites,12,13 mesoporous Au, Pt or Pd/CeO2,14–16 VOx/MCM,17
macro-mesoporous Pt/g-Al2O3,18 Pd or Pt/TiO2,19–24 Pt/
mesoporous ferrihydrite25 and porous MnO2.26,27 Various
organic templates were used in the preparation of TiO2 with
desired porosity, such as surfactants,28,29 block copolymers30–32
and even small organic molecules including salicylic acid and
aspartic acid.33 However, these organic templates generally have
a high price, which hinders their potential for large-scale
applications. Another issue is that the noble metal catalyst
aState Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry
and Chemical Engineering, Hunan University, Changsha 410082, China. E-mail:
zschao@yahoo.com
bSchool of Chemical & Biomolecular Engineering and RBI, Georgia Institute of
Technology, 500 10th Street N.W., Atlanta, GA 30332, USA
cCollege of Materials Science and Engineering, Changsha University of Science and
Technology, Changsha, Hunan 410114, China
dNational Institute of Clean-and-Low-Carbon Energy, Beijing 102211, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra10314c
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loading is still high (1–2.5%) to reach effective formaldehyde
oxidation.
Biomass materials have low cost and natural hierarchal
structures in the range from millimeters to nanometers,34 which
can be used as natural templates for porous material fabrica-
tion. TiO2 with a porous structure has been prepared by bio-
templating of naturally grown biomass materials, such as
wood and bamboo;22,35 however, there is no reported example
on the use of the material as a catalyst in reactions such as
organic oxidation. Herein, we presented a wood templated TiO2/
C material having biomimetic channel structures. The obtained
material was different from the supported catalysts or core–
shell structure materials, in which the catalyst layers are only
coated inside or outside the porous structure. Wood templated
TiO2/C exhibited a hybrid structure; this resulted in the gener-
ation of TiO2 nanocrystals, which were homogenously distrib-
uted inside the porous carbon framework because the Ti
precursor penetrated into wood tissues before catalyst sinter-
ing. With an extremely low loading of Pt, this type of hierarchal
structured material showed highly effective formaldehyde
oxidation behavior even under room temperature.
Fig. 2 SEM images of TiO2/C material containing biomimetic channels
prepared by a wood template after sintering at 400 ꢀC (A–D), 500 ꢀ
(E) and 600 ꢀC (F).
C
Results and discussion
Fig. 1 shows the preparation process and schematic illustration
of the obtained TiO2/C hybrid porous structure. Simple
impregnation of wood chips in the organic titanium precursor
and the following drying process were repeated alternately.
Aer the Ti precursor penetrated into wood tissues, the Pt
precursor also inltrated into wood and then was calcinated
under a controlled temperature and atmosphere.
The morphology of biomimetic channel-containing TiO2/C
material prepared by the wood template is shown in Fig. 2,
showing multi-scaled hierarchal structures. As shown in Fig. 2A,
ꢀ
the channel structure is formed aer sintering at 400 C. This
could be produced by the xylem vessels in wood. During the
impregnation process, the organic titanium precursor Ti(OBu)4
diffused into the xylem vessels and tissues or was coated on the
surface of vessel walls (Fig. 1). Furthermore, pre-formed TiO2 sol
could also be lled into the vessels of wood; aer solvents
evaporated, the TiO2 sol was xed on the vessel walls. The TiO2
precursor layer could be increased by repeating the impregna-
tion and drying processes alternatively. With sintering at a high
temperature, the organic wood components, including hemi-
cellulose, cellulose and lignin, were converted to porous carbon.
The TiO2 precursor was transformed into TiO2 and the whole
material maintained the physical structure of the wood
template. The formed TiO2/C channels exhibited diameter of ca.
20 mm, which was the same as the size of xylem vessels in wood.
Some pits were observed in the TiO2 channels. Pits are cavities
located on wood cell walls, which are essential components for
water-transport system in wood.36 The pitted structure was
maintained perfectly through the impregnation method aer
sintering, which increased the porosity and helped improve the
catalytic performance over the obtained material. As shown in
the magnied images (Fig. 2C and D), the pits exhibit a cylin-
drical shape with diameter of ca. 10 mm.
