E. OZKAN: COMPARISON OF NITROGEN-DOPED PHOTOCATALYTIC SURFACES SYNTHESIZED BY PVD ...
775–781
COMPARISON OF NITROGEN-DOPED PHOTOCATALYTIC
SURFACES SYNTHESIZED BY PVD AND SOL-GEL METHODS
PRIMERJA V A FOTOKATALITI^NIH POVR[IN, SINTETIZIRANIH
S PVD IN SOL-GEL METODAMI
Erhan Ozkan
*
Dikkan R&D Center, Izmir, Turkey
Prejem rokopisa – received: 2024-03-08; sprejem za objavo – accepted for publication: 2024-10-14
doi:10.17222/mit.2024.1132
The aim of this study was to produce photocatalytic TiO 2–xN x coatings that can be active in visible light using different methods.
Physical vapour deposition (PVD) and sol-gel methods were preferred for these coatings. Thin films were synthesized by dip
coating on a glass substrate using the sol-gel method. In addition, thin glass film coatings were obtained by applying an arc for
one minute to the glass films using the PVD method. Since the coating phase is important in terms of photoactivity, a phase
analysis was performed using XRD. The obtained surfaces will be used in antibacterial applications. Therefore, the thickness of
the coatings was determined with the X-Ray refraction method, and their optical band gap was measured. Based on these values,
it was observed that nitrogen has a reducing effect on the optical band gap in titanium oxide-based coatings. The aim of nitrogen
doping was to enhance photoactivity by adding an additional band between the valence band and conduction band of a
photocatalytic surface. After these experiments using rhodamine-B and methylene blue solutions, specimens’ photocatalytic ef-
fects under fluorescent, sun and UV light were tested. It was determined that nitrogen’s decreasing effect on the optical band
gap results in increased photoactivity with both PVD and sol-gel techniques. In addition, it was found that the coatings made
with PVD exhibited a more controlled structure in a shorter time, while the production of sol-gel coatings was a much cheaper
method, with low investment costs.
Keywords: TiO 2, sol-gel, PVD, photocatalysis, thin film
V ~lanku avtor opisuje {tudijo izdelave fotokataliti~nih prevlek na osnovi TiO 2–xN x, ki so lahko aktivne v obmo~ju vidne
svetlobe. Prevleke se lahko izdeluje z razli~nimi postopki. Avtor opisuje njihovo izdelavo s postopkom nana{anja v parni fazi
(PVD; angl.: Physical Vapour Deposition) in tako imenovano Sol-Gel metodo izdelave tanke plasti s potapljanjem steklene
podlage. Pri PVD metodi so tanko prevleko na stekleni podlagi dobili z delovanjem enominutnega obloka na stekleni film.
S stali{~a fotoaktivnosti je fazna sestava prevlek pomembna, zato so izdelane prevleke, uporabne za antibakterijske aplikacije,
analizirali z rentgensko difrakcijo (XRD). Debeline prevlek so bila dolo~ene z metodo loma in odboja rentgenskih `arkov.
Izmerili so tudi {irino opti~ne pasovne re`e. Na osnovi izmerjenih vrednosti je avtor opazoval u~inek du{ika na zmanj{evanje
{irine opti~ne pasovne re`e na prevlekah, ki temeljijo na titanovem dioksidu (TiO 2). Razlog za dopiranje z du{ikom je bil
pove~evanje fotoaktivnosti prevlek z dodajanjem dodatnega pasu med valen~nim in prevodnim pasom fotokataliti~ne povr{ine.
Po teh eksperimentih je avtor uporabil raztopini Rodamina-B in metilensko modre za testiranje vzorcev v fluorescen~ni, vidni
(son~ni) in UV svetlobi. Z eksperimenti je potrdil zmanj{evalni u~inek du{ika na {irino re`e opti~nega pasu, kar je povzro~ilo
pove~anje fotoaktivnosti prevlek, izdelanih tako s PVD kot tudi s Sol-Gel tehnikami. [tudija je tudi pokazala, da imajo PVD
prevleke bolj kontrolirano mikrostrukturo in kraj{i ~as aktivacije, medtem ko je izdelava prevlek s Sol-Gel postopkom cenej{a in
zahteva manj{e investicijse stro{ke.
