Efficient photocatalytic degradation of gas-phase formaldehyde by Pt/TiO2 nanowires in a continuous flow reactor

Article abstract of DOI:10.1002/cctc.202000837

Herein, we investigated the photocatalytic degradation of gas-phase formaldehyde (HCHO) on Pt deposited TiO₂ nanowires (Pt/TiO₂NW) at continuous flow. Formaldehyde is decomposed into CO₂ and H₂O in a homemade tube reactor under the LED irradiation. The reactor can monitor online various parameters such as formaldehyde concentration, light intensity, humidity, and temperature. The results indicated that the formaldehyde degradation rate of Pt/TiO₂NW increased at continuous flow compared with TiO₂ nanowires. Under ultraviolet and visible LED light irradiation, the stable time of degrading low-concentration formaldehyde by Pt/TiO₂NW was 5.6 times that of TiO₂NW. Higher ambient humidity facilitates the formaldehyde degradation of Pt/TiO₂NW by increasing the hydroxyl radical (^.OH) and superoxide radical (^. (Formula presented.)).

Full text of DOI:10.1002/cctc.202000837

The European Society Journal for Catalysis
Supported by
Accepted Article
Title: Efficient photocatalytic degradation of gas-phase formaldehyde
by Pt/TiO2 nanowires in a continuous flow reactor
Authors: Yongping Zhang, Wenyu Diao, Hongyue Cai, Lu Wang, and
Xi Rao
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To be cited as: ChemCatChem 10.1002/cctc.202000837
Link to VoR: https://doi.org/10.1002/cctc.202000837
01/2020

10.1002/cctc.202000837
ChemCatChem
Efficient photocatalytic degradation of gas-phase
formaldehyde by Pt/TiO2 nanowires in a continuous
flow reactor
Wenyu Diao, Hongyue Cai, Lu Wang, Dr. Xi Rao, and Prof. Yongping Zhang*
School of Materials and Energy, Southwest University, Chongqing 400715, China
ABSTRACT: Herein, we investigated the photocatalytic degradation of gas-phase formaldehyde
(HCHO) on Pt deposited TiO2 nanowires (Pt/TiO2NW) at continuous flow. Formaldehyde is
decomposed into CO2 and H2O in a homemade tube reactor under the LED irradiation. The reactor
can monitor online various parameters such as formaldehyde concentration, light intensity,
humidity, and temperature. The results indicated that the formaldehyde degradation rate of
Pt/TiO2NW increased at continuous flow compared with TiO2 nanowires. Under ultraviolet and
visible LED light irradiation, the stable time of degrading low-concentration formaldehyde by
Pt/TiO2NW was 5.6 times that of TiO2NW. Higher ambient humidity facilitates the formaldehyde
degradation of Pt/TiO2NW by increasing the hydroxyl radical (·OH) and superoxide radical (O2
).
KEYWORDS: TiO2 nanowires; Pt nanoparticle; photocatalysis; formaldehyde.
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1. Introduction
In recent years, a large number of volatile organic compounds (VOC) have been used in decoration
materials and furniture production, which polluted severely the in-door air on which humans
depend. Volatile organic compounds include formaldehyde (HCHO), NOx, SO2, CO2 and a series
of toxic and harmful substances.[1-4] Among these pollutants, formaldehyde is one of the most
widely used organic substances and the main source of air pollution.[3,5] Formaldehyde is a highly
toxic substance and has been listed as a suspected carcinogen for humans by the International
Cancer Research Center (IAPC). Excessive formaldehyde intake can cause symptoms of cough,
chest stuffiness, dizziness, and even leukemia and chromosomal mutations, which would seriously
jeopardize the human health.[6] The conventional methods for removing formaldehyde include
adsorption purification, biodegradation, thermal catalysis, photocatalysis, HCHO capture and so
on. [7-13] Of the several methods for removing formaldehyde in in-door environments, the most
economical and convenient method is photocatalytic degradation of formaldehyde. The advantages
included high removal efficiency, wide application range, simple equipment operation and no
secondary pollutant. Therefore, photocatalytic technology has attracted tremendous attention in
the application of eliminating formaldehyde.