Different samples were prepared under the sintering
temperatures of 400, 500 and 600 ꢀC in this study. The samples
showed similar structures, i.e., hierarchical channels. The ob-
tained morphologies under sintering at 500 and 600 ꢀC are
shown in Fig. 2E and F. The SEM images verify the successful
preparation of a porous TiO2 material templated by wood.
Fig. 1 Schematic illustration of wood templated biomimetic TiO2/C
hybrid material preparation.
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Before sintering, the catalyst (Pt) precursor was loaded into
RSC Advances
XA ¼ 1/(1 + 1.265IR/IA) ꢂ 100%
XR ¼ 1/(1 + 0.8IA/IR) ꢂ 100%
(1)
(2)
the channel structure of the material. The loading process was
similar to the preparation of a TiO2 layer, but a solution of
H2PtCl6 dissolved in isopropanol was used. The desired amount
of catalyst could be reached by repeating the impregnation and
drying processes. The advantage of the impregnation method
for catalyst loading is the homogenous dispersion of the cata-
lyst. In order to investigate the chemical composition,
elemental mapping was performed using energy-dispersive
spectrometry (EDS) (shown in ESI, Fig. S1.†). For the sample
calcined at 400 ꢀC, the results showed that the TiO2 component
included 25.3% and 74.5% of carbon and 0.1% of Pt loading
amount. The exact Pt contents in the prepared catalysts were
measured by an inductively coupled plasma mass spectrometer
(ICP-MS), showing that the samples calcined at 400, 500 and
600 ꢀC contained 0.092%, 0.095% and 0.098% weights of Pt,
respectively. In addition, the catalysts with different amounts of
Pt loading were studied, and Pt loadings were found to be
0.063% and 0.041% (shown in ESI Table S1†).
Here, IA is the anatase phase intensity at 2q ¼ 25.25ꢀ; IR is the
intensity of rutile peak at 2q ¼ 27.42ꢀ.
The calculation results showed that the anatase phase
ꢀ
accounted for 63.5% in the sample sintered at 400 C, but this
value signicantly decreased to 16.8% when a high sintering
temperature of 600 C was applied (Table 1). The average crys-
talline size of obtained TiO2 was calculated by Debye–Scherrer
equation, indicating that the crystal size increased at a high
calcination temperature.
ꢀ
To investigate the phase transition behavior with the wood
template, TiO2 samples were prepared using the sol–gel method
without wood template but with the same calcination condi-
tions. The XRD characterization showed a high content ratio of
anatase phase in the TiO2 samples prepared using the sol–gel
method (shown in ESI, Fig. S2.†). However, in wood templated
TiO2 preparation, all samples showed anatase and rutile mixed
phases. These results indicated that the wood template actually
promoted the anatase-to-rutile phase transition in TiO2
powders because the transformation behavior can be affected
by many factors such as impurities in wood, grain sizes of
formed TiO2 crystals, preparation methods and annealing
conditions.