Klju~ne besede: titanov dioksid (TiO 2), postopka Sol-Gel in PVD, fotokataliza, tanki filmi
1 INTRODUCTION
The term photocatalysis describes reactions that are
activated by light radiation. Since environmental pollu-
tion is an important problem in today’s industrial world,
research on photocatalysis is gaining in importance.
1–3
The decrease in natural water resources together with the
pollution of the limited amount of domestic water due to
industrial and environmental wastes has become one of
the serious problems today’s world.
4
Chlorine used in
water sterilization not only emits an irritating odour, but
also causes the formation of harmful tri-halo-methane
compounds, which can cause cancer as a result of the
chemical reaction with the substances to be removed.
5
Photocatalysis has gained prominence as an effective
method for decomposing organic compounds in the sys-
tem, addressing many of the above-mentioned problems.
Photocatalysts are semiconductor materials that are acti-
vated by ultraviolet (UV) light and form a strong oxidiz-
ing environment.
6
Bacteria and organic compounds stuck
on the surface can be easily removed from the environ-
ment with the help of this oxidizing powder. In other
words, photocatalysts are known as catalysts activated by
the effect of light. By absorbing light, they reach a
higher energy level and transfer the energy to the reac-
tive material. In this way, a chemical reaction begins. An
alloy of metal and semimetal can be used as a photo-
catalyst. Initially, Fe
2
O
3
,
7
ZnO,
8
SrTiO
3
,
9
GaAs,
10
GaP,
11
CdS
12
and WO
3
13
can be given as examples of
semiconductor photocatalysts. The most widely used
Materiali in tehnologije / Materials and technology 58 (2024) 6, 775–781 775
UDK 549.514.6:681.7.064.45 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek Mater. Tehnol.
*Corresponding author's e-mail:
erhan.ozkan@dikkan.com (Erhan Ozkan)

photocatalyst in applications is TiO
2
with an energy
range of 3.2 eV .
14
In order to change this range for differ-
ent applications, Fe, Al, Cu, V , Pt, Cr, Ag and rare earth
elements have been used.
TiO
2
based oxide films can be obtained with high in-
vestment costs and advanced technological equipment
required for chemical vapour deposition,
16
physical
vapour deposition,
17
and molecular beam epitaxy.
18
How-
ever, they can also be synthesized with lower costs using
the sol-gel technique for the synthesis of thin film coat-
ings. This technique has advantages such as being able to
control chemical reactions, obtaining a homogeneous
structure, performing processes at low temperatures, low
energy costs and not reacting with the substrate; how-
ever, there are also some disadvantages of producing
TiO
2
thin films with the sol-gel method. These disadvan-
tages include the fact that titanium alkoxide does not dis-
solve in most alcohols, the labour cost of the thin films
produced with this method is high and takes a long time,
the high shrinkage during synthesis, the presence of
microporosities in the coating, and the processing with
organic solvents that are harmful to health.
19–22
In this study, a titanium dioxide material with added
nitrogen, intended for the production of a photocatalytic
surface, used in antibacterial applications, was synthe-
sized on glass surfaces using the sol-gel and PVD meth-
ods. The microstructures of the synthesized coatings
were determined according to the phases identified with
EDS and XRD, and their thermal and surface adhesion
properties were investigated. Phase analyses of these
coatings were performed using XRD, a thermal analysis
was performed using DTA/TG, and surface structures
were observed using SEM and AFM devices. According
to the results, the coatings produced with the PVD tech-
nique showed good adhesion to the surface and a high
deposition rate; they required low temperatures during
deposition, and no additional heat treatment compared to
the sol-gel technique. The aim of this study was to make
a comprehensive comparison of the two methods – PVD,
an expensive method, and sol-gel, a cheap and widely
preferred method.
