Assessing the photocatalytic activity of europium doped TiO2 using liquid phase plasma process on acetylsalicylic acid

Article abstract of DOI:10.1016/j.cattod.2020.06.004

In this study, europium (Eu) was precipitated in TiO₂ powder using liquid phase plasma (LPP) process to prepare a photocatalyst with higher activity, even in the visible light range. Eu was uniformly deposited on the surface of TiO₂ by the LPP method. It was observed that the amount of Eu precipitated on the TiO₂ surface increased with increasing precursor concentration. XPS and EDS analysis showed that Eu was precipitated as europium oxide. The precipitation of Eu shifted the position of the Raman peak to a higher wavelength; with higher Eu content, the band gap energy decreased. Particularly, the photocatalytic efficiency of the Eu doped TiO₂ photocatalyst (EDTP) in the visible light source was much higher than that of bare TiO₂, and with higher Eu content, the photocatalytic activity was improved. Acetylsalicylic acid was attacked by HO? produced on the EDTP's surface and assumed to be finally mineralized to H₂O and CO₂ via two decomposition pathways, namely, decarboxylation and deacetylation.

Full text of DOI:10.1016/j.cattod.2020.06.004

Journal Pre-proof
Assessing the photocatalytic activity of europium doped TiO2 using liquid
phase plasma process on acetylsalicylic acid
Sang-Chul Jung (Conceptualization) (Investigation) (Data curation)
(Writing - original draft)<ce:contributor-role>Writing - review and
editing), Hye-Jin Bang (Investigation) (Data curation), Heon Lee
(Investigation) (Data curation), Hyung-Ho Ha (Data curation)
(Validation), Young Hyun Yu (Data curation) (Validation), Sun-Jae
Kim (Data curation) (Validation), Young-Kwon Park
(Conceptualization) (Data curation) (Validation) (Writing - original
draft)<ce:contributor-role>Writing - review and editing)
PII:
S0920-5861(20)30389-8
DOI:
https://doi.org/10.1016/j.cattod.2020.06.004
CATTOD 12922
Reference:
To appear in:
Catalysis Today
Received Date:
Revised Date:
Accepted Date:
28 February 2020
9 May 2020
3 June 2020
Please cite this article as: Jung S-Chul, Bang H-Jin, Lee H, Ha H-Ho, Yu YH, Kim S-Jae, Park
Y-Kwon, Assessing the photocatalytic activity of europium doped TiO2 using liquid phase
plasma process on acetylsalicylic acid, Catalysis Today (2020),
doi: https://doi.org/10.1016/j.cattod.2020.06.004

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Assessing the photocatalytic activity of europium doped TiO2 using liquid
phase plasma process on acetylsalicylic acid
Sang-Chul Junga, Hye-Jin Banga, Heon Leea, Hyung-Ho Hab, Young Hyun Yub,
Sun-Jae Kimc, Young-Kwon Parkd, *
a Department of Environmental Engineering, Sunchon National University, 255 Jungang-ro,
Sunchon, Jeonnam 57922, Republic of Korea
b College of Pharmacy, Sunchon National University, 255 Jungang-ro, Sunchon, Jeonnam
57922, Republic of Korea
c Faculty of Nanotechnology and Advanced Materials Engineering, Sejong University, 209
Neungdong-ro, Gwangjin-gu, Seoul 05006, Republic of Korea
d School of Environmental Engineering, University of Seoul, 163 Seoulsiripdaero,
Dongdaemun-gu, Seoul 02504, Republic of Korea
*Corresponding author e-mail: catalica@uos.ac.kr
Graphical abstract
1

Highlights
 LPP method synthesizes high efficiency visible light-responsive
photocatalyst.
 The element Eu was distributed evenly on the TiO2 surface in oxide
form.
 The higher the doping amount of Eu, the lower the band gap energy.
 The higher the doping amount of Eu, the better the photolysis activity.
 Two preferred routes were recommended for the photocatalytic
degradation pathway.
Abstract
In this study, europium (Eu) was precipitated in TiO2 powder using liquid phase plasma
(LPP) process to prepare a photocatalyst with higher activity, even in the visible light range.
2

