Yingcho Liu, Jinhu Chen,b, Yuqiong Li,b,*, Cuihu Zho,b

a School of Chemistry & Chemical Engineering, School of Resources, Environment and Materials, Guangxi University, Nanning 530004, China

b Guangxi Key Laboratory of Processing for Non-ferrous Metal and Featured Materials, Guangxi University, Nanning 530004, China

Keywords:Chalcopyrite Water molecule Oxygen molecule Co-adsorption

A B S T R A C T Chalcopyrite is a common copper-bearing mineral with antiferromagnetic properties.However, this property has rarely been considered in previous studies for detailed adsorption behaviors of molecules on chalcopyrite.Based on density functional theory (DFT), new adsorption pathways by H2O and O2 on the chalcopyrite metal terminated(112)surface((112)-M)is found in this work.First,through simulating the adsorption of an isolated water molecule and monolayer water molecules, it is confirmed that H2O molecules tend to adsorb on the surface Fe atoms more than on the surface Cu atoms.Then, we studied various adsorption behaviors of the O2 molecule.It is found that the adsorption on the hollow Fe—Fe site is the most stable case; however, O2 is undissociated.Two adsorption cases will happen when H2O—O2 adsorb simultaneously on the surface.For the S site,the H2O molecule thoroughly dissociated and formed S—O species, and the other case is H2O undissociated adsorbing at the Cu site.For the former case, it is interesting that H2O is dissociated before O2.Ⓒ2023 Published by Elsevier B.V.on behalf of China University of Mining & Technology.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

1.Introduction

Chalcopyrite (CuFeS2), the most plentiful copper-bearing mineral, accounts for approximately 70% of the world’s total copper[1].Froth flotation and hydrometallurgy are the most commonly used methods for the beneficiation of copper-bearing ores [2–4].After interaction with the H2O and O2molecules, the surfaces of sulfide minerals are prone to oxidation,resulting in a large number of soluble sulfur oxides, including sulfates [5].The oxidation behavior of chalcopyrite is crucial in flotation and hydrometallurgical processes.

Through zeta potential measurement and X-ray photoelectron spectroscopy (XPS) testing, Fairthorne et al.[5] investigated the oxidation behaviors during the flotation process of chalcopyrite.They found that the surface is hydrophobic because of dissolving Fe2+and Cu+, while the surface is hydrophilic because of the influence of the metal hydroxide.Therefore,oxidation behaviors change the property of the chalcopyrite surface and consequently affect its flotation performance.Dutrizac[6],Parker et al.[7],and Yang et al.[8] used scanning electron microscopy (SEM), X-ray diffraction(XRD), XPS, and other analysis techniques to explore the change of the chalcopyrite surface layer in the leaching process.Some researchers believe that neither thiosulphate nor polysulphide species were directly detectable as surface intermediates [7,8].The jarosite is the main product during the chalcopyrite bacterial leaching, which has serious passivation effects.

By XPS[9],scanning photoelectron microscopy(SPEM)[11],and SEM[10],some scholars have investigated the oxidation mechanism of chalcopyrite.Oxidation behavior that preferentially occurs at surface iron sites is their unanimous conclusion.Furthermore,Li et al.[11]concluded that the mechanism offormation on the chalcopyrite surface is consistent with that on the pyrite surface, and the oxidation state of Cu on chalcopyrite remains+1 before and after oxidation.This finding is in line with Li et al.[12] that the valence states of Fe and Cu atoms in the chalcopyrite are+3 and+1,respectively.In addition,density functional theory(DFT)has been utilized by many researchers to study the oxidation mechanism [13–21,28,33,34] and the hydration [35–38] of minerals.For chalcopyrite,de Lima et al.[19]performed a detailed analysis of the reconstitution of chalcopyrite (001)-S, -M and the adsorption behaviors of the H2O molecule on two kinds of reconstructed chalcopyrite surfaces based on DFT.They showed that H2O molecules are preferentially adsorbed on the (001)-S Fe site by forming Fe—O bonds.Furthermore, the adsorption energy is about -95.5 kJ/mol, which is lower than that of the adsorption of the Cu site by 25.1 kJ/mol.On this basis,Xiong et al.[20]investigated the adsorption behavior of the O2molecule and H2O—O2co-adsorption on the chalcopyrite(001) surface by XPS and DFT.They also found that oxidation at the chalcopyrite surface occurs preferentially at the Fe site,forming FeO(OH)products.Wei et al.[21]studied the oxidation mechanism of chalcopyrite (112)-M and -S surface.Through the adsorption of the H2O molecule on the chalcopyrite surface,they concluded that the exposure of S atoms on the CuFeS2surface leads to natural hydrophobic properties.