2 EXPERIMENTAL PART
2.1 PVD
A (30 × 40 × 3) mm quartz glass material was used as
the base material. Glass samples were used because their
optical properties could be measured. The purpose of us-
ing quartz glass was to prevent sodium migration into the
coated film, otherwise encountered in normal glass, thus
increasing photoactivity. For this purpose, preliminary
preparations were made by passing the glass samples
through acetone, isopropanol and pure water ultrasonic
baths and then dried in an atmospheric environment with
argon gas. Surface cleaning is based on removing parti-
cles from the sample surface by splashes caused by the
high potential difference of argon gas emanating from
the neutral molecule source.
Magnetic focus was used during the coating when the
total pressure was 7.5 · 10
–3
torr, the total current was
50 A, and the duration was 1 min. The samples were
covered at different nitrogen/oxygen ratios at room tem-
perature, with a nitrogen gas flow of 60 sccm. Table 1
shows different coating parameters.
Table 1: PVD coating parameters
Sample Composition
1T i N
2 5 0%N 2
–5 0%O
2
3 2 5%N
2
–7 5%O
2
4 1 5%N
2
–8 5%O
2
5 1 0%N
2
–9 0%O
2
6 5%N
2 –9 5%O
2
7 Pure TiO
2
2.2 SOL-GEL
In our experimental studies, titanium (IV) iso-
propoxide (Ti[OCH(CH
3
)
2
]
4
, 99.999 % purity, Sigma
Aldrich) as the starting material, ethanol (C
2
H
5
OH) as
the solvent, hydrochloric acid (HCl) as the catalyst were
used to obtain a TiO
2
-based sol solution. Pure water
(H
2
O) was used for the hydrolysis of metal alkoxides.
Hydrolysis and condensation reactions of titanium
alkoxide are extremely exothermic forms a white precip-
itate in the presence of water or with moisture in the air.
Therefore, acetyl acetone (C
5
H
8
O
2
, at least 99 % purity,
Merck) was used to control the reactions and avoid flash
precipitates or the formation of an unstable colloidal so-
lution during polycondensation. Urea (NH
2
CONH
2
,
Merck) was preferred as the nitrogen additive. Two dif-
ferent solutions were prepared for the TiO
2
sol solution.
To obtain the first solution, 1.5 mL of titanium (IV)
isopropoxide was dissolved in 10 mL of ethanol by mix-
ing them with a magnetic stirrer; then 0.35 mL of acetyl
acetone was added and stirring was continued for
30 min. For the second solution, 0.92 mL of HCl,
0.15 mL of distilled water and 10 mL of ethanol were
mixed. Then, these two solutions were combined, and
mixing was continued for another 30 min. While prepar-
ing the doped TiO
2
solution, the additives were dissolved
in 5 mL of ethanol at the determined rates and added to
the main solution and the mixing process was continued.
Additives were incorporated by setting the molar ratio of
the additive starting material to the titanium starting ma-
terial, and sample names were coded according to these
ratios. In the experimental studies, the maximum solubil-
ity limit of urea used for the nitrogen additive in ethanol
(RN: 2) and the additive ratios were determined by con-
sidering the literature.
23
Accordingly, the molar ratios of
additives to titanium (IV) isopropoxide were determined
for nitrogen, RN: 0.1, 1, and 2. The prepared solutions
were kept at room temperature for one day and aged, and
then the coating process was started.
