Air pollutants, such as carbon dioxide (CO2), hydrogen cyanide (HCN), and methane (CH4), can harm the respiratory organs of humans and cause several diseases. This study successfully utilized a photocatalyst from TiO2 with Co(NO3) doped to degrade these air pollutants from waste burning. The photocatalyst layer was produced by dissolving TiO2 and Co(NO3)2 in distilled water, and then the solution was coated on a mica surface using a spray coating method. The coated mica was then dried in an oven. The crystallite structure of TiO2/Co(NO3)2 was analyzed by X-ray diffraction. The obtained crystallite size was (15.38 ± 0.03) nm with lattice parameters a and c were (3.8 ± 0.3) Å and (9.3 ± 0.3) Å, respectively, which shows that it is an anatase phase. The band gap energy was measured by diffuse reflectance UV-visible spectroscopy and analyzed using Tauc's plot method. The measured band gap energy of the photocatalyst was 2.81 eV, which can be easily activated by ultraviolet (UV) light. The photocatalyst sheets successfully degraded air pollutants from waste burning, including 53.139\% CO2 for 4 hours, 100\% HCN for 10 minutes, and 72.381\% CH4 for 40 minutes. Therefore, the fabricated photocatalyst in this study can potentially be an alternative to degrading air pollutants, especially CO2, HCN, and CH4.
Keywords:
Photocatalyst TiO2 Co(NO3)2 Air Pollutants UV Light
INTRODUCTION
Fresh air is a very important element for living things. However,
the fresh air issue has recently taken center stage because of air
pollution. Air pollution is a mixture of gases and particles produced
by many sources, such as the smoke of cigarettes, vehicles, industry,
agriculture, combustion, and natural sources
1,2,3.
Several gases widely known as air pollutants include
\mathrm{SO_{2}}SO2,
\mathrm{NOx}NOx,
\mathrm{NH_{3}}NH3,
and \mathrm{CO}CO,
as well as greenhouse gases such as \mathrm{CO_{2}}CO2,
\mathrm{CH_{4}}CH4,
and \mathrm{N_{2}O}N2O4,5. These
pollutants pose significant risks to human health, particularly when
they infiltrate indoor spaces through air vents. Confined within walls
and roofs, these gases are impeded from dispersing naturally with the
wind. Consequently, occupants inhale the pollution readily, leading to
many health issues and compromising the overall comfort of the indoor
environment 6.
Researchers have made various efforts to reduce air pollutants.
Photocatalysis, an environmentally friendly and sustainable technique,
holds great promise for degrading these pollutants
7,8,9.
Photocatalyst is a catalytic process whose success depends on light
absorption capability, active site density, redox capacity, and the
rate of light-triggered electron-hole recombination
10. Titanium dioxide
(\mathrm{TiO_{2}}TiO2)
is one of the most excellent and popular semiconductor photocatalysts,
with good photosensitivity and chemical stability, non-toxicity, and
low cost 11,12.
\mathrm{TiO_{2}}TiO2
has a crystallite size of 19.82 nm
13. This crystal is divided into
three polymorphic forms: rutile, anatase, and brookite
14,15.
\mathrm{TiO_{2}}TiO2
is used exclusively as a white pigment and has been widely used as a
base material for producing sunscreen, photocatalysts, and solar cells
16. However, this
photocatalyst has limited optical and electronic properties that are
active only when exposed to UV light
17, which is only ± 5% of solar energy
18. The band gap energy on
\mathrm{TiO_{2}}TiO2
is about 3.23 eV 19.
Figure 1. The chamber of photocatalyst test. The smoke sample
flows from the burning box to the chamber. UV lamps are used as
light sources.
Modifying the surface of \mathrm{TiO_{2}}TiO2
by incorporating other materials is recognized as an effective
technique to enhance the efficiency of sunlight utilization and
broaden its photocatalytic activity
13. Doping of metal ions (such as
Fe, Co, Ag, Ni) and non-metallic elements (such as C, N, F, S) or
carbon-containing materials (such as carbon nanotubes, flora, and
graphene oxide) can improve the photocatalytic properties of
\mathrm{TiO_{2}}TiO213,17. Among
these materials, Co can effectively enhance the photocatalytic
activity of \mathrm{TiO_{2}}TiO220. When Co is introduced into the
\mathrm{TiO_{2}}TiO2
material, it acts as an impurity within the conduction band, leading
to an electronic transition, namely the band gap transition from the
valence band consisting of O 2p orbitals to the Co 3d and Ti 3d
conduction bands. This intensity indicates that
\mathrm{TiO_{2}}TiO2/Co
has good photocatalytic activity. After electron excitation, the
photogenerated electrons are reserved in the conduction band, which
are further transferred to the surface of catalyst particles to be
captured by \mathrm{O_{2}}O2
molecules adsorbed on the surface. The photogenerated holes in the
valence band are trapped by hydroxyl molecules and water as active
radicals to oxidize organic compounds
20.