The principle of photocatalytic oxidation is that when the energy of incident light is greater than
the band gap of catalysts, the valence band electrons are excited to the conduction band to generate
photo-generated electron-hole pairs, and the charge is transferred between the electron-hole pair
and the adsorbant (reactant) on the semiconductor surface. Then occurs the photo-oxidation
reaction. Semiconductor photocatalysts commonly used included ZnO, CeO2, g-C3N4, MnO2, TiO2
and Bi2O3, and various composites of these compounds.[10, 12, 14-17] TiO2, as the most classic
semiconductor photocatalysts, was widely used in polluted air purification due to its stable
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chemical properties, high catalytic activity, easy preparation and non-toxic. [10, 18-20] Titanium
dioxide is irradiated by ultraviolet light to generate electron-hole pairs. The electron-hole pairs
-
react with oxygen and water in the surrounding air to generate •OH and •O2 . Both of them have
strong oxidizing ability to oxidize and decompose formaldehyde into CO2 and H2O. However, as
a wide bandgap semiconductor, titanium dioxide only responds in the ultraviolet (UV) region and
has a small surface area, which limits the wider application of TiO2 under visible light.
Commercially available P25 titanium dioxide has a very limited photocatalytic activity to degrade
formaldehyde. Recently, a high performance TiO2 nanowires (TiO2NW) photocatalyst was
successfully prepared by hydrothermal method to decompose gaseous formaldehyde into CO2 and
H2O in a homemade tube reactor without secondary pollution under UV irradiation.[10] TiO2NW
was synthesized by hydrothermal method to increase specific surface area and surface active sites
to improve its photocatalytic efficiency and enhance visible light response. Moreover, researchers
found that noble metals (Pt, Au, Ag, Pd, Rh, and Ru) loading further improved the photocatalytic
performance.[20-28] Among them, Pt supported on TiO2 can improve quantum efficiency and
enhance photocatalytic activity with Pt loading not exceeding 0.2 wt%. Therefore, it can be
predicted that the photocatalytic oxidation performance of TiO2 nanowires could be improved
further by depositing Pt nanoparticles.
Herein, Pt/TiO2 nanowires were prepared and the photocatalytic degradation of gas-phase
formaldehyde was studied in a self-made reactor. The photocatalytic degradation of low-
concentration formaldehyde at gas-phase flowing was monitored in real time and the effects of
light intensity, air humidity and formaldehyde concentration were investigated.
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2. Experimental
2.1 Reagents
Titanium (IV) oxide (AeroxideTM P25), chloroplatinic acid solution (H2PtCl6, 8 wt% in water),
sodium hydroxide (NaOH, 98%), hydrochloric acid solution (HCl, 1 M) were purchased from
Sinopharm Chemical Reagent Co. Ltd. All chemicals were analytical grade and used without
further purification. Deionized water was utilized throughout this study.
2.2 Synthesis of TiO2 nanowires
3 g of titanium (IV) oxide (AeroxideTM P25) was dispersed in 300 mL of a 10 M NaOH solution
under ultrasonic stirring, and the mixture was transferred to a 500 mL hydrothermal autoclave
heated continuously at 165 °C for 48 h. The white precipitate obtained from the autoclave was
washed with HCl solution to pH neutral. Then, Na+ was replaced with 600 mL of a 0.1 M HCl
solution for 24 h. Finally, the precipitate was dried to obtain a white titanate solid powder. The
titanate powder was annealed at 700 °C for 90 min, with a heating rate was 3 °C/min to obtain
TiO2 nanowires, labeled as TiO2NW.
2.3 Preparation of Pt/TiO2 nanowires
Pt deposited TiO2 was prepared by a photodeposition method. Three portions of the above-
mentioned white titanate powder (0.5 g) were dispersed in 30 mL deionized water ultrasonically,
and adding 0.075 wt%, 0.1 wt%, and 0.125 wt% H2PtCl6 (ratio of H2PtCl6 to titanate) under stirring,
respectively. The mixtures were irradiated with a 500 W Xe lamp with a light intensity of 100
mW/cm2 for 30 min under continuous magnetic stirring. After being centrifuged and dried at 80 °C,
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the sample was annealed at 700 °C for 90 min with heating rate of 3 °C/min. The resulting samples
were denoted as 75 PT, 100 PT, and 125 PT, respectively.