E. OZKAN: COMPARISON OF NITROGEN-DOPED PHOTOCATALYTIC SURFACES SYNTHESIZED BY PVD ...
776 Materiali in tehnologije / Materials and technology 58 (2024) 6, 775–781

SiO
2
interlayer coatings were applied to all samples
in order to prevent the diffusion of alkali ions (Na
+
)i n
the soda-lime glass used as the substrate. Tetraethyl-
orthosilicate (Si(OC
2
H
5
)
4
, TEOS, 99.999 % purity,
Sigma Aldrich) as the starting material for the SiO
2
interlayer film, ethanol (C
2
H
5
OH) as the solvent, hydro-
chloric acid (HCl) as the catalyst, and purified water
(H
2
O) for the hydrolysis of metal alkoxides were used in
molar ratios of 1:4:0.3:4, respectively. In the preparation
of SiO
2
-based solutions, TEOS was first dissolved in eth-
anol by stirring it for about 30 min. Then, distilled water
and hydrochloric acid were added, and mixing was con-
tinued for another 2 h. The solutions were aged at room
temperature for 2 d. After the aging process, the pre-
pared sol solutions were used to obtain thin films and
powder photocatalysts. In order to prepare powder
photocatalysts, sol solutions were dried at 100 °C for
24 h; water and alcohol were removed from their struc-
tures and samples in the xerogel form were obtained. For
the thin film photocatalyst production, the prepared solu-
tions were applied onto Corning® 2947 soda-lime glass
surfaces using the dip coating method. Before the coat-
ing, the glass substrates were cleaned in an ultrasonic
bath by holding them in acetone, ethanol, methanol and
distilled water, respectively. During the coating, one side
of the glasses was masked with a tape so that only one
surface was covered. All the coatings were formed at an
immersion speed of 100 mm/min in a Teknosem TDC-10
coating device. The coated glasses were dried in an oven
at 100 °C. TiO
2
coatings were applied onto the substrates
both with and without an SiO
2
interlayer. SiO
2
interlayer
coated glasses were heat treated for1ha t5 0 0° Ci na
Nabertherm furnace to ensure the crystallization of the
interlayer coating before being used as the substrate.
Heat treatment at a rate of 10 °C/min was applied to
obtain the anatase phase in doped and undoped TiO
2
thin
films and powder samples. They were heat treated in the
Nabertherm oven at 500 °C for 1 h, then rapidly cooled
in a controlled manner at a rate of 5 °C/min. The process
flow chart is given in Figure 1.
2.3 Characterization
Coating thicknesses were determined by X-ray
refractometry. Thin-film geometry was used because the
coating thickness was in the nanometer range. The  an-
gle was chosen as 0.5° and scans were made between
0.6° and 1.6°.
The crystal structure of thin-film coatings was inves-
tigated with a Phillips 3710 low-angle X-ray diffracto-
meter under CuK
 irradiation, at a 40 kV voltage and
40 mA current. Since the coating thickness was nano-
metres and the peaks were desired to be seen completely
and clearly, the scanning speed was at 0.01 °/sec over 2 angles from 20° to 120°.
Optical band gap measurement was made to get an
idea about the activation energies of the coatings under
visible light using the values found with the forbidden
band energy measurement. An Aquila NKD device was
used for the optical band gap measurement. With this de-
vice, the permeability and reflectivity of the material for
each wavelength is graphically obtained by sending laser
radiation at a constantly changing wavelength to the
sample placed on the insole. These raw data obtained
were likened to certain mathematical functions, from
which the refractive index of sample n and extinction co-
efficient k were found. Using Equation (1), the absorp-
tion coefficient (alpha) was calculated in 1/meter.
  =
4kπ
(1)
After calculating the alpha value, the graphical
method was used to calculate the forbidden band energy.
For this, an energy value was first calculated using Equa-
tion (2).
E
hc
=
 (2)
The energy value calculated from the joule measure-
ment was converted into eV units, and a graph of these
values was drawn using Equations (3), (4) or (5) for each
sample depending on whether the electron transition was
indirect or direct. If the electrons were assumed to make
an indirect transition, Equation (4) was used, and if they
were assumed to be directly transferred, Equation (5)
was used.
eV
hc
/cm=  (3)
(/ eV
hc
cm)
2
=
⎛ ⎝ ⎜ ⎞ ⎠ ⎟   2
(4)
(/ eV
hc
cm) =
⎛ ⎝ ⎜ ⎞ ⎠ ⎟   (5)
From the graph drawn in this way, a tangent is drawn
from the end points where the curve becomes linear, and
the point where these tangent cuts the horizontal axis
gives the optical band gap of the material.