Chalcopyrite is a typical semiconductor material and has an antiferromagnetic property with oxidation of Fe3+Cu+S2[11,12,23]; however, most DFT calculations did not take into account this case for the related studies on the chalcopyrite.Our previous results show that the properties of chalcopyrite are accurately understood by setting the antiferromagnetic and Hubbard correction +U [12].Using the DFT+U methodology, Khaledialidusti et al.[23]analyzed the surface property of the CuFeS2(100)surface and studied the adsorption behaviors of the CO2on that surface.They found two kinds of most stable adsorption configurations,with adsorption energies of -22.8 and -11.7 kJ/mol, respectively.In contrast,the CO2molecule maintains its almost linear structure while the two oxygen atoms in the C—O bond are elongated.This suggests that the calculation methods for the chalcopyrite system are essential.

In the present work,based on the DFT,the adsorption behavior of the H2O—O2molecules on the chalcopyrite metal terminated(112)surface((112)-M)has been studied.Various adsorption configurations on the chalcopyrite (112)-M surfaces have been studied, trying to comprehend the effect of different magnetic metal atoms on the chalcopyrite (112)-M surface for the H2O and O2molecule’s adsorption at a molecular level.

2.Computational method and model

CASTEP module, GGA-PW91 functional in MS software, is adopted in this calculation [24–26].The ultrasoft pseudopotential is chosen to calculate metal atoms’ valence electrons (Cu 3d94s2,Fe 3d64s2, and S 3s23p4) [27].The cutoff energy is tested as 400 eV.Other parameters: the convergence tolerance energy, the max force, the max stress, and the max displacement is 2.0×10–5eV/atom, 0.05 eV/Å, 0.1 GPa, 0.002 Å, respectively.The dispersion correction (DFT-D) is used to calculate the van der Waals force between water molecules and the dispersion correction scheme(OBS) is used in the CASTEP module, as described by Ortmann et al.[40].The k-point (3×2×1) is set as the medium precision.In this manuscript,the Mulliken population and charge are found from the calculation output file in the MS software.

In our previous study [12], the Hubbard U correction and antiferromagnetic calculation are vital for the accuracy of the simulation calculation of chalcopyrite.Therefore, antiferromagnetic calculations were also performed for chalcopyrite in this study,and the Hubbard U correction with a U value of 2.0 eV was adopted for the treatment of Fe 3d.As shown in Fig.1a, chalcopyrite(CuFeS2) belongs to the tetragonal and the symmetry groups are I42d.The cell parameter of the chalcopyrite in this study is a=b=5.2927 Å, c=10.3875 Å.The experimental value (a=b=5.290 Å, c=10.4217 Å) is reported by Knight et al.[41] The band gap of the bulk is 0.53 eV,which is consistent with the experimental value (0.5 eV) [42].Through coordinating with four S atoms,both Cu and Fe atoms in the chalcopyrite belong to a tetragonal structure.And the setting methods of the magnetic parameter are also shown in Fig.1a.Based on reference [22], the 112-M surface is the most stable cleavage.Moreover, the surface was tested with and without the U parameter and dispersion correction.The surface energy was calculated as Eq.1:

It is found that the surface energy of the surface without the U parameter and dispersion correction is only 0.28 J/m2.The surface energy of the surface with the U parameter and dispersion correction is 0.67 J/m2.Chen et al.[43] and Thinius et al.[44] found the surface energy of the chalcopyrite (an oxidation state of Fe3+Cu1+-S2) (112) surface is 0.61 J/m2and 0.56 J/m2by DFT.It is indicated that the surface energy of the(112)-M surface with the U parameter and dispersion correction is closer to the literature values.As demonstrated in Fig.1b, the calculated cleavage model contains 10 atomic layers,constraining bottom six atom layers,cut out from the optimized bulk, with the thickness of the vacuum layer set to 15 Å.The cell parameter of the surface is a=7.48 Å, b=12.80 Å,and c=35.96 Å.The triple-coordinated metal atoms were exposed on the (112)-M surface due to the fracture of Me—S bonds.