Hosseini et al. found that a fabricated photocatalytic mixed matrix
membrane containing Co and \mathrm{TiO_{2}}TiO2
nanoparticles was suitable for the photocatalytic separation of
2,4-dichlorophenol 13. Khaki et
al. also researched Co and \mathrm{TiO_{2}}TiO2,
which resulted in the bandgap energy of the transition metal Co-doped
with \mathrm{TiO_{2}}TiO2
being lower than that of \mathrm{TiO_{2}}TiO2,
which is 2.96 eV 17. In addition to its
utilization in liquid samples, \mathrm{TiO_{2}}TiO2
can also be used in gas samples. Mamaghani et al. carried out
hydrothermal/solvothermal synthesis and processing of
\mathrm{TiO_{2}}TiO2
as an effective photocatalyst for the degradation of air pollutants
21. Therefore,
research on photocatalysts for the degradation of air pollutants is
possible.
In this study, \mathrm{TiO_{2}}TiO2
with a Co-doped photocatalyst was fabricated. To assess the impact of
Co doping on the crystallite structure of
\mathrm{TiO_{2}}TiO2,
X-ray diffraction (XRD) patterns were conducted. Additionally, to
confirm that Co doping reduces the band gap energy of
\mathrm{TiO_{2}}TiO2,
testing was performed using diffuse reflection UV-visible (DR UV-Vis)
spectroscopy. The photocatalyst was tested to degrade the air
pollutants, namely \mathrm{CO_{2}}CO2,
HCN, and \mathrm{CH_{4}}CH4,
from waste burning under UV light irradiation. Gas concentrations were
detected by a gas chromatography thermal conductivity detector
(GC-TCD) and gas chromatography-mass spectroscopy (GC-MS).
MATERIAL AND METHODS
Materials and Instruments
The titanium dioxide (\mathrm{TiO_{2}}TiO2)
(anatase-type) powder is produced by Sigma Aldrich. Cobalt nitrate
powder (\mathrm{Co(NO_{3})2}Co(NO3)2)
was purchased from Nitra Kimia, Indonesia. UV lamp (220V, 50 Hz, 6W)
was used as light sources. X-ray diffraction (Shimadzu XRD-6000) and
diffuse reflectance UV-visible spectroscopy (Shimadzu UV-1700) were
used to characterize the photocatalyst doped. Contaminated smoke is
generated from burned waste such as plastic, paper, cardboard, and
dry leaves. The 5-mL venoject tube was used to collect the smoke
samples. Gas chromatography thermal conductivity detector (GC-TCD,
Shimadzu GC 8A) and gas chromatography-mass spectroscopy (GC-MS,
Shimadzu QP 2010 SE) were utilized to measure the concentration of
the molecules of the samples.
Method and Procedure
The testing chamber in this study was constructed using a
modified hexagonal prismatic glass container with a hole for smoke
and a hole for sample collection. UV lamps were installed inside the
chamber as UV light sources. A fan was installed in one of the holes
to introduce smoke so that the smoke would be attracted and enter
the chamber. An illustration of the photocatalyst fabrication
process and the test chamber are shown in Fig. 1. In this
study, the \mathrm{TiO_{2}}TiO2
photocatalyst was doped with Co derived from
\mathrm{Co(NO_{3})2}Co(NO3)2.
40 mg of \mathrm{TiO_{2}}TiO2
and 10 mg of \mathrm{Co(NO_{3})2}Co(NO3)2
were dissolved in 5 mL of distilled water and stirred with a
stirring speed of 570 rpm for 2 hours at room temperature to produce
a homogenous photocatalyst solution. The solution was then sprayed
on two sheets of mica (13 × 29 cm) coated with aluminum foil for
photocatalyst test under UV light. These sheets aim to cover the
glass in the test room so that UV light does not radiate out. After
spraying on the mica, the solution was dried in a furnace at 90
^\circ∘C
for 1 hour. Then, the mica was mounted on the inner side of the test
chamber.
