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Sn3C2 monolayer with transition metal adatom for gas sensing: a density
functional theory studies
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Nanotechnology
Nanotechnology 32 (2021) 355502 (9pp) https://doi.org/10.1088/1361-6528/ac04d0
Sn3C2 monolayer with transition metal
adatom for gas sensing: a density functional
theory studies
K O Obodo1,∗ , C N M Ouma1 , J T Obodo2, G Gebreyesus3, D P Rai4,
A M Ukpong5 and B Bouhafs6
1HySA Infrastructure Centre of Competence, Faculty of Engineering, North-West University (NWU), P.
Bag X6001, Potchefstroom, 2520, South Africa
2 Physics Department, University of Nigeria, Nsukka, Nigeria
3Department of Physics, School of Physical and Mathematical Sciences, College of Basic and Applied
Sciences, University of Ghana, Ghana
4 Physical Sciences Research Center (PSRC), Pachhunga University College Aizawl, Mizoram, 796001, India
5 Theoretical and computational Condensed Matter and Materials Physics Group, School of Chemistry and
Physics, University of Kwazulu-Natal, Pietermaritzburg, South Africa
6 Laboratoire de Modélisation et Simulation en Sciences des Matériaux, Université Djillali Liabés de Sidi
Bel-Abbés, Sidi Bel-Abbés, 22000, Algeria
E-mail: ko.obodo@nwu.ac.za, obodokingsley@gmail.com, Moro.Ouma@nwu.ac.za, einsteindgreat@
gmail.com, garu.gebreyesus@yahoo.com, dibya@pucollege.edu.in, ukponga@ukzn.ac.za and bbouhafs@
gmail.com
Received 24 February 2021, revised 3 May 2021
Accepted for publication 25 May 2021
Published 9 June 2021
Abstract
The gas sensing properties of pristine Sn3C2 monolayer and different transition metal adatom
(TM-Sn3C2, where TM=Fe, Co, Ni, Cu, Ru, Rh, Pd and Ag) was investigated using van der
Waals corrected density functional theory. The understanding and potential of use of Sn3C2
monolayers as sensors or adsorbent for CO, CO2, NO, NO2 and SO2 gaseous molecules is
evaluated by calculating the adsorption and desorption energetics. From the calculated adsorption
energies, we found that the pristine Sn3C2 monolayer and 3d TM has desirable properties for
removal of the considered molecules based on their high adsorption energy, however the 4d TM is
applicable as recoverable sensors. We applied an Arrhenius-type equation to evaluate the recovery
time for the desorption of the molecules on the pristine and TM adatom on Sn3C2 monolayer. We
found that the negative adsorption energies from −1 to −2 eV of the molecules resulted in easier
recovery of the adsorbed gases at reasonable temperatures compared to adsorption energies in
between 0 and −1 eV (weakly physiosorbed) and below −2 eV (strongly chemisorbed). Hence,
we obtained that the Rh–Sn3C2, Ru–Sn3C2, Pd–Sn3C2, Pd–Sn3C2, and Rh–Sn3C2 monolayers are
good recoverable scavengers for the CO, CO2, NO, NO2, and SO2 molecules. The current
theoretical calculations provide new insight on the effect of TM adatoms on the structural,
electronic, and magnetic properties of the Sn3C2 monolayer and different transition metal adatom
as well as shed light on their application as gas sensors/scavengers.
Supplementary material for this article is available online
Keywords: gas sensing, 2D monolayer, transition metal adatom, density functional theory
(Some figures may appear in colour only in the online journal)
∗ Author to whom any correspondence should be addressed.
0957-4484/21/355502+09$33.00 1 © 2021 IOP Publishing Ltd Printed in the UK
Nanotechnology 32 (2021) 355502 K O Obodo et al
1. Introduction considered were observed in the presence of the 3d transition
metals (Fe and Co), whereas all the considered 4d transition
The detection and sensing of organic, volatile, and toxic metals showed weaker molecular adhesion based on density
gaseous species at very low levels is essential in the mon- functional theory calculations [35]. This implies that the
itoring, evaluation and setting standards for environmental Sn3C2 monolayer can be applied for the sensing and
protection [1, 2]. The discovery of new materials with high scavenging of the following gases: CO, CO2, NO, NO2 and
sensitivity to volatile and toxic gases, low cost and rapid SO2. The recovery time of these gases on the considered
response to different chemical species is an on-going effort monolayers was presented to highlight their reusability. We
using theoretical and experimental methods [2–8]. obtained that the Rh–Sn3C2, Ru–Sn3C2, Pd–Sn3C2,
The discovery of 2D Ti3C2 nano-material produced at Pd–Sn3C2, and Rh–Sn3C2 monolayers are good recoverable
room temperature from the exfoliation of Ti3AlC2 have scavengers for CO, CO2, NO, NO2, and SO2 molecules.
opened the way for synthesis of other 2D materials [9–11].