The O2and H2O were placed inside a cubic box with lengths of 20×20×20 Å for optimization, before the adsorption on the mineral surface.In addition, water and oxygen molecules are placed vertically above the surface in a horizontal position at a distance of about the sum of the radii of the oxygen and metal atoms to simulate the adsorption process.The equation of the adsorption energy of H2O,O2molecule,and co-adsorption is shown in Eq.(2):

where the Eadsis the adsorption energy, Emolecule, Esurface, and Emolecule/surfacerepresent the energy of the H2O and O2molecule,the surface energy before adsorption,and the energy of the surface of the adsorbed molecules, respectively.

By using the DFTB+ module, molecular dynamics (MD) simulations were performed to study the adsorption behaviors of one and two monolayer water molecules and H2O—O2molecules on the chalcopyrite (112)-M surfaces.The module is based on the tight binding (DFTB) method based on a second-order expansion of the Kohn-Sham total energy in density functional theory (DFT) with respect to charge density fluctuations [39].The NVT ensemble was used.The system temperature was set to 298 K and controlled by a Nos´e thermostat.The simulation was performed with a time step of 1 fs and a total simulation time of 0.6 ps.

3.Results and discussion

3.1.Adsorption of water molecules

The adsorption structure of an isolated H2O molecule on the metal and sulfur atom of the chalcopyrite surface is displayed in Fig.2.Some studies have demonstrated that the adsorption of H2O molecules occurs preferentially on the Fe site [19–21].Our calculated results show the adsorption energy on the Fe site is -43.36 kJ/mol, while that on the Cu site is -11.14 kJ/mol.This suggests that H2O molecules tend to occur adsorption behavior with surface Fe atoms.This adsorption energy is close to the result of Wei et al.(-41.65 kJ/mol)[21].In addition,when the H2O molecule adsorbed on the S site, the distance between the S and the O atom is 3.32 Å and the Eadsis only -2.86 kJ/mol, indicating that the S site is not favorable for the adsorption of water molecules.

It is clear from the adsorption configuration that the bond length of Fe—O (2.16 Å) is relatively smaller than that of Cu—O(2.44 Å).This is in line with de Lima et al.[19], who simulated the interaction between an isolated H2O molecule and the chalcopyrite (001)-S.They reported that the distance between the Fe atom and O atom and between the Cu atom and O atom are 2.18 and 2.85 Å, respectively.

Surprisingly, the chalcopyrite surface structure is significantly changed due to the H2O molecule adsorption.As Fig.2 shows,the displacement of atoms on the mineral surface varies in different directions.As listed in Table 1, the chalcopyrite surface atoms are displaced to the greatest extent mainly in the Z-axis,while to a lesser extent in the other directions.More displacement (-0.11 Å)for Cu2 than Fe2 in the negative direction along the Z-axis,indicating weaker adsorption.

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de Lima et al.[19] found that the Eadsof the H2O molecule on the pyrite (100) surface obtained by Stirling et al.[14] (about-41.8 kJ/mol) is higher than that on the CuFeS2(001)-S surface’s Fe site.They suggested that the shorter distance of S—H bonds for the adsorption of the H2O molecule on the chalcopyrite(001)-S surface is the main reason for this.The Eadsof H2O molecules on the Fe atom of the pyrite (100) surface in the range of(54.4–65.7 kJ/mol) [13–15] is about 20 kJ/mol more negative than that on the Fe atom of the CuFeS2(112)-M surface.So,the interaction between the H2O molecule and the chalcopyrite(112)-M surface is weaker than that on the pyrite surface.By comparing the adsorption configuration of the H2O molecule on the chalcopyrite(112)-M surface with that on the pyrite (100) surface [15], it is found that the distance of the Fe—O bond is close to each other on the surface of both minerals, while the distance of the S—H bond for the chalcopyrite surface is longer than that on the pyrite surface.

Table 1 Atomic displacement and coordination of chalcopyrite (112)-M surface after water molecule adsorption.