Figure 2. XRD pattern of \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
photocatalystFigure 3. Absorbance spectrum of \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
The photocatalyst was synthesized in solid phase (powder) for
material characterization and then tested using XRD to determine the
type of crystal. Analysis was carried out with diffraction angles
(2\thetaθ)
in the range of 3^\circ∘C–80^\circ∘C
and scanned continuously at a scan rate of 4 degrees·s-1.
XRD was conditioned at a voltage of 40 kV with a current of 30 mA.
The resulting data are 2\thetaθ
and intensity, then presented in a graph to determine the intensity
peaks. The values calculated in XRD are crystallite size (t) and
lattice parameters (a and c) with the following equations (Eq. 1 and
Eq. 2).
where K is Scherrer constant (0.9),
\lambdaλ
is X-ray wavelength (0.154 nm), \betaβ
is the full width at half the maximum intensity of the reflection
peak, \thetaθ
is diffraction angle, d is the distance between Bragg planes, and
(hkl) is miller index 16.
Photocatalysts synthesized in the solid phase (powder) are also
tested using DR UV-vis spectroscopy to ensure photocatalyst band gap
energy changes after doping with \mathrm{Co(NO_{3})2}Co(NO3)2.
Data acquisition is performed at a wavelength of 200–800 nm every 1
nm. The data results were then analyzed using Tauc’s Plot method,
which is the relationship between absorption coefficient
(\alphaα)
and incident photon energy hf in the form of (Eq. 3):
Figure 4. Tauc’s plot on \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
where \alphaα
is the absorbance coefficient used in the Tauc Plot method, h is the
photon energy (eV), c is a constant, and Eg is the band gap energy.
The value of m depends on the type of transition: m = 1/2 for direct
and permitted transitions, m = 2 for indirect transitions, and m =
3/2 for forbidden transitions
22. OriginLab software was
used to determine the bandgap energy of the photocatalyst.
The photocatalyst test begins by filling the chamber to the brim
with polluted smoke/gas by capturing the combustion exhaust using a
funnel and hose connected to the vent hole in the chamber. The UV
lamp is then turned on. Gas samples were taken with a syringe
directly into a 5 mL venoject tube to preserve the gas. In the first
test to observe the degradation of \mathrm{CO_{2}}CO2,
samples were taken every 2 hours from before the reaction occurred
(t = 0 s) to 6 hours. In the second test to observe the degradation
of HCN and \mathrm{CH_{4}}CH4,
samples were collected every 10 minutes from pre-reaction (t = 0 s)
to 40 minutes.
Gas samples stored in venoject tubes were analyzed by GC-TCD and
GC-MS to determine changes in the \mathrm{CO_{2}}CO2,
HCN, and \mathrm{CH_{4}}CH4
concentrations after the photocatalyst test. The concentration of
the molecules in the gas is indicated by the percentage of the area
of the peaks on the graph produced by the detector. The percentage
of \mathrm{CH_{4}}CH4
and \mathrm{CO_{2}}CO2
degradation is calculated using the following equation (see Eq.
4).
where Ct is the concentration of the molecule at time t, and
\mathrm{C_0}C0
is the initial concentration of the molecule
13
RESULTS AND DISCUSSION
Crystral Size Analysis of \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
Photocatalyst
The crystal structure of the photocatalyst layer used in this
study was analyzed using an X-ray diffractometer (XDR). The data
obtained was further analyzed using OriginLab software to determine
the diffraction peaks. The peaks are the scattering of light hitting
the \mathrm{TiO_{2}}TiO2/Co
crystal, which interferes constructively. The XRD patterns of
\mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
photocatalyst is shown in Fig 2.
Based on Fig. 2, diffraction peaks indicate that X-rays
hit the crystal plane. Four diffraction peaks are visible on the
\mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
, namely at 2\thetaθ
of 22.526^\circ∘C,
25.013^\circ∘C,
37.552^\circ∘C,
and 47.761^\circ∘C.
