Structural and electronic properties of H₂, CO, CH₄, NO, and NH₃ adsorbed onto Al₁₂Si₁₂ nanocages using density functional theory

Abstract

In this study, the adsorption of gases (CH₄, CO, H₂, NH₃, and NO) onto Al₁₂Si₁₂ nanocages was theoretically investigated using density functional theory. For each type of gas molecule, two different adsorption sites above the Al and Si atoms on the cluster surface were explored. We performed geometry optimization on both the pure nanocage and nanocages after gas adsorption and calculated their adsorption energies and electronic properties. The geometric structure of the complexes changed slightly following gas adsorption. We show that these adsorption processes were physical ones and observed that NO adsorbed onto Al₁₂Si₁₂ had the strongest adsorption stability. The E _g (energy band gap) value of the Al₁₂Si₁₂ nanocage was 1.38 eV, indicating that it possesses semiconductor properties. The E _g values of the complexes formed after gas adsorption were all lower than that of the pure nanocage, with the NH₃–Si complex showing the greatest decrease in E _g. Additionally, the highest occupied molecular orbital and the lowest unoccupied molecular orbital were analyzed according to Mulliken charge transfer theory. Interaction with various gases was found to remarkably decrease the E _g of the pure nanocage. The electronic properties of the nanocage were strongly affected by interaction with various gases. The E _g value of the complexes decreased due to the electron transfer between the gas molecule and the nanocage. The density of states of the gas adsorption complexes were also analyzed, and the results showed that the E _g of the complexes decreased due to changes in the 3p orbital of the Si atom. This study theoretically devised novel multifunctional nanostructures through the adsorption of various gases onto pure nanocages, and the findings indicate the promise of these structures for use in electronic devices.

1 Introduction

Since Kroto et al. (1985) discovered (C₆₀) fullerene, nanomaterials have gradually become a popular research topic due to their unique properties and wide range of applications (Goroff, 1996; Diederich and Gómez-López, 1999; Kataura et al., 2002; Martín, 2006). Instead of using only C to construct fullerenes, researchers have turned to fullerenes made from other elements, especially elements from group Ⅲ of the periodic table and the group V elements that are adjacent to C. These fullerenes include B₁₂N₁₂, Al₁₂N₁₂, B₁₂P₁₂, and Al₁₂P₁₂ (Beheshtian et al., 2012a; Beheshtian et al., 2012b; Beheshtian et al., 2012c; Rad and Ayub, 2016; Hussain et al., 2020a). In addition, researchers have used elements from groups Ⅱ and Ⅵ to construct similar fullerene structures, such as Be₁₂O₁₂, Mg₁₂O₁₂, Ca₁₂O₁₂, and all-boron fullerene (Kakemam and Peyghan, 2013; Zhai et al., 2014; Rezaei-Sameti and Abdoli, 2020; Ahsan et al., 2021). Other fullerenes are made from transition elements and oxygen element (de Oliveira et al., 2015). Nanocages with the general formula (XY)₁₂, where n is the number of atoms, are more popular among researchers because they are more stable (Strout, 2000). Many types of nanostructures exist, among which inorganic nanostructures have attracted the attention of researchers due to their extremely high stability and asymmetric charge distribution (Dai, 2002; Tasis et al., 2006; Bindhu et al., 2016). The study of fullerene structures is a critical branch of nanotechnology because of their applications in electronic devices, special materials, and environmental processes. Shakerzdeh et al. (2015) studied the properties of alkali metals (Li, Na, and K) interacting with Be₁₂O₁₂ and Mg₁₂O₁₂ nanoclusters. Doping with alkali metals can significantly improve the non-linear optical response of nanocages. Beheshtian et al. (2012c) have studied the adsorption of NO and CO by Al₁₂N₁₂. Due to the different changes in the E _g (energy band gap) of NO and CO when adsorbed, resulting in different changes in electrical conductivity, Al₁₂N₁₂ clusters may selectively detect NO molecules when CO molecules are present. Vergara-Reyes et al. (2021) studied the adsorption of NO on the C₃₆N₂₄ fullerene, providing a possible carrier/protector of nitric oxide and thus fulfill its correct biological functions. Escobedo et al. (2019) conducted the effect of chemical order on the structural and physicochemical properties of B₁₂N₁₂ fullerene. Bautista Hernandez et al. (2022) found that the (TiO₂)₁₉ cluster is a good candidate for storing various gases, and can also be used as a hydrogen storage device.

