Size-controlled synthesis of porous ZnSnO3nanocubes for improving formaldehyde gas sensitivity

Article abstract of DOI:10.1039/d1ra01852c

During the detection of formaldehyde, sensitivity and selectivity is still a challenging issue for most reported gas sensors. Herein, an alternative formaldehyde chemosensor that is based on porous ZnSnO₃nanocubes was synthesized. The products are characterized by XRD, SEM, TEM (HRTEM), XPS, PL measurements and N₂adsorption-desorption. The size of the ZnSnO₃nanocubes is about 100 nm and the corresponding specific surface area is 70.001 m²g^?1. A gas sensor based on these porous ZnSnO₃nanocubes shows high sensitivity and selectivity to formaldehyde. The porous ZnSnO₃nanocube sensor could detect 50 ppm formaldehyde at about 210 °C with a response value of 21.2, which is twice as much as ethanol, and 3 times that of the other five gases. Moreover, the response of the sensor had an acceptable change after a pulse test for 90 days. The sensor can detect formaldehyde with a minimum concentration of 1 ppm, and it has a good linear relationship between 1-50 ppm formaldehyde. The gas sensor based on porous ZnSnO₃nanocubes can be utilized as a promising candidate for a practical detector of formaldehyde due to its high gas response and excellent selectivity.

Full text of DOI:10.1039/d1ra01852c

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Size-controlled synthesis of porous ZnSnO3
nanocubes for improving formaldehyde gas
sensitivity
Cite this: RSC Adv., 2021, 11, 20268
a
c
Jiaoling Zheng,†a Huanhuan Hou,†ab Hao Fu,cd Liping Gao
*
*
and Hongjie Liu
During the detection of formaldehyde, sensitivity and selectivity is still a challenging issue for most reported
gas sensors. Herein, an alternative formaldehyde chemosensor that is based on porous ZnSnO3 nanocubes
was synthesized. The products are characterized by XRD, SEM, TEM (HRTEM), XPS, PL measurements and N2
adsorption–desorption. The size of the ZnSnO3 nanocubes is about 100 nm and the corresponding specific
surface area is 70.001 m2 gꢀ1. A gas sensor based on these porous ZnSnO3 nanocubes shows high sensitivity
and selectivity to formaldehyde. The porous ZnSnO3 nanocube sensor could detect 50 ppm formaldehyde
at about 210 ꢁC with a response value of 21.2, which is twice as much as ethanol, and 3 times that of the
other five gases. Moreover, the response of the sensor had an acceptable change after a pulse test for
90 days. The sensor can detect formaldehyde with a minimum concentration of 1 ppm, and it has
a good linear relationship between 1–50 ppm formaldehyde. The gas sensor based on porous ZnSnO3
nanocubes can be utilized as a promising candidate for a practical detector of formaldehyde due to its
high gas response and excellent selectivity.
Received 9th March 2021
Accepted 7th May 2021
DOI: 10.1039/d1ra01852c
rsc.li/rsc-advances
formaldehyde detection methods, including spectroscopy,6
uorescence,7 polarography,8 chromatography,9 semiconductor
gas sensors10 etc. Among these tested methods, semiconductor
gas sensors have attracted great attention due to their conve-
nient portability, low power consumption, high sensitivity and
good selectivity.