The Sn3C2 belongs to vast class of materials referred to as
MXenes [12], which comprises of several layered ternary 2. Computational details
carbides and nitrides. These materials can be exfoliated or
cleaved from the vast group of ternary carbides and nitrides In this study, spin-polarised calculation density functional
materials with Mn+1AX [13–15] chemical formula (n=1, 2, theory calculations [36, 37] were performed using CASTEP
or 3; M=early transition metal; A=A-group (mostly code [25, 38] as implemented in the Materials Studio pack-
groups 13 and 14) element, and X=C and/or N) or che- age. The GGA-RPBE [39] exchange correlation functional
mical synthesised. Recently, 3D framework [1] was fabricated and the on the fly generated ultra-soft pseudopotential was
for acetone, methanol and ethanol gas sensing. 2D V2CTx applied [40]. The hexagonal lattice representation of the
sensor devices consisting of single-/few-layer 2D V2CTx on Sn3C2 monolayer in the P-3M1 space group has been inves-
polyimide film were fabricated and shown to detect both polar tigated in this study. The Tkatchenko–Scheffler method [41]
and nonpolar chemical species including hydrogen and for semi-empirical dispersion correction was applied to
methane with a very low limit of detection of 2 and 25 ppm, account for the van der Waals interaction in the system. Also,
respectively, at room temperature (23 °C) [16]. 2D Ti3C2Tx the self-consistent dipole correction was included in this
MXenes was fabricated and shown to possess high metallic study.
conductivity for low noise and a fully functionalized surface A k-point mesh separation of 0.07 Å−1, kinetic energy
for a strong signal. The Ti3C2Tx greatly outperform the sen- cut-off of 549.7 eV and 10
–6 eV/atom convergence criteria
sitivity of conventional semiconductor channel materials for for the calculated total energies was used to optimise the unit
volatile organic compound with extremely low signal to noise cell of Sn3C2 (where Sn=3 and C=2 atoms) monolayer
ration compared to the best known sensors [17]. The study (see figure 1). The forces in the Sn3C2 monolayer were
also considered the role of CO2 gas and ethanol vapour on the converged up to 0.03 eV Å
−1 for the full geometric optim-
interlayer swelling of Ti3C2Tx MXene and its influence on the isation. A 4×4×1 Sn3C2 super-cell (where Sn=48 and
gas sensing performance [18]. Numerous investigations have C=32 atoms) with vacuum distance of 18 Å was created
been carried out on different MXenes as well as 2D materials from the unit cell and used for the adsorption energies calc-
as possible catalyst, support, battery material, etc [11, 18–24]. ulation and the applied vacuum distance applied is appro-
To the best of knowledge, no studies have been carried out on priate to prevent interactions between periodic images [31].
pristine or adatom Sn3C2 monolayer as a possible scrubber/ The same convergence criteria used for the unit cell calcul-
scavenger for these five common industrial exhaust gases, ation was enforced for the super-cell calculation, however in
which are CO, CO2, NO, NO2 and SO2. The use of Sn and C this case only the atomic positions were optimised.
atoms are the primary materials is motivated by the low cost To determine the local stability of the Sn3C2 monolayer,
of these materials. the phonon frequencies at the high symmetry points (G-M-K-
The current study applied density functional theory G) were calculated using density functional theory perturba-
calculation as implemented in the CASTEP [25, 26] code to tion theory with the linear response approximation as
investigate the effects and interactions of single adatom implanted in the Materials Studio package [42]. The q-vector
transition metal (TM=Cr, Mn, Fe, Mo, Ru, W and Os) on grid spacing for interpolation of 0.02 Å−1, convergence
Sn3C2 monolayer with underlying hexagonal symmetry tolerance of 1.0
–5 eV Å−2, and dispersion separation of
similar to Ti3C2 MXene monolayer as a scavenger of the CO, 0.015 Å
−1 is applied.