For China in particular and the rest of the world in general, fossil fuel use must be scaled back, and hydrogen, which has the highest calorific value per unit mass of fuels and produces only water during combustion, is an attractive alternative (Yilanci et al., 2009; Züttel et al., 2010; Mazloomi and Gomes, 2012). Technologies for capturing pollutants and greenhouse gases from the atmosphere will also play a key role in our fight against climate change (Cazorla-Amorós et al., 1996; Zhang et al., 2008; Mastalerz et al., 2011).

Oku et al. (2004) synthesized the first inorganic nanocages in 2004 before the later emergence of B₁₂N₁₂, Al₁₂N₁₂, B₁₂P₁₂, and Al₁₂P₁₂ nanocages. Yarovsky and Goldberg, (2005) studied the adsorption of H₂ by Al₁₃ clusters using DFT (density functional theory). Thereafter, Felício-Sousa et al. (2021) examined the adsorption properties of H₂, CO, CH₄, and CH₃OH on Fe₁₃, Co₁₂, Ni₁₃, and Cu₁₃ clusters using an ab initio investigation. Tan et al. (2022) studied clusters of different numbers of Al atoms. Yang et al. (2018) predicted the properties of electron redundant Si_nN_n fullerenes. Metal oxide nanocages are also a popular area of research; Otaibi et al. conducted a theoretical study on the adsorption of glycoluril by Mg₁₂O₁₂ nanocages (Al-Otaibi et al., 2022). Some nanocages exhibit unique electronic properties after doping with alkali metals, and these have also been widely studied (Ahsin and Ayub, 2021). We replaced the N atoms in Al₁₂N₁₂ with Si atoms to investigate a more diverse range of materials than those in the literature. In this study, we adopted DFT to analyze the properties of Al₁₂Si₁₂, such as its stability, after the adsorption of CH₄, CO, H₂, NO, and NH₃.

2 Computational methodology

An Al₁₂Si₁₂ nanocage was selected as the model adsorbent. Geometry optimization was performed using hybrid functional DFT (B3LYP) (Becke, 1993) implemented in Gaussian 09 (Frisch et al., 2004). B3LYP is a suitable and widely accepted functional for nanoclusters (Chen et al., 2009; Hussain et al., 2020b). The mixed basis set 6-31G (d, p) was used. Gas molecules CH₄, CO, H₂, NO, and NH₃ were adsorbed onto Al₁₂Si₁₂ nanocages using the same method. Two adsorption sites on the Al₁₂Si₁₂ nanocage were considered. Vibration frequencies were also calculated at equivalent levels to verify that all stationary points corresponded to true minima on the potential energy surface. Geometry optimization was conducted, and D _ads (distance of adsorption), E _ads (adsorption energy), E _HOMO (energy of the highest occupied molecular orbital), E _LUMO (energy of lowest unoccupied molecular orbital), DOS (density of states), and Q _T (Mulliken charge transfer) were calculated to determine the adsorption mechanism.

The stability of the Al₁₂Si₁₂ nanocage was examined in terms of E _coh (cohesive energy), which can be determined by calculating the average energy difference of each atom before and after bonding using the following equation:

$$E_{\mathrm{c}\mathrm{o}\mathrm{h}}=\frac{E_{\mathrm{t}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}}-12\left(E_{\mathrm{A}\mathrm{l}}+E_{\mathrm{S}\mathrm{i}}\right)}{24}$$

where E _Al and E _Si are the energies of non-interacting Al and Si atoms, respectively, and E _total is the energy of the Al₁₂Si₁₂ nanocage.

