This document describes a study that investigates using a titanium-doped hexagonal boron nitride (h-BN) monolayer for capturing and dissociating carbon dioxide (CO2) molecules. Various adsorbates including BeH2O, LiH2O, NaH2O, and BeO were modeled on the surface using first-principles calculations. BeH2O was found to help dissociate CO2 into CO molecules by acquiring one oxygen atom. Adsorption energies indicated the process was exothermic and stable. Band structure and partial density of states plots showed the system was sensitive to adsorbates and exhibited chemisorption and physisorption behaviors.

1. Materials Today Communications
Investigating CO2 capture and direct dissociation through AEM/H2O compounds
adsorption on Ti-doped h-BN monolayer system; FPS-MD Calculations
--Manuscript Draft--
Manuscript Number: MTCOMM-D-23-12166
Article Type: Full Length Article
Section/Category: Computational materials science
Keywords: h-BN; CO2 capture; adsorption; CO2 dissociation
Corresponding Author: Danish Hussain, PHD
National University of Sciences and Technology
PAKISTAN
First Author: Danish Hussain, PHD
Order of Authors: Danish Hussain, PHD
Muhammad Rafique
Basheer Ahmed Kalwar
Abstract: Titanium doped h-BN sheet is investigated for capture and dissociation of CO2
molecule with the adsorption of BeH2O, LiH2O, NaH2O and BeO compounds based
on First-Principles and Molecular Dynamics (FPS-MD) calculations. BeH2O cluster
helped the dissociation of CO2 into CO molecules by acquiring one O atom to its
structure. Calculated adsorption energies indicate that the impurity substitution and
adsorption process is exothermic and stable which can be adopted for experimental
work. The interaction of CO2 with Ti atom is ionic in nature as O atom of CO2 molecule
makes ionic bond with Ti atom for all configurations. Band structure plots were
calculated, which indicated that Ti-doped h-BN sheet band gap varies significantly
when CO2 and other compounds are adsorbed on its surface thus proving the
sensitivity of Ti-h-BN towards adsorbate systems. Obtained PDOS plots show stronger
hybridization peaks between the orbitals of CO2 molecules, adsorbate compounds and
the Ti atom in deep valence bands thus indicating the chemisorption and physisorption
behaviors. Transition state search and activation energy barrier calculations were
performed to explain the dissociation process of CO2 molecule. Through molecular
dynamics calculations, obtained energy and temperature plots were depicting smooth
trend in their profile thus suggesting stabilized structures.
Suggested Reviewers: Syed Rizwan, PHD
Prof, NUST
syedrizwan@sns.nust.edu.pk
He is expert in the field.
Ahad Ghaemi, PHD
Prof, Iran University of Science and Technology
aghaemi@iust.ac.ir
He has publicaitons in the same field.
Maohong Fan, PHD
Prof, University of Wyoming
mfan@uwyo.edu
He is an expert.
Opposed Reviewers:
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2. Dear Editors:
We would like to submit our manuscript entitled “Investigating CO2 capture
and direct dissociation through AEM/H2O compounds adsorption on Ti-doped h-BN
monolayer system; FPS-MD Calculations”, which we wish to be considered for
publication in “Materials Today Communications”. No conflict of interest exists in the
submission of this manuscript, and is approved by authors for publication. I would
like to declare on behalf of my co-authors that the work described was original
research that has not been published previously, and not under consideration for
publication elsewhere, in whole or in part. All the authors have approved the
manuscript that is enclosed.
Titanium (Ti) atom doped monolayer h-BN sheet is investigated for capture
and dissociation of CO2 molecule with the composite adsorption of BeH2O, LiH2O,
NaH2O and BeO compounds based on density functional theory (DFT) calculations.
These adsorbates were adopted to analyze the CO2 capturing and dissociation capacity
of Ti-doped h-BN sheet. Out of all these compounds only BeH2O cluster helped the
dissociation of CO2 into CO molecules by acquiring one O atom to its structure.
Calculated adsorption energies indicate that the impurity substitution and adsorption
process is exothermic and stable which be adopted for experimental work. Through
charge difference diagrams it is evident that the interaction of CO2 with Ti atom is
ionic in nature as O atom of CO2 molecule makes ionic bond with Ti atom for all
configurations. To further determine the sensitivity towards CO2 molecules of these
complex systems, band structure plots were calculated, which indicated that Ti-doped
h-BN sheet band gap varies significantly when CO2 and other compounds are
adsorbed on its surface thus proving the sensitivity towards adsorbate systems.
Further, partial density of states (PDOS) plots were calculated to determine the
hybridization process between CO2 molecules, adsorbate compounds and the Ti doped
h-BN sheet. Obtained PDOS plots show stronger hybridization peaks between the
orbitals of CO2 molecules, adsorbate compounds and the Ti atom in deep valence
bands thus indicating the chemisorption and physisorption behaviors. Transition state
search and activation energy barrier calculations were performed to explain the
dissociation process of CO2 molecule. Molecular dynamics calculations were
performed for all systems at a given temperature of 400K having 0.5fs time step for
6000 NSW in order to determine their stability, energetics and temperature variations.
Obtained energy and temperature plots were depicting smooth trend in their profile
thus suggesting stabilized structures. I hope this paper is suitable for “Materials Today
Communications”.
Thank you and best regards.
Yours sincerely,
All Authors
Cover Letter