These diffraction peaks were compared with the
\mathrm{TiO_{2}}TiO2
standard diffractogram from the Joint Committee on Powder
Diffraction Standars-International Center for Diffraction Data
(JCPDS-ICDD) No. 21–1272. The first peak did not find its Miller
index from these data, so further analysis could not be performed.
Meanwhile, the Miller indices at 2\thetaθ
of 25.013^\circ∘C,
37.552^\circ∘C,
and 47.761^\circ∘C
are (101), (004), and (200), respectively. The results of this
crystal field analysis indicate that the detected material is
anatase-type \mathrm{TiO_{2}}TiO214,15,19.
The highest diffraction peak of the \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
photocatalyst is located at 2\thetaθ
of 25.013^\circ∘C
with plane (101). The peak appears due to the effect of the addition
of \mathrm{Co(NO_{3})2}Co(NO3)2
on \mathrm{TiO_{2}}TiO2,
which then characterizes the material we produce. Through the
calculations in Eq. 1 and Eq. 2, the values in Table 1 are
obtained.
Table 1.
a
c
± 0.03
± 0.3
± 0.3
Figure 5. Percentage degradation of
\mathrm{CO_{2}}CO2
pollutant of waste burning using \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
photocatalyst under UV light irradiation Figure 6. Percentage degradation of
\mathrm{CH_{4}}CH4
and HCN pollutants from waste burning using
\mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
photocatalyst under UV irradiation
Based on the calculations performed, the crystallite size of the
\mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
is (15.38 ± 0.03) nm. The crystallite size is smaller than pure
\mathrm{TiO_{2}}TiO2,
which is 19.82 nm 13. Co ions in
the lattice seem to form a complex with oxygen on
\mathrm{TiO_{2}}TiO2,
thus suppressing the growth of \mathrm{TiO_{2}}TiO2
crystals 13. This small
crystallite size makes the surface of the material high, allowing
the crystals to be evenly distributed. Meanwhile, the obtained
lattice parameters (a and c) belong to anatase type
\mathrm{TiO_{2}}TiO215. Although the value is different, it is
still within the calculation error range. Small differences from the
calculation with the reference (a = 3.784 and c = 9.515
15,23) result from the
addition of \mathrm{Co(NO_{3})2}Co(NO3)2
on \mathrm{TiO_{2}}TiO2.
This indicates that the doping used does not significantly change
the crystal structure of \mathrm{TiO_{2}}TiO2.
Therefore, \mathrm{Co(NO_{3})2}Co(NO3)2
doping does not inhibit the catalytic function of
\mathrm{TiO_{2}}TiO2.
Band Gap Energy of \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
Photocatalyst
The band gap energy of \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
photocatalyst was analyzed using DR UV-vis spectroscopy in a
wavelength range of 200–800 nm. The increasing absorbance value
indicates that the intensity of the absorbed light is becoming
greater, resulting in many free electrons that will fill the
conduction band and produce an electric current. The absorbance of
\mathrm{TiO_{2}}TiO2
and \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
is shown in Fig. 3.
From the absorbance spectra, it can be seen that the highest
absorbance on \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
occurs when exposed to a wavelength of 283 nm, then drops and rises
again at 363 nm, then drops dramatically and rises slowly to peak at
583 nm (see Fig. 3). When compared with the absorption
spectrum of pure \mathrm{TiO_{2}}TiO224, there are differences in the
wavelength of maximum absorption. In pure
\mathrm{TiO_{2}}TiO2,
there is only one maximum absorbance peak at a wavelength of 302 nm
24. The difference in absorbance
spectra was believed to be an impact of the addition of
\mathrm{Co(NO_{3})2}Co(NO3)2
and affects the photocatalyst’s ability to absorb light. The value
of the band gap energy is very important because it affects the
ability of the material to form electrons and holes. This energy
determines how much photon energy is required to activate the
photocatalytic process. The lower the band gap energy of a material,
the lower the photon energy required to initiate photocatalysis. The
band gap energy of the materials used in this study was calculated
using Tauc’s Plot method. The data obtained from the DR UV-vis
spectroscopy was processed in OriginLab software to obtain a graph
absorption coefficient (\alphaα
vs the photon energy (hf). Then, extrapolation was performed in the
region of the curve that increased sharply, as shown in Fig
4.2
vs the photon energy (hf). Then, extrapolation was performed in the
region of the curve that increased sharply, as shown in Fig
[FIGREF:4].