Fig. 4 shows the nitrogen adsorption isotherms and pore size
distribution curves of the obtained porous TiO2 material tem-
plated by wood. The isotherm curves of all samples can be
classied as type-IV isotherms based on the Brunauer–Deming–
Deming–Teller classication,41 indicating the mesoporous
structure in the obtained TiO2/C material. The isotherms show
hysteresis loops that have an H3-type shape,42 suggesting the
presence of a layered structure with slit-like pores (multi-
channel structures in this material). These results were
consistent with the structure observed using SEM. The speciꢀc
surface area was 41.5 m2 gꢃ1 for the sample sintered at 400 C
and the value slightly decreased with the high sintering
X-ray diffraction (XRD) was employed to study the crystalline
phase of prepared porous TiO2/C materials. Fig. 3 shows the
XRD patterns of different samples calcined at 400, 500 and
ꢀ
600 C. As the calcination temperature increased, the intensity
of XRD peak increased, indicating the increase in crystallinity of
TiO2 compared to the amorphous phase. The XRD peaks could
be identied by comparing with the standard diffraction peaks
of anatase and rutile TiO2, showing that the samples contained
both anatase and rutile phases of TiO2. The XRD peaks at 2q ¼
25.25ꢀ (101) and 2q ¼ 48.03ꢀ (200) veried the formation of the
anatase phase, while the peaks at 2q ¼ 27.42ꢀ (110) and 2q ¼
36.08ꢀ (101) indicated the presence of the rutile phase.37,38
Signicant phase transformation from anatase to rutile was
observed under a high sintering temperature. The ratio of
anatase to rutile can be estimated by the intensity of charac-
teristic diffraction peaks of both phases. According to the
Spurr–Meyers equation, the weight percentages of anatase (XA)
and rutile (XR) can be calculated as follows:39,40
ꢀ
temperatures of 500 and 600 C. The pore volumes of the ob-
tained TiO2/C material were in the range of 0.055–0.033 cm3
gꢃ1. The specic surface areas and pore volumes of obtained
samples in this study were similar to those of previously re-
ported biomass templated materials.35,43 The corresponding
pore size distribution curves show that the wood templated
TiO2 materials have meso-pores with width of 2–10 nm (shown
in ESI, Table S2.†). It should be noted that some pores exhibited
large size of 12–18 nm. The large-sized pores could be formed by
wood template removal during sintering. The micro-sized
Table 1 Weight percentage (X) and crystalline size (D) of anatase (A)
and rutile (R) phases in prepared TiO2 samples
Temp. (ꢀC)
XA (%)
XR (%)
DA (nm)
DR (nm)
400
500
600
63.5
28.7
16.8
36.2
71.0
83.0
20.3
27.0
30.5
119.8
120.5
131.7
Fig. 3 XRD patterns of the obtained TiO2 material sintered at 400, 500
and 600 ꢀC for 4 hours (o denotes rutile phase and * denotes anatase
phase).
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Fig. 4 Nitrogen adsorption/desorption isotherm curves (A) and cor-
responding pore-size distribution curves (B) of prepared TiO2 materials
under different sintering temperatures.
channel and nano-sized pore structure formed a hierarchal
channel system in the TiO2 material, which largely improved
the catalytic behavior in formaldehyde oxidation.
Fig. 6 TGA curves of wood samples impregnated with TiO2 and
catalyst precursors. (A) Constant temperature at 400 ꢀC for 1 hour
under air atmosphere; (B) 500 ꢀC; (C) 600 ꢀC.
The chemical status of the elements in the samples was
analysed by X-ray photoelectron spectroscopy (XPS). XPS survey
spectra (Fig. 5A) of prepared samples indicate the presence of C,
Ti, O and Pt and the corresponding photoelectron peaks are
located at binding energies of 284.8 (C 1s), 458.8 (Ti 2p), 529.8
(O 1s) and 70.6 eV (Pt 4f). Fig. 6 shows the high-resolution XPS
spectra of Pt 4f, Ti 2p and O 1s of the prepared samples. The
peaks at 71.1 and 74.3 eV could be attributed to Pt 4f7/2 and Pt
4f5/2 bands for metallic Pt (Pt0), respectively.44,45 For Pt2+ and
binding energy of O 1s of TiO2 lattice oxygen (Ti–O–Ti).20,45
A
signicant shoulder peak at ca. 533 eV appeared beside the Ti–
O–Ti peak in the spectrum of the sample sintered at 400 ꢀC. This
shoulder peak included two tting peaks: one at 531.6 eV, which
can be ascribed to the oxygen in Ti–OH group on the TiO2
surface, and the other at 533.8 eV, which can be ascribed to
organic oxygen in C–O bonds.47 These results indicated that
there is a small amount of organic residues in the sample aer
sintering at 400 ꢀC in air for 4 hours. The C–O peak disappeared
in the spectra of the samples sintered at 500 and 600 ꢀC, which
indicated that the organic components of wood were completely
oxidized at high sintering temperatures. The Ti–OH peak also
reduced with increase in the sintering temperature. The Ti–OH
group, which was certicated to be active in the oxidation of
formaldehyde, could be formed by the adsorption of oxygen or
H2O molecules on the surface of TiO2. Therefore, the sample
that has a large ratio of Ti–OH groups could have high catalytic
activity.