1. Introduction
VOC pollutants, such as ethanol, ammonia, acetone, formal-
dehyde and benzene etc., have attracted extensive attention due
to their toxicity to humans and atmospheric pollution.1,2 The
most concerning among VOCs is formaldehyde due to its car-
cinogenicity, according to the World Health Organization
(WHO), and it is the main pollutant resulting from home
decoration.3 The Standardization Administration of the
People’s Republic of China has regulated the indoor permis-
sible release with a limit of 0.1 ppm,4 and the American
Conference of Governmental Industrial Hygienists (ACGIH) has
recommended a threshold limit value of 0.1 ppm for formal-
dehyde.5 Long term exposure to formaldehyde can cause serious
damage to human sensory organs, and can even lead to cancer.4
Therefore, real-time and effective formaldehyde monitoring
methods are needed to prevent it from exceeding the threshold
for danger and thereby affecting human health and causing
environmental pollution. There are many common
Sensitive materials are the core components of semi-
conductor gas sensors. Traditional semiconductor sensing
materials include ZnO,11 SnO2,12 In2O3,13 WO3,14 etc. However,
a single component usually cannot fulll all of the require-
ments such as high response and selectivity, low operation
temperature and good stability.15 Therefore, more and more
researchers have committed to developing multi-component
materials. As a famous multifunctional material, zinc stan-
nate (ZnSnO3) has attracted considerable attention due to its
potential applications in the elds of photocatalysis,16 gas
sensing,17–20 Li-ion batteries,21etc. In recent years, the gas-
sensing properties of ZnSnO3 with different morphologies
have been studied, such as cubic ZnSnO3,22,23ZnSnO3 nano-
spheres,24,25 ZnSnO3 nanorods,26 etc. Among these structural
materials, porous materials have attracted great attention due
to the improvement of the gas sensitivity of the materials. The
inherent reason is that porous structures have large specic
surface areas and more reaction sites,27,28 which are benecial
for gas diffusion and mass transport,29,30 promoting oxygen
adsorption, and thereby enhancing the gas response of the
materials. For example, the porous NiO nanotetrahedra
prepared by Fu et al. showed excellent gas-sensing performance
toward formaldehyde.31 A hierarchical porous LaFeO3 material
aSchool of Materials and Chemical Engineering, Chuzhou University, Chuzhou,
239000, China. E-mail: gaozhangping@163.com
bSchool of Chemistry and Chemical Engineering, Anhui University of Technology,
Ma’anshan, 243000, China
cDepartment of Science and Technology, Shiyuan College of Nanning Normal
University, Nanning, 530226, China. E-mail: hongjieliu2008@163.com
dSchool of Chemistry & Chemical Engineering, Guangxi University, Nanning, 530004,
China
† These authors contributed equally to this work.
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was prepared via a low-cost and simple method, which could Field-emission scanning electron microscopy (FESEM) (Hitachi
detect 50 ppb formaldehyde.32 3D ordered porous SnO2 with SU5000, Japan) and transmission electron microscopy (TEM)
a controllable pore diameter was used with enhanced formal- (FEI Tecnai G2 f20 twin, 200 kV) were used to characterize the
dehyde sensing performance.33 Therefore, it is a feasible and morphologies of the materials. The decomposition process of
good approach to synthesize a porous ZnSnO3 material to detect the precursors was investigated using a SDT-Q600 thermal
formaldehyde gas.
analyzer with a heating rate of 10 ꢁC minꢀ1 under N2 atmo-
In this work, porous ZnSnO3 nanocubes were synthesized by sphere. The nitrogen (N2) adsorption–desorption study was
a facile, template-free hydrothermal method combined with conducted using a Gemini V2380. Brunauer–Emmett–Teller
subsequent calcination. The size of the porous ZnSnO3 nano- (BET) measurements were used to determine the specic
cubes is 100 nm and the material has a large specic surface surface area and pore volume. Room temperature PL
area of 70.001 m2 gꢀ1. The as-prepared porous ZnSnO3 nano- measurements were performed on a steady state and transient
cube sensor shows excellent gas-sensing properties toward state uorescence spectrometer (HORIBA TCSPC FluoroLog-3,
formaldehyde gas. The sensor exhibits a high response (21.2) to USA). Elemental and solid surface analyses of the material
50 ppm of formaldehyde at 210 ꢁC and good selectivity, making were performed using X-ray photoelectron spectroscopy (XPS)
it a promising candidate for a practical detector of formalde- (Thermo Scientic ESCALAB 250Xi, Al Ka X-ray
hyde gas.
monochromator).