2.4 Characterization
The samples were characterized with a Shimadzu XRD7000 X-ray diffractometer (XRD), Zeiss
Libra200FE transmission electron microscope (TEM), field emission scanning electron
microscope (FESEM, JSM-7800F10100), X-ray photoelectron spectroscopy (XPS)
(VGESCALAB 250 spectrometer), UV-Vis spectrophotometer (Agilent Cary 5000),
photoluminescence spectrum (PL) (Hitachi F-7000), electron paramagnetic resonance (EPR)
spectrometer (Bruker EMXnano), and nitrogen adsorption-desorption isotherms (Quadrasorbevo
2QDS-MP-30). Electrochemical tests were performed on an AUTOLAB workstation (model
PGSTAT 302N) using a three-electrode system at room temperature. An FTO conductive glass
film with an area of 2 cm2 was used as the working electrode, the electrolyte was a 0.5 M Na2SO4
solution, the light source was a 500 W xenon lamp, the wavelength range was 250-780 nm, and
the light intensity was 110 mW/cm2.
2.5 Photocatalytic degradation of formaldehyde
The photocatalytic degradation of gas formaldehyde was performed at room temperature using a
home-made reactor at continuous flow, as shown in Figure S1. 10 mg catalyst was filled into ϕ3
mm quartz tube, and the two ends are blocked by a small amount of asbestos. Prior to the
degradation reaction, the formaldehyde flow rate was well controlled to achieve an adsorption-
desorption equilibrium. The surface of the quartz tube is irradiated with a set of LED lamp. The
efficiency of photocatalytic degradation of formaldehyde was calculated by comparing the change
in formaldehyde concentration after passing through a quartz tube. The formaldehyde
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concentration before and after the photocatalytic reaction was monitored the formaldehyde sensor
(Dart Sensor Ltd, UK). The formaldehyde degradation rate was calculated according to the
following equation:
Degradation rate η = (CtC0)/C0
Where C0 is the equilibrium concentration of HCHO at adsorption-desorption equilibrium, and
Ct is the HCHO concentration at reaction time t.
3. Results and discussion
Figure 1 shows the XRD patterns of TiO2, 75 Pt/TiO2, 100 Pt/TiO2, and 125 Pt/TiO2. The main
diffraction peaks of TiO2 are located at 25.3 °, 37.0 °, 37.7 °, 38.6 °, 48.1 °, 53.9 °, 55.1 °, 62.2 °,
and 62.7 °, corresponding to the (101), (103), (004), (112), (200), (105), (211), (213), and (204)
crystal planes of anatase phase (JCPDS 99-0008). The diffraction peaks of 75 Pt/TiO2 at 26.7 °
and 43.1 ° correspond to the characteristic planes (110) and (210) of the rutile phase (JCPDS 21-
1276), respectively. The diffraction peak at 2θ at 62.7 ° corresponds to the (002) crystal plane of
the rutile phase, overlapped with the (204) plane of the anatase phase. For 100 Pt/TiO2, the
diffraction peak at 2θ of 35.5 ° is related to the characteristic plane (101) of the rutile phase. Upon
loading 0.1 wt% Pt, the non-stable crystal plane (101) in the rutile phase was exposed. XRD pattern
shows that there appears rutile phase in TiO2 nanowires for 75 Pt/TiO2, 100 Pt/TiO2, 125 Pt/TiO2
after loading Pt. 75 Pt/TiO2 exposed the rutile (110) plane, while 100 Pt/TiO2 exposed the (101)
crystal plane, which is less stable than (110), causing more oxygen vacancy defects.
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Figure 1 XRD patterns of TiO2 and Pt/TiO2 nanowires. R, A, and B represent rutile, anatase, and
brookite, respectively.
Figures 2(a-d) show the FESEM images of TiO2NW, 75 Pt/TiO2, 100 Pt/TiO2, and 125 Pt/TiO2. It
shows that the nanowires have a diameter of 30-80 nm and a length of more than 5 μm. The loading
of Pt has no effect on the morphology of TiO2 nanowires. Figures 2 (e-f) are TEM images of 100
Pt/TiO2. The high-resolution TEM lattice fringe pattern shows that the crystal plane spacing is
0.35 nm, which corresponds to the (101) crystal plane of the anatase phase TiO2. [10, 23-25] Figure
2(f) shows that Pt nanoparticles uniformly distributed on the nanowires, indicating that Pt/TiO2
was prepared successfully. The TEM-EDS mapping in Figure 2(g) further confirmed that the Pt
nanoparticle supported on TiO2 nanowires.