CO2, NO, NO2 and SO2 gaseous species. The introduction of The calculated adsorption energy (EAd-TM) for the TM
dopant or adsorbate atoms have been shown to modulate the adatom on the Sn3C2 monolayer surface (TM-Sn3C2) was
structural, electronic and optical properties of various host 2D obtained using:
materials [10, 27–34]. The use of adatoms on the Sn3C2
monolayer is applied in this study to understand the role of 3 E = Ed Ad-TM TM-Sn3C2 - ESn3C2 - mTM, (1)
and 4d transition metal adsorbates (where 3d=Fe, Co. Ni, where ETM-Sn C and ESn C are the calculated total energies3 2 3 2
Cu and 4d=Ru, Rh, Pd, Ag) on the Sn3C2 monolayer for of TM-Sn3C2 and pristine Sn3C2 super cells, respectively.
scavenging and detection of light molecules in the atmos- mTM is the chemical potential for the TM adatom. These were
phere. Stronger molecular adhesion of all the molecules determined from their respective bulk unit cells.
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Nanotechnology 32 (2021) 355502 K O Obodo et al
Figure 1. Atomic structures of the pristine Sn3C2 monolayer and position of the likely TM adsorbate is indicated; where blue, and grey
represents the Sn, and C atoms respectively.
Table 1. Different adatoms, electronic configurations (EC), atomic radii (AR in pm) adsorption energy (EAd-TM in eV), total magnetisation
(Tot Mag in ħ/2), bond-length of transition metal adatoms to the surface species (TM-Snx, where x=1, 2 and 3), average bond-length
(TM-Snavg) in angstroms.
Adatom EC AR EAd-TM Tot Mag TM-Sn1 TM-Sn2 TM-Sn3 TM-Snavg
Fe [Ar]3d64s2 156 −2.90 4.25 2.9473 3.2908 3.3715 3.2032
Co [Ar]3d74s2 152 −2.28 2.98 2.9829 3.1658 3.2100 3.1196
Ni [Ar]3d84s2 149 −4.59 −1.41 3.0861 3.2748 3.2752 3.2120
Cu [Ar]3d104s1 145 −4.81 0.00 2.5864 2.5887 2.6245 2.5999
Ru [Kr]4d75s1 178 −8.25 3.86 2.5766 2.5770 2.5770 2.5768
Rh [Kr]4d85s1 188 −9.27 0.00 2.5379 2.5854 2.5379 2.5537
Pd [Kr]4d10 169 −5.66 0.00 2.7897 2.9399 3.0969 2.9421
Ag [Kr]4d105s1 165 −4.64 0.00 3.17717 3.18883 3.33316 3.2331
The molecular adsorption energy (EAd-M) of each gas- The calculated phonon dispersion plot and density of
eous molecules on the pristine and TM-Sn3C2 monolayers phonon states are presented in figures 2(a) and (b), respec-
was evaluated using the equation [43]: tively. No negative/imaginary phonon modes in the phonon
( ) dispersion plot and density of phonon states was observed inEAd-Mol = ETM-Sn3C2+Mol - ETM‐Sn3C2 - mMol. 2 the Sn3C2 monolayer unit cell. This implies that the Sn3C2
The ETM-Sn C +Mol, ETM+Sn C and mMol are total ener- monolayer is dynamically stable. The calculated phonon3 2 3 2
gies of the pristine or TM-Sn3C2 monolayers with the various modes are comprised of two section, which ranges from 0 to 6
molecules, total energies of the pristine or TM-Sn3C2 THz and 7 to 14 THz. The lower modes are governed by the
monolayers and the chemical potential of the various mole- Sn atoms whereas the higher modes are governed by the C
cules considered. The mgas is evaluated using the calculated atoms. This is consistent with previous studies [48, 49] which
total energy of the CO, CO2, NO, NO2 and SO2 molecules. shows that heavy atoms make up the lower modes.
