Visible light-induced photocatalytic degradation of gas-phase acetaldehyde with platinum/reduced titanium oxide-loaded carbon paper

Article abstract of DOI:10.1039/c7ra10778a

Visible light-induced degradation of gas-phase acetaldehyde (CH₃CHO) is investigated using O-deficient reduced TiO_2-x-loaded carbon paper. The carbon paper is synthesized by the pyrolysis of a filter paper, and the reduced TiO_2-x is prepared by the magnesiothermic reduction of commercial anatase TiO₂. The surface areas of the non-carbonized filter paper and carbon papers obtained by carbonization at 400, 600, 800, and 1000 °C are 4.31 m² g^-1, 13.57 m² g^-1, 466.81 m² g^-1, 461.60 m² g^-1, and 26.28 m² g^-1, respectively. Although the as-prepared carbon papers possess much lower specific surface areas than that of commercial activated carbon (2200 m² g^-1), the carbon papers show better adsorption capabilities. The O-deficient reduced TiO_2-x samples exhibit strong visible-light absorption, and the reduced TiO_2-x-loaded carbon papers induce rapid degradation of CH₃CHO and simultaneous generation of CO₂ in both closed-circulation and continuous-flow modes under visible light irradiation (λ > 420 nm), attributed to the efficient adsorption of gas-phase CH₃CHO by the carbon paper and the rapid and complete degradation of CH₃CHO to CO₂ by the active reduced TiO_2-x. This strongly suggests that the reduced TiO_2-x-loaded carbon paper is an efficient composite photocatalyst for the visible light-induced photocatalytic degradation of gas-phase CH₃CHO.

Full text of DOI:10.1039/c7ra10778a

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Visible light-induced photocatalytic degradation of
gas-phase acetaldehyde with platinum/reduced
titanium oxide-loaded carbon paper†
Cite this: RSC Adv., 2017, 7, 50693
a
b
Minsun Kim,a Ha-Young Leeb and Jong-Sung Yu
*
*
Soonhyun Kim,
Visible light-induced degradation of gas-phase acetaldehyde (CH3CHO) is investigated using O-deficient
reduced TiO2ꢀx-loaded carbon paper. The carbon paper is synthesized by the pyrolysis of a filter paper,
and the reduced TiO2ꢀx is prepared by the magnesiothermic reduction of commercial anatase TiO2. The
surface areas of the non-carbonized filter paper and carbon papers obtained by carbonization at 400,
600, 800, and 1000 ꢁC are 4.31 m2
respectively. Although the as-prepared carbon papers possess much lower specific surface areas than
that of commercial activated carbon (2200 m2 ꢀ1), the carbon papers show better adsorption
g g g g ,
ꢀ1, 13.57 m2 ꢀ1, 466.81 m2 ꢀ1, 461.60 m2 ꢀ1, and 26.28 m2 gꢀ1
g
capabilities. The O-deficient reduced TiO2ꢀx samples exhibit strong visible-light absorption, and the
reduced TiO2ꢀx-loaded carbon papers induce rapid degradation of CH3CHO and simultaneous
generation of CO2 in both closed-circulation and continuous-flow modes under visible light irradiation
(l > 420 nm), attributed to the efficient adsorption of gas-phase CH3CHO by the carbon paper and the
rapid and complete degradation of CH3CHO to CO2 by the active reduced TiO2ꢀx. This strongly suggests
that the reduced TiO2ꢀx-loaded carbon paper is an efficient composite photocatalyst for the visible
light-induced photocatalytic degradation of gas-phase CH3CHO.