2.3. Gas response test
2. Experimental section
The experimental equipment used for the various VOC gas tests
in the manuscript is consistent with that of our previous
report.34 First of all, the sample and adhesive were fully ground
in an agate mortar to form a gas sensing paste. The paste was
then coated on the alumina ceramic tube, on which was loaded
two Au electrodes and four Pt wires. Aer drying for 15 min
under IR radiation, the alumina ceramic tube was sintered at
500 ꢁC for 2 h, and then welded to the pedestal. Finally, the
sensor was aged at 250 ꢁC for 7 days to increase its stability. The
gas sensing properties were measured using a WS-30A system
(Wei Sheng Instruments Co., Zhengzhou, China) under labo-
ratory conditions. The relative humidity of the test was about
50%. The circuit voltage (Vc) was set at 5 V, and the output
voltage (Vout) was set as the terminal voltage of the load resistor
(RL). The gas response of the sensor in this paper was dened as
S ¼ Ra/Rg (reducing gases) or S ¼ Rg/Ra (oxidizing gases). The
response or recovery time was expressed as the time taken for
the sensor output to reach 90% of its saturation aer applying
or switching off the gas in a step function.
All of the reagents (analytical-grade purity) were purchased from
the Shanghai Chemical Reagent Co. Ltd. (Shanghai, China) and
were used without further purication. Deionized water was
used throughout the experiments.
2.1. Material synthesis
A typical synthesis procedure of the porous ZnSnO3 cubes was
as follows: 1.0518 g of tin tetrachloride pentahydrate (SnCl4-
$5H2O) and 0.6659 g of zinc acetate (Zn(AC)2$2H2O) were dis-
solved in 20 mL of deionized water under vigorous stirring at
room temperature, followed by the addition of 3 M NaOH
aqueous solution. Then, the solution was transferred into
a Teon-lined stainless-steel autoclave with a capacity of 80 mL
ꢁ
and maintained at 160 C for 2 h. Aer cooling down to room
temperature, the white precipitate was ltered, washed with
distilled water and alcohol 4 times to remove the ions possibly
remaining in the nal product, and then dried in air at 60 ꢁC for
12 h. Finally, the as-obtained precipitate was calcined at 500 ꢁC
with heating rate of 2 ꢁC minꢀ1 in a muffle furnace for 2 h. The
synthesis process of the nanocubes is shown in Fig. 1.
2.2. Material characterization
Powder X-ray diffraction measurements were performed with
a Bruker D8 ADVANCE X-ray diffractometer in a scanning range
of 10–70ꢁ (2q) at a rate of 0.03ꢁ (2q) per s with Cu Ka radiation.
Fig. 2 XRD patterns of the ZnSn(OH)6 precursor (a) and porous
Fig. 1 The synthesis process of the ZnSnO3 nanocubes.
ZnSnO3 nanocubes (b).
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peak can be observed, which is related to amorphous ZnSnO3.
Through careful observation of the ZnSn(OH)6 precursor
(Fig. 2a), an impurity peak can be seen near the (220) crystal
plane, which may due to the decomposition of the precursor
under hydrothermal conditions (high temperature and high
pressure), which will be further conrmed by TG analysis.
TG analysis was carried out to examine the conversion
process of the precursors during calcination. Fig. 3 shows the
TG anaꢁlysis of the precursor. The weight loss of 7.75% from 40
to 160 C is attributed to the removal of the existing adsorbed
water in the precursor. It can be seen from the TG curve that
there is a weight loss of 12.2% at high temperatures (160–500
ꢁC), which is attributed to the removal of hydroxyl to generate
zinc stannate and water. When the temperature reaches 500 ꢁC,
the thermogravimetric curve levels off, showing that the zinc
stannate product has been completely achieved. The rate of
weight loss is 12.2%, which is less than theoretical value
3. Results and discussion
3.1. Material characterization
Fig. 2 shows the XRD patterns of the ZnSn(OH)6 precursor
(Fig. 2a) and porous ZnSnO3 nanocubes calcined at 500 ꢁC
(Fig. 2b). From Fig. 2a, the peaks in the XRD pattern can be
indexed to the cubic phase of ZnSn(OH)6 (JCPDS no. 74-
1825),which is consistent with the literature reports.35 The
strong intensity of the crystallization peaks indicates the good
crystallinity of the material. As shown in Fig. 2b, only one broad
(18.88%). The reason is that part of the ZnSn(OH)
has
6
decomposed into ZnSnO3 under the hydrothermal process,
which is consistent with the XRD analysis.