Eu was uniformly deposited on the surface of TiO2 by the LPP method. It was observed that
the amount of Eu precipitated on the TiO2 surface increased with increasing precursor
concentration. XPS and EDS analysis showed that Eu was precipitated as europium oxide.
The precipitation of Eu shifted the position of the Raman peak to a higher wavelength; with
higher Eu content, the band gap energy decreased. Particularly, the photocatalytic efficiency
of the Eu doped TiO2 photocatalyst (EDTP) in the visible light source was much higher than
that of bare TiO2, and with higher Eu content, the photocatalytic activity was improved.
Acetylsalicylic acid was attacked by HO∙ produced on the EDTP’s surface and assumed to be
finally mineralized to H2O and CO2 via two decomposition pathways, namely,
decarboxylation and deacetylation.
Keywords: TiO2 photocatalyst, Liquid phase plasma, Acetylsalicylic acid, reaction rate
constant, degradation mechanism
1. Introduction
Anti-inflammatory drugs (AIDs) are one of the most widely used drug groups in the
world and have persistent toxicity [1]. About 50 kinds of AIDs are commonly used, such as
aspirin, ibuprofen, and diclofenac. Aspirin, also known as acetylsalicylic acid (ASA), is
derived from salicylic acid. Several studies have reported the presence of these
pharmaceutical compounds in lakes, rivers, and freshwater environments [2–4].
Pharmaceutical wastewaters (PWWs) that contains recyclable and toxic organic compounds
can lead to very serious water environmental problems [5]. These organics have a high
3

resistance to microbial degradation or utilization, especially at high concentrations [6]. Thus,
increased emissions of PWW cannot be fully treated with conventional biological treatment
alone [7]. To meet increasingly stringent discharge wastewater standards, these PWWs must
be treated with powerful and advanced treatment technologies.
Recently, advanced oxidation processes (AOPs) have been applied to treat PWWs
[8,9]. These processes use a variety of reactive radical species (e.g., hydroxyl and oxygen
radicals) to effectively remove non-biodegradable contaminants from the water environment.
Ozonation, Fenton reaction, ultraviolet (UV) decomposition, liquid phase plasma
decomposition, and photocatalytic reactions are known as representative members of AOPs
[10–13]. Among these processes, a combination of TiO2 as a photocatalyst and UV light has
been found to degrade organic pollutants into biodegradable or inorganic materials (CO2 and
H2O) using highly reactive hydroxyl radicals [14–16].
The most significant hurdle to the use of TiO2 as a photocatalyst is its large band gap
(anatase: 3.2 eV, rutile: 3.0 eV) [17,18]. Owing to this large band gap, TiO2 photocatalysts
should only utilize less than 5% of the UV radiation reaching the Earth's surface [19,20].
Thus, to overcome the limitations of the TiO2 photocatalyst, a system for adding hydrogen
peroxide, ozone, and microwaves was introduced [21,22]. A fundamental solution is the
doping of TiO2 with nonmetals, transition metals, and rare earth elements [23–25]. Of these,
rare earth-doped TiO2 is known to have adsorption wavelength shifted to visible light region
or to reduce electron-hole recombination. [26].
Among various doping techniques that are applied to TiO2 photocatalysts, a method
of attachment using a plasma generated in a liquid phase has recently been attempted [27–29].
Liquid phase plasma (LPP) methods have been applied to prepare nanocomposites and
nanoparticles in the plasma field [30–32]. The LPP process can easily produce nanostructures
using a single process with various precursors and without adding a reducing agent.
4