Received 29th September 2017
Accepted 21st October 2017
DOI: 10.1039/c7ra10778a
rsc.li/rsc-advances
compound that causes sick-house syndrome.13–15 The complete
degradation of gas-phase CH3CHO to CO2 can be achieved with
TiO2 or Au-loaded TiO2 under UV irradiation.16,17 Recently, the
visible light-induced photocatalytic removal of gas-phase
CH3CHO was also investigated using visible light-responsive
modied photocatalysts including zeolite/WO3–Pt hybrids,18
Mn4+-doped TiO2,19 and N-doped TiO2.20
For air purication, photocatalysts immobilized on support
materials are usually employed. The surface area and activity of
the catalyst are oen reduced by immobilization. Therefore,
support materials with high surface areas are preferred for
photocatalyst immobilization. The composite materials gener-
ated can show synergetic effects on adsorption and photo-
catalysis.21 Activated carbon is one such commonly used
support material;22–24 it has a high surface area that can enhance
adsorption and photocatalytic activity. Previously, we prepared
TiO2-embedded carbon nanobers (CNFs) and core–shell-
structured CNF–TiO2 nanotubes for the photocatalytic oxida-
tion of gaseous CH3CHO.25,26 CNF mats prepared by electro-
spinning and subsequent carbonization did not adsorb gas-
phase CH3CHO, but the convenient application of CNF mats
suggests that mats with improved adsorption of gas-phase
CH3CHO could be widely used.
1. Introduction
TiO2 photocatalysis has been extensively studied in applications
for air and water purication.1–5 Photocatalytic reactions are
initiated by the absorption of ultraviolet (UV) photons, which
concurrently generate conduction-band (CB) electrons and
valence-band (VB) holes in the TiO2 lattice. The VB holes are
strong oxidants and react with surface –OH groups to produce
cOH radicals. The remediation power of TiO2 photocatalysts is
largely attributed to the strong oxidation potential of these cOH
radicals. However, the wide band gap of TiO2 limits the range of
solar light wavelengths that can be utilized for catalysis. Several
strategies have been investigated to enhance the solar light
absorption of TiO2, including metal and non-metal doping,6–8
coupling of low-band gap materials,9,10 and dye
sensitization.11,12
Many researchers focus on the photooxidation of gas-phase
acetaldehyde (CH3CHO),
a
prevalent volatile organic
aSmart Textile Convergence Research Group, Daegu Gyeongbuk Institute of Science and
Technology (DGIST), Daegu, 42988, Republic of Korea. E-mail: sh2358@dgist.ac.kr;
Fax: +82-53-785-3439; Tel: +82-53-785-3410
bDepartment Energy Science and Engineering, Daegu Gyeongbuk Institute of Science
and Technology (DGIST), Daegu, 42988, Republic of Korea. E-mail: jsyu@dgist.ac.
kr; Fax: +82-53-785-6409; Tel: +82-53-785-6443
Recently, O-decient black or reduced TiO2ꢀx samples have
attracted great attention as new photocatalysts for light-induced
water splitting towards H2 production.27 The reduction of TiO2
generates many surface defects, Ti3+ species, and O vacancies,
† Electronic
supplementary
information
(ESI)
available:
N2
absorption–desorption isotherms and thermal decomposition curves of
synthesized materials. See DOI: 10.1039/c7ra10778a
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which contribute to improved light absorption.28,29 We also (Millipore), washed with methanol solution, and dried at 80 ꢁC
investigated a new approach for a defect-induced TiO2ꢀx solar in an oven to obtain Pt/rT. The photocatalyst was then loaded on
photocatalyst for H2 production from water and CO2 reduction the FPC. A 5 mL suspension of photocatalyst in distilled water
to fuel.30,31 However, the approach has not yet been applied to was pipetted onto the center of each FPC specimen. Aer the
the degradation of environmental pollutants.
dispersion of the suspension, the FPC was dried at 80 ꢁC in an
In this study, carbon paper was synthesized by the simple oven. The mass of the photocatalyst (Pt/rT-FPC or Pt/rT) in the
pyrolysis of a lter paper, and O-decient reduced TiO2ꢀx was sample holder was approximately 10 mg for each loading.
prepared by the magnesiothermic reduction of commercial
anatase TiO2. Then, Pt-deposited reduced TiO2ꢀx (Pt/rT) nano-
particles were loaded on the as-prepared carbon papers. The
physicochemical properties of the Pt@reduced TiO2ꢀx-loaded
carbon paper (Pt/rT-FPC) were measured. The adsorption of gas-
phase CH3CHO by the lter paper carbon (FPC) or Pt/rT-FPC
and the visible light-induced photocatalytic oxidation of
adsorbed CH3CHO over the Pt/rT-FPC were investigated.