The change in the electronic properties before and after the adsorption of the H2O molecule is analyzed by Mulliken charge populations.As Table 2 shows,the chalcopyrite surface loses electrons after interacting with H2O molecules,but the number of electron transfers on the Fe site is higher than that on the Cu site.The Fe 3d orbitals gain the most electrons.In contrast,the Cu s,p,and d orbitals involve a small number of electron transfers, suggesting that the reactivity of Fe 3d orbitals is more than that of the Cu 3d orbitals.Moreover,the bond population of Fe—O(0.14)is more significant than that of Cu—O(0.04),suggesting a more vital covalent interaction between Fe—O.By comparing the bond population and bond length before and after adsorption, it is found that the bond population changes little.This phenomenon indicates that the covalence of the chalcopyrite surface is not changed.

As shown in Fig.3,the monolayer H2O molecule adsorption was studied by placing six water molecules at three Fe and Cu sites,respectively.It is found that monolayer water molecules are oriented, and O—H bonds are formed between oxygen and hydrogen atoms.De Lima et al.[19] have studied the adsorption of monolayer water molecules (four water molecules) only absorbing on four Fe sites.They found that compared to single-molecule adsorption, the Eadsof the monolayer H2O molecule increased by almost 8.4 kJ/mol.Each H2O molecule bonds with corresponding Fe atoms (the distance is ranged from 2.43 to 2.47 Å).Our results show that the bond length of Fe—O is about 2.3 Å after adsorption.Compared with an isolated water molecule adsorption, the M—O bond length is more extensive,resulting in the interaction between water molecules and chalcopyrite (112)-M surface being weaker due to the interactions between water molecules.Furthermore,the proportion of M—O bond length increase is higher than that of the pyrite surface [32], suggesting the chalcopyrite surface is more hydrophobic than the pyrite surface.

Fig.3.Adsorption configuration of monolayer water molecules on chalcopyrite (112)-M surface.Note: The number denotes the bond length in Å.Blue dotted lines are hydrogen bonds.(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Table 2 Charge populations of metal atoms and Mulliken bond populations of metal-O and before and after the H2O molecule adsorption.

The dynamic simulation was carried out at 298 K to study the adsorption structure different from that at 0 K.Fig.4 shows the configuration of one and two monolayer water molecules at 298 K.It is found that no matter how many layers of water molecules are adsorbed, water molecules are regularly arranged, and hydrogen bonds are formed between O atoms and H atoms of water molecules.Foucaud et al.[35] have shown for fluorite that half of water molecules are far away from the surface,while without ab initio molecular dynamics(AIMD)all water molecules have been in the same plane.In our study, it is found that the bond length between the Fe atom and the O atom is lower than that between the Cu atom and the O atom under the dynamic simulation.Therefore,compared with the Cu site on the chalcopyrite surface, water molecules are more inclined to adsorb on the Fe site.

Fig.4.Dynamic simulation results of H2O molecules adsorption on the chalcopyrite (112)-M surface at 298 K.Note: The number denotes the bond length in Å.Blue dotted lines are hydrogen bonds.(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

3.2.Adsorption of oxygen molecule

Although many experimental and theoretical studies have been done on the oxidation behaviors of chalcopyrite,we found it is still incomplete, and further investigation is needed.Based on DFT,Xiong et al.[20] proved that the O2molecules are more inclined to adsorb at Fe sites than at Cu sites.As shown in Fig.1, there are six potential adsorption sites (Fe—Cu site, Fe—Fe site, Cu—Cu site, Fe—S site, Cu—S site, and S—S site) on the chalcopyrite(112)-M surface where the previous publications have not noted.By placing O2molecules on the above sites,the difference between the above sites for the adsorption behaviors of O2molecules is investigated.The adsorption structure and relevant Eadsof the O2molecule on the chalcopyrite (112)-M surface are presented in Fig.5.

Fig.5.Adsorption configuration of an isolated O2 molecule on chalcopyrite (112)-M surface.Note: The numbers represent the bond length in unit Å.

Interestingly, in the case of placing O2on the Fe—S site, Cu—S site, and S—S site, the O2molecule is not adsorbed at the S site but shifted to the Fe and Cu sites, suggesting that the S site is not favorable to the adsorption of O2molecules.As shown in Fig.5a–c,the Eadsof the O2molecule on Fe—Fe is the most negative(-239.0 kJ/mol), and that of the Fe—Cu site is the second(-207.0 kJ/mol), while the adsorption energy on Cu—Cu is only about -76.9 kJ/mol.Therefore, we think that the interaction between the O2molecule and the surface Fe site is stronger than that on the surface Cu site.