In this study, a visible light-responsive photocatalyst was prepared by precipitating
europium (Eu) on TiO2, using the LPP process. The optical and physicochemical properties of
the Eu doped TiO2 photocatalyst (EDTP) were measured using various analyzers.
Photodegradation activity of the synthesized EDTP was evaluated with the bare TiO2
photocatalyst in UV and visible light. The photodegradation mechanism was investigated by
analyzing the intermediates generated from the decomposition of ASA using the EDTP.
2. Materials and methods
2.1 Materials
TiO2 powder, the base material of the EDTP and commercially named P-25 (anatase 85%
and rutile 15% mixture, average particle size 25 nm), was obtained from and manufactured by
Degussa Corporation (Germany). The Eu precursor used as a dopant was EuCl3 · 6H2O and
obtained from Sigma-Aldrich Corporation (USA). Deionized (DI) water, obtained from
Daejung Company (Korea), having a conductivity of 2 siemens/cm or less was used to prepare
an aqueous reactant solution. The photocatalytic degradation target aqueous reactant solution
was prepared using ASA (C9H8O4) purchased from Sigma-Aldrich Corporation (USA).
2. 2. Preparation of EDTP
Europium was precipitated on TiO2 powder by applying the LPP process, and a schematic
of the LPP system used in this study is shown in Fig. S1 (supplementary material). A
cylindrical batch reactor made of quartz was filled with an aqueous reactant solution in which
TiO2 powder and Eu precursor were dispersed, and plasma was generated in the solution. A
tungsten electrode with a thickness of 2 mm wrapped in an insulator in the middle part of the
reactor is located on both sides while maintaining an inter-electrode spacing of 1 mm, and a
5

high voltage is supplied using a power supply to form a plasma field. (S1 (c)). The aqueous
reactant solution was maintained at 288 K using a cooling bath and was circulated to the
reactor. In this study, direct pulse type electric plasma was used to prevent electrode corrosion
and to clean electrode tips. The pulse width applied in the experiment was 5 μs (S1 (b)), and
the frequency and applied voltage were maintained at 30 kHz and 250 V, respectively. Photo
S1 (a) showed the plasma generated between the tungsten electrode tips. Similar LPP devices
have been used in previous studies, and detailed specifications and operating methods are
described in the literature [28,32].
P-25 (0.5 g), the base material, was added to DI water (250 ml), followed by stirring for
300 sec, and sonification for 120 sec in to prepare a solution in which TiO2 powder was
uniformly dispersed. EuCl3 was added to the prepared solution at a constant concentration (5
and 10 mM), and then stirred for 10 min to completely dissolve the resulting LPP aqueous
reactant solution. After adding the prepared aqueous reactant solution to a quartz reactor,
plasma was generated for 1 h to precipitate Eu on TiO2 powder. At the end of the LPP
reaction, the aqueous reactant solution was separated into a solution and a precipitate by
centrifugation (×10,000 rpm). The separated precipitate was washed with DI water and
centrifuged three times to remove unreacted impurities. The final precipitate was dehydrated
using a vacuum dryer at 383 K for 24 h.
2.3. Determination of photocatalytic activity
The photocatalytic activity of EDTPs prepared by the LPP method was evaluated using
ASA, one of the PWWs detected in the water environment. Photocatalytic decomposition of
ASA using the EDTP was carried out using UV LED and blue LED light sources. The LED
light source photocatalytic decomposition apparatus is shown in Fig. S2 (c). The external
photograph of the light source module equipped with 100 LED lamps used for the
6