E _ads is defined as follows:

$$E_{\mathrm{a}\mathrm{d}\mathrm{s}}=E_{\mathrm{a}\mathrm{d}\mathrm{s}\mathrm{o}\mathrm{r}\mathrm{b}\mathrm{a}\mathrm{t}\mathrm{e}@\mathrm{n}\mathrm{a}\mathrm{n}\mathrm{o}\mathrm{c}\mathrm{a}\mathrm{g}\mathrm{e}}-E_{\mathrm{a}\mathrm{d}\mathrm{s}\mathrm{o}\mathrm{r}\mathrm{b}\mathrm{a}\mathrm{t}\mathrm{e}}-E_{\mathrm{n}\mathrm{a}\mathrm{n}\mathrm{o}\mathrm{c}\mathrm{a}\mathrm{g}\mathrm{e}}$$

Here, E _{adsorbate@nanocage}, E _adsorbate, and E _nanocage are the total energies of an adsorbate adsorbed onto the pure nanocage, of the adsorbate, and of the pure nanocage, respectively. A negative value of E _ads corresponds to exothermic adsorption. The more negative the adsorption value, the stronger the adsorption capacity. The DOS was generated in Multiwfn (O'Boyle et al., 2008).

3 Results and discussion

3.1 Geometrical characteristics

3.1.1 Al₁₂Si₁₂ structure

The optimized structures of the bare nanocage comprising eight hexagons and six tetragon rings are given in Figure 1. In this nanocage, two non-equivalent bonds exist: one between the tetragon and hexagon ring, and the other between the two hexagonal rings, represented as b ₆₄ and b ₆₆, respectively. The lengths of b ₆₄ and b ₆₆ are 2.47 and 2.43 Å, respectively. The calculated E _coh of Al₁₂Si₁₂ is −3.11 eV with zero point energy (ZPE) correction (Buelna-García et al., 2022). The calculated E _coh of each atom is closer to the reported E _coh of the most stable inorganic analogue, B₁₂N₁₂. The experimental and theoretical reported E _coh of B₁₂N₁₂ are −4.00 (Pokropivny et al., 2000) and −6.06 eV (Pokropivny and Ovsyannikova, 2007), respectively. As indicated by these results, the Al₁₂Si₁₂ nanocage is highly stable.

FIGURE 1.

Stable configurations of nanocage complexes.

3.1.2 Al₁₂Si₁₂–gas molecule structure

CH₄, CO, H₂, NO, and NH₃ were selected as the target adsorbates. We performed sufficient structural optimization of the Al₁₂Si₁₂ nanocage containing CH₄, CO, H₂, NO, and NH₃ molecules. For each gas molecule, two different adsorption sites above the Al and Si atoms on the nanocage surface were considered. Each gas is discussed with respect to adsorption at each of the two nanocage positions. The bond length (b ₆₄ and b ₆₆), D _ads value (defined as the center to center distance between the atoms of the nanocage and gas molecule that are closest to each other), and E _ads value are listed in Table 1. According to previous studies, the threshold E _ads at which physisorption becomes chemisorption is approximately 23.00 kcal/mol (1.00 eV) (Jouypazadeh and Farrokhpour, 2018; Nagarajan and Chandiramouli, 2019; Swetha et al., 2020). D _ads must be < 2.00 Å for chemisorption to occur (Contreras et al., 2014). As shown in Table 1, the adsorption processes were all physical, and NO adsorbed above the Al atom of the nanocage had the strongest adsorption stability.

TABLE 1.

Bond length (b ₆₆ and b ₆₄), distance of adsorption (D _ads) and energy of adsorption (E _ads).

Complexes	b 66 (Å)	b 64 (Å)	D ads (Å)	E ads (kcal/mol)	Complexes	b 66 (Å)	b 64 (Å)	D ads (Å)	E ads (kcal/mol)
Al12Si12	2.43	2.47	—	—	Al12Si12	2.43	2.47	—	—
CH4-Al	2.47	2.43	5.76	−1.00	CH4-Si	2.47	2.43	7.36	−1.02
CO-Al	2.47	2.43	4.51	−1.05	CO-Si	2.47	2.43	4.39	−0.96
H2-Al	2.47	2.43	4.52	−12.37	H2-Si	2.47	2.43	3.92	−12.34
NO-Al	2.47	2.43	3.94	−15.35	NO-Si	2.47	2.43	5.58	−15.18
NH3-Al	2.47	2.43	6.11	−0.55	NH3-Si	2.47	2.42	3.48	−1.23

The calculated stable configurations (local minima) are summarized in Figure 1. When the gas was adsorbed onto the Al or Si atom of the Al₁₂Si₁₂ nanocage, slight local structural deformation of both the molecule and the nanocage occurred. The b ₆₆ and b ₆₄ bonds and angles remained almost unchanged. The adsorption that induced greatest change was that of NH₃ onto the Si atom; it changed the lengths of b ₆₆ and b ₆₄ by 0.005 and 0.006 Å, respectively. The smallest change was caused by the adsorption of NO onto the Al atom; it changed the lengths of b ₆₆ and b ₆₄ by 0.0003 and 0.0204 Å, respectively.