Pt4+, the binding energies were reported as ca. 73.0 and 74.7 eV
46
for 4f7/2 and 76.4 and 78.1 eV for 4f5/2
. The Pt 4f XPS spectra
veried the reduction of Pt during the sintering process by wood
because there was no post reduction treatment by H2 gas in this
study. Wood acted as both a structural template and reduction
agent of Pt catalyst in the preparation process. The Ti 2p spectra
are shown in Fig. 5C. The peaks at ca. 464.0 and 458.2 eV were
ascribed to Ti 2p1/2 and Ti 2p3/2 of Ti4+ in TiO2, respectively. The
O 1s spectra are shown in Fig. 5D, which include many over-
lapped peaks. The tting peak at ca. 530 eV represents the
In order to investigate mass changes during the sintering
process, thermogravimetric analysis (TGA) was performed
under air atmosphere. The wood samples aer the impregna-
tion of TiO2 and Pt precursors were used for TGA measure-
ments. With the increase in temperature, TiO2 and catalyst
precursors were transformed into crystalline and metallic
forms, and wood was decomposed to carbon. The TGA curve
with the temperature up to 400 ꢀC is shown in Fig. 6A. The
sample mass continuously decreased with increasing tempera-
ture and constant temperature sintering. The mass loss rate
curve shows that the temperature at the highest decomposition
ꢀ
rate of wood is 350 C. However, the mass loss rate curve with
ꢀ
the temperature up to 500 C indicates two highest decompo-
sition rate temperatures of 350 and 500 ꢀC, as shown in Fig. 6B.
The possible reason is that wood could be pyrolyzed and
ꢀ
carbonized under a low temperature of 350 C and oxidized at
Fig. 5 XPS survey spectra (A) of the obtained catalysts and high
resolution spectra of Pt 4f (B), Ti 2p (C) and O 1s (D) of prepared TiO2
samples under different sintering temperatures.
a high temperature of 500 ꢀC. Compared with the TGA curve of
the original wood template, the result showed that the highest
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decomposition rate temperatures of wood chips were 350 and catalyst bed, which indicated low conversion of formaldehyde
ꢀ
380 C (shown in ESI, Fig. S3.†). It should be noted that mass oxidation. The high catalytic performance of wood templated
was continuously lost at the constant temperature of 500 ꢀC porous TiO2 can be ascribed to the channelled micro–nano
(shown in the curve in Fig. 6B). The organic residues could be hierarchal porous structure and the synergism of anatase–rutile
completely oxidized if there was sufficient reaction time. The mixed phases. The chemical analysis of oxidation products in
TGA curve with the temperature up to 600 ꢀC has similar result the out stream was conducted. It veried that HCHO was
compared with the curve of 500 ꢀC. The sample mass was stable completely oxidized to CO2 because no CO was detected, as
aer 1 hour sintering at 500 or 600 ꢀC, indicating complete shown in Fig. 7B.
removal of wood template.