3. Graphical Abstract Click here to access/download;Graphical Abstract;Graphical Abstract.jpeg

4. Investigating CO2 capture and direct dissociation through AEM/H2O compounds
adsorption on Ti-doped h-BN monolayer system; FPS-MD Calculations
Muhammad Rafique(a),
*)
, Danish Hussain(b)
, Basheer Ahmed Kalwar(c)
(a),
*)
School of Energy Science and Engineering, Harbin Institute of Technology,92 West Dazhi Street, Harbin 150001, PR China
(b)
Department of Mechatronics Engineering, National University of Science and Technology, (NUST), Islamabad 54000, Pakistan
(c)
College of Electrical Engineering and New Energy, China Three Gorges University, Yichang 443002, China
rafique@hit.edu.cn
Abstract:
Titanium doped h-BN sheet is investigated for capture and dissociation of CO2 molecule
with the adsorption of BeH2O, LiH2O, NaH2O and BeO compounds based on First-Principles
and Molecular Dynamics (FPS-MD) calculations. BeH2O cluster helped the dissociation of CO2
into CO molecules by acquiring one O atom to its structure. Calculated adsorption energies
indicate that the impurity substitution and adsorption process is exothermic and stable which can
be adopted for experimental work. The interaction of CO2 with Ti atom is ionic in nature as O
atom of CO2 molecule makes ionic bond with Ti atom for all configurations. Band structure plots
were calculated, which indicated that Ti-doped h-BN sheet band gap varies significantly when
CO2 and other compounds are adsorbed on its surface thus proving the sensitivity of Ti-h-BN
towards adsorbate systems. Obtained PDOS plots show stronger hybridization peaks between the
orbitals of CO2 molecules, adsorbate compounds and the Ti atom in deep valence bands thus
indicating the chemisorption and physisorption behaviors. Transition state search and activation
energy barrier calculations were performed to explain the dissociation process of CO2 molecule.
Through molecular dynamics calculations, obtained energy and temperature plots were depicting
smooth trend in their profile thus suggesting stabilized structures.
Keywords: h-BN; CO2 capture; Adsorption; CO2 dissociation;
1. Introduction:
Leveraging the wonderous properties of graphene and graphene-like two-dimensional (2D)
materials in field of carbon dioxide (CO2) capture, storage, conversion and utilization has been
increased two-fold in the current decade as the world moves towards the carbon neutralization
goal [1-3]. Current decade has seen rapid rise and excessive emission of toxic and hazardous
gases into the environment because of increased industrialization and urbanization, thus adding
fuel to the fire of global warming [4, 5]. The main precursor to the global warming is CO2 gas,
greatly produced by enhanced use of fossil fuels, which directly and indirectly damages the earth
ecosystem [6]. Hence, the current hour demands the novel carbon neutralization techniques to
tackle the deteriorating environmental conditions. To deal with above mentioned problem, one of
the ways to tackle these environmental conditions is the conversion of CO2 into valuable carbon-
based fuel products [7]. The process of direct splitting of CO2 can produce CO, which in turn is a
treasured chemical feedstock [8]. Furthermore, CO2 dissociation into CO is considered as the
elementary step for the CO2 reforming into CH4 [9, 10]. CO2 activation and the dissociation of its
C═O bond is also the basic step for the photoreduction of CO2 [11]. Furthermore, CO2
conversion to CO*
is the first step for CO2 methanation reaction pathway (i.e., CO2
*
→CO*
→C*
Manuscript File Click here to view linked References

5. →CH*
→CH2
*
→ CH3
*
→CH4
*
) [12, 13]. Besides, CO2 dissociation to CO*
is very vital for CO2
hydrogenation on catalysts such as Co embedded Cu, that can enhance hydrogenation, proceeded
by CO*
→HCO*
→H2CO*
→H3CO*
→H3COH to change CO2 to methanol [14]. Currently, the
research for CO2 gas capturing and dissociation is focused on 2D materials sensors based on
graphene [15] and graphene-like materials such as, black phosphorene [16], germanene and
silicene [17], aluminum nitride (AlN) and indium nitride (InN) [18], transition metal
dichalcogenide (TMD) [19, 20] and hexagonal boron nitride (hBN) [21] attributed to their high
surface to volume ratio, structural diversities and application tailored physical properties.
Although, the 2D materials are being considered as the savior for toxic gas problems, but these
systems are still in their infant states due to certain limitations such as unavailability of dangling
nature, zero/negligible band gaps [22], impractical sensitivity and selectivity under elevated
environment conditions such as increased temperatures and pressures, which limit their
functionality in CO2 gas capturing and dissociation process [23]. Owing to these problems, it is
mandatory to search for and design stable hybrid 2D systems which can offer, quick response
time, enhanced sensitivity and selectivity, suitable dissociation cycle and should not be prone to
elevated temperature conditions. Among these 2D materials hexagonal Boron Nitride (h-BN),
also known as “white graphene” is widely acknowledged and adopted for gas sensing and
capturing applications due to its distinct properties of enhanced thermal conductivity, stable
structure at high temperatures and insulating band gap thus making it a viable candidate for CO2
gas sensing and capturing material even under elevated environment conditions [24, 25]. Most of
earlier studies suggest that when used in its pure state, monolayer h-BN based biosensors provide
inconsistent and unsatisfactory results due to the instant release and recovery, poor reactive
response and selectivity of foreign gas molecules subjected to its intrinsic chemical inertness
[26-29]. Hence the suitable way to deal with this problem is the surface tailoring [30, 31] and
geometry modifications through foreign element doping [32-34] and defect engineering such as
vacancy formation and stone wales defects [35, 36] in order to enhance the gas sensing and
capturing capability of monolayer h-BN systems. Most of recent studies has already proven that
metal atom decoration of 2D materials can significantly enhance their gas sensing properties [37,
38], recent study carried out on Ti-Pd doped h-BN with varying doping configuration and sites
for CO capturing and sensing indicate that Ti-Pt doped h-BN at B and N vacancies can hold CO
molecule through chemisorption and adsorption techniques, respectively with satisfied energy
ranges [39]. Very recently, an in-depth study was carried out for capturing of five different types
of gases (i.e., H2, N2, CO, NO and CO2) on various metal atom doped h-BN systems. From all
the metal dopant h-BN sheets, Ti-doped h-BN sheet was found to be a stable gas sensing
material having 12.9 eV strong binding energy and effective gas sensing ability [40]. In terms of
experimental design of monolayer h-BN, high quality 2D h-BN sheets have been synthesized
successfully through molecular beam epitaxy (MBE), chemical vapor deposition (CVD) and
metal–organic chemical vapor deposition (MOCVD). Further, transition metal atom doped h-BN
sheets have also been studied experimentally for surface activation in economic and environment
friendly way [27, 41]. In addition to this, our research group has already been performing the