The morphology and micro-structure are observed using
scanning electronic microscopy (SEM) and transmission elec-
tron microscopy (TEM), respectively. From Fig. 4a, it can be seen
that the products are uniform nanocubes. Meanwhile, the cor-
responding element mapping images of ZnSnO3 are shown in
Fig. 4b, demonstrating that the Zn, Sn and O elements are well
distributed homogenously throughout the whole area. The TEM
image (Fig. 4c) shows that the products have porous structures,
Fig. 3 TG curve of the ZnSn(OH)6 precursor.
Fig. 4 (a) SEM images and (b) SEM-EDS mapping of the porous ZnSnO3 nanocubes; (c) TEM and (d) SAED images of the porous ZnSnO3
nanocubes.
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Fig. 5 XPS spectra of the ZnSnO3 hollow microspheres: (a) survey spectrum, (b) Zn region, (c) Sn region and (d) O region.
which are assembled from tiny nanocrystals. Thermal decom- 284.8 eV. Fig. 5a shows the survey XPS spectrum of the porous
position of the precursor in air at a high temperature yields ZnSnO3 nanocubes. This clearly reveals that the obtained
porous ZnSnO3 cubes, which is due to the alkaline (NaOH) product contains Zn, Sn and O elements, as well as C contam-
etching and the release of H2O.36 It can be seen from Fig. 4d that ination. The two peaks (Fig. 5b) at 1022.03 eV and 1044.83 eV
the diffraction ring is a dispersion ring, which proves that the are attributed to Zn 2p3/2 and Zn 2p1/2 for the Zn2+ state,
material is an amorphous structure, corresponding with the respectively. As shown in Fig. 5c, the peaks located at 486.58 eV
XRD analysis. Due to the ultrane size and disordered distri- and 495.03 eV correspond to Sn 3d5/2 and Sn 3d3/2 for the Sn4+
bution of the ZnSnO3 nanocrystals, from a macro perspective, state, respectively. The peak centered at ꢂ530.1 eV belongs to O
the assembled ZnSnO3 cores behave similarly to an amorphous 1s. From the XPS-peak-differentiating analysis, we could clearly
material and are therefore considered amorphous structures, see that there are two separate peaks; one peak at 530.34 eV is
which are more effective than large crystals in overcoming determined to be from the lattice oxygen (OL), while the other
electrochemical and mechanical degradation.37–39
Surface sensitive X-ray photoelectron spectroscopy (XPS) was (Ov) (Fig. 5d).
one located at ꢂ531.45 eV is attributed to the oxygen vacancies
conducted to elucidate the chemical composition of the porous
The ZnSnO3 nanocubes exhibit a porous structure and it is
ZnSnO3 nanocubes and the chemical states of Sn, Zn and O in therefore interesting to study the surface area and the pore size
ZnSnO3. The binding energies obtained from the XPS spectra of these nanocubes. Fig. 6a shows a typical N2 adsorption and
were calibrated with reference to the signal from C 1s at desorption isotherm for the porous ZnSnO3 nanocubes. The N2
Fig. 6 N2 adsorption–desorption curves (a) and corresponding pore size distribution curve (b) of the porous ZnSnO3 nanocubes.
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Fig. 7 shows the PL spectrum of the prepared porous ZnSnO3
nanocubes. The PL spectrum of the porous ZnSnO3 nanocubes
displays a near-band-edge excitonic emission ranging between
360 and 480 nm which is similar to that reported in the litera-
ture.40 The blue–green light luminescence from the as synthe-
sized porous ZnSnO3 nanocubes can be attributed to the
oxygen-related defects that have been introduced during
growth. The emission peak at 394 nm is believed to be due to
the oxygen vacancies which can combine with the holes of the
++
41
valence band to form VO
.
The emission peak at 437 nm is
attributed to the Sn interstitials.42,43 The emission at 446 nm is
attributed to the transition from shallow donors (oxygen
vacancies) to the valence band.43,44 The existence of oxygen
vacancies promotes the formation of adsorbed oxygen,45 which
in turn promotes the reaction of the gas and the adsorbed
oxygen, and ultimately improves the sensitivity of the sensor.
Fig. 7 Photoluminescence spectrum of the ZnSnO3 nanocubes at
room temperature, lex ¼ 325 nm.