The conversions of formaldehyde oxidation reaction on
The catalytic behavior of the prepared porous TiO2 material different prepared catalysts under different reaction tempera-
was evaluated in a xed bed reactor. Gaseous HCHO and humid tures (20–35 ꢀC) and humidities are summarized in Fig. 7C and
air gas (water vapor 50%) were introduced into the reactor tube, D. The results indicated that the wood templated TiO2 catalyst
and the HCHO concentration was measured at the outlet of the materials have high catalytic performances in our test time. The
reactor. The concentrations of HCHO in the stream owing in sample sintered at 400 ꢀC exhibited higher formaldehyde
and out of the reactor were measured. As shown in Fig. 7A, the oxidation conversion than the samples sintered at 500 and
HCHO concentration signicantly decreases from the initial 600 ꢀC. This result could be explained by the crystalline phase of
104 ppm to ca. 0.2–0.5 ppm at the reaction temperature of 35 ꢀC. TiO2 and the amount of hydroxyl groups (Ti–OH) on the surface
These results showed high catalytic oxidation performance of of the TiO2 material. Previous studies show that anatase TiO2
formaldehyde over the catalyst with a low Pt loading (0.09%). has higher catalytic activity than rutile TiO2.44,45,48 Therefore, the
Anatase phase TiO2 was prepared by the sol–gel method without sample sintered at a low temperature exhibited a high content
a wood template. The catalytic performance evaluation showed of anatase phase, resulting in high catalytic activity. In addition,
that 44 ppm of HCHO still remained in the downstream of the high amount of surface hydroxyl groups led to high oxida-
tion conversion of formaldehyde, which was veried by reported
studies.48,49 The high Ti–OH ratio conrmed by XPS for the
sample sintered at 400 ꢀC also improved the catalytic perfor-
mance of formaldehyde oxidation. The formaldehyde oxidation
performance was related to the humidity of air (Fig. 7D). When
dry air was introduced in the oxidation reaction, the conversion
slightly decreased. This was because the moisture in air could
be adsorbed and reacted with the surface of TiO2, resulting in
increase in the concentration of hydroxyl groups on the catalyst
surface.50
The catalysts with different Pt loading amounts were also
evaluated in formaldehyde oxidation in a xed bed reactor
(Fig. 7E). The catalyst with 0.092% Pt content showed the
highest oxidation conversion (close to 100%). By slightly
decreasing the Pt loading amount to 0.063%, the catalyst still
showed high performance with the conversion higher than
95%. However, the conversion decreased to around 85% when
0.041% Pt was loaded. Compared with the performance of the
sol–gel catalyst without a wood template, the conversion was as
low as 60%. The durability of wood templated catalyst was
investigated as well. As shown in Fig. 7F, the porous TiO2
catalyst calcined at 400 ꢀC maintains high performance in
a long test time of 12 hours, showing only 2% decrease in
conversion.
Fig. 8 illustrates the reaction process between moisture and
TiO2 surface. The formed hydroxyl groups were active sites for
formaldehyde adsorption. The oxidization reaction started with
the adsorption of formaldehyde on the TiO2 surface and oxygen
on the Pt catalyst surface. The absorbed formaldehyde mole-
Fig. 7 Catalytic oxidation of formaldehyde over prepared porous TiO2
catalyst material. (A) The HCOH concentration in upstream and
downstream of reactor bed by using different prepared catalysts. (B)
The CO2 and CO measurements in the reaction of wood templated cules were then transformed to formic acid over the Pt catalyst
catalyst (0.092% Pt content, calcined at 400 ꢀC). (C) Performances of
surface. With the elimination of H2O and CO2, the catalyst
surface could be restored to the initial state, as shown in Fig. 8B.
The wood templated channel structure largely improved the
reactant and product diffusion and catalytic performance.
catalysts with 400–600 ꢀC calcination temperatures. (D) Perfor-
mances of catalysts (0.092% Pt content, calcined at 400 ꢀC) under
different reaction temperatures and air humidities. (E) Conversions of
catalysts with different Pt loading amounts. (F) Long time durability
test.
Therefore, this prepared biomimetic TiO2 material showed
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to form 20 wt% solution with stirring (noted as solution A).
Water (2 wt%)–isopropanol solution (10 mL) was used as solu-
tion B, which was slowly added to 10 mL solution A with stir-
ring. Aer aging for 1 hour with stirring, the clear and
transparent Ti precursor solution was obtained. Pre-treated
wood chips were impregnated in the precursor solution under
ux for 4 hours and then removed from the solution and dried
at 120 ꢀC for 2 hours. This process was repeated until the weight
of wood chips increased by 20%.