In the Al atom adsorption group, the E _ads of CH₄–Al, CO–Al, NH₃–Al, NO–Al, and H₂–Al were −1.00, −1.05, −0.55, −15.35, and −12.37 kcal/mol, respectively. The adsorption stability of the NO and H₂ analytes was much better than that of the others. The D _ads values of NO–Al and H₂–Al were 3.94 and 4.52 Å, respectively. For NO–Al, the N–O bond length increased from 1.06 Å in isolated NO to 1.16 Å in the adsorbed state. When Al₁₂Si₁₂ adsorbed H₂, the H–H bond length increased from 0.6 Å in isolated H₂ to 0.74 Å in the adsorbed state. The D _ads between the gas molecule and the Al atom of the nanocage were 5.76 and 4.51 Å for CH₄–Al and CO–Al, respectively. The C–H bonds of CH₄–Al and the C–O bond of CO–Al also became slightly longer. The lengths of the four C–H bonds of CH₄–Al increased by 0.02269, 0.02286, 0.02290, and 0.02313 Å. The length of the C–O bond of CO–Al increased by 0.02 Å. The D _ads of NH₃–Al was 6.11 Å. The length of the three N–H bonds in the NH₃ molecule increased by 0.015636, 0.01599, and 0.01542 Å. Among these complexes, the three N–H bonds of NH₃–Al had the smallest increase in length.

In the Si atom adsorption group, the E _ads of CH₄–Si, CO–Si, NH₃–Si, NO–Si, and H₂–Si were −1.02, −0.96, −1.23, −15.18, and −12.34 kcal/mol, respectively. The D _ads values of CH₄–Si, CO–Si, NH₃–Si, NO–Si, and H₂–Si were 7.36, 4.39, 3.48, 5.58, and 3.92 Å, respectively. In the Si atom adsorption group of complexes, both nanocages and gas molecules changed slightly. The length of the four C–H bonds increased by 0.02253, 0.02268, 0.02284, and 0.02315 Å. The length of the C–O bond increased by 0.02214 Å. The three N–H bonds increased in length by 0.01504, 0.01483, and 0.01485 Å. The lengths of the N–O bond and H–H bond increased by 0.09682, and 0.14372 Å, respectively. Among these complexes, the lengths of the three N–H bonds of NH₃–Si increased by the least, but they increased by more than those of the three N–H bonds of NH₃–Al in the Al group.

3.2 Electronic properties

3.2.1 Mulliken charge and energy band gap analysis

Detailed information including the E _HOMO and E _LUMO, Q _T, and the △E _g (change in, E _g of nanocage upon adsorption) values is listed in Table 2.

TABLE 2.

The Energy of HOMO (E _HOMO), energy of LUMO (E _LUMO), energy band gap (E _g), change of E _g of nanocage upon the adsorption process (△E _g), Mulliken charge transfer (Q_T).

Complexes	E LUMO (eV)	E HOMO (eV)	E g (eV)	△E g (eV)	Q T (|e|)	Complexes	E LUMO (eV)	E HOMO (eV)	E g (eV)	△E g (eV)	Q T (|e|)
Al12Si12	−3.61	−4.99	1.38	—	—	Al12Si12	−3.61	−4.99	1.38	—	—
CH4-Al	−3.69	−5.00	1.31	−0.06	−0.0022	CH4-Al	−3.69	−5.00	1.31	−0.07	−0.0008
CO-Al	−3.67	−4.97	1.30	−0.08	0.0480	CO-Al	−3.69	−5.00	1.31	−0.07	0.0001
H2-Al	−3.69	−4.99	1.30	−0.08	0.0197	H2-Al	−3.69	−5.00	1.31	−0.07	0.0224
NO-Al	−3.70	−4.99	1.29	−0.09	0.0190	NO-Al	−3.68	−5.00	1.32	−0.06	0.0021
NH3-Al	−3.74	−5.05	1.31	−0.07	−0.0021	NH3-Al	−3.76	−4.99	1.23	−0.15	0.1177