2.3. Characterizations
Surface morphology images were obtained using a eld-
emission scanning electron microscope (FE-SEM, Hitachi S4-
8020, Japan). Transmission electron micrographs were ob-
tained on a high-resolution transmission electron microscope
(HR-TEM, Hitachi HF-3300, Japan). X-ray diffraction (XRD)
patterns were obtained with an X-ray diffractometer (Pan-
alytical, Empyrean, 40 kV, 30 mA) using Cu Ka1 radiation (l ¼
0.154178 nm) and a quartz monochromator. Raman spectra of
the samples were analyzed by a Raman spectrophotometer
(Thermo Scientic, Nicolet Almega XR) in the wavenumber
range of ꢂ100 to 4000 cmꢀ1 using a 532 nm laser. The Bru-
nauer–Emmett–Teller (BET) surface areas were determined
from the N2 adsorption–desorption isotherms obtained at 77 K
(ASAP 2020 Micromeritics). The surface compositions were
measured by X-ray photoelectron spectroscopy (XPS, Thermo
Scientic, Escalab 250Xi) using the Mg-Ka line (1253.6 eV) as
the excitation source. The light absorption was analyzed by UV-
visible diffuse reectance spectroscopy (DRS) using a Cary
series spectroscope (Cary 5000, Agilent Technologies).
2. Experimental details
2.1. Preparation of carbon paper from lter paper
Carbon paper was prepared from a lter paper (Hyundai Micro
Co., Ltd.). The lter paper was carbonized at 400, 600, 800, or
1000 ꢁC for 2 h under continuous-ow Ar gas. The temperature
was increased at the rate of 5 C minꢀ1. The prepared samples
ꢁ
are hereinaer denoted as FPC-x where x indicates the
carbonization temperature. For comparison, two different
carbon materials of CNFs prepared by a previously reported
method32 and commercial activated carbon (MSC, MSC-30,
Kansai Coke and Chemicals Co., Ltd, Japan) were also used as
substrates.
2.4. Visible light-induced gas-phase CH3CHO oxidation
2.2. Synthesis of reduced TiO2ꢀx and preparation of reduced
TiO2ꢀx-FPC
Photocatalytic oxidation experiments were performed by two
different methods of closed-circulation mode and continuous-
O-decient reduced TiO2ꢀx was synthesized by a magnesiother- ow mode. In closed-circulation mode, the photocatalytic
mic reduction of commercial anatase TiO2 as previously re- oxidation of gaseous CH3CHO was determined in a closed
ported.30,31 A 4 g sample of commercial anatase TiO2 (CT, circulating stainless steel reactor with a volume of 150 cm3 that
particle size <25 nm, Sigma Aldrich) was mixed with the desired could be divided into two parts (upper and lower) by a control
amount of Mg powder. The mixed powder was placed in a tube valve, similar to the reactor in a previously reported experi-
furnace and heated at 500 C for 8 h under owing 5% H2/Ar. ment.25 The gases used were CH3CHO (300 ppmv N2) as
ꢁ
Aer annealing, the Mg-treated sample was stirred in 2.0 M HCl a CH3CHO standard, O2 (99.9999%), and Ar (99.9999%) as the
solution for 1 day and then washed with distilled water and carrier gas. The concentrations of CH3CHO and O2 were 80
ethanol to remove MgO and other Mg impurities.ꢁThe washed ppmv and 20%, respectively. A sample of reduced TiO2ꢀx-loaded
Mg-free reduced TiO2ꢀx samples were dried at 80 C. Different FPC was placed in the lower reactor. Each sample weighed
reduced samples prepared with 0.5 and 0.75 molar ratios of Mg approximately 15 mg. The mixed gas passed through the empty
per molar amount of CT are denoted as rT-0.5 and rT-0.75, upper reactor, and the concentration of CH3CHO in the exit
respectively. For comparison, a commercial photocatalyst of stream was monitored until it reached a constant value. The gas
P25 TiO2 (P25, Aeroxide) was also used.