During the study of the coatings, photoactivity exper-
iments were applied in three different ways. First, the
visible light degradation of the methylene blue solution
of the samples was investigated. In the second experi-
ment, rhodamine-B solution was used and the effect of
UV light was also investigated. In the next measurement,
E. OZKAN: COMPARISON OF NITROGEN-DOPED PHOTOCATALYTIC SURFACES SYNTHESIZED BY PVD ...
Materiali in tehnologije / Materials and technology 58 (2024) 6, 775–781 777
Figure 1: Workflow diagram of the process

the degradation of rhodamine-B was investigated in the
samples under sunlight.
Methylene blue (C
16
H
18
ClN
3
S) is a blue liquid, and
the blue colour becomes lighter as its concentration de-
creases in the solution. The solution used had a concen-
tration of 1.4 × 10
5
M. The samples were placed in a spe-
cial test container with a gap of 18 cm under a
fluorescent lamp (Philips TDL 18/54 Daylight) irradiated
with a visible light of 18-Watt power. Seven coated glass
samples and one uncoated glass sample were placed in
the system. 10 mL of methylene blue solution was added
to the samples. The initial absorbance of the solution was
measured with a JASCO V-530 UV/VIS Spectrophoto-
meter.
Rhodamine-B solution, which is more sensitive, was
used to obtain more sensitive data in the studies under
UV light. Rhodamine B is pink in colour and it lightens
as its concentration in the solution decreases. The con-
centration of the solution used was 2 mg/lt.
3 RESULTS
Thermal properties of titanium oxide-based powders
observed with a Perkin Elmer DTA/TG device under an
argon atmosphere at a 100 ml/flow rate are shown in
Figure 2.
Based on the TG/DTA results, annealed TiO
2
coat-
ings’ XRD patterns are given in Figure 3.
Microstructure properties of the coatings were deter-
mined with a Philips Excell 30 S FEG SEM device. Fig-
ure 4 shows SEM photographs of the coatings obtained
with the sol-gel (left) and PVD (right) methods.
Coating thicknesses are given in Table 2.
Table 2: Coating thicknesses
Sample Composition PVD (nm) Sol-gel (nm)
1 TiN 138 380
2 5 0%N 2
–5 0%O
2
141 425
3 2 5%N 2
–7 5%O
2
139 397
4 1 5%N 2 –8 5%O
2 140 551
5 1 0%N 2 –9 0%O
2 139 329
6 5%N 2
–9 5%O
2
141 442
7 Pure TiO 2
140 298
E. OZKAN: COMPARISON OF NITROGEN-DOPED PHOTOCATALYTIC SURFACES SYNTHESIZED BY PVD ...
778 Materiali in tehnologije / Materials and technology 58 (2024) 6, 775–781
Figure 2: DTA/TG curve of the TiO
2
powders
Figure 4: SEM images of the coatings produced with: a) sol-gel and b) PVD
Figure 3: XRD results of unadulterated TiO
2
powders heat treated at
different temperatures

Grain sizes determined with the Sherer method are
given in Table 3.
Table 3: Average grain sizes of the coatings
Sample Composition PVD (nm) Sol-gel (nm)
1 TiN 14.27 31.02
2 5 0%N 2
–5 0%O
2
13.64 28.31
3 2 5%N 2
–7 5%O
2
13.59 24.21
4 1 5%N 2
–8 5%O
2
13.23 23.30
5 1 0%N 2 –9 0%O 2 12.21 22.91
6 5%N 2
–9 5%O
2
12.05 18.13
7 Pure TiO 2
11.79 11,30
Band gap values that occur when the coatings were
passed directly and indirectly are shown in Table 4.