photocatalysis reaction (S2 (a)) and the internal photograph of the light source module with
the LED lamps turned on are shown in Fig. S2 (b). Table 1 shows the optical characteristics of
the LED lamps used in the LED light module manufactured in this study.
ASA photocatalysis using the EDTP proceeded as follows. An ASA solution of 1,000 ppm
concentration was prepared as a stock solution, and 0.6 L of ASA solution of 50 ppm
concentration was prepared by diluting it 20 times in the decomposition reaction experiment.
0.3 g of the EDTP was added to the ASA solution and uniformly dispersed by stirring. The
ASA solution in which EDTP was dispersed was put in a solution storage tank and circulated
in a photoreactor using a roller pump to cause photocatalytic decomposition of ASA. The
circulation flow rate of the aqueous reactant solution was 500 ml/min, and samples were taken
at regular time intervals. Samples were collected by centrifugation and syringe filter to
remove the EDTP in solution and then the ASA concentration was measured. High-
performance liquid chromatography (HPLC) (Agilent 1260 Infinity; Agilent Technologies,
USA) was used to measure the ASA concentrations over the reaction times. At this point, the
photocatalytic decomposition of ASA was assumed to be a pseudo 1st order degradation
reaction, and the decomposition rate was calculated. The detailed conditions of the HPLC are
described in the Supplementary Materials.
3. Results and discussion
3.1 Characterization of the EDTP
The chemical composition of EDTPs prepared using the LPP process, shown in Table 2,
was measured by energy dispersive X-ray spectroscopy (EDS) of a field emission scanning
electron microscope (FE-SEM, JEOL-JSM-7100F). The numbers attached to the EDTP
7

indicate the mole concentration of the Eu in the aqueous reactant solution. For bare TiO2 (P-
25), the atomic percentage ratios of titanium and oxygen are 33.13 and 66.87 At. %,
respectively, and they correspond to the chemical structure of pure TiO2. In the case of the
EDTP, the composition of Eu increased as the composition of titanium and oxygen decreased,
and it increased in proportion to the concentration of the Eu in the aqueous reactant solution
[33]. Eu3+ ions present in the aqueous reactant solution are reduced by electrons in the plasma
field and precipitated on the surface of TiO2 [34,35]. Additionally, the atomic% of oxygen in
EDTPs increased, and from these results, it could be inferred that the Eu precipitated on the
TiO2 surface was in oxide form.
To examine the morphology and elemental distribution of EDTPs prepared using the LPP
process, the analysis was performed using high-resolution field emission transmission electron
microscopy (HR-FETEM, JEOL-JEM-2100F) and EDS attached to HR-TEM. The TEM
image shown in Fig. 1 (a) is a real image of EDTP-10 prepared by the LPP method. The
particle size of the EDTP was 15–40 nm, consistent with the average size of TiO2 (P-25) used
as the base material. Fig. 1 (b), (c), and (d) show the EDS mapping results for the elements Ti
(green dot), O (white dot) and Eu (yellow dot). This was found to be in agreement with the
shape of the EDTP nanoparticle cluster in Fig. 1 (a). Additionally, it can be seen in the image
(d) that the elemental Eu is very uniformly dispersed on the TiO2 surface. These results
indicate that Eu ions present in aqueous solution dissociated from precursors were uniformly
precipitated on the TiO2 surface by the LPP process.
Meanwhile, the optical emission spectrum (OES) of radicals generated in the aqueous
reactant solution was measured using an optical fiber spectrometer (Avantesie, AvaSpec-
3600) installed in the LPP reactor. Fig. S3 (a) shows the OES measured in the LPP reaction
using DI water. In DI water, peaks due to hydroxyl radicals (309 nm), excited hydrogen (486
nm and 656 nm), and excited oxygen (777 nm and 844 nm) were observed. Fig. S3 (b) shows
8