Catalyst precursor solution was obtained by dissolving
chloroplatinic acid (H2PtCl6) in isopropanol (nal H2PtCl6
concentration, 0.1 wt%). The wood chips aer Ti precursor
solution treatment were impregnated in catalyst precursor
solution at 50 ꢀC for 2 hours with stirring and then dried in an
oven overnight. With repeated impregnation and drying
processes, different amounts of Pt catalyst loadings could be
achieved. Finally, the obtained wood chips were sintered in N2
ow. Different samples were prepared at the sintering tempꢃer1-
Fig. 8 Schematic illustration of reactant and product diffusion in
wood templated catalyst (A) and possible mechanism diagram for
HCHO oxidation (B).
atures of 400, 500 and 600 ꢀC with the heating rate 10 ꢀC min
.
Fig. 1 shows the synthesis process of wood templated TiO2
catalyst material.
good catalytic performance even at an extremely low Pt catalyst
loading.
Characterizations
The amount of loaded Pt was measured by an inductively
coupled plasma mass spectrometer (ICP-MS, NexIon, Perkin-
Elmer). Before measurement, the samples were dissolved in
aqua regia (HNO3 : HCl ¼ 1 : 3 v/v) with the heating of micro-
wave oven. Aer cooling, HF solution was added and mineral-
ized to obtain a clear solution. The morphology of obtained
porous TiO2 catalyst material was characterized by scanning
electron microscopy (SEM, Zeiss Ultra60 FE-SEM instrument)
coupled with INCA 200 X-Sight de Oxford instruments for
energy-dispersive X-ray spectroscopy (EDS) analysis. The formed
TiO2 crystalline phase was veried by powder X-ray diffraction
(PXRD). PXRD was conducted using a PANalytical X'Pert X-ray
diffractometer coupled with X'Celerator detector and Cu Ka (l
Conclusions
TiO2 catalyst materials containing biomimetic channels were
successfully prepared by a wood template. SEM images veried
the hierarchal channel structure (width ca. 20 mm) formed by
xylem vessels in wood. BET analysis showed that the prepared
TiO2 material exhibited 2–10 nm mesopores, which could be
formed by small structures in wood-like pits. XRD showed that
the prepared TiO2 is a mixture of anatase and rutile phases. XPS
certied the presence of metallic Pt, which is the active
component in the oxidation of formaldehyde. The results of
catalytic performance evaluation showed that the prepared TiO2
catalysts have high oxidation conversion of formaldehyde.
˚
¼ 1.5418 A). X-ray photoelectron spectroscopy (XPS) analysis
was performed with a Thermo K-Alpha instrument equipped
with monochromatic AlKa radiation at 1486.6 eV X-ray source.
N2 physisorption isotherms were collected at 77 K on a Quad-
rasorb system from Quantachrome Instruments. Before the
measurements, the sample (ꢁ50 mg) was degassed under
Experimental section
Material
Birch wood chips were supplied by timber trading market.
Isopropanol (i-PrOH), benzene (C6H6), titanium butoxide (Ti
[O(CH2)3CH3]4) and chloroplatinic acid (H2PtCl6) were
purchased from Alfa Aesar.
ꢀ
dynamic vacuum at 150 C for 18 hours. TGA analysis results
were obtained using an STA 6000 Simultaneous Thermal
Analyzer (PerkinElmer) with the heating rate of 10 ꢀC minꢃ1 and
air ow of 10 mL minꢃ1
.
Fabrication method
Catalytic formaldehyde oxidation test
Birch wood was cut into chips with size of 4 mm ꢂ 2 mm ꢂ 1
mm. The wood chips were pre-treated with mixed organic The catalytic formaldehyde oxidation test was performed in
solvent (volume of benzene to absolute ethanol was 2 : 1) under a xed-bed quartz ow reactor with a gas mixture of air con-
reux for 6 hours to remove the extractives in wood. Aer taining 100 ppm HCHO at a low rate 50 cm3 minꢃ1. The
solvent was evaporated at 80 C, the wood chips were washed humidity of air gas was controlled at 50% by bubbling through
with deionized water at 80 ꢀC for several times and then dried in water. The concentrations of HCHO, CO and CO2 were analyzed
ꢀ
oven overnight.
by gas chromatography (GC).