In the Al atom adsorption group, the Mulliken charge analysis shows that the number of transferred electrons in CH₄–Al, CO–Al, NH₃–Al, NO–Al, and H₂–Al were −0.0020, −0.0480, −0.0021, 0.0190, and 0.0197 |e|, respectively. The E _g of CH₄–Al, CO–Al, NH₃–Al, NO–Al, and H₂–Al are 1.31, 1.30, 1.31, 1.29, and 1.30 eV, respectively. The E _g of these complexes was lower than that of the pure nanocage, and this decrease was largest in the NO complex, at 0.09 eV, and smallest in the CH₄ complex, at 0.06 eV.

In the Si atom adsorption group, the Mulliken charge analysis demonstrated that the number of transferred electrons in CH₄–Si, CO–Si, NH₃–Si, NO–Si, and H₂–Si were −0.0008, 0.0001, 0.1177, 0.0021, and 0.0224 |e|, respectively. The E _g of CH₄–Si, CO–Si, NH₃–Si, NO–Si, and H₂–Si was 1.31, 1.31, 1.23, 1.31, and 1.31 eV, respectively. The E _g values of these complexes were also lower than that of the pure nanocage, with the NH₃ complex exhibiting the greatest decrease, at 0.15 eV, and the NO complex exhibiting is the smallest decrease at 0.06 eV.

As demonstrated in Table 2, the E _LUMO values of these complexes were slightly lower than those of the pure nanocage, but their E _HOMO values did not vary much from those of the pure nanocage. The adsorption stability of the Si adsorption group of complexes is similar to that of the Al adsorption group. However, the adsorbates in the Si adsorption group transferred fewer electrons than the corresponding adsorbates in the Al adsorption group, except for the H₂ and NH₃ analytes. The N atom gained electrons, and the three H atoms lost electrons in the NH₃–Al adsorption. However, the N atom and the three H atoms all lost electrons in the NH₃–Si adsorption due to the difference in adsorption position. The adsorption stability of NH₃–Si was higher than that of NH₃–Al due to the short adsorption distance and the large number of transferred electrons in the NH₃–Si adsorption.

3.2.2 Frontier molecular orbitals and DOS

To further analyze the effect of gas molecules on the electronic properties of nanocages, the HOMO (highest occupied molecular orbital), LUMO (lowest unoccupied molecular orbital) and DOS of isolated and complexed nanocages were analyzed. The HOMO and LUMO distributions of Al₁₂Si₁₂ from a vertical perspective are shown in Figure 2. The HOMO primarily serves as an electron donor, and the LUMO primarily serves as an electron acceptor (Dai, 2002). For the HOMO of the pure Al₁₂Si₁₂ nanocage, the positive and negative areas alternate between Al and Si atoms (in Figure 2 the red area is negative, the green area is positive). However, for the LUMO of the pure Al₁₂Si₁₂ nanocage, the positive and negative areas alternated between the inside and outside of the nanocage and the HOMO and LUMO were distributed on the same plane. The obtained frontier molecular orbital energies (E _HOMO and E _LUMO) and the calculated, E _g value of the nanocages are shown in Table 2. The E _g of Al₁₂Si₁₂ was approximately 1.38 eV, demonstrating its semiconductor properties.

FIGURE 2.

HOMO and LUMO distributions of nanocage complexes.

The HOMO and LUMO plots of the complexes are displayed in Figure 2. The lower the E _g value, the more easily a molecule was excited. In the Al adsorption group, the HOMO and LUMO of complexes were almost unchanged. After gas adsorption, the distribution positions of the HOMO and LUMO changed from being on the same plane to being perpendicular to each other. In the Si adsorption group, the HOMO and LUMO of CO–Si remained on the same plane after adsorption. This may be due to the low number of electron transfers. In NH₃–Si, the LUMO distribution was in the NH₃ molecule. This may be because NH₃–Si has the shortest adsorption distance and the greatest charge transfer. In NO–Si, part of the HOMO is transferred to the quadrilateral ring opposite the top and bottom. This is most likely because the HOMO energy level of NO–Si is lower than that of NO–Al.