6. first-principles calculations on transition metal atom dopant 2D sheets for the modification of
their physical properties [42-45] as well as their applications in hydrogen and CO2 capture and
storage [46-48]. Keeping in view of our previous investigations and the literature available, it can
be generalized that Ti-functionalized h-BN can be considered as an efficient system with target
application of CO2 gas capture and conversion system. Since, CO2 is an inert gas having C atom
covalently bonded with two O atoms and this tri-molecular gas seldom reacts with other
substances. Further, C-O covalent bonding in CO2 is quite strong, thus extra catalytic reaction is
necessary for its dissociation. Although much has been said and worked upon Ti-doped h-BN
system for CO2 capturing, but it doesn’t help in the dissociation process of CO2 into CO
molecule. Hence, in this work we have adopted the adsorption of various compounds such as
BeH2O, LiH2O, NaH2O and BeO to support dissociation process of CO2 into CO molecule. To
support and verify the CO2 capturing and dissociation behavior of given systems, the calculations
for adsorption energy, electronic properties, PDOS, Charge Difference, Activation Energy
Barrier and TS search were performed, respectively [49].
Organization of this work is as follows: calculation details and geometry of doped and
adsorbed h-BN systems are introduced in Sec II; electronic properties, charge difference and
other results related to CO2 capture and dissociation process are depicted and discussed in Sec
III; finally, a general conclusion and summary of this work is detailed in Sec IV, respectively.
2. Materials, Methods and Formulations
Given First-principles calculations were done through of Vienna ab-initio Simulation
Package (VASP) [10] which adopts projector-augmented-wave (PAW) formalism. Perdew-
Burke-Ernzerhof (PBE) [11] exchange-correlation (XC) functional of the generalized gradient
approximation (GGA) was utilized since it is known for effective cluster [12] and surface-based
calculations [13,14]. For stable geometry optimization, the energy convergence standard is set to
1×10-6
eV/atom and Hellmann-Feynman forces parameter is set up to 0.01 eV/Å. The plane wave
cut-off energy is fixed at 415 eV and a regular Monkhorst-pack grid of 9×9×1 k point was
adopted. A 15 Å vacuum thickness is applied along the Z-direction, so as to reject the interaction
between neighboring cells. Grimme’s DFT-D2 approach was applied for the consideration of
weak van der Waals (vdW) interactions [50]. VESTA tool was utilized for the visualization of
atomic structures and charge difference diagrams, respectively [51]. To deal with partial
occupancy issues, Gaussian smearing technique was employed. For transition state calculations,
Materials Studio Software package was utilized. Molecular dynamics (MD) calculations were
performed adopting Nosé-Hoover thermostat and a canonical ensemble (NVT) [52, 53] at a
temperature of 400 K. Given systems were thermalized using a time step of 0.5fs for 6000 NSW
and until the equilibrium is achieved. In order to ensure the stability of Ti-doped h-BN systems,
formation and binding energies were calculated using equation (1) and (2), respectively [25] and
the results are analyzed in next section;
𝐸𝑓 = 𝐸𝑇𝑖−ℎ𝐵𝑁 − 𝜇𝑇𝑖 + 𝜇𝐵 + 𝜇𝑁 − 𝐸𝑝𝑟𝑖𝑠𝑡𝑖𝑛𝑒 ℎ𝐵𝑁 (1)
𝐸𝑏 = 𝐸𝑇𝑖−ℎ𝐵𝑁 − 𝐸𝑣 − 𝐸𝑇𝑖 (2)