was then circulated in the reactor by the pump. Next, the
Pt/rT photocatalysts were synthesized through the well- circulated gas was passed through the lower reactor by using the
documented photodeposition method.33 The reduced TiO2ꢀx valve to make contact with the surface of the sample in the lower
photocatalyst (0.5 g Lꢀ1) was dispersed in 10 vol% methanol, reactor. Aer adsorption equilibrium with the surface of the
and a proper amount of x mole chloroplatinic acid hexahydrate sample was established in the dark, the sample was illuminated
solution was added dropwise to this dispersion under vigorous with UV light (150 W Xe arc lamp, Abet Technologies). The
stirring for 30 min. The Pt : photocatalyst weight ratio was distance between the sample and the lamp was 15 cm, and
0.005 : 1. The suspension was illuminated with UV light (300 W a cut-off lter (l > 295 nm for UV irradiation or l > 420 nm for
Xe arc lamp, Newport) through a 10 cm infrared (IR) water lter visible irradiation) was used. The removal of CH3CHO was
and a UV cutoff lter (l > 295 nm) for 30 min. The suspension monitored using a gas chromatograph (GC, HP6890, Agilent)
was ltered using 0.45 mm polytetrauoroethylene (PTFE) lters equipped with a Porapak Q column, a ame ionization detector
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(FID), a CO2 methanizer (Ni catalyst), and a gas-sampling valve. FPC-400, FPC-600, FPC-800, and FPC-1000 are 0.62, 0.65, 0.89,
In the continuous-ow mode, the photocatalytic oxidation of and 0.96, respectively. This implies increasing structural order
gaseous CH3CHO was performed in the same 150 cm3 stainless in the FPC with increasing carbonization temperature, consis-
steel reactor without division. The mixed gas was fed to the tent with the results reported for other cellulose materials.36 The
reactor at the total ow rate of 100 mL minꢀ1. The concentra- XRD patterns and Raman spectra obviously demonstrate that
tions of CH3CHO and O2 were 60 ppmv and 20%, respectively. graphitized carbon forms during carbonization, with increasing
The gas residence time in the reactor was 1.5 min. All other formation at higher carbonization temperatures.
experimental conditions were the same as those in the closed-
circulation experiments.
The N2 adsorption–desorption isotherms of the lter paper
and FPCs are shown in Fig. S1.† The BET surface areas of the
lter paper, FPC-400, FPC-600, FPC-800, and FPC-1000 were
4.31 m2 gꢀ1, 13.57 m2 gꢀ1, 466.81 m2 gꢀ1, 461.60 m2 gꢀ1, and
26.28 m2 gꢀ1, respectively. The surface areas increase signi-
cantly for papers carbonized at temperatures of 400 and 800 ꢁC,
and then decrease with the increase of temperature from 800 to
1000 ꢁC. The release of volatile compounds favors the formation
of pores, which create the high surface areas of FPC-600 and
3. Results and discussion
3.1. Characterization of FPCs
Fig. 1 shows photographs and SEM images of the lter paper
and the FPC-600. The lter paper is obviously transformed to
carbon paper, as shown in Fig. 1a and c. The lter paper and the
FPC-600 both contain bers with some degree of variation in
diameter. The diameters of the bers are not strongly affected
by the carbonization, but do show slight shrinkage.
ꢁ
FPC-800. At 1000 C, structural ordering and merging of pores
decreases the surface area of the FPC.
Fig. 2a shows the XRD patterns of the lter paper, FPC-600,
and FPC-800. The lter paper pattern exhibits two major
peaks, a weak diffraction peak centered at 15.1ꢁ and a strong
diffusion diffraction peak centered at 22.5ꢁ, which are consis-
tent with previously reported results.34 The FPC patterns each
exhibit one broad peak centered at 23ꢁ, indicating amorphous
carbon.23 The intensities of the diffraction peaks are increased
as the temperature of carbonization is increased. Fig. 2b shows
the Raman spectra of the lter paper and the FPCs. The FPC
spectra show two characteristic peaks centered at 1350 cmꢀ1
and 1580 cmꢀ1 corresponding to the D and G bands, respec-
tively.35 These characteristic peaks become sharper and more
intense with increased carbonization temperature. The D and G
bands are associated with the vibrations of sp2 carbon atoms
with dangling bonds; the integrated intensity ratio (ID/IG)
corresponds to the degree of graphitization. The ID/IG ratios for
3.2. Gas-phase CH3CHO adsorption on FPCs
The capability of FPCs to adsorb gaseous CH3CHO was
compared with those of commercially available activated
carbon (MSC), CNF, and non-carbonized lter paper. Fig. 3a
shows that the dark adsorption of gaseous CH3CHO on lter
paper and CNF does not occur at all, whereas MSC exhibits
strong dark adsorption of CH3CHO. However, FPC-800 shows
better CH3CHO adsorption than MSC does. The CH3CHO
adsorption may be inuenced by the carbonization tempera-
ture. Therefore, the carbonization temperature-dependent
adsorption of CH3CHO is analyzed as shown in Fig. 3b. The
FPCs, except FPC-1000, exhibit strong CH3CHO adsorption.