Table 2.
Time (hours)
Retention time (min)
Area (%)
Compound name
Degradation (%)
CO2
CO2
CO2
CO2
Table 3.
Time (min)
Retention time (min)
Area (%)
Similarity Index
Compound name
Degradation (%)
HCN
CH4-D4
-
-
-
HCN
CH4
-
-
-
HCN
-
-
-
CH4
-
-
-
HCN
CH4
The red line in Fig. 4 is an extrapolation line made
using Tauc’s plot method, which shows the material’s band gap. The
band gap energy of \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
was obtained from the extrapolation line, which is 2.81 eV. The
anatase band gap energy of \mathrm{TiO_{2}}TiO2,
which was initially 3.2 eV 19,
becomes smaller after adding \mathrm{Co(NO_{3})2}Co(NO3)2.
The reduction in band gap energy, attributed to the presence of Co
as a transition metal, induces the formation of an impurity state
between the conduction band and the valence band in
\mathrm{TiO_{2}}TiO2.
As the band gap is smaller due to the incorporation of Co into the
\mathrm{TiO_{2}}TiO2
lattice, the absorption edge shifts towards longer wavelengths
(redshift). In this investigation, to surpass the band gap energy of
2.81 eV, light with a wavelength of 441.52 nm was necessary to
activate the photocatalyst.
The Mechanism Of Degradation Of
\mathrm{CO_{2}}CO2
and \mathrm{CH_{4}}CH4
Air Pollutants with \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
Photocatalyst
The degradation process of air pollutants can be carried out by
the photocatalytic process on \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2.
Photocatalyst materials typically exist in semiconductors, capable
of initiating chemical reactions upon exposure to photon energy
surpassing the band gap energy. Initially,
\mathrm{TiO_{2}}TiO2
has a band gap energy of 3.2 eV 19.
However, after adding \mathrm{Co(NO_{3})2}Co(NO3)2,
the band gap energy becomes 2.81 eV due to
\mathrm{Co^2+}Co2+
replacing \mathrm{Ti^4+}Ti4+
in the \mathrm{TiO_{2}}TiO2
crystal structure. The size of \mathrm{Co^2+}Co2+
ions (radius 0.074 nm) is almost similar to
\mathrm{Ti^4+}Ti4+
(radius 0.068 nm), allowing them to enter the
\mathrm{TiO_{2}}TiO2
crystal to decrease the band gap and increase the activity of the
photocatalyst 13.
Photons with energy greater than 2.81 eV, such as UV light, can
cause electronic transitions from the valence band to the conduction
band. Electrons in the O 2p orbitals in the valence band are excited
to the Co 3d and Ti 3d orbitals in the minimum conduction band. The
presence of valence band electrons creates holes (hvb+)
due to electron donors. Meanwhile, the conduction band produces
electrons (ecb-) as electron acceptors. This process is
where the decomposition begins. The holes will interact with the
water molecules in the air, while the electrons will interact with
the oxygen in the air. The reaction of electrons and holes with
oxygen and water produces hydroxyl radicals, which can break down
organic polymers such as \mathrm{CH_{4}}CH4.
On the other hand, \mathrm{CO_{2}}CO2
can be degraded due to adsorption by the photocatalyst layer but
cannot be chemically decomposed. The chemical reaction that occurs
is as follows 25.
Degradation Of Air Pollutants With Photocatalysts Under Ultraviolet Light Irradiation
The first energy source used is ultraviolet light
(\lambdaλ
< 400 nm), which has energy greater than 2.81 eV, the bandgap
energy of \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
photocatalyst. This energy can activate the photocatalytic process
on the photocatalyst layer. In the first observation (i.e.,
degradation of \mathrm{CO_{2}}CO2),
time variations of 0, 2, 4, and 6 hours were used (see Table
2). GC-TCD detected the concentration of the
\mathrm{CO_{2}}CO2.
The GC-TCD instrument can only make semi-quantitative measurements,
which is the amount of molecular concentration expressed in the
percentage range based on the compound’s retention time. Retention
time is the required time for the analyte to be injected until the
detector captures the signal in the form of a peak plot generated by
the instrument. The peaks of the graph have an area whose percentage
represents the concentration of the compounds detected in the gas
being analyzed. The degradation percentage is calculated using Eq. 4
based on these concentrations.