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Figure 2 SEM images of TiO2 (a), 75 Pt/TiO2 (b), 100 Pt/TiO2 (c), and 125 Pt/TiO2 (d). TEM
images with different magnifications (e-f) of 100 Pt/TiO2. (g) STEM image and corresponding
EDS mapping profiles for Ti, O, and Pt.
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Figure 3 XPS spectra of Ti 2p (a), O 1s (b), and Pt 4f (c) for TiO2 and 100Pt/TiO2.
The oxidation state and surface chemical composition of the sample were analyzed by XPS, as
shown in Figure 3. The high-resolution Ti 2p spectra show two symmetrical peaks, located at 459.3
and 465.1 eV, respectively, which can be ascribed to the spin splitting orbits of Ti 2p3/2 and 2p1/2.
The XPS spectrum of O 1s can be fitted as three peaks at binding energies of 529.6, 531.1, and
532.1 eV, corresponding to the oxygen atoms in Ti-O and the adsorbed oxygen and adsorbed water.
The atomic ration of Ti/O is close to the chemostoichiometry of 1:2 of TiO2. The binding energies
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of TiO2 and 100PT are similar, which is a typical feature of coordination between Ti (IV) and O
atoms. The high-resolution spectrum of Pt 4f shows two symmetrical peaks located at 73.9 and
77.9 eV, respectively, corresponding to spin-split of Pt4f7/2 and 4f5/2. The results showed that the
single surface mass of Pt was successfully loaded on the sample surface, indicating that Pt was
successfully loaded onto TiO2 by photodeposition. [26-28] The atomic ration of Pt/TiO2 is about
0.05%. Thus, the weight ration of Pt to TiO2 is closed to 0.1 wt%.
Figure 4(a) shows UV-vis diffusion reflectance spectroscopy. The absorption edge is 389 nm for
TiO2 and Pt/TiO2, and the band gap value is 3.18 eV, indicating that the band gap remains
unchanged upon Pt loading. The absorption intensity is improved from UV to visible light range
after Pt deposition. The enhanced absorption of Pt/TiO2 indicated that Pt loading facilitates the
photocatalytic activity. Figure 4(b) shows PL spectra of TiO2 and Pt/TiO2 with the excitation
wavelength of 290 nm. It shows the fluorescence quenching phenomenon with PL intensity: 100
PT<75 PT<125 PT<TiO2. The loading of noble metal Pt facilitates the separation of electron-hole
pairs.
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Figure 4 UV-vis spectra (a) and PL spectra (b) for TiO2 and Pt/TiO2.
Figure 5(a) shows the instant photocurrent response, all of which exhibit fast photocurrent
responses. The photocurrent test after 5 cycles tends to be stable, there is no significant decrease
in the last 5 cycles, and it has good repeatability. It shows that TiO2 and Pt/TiO2 exhibit high
stability under ultraviolet light. At the same bias voltage, the stable photocurrent value of a 100
PT electrode is three times that of a TiO2 electrode, which means that 100 PT can generate more
photoelectrons and achieve effective separation of electron-hole pairs. [29] Pt load is conducive to
improving the instant photocurrent response, and is beneficial to the generation and regeneration
of electron-hole pairs. 100 PT has the highest photocurrent response. The electrochemical
impedance spectroscopy (EIS) of TiO2 nanowires is shown in Figure 5(b). As the Pt load increases,
the arc radius of the electrode decreases, indicating that the interface charge transfer resistance of
the working electrode is reduced, which can effectively promote the transport and separation of
photo-generated carriers in the photocatalytic reaction. That indicated that the load of Pt is
beneficial to the charge migration, thereby improving photocatalytic efficiency. Figures 5(c) and
(d) show the Mott-Schottky curves of TiO2 and 100 PT at 1000 Hz. The tangent slope of curves is
positive, indicating that TiO2 is a typical n-type semiconductor. The intercept of the tangent and
abscissa of the MS curves represents the flat band potential. The flat band potentials of TiO2 and
100 Pt/TiO2 are -1.057 and -1.116 V, respectively. The conduction band positions are
approximately -1.06 eV and -1.12 eV, respectively. That shows the negative shift of the conduction
band position after Pt loaded TiO2, and the band gap value of 3.18 eV determined by the UV-vis
spectrum. The positions of the valence bands are calculated to +2.12 eV and +2.06 eV, respectively.