Fig. 3c shows the relationship between the amount of adsorbed
CH3CHO and the BET surface area. The dark adsorption
capacity of CH3CHO follows the order of FPC-600 > FPC-800 >
FPC-400 [ MSC [ FPC-1000. Although the specic surface
areas of FPCs are much lower than that of MSC, the adsorption
capacities of FPCs, except that of FPC-1000, exceed that of MSC.
The adsorption of CH3CHO on the surfaces of the carbon
materials depends on the surface chemistry as well as the
microporosity.37 The atomic ratio of O in the FPCs is higher
than that in MSC (Fig. S3†). Therefore, enhanced adsorption of
CH3CHO appears in FPCs bearing O-containing functional
groups. These results were obtained in the closed-circulation
system. Similar tendencies were more clearly observed in the
continuous-ow system during the photocatalytic oxidation
experiments. Additionally, CH3CHO showed no oxidation under
UV irradiation on FPCs without photocatalyst.
3.3. Visible light-induced activity of reduced TiO2ꢀx
The visible light-induced photocatalytic oxidation of gas-phase
CH3CHO was further investigated using Pt/rT-FPC. Previously,
reduced TiO2ꢀx exhibited high activity for the visible light-
induced production of H2 (ref. 30) and photocatalytic reduc-
tion of CO2.31 In Fig. 4a, the reduced TiO2ꢀx samples clearly
illustrate extended absorbance in the visible region as well as
the UV region compared to that of commercial pristine TiO2,
Fig. 1 Photographs and SEM images of (a, b) filter paper and (c, d)
carbon paper after carbonization at 600 ꢁC (FPC-600).
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Fig. 2 (a) XRD patterns and (b) Raman spectra of filter paper and FPCs. (c) Ratio of intensity of D to G peaks in Raman spectra for carbon papers as
a function of carbonization temperature.
which shows only UV-region absorption. Our previous work induces modications on the surfaces of the reduced TiO2ꢀx
revealed that visible light absorption is related to the presence particles, as reected in the enhanced light absorption and
of Ti3+ 31 The absorption of light increases as the amount of Mg color changes of the reduced samples. The magnesiothermic
.
used in the reduction increases, as observed for rT-0.5 and rT- reduction of TiO2 follows the reaction shown below. The strong
0.75; this is also reected in the color change of the samples reduction powder of Mg causes the pristine TiO2 to lose the
from white to yellow and gray for pristine TiO2, rT-0.5, and rT- framework of O on the surface of the TiO2 particles, generating
0.75, respectively. The XRD patterns of the different samples reduced O-decient TiO2ꢀx and MgO. The light absorption in
are presented in Fig. 4b. Despite the color changes, the reduced the visible region is increased, and the color darkens because of
samples still show predominantly anatase-phase TiO2. the increased surface modication of the reduced samples with
Although the XRD analysis indicates no major structural increased amounts of Mg. In the given reaction conditions, this
changes during Mg reduction, the Mg treatment probably modication occurs only on the surface of the reduced sample;
Fig. 3 (a, b) Time-profile CH3CHO concentration on the FPC before and after UV irradiation in closed-circulation mode. (c) The relationship
between the CH3CHO adsorption capacity and BET surface area of the FPC.
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Fig. 4 (a) DRS absorbance and (b) XRD patterns of CT, rT-0.5, and rT-0.75.
thus, the inner part of the reduced sample has the anatase TiO2 slightly reduced and CO2 production is negligible. Under UV
structure, as indicted by the XRD patterns in Fig. 4b.
irradiation, however, the CH3CHO is degraded and CO2 imme-
diately produced. The concentrations of CH3CHO and CO2 reach
steady-state levels aer several minutes, indicating that estab-
lishing adsorption–desorption equilibrium under UV illumina-
tion requires a long time. Meanwhile, the concentration of CO2
on rT-0.75 is higher than that on either P25 or rT-0.5. This implies
that the photocatalytic oxidation of CH3CHO is faster on rT-0.75.