7. where, 𝐸𝑇𝑖−ℎ𝐵𝑁, 𝐸𝑝𝑟𝑖𝑠𝑡𝑖𝑛𝑒 ℎ𝐵𝑁 are the obtained total energies of Ti-doped h-BN and pristine h-BN
monolayer systems, respectively. The terms 𝜇𝑇𝑖, 𝜇𝐵 and 𝜇𝑁 correspond to the chemical potentials
of Ti, B and N atoms respectively. Similarly, to determine the effectiveness of adsorption of CO2
gas molecules on Ti-doped, BeH2O, LiH2O, NaH2O and BeO adsorbed compounds on h-BN
systems, adsorption energy was calculated using equations 3 given below [25];
𝐸𝑎𝑑𝑠𝐶𝑂2
= 𝐸𝐶𝑂2+𝑎𝑑𝑠𝑜𝑟𝑏𝑎𝑡𝑒+𝑇𝑖−ℎ𝐵𝑁 − 𝐸𝑇𝑖−ℎ𝐵𝑁 − 𝐸𝑎𝑑𝑠𝐶𝑂2
− 𝐸𝑎𝑑𝑠𝑜𝑟𝑏𝑎𝑡𝑒 (3)
where, 𝐸𝑇𝑖−ℎ𝐵𝑁, 𝐸𝐶𝑂2+𝑎𝑑𝑠𝑜𝑟𝑏𝑎𝑡𝑒+𝑇𝑖−ℎ𝐵𝑁 are the obtained total energies of Ti-doped h-BN and
CO2, BeH2O, LiH2O, NaH2O and BeO adsorbed and Ti-doped h-BN systems, respectively.
𝐸𝑎𝑑𝑠𝐶𝑂2
and 𝐸𝑎𝑑𝑠𝑜𝑟𝑏𝑎𝑡𝑒 terms refer to the energies of CO2 molecule and other adsorbate
compounds, respectively.
3. Results and discussions
The obtained results along with appropriate analysis and discussion follows as under:
3.1. Structure and energetics of CO2, BeO, BeH2O, LiH2O and NaH2O adsorbed Ti-doped hBN
systems
Here, we analyze the capturing and dissociation process of CO2 gas on Ti-doped h-BN
system adsorbed with BeH2O, LiH2O, NaH2O and BeO compounds, respectively.
Figure 1 (a-d): Side views of atomic structures of CO2 and BeO, BeH2O, LiH2O and NaH2O compounds placed on
Ti-doped hBN systems before relaxation and optimization process. Here, “W” indicates H2O molecules throughout
the manuscript.
Prior to relaxation and geometry optimization process, CO2 molecule and other adsorbate
compounds were placed on the surface of Ti-doped h-BN systems as illustrated by the side views
in Figs. 1(a)-(d), respectively. It can be clearly seen that these adsorbate compounds are dangling
freely on the surface. However, when they are allowed to relax they tend to create bonding
between adsorbate entities along with the attachment towards Ti atom which can further be seen
in the relaxed geometries as provided in Figs. 2(a)-(d), respectively.
(a) (b)
BeOads Ti-hBN
CO2
BeWads Ti-hBN
CO2
(c) (d)
LiWads Ti-hBN
CO2
NaWads Ti-hBN
CO2

8. Figure 2 (a-d): Top views of atomic structures of fully relaxed CO2 adsorbed on hybrid Ti-doped h-BN systems.
(a*-d*) represent the side views of the corresponding systems, respectively. Bond lengths of Ti-N, Ti-O, C-O and
others are also presented in Å, respectively. “W” indicates H2O molecules throughout the manuscript.
As discussed, it has been widely studied about the Ti-doped h-BN for various gas sensing
and capturing applications, but here we add some other adsorbate compounds to support the
capturing and dissociation process of CO2 gas molecule. The relaxed geometries of
aforementioned systems along with the bond distance in Å between constituent atoms of given
systems are depicted in Figs. 2(a)-(d), respectively. Firstly, to ensure the stability of Ti-doped h-
BN systems, we calculated its formation and binding energies using equation (1) and (2),
respectively. Obtained formation and binding energy of Ti doped h-BN systems was found to be
-3.16 eV and -11.98 eV, respectively, which is in consensus with some earlier reports [24, 25,
48]. In terms of relaxation, it is stated that the tight energy convergence value i.e., 1×10-6
eV/atom was utilized and all the constituent atoms were free to relax without any constraints.
Most of the geometries were allowed to relax until the mentioned energy criteria was not
BeOads Ti-hBN BeWads Ti-hBN
LiWads Ti-hBN NaWads Ti-hBN
CO2
(a)
CO2
(b)
CO2
(c)
CO2
(d)
(a)* (b)*
(c)* (d)*
BeOads Ti-hBN
CO2
BeWads Ti-hBN
CO2
LiWads Ti-hBN
CO2
NaWads Ti-hBN
CO2
1.92
1.89
1.90
2.17
1.40
1.20
1.43
1.40
1.90 1.92
1.89
1.86
1.42
1.63
1.2
1.92
1.89
1.90
1.89
1.92
1.89
2.07
1.86
1.36
1.24
1.82
2.07
2.25
2.20
1.34
1.24