For further confirmation of the electronic behavior of these complexes, DOS analyses were performed (shown in Figures 3, 4). The orbitals in the lower energy region of Al₁₂Si₁₂ were mainly the 3p orbitals of the Si and Al atoms. At approximately −0.26 a.u., 3s orbitals of both the Al atoms and the Si atoms were maily present. The HOMO–LUMO energy level was composed mainly of the 3p orbitals of the Si and Al atoms, whereas the 3s orbitals of Al atoms were also present near the LUMO energy level.

FIGURE 3.

DOS (density of states) of nanocage complexes.

FIGURE 4.

DOS (density of states) of nanocage complexes.

The effect of the gas molecular orbital on the complex orbital when the nanocage adsorbed some gases was not significant (atomic orbitals that do not contribute to the total orbitals are not depicted in Figures 3, 4). We divided the complexes into two groups: The first including gas molecular orbitals that did not contribute to the total orbitals of the complexes, and the second including the gas molecular orbitals that contributed to the total orbitals of the complexes. In the first group, after gas adsorption, a new peak at 0.2 a.u. appeared, resulting in a slight decrease in the HOMO of the complexes (except for CO–Al). In addition, due to the adsorption of the gas molecule, the 3s orbital of the Al atom produced a small peak at −0.12 a.u. (shown by the blue curve), causing the peak at −0.11 a.u. to shift to the right slightly. This may be the reason for the decrease in LUMO energy level. In the second group, after gas adsorption, a new peak also appeared at 0.2 a.u.. The 3p orbital of the N atom in NH₃–Al peaked at −0.27 a.u., whereas it peaked at −0.28 a.u. in NH₃–Si (depicted by the brown curve). The 3p orbitals of the N and O atoms in NO–Al and NO–Si had peaks at −0.23 and −0.12 a.u. (the brown curve and the orange curve), respectively. Moreover, the peak value of the 3p orbital of the O atom was greater than that of the N atom. However, compared with the first group, the new peaks in the second group caused almost no decrease in HOMO and LUMO energy levels. The peak generated at 0.2 a.u. of the 3p orbital of the Si and Al atoms was the main reason for the reduction in HOMO energy level.

4 Conclusion

DFT calculations were performed to investigate the equilibrium geometries, stabilities, and electronic properties of gases adsorbed onto Al₁₂Si₁₂ nanocages. The E _g value of Al₁₂Si₁₂ was 1.38 eV, demonstrating the semiconductor properties of the nanocage. We performed structural optimization of Al₁₂Si₁₂ nanocages with adsorbed CH₄, CO, H₂, NO, and NH₃ molecules to study their adsorption energies, equilibrium geometry, and electronic properties. Two adsorption positions on the nanocage were studied. The adsorption energy of these complexes demonstrated that the adsorption of these gases by Al₁₂Si₁₂ nanocages is physical. Our findings reveal that the stabilities of the complexes are as follows: Al₁₂Si₁₂–NO > Al₁₂Si₁₂–H₂ > Al₁₂Si₁₂–NH₃ >Al₁₂Si₁₂–CH₄ >Al₁₂Si₁₂–CO. The geometric structure of the nanocage changed slightly following adsorption of molecules. The E _g of the complexes was lower than that of the pure nanocage due to the electron transfer between the gas molecules and the nanocage. The more electrons were transferred, the greater the decrease in E _g. Except for the 3p orbitals of the N and O atoms, the orbitals of the gas molecules did not contribute to the total orbitals of the complexes. The 3p orbitals of the Si atoms in the Al₁₂Si₁₂ nanocage are the main reason for the change in HOMO–LUMO energy levels detected.

Funding Statement

This work was supported by the National Natural Science Foundation of China, grant number 42167016. The Natural Science Foundation of Ningxia Province in China, grant number 2022AAC03123. The Key Research and Development Program of Ningxia Province in China, grant number 2020BEB04003, and the fifth batch of the Ningxia Youth Science and Technology Talents Project, grant number NXTJGC147.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

Conceptualization, L-KL and K-NL; methodology, K-NL; software, W-LX; validation, Y-QM; formal analysis, L-KL; investigation, BH; resources, BH; data curation, K-NL; writing original draft preparation, L-KL; writing—review and editing, K-NL; visualization, W-LX; supervision, K-NL; project administration, BH; funding acquisition, K-NL. All authors have read and agreed to the published version of the manuscript.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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