The CH3CHO degradation and the CO2 production under UV
irradiation remain almost identical throughout repeated cycling.
However, although the reduced TiO2ꢀx absorbs visible light, the
visible light-induced photocatalytic oxidation of CH3CHO occurs
on neither rT-0.5 nor rT-0.75. This can be attributed to the rapid
recombination of the electron–hole pairs produced under visible
irradiation. Therefore, Pt must be photodeposited onto the
reduced TiO2ꢀx surface for the efficient separation of the photo-
generated electron–hole pairs.
TiO2 + Mg / TiO2ꢀx + MgO
(1)
The photocatalytic oxidation of CH3CHO by reduced TiO2ꢀx
under visible light was performed in continuous-ow mode.
Fig. 5a shows the photocatalytic oxidation of CH3CHO on
reduced TiO2ꢀx and P25 TiO2. The dark adsorption capacities
on the surfaces of the reduced TiO2ꢀx and P25 TiO2 are much
lower than those of reduced TiO2ꢀx immobilized on the FPCs.
Under visible irradiation, the concentration of CH3CHO is only
Fig. 6 shows HR-TEM images of Pt/P25, Pt/rT-0.5, and Pt/rT-
0.75. In all cases, Pt is deposited similarly. The photocatalytic
oxidation of CH3CHO on Pt-deposited P25 and reduced TiO2ꢀx
was also investigated. As shown in Fig. 5b, under visible irradi-
ation, the CH3CHO is degraded with simultaneous CO2 produc-
tion on Pt/rT-0.5. The concentrations of CH3CHO and CO2 do not
reach a steady-state level because of the offsets of the adsorption
and the photocatalytic oxidation of CH3CHO. This implies that Pt
deposition inhibits the recombination of charge carriers created
by absorbing visible light and thereby enables visible light-
induced CH3CHO degradation. The photocatalytic reaction of
CH3CHO oxidation into CO2 can be written as follows:
Pt/TiO2ꢀx + hn / h+(Pt/TiO2ꢀx) + eꢀ(Pt/TiO2ꢀx
CH3CHO + 10h+(Pt/TiO2ꢀx) + 3H2O / 2CO2 + 10H+ (3)
)
(2)
2.5O2 + 10eꢀ(Pt/TiO2ꢀx) + 10H+ / 5H2O
(Total) CH3CHO + 2.5O2 / 2CO2 + 2H2O
(4)
(5)
On Pt/rT-0.75, the CH3CHO is degraded but no CO2 is
observed, which could be attributed to the production of some
undetected intermediates by the visible light-induced
Fig. 5 Dark adsorption and photocatalytic oxidation of CH3CHO
under visible and UV irradiation on (a) bare photocatalyst and (b) Pt-
deposited photocatalyst in continuous-flow mode.
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Fig. 8 Dark adsorption and photocatalytic oxidation of CH3CHO on
the Pt/P25-FPC-600, Pt/rT-0.5-FPC-600, and Pt/rT-0.75-FPC-600
under visible irradiation in closed-circulation mode.
deposition is not signicant. Moreover, the CH3CHO degrada-
tion and the CO2 production under UV irradiation remain
almost identical throughout repeated cycling, as with the
results obtained in the absence of Pt.
3.4. Visible light-induced gas-phase CH3CHO oxidation
The visible light-induced photocatalytic oxidation of gas-phase
CH3CHO using reduced TiO2ꢀx-loaded FPC was investigated.
Based on the above results, we investigated visible light-induced
gas-phase CH3CHO oxidation using the Pt-deposited photo-
catalysts and FPC-600. We observed cross-sectional SEM images
Fig. 6 High-resolution TEM images of (a, b) Pt/P25, (c, d) Pt/rT-0.5, and analyzed the elemental composition of the Pt/rT-0.5 loaded
and (e, f) Pt/rT-0.75.
on the FPC-600 by energy-dispersive X-ray spectroscopy (EDS)
mapping, as shown in Fig. 7a and 8b. The Pt/tT-0.5 is well
loaded and easily distinguishable on the FPC-600. The amount
degradation of CH3CHO. Meanwhile on Pt/P25, CH3CHO is not
degraded under visible irradiation. The photocatalytic degra-
dation rates of CH3CHO on Pt/P25, Pt/rT-0.5, and Pt/rT-0.75
under UV irradiation are much higher than those under
visible irradiation. Compared to the results obtained in the
absence of Pt, the photocatalytic activities for CH3CHO degra-
dation under UV irradiation are not signicantly enhanced.