9. achieved by the given systems. Regarding geometry parameters, a 4×3×1 supercell of h-BN was
adopted with Ti doped at B-vacancy, since earlier literature reported the suitable site for Ti atom
substitution to be at the B vacancy, respectively [25, 39].
Atomic structure of all given systems, along with the bond length between N-B atoms, N-Ti
atoms, C-O atoms of CO2 molecules are presented in Fig. 2(a)-(d), respectively. Through the
structural diagrams provided in Figs. 2(a)-(d), it is evident that the CO2 molecule interacts with
Ti impurity through chemisorption process as for each case, there is evident bonding between Ti
and O atom of CO2 molecule with the average bond length of 2.1Å for each case. In addition,
other adsorbate entities do not disturb or reduce the interaction of CO2 molecule with the host
sheet, rather these adsorbates also adopt chemisorption behavior with CO2 molecule, as in each
case it can be seen that the adsorbate compounds formulate bonding with the O atom of CO2
molecule. In only case of BeH2O adsorption with CO2 molecule on Ti-doped h-BN, it can be
clearly seen in Fig 2(b-b*), that the CO2 molecule splits into CO and O atom whereby donating
O atom to the adsorbate compound, hence providing the possibility of CO2 dissociation process
[54]. After CO2 adsorption, bond length of the host sheet atoms and of the adsorbate compounds
are calculated. The change calculated in B-N bond length around the impurity site occurs in
range of 1.36-1.39Å respectively. Similarly, the N-Ti bond length was in the range of 1.89-2.07
Å respectively. The C-O atom bond length was found to be in the range of 1.24-1.40 Å. These
results are in consensus with previous studies carried out in this regard [25, 48, 55, 56].
Similarly, to determine the effectiveness of adsorption behavior of CO2 molecule on given h-BN
systems, we calculated the adsorption energy for all given systems using equation 3 mentioned
above and the results are provided in table 1, respectively. Obtained adsorption energies adopt
negative values which suggests that the adsorption occurs through exothermic reactions and can
be considered as energetically favorable [54, 57, 58]. The average equatorial bond lengths
between, N-B, N-Ti, C-O, Ti-O and adsorbate-O atoms is also given in table 1 below;
Table 1: The adsorption energy (Eads), bond length of N-B, N-Ti, C-O, Ti-O and adsorbate-O atoms
System Eads (eV) N-B (Å) N-Ti (Å) C-O (Å) Ti-O (Å) Ads-O (Å)
CO2BeOadsTi-hBN -2.88 1.39 1.90 1.40 2.17 1.43
CO2BeWadsTi-hBN -2.91 1.40 1.90 --- 1.86 1.42
CO2LiWadsTi-hBN -3.07 1.40 1.90 1.36 2.07 1.86
CO2NaWadsTi-hBN -3.11 1.41 1.90 1.34 2.07 2.25
3.2 Molecular dynamics (MD) calculations on CO2, BeO, BeH2O, LiH2O and NaH2O
compounds adsorbed on Ti-doped hBN systems
In order to further verify the feasibility and thermodynamic stability of CO2 adsorption on
Ti-doped h-BN along with added adsorbates compounds under elevated environmental
conditions, the MD investigations were carried out on all given systems and obtained results are
provided in Fig. 3(a-c), respectively. The total energies, the temperature variations and Pair-
Correlation Function (PCF) plots for all given systems were calculated using 6000NSW with
0.5fs time steps at 400K temperature and are shown in Fig. 3(a-c), respectively. It is evident from
Fig. 3(a) that total energy of all systems displays oscillations within a small range, suggesting the
thermodynamic stability of given systems at 400K temperature value. Similarly, for temperature
graphs shown in Fig 3(b), the temperature oscillates being centered at 350K throughout the

10. simulation time. This authenticates that all systems are thermodynamically stable even at
elevated temperature and show no premature release of adsorbates. From PCF plot shown in Fig.
3(c), it provides two major peaks at 1.75 Å and 2.5 Å, indicating that majority of the atoms are
compacted together within average distance between 1.75-2.5 Å, suggesting the 2D planar
behavior of host sheet elements. However, adsorbates tend to have increased radial distribution
as they may move away and get attached back to the decorated surface of monolayer sheets
during MD simulation steps. Further, PCF of all given systems correlate very acutely as the plots
of given systems are overlapping each other as shown in Fig. 3(c), respectively. These
descriptions agree well with earlier available studies in this regard [25, 59].
Figure 3: (a) Total Energy eV/Cell, (b) Temperature (K) and (c) Pair-Correlation Function (PCF) plots
obtained for 6000 NSW at 400K with 0.5fs time step for given systems, respectively.
3.3 Band Structure, Density of States and Charge Difference Diagrams of CO2, BeO, BeH2O,
LiH2O and NaH2O compounds adsorbed on Ti-doped hBN systems
Here, we thoroughly investigate the electronic structures and partial density of states plots
(PDOS) for all mentioned systems through FPS-DFT method to determine the sensitivity
towards CO2 molecule of adsorbed and doped h-BN systems. Band diagrams and partial DOS
plots were calculated for given systems adopting Γ- M - K - Γ path in the I.B.Z (Irreducible
Brillouin Zone) using 40 K-points grid in order to attain the fine quality band structure diagrams
(a)
(b)
(c)