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The negative shift of the valence band is more conducive to the production of the more oxidative
O-2
, which is beneficial to the occurrence of photocatalytic oxidation reactions.
Figure 5 Transient photocurrents (a) and EIS (b) spectra of TiO2 and Pt/TiO2. Mott-Schottky plots
of TiO2 (c) and 100 PT (d).
The photocatalytic oxidation of formaldehyde was carried out on a home-made reactor with a
quartz tube filled with 10 mg photocatalyst under the 420 nm LED irradiation with light intensity
of 6 W at the environmental temperature of 19 °C. The formaldehyde concentration was set to 0.5
mg/m3, and the flow rate at 50 mL/min. The ambient humidity was fixed at 80%. The inlet and
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outlet of formaldehyde were monitored to determine the degradation rate. Figure 6(a) shows the
degradation performance of four catalysts. After the adsorption equilibrium is reached, the light
was turned on to degrade the formaldehyde. The outlet concentration of formaldehyde gradually
decreased to 0, indicating all catalysts can degrade the formaldehyde completely in a short time
interval. However, the outlet formaldehyde concentration rises a little after a period of degradation
and eventually reaches the equilibrium saturation. The degradation equilibrium of formaldehyde
is 0.06, 0.09, 0.02, and 0.08 mg/m3 for TiO2NW, 75Pt/TiO2, 100Pt/TiO2, and 125Pt/TiO2,
respectively. Accordingly, the degradation rate is 88%, 82%, 99%, 84% for TiO2NW，75Pt/TiO2,
100Pt/TiO2, and 125Pt/TiO2, respectively. Figure 6(b) shows the detailed diagram of the
corresponding degradation performance. The time taken to decompose formaldehyde completely
is 4.98, 3.92, 4.45, and 3.58 min for TiO2, 75 PT, 100 PT, and 125 PT, respectively. The
degradation rate of formaldehyde increases after loading Pt nanoparticles on TiO2 nanowires, and
100Pt/TiO2 takes only 4.45 min, being slightly shorter than 4.98 min of TiO2. Figure 6(c) shows
the details of the stable time of formaldehyde degradation. There exists a stable time period before
the outlet concentration begin to increase and eventually reaches the equilibrium. The stable time
was 16.20, 19.57, 90.89, 29.62 min, for TiO2, 75 PT, 100 PT, 125 PT 100 PT, respectively. For
100 Pt, the stable time was about 5.6 times that of TiO2. Figure 6(d) shows the cycle stability test
of 100 PT degradation of formaldehyde. The formaldehyde degradation under 420 nm UV (6 W)
light has been tested at first, and the degradation equilibrium has finally been reached so that the
formaldehyde degradation test under this condition cannot reach a 100% degradation. By turning
on the strong ultraviolet (11.2 W) at 420 nm, the formaldehyde can reach 100% degradation. After
50 cycles in 50 hours, the photocatalytic performance of formaldehyde degradation did not
decrease, indicating that the 100PT photocatalyst is very stable, and can be used continuously.
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Figure 6 Degradation performance of flowing gas-phase formaldehyde (a-c). The stability test of
100Pt/TiO2 (d). CH1, inlet formaldehyde concentration fixed at 0.5 mg/m3; CH2, outlet
formaldehyde concentration.
The photocatalytic degradation of formaldehyde under different humidity was carried out under
irradiation using the 365 nm LED light with an intensity of 1.8 W. Figure 7(a-b) shows the
photocatalytic degradation of formaldehyde at the humidity of 80%, while Figure 7(a’-b’) shows
the measurements at the humidity of 60%. At ambient humidity of 80%, the time required for
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formaldehyde degradation of 100 PT is 10.63 min. As the humidity decreases to 60%, the time
required for the degradation 100 PT is 43.4 min. Under the ambient humidity of 80%, the stable
degradation lasts for more than 50 h, while the stable time decreased to 40 h at ambient humidity
of 60%, indicating that humidity increase facilitates the continuous and stable degradation of low-
concentration formaldehyde. Properly increasing the humidity is beneficial to the degradation of
formaldehyde gas and can improve the stability of the material's continuous degradation of low
concentration of formaldehyde. The blank test and the photocatalytic degradation for P25 were
shown in Figure 7(a) as reference.
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Figure 7 Effect of humidity on the formaldehyde degradation. (a-b) humidity at 80%, (a’-b’)
humidity of 60%.