This implies that UV light-induced charge separation occurs
efficiently on P25, rT-0.5, and rT-0.75, so the effect of Pt
of Pt/tT-0.5 nanoparticles on the surface of the FPC-600 is
indirectly calculated from the thermogravimetric analysis (TGA)
results (Fig. S2†). Fig. S2a† shows that the decomposition of Pt/
rT-0.5 loaded on FPC-600 begins at approximately 400 C and
stops at 500 ꢁC. The weight loss of Pt/rT-0.5 loaded on the FPC-
600 is approximately 47%.
Fig. 8 shows the photocatalytic oxidation of CH3CHO on Pt/
rT-0.5, Pt/rT-0.75, and Pt/P25 loaded on FPC-600 in closed-
circulation mode. All cases show strong dark adsorption of
ꢁ
Fig. 7 Cross-sectional SEM images of Pt/rT-0.5 loaded on FPC-600.
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Fig. 9 Dark adsorption and photocatalytic oxidation of CH3CHO on the Pt/rT-0.5-FPC-600 under visible irradiation in continuous-flow mode.
CH3CHO, similar to the dark adsorption of CH3CHO on the FPC electrons are transferred to the carbon paper, which would
without Pt/rT-0.5, Pt/rT-0.75, or Pt/P25. Upon visible irradiation, promote electron–hole pair separation; this implies that the
the Pt/rT-0.5 loaded on the FPC-600 shows rapid degradation of carbon paper could function as an electron-transfer mediator as
CH3CHO and simultaneous generation of CO2. The photo- well as a support material.32,38 A schematic of the visible light-
catalytic oxidation of CH3CHO on Pt/rT-0.5-FPC-600 is also per- induced photocatalytic degradation of gas-phase CH3CHO
formed in continuous-ow mode under repeated experiments, as using reduced TiO2ꢀx-loaded FPC is shown in Fig. 10.
shown in Fig. 9. The photocatalytic oxidation of CH3CHO to CO2
is strongly dependent on the ow rates of 25, 50, and 100
mL minꢀ1, which relate directly to the residence times of 6, 3, and
1.5 min, respectively. For all cases, the concentration of CH3CHO
does not reach steady-state levels within 30 min. At the highest
ow rate, CO2 production is rapidly saturated and its concen-
tration remains constant under repeated experiments. However,
at the lowest ow rate, the concentration of CO2 does not reach
a steady-state level but CO2 production from the photocatalytic
oxidation of CH3CHO is dramatic, possibly because of the longer
residence time. The photocatalytic oxidation of CH3CHO to CO2
was repeated up to six times. The result demonstrates the good
stability of Pt/rT-0.5-FPC-600. Investigations to improve the
operation conditions are needed for photocatalytic oxidation
applications. Even with a small amount of Pt/rT-0.5, the photo-
catalytic oxidation of CH3CHO under visible irradiation occurs in
a few minutes. The FPC-600 efficiently adsorbs the CH3CHO, and
Pt/rT-0.5 rapidly and completely degrades the CH3CHO to CO2,
even under visible irradiation. It is also possible that some
Fig. 10 Schematic of the visible light-induced photocatalytic degra-
dation of gas-phase CH3CHO using reduced TiO2ꢀx-loaded carbon
paper.
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rst time. The FPC was synthesized by the simple pyrolysis of
lter paper; its surface area was strongly affected by the
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Acknowledgements
This work was supported by the DGIST R&D Program of the
Ministry of Science, ICT & Future Planning (17-NT-02 and 17-01-
HRLA-01). This work was also supported by Basic Science
Research Program, through the National Research Foundation
of Korea (NRF), funded by the Ministry of Science, ICT & Future
Planning (2017R1A2B4003919).
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50700 | RSC Adv., 2017, 7, 50693–50700
This journal is © The Royal Society of Chemistry 2017