The Ti precursor was prepared by partial hydrolysis of tita-
The conversion of HCHO was calculated according to the
nium butoxide. Titanium butoxide was dissolved in isopropanol following equation:
3970 | RSC Adv., 2019, 9, 3965–3971
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20 L. Nie, J. Wang and J. Yu, RSC Adv., 2017, 7, 21389–21397.
21 Z. Schnepp, S. C. Wimbush, S. Mann and S. R. Hall,
CrystEngComm, 2010, 12, 1410–1415.
22 S. De, S. Dutta, A. K. Patra, B. S. Rana, A. K. Sinha, B. Saha
and A. Bhaumik, Appl. Catal., A, 2012, 435–436, 197–203.
23 F. Xu, Y. Le, B. Cheng and C. Jiang, Appl. Surf. Sci., 2017, 426,
333–341.
24 J. Peng, X. Wu and S. Wang, RSC Adv., 2017, 7, 13536–13542.
25 Z. Yan, Z. Xu, J. Yu and M. Jaroniec, Environ. Sci. Technol.,
2015, 49, 6637–6644.
HCHO concentration in out-stream
HCHO concentration in in-stream
HCHO conversion ¼ 1 ꢃ
ꢂ 100%
Conflicts of interest
There are no conicts to declare.
Acknowledgements
26 H. Tian, J. He, X. Zhang, L. Zhou and D. Wang, Microporous
Mesoporous Mater., 2011, 138, 118–122.
27 J. Wang, P. Zhang, J. Li, C. Jiang, R. Yunus and J. Kim,
Environ. Sci. Technol., 2015, 49, 12372–12379.
28 M. M. Yusuf, H. Imai and H. Hirashima, J. Non-Cryst. Solids,
2001, 285, 90–95.
This work was supported by the National Natural Science
Foundation of China (Grant 21376068).
References
29 H. Hirashima, H. Imai and V. Balek, J. Non-Cryst. Solids,
2001, 285, 96–100.
1 IARC, Monographs on the Evaluation of Carcinogenic Risks to
Humans, 2006, vol. 88, pp. 217–375.
2 T. Salthammer, S. Mentese and R. Marutzky, Chem. Rev.,
2010, 110, 2536–2572.
3 J.-P. Bellat, I. Bezverkhyy, G. Weber, S. Royer, R. Averlant,
J.-M. Giraudon and J.-F. Lamonier, J. Hazard. Mater., 2015,
300, 711–717.
30 H. S. Yun, K. Miyazawa, H. S. Zhou, I. Honma and
M. Kuwabara, Adv. Mater., 2001, 13, 1377–1380.
31 E. Ortel, S. Sokolov, C. Zielke, I. Lauermann, S. Selve, K. Weh,
B. Paul, J. Polte and R. Kraehnert, Chem. Mater., 2012, 24,
3828–3838.
32 W. Zhou, F. Sun, K. Pan, G. Tian, B. Jiang, Z. Ren, C. Tian and
H. Fu, Adv. Funct. Mater., 2011, 21, 1922–1930.
33 S. Dutta, S. De, A. K. Patra, M. Sasidharan, A. Bhaumik and
B. Saha, Appl. Catal., A, 2011, 409–410, 133–139.
34 N. Daud and R. Shanks, Composites, Part A, 2014, 62, 11–15.
35 J. Cao, O. Rusina and H. Sieber, Ceram. Int., 2004, 30, 1971–
1974.
36 B. Choat, A. R. Cobb and S. Jansen, New Phytol., 2008, 177,
608–626.
37 Y.-F. Chen, C.-Y. Lee, M.-Y. Yeng and H.-T. Chiu, J. Cryst.
Growth, 2003, 247, 363–370.
38 S. Dai, Y. Wu, T. Sakai, Z. Du, H. Sakai and M. Abe, Nanoscale
Res. Lett., 2010, 5, 1829.