Table 4: Coatings’ band gap values
Sample Composition
Direct PVD
(eV)
Direct-sol-gel
(eV)
1 TiN 2.73 3.29
2 5 0%N 2
–5 0%O
2
2.71 3.21
3 2 5%N 2
–7 5%O
2
2.96 3.30
4 1 5%N 2 –8 5%O 2 2.99 3.34
5 1 0%N 2 –9 0%O 2 2.92 3.33
6 5%N 2
–9 5%O
2
2.85 3.32
7 Pure TiO 2
00
In Table 5, degradation rates of the samples exposed
to sunlight for3hi nrhodamine-B, depending on the
Ti/N ratios are given.
Table 5: Coatings’ band gap values
Sample Composition
Decomposi-
tion (PVD)
Decomposi-
tion (sol-gel)
1 TiN 0.68 0.11
2 5 0%N 2 –5 0%O 2 0.52 0.09
3 2 5%N 2
–7 5%O
2
0.32 0.07
4 1 5%N 2
–8 5%O
2
0.23 0.05
5 1 0%N 2 –9 0%O 2 0.19 0.02
6 5%N 2 –9 5%O 2 0.12 0.01
7 Pure TiO 2
00
Table 6 shows the photoactivity experiment results
obtained with PVD and sol-gel.
Table 6: Photoactive dissociation rates of PVD and sol-gel coatings
Sample Composition
Dissociation
percentage
(PVD)
Dissociation
percentage
(sol-gel)
1 TiN 68.1 11.2
2 5 0%N 2
–5 0%O
2
51.8 8.98
3 2 5%N 2
–7 5%O
2
32.4 7.01
4 1 5%N 2
–8 5%O
2
23.1 4.99
5 1 0%N 2 –9 0%O
2 18.9 1.97
6 5%N 2 –9 5%O
2 11.9 1.11
7 Pure TiO 2
00
AFM images obtained to compare the homogeneities
of coatings produced by sol-gel and PVD are shown in
Figure 5.
4 DISCUSSION
According to the results of the thermogravimetric
analysis, there was weight loss due to the evaporation of
the remaining water from the solution up to 300 °C; de-
composition and combustion of organic components
were also observed. A strong exothermic reaction at a
peak temperature of 400 °C shows the crystallization of
the anatase phase from the amorphous structure. A very
low weight loss after 500 °C reveals that the structure
consists entirely of TiO
2
. It was determined that the low
intensity endothermic peak at the 800 °C range belongs
to the anatase rutile phase transformation reaction.
As a result of the XRD analysis of the samples heat
treated at(400, 500 and 600) °C, it was determined that
all the peaks observed belong to the anatase phase of
TiO
2
(ICDD: 01-089-4921) and the peak intensities in-
creased with increasing heat treatment temperature. In
addition, it was determined that the anatase rutile phase
transformation did not occur under the applied heat treat-
ment conditions.
E. OZKAN: COMPARISON OF NITROGEN-DOPED PHOTOCATALYTIC SURFACES SYNTHESIZED BY PVD ...
Materiali in tehnologije / Materials and technology 58 (2024) 6, 775–781 779
Figure 5: AFM images of the coatings produced by: A) PVD and B) sol-gel

According to the XRD results, it was determined that
only the anatase phase crystallized in all undoped and
doped samples, and the nitrogen addition did not cause
any phase transformation or the formation of a new
phase with the selected doping ratios. In addition, it was
determined that the nitrogen addition reduced the peak
intensities of the anatase phase. The decrease in peak in-
tensities as a result of doping indicates that the degree of
crystallinity decreases due to lattice distortion or stress,
as stated in the literature
24
.
According to the particle size results found with the
Scherrer method, the particle size of the undoped TiO
2
photocatalysts was approximately 13.5 nm. In the litera-
ture, it is mentioned that the anatase phase is more domi-
nant than the rutile phase in structures with particle sizes
below 14 nm.
25
The facts that only the anatase phase is
seen in the structure and that the average particle size
values are below this limit confirm this situation. Nitro-
gen addition was found to increase the particle size.
These particle sizes are consistent with the results from
the literature.
26
The obvious difference between the PVD
and sol-gel methods becomes clear after this stage.
While the particle size and coating thickness can be kept
under control with the PVD method, these values show
variability and unusual differences compared with the
sol-gel method.