3.2. Gas-sensing performance
sorption isotherm of the porous ZnSnO3 nanocubes can be
During gas testing, the operation temperature is a very impor-
tant factor. Changes in the operating temperature could inu-
ence the reaction kinetics of the gas molecules and oxygen
adsorbed on the material’s surface.46 The relationship between
the response and the operating temperature of the sintered
sensor was investigated, and is shown in Fig. 8a. The results
showed that the response of the sensor increases at rst and
then decreases with the change of working temperature in the
temperature range from 130 to 400 ꢁC. At a lower temperature,
the oxygen adsorption rate is greater than the desorption rate.
With the increase of temperature, the molecular weight of
categorized as type IV based on IUPAC classication. The BET
surface area of the product was calculated to be 70.001 m2 gꢀ1
.
The corresponding BJH pore size distribution plot (Fig. 6b) of
the porous ZnSnO3 nanocubes shows that the average pore size
of this sample is around 3.4 nm, which corresponds with the
TEM in Fig. 4c. The results show that the ZnSnO3 nanocubes
have a large specic surface area and abundant interface/
microporous structures. A porous structure is conducive to
the rapid diffusion of the gas, thereby, improving the gas-
sensing properties of porous materials.34
Fig. 8 (a) Sensitivity of the porous ZnSnO3 nanocube sensor to 50 ppm formaldehyde under different test temperatures; (b) response–recovery
curve of the porous ZnSnO3 nanocube sensor to 50 ppm formaldehyde at 210 ꢁC; (c) typical dynamic response–recovery curve of the porous
ZnSnO3 nanocube sensor to 1–200 ppm formaldehyde. The inset shows the curve of the sensor resistance to 1–200 ppm formaldehyde; (d) the
response value curve of the porous ZnSnO3 nanocube sensor to 1–200 ppm formaldehyde.
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oxygen adsorbed on the surface of the gas-sensing material relationship between the sensor response and the formalde-
increases, and the sensitivity of the gas-sensing material hyde concentration, while at higher concentrations (>50 ppm)
increases. At a higher temperature, the oxygen adsorption rate the surface coverage tends to saturate and hence leads to
is weaker than the desorption rate, and the adsorbed oxygen a saturation of the response. Under the operating temperature
molecules are desorbed, so the sensitivity decreases with the of 210 ꢁC, the sensor could detect 1 ppm formaldehyde with
increase of temperature.47 The porous ZnSnO3 nanocube sensor a sensitivity of 4.4 (Fig. 8d).
ꢁ
had a high response (21.2) to 50 ppm formaldehyde at 210 C,
Gas-sensing repeatability is an important parameter to
and the adsorption–desorption rate reaches equilibrium. Thus, evaluate the gas-sensing ability of semiconductor materials.
the operating temperature of 210 ꢁC was selected as the The porous ZnSnO3 nanocube sensor was investigated with
optimum operating temperature for subsequent testing. Fig. 8b 50 ppm formaldehyde for 5 cycles at 210 ꢁC (Fig. 9a). The
shows the response–recovery curve of the porous ZnSnO3 response time and the recovery time, as well as the response
nanocube sensor to 50 ppm formaldehyde at 210 ꢁC. Under the values, are almost reproducible between 50 ppm formaldehyde
ꢁ
test temperature of 210 C, the response and recovery times of and ambient air, which indicate that the sensor has good
the porous ZnSnO3 nanocube sensors to 50 ppm formaldehyde reversibility and repeatability for the detection of formaldehyde.