The calculation result shows increased
\mathrm{CO_{2}}CO2
degradation at 2 and 4 hours (see Fig. 5). The increase in
the degradation percentage with the irradiation time is caused by
the number of electrons excited from the valence band to the
conduction band to produce free electrons on the surface of the
photocatalyst layer, which interacts with
\mathrm{CO_{2}}CO2
in the air. The ability of the photocatalyst to degrade
\mathrm{CO_{2}}CO2
pollutants reaches a maximum of 53.14% for 4 hours (see Table
2). However, the percentage decreased drastically to 10.84%
at 6 hours, and there was a possibility of the photocatalyst
experiencing saturation, so its degradation ability decreased.
Saturation may occur because \mathrm{CO_{2}}CO2
previously adsorbed on the photocatalyst’s surface blocks the
photocatalytic process. Another possibility is that
\mathrm{CO_{2}}CO2
is desorbed, increasing the measured concentration.
Furthermore, the degradation ability of the
\mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
photocatalyst under UV light irradiation was observed with time
variations of 0, 10, 20, 30, and 40 minutes using GC-MS to observe
the degradation of HCN and \mathrm{CH_{4}}CH4.
Similar to GC-TCD, GC-MS can only make semiquantitative measurements
by area percentage. GC-MS uses the similarity index (the degree of
similarity of the detector data to the instrument’s reference) to
determine which molecules are detected in the peaks of the graph
produced by the detector.
In the second observation (i.e., degradation of HCN and
\mathrm{CH_{4}}CH4
under UV light), Table 3 shows no HCN and
\mathrm{CH_{4}}CH4
molecules initially (t = 0 s). After the photocatalyst was activated
with UV light energy, the HCN molecule no longer appeared during the
observation. The phenomenon shows that the photocatalyst can degrade
HCN within 10 minutes (see Fig. 6). Meanwhile, the
\mathrm{CH_{4}}CH4
molecule experienced a degradation of 60.95% in the first 10 minutes
and an increase in the percentage of degradation to 100% in the
first 20 minutes. However, the \mathrm{CH_{4}}CH4
molecule suddenly reappeared in 40 minutes with a degraded
percentage of 72.38%. This phenomenon is possibly due to the
photocatalyst experiencing saturation, which decreases the
photocatalyst’s ability to degrade.
CONCLUSION
The doping of \mathrm{Co(NO_{3})2}Co(NO3)2
onto the \mathrm{TiO_{2}}TiO2
photocatalyst was successfully carried out. The crystallite size of
the photocatalyst after doping is (15.38 ± 0.03) nm, while the lattice
parameters a and c are (3.8 ± 0.3) Å and (9.3 ± 0.3) Å, respectively.
These results indicate that Co doping does not change the crystal
structure of \mathrm{TiO_{2}}TiO2,
namely the anatase phase. Furthermore, the band gap energy decreased
after doping to 2.81 eV, which UV light can easily transmit. As a
result, the \mathrm{TiO_{2}}TiO2/\mathrm{Co(NO_{3})2}Co(NO3)2
photocatalyst successfully degraded \mathrm{CO_{2}}CO2
gas pollutants by 53.139% for 4 hours, HCN by 100% for 10 minutes, and
\mathrm{CH_{4}}CH4
by 72.381% for 40 minutes under UV light irradiation.
Acknowledgments
Kamila Munna acknowledges an undergraduate scholarship from the
Ministry of Education, Culture, Research, and Technology of the
Republic of Indonesia through the Bidikmisi program and a master
scholarship from the Ministry of Finance through the Indonesian
Endowment Fund for Education (LPDP). Rizky Aflaha acknowledges a Ph.D.
scholarship from the Ministry of Education, Culture, Research, and
Technology of the Republic of Indonesia through the PMDSU program. The
authors thank Mr. Dhe, Eka Dwi Lestari, and Nurul Imani Istiqamah, who
helped greatly in the Materials Physics Laboratory at Gadjah Mada
University.
References
1.
Zhang Junfeng (Jim), Smith Kirk R Indoor air pollution: a global health concern. British Medical Bulletin 68 ( 1 ) 209 – 225 ( 2003 ).