UV-Vis spectra obtained by examining the absorption
behaviour of doped and undoped TiO
2
photocatalysts
were evaluated and according to the obtained absorption
spectra, it was determined that N doping shifts the ab-
sorption limit of TiO
2
to higher wavelengths, but signifi-
cantly reduces the absorption amount of TiO
2
photocatalysts in a wavelength range of 300–500 nm.
When the calculated optical band gap energies of the
samples were evaluated, it was determined that N addi-
tions increased the band gap energy, and the highest eV
values were observed in samples with a 50-% N addition.
When the calculated eV values of the thin film samples
were compared, it was observed that the band gap ener-
gies of the powder samples were lower than those of the
thin film samples. In addition, it was determined that the
lowest band gap energy values for both PVD and sol-gel
samples were obtained for undoped samples, and N-dop-
ing increased the band gap energy. When these results
were compared with the literature, it was determined that
the band gap energy of TiO
2
aligned with the literature
values and that non-metallic additives increased the band
gap energy to a degree similar to the one observed in this
study.
27
The photocatalytic activities of thin-film and pow-
dered photocatalysts, used under ultraviolet (UV) and
visible light sources, cause the degradation of methylene
blue and rhodamine-B. Rhodamine-B photocatalytic
degradation is a first-order reaction; its reaction rate (k)
is determined according to Equation (6) where C is the
rhodamine-B concentration, C
0
is the initial concentra-
tion of rhodamine-B, k is the rate constant, and t is the
time.
28
ln
c
c
kt
0
=⋅ (6)
According to the results obtained, it was determined
that the undoped TiO
2
photocatalyst had the highest rate
constant under UV light, while the rhodamine-B solution
without a photocatalyst had the lowest rate constant. It
was determined that the photocatalytic rate constant de-
creased with the nitrogen addition and the 50 %N-TiO
2
sample had the lowest rate constant.
When the photocatalytic activity results were found
for thin films, it was determined that the photocatalytic
activity of the TiO
2
thin film coatings made with PVD
was quite high compared to the thin film coatings made
with sol-gel. When the photocatalytic activity results
were determined in general, it was observed that increas-
ing N-ratio increased the photocatalytic activity. The
high photocatalytic activity values of thin films, attrib-
uted to their large surface area, also align with the calcu-
lated optical band gap energy values and results from the
literature.
29
5 CONCLUSIONS
TiN, Ti-O-N and TiO
2
thin films were applied onto a
quartz glass substrate using the cathodic arc PVD and
sol-gel methods. All coatings made with the sol-gel
method, except for TiN, exhibited an amorphous struc-
ture and the anatase phase, which was formed after heat
treatment; on the contrary, all coatings made with PVD
were detected in the anatase structure.
After the microstructure analysis, it was determined
that the surfaces of the coatings produced with sol-gel
were heterogeneous, and the grains in their microstruc-
tures were larger. The control of the coating thickness
was more difficult, and the process took a long time.
With both methods, the effect of nitrogen on the
photocatalytic activity was clearly observed, and a direct
effect of the grain size on the coating quality was identi-
fied.
In conclusion, it was proven that this coating can be
photoactive under visible light due to nitrogen doping in
TiO
2
, regardless of the method used. It is clear that the
photocatalyst TiO
2
, when activated by visible light, will
have more applications in daily life. In our world, which
has experienced a pandemic such as Covid-19, it finds
wide application in areas requiring high levels of hy-
giene.
Acknowledgement
I would like to thank the ITU Materials Science Lab-
oratory for its support to our project titled “Investigation
of Photocatalytic Activity of Nitrogen Doped TiO
2
Coat-
ings Synthesized by Sol-Gel and PVD Methods”, which
E. OZKAN: COMPARISON OF NITROGEN-DOPED PHOTOCATALYTIC SURFACES SYNTHESIZED BY PVD ...
780 Materiali in tehnologije / Materials and technology 58 (2024) 6, 775–781

was supported within the scope of the R&D Innovation
Support Program.
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