The stability of the TM-Sn3C2 monolayers considered was Next, the preferred adsorption site of TM adatoms on the
argued purely based on the formation energetics due to the pristine Sn3C2 super-cell surface was evaluated using Ru
system size and the different configurations considered. This atom to test different possible sites. The different possible
allows the computations to be tractable. This is in line with adsorption sites were considered and used to determine the
other previous studies [44–46]. preferential adsorption site (see figure 1 and S. table 10
(available online at stacks.iop.org/NANO/32/355502/
mmedia)). In figure 1, three of the likely sites was indicated
3. Results and discussions and several other sites was The adsorption energy (EAd-TM)
for the TM adsorption onto the most favourable site is eval-
3.1. Geometric, phonon properties, and electronic structure uated using the equation giving in equation (1). The preferred
The Sn3C2 monolayer was found to have a non-magnetic transition metal adatom location on the Sn3C2 monolayer is
ground state with a formation energy of −2.78 eV. This for- found to be the carbon hollow site, which is approximately in
mation energy of the Sn3C2 monolayer is calculated using the the centre of a triangle formed from three Sn atoms as pre-
procedure given in previous studies [47]. The implication is that sented in S. table 10 and figure 1. This site was used to study
the formation of Sn3C2 monolayer is energetically favourable. all the other adatoms considered as shown in table 1. The
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Nanotechnology 32 (2021) 355502 K O Obodo et al
Figure 2. Calculated phonon frequencies of the Sn3C2 monolayer unit cell: (a) phonon dispersion plot (THz), and (b) density of phonon states
(1/THz) plot.
adsorption of all the considered TM adatoms on the Sn3C2 evaluate the effect on adatom. The preferred adsorption
monolayer have negative EAd-TM, which implies that the location was used to evaluate the adsorption energies of the
formation of these structures is feasible. The EAd-TM for the different molecules. The calculated adsorption energies of the
4d TM adatoms was found to be generally higher as com- CO, CO2, NO, NO2, SO2 on the Sn3C2 monolayer and
pared to the 3d TM adatoms. This result showed that the 4d TM-Sn3C2 modified surface is presented in figure 3 and
TM binds stronger to the Sn3C2 monolayer. table 2.
The ground state of pristine Sn3C2 monolayer is obtained For the molecules considered, the 3d transition metal
to be a non-magnetic metal, whereas the introduction of TM (Co, Cu, Fe and Ni) and Ru adatoms on Sn3C2 monolayer as
adatoms on the Sn3C2 monolayer surface (TM-Sn3C2) resul- well as pristine Sn3C2 monolayer have relatively lower EAd-M
ted in changes to the magnetic character. However, all the −6 to −2 eV compared with the 4d transition metal (Ag, Pd
monolayers remain metallic. It is observed that the ground and Rh) adatoms on Sn3C2 monolayer with EAd-M from −3
state structure of these TM adatoms (Fe, Co, Ni and Ru) on to −0.4 eV. The results indicate that the presence of 3d
the Sn3C2 monolayer becomes magnetic as shown in table 1 transition metal (Co, Cu, Fe and Ni) and Ru adatoms on the
with highest magnetisation obtained as a result of the Fe Sn3C2 monolayer exhibit stronger sensing properties in
adatom on Sn3C2 monolayer, whereas the other TM adatoms comparison with the 4d transition metal (Ag, Pd and Rh)
(Cu, Rh, Pd, Ag) have non-magnetic ground state. This adatoms on Sn3C2 monolayer. The implication of this
induced magnetisation can be attributed to the non-filled 3d observation is that Co, Cu, Fe and Ni and Ru on the Sn3C2
(Fe, Co and Ni) orbital as well as the odd filling of the 4d Ru monolayer would bind release the adsorbed gaseous mole-
orbital in comparison with the other dopant atoms with filled cules tightly and not readily release the adsorbed gaseous
3d (Cu) and 4d (Pd and Ag), and even filling of the 4d Rh molecules in comparison with the Ag, Pd and Rh on the
orbital. The bond distance (TM-Snx, where x=1, 2 and 3) is TM-Sn C surfaces. Thus, negative adsorption energies
the distance between the transition metal atom and the top- 3 2
within the range of −1 to −2 eV are essential for good reu-
most tin metal and the average bond distance (TM-Snavg) sable gas scavengers. The desorption of the gaseous mole-
between the adatoms and the Sn surface species was eval-
cules would be further explored in detail in the next section.