11. and a 19 × 19 × 1 Γ-centered BZ sampling for PDOS plots, respectively. The energy eigenvalues
smearing was gained through Gaussians of width of 0.02 eV energy.
3.3.1 Band structure diagrams
Prior to the investigation for the band structures of CO2 molecule adsorbed on h-BN
decorated surfaces, we designed the band structure of pure and Ti-doped h-BN monolayer in
order to validate our computational techniques and are presented in Fig. 4(a-b), respectively.
Pure h-BN band structure displays insulating behavior having ~4.5 eV band gap as shown in Fig.
4(a), whereas after Ti atom doping surface impurities are observed near the Fermi energy level as
shown in Fig. 4(b), respectively. These results agree well with earlier available reports, thus
validating our computational techniques [36, 42, 43, 45, 48].
Figure 4 (a-b): Band structure diagrams of pure and Ti-doped hBN, respectively.
After validation of the band diagrams of pure and Ti-doped h-BN systems, we calculated the
band structure diagrams CO2, BeO, BeH2O, LiH2O and NaH2O compounds adsorbed on Ti-
doped h-BN systems and are presented in Fig. 5(a-d), respectively. As evident from the band
diagrams shown in Figs. 5(a-d) respectively, CO2 and other adsorbate compounds significantly
modify the band structures of Ti-doped h-BN, thus suggesting its higher sensitive nature towards
CO2 molecule as observed through the band gap variations, accordingly. The CO2 and BeO
compound adsorption on Ti-doped h-BN induces a band gap of ~ 2.2 eV thus producing
semiconducting effect as visible in Fig. 5(a), whereas, when CO2 molecule is adsorbed along
with BeH2O compound, Ti-doped h-BN is converted to semimetal as impurity bands appear at
the Fermi Energy (EF) Level as evident in Fig. 5(b), respectively. Likewise, during CO2 molecule
adsorption along with LiH2O and NaH2O compounds on Ti-doped h-BN, a significant band gap
is achieved for both these cases having almost similar values of ~2.6 eV as shown in Figs. 5(c)
and (d), respectively. As evident, these adsorbates significantly alter the electronic structure,
which suggests that the host sheet accepts the adsorbate entities indicating the real capture of
CO2 molecule upon the surface along with other adsorbate compounds. In general description, it
can be summarized that our technique of adding further adsorbates does not disturb or reduce the
CO2 molecule interaction with Ti-doped h-BN rather in particular case of BeH2O compound, it
supports the dissociation of CO2 molecule as mentioned above. Our predictions sits well with
earlier studies too [36, 42, 43, 45, 48].
(a)
(b)

12. Figure 5 (a-d): Band structures of CO2 and other compounds adsorbed on Ti-doped h-BN systems).
Later, to determine the selectivity of CO2 molecule by the complex h-BN systems, we need
to determine the variation in the band gaps after CO2 molecule adsorption. It can be clearly
observed that, significant band gap variation is achieved indicating the higher selectivity towards
CO2 gas and other compound molecules. Band gap variation is in range from 52-69% in terms of
h-BN band gap as a base value. This higher variation in percentage of band gap indicates
superior selectivity of CO2 gas molecule by the given systems.
3.3.2 Partial Density of States (PDOS) plots
To further support and elucidate CO2 molecule and other adsorbate interaction behavior with
Ti doped h-BN monolayer, extended PDOS plots were calculated and are shown in Figs. 6(a-d),
respectively. As seen in Fig. 6(a) that, the orbitals of Ti atom, O atom of CO2 and Be atoms show
overlapping peaks at -3.8 eV while orbitals of Be and O atom of CO2 hybridize in deep valence
band at -10 eV. This corroborates that CO2 is heavily influenced by hybridization with BeO and
Ti atom. In Fig. 6(b), it can be noticed that density peaks of CO do not overlap with any other
compound except dissociated O atom at -4.5 eV, indicating physical adsorption. Whereas
orbitals of dissociated O atom are hybridized with orbitals of Be, Ti and water molecule at -6.9
eV. Similarly, there are multiple hybridizing density peaks which can be seen in Fig. 6(c) at -9, -
7.8, -6.8 eV and energy interval from -4.2 to -3.8 eV. Such multiple hybridizations of various
compounds at different energy levels in valence band show that CO2, Li, and water molecules
are tightly chemisorbed with Ti-hBN substrate. Likewise, in Fig. 6(d) multiple hybridizing
density peaks of orbitals of CO2, Ti and water molecule are present at -8.9, -7.7, -6.9, -5.9, -3.5
and at -0.1 eV in valence band. Again these multiple hybridizing peaks illustrate that CO2 and
water molecules are tightly adsorbed on Ti doped hBN substrate. However only one hybridizing

13. peak of orbitals of Na is present at -7.0 eV, which indicates that Na is physically adsorbed in the
system [60, 61]. A general conclusion can be formed from given PDOS plots that, CO2 strongly
adsorbs on the Ti doped h-BN surface along with the significant adsorption of BeO, BeH2O,
LiH2O, and NaH2O compounds. Hence, it can be postulated that, these compounds support the
adsorption behavior of CO2 molecule instead of breaking its adsorption process.
Figure 6: PDOS diagrams of (a) CO2/BeO (b) CO2/BeH2O (c) CO2/LiH2O and (d) CO2/NiH2O compounds adsorbed
on Ti-doped h-BN systems, respectively.
3.3.3 Charge Difference Diagrams (CDD)
To explain the CO2 molecule interaction with BeO, BeH2O, LiH2O and NaH2O compounds
along with Ti-doped h-BN systems, we analyzed the CDDs in order to determine the charge
transfer phenomenon. The given CDDs were obtained by using the expression 𝛥𝜌 =
𝜌𝑎𝑑𝑠𝑜𝑠+𝑇𝑖−ℎ𝐵𝑁 − 𝜌𝑇𝑖−ℎ𝐵𝑁 − 𝜌𝑎𝑑𝑠𝑜𝑠 , here, the term 𝜌𝑎𝑑𝑠𝑜𝑠+𝑇𝑖−ℎ𝐵𝑁 defines the total charge of
system including CO2 molecules, other adsorbate compounds and Ti-doped h-BN system,
𝜌𝑇𝑖−ℎ𝐵𝑁 term defines total charge of Ti-doped h-BN system and the term 𝜌𝑎𝑑𝑠𝑜𝑠 defines total
charge of adsorbate entities available on the surface of Ti-doped h-BN system, respectively. Top
and side views of resulting CDDs are presented in Figs. 7(a)-(d), respectively. Here, the electron
loss and gain between atoms is depicted by cyan and yellow colored iso-surfaces, respectively.
As evident from charge difference diagrams provided in Figs. 7(a)-(d), respectively, the
major chunk of charge is accumulated across the adsorbates and at the Ti atom dopant site,
(a) (b)
(c) (d)