are 53 s and 10 s, respectively. Due to the porous structure Fig. 9c shows the gas sensing stability of the sensor. It can be
having more active sites, more gas can diffuse into the material seen that the responses of the sensor had an acceptable change
during the adsorption process and more oxygen is needed to aer a pulse test for 90 days, indicating the good stability of the
deplete the electrons in the material during desorption, which sensor. Gas selectivity is also an important index to evaluate the
eventually increases the response recovery time. The relation- gas sensitivity. To detect the selectivity of the sensor, the
ship between the response and the formaldehyde concentration sensitivities of the porous ZnSnO3 nanocube sensor to different
for the porous ZnSnO3 nanocube sensor can be observed in 50 ppm gases were tested at 210 ꢁC. It can be seen from Fig. 9b
Fig. 8c and d. From the dynamic response curves in Fig. 8c, we that the response of the sensor to formaldehyde is signicantly
can see that the response amplitude increases with the increase higher than that of other gases. The sensitivity (21.2) of the
of formaldehyde concentration in the range of 1–200 ppm. The sensor to formaldehyde is twice as much as ethanol (11.2) and 3
inset of Fig. 8c shows the curve of the sensor resistance to 1– times that of the other ve gases, indicating that the prepared
200 ppm formaldehyde. With the increase of the gas concen- porous ZnSnO3 nanocube sensor has good selectivity.
tration, the resistance of the material decreases. At lower
Table 1 shows the formaldehyde sensing performances of
concentrations (1–50 ppm), the sensor exhibits a linear various ZnSnO3 based gas sensors. Obviously, the response of
Fig. 9 (a) Repeatability of the porous ZnSnO3 nanocube sensor to detect 50 ppm formaldehyde; (b) response values of the porous ZnSnO3
nanocube sensor to different gases (all gas concentrations are 50 ppm); (c) long-term stability of the porous ZnSnO3 nanocube sensor to detect
50 ppm formaldehyde.
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Table 1 Comparison of the sensing performances of various ZnSnO3-based gas sensors toward formaldehyde
Operating tem.
(ꢁC)
Concentration
(ppm)
Materials
Response (Ra/Rg)
Ref.
ZnSnO3 hollow microspheres
ZnSnO3 nanosheets
ZnSnO3/wt 10% SnO2 concave microcubes
Porous ZnSnO3 cubes
ZnSnO3 hollow microspheres
ZnSnO3 hollow nanocubes
Hierarchical ZnSnO3 nanocages
Hollow ZnSnO3 cubic nanocages
Porous ZnSnO3 nanocubes
270
300
260
240
280
280
270
210
210
50
20
50
100
100
100
50
ꢂ5
ꢂ3
ꢂ5
15
ꢂ5
ꢂ6
2
48
49
50
35
51
52
53
54
50
50
5.4
21.2
Present work
the porous ZnSnO3 nanocubes is much higher than those of
mesoporous ZnSnO3 hollow microspheres,48 ZnSnO3 nano-
sheets,49 ZnSnO3/wt 10% SnO2 concave microcubes,50 porous
ZnSnO3 cubes,35 ZnSnO3 hollow microspheres,51 ZnSnO3 hollow
nanocubes,52 hierarchical ZnSnO3 nanocages53 and hollow
ZnSnO3 cubic nanocages.54 The gas sensing response
enhancement may be attributed to the porous structure and the
more numerous active centers obtained from the enhanced
oxygen vacancy defects on the porous nanostructure, as shown
in the PL spectra.
O2(g) / O2(ads)
(1)
(2)
(3)
(4)
O2(ads) + eꢀ / O2ꢀ(ads)
O2ꢀ(ads) + eꢀ / 2Oꢀ(ads)
O2ꢀ(ads) + eꢀ / 2O2ꢀ(ads)
Upon exposure to a reducing gas, the gas could react with the
chemisorbed oxygen and then return the electron to the
conduction band of the sensing material, decreasing the resis-
tance of the sensor (Fig. 10a). This process leads to a shrinking
electron transport barrier and a reduced electron depletion
barrier, which greatly reduces the thickness of the depletion
layer, resulting in a low resistance state (Rg) (Fig. 10b). The
occurring reaction can be explained as followed:
3.3. Gas-sensing mechanism
ZnSnO3 is a typical surface-controlled gas-sensitive material.