uated and presented in table 1. The shortest bond distances of
2.5379 Å and 2.5770 Å were obtained for the Rh and Ru All the considered gaseous molecules on the pristine and TM
adatoms on the Sn C monolayer, whereas the largest bond doped Sn3C2 monolayer had the molecules adsorbed intact3 2
distances of 3.2331 and 3.2120 Å were obtained for the Ag except for the NO molecule on the Fe−Sn3C2 monolayer. The
and Ni adatoms on the Sn3C monolayer. The calculated
NO molecule dissociates to the N and O atoms with a
2
TM-Sn bond distance does not follow any speci c trend separation distance of 2.259 Å compared with an averageavg fi
with respect to the atomic radii. Also, going through the bond distance of about 1.18 A. The N and O atoms have a
groups or periods, no specific trend was observed with respect bond distance of 1.623 Å and 1.678 Å respectively with the
to the evaluated bond distance. Fe surface adatom.
We have observed from presented in figure 3 and table 2
that: (i) the Rh–Sn3C2 monolayer have comparable higher
3.2. Adsorption of different molecules on pristine and adsorption energies than the pristine and doped monolayer for
TM-Sn3C2 monolayer the CO2 and SO2 molecules with adsorption energies of
The adsorption of the molecules (CO, CO2, NO, NO2, SO2) −0.49 and −1.31 eV, (ii) the Pd–Sn3C2 monolayer have
on pristine Sn3C2 monolayer was evaluated by considering comparable higher adsorption energies than the pristine and
different sites and the lowest energy site was taken as the adatom Sn3C2 monolayer for the NO and NO2 molecules with
preferred adsorption location. For the TM-Sn3C2 modified adsorption energies of −1.23 and −1.53 eV, and (iii)
surface, the molecules were adsorbed on the adatom to Ag−Sn3C2 monolayer have comparable higher adsorption
4
Nanotechnology 32 (2021) 355502 K O Obodo et al
Figure 3. Calculated adsorption energies (in eV) for the different gaseous molecules on the pristine Sn3C2 monolayer and TM-Sn3C2
monolayers. The insert shows the monolayer with lowest adsorption energies for the gaseous molecules.
Table 2. Calculated adsorption energies (in eV) for the different molecules on the pristine Sn3C2 monolayer and TM-Sn3C2 monolayers.
Adatom Sn3C2 Fe Co Ni Cu Ru Rh Pd Ag
CO −3.42 −4.88 −4.77 −5.05 −2.71 −2.95 −1.56 −1.79 −1.53
CO2 −3.32 −3.63 −3.51 −2.92 −1.99 −1.64 −0.49 −0.51 −0.90
NO −3.43 −6.12 −5.64 −4.40 −2.41 −3.48 −2.04 −1.29 −1.45
NO2 −4.11 −5.30 −5.58 −4.15 −3.04 −4.34 −2.20 −1.53 −2.25
SO2 −3.67 −4.29 −4.25 −3.63 −2.67 −2.81 −1.31 −1.52 −1.46
energies than the pristine and doped monolayer for the CO major drawback in terms of usage of these surfaces, where
molecule with adsorption energies of −1.53 eV. These recovering the catalytic surface for subsequent use would
negative adsorption energies within the range of −1 to result in longer recovery time (τ). The τ for the desorption of
−2 eV, which are essential for reusable gas scavengers. The the gaseous molecules (CO, CO2, NO, NO2, SO2) on pristine
relative difference in the adsorption energy for the CO Sn3C2 monolayer was evaluated using the Arrhenius-type
molecule on the Ag−Sn3C2 monolayer compared with the equation given below [2, 50, 51]:
Rh–Sn3C2 is about 0.02eV. Thus, the Rh–Sn3C2 monolayer
might as well be suited for the use as a gas scavenger for the t = n-1e(-EAd/KBT )0 , (3)
CO molecule as well as the CO2. For one time use materials,
stronger adsorption and sensing of these gaseous molecules where T is temperature, KB the Boltzmann’s constant and