the OES of the LPP reaction solution in which the Eu precursor is dissolved, and many weak
peaks are formed along with the peaks observed in DI water. The spectrum at the top of Fig.
S3 (b) is an enlarged spectrum of wavelengths from 380 nm to 470 nm. Peaks by Eu ions (382
nm, 393 nm, 397 nm, 413 nm, 420 nm, 444 nm, 459 nm, 463 nm, and 466 nm) were observed
[36].
In this study, Raman spectroscopy with a laser wavelength of 532 nm was used for the
structural characterization of EDTPs prepared by the LPP method. The Raman spectrum of
bare TiO2 and the EDTPs was shown in Fig. 2. Anatase TiO2 is known to have six Raman-
active modes (A1g + 2B1g + 3Eg). The bare TiO2 used in this study showed peaks at 145 nm
(Eg), 198 nm (Eg), 399 nm (B1g), 517 nm (B1g), and 640 nm (Eg), indicating an anatase phase
[33,37]. In the Raman spectra of the EDTPs, no new peak was observed due to impurity-
related modes, and only the position of the Raman peaks shifted. Especially, the Eg mode of
145 cm-1 shifted to higher wavelengths presumably because the crystallite size decreased [38].
Additionally, the intensity decreased with increasing Eu doping composition. This is assumed
to be due to the breakdown of long-range translational crystal symmetry as defects are
induced in the crystal lattice [33,38].
The chemical state of the EDTP-10 synthesized by the LPP method was confirmed by
XPS and is shown in Fig. 3. Fig. 3 (a) shows the survey XPS spectrum of the EDTP-10 and
strong peaks due to Ti2p and O1s were observed at binding energy (BE) of 458 eV and 530
eV, respectively. Additionally, peaks by Eu3d were observed at BE 1,120 ~ 1,170 eV, and it
was confirmed that Eu was doped on the TiO2 surface. The chemical composition obtained
from the survey XPS spectrum in Fig. 3 (a) showed similar values to the EDS results. The
high-resolution XPS spectrum for the Ti2p region was shown in Fig. 3 (b). Peaks by Ti2p3/2
and Ti2p1/2 were observed at 458.2 eV and 463.9 eV, and the spin-orbital splitting between the
two peaks was 5.7 eV. This is due to the crystal lattice of Ti4+, and no phase transition of TiO2
9

was caused by Eu doping [39–41]. Fig. 3 (c) is the high-resolution XPS spectrum of the O1s
region. The strong peak at BE 529.4 eV represents the Ti-O bond caused by the O2- of the
TiO2 lattice, and the peak at 531.4 eV is due to surface hydroxy group or adsorbed oxygen
[41,42]. The small peak at BE 532.7 eV is assumed to be due to the C-O bond of the carbon
tape used to fix the samples [43]. In the Eu3d region spectrum in Fig. 3 (d), the peaks at BE
1125.1 eV and 1154.2 eV are peaks caused by divalent Eu (Eu2+), and the peaks at 1134.1 eV
and 1164.3 eV are due to trivalent Eu (Eu3+). From the XPS analysis result, it is determined
that the Eu element precipitated to the TiO2 surface by the LPP process exists in the form of
europium oxide [44–47].
In this study, the objective was to produce visible photoresponsive photocatalysts. The
optical properties of bare TiO2 and EDTPs were measured by UV-Vis diffuse reflectance
spectroscopy (UV-DRS, Shimadzu, UV-2450), and the results are shown in Fig. 4. As the Eu
element precipitates on the TiO2 surface through the LPP process, the absorption peak is red
shifted and determined by the Eu doping content. The red shift reduces the band gap energy
by facilitating the charge-transfer transition between the conduction or valence band of the
rare earth Eu and TiO2. [48]. The adsorption edges of the bare TiO2 were 389 nm, and the
adsorption edges of Eu doped EODTP-5 and EODTP-10 were 397 nm and 408 nm,
respectively. For the band gap energies of Bare TiO2 and EDTPs, the adsorption edge
obtained from UV-DRS was calculated by the kubelka-Munk formula. The calculated band
gap energy of bare TiO2 was 3.18 eV, and the band gap energy of Eu doped EODTP-5 (3.12
eV) and EODTP-10 (3.03 eV) decreased. From the results of the DRS analysis, it was found
that the EDTP prepared by the LPP method is a photocatalyst capable of responding to visible
light.
3.2 Photocatalytic activity of EDTP
10