39 H. Ijadpanah-Saravy, M. Safari, A. Khodadadi-Darban and
A. Rezaei, Anal. Lett., 2014, 47, 1772–1782.
40 Y. V. Kolen'ko, A. A. Burukhin, B. R. Churagulov and
N. N. Oleynikov, Mater. Lett., 2003, 57, 1124–1129.
41 K. Sing, Pure Appl. Chem., 1982, 54, 2201–2218.
42 N. A. Seaton, Chem. Eng. Sci., 1991, 46, 1895–1909.
43 M. Zhou, D. Zang, X. Zhai, Z. Gao, W. Zhang and C. Wang,
Ceram. Int., 2016, 42, 10704–10710.
4 G. de Falco, M. Barczak, F. Montagnaro and T. J. Bandosz,
ACS Appl. Mater. Interfaces, 2018, 10, 8066–8076.
5 D. Chen, Z. Qu, Y. Sun and Y. Wang, Colloids Surf., A, 2014,
441, 433–440.
6 F. Lin, G. Zhu, Y. Shen, Z. Zhang and B. Dong, Appl. Surf. Sci.,
2015, 356, 150–156.
7 K. Feng, D. Rong, W. Ren and X. Wen, Mater. Express, 2015, 5,
371–375.
8 Z. Wu, Q. Li, D. Feng, P. A. Webley and D. Zhao, J. Am. Chem.
Soc., 2010, 132, 12042–12050.
9 R. Averlant, S. Royer, J.-M. Giraudon, J.-P. Bellat,
I. Bezverkhyy, G. Weber and J.-F. Lamonier, ChemCatChem,
2014, 6, 152–161.
10 G. J. Kim, S. M. Lee, S. Chang Hong and S. S. Kim, RSC Adv.,
2018, 8, 3626–3636.
11 L. Nie, J. Yu, M. Jaroniec and F. F. Tao, Catal. Sci. Technol.,
2016, 6, 3649–3669.
12 S. Song, X. Wu, C. Lu, M. Wen, Z. Le and S. Jiang, Appl. Surf.
Sci., 2018, 442, 195–203.
13 J. Ding, Z. Rui, P. Lyu, Y. Liu, X. Liu and H. Ji, Appl. Surf. Sci.,
2018, 457, 670–675.
14 B. Liu, Y. Liu, C. Li, W. Hu, P. Jing, Q. Wang and J. Zhang,
Appl. Catal., B, 2012, 127, 47–58.
15 H. Tan, J. Wang, S. Yu and K. Zhou, Environ. Sci. Technol.,
2015, 49, 8675–8682.
16 Z. Yan, Z. Xu, J. Yu and M. Jaroniec, Appl. Catal., B, 2016, 199,
458–465.
44 L. Nie, J. Yu, X. Li, B. Cheng, G. Liu and M. Jaroniec, Environ.
Sci. Technol., 2013, 47, 2777–2783.
45 L. Qi, B. Cheng, J. Yu and W. Ho, J. Hazard. Mater., 2016, 301,
522–530.
46 Y. Nagai, H. Shinjoh and K. Yokota, Appl. Catal., B, 2002, 39,
149–155.
47 D. W. Kwon, P. W. Seo, G. J. Kim and S. C. Hong, Appl. Catal.,
B, 2015, 163, 436–443.
¨
¨
17 H. Berndt, A. Martin, A. Bruckner, E. Schreier, D. Muller,
¨
H. Kosslick, G. U. Wolf and B. Lucke, J. Catal., 2000, 191,
48 C. Zhang and H. He, Catal. Today, 2007, 126, 345–350.
49 C. Zhang, H. He and K.-i. Tanaka, Appl. Catal., B, 2006, 65,
37–43.
384–400.
18 L. Nie, A. Meng, J. Yu and M. Jaroniec, Sci. Rep., 2013, 3, 3215.
19 C. Zhang, Y. Li, Y. Wang and H. He, Environ. Sci. Technol.,
2014, 48, 5816–5822.
50 T. Hanawa, J. Periodontal Implant Sci., 2011, 41, 263–272.
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