are paramount, therefore the 3d transition metal dopant atoms (8.318×10
–3 kJ (mol*K)−1) n-10 is the attempt frequency
would be better suited than the suggested 4d transition metal (10
12 S−1).
dopant atoms. For reusability, weaker adsorption is para- The equation considers the relationship between the
mount as demonstrated in previous studies [6]. Thus, the temperature and the rate constant of a given chemical reac-
desorption of the gaseous molecules on the above suggested tion. The above expression is based on transition state theory
possible candidate monolayers is discussed. and van’t Hoff–Arrhenius expression. Equation (3) shows an
exponential relation between the recovery time and the cal-
3.3. Desorption of different gaseous molecules on pristine and culated temperature. Thus, the Sabatier principle is of con-
TM-Sn C sequence, where a balance between the adsorption energy and3 2 monolayer
recovery time is needed to have either an irreversible or
The pristine and TM adatoms on Sn3C2 monolayer adsorb the reversible gas scavenger. Based on this, the optimal adsorp-
different gaseous molecules strongly to their surface of the tion energy for reusable gas scavengers is between −1 and
structure. This strong binding observed on the surface −2 eV.
demonstrate that the TM doped, and pristine Sn3C2 mono- In figure 4, the recovery time in log scale (base 10) for
layer are applicable as sensors/scavengers for these gaseous different adsorbed gases (CO, NO, NO2 and SO2) as a
molecules (CO, CO2, NO, NO2, SO2). The energetics of the function of different temperatures (298, 373 and 473 K) at the
gaseous molecules show strong binding on the considered most optimal surfaces as found in section 3.2 is presented
surfaces. The observed high adsorption energetics have a except for CO2, whereas the recovery time as a function of
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Nanotechnology 32 (2021) 355502 K O Obodo et al
This implies that the molecules are physiosorbed and the
desorption time is very low making these configurations not
feasible as scavengers. The Ru–Sn3C2 and Cu–Sn3C2
monolayers with energy range between −1 and −2 eV would
form better recoverable sensors/scavengers of CO2 molecule
as shown in S. table 2.
For the monolayer configurations with lower adsorption
energies such as pristine Sn3C2, Ni–Sn3C2, Fe–Sn3C2, and
Co–Sn3C2 the desorption of the adsorbed molecules (CO,
CO2, NO, NO2 and SO2) occurs at significantly higher tem-
peratures (473 K and above) and long-time (1030–1055 s) as
presented in figure 6. The application of high temperature
could lead to the degradation and de-activation of these
monolayers. Hence, lower adsorption energy is proportional
to exponentially prolonged desorption time and vice versa.
Therefore, pristine and 3d TM-Sn3C2 monolayers would be
applicable as highly sensitive irreversible sensors/absorbers
Figure 4. Calculated recovery time in log scale of base 10 (in s) as a rather than ideal reversible scavengers. Other materials have
function of different temperatures (in K) for different CO, NO, NO2, been investigated for the adsorption of these gases such as
and SO2 molecules with the highest adsorption energy. graphene [52], pristine and defective MoS2 [53–57], pristine
and defective MoSe2 [4, 58], InN [59], borophene [60], etc
temperature for CO2 is presented in figure 4. The optimal [61–63]. The considered pristine and TM-Sn3C2 monolayer
adsorption energy for reusable gas scavengers is between −1 adds to this class of materials, which can be used to sense/
and −2 eV. This would result in reasonable desorption time scavenger gaseous molecules and offers different temperature
and temperatures. The NO2 and CO molecules have similar regime as well as binding strength with varied applicability.
desorption time on the configurations with the highest
adsorption energy, hence overlay on each other in figure 4
(see S. tables 8 and 9). The temperature range is essential to 4. Conclusions
maintain the integrity of the Sn3C2 monolayer and prevent
disintegration. For the CO2 molecule adsorbed on the pristine In the current study, density functional theory-based calcu-
and adatom Sn3C2 monolayers, the highest adsorption energy lations were carried out to study the influence of different
of −0.49 eV would result in desorption of the CO2 molecule transition metal adatom on Sn3C2 monolayer towards the
below room temperature and almost spontaneous (10–5 S). adsorption of the CO, CO2, NO, NO2, and SO2 toxic gases. A
This implies that for practical application above room temp- predicted thermodynamic Sn3C2 monolayer was established
erature this material is impractical. At room temperature using arguments based on the phonon frequencies and cal-
(298 K) and boiling point of water (373 K), the time required culated formation energy. The calculated binding energies of
for the desorption of the CO, NO, NO2, and SO2 molecules the transition metal atoms (3d=Fe, Co. Ni, Cu and
on the Ag–Sn3C2, Pd–Sn3C2, Pd–Sn3C2, and Ag–Sn3C2 4d=Ru, Rh, Pd, Ag) show that the various considered
monolayers respectively is relatively longer when compared adatoms stably bind on the Sn3C2 monolayer.