In this study, the photocatalytic activity of EDTPs prepared by the LPP process was
evaluated in ASA—one of the pharmaceutical ingredients. As a light source for
photocatalysis, a self-made LED light module using a UV and blue LED was used.
Degradation of the ASA was assumed to be a pseudo 1st order degradation reaction, and the
degradation rate was measured and compared with bare TiO2. Fig. 5 shows the degradation
rate in ASA degradation using the bare TiO2 and EDTPs as photocatalysts under UV light
(λmax = 375 nm). The concentration of the ASA decreased as the decomposition occurred
through excitation of the photocatalyst by UV light, and the rate of ASA degradation by the
EDTPs precipitated with Eu was faster than that of the bare TiO2. As Eu is precipitated on the
TiO2 surface, Ti4+ can be converted to Ti3+ by charge compensation. Ti3+ acts as a trap to
increase the adsorption of the reactant, as well as to reduce the recombination of
photogenerated electron-holes [42]. Eventually, the decomposition rate of ASA was
accelerated by Eu precipitated in TiO2. For bare TiO2, the ASA degradation rate constant k
was 9.37 × 10-3 min-1, and for the EDTPs it was 10.08 × 10-3 min-1 (EDTP-5) and 10.65 × 10-3
min-1 (EDTP- 10). The degradation rate of EDTPs was improved by about 7–14% compared
to that of bare TiO2 and was proportional to the precipitated amount of Eu.
The results of the ASA degradation using bare TiO2 and the EDTPs under blue light
(λmax = 465 nm) were shown in Fig. 6. It can be seen that there is barely a decomposition of
ASA by bare TiO2; the decomposition reaction rate constant k was measured as 0.140 × 10-3
min-1. The band gap energy of bare TiO2 was 3.18 eV, which is considered to be because
excitation of bare TiO2 is difficult to occur by blue light. On the other hand, the
decomposition reaction of ASA by the EDTPs occurred, and the decomposition reaction rate
was proportional to the amount of Eu precipitated on the TiO2 surface. As Eu precipitated, a
new energy level was formed below the conduction band of TiO2, and the band gap energy
decreased, suggesting that the EDTP is excited by blue light absorption [41]. It is also
11

believed that the production of superoxide radicals is increased by adsorbed oxygen
enhancement with inhibition of electron-hole recombination by the electron trap effect of Eu
[41,49]. Degradation rate constants k of EDTP-5 and EDTP-10 were measured to be 0.685 ×
10-3 min-1 and 1.475 × 10-3 min-1, respectively, and were significantly improved by 5 to 10
times compared to bare TiO2.
In order to evaluate the reusability of EDTPs prepared by the LPP method, ASA
degradation reaction was performed 10 times under UV light conditions using EDTP-5 and
10, and ASA degradation rate was measured and compared for each number of times.
Compared to the case where the ASA degradation experiment was first performed and 10
times, the ASA degradation reaction rate was decreased, EDTP-5 was decreased by 3.42%,
and EDTP-10 was decreased by 4.53%. On the other hand, EDTPs prepared by the LPP
method showed a significant decrease in reusability at the initial stage of use, but maintained
reusability beyond a certain number of uses.
3.3 Mechanism of decomposed ASA by EDTP
The decomposition of ASA was carried out using EDTP-10 prepared by the LPP method,
and intermediate-byproducts generated during the reaction were measured by HPLC/MS.
Table 3 shows the m/z, compound name, and chemical structure of the detected intermediate-
byproducts. Four intermediate-byproducts resulting from the degradation of ASA were
detected.
Based on the intermediate-byproducts obtained from LC/MS, the degradation reaction
pathway of ASA using the EDTP is shown in Fig. 7. The two degradation pathways are
expected to be decarboxylation or deacetylation of ASA through photocatalytic degradation by
the EDTP. The first degradation pathway is decomposed to phenyl acetate (2) by
decarboxylation (a) of the side chain of ASA by strong oxidizing species such as hydroxyl
12