To better understand the adsorption behaviors between O2molecules and metal atoms, the vertical adsorption behavior of the O2molecule on the chalcopyrite surface Cu and Fe sites were studied, as shown in Fig.5d and Fig.5e.After the vertical adsorption of oxygen molecules,the Cu atom moves toward the negative direction of the Z-axis with an adsorption energy of about-44.1 kJ/mol, while the Fe atom moves toward the opposite direction with an adsorption energy of about -176.2 kJ/mol, suggesting that the oxygen molecule preferentially interacts with Fe atoms more than Cu atoms.This is consistent with previous results [20,21].However, it is noted that the adsorption site of the O2molecule on the chalcopyrite surface in our result is different from the previous studies.In our study,O2is adsorbed at the hollow Fe—Fe site,forming Fe—O—O—Fe species (O2adsorbing at two Fe sites), but not O—O—Fe species (O2adsorbing at the same Fe site) [20,21].

In addition, it is distinctly found that when the O2molecule adsorbed on the chalcopyrite(112)-M surface,dissociative adsorption has not occurred.Adsorption behaviors of the O2molecule on the chalcopyrite(112)-M surface are distinct from that on the pyrite(100)surface.Li et al.[15]published the idea that when oxygen molecules are adsorbed to Fe—S, and S—S sites on the surface of pyrite,respectively,S—O bonds are formed.In addition,in our simulation, the bond length of Fe—O is about 1.9 Å, which is longer than that on the pyrite surface, about 1.7 Å [15].

Consistent with the adsorption of H2O molecules, significant relaxation phenomena also arise on the surface where oxygen molecules are adsorbed, as shown in Fig.5.After the adsorption of the O2molecule on the Fe site, the Fe atom relaxes in the positive direction along the Z-axis,which differs from the behavior that occurs with the adsorption of water molecules,about 0.2 Å,which is about 0.1 Å longer than that on the Cu site.On the contrary,the surface S atom has moved about-0.5 Å in Z-axis reverse direction.When the O2molecule was vertically adsorbed on the Fe and Cu atoms (Fig.5e and Fig.5d, separately), the Fe atom relaxes in the positive direction along the Z-axis by 0.39 Å.In comparison, Cumoves in the negative direction by 0.84 Å.The above phenomenons suggest that oxygen molecules preferentially adsorb Fe atoms.In addition, it suggests that the surface structure of CuFeS2is obviously modified by the adsorption of the O2molecule.

Table 4 Bond Mulliken population and length of Fe—S before and after co-adsorption.

Listed in Table 3,after the adsorption of O2molecules,the Mulliken population of Fe—S bonds on the surface becomes significantly smaller, and the bond length obviously increases,indicating that the surface becomes less covalent and more hydrophilic.

3.3.Water and oxygen co-adsorption

The co-adsorption of H2O—O2molecules was investigated by placing both H2O and O2molecules on the surface simultaneously.Based on the O2molecule adsorption, only the adsorption of the oxygen molecule on the Fe—Fe site is considered.As shown in Fig.6, the optimization configurations of the H2O molecule on the S-site and Cu-site are compared.It is found that the Eadsfor the co-adsorption is more significant than that of a single molecule,about -340 kJ/mol.The H2O molecule is undissociated on the Cu site (Fig.6a), while the wholly dissociated behavior occurs on the S site (Fig.6b), generating two —H and one —O species.The H2O molecule dissociates to produce two H atoms and one O atom,where the O atom bond with the surface S atom to form the S—O product, and two H atoms bond with two O atoms dissociating from the O2molecule to form —OH, which then combines with the surface Fe atom to form Fe—OH.The bond length of S—O and the Fe—O is 1.59 Å and about 1.80 Å,respectively.It is the first time to confirm the product of S—O species by DFT, which is consistent with the experimental results[7,29–31].This is consistent with the result of Buckley and Woods, using XPS analysis, who [9] found that when the fresh chalcopyrite fracture surface started to burst into the air, the concentration of Cu and S atoms on the surface decreased.The concentration of hydroxyl iron was enriched.TheMulliken population of Fe—S bonds on the surface are listed in Table 4.It is found that after the co-adsorption,the bond Mulliken population and length show the same pattern as the adsorption of the oxygen molecule.Meanwhile,the hydrophilic Fe—OH specie is formed.The result indicates the surface becomes more hydrophilic.

Table 5 The adsorption energy and bond length of an isolated water molecule adsorption and H2O—O2 co-adsorption.