Lin Chia-Ching, Chiu Chien-Chih, Lee Po-Yen, Chen Kuo-Jen, He Chen-Xi, Hsu Sheng-Kai, Cheng Kai-Chun The Adverse Effects of Air Pollution on the Eye: A Review. International Journal of Environmental Research and Public Health 19 ( 3 ) 1186 ( 2022 ).
Gumtorntip Wanitcha, Kasitanon Nuntana, Louthrenoo Worawit, Chattipakorn Nipon, Chattipakorn Siriporn C. Potential roles of air pollutants on the induction and aggravation of rheumatoid arthritis: From cell to bedside studies. Environmental Pollution 334 122181 ( 2023 ).
Tran Vinh Van, Park Duckshin, Lee Young-Chul Indoor Air Pollution, Related Human Diseases, and Recent Trends in the Control and Improvement of Indoor Air Quality. International Journal of Environmental Research and Public Health 17 ( 8 ) 2927 ( 2020 ).
He Fei, Jeon Woojung, Choi Wonyong Photocatalytic air purification mimicking the self-cleaning process of the atmosphere. Nature Communications 12 ( 1 ) 2528 ( 2021 ).
Kristyawan I P A, Indra A, Suradharmika I G A, Setiaji G, Putri N C, Oka I W The effect of adding photocatalyst ceramics on reducing particulate matter in indoor air purification systems. IOP Conference Series: Earth and Environmental Science 1108 ( 1 ) 012008 ( 2022 ).
Chen Ruimin, Li Jieyuan, Wang Hong, Chen Peng, Dong Xing'an, Sun Yanjuan, Zhou Ying, Dong Fan Photocatalytic reaction mechanisms at a gas–solid interface for typical air pollutant decomposition. Journal of Materials Chemistry A 9 ( 36 ) 20184 – 20210 ( 2021 ).
Ahmad Irshad, Zou Yanhong, Yan Jiaying, Liu Yuyu, Shukrullah Shazia, Naz Muhammad Yasin, Hussain Humaira, Khan Waheed Qamar, Khalid N.R. Semiconductor photocatalysts: A critical review highlighting the various strategies to boost the photocatalytic performances for diverse applications. Advances in Colloid and Interface Science 311 102830 ( 2023 ).
Armaković Sanja J., Savanović Maria M., Armaković Stevan Titanium Dioxide as the Most Used Photocatalyst for Water Purification: An Overview. Catalysts 13 ( 1 ) 26 ( 2022 ).
Khaki Mohammad Reza Delsouz, Shafeeyan Mohammad Saleh, Raman Abdul Aziz Abdul, Daud Wan Mohd Ashri Wan Application of doped photocatalysts for organic pollutant degradation - A review. Journal of Environmental Management 198 78 – 94 ( 2017 ).
Lee Heon, Park Young-Kwon, Kim Sun-Jae, Kim Byung-Hoon, Jung Sang-Chul Titanium dioxide modification with cobalt oxide nanoparticles for photocatalysis. Journal of Industrial and Engineering Chemistry 32 259 – 263 ( 2015 ).
Na-Phattalung Sutassana, Harding David J., Pattanasattayavong Pichaya, Kim Heungsik, Lee Jihye, Hwang Dae-Woong, Chung Taek Dong, Yu Jaejun Band gap narrowing of TiO2 nanoparticles: A passivated Co-doping approach for enhanced photocatalytic activity. Journal of Physics and Chemistry of Solids 162 110503 ( 2022 ).
Mamaghani Alireza Haghighat, Haghighat Fariborz, Lee Chang-Seo Hydrothermal/solvothermal synthesis and treatment of TiO2 for photocatalytic degradation of air pollutants: Preparation, characterization, properties, and performance. Chemosphere 219 804 – 825 ( 2019 ).
Fonseca-Cervantes Omar Ricardo, Pérez-Larios Alejandro, Romero Arellano Víctor Hugo, Sulbaran-Rangel Belkis, Guzmán González Carlos Alberto Effects in Band Gap for Photocatalysis in TiO2 Support by Adding Gold and Ruthenium. Processes 8 ( 9 ) 1032 ( 2020 ).
Nasikhudin, Diantoro M, Kusumaatmaja A, Triyana K Study on Photocatalytic Properties of TiO $_{\textrm2}$ Nanoparticle in various pH condition. Journal of Physics: Conference Series 1011 012069 ( 2018 ).