14. which indicates the localized charge transfer behavior i.e., impurity atom Ti sharing its charges
to hold the adsorbate compounds.
Figure 7: Top and side* views of charge difference diagrams of (a,a*) CO2BeO (b,b*) CO2BeH2O (c,c*) CO2LiH2O
and (d,d*) CO2NaH2O adsorbed on Ti-doped h-BN monolayer systems with iso-surface value 0.003 e/Å.
Further, as seen from side views of charge difference diagrams of Figs. 7(a)-(d), the yellow
and cyan iso-surfaces are overlapping each other at each adsorbate element sites, which indicates
covalent type of charge sharing. In case of O atom and Ti bonding, the O atom of CO2 holds
maximum yellow iso-surface whereas Ti atom holds cyan iso-surface which indicates the
(a) (b)
(c) (d)
(a*)
(b*)
(c*) (d*)

15. transfer of charge from Ti to O atom thus indicating ionic bonding nature between these two
elements. If we further analyze the charge transfer behavior among the adsorbates only, it can be
seen that in each case, O atom largely attains yellow color and its neighboring space is filled with
cyan color which indicates that the charge is depleted in the vicinity of O atom thus indicating
stronger interaction strength between CO2 molecule and remaining adsorbate compounds,
respectively.
3.4. Activation Energy Barrier
To check the feasibility of various adsorbents for dissociation of CO2, we have calculated
activation energy barrier. According to Brønsted-Evans-Polanyi (BEP) relation [62], activation
energy barrier of transition state can be calculated by adsorption energy of system. We have
calculated activation energy barrier (EAEB) of adsorbents through:
EAEB = ETS ˗ EADC
where ETS and EADC denote transition state energy and adsorption energy of compounds.
Obtained values of activation energy barrier and bond length of O-C of CO2 molecule with
decoration of various compounds are presented in Table 2. EAEB of various compounds for
dissociation of CO2 follows the order: Ti-hBN > NaH2O_Ti-hBN > LiH2O_Ti-hBN > BeO_Ti-
hBN > BeH2O_Ti-hBN. Since EAEB of Ti-hBN is highest among five systems so it cannot be a
used as activating agent for dissociation of CO2. EAEB of Ti-hBN (3.77 eV) is far less than
activation energy barrier without catalysts (5.52 eV) [13]. The order of elongation of O-C bond
length of CO2 molecule follows the order: BeH2O_Ti-hBN > BeO_Ti-hBN > LiH2O_Ti-hBN >
NaH2O_Ti-hBN > Ti-hBN. Elongation of O-C bond length of CO2 in response to decoration of
various compounds except BeH2O_Ti-hBN could not reach the threshold of breakage of O-C of
CO2 bond (Å). However, decoration of BeO_Ti-hBN, LiH2O_Ti-hBN and NaH2O_Ti-hBN has
promoted the reduction of activation energy barrier. Through activation energy barrier
calculations for all given systems, it can be postulated that, only the adsorption of BeH2O can
reduce the activation energy barrier to dissociate CO2 molecule. Although as mentioned above,
remaining compounds (i.e., BeO, LiH2O and NaH2O) may not help in CO2 molecule dissociation
process but they help in reducing activation energy barrier of CO2 molecule.
Table 2: The adsorption energy (Eads), bond length of N-B, N-Ti, C-O, Ti-O and adsorbate-O atoms
System EAEB (eV) Eads (eV) O-C (Å)
Ti-hBN 3.77 -3.9 ---
CO2NaWadsTi-hBN 2.43 -3.11 1.34
CO2LiWadsTi-hBN 2.31 -3.07 1.36
CO2BeOadsTi-hBN 2.02 -2.91 1.40
CO2BeWadsTi-hBN 1.42 -2.88 ---
The adsorption energy and energy barrier relationship is presented in Fig. 8(a), in order to
analyze and understand the catalytic reaction process and acquire guidance for selective design
of efficient catalysts as per adsorption energy values. Given diagram of Fig. 8 clearly illustrates
that there is nearly a linear relationship between the adsorption energy and energy barrier for
CO2 activation on the four catalyst compounds investigated here. Subjected to variations in
geometrics and electronic properties among these four compounds, the energy barrier is not
perfectly linear to adsorption energy [13]; however, slope of given curve shows positive trend,