radicals from the EDTP [50,51]. It is converted into phenol (4) by cleavage of C-O bond of
phenyl acetate and then forms hydroquinone (5) by hydroxylation. After that, it is converted
into 1,4-benzoquinone and decomposed into maleic acid and fumaric acid by a ring opening
reaction [50–52]. In the second pathway, hydroxyl radicals attack the C=O bonds in the ASA
side chain, resulting in deacetylation (b), which in turn converts into salicylic acid (3) [51].
Salicylic acid is subsequently converted into some phenol (4) or to 2,4-dihydroxybenzoic acid
by hydroxyl radical and electrophilic addition [50, 51, 53]. 2,4-dihydroxybenzoic acid is
converted to maleic acid and fumaric acid by a ring opening reaction and finally mineralized
to H2O and CO2 [53,54].
4. Conclusion
In this study, the LPP process was introduced to precipitate Eu elements on the TiO2 surface,
and the photocatalytic efficiency of the prepared Eu doped TiO2 was evaluated for ASA, a
pharmaceutical ingredient. As the precursor’s concentration increased, the amount of Eu
precipitated on the TiO2 surface increased. Further, it was found by EDS analysis that the
precipitated Eu was in oxide form. It was observed that Eu was uniformly precipitated by the
LPP method on the TiO2 surface, having a size of 15 to 40 nm, using HR-TEM. No new peak
was observed due to impurity-related modes in the EDTPs, but the position of the Raman
peak shifted to a higher wavelength. From the high-resolution XPS spectrum, it was
confirmed that the elemental Eu precipitated on TiO2 surface by LPP process, existed in
europium oxide form. The decrease in band gap energy of the EDTP was confirmed by UV-
DRS analysis; the higher is the content of Eu, the lower is the band gap energy. The
photocatalytic efficiency of the EDTPs was much higher than that of bare TiO2 in the visible
light source; the higher the content of Eu, the better is the photocatalytic activity. HPLC/MS
13

was used to detect four intermediate-byproducts generated in the decomposition of ASA, and
based on this, two degradation pathways were predicted. It was finally mineralized to CO2 and
H2O following two decomposition pathways by decarboxylation and deacetylation when
attacked by hydroxyl radicals (HO∙). Through this study, it was confirmed that photocatalytic
efficiency can be improved and visible light response photocatalysts can be applied by doping
rare earth elements on the TiO2 surface, and it is considered to be applicable to fields such as
decomposition of environmental pollutants.
CRediT author statement
Sang-Chul Jung: Conceptualization, Investigation, Data curation, Writing- Original draft
preparation, Writing- Review and Editing
Hye-Jin Bang: Investigation, Data curation,.
Heon Lee: Investigation, Data curation.
Hyung-Ho Ha: Data curation, Validation
Young Hyun Yu: Data curation, Validation
Sun-Jae Kim: Data curation, Validation
Young-Kwon Park: Conceptualization, Data curation, Validation, Writing- Original draft
preparation, Writing- Review and Editing
Declaration of interests
The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This research was supported by Basic Science Research Program through the National
Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-
2018R1D1A1B07049595).
14

15

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Captions for Figures
Fig. 1. HR-TEM real image (a), Ti element mapping (b), O element mapping (c) and Eu
element mapping (d) of EDTP-10 prepared using LPP process.
Fig. 2. Raman spectra of Eu-doped TiO2 photocatalysts and bare TiO2.
Fig. 3. XPS spectrum of EDTP-10 prepared using the LPP process: survey (a), Ti2p (b), O1s
(c), and Eu3d (d).
Fig. 4. Comparison of diffuse reflectance spectrum of bare TiO2 and prepared EDTPs.
Fig. 5. ASA degradation rate of bare TiO2 and EDTPs using UV LED light source.
Fig. 6. ASA degradation rate of bare TiO2 and EDTPs under blue LED light conditions.
Fig. 7. Proposed pathways for the photocatalytic degradation of ASA.
21

Fig. 1. Jung et al.,
22

Fig. 2. Jung et al.,
23

Fig. 3. Jung et al.,
24

15
10
5
Bare TiO2
EDTP-5
EDTP-10
0
250
300
350
400
450
Wavelength (nm)
Fig. 4. Jung et al.,
25

Fig. 5. Jung et al.,
26

Fig. 6. Jung et al.,
27

Fig. 7. Jung et al.,
28