Fig. 10 shows the schematic diagrams of the gas sensing
mechanism of the porous ZnSnO3 nanocube sensor. In the air,
oxygen atoms permeate through the surface of the material
through physical adsorption and chemical adsorption, and
capture electrons in the material to form negative O2ꢀ, O2ꢀ, and
Oꢀ species,55 resulting in an increase in the resistance of the
ZnSnO3 sensor, which can be described as follow:
HCHO(gas) / HCHO(ads)
(5)
(6)
HCHO(ads) + 2Oꢀ(ads) / CO2 + H2O(g) + 2eꢀ
When the gas is desorbed from the surface of the material,
the electrons in the material will continue to react with oxygen
to produce the corresponding adsorbed oxygen. In addition to
the grain size effect, the excellent formaldehyde sensing prop-
erties of the porous ZnSnO3 nanocubes can be attributed to the
porous structure and large specic surface area (70.001 m2 gꢀ1),
which means that more formaldehyde and oxygen molecules
can be adsorbed on the ZnSnO3 surface.
4. Conclusions
In summary, porous ZnSnO3 nanocubes are successfully
synthesized by a facile hydrothermal method combined with
subsequent calcination. The size of the ZnSnO3 nanocubes is
about 100 nm and the corresponding specic surface area is
70.001 m2 gꢀ1. The porous structure could increase the
concentration of the oxygen vacancies, thereby increasing the
number of active sites, which is veried by the TEM and PL
results. The gas sensing performance showed that the porous
ZnSnO3 nanocubes sensor could detect 50 ppm formaldehyde at
about 210 ꢁC with a response value of 21.2, which is 3 times that
Fig. 10 Schematic diagrams of the gas sensing mechanism of the
porous ZnSnO3 nanocube sensors. (a) Schematic diagram of the
resistance change; (b) schematic diagram of the energy band theory. of the other gases. The sensor has a higher sensitivity which
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may possibly result from the porous structure and more
numerous exposed active sites. Aer 90 days of testing, the
sensor still has high sensitivity to formaldehyde. Therefore, the
prepared porous ZnSnO3 nanocubes can be regarded as one of
9 X. L. Wang and L. Zhang, Headspace-Gas Chromatography
Method for Determination of Formaldehyde Content in
Wastewater, IOP Conf. Ser.: Mater. Sci. Eng., 2021, 647,
012155.
the promising sensing materials for the efficient detection of 10 Z. J. Wang, J. Liu, F. J. Wang, S. Y. Chen, H. Luo and X. B. Yu,
formaldehyde.
Size-Controlled Synthesis of ZnSnO3 Cubic Crystallites at
Low Temperatures and Their HCHO-Sensing Properties, J.
Phys. Chem. C, 2010, 114, 13577–13582.
Author contributions
11 L. Q. Shi, J. B. Cui, F. Zhao, D. J. Wang, T. F. Xie and Y. H. Lin,
High-performance formaldehyde gas-sensors based on
three-dimensional center-hollow ZnO, Phys. Chem. Chem.
Phys., 2015, 173, 1316–31323.
12 Y. X. Li, N. Chen, D. Y. Deng, X. X. Xing, X. C. Xiao and
Y. D. Wang, Formaldehyde detection: SnO2 microspheres
for formaldehyde gas sensor with high sensitivity, fast
response/recovery and good selectivity, Sens. Actuators, B,
2017, 238, 264–273.
Jiaoling Zheng: experimental operation, writing – review &
editing. Huanhuan Hou: experimental operation. Hao Fu: data
curation, formal analysis. Liping Gao: conception, supervision,
data curation. Hongjie Liu: data curation, formal analysis.
Conflicts of interest
There are no conicts to declare.
13 Z. H. Tao, Y. W. Li, B. Zhang, G. Sun, M. Xiao, H. Bala,
J. L. Cao, Z. Y. Zhang and Y. Wang, Synthesis of urchin-
like In2O3 hollow spheres for selective and quantitative
detection of formaldehyde, Sens. Actuators, B, 2019, 298,
126889.
Acknowledgements
The authors acknowledge the Science and Technology Plan
Project of Chuzhou (2019ZN005) and the College Students
´
Innovation
(202010377023).
and
Entrepreneurship
Training
Project 14 B. Bouchikhi, T. Chludzinski, T. Saidi, J. Smulko, N. E. Bari,
H. Wen and R. Ionescu, Formaldehyde detection with
chemical gas sensors based on WO3 nanowires decorated
with metal nanoparticles under dark conditions and UV
light irradiation, Sens. Actuators, B, 2020, 320, 128331.
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