16. suggesting the increase in adsorption energy will cause increase in activation energy barrier.
Through activation energy barrier, one can easily determine the dissociation behavior of CO2
with available catalytic compounds, respectively.
3.5. Transition states for the direct dissociation of CO2
Transition states of direct dissociation of CO2 into CO and O during adsorption of BeH2O
compound has been explored by presenting three transition structures and respective energy in
Fig. 8(b-d), respectively. From Fig. 8(b), it can be noticed that O-C-O angle has been bent to
128˚ from straight and bond length of Be-O has elongated to 1.645 Å at reactant (Initial) state. In
transition state (TS) shown in Fig. 8(c), one O atom of CO2 molecule elongates and gets attached
to Ti and Be atom, respectively. Elongated C-O bond length reaches to 2.191 Å, that shows the
breaking intent of O atom from CO2 molecule. Finally, at the product (final) state as shown in
Fig. 8(d), the bond length between broken O and Be atoms comes in range of 1.453 Å and the
bond length between Ti and broken O atom reaches to 1.858 Å, respectively [13]. Transition
State results were visualized through Materials Studio Software package; hence the color scheme
looks different from abovementioned figures.
Figure 8: (a) Relationship between adsorption energy and energy barrier, atomic structure of CO2BeH2O adsorbed
Ti-doped hBN system during transition state calculations (b) Reactant (Initial) State (c) Transition State (TS) (d)
Product (Final) state and (d) the energy profile obtained during TS calculations, respectively.
Conclusions
In conclusion, we investigated particularly the CO2 molecule adsorption and direct
dissociation capability of Ti-doped h-BN sheet along with different adsorbates compounds (i.e.,
BeH2O, LiH2O, NaH2O and BeO) based on FPS-DFT calculations. Through negative adsorption
(a) (b)
(c) (d)

17. energies obtained in range of -2.88 to -3.11 eV, it can be stated that the CO2 strongly adsorbs on
these systems and will not be released easily thus rejecting the notion of instant release. Further,
among all these compounds adsorbed on Ti-doped h-BN, only BeH2O adsorption with CO2
molecule, caused the direct dissociation of CO2 into CO molecule and O atom. Through obtained
total energy, temperature and PCF plots of MD calculations, minute variation in the energy and
temperature profiles of given systems were observed thus suggesting stabilized geometrical
systems with captured CO2 molecules. From band structure and PDOS plots, the sensitivity and
selectivity of CO2 molecules is analyzed as after adsorption, significant band gap variations are
achieved in range of 2.2 to 2.6 eV depending upon the type of adsorbate systems. PDOS plots
further supported the notion of CO2 molecule adsorption as strong hybridization peaks between
the orbitals of CO2 molecule and constituent adsorbate compounds and Ti atom were found in
deep valence shells thus supporting the capturing of CO2 on Ti-doped hBN surface. Charge
difference diagrams signify the electronic interaction behavior as adsorbate elements are
anchored by the Ti atoms, since Ti atom shares its electrons to hold the CO2 molecule and other
adsorbate elements. Further, to elucidate the dissociation process of CO2, activation energy
barrier and Transition state calculations were performed. Almost linear relation between
Activation Barrier Energy and adsorption energy is achieved, suggesting the catalytic support of
compounds. Only, BeH2O adsorbed compound reduced the barrier energy, thus causing the
dissociation of CO2 molecule. Transition state images were also provided to indicate the reaction
path during dissociation of CO2 molecule. In generalized conclusion, it can be stated that Ti-
doped monolayer h-BN sheet is a viable candidate for CO2 capturing process, and also the
additional adsorbate compounds can be added along the surface to enhance the capturing and
direct dissociation process of CO2 molecules. This study can serve as the basis of experimental
extrapolation of CO2 capture and conversion through h-BN monolayer systems with additional
adsorbate atoms and molecules with catalytic properties.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (No.
51876049) and Pakistan Science Foundation (No:PSF/RES/S-MUET/ENGG (187)). In addition,
we would like to acknowledge the support that NVIDIA provided us through the GPU Grant
Program.
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Data Availability
The processed data related these findings is part of the paper.

22. Dear Editors:
We would like to submit revised manuscript entitled “Investigating CO2 capture
and direct dissociation through AEM/H2O compounds adsorption on Ti-doped h-BN
monolayer system; FPS-MD Calculations”, which we wish to be considered for
publication in “Computational Material Science”. No conflict of interest exists in the
submission of this manuscript, and is approved by authors for publication. I would like
to declare on behalf of my co-authors that the work described was original research that
has not been published previously, and not under consideration for publication
elsewhere, in whole or in part. All the authors have approved the manuscript that is
enclosed.
Thank you and best regards.
Yours sincerely,
All Authors
Declaration of Interest

23. Author Statement
We, the authors of the manuscript titled "Investigating CO2 capture and direct
dissociation through AEM/H2O compounds adsorption on Ti-doped h-BN monolayer
system; FPS-MD Calculations," are pleased to submit our work to Materials Today
Communications.
I would like to declare on behalf of my co-authors that the work described was
original research that has not been published previously, and not under consideration
for publication elsewhere, in whole or in part. All the authors have approved the
manuscript that is enclosed. We are confident that our work aligns with the mission of
Materials Today Communications to publish high-impact research that advances the
understanding of materials science.
We appreciate the consideration of our manuscript and look forward to the possibility
of sharing our findings with the Materials Today Communications community.
Sincerely,
Muhammad Rafique
Danish Hussain
Basheer Ahmed Kalwar
Authors statement