Fig.6.The co-adsorption configuration of H2O and O2 molecule on the chalcopyrite (112)-M surface.Note: The numbers represent the bond length in unit Å.

It is noteworthy that the H2O—O2co-adsorption promotes the O2and H2O molecule dissociation (Fig.6b).The distance of the metal-O bond and the Eadsof the adsorption of the H2O molecule,the O2molecule,the H2O—O2molecule on the chalcopyrite surface are listed in Table 5.From Table 5,it can be seen that the Cu—O distance is about 2.44 Å when an isolated H2O molecule is at the Cu site, while the Cu—O distance is about 2.14 Å after co-adsorption with the O2molecule, indicating that the O2molecule adsorption promotes the H2O molecule adsorption, while the H2O molecule does not dissociate.In addition,without the H2O molecule adsorption, the O2molecule was not dissociated, while after the H2O molecule adsorption, the O—O distance increased from about 1.38 to 3.66 Å at the Fe site, indicating that O2molecules were completely dissociated, while H2O molecules at the S site were wholly dissociated.The above results indicate that in the case of H2O—O2co-adsorption, both H2O and O2molecules can promote each other’s adsorption on the chalcopyrite surface and thus the oxidation of the mineral surface respectively.

When the undissociated H2O molecule co-adsorbs with an O2molecule, the Fe—O bond is about 1.88 Å larger than the dissociated case.Therefore, when an H2O molecule on the S-site coadsorbs with an O2molecule on the Fe—Fe site,dissociated adsorption is promoted.As listed in Table 5,the difference in the adsorption energy and bond length between an isolated water molecule adsorption and H2O—O2co-adsorption is discussed.It is found that after co-adsorption, the bond length of Cu—O decreases by about 0.3 Å, and both configurations have more negative adsorption energies.These phenomena show that the oxygen molecules promote the adsorption of water molecules.

Fig.7 shows the reaction pathway of the H2O—O2co-adsorption on the chalcopyrite(112)-M surface.Through the change in energy,the interaction process between H2O molecules and O2molecules can be analyzed.As shown in Fig.7a,in the co-adsorption process,the oxygen molecule was preferentially dissociated.Then, the water molecules dissociate, forming two H and one O species simultaneously, with the O specie adsorbing on the S site.Finally,the two O atoms bond to the H atoms dissociating from the H2O molecule and forming two Fe-OH species on the surface.In addition, the O atom which dissociates from the H2O molecule combined with the S atom, generating the S—O species.Through analyzing the co-adsorption process of H2O—O2on the chalcopyrite (112)-M surface, it is found that two H in H2O dissociates simultaneously, and the O2molecule dissociates after reacting with H atoms, producing two Fe—OH species simultaneously.Li et al.[15] studied the interaction process between H2O—O2molecules and between them and the pyrite surface.They found that the H2O molecule is dissociated in steps into —OH and —H.

In addition, the adsorption configuration of H2O—O2coadsorption is simulated by the molecule dynamic at 298 K.As shown in Fig.8, Cu—OH, Fe—OH, and Fe—O species were found on the chalcopyrite surface.This result reveals that after the H2O—O2co-adsorption, the chalcopyrite surface becomes more hydrophilic.

4.Conclusions

Based on DFT, the interaction between H2O—O2molecules and the chalcopyrite (112)-M surface was comprehensively studied,considering the influence of an antiferromagnetic property.The results show that compared to the Cu atom on the surface of chalcopyrite,H2O molecules preferentially adsorb to the Fe atom on its surface.In addition, the adsorption behavior of O2molecules also shows this phenomenon.Moreover,it is concluded that the configuration of the chalcopyrite (112)-M surface is clearly changed by the molecule adsorption.Under the conditions of co-adsorption,two adsorption cases will happen when H2O—O2adsorb simultaneously on the surface.For the S site,the H2O molecule thoroughly dissociated and form S—O species,and the other is H2O undissociated adsorbing at the Cu site.Through analyzing the interaction energy between H2O molecules and O2molecules during the coadsorption process, we found that the oxygen molecule was preferentially dissociated, and O species dissociated from the oxygen molecule reacted with H species in the water molecule,producing Fe—OH simultaneously.

Acknowledgments

The authors are grateful for the financial support provided by the National Natural Science Foundation of China (NSFC) (Nos.51974094, 51964004, and U20A20269).