Figure 8 shows the degradation performance of four catalysts with inlet concentration of 1.0 mg/m3.
After the adsorption equilibrium is reached, the light is turned on to degrade the formaldehyde.
The outlet concentration of formaldehyde gradually decreased. However, the outlet formaldehyde
concentration rises a little after a period of degradation and eventually reaches the equilibrium
saturation. he degradation rate is 88%, 86%, 92%, 87% for TiO2NW，75Pt/TiO2, 100Pt/TiO2, and
125Pt/TiO2, respectively. The results show that the degradation rate is related to the formaldehyde
concentration. The catalysts decompose formaldehyde partially at higher inlet concentration.
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Figure 8 Degradation performance of flowing gas-phase formaldehyde. CH1, inlet formaldehyde
concentration fixed at 1.0 mg/m3; CH2, outlet foamaldehyde concentration.
In order to explore the photocatalytic mechanism of formaldehyde degradation by TiO2 and
Pt/TiO2, 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used as active species trapping agent to
detect radicals over photocatalysts under visible light irradiation, as shown in Figure 9. Under dark
and visible light conditions, absolute methanol was used as solvent to test the DMAPO2 of TiO2
and Pt/TiO2, respectively. Figure 9(a) showed that both TiO2-methanal and TiO2-water had no
characteristic EPR signals in the dark state, and the DMAP O2 (superoxide radicals) and
DMPO·OH (hydroxyl radicals) characteristic peaks appeared under visible light irradiation. As
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shown in Figure 9(b), the DMAPO2 and DMPO·OH characteristic peaks for Pt/TiO2 appeared
under visible light conditions, respectively. There was no characteristic signal under dark

conditions. DMAP
and DMPO·OH characteristic peak was generated under visible light
O2
irradiation, indicating that O2 and ·OH active species were generated by the interaction of
photoinduced electrons and holes. The EPR experiments showed that hydroxyl radical (·OH) and

superoxide radical (
) were the main reactive oxygen species (ROS) involved in the
O2
photocatalysis. The reactive oxygen species (ROS) were generated through the interaction of
photoinduced charge carriers with H2O and O2 adsorbed on the catalyst surface. Under visible light
irradiation, the photoinduced electrons are trapped by O2 to yield O2 , and O2 react with water
to form OH. HCHO is then oxidized into formate species with the surface OH. Holes in VB
directly oxidize OH and/or water to produce ·OH. Subsequently, the formate is further oxidized
to CO2 and H2O by ·OH. [30, 31]
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Figure 9 EPR spectra in methanol dispersion for DMPO O-2 and aqueous dispersion for
DMPO·OH for TiO2 (a) and 100PT (b) in the dark and under visible light irradiation (λ> 420 nm).
4. Conclusion
In summary, the loading of Pt nanoparticles on TiO2 nanowires promoted the photocatalytic
degradation of gas-phase HCHO at low concentrations. Under visible light irradiation, the outlet
concentration of formaldehyde decreased exponentially to zero, and maintained for a certain time
interval, then reached the degradation equilibrium at the inlet concentration of formaldehyde fixed
at 0.5 mg/m3. 100 Pt/TiO2 maintained the 100% formaldehyde degradation for the longest time,
and the highest equilibrium formaldehyde degradation rate among all catalysts. The photocatalytic
performance of formaldehyde degradation did not show any observable decrease for undergoing
50 degradation cycles, indicating that the 100 Pt/TiO2 photocatalyst is very stable. The degradation
rate of HCHO increases with increasing ambient humidity by increasing the hydroxyl radical
(·OH) and superoxide radical (O2 ). The experimental results show that a small amount of Pt
nanoparticles loaded on titanium dioxide is conducive to the degradation of low-concentration
formaldehyde, and appropriately increasing the ambient humidity is beneficial to the degradation
of formaldehyde.
AUTHOR INFORMATION
Corresponding Author
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*The authors to whom correspondence should be addressed. zhangyyping6@swu.edu.cn,
zhangyyping@yahoo.com (Y. Zhang).
Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval
to the final version of the manuscript.
Conflicts of interest
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was supported by the National Natural Science Foundation of China (51801164),
Fundamental Research Funds for Central Universities (XDJK2020C005), Venture & Innovation
Support Program for Chongqing Overseas Returnees (cx2018080).
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Graphical abstract:
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The photocatalytic oxidation mechanism of formaldehyde degradation.
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