with the 473 K temperature. Considering the NO molecule on The calculated adsorption energies of the CO, CO2, NO,
the Pd–Sn3C2 monolayer as presented in figure 4 and table 3, NO2, and SO2 molecules obtained on the pristine and
the recovery time for the desorption of the molecule at room TM-Sn3C2 monolayer are all negative. This implies that the
temperature is 5577, 179 805 s (∼1010). If the temperature of considered configurations will bind the CO, CO2, NO, NO2,
the Pd–Sn3C2 monolayer is increased to 473 K, the recovery and SO2 molecules stably. The TM (3d)-Sn3C2 monolayers
time for the desorption of the NO molecule is 50.2 s (∼102). were found to bind the CO, CO2, NO, NO2, and SO2 mole-
This implies that the CO, NO, NO2, and SO2 molecules on cules stronger compared with the TM (4d)-Sn3C2 monolayers.
the Ag–Sn3C2, Pd–Sn3C2, Pd–Sn3C2, and Ag–Sn3C2 mono- The recovery time for the desorption of the molecules on
layers can operate stably at 298 and 373 K temperatures. It is the pristine and TM-Sn3C2 monolayers was evaluated using
worth stating that the scavenging of these gaseous molecules an Arrhenius-type equation. We determined that negative
should operate stably also at lower temperatures with deso- adsorption energies within the range of −1 to −2 eV for the
rption highly unlikely. However, at significantly higher tem- gaseous molecules resulted in the desorption of the gaseous
peratures (598 and 798 K), the desorption of these gases molecules at moderate time for slightly elevated temperatures
readily occurs based on equation (3). ∼473 K. At adsorption energies of 0 to −1 eV, the gaseous
Figure 5 shows the recovery time versus temperature for species physiosorbed. Thus, from the calculated recovery
the CO2 molecule adsorbed on the pristine and TM adatom time, the desorption of the gaseous molecules occurs almost
Sn3C2 monolayers. For the Pd–Sn3C2, Rh–Sn3C2 and instantaneous, hence those TM-Sn3C2 monolayers would not
Ag–Sn3C2 monolayers, the adsorption energies (recovery be ideal as scavengers/sensors. We found that the Rh–Sn3C2,
time) are −0.49 eV, −0.51 eV and −0.90 eV respectively. Ru–Sn3C2, Pd–Sn3C2, Pd–Sn3C2, and Rh–Sn3C2 monolayers
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Nanotechnology 32 (2021) 355502 K O Obodo et al
Table 3. Calculated recovery time (in s) as a function of different temperatures (in K) for different gaseous molecules.
Configurations 473 (K) 373 (K) 298 (K)
(Ag–Sn3C2, ‘CO’) 17, 916.37 s 408, 027, 845.7 s 6.27977 ´ 1013 s
(Rh–Sn3C2, ‘CO2’) 0 s 0(s) 0 s
(Pd–Sn3C2, ‘NO’) 50.2 s 236, 489.12 s 5, 577, 179, 805 s
(Pd–Sn3C2, ‘NO2’) 22, 184.89 s 535, 030, 171.3 s 8.8156 ´ 1013 s
(Rh–Sn3C2, ‘SO2’) 94.91 s 530, 372.03 s 15, 327, 276, 602 s
Acknowledgments
The authors thank the Centre for High Performance Com-
puting (CHPC) in Cape Town, South Africa, for the com-
putational resources used in the current study. KOO
acknowledges the HySA-Infrastructure Centre of Compe-
tence, Faculty of Engineering, North-West University for
their financial support via KP5 grant.
Data availability statement
All data that support the findings of this study are included
within the article (and any supplementary files).
Conflicts of interest
No conflicts of interest to declare.
Figure 5. Calculated recovery time in log scale of base 10 (in s) as a
function of different temperatures (in K) for CO2 gaseous molecules
on the different considered configurations.
ORCID iDs
K O Obodo https://orcid.org/0000-0002-1428-2761
C N M Ouma https://orcid.org/0000-0001-7328-2254
A M Ukpong https://orcid.org/0000-0001-6712-7821
B Bouhafs https://orcid.org/0000-0002-0110-9003
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