Quantum simulation of the adsorption of toxic gases on the surface of borophene

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY TA THI LUONG QUANTUM SIMULATION OF THE ADSORPTION OF TOXIC GASES ON THE SURFACE OF BOROPHENE MASTER'S THESIS Hanoi, 2019 VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY TA THI LUONG QUANTUM SIMULATION OF THE ADSORPTION OF TOXIC GASES ON THE SURFACE OF BOROPHENE MAJOR: NANOTECHNOLOGY CODE: PILOT RESEARCH SUPERVISOR: Dr DINH VAN AN Hanoi, 2019 ACKNOWLEDGMENT First of all, I sincerely appreciate the great help of my supervisor, Dr Dinh Van An Thank you for all your thorough and supportive instructions, your courtesy, and your encouragement This thesis absolutely could not be conducted well without your dedicated concerns Second of all, I would like to show my gratefulness to Prof Morikawa Yoshitada, my supervisor during my internship time at Osaka University Your guidance helps me a lot to get a more profound insight into my research topic as well as researchrelated works Third of all, I want to express my warm thanks to my classmate, Pham Trong Lam Thanks to you, I got acquaintance more easily with computational material science Thank you for your willingness to help; it means a lot to me Last but not least, I also would like to thank Vietnam Japan University and the staff working here for their necessary supports This research is funded by National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.01-2018.315 i CONTENTS Page Acknowledgment i CONTENTS ii LIST OF TABLES iv LIST OF FIGURES v LIST OF ABBREVIATIONS vii ABSTRACT viii Chapter INTRODUCTION 1.1 Background of the research .1 1.2 Objectives and subjects of the research .2 1.2.1 Adsorbent material: Borophene 1.2.2 Gas molecules 1.3 Toxic gases adsorption on two-dimensional materials 1.3.1 Gas adsorption on other two-dimensional materials 1.3.2 Adsorption application of borophene 1.4 Thesis outline .9 Chapter THEORETICAL BASICS AND METHODS 11 2.1 Density Functional Theory 11 2.2 Vasp 15 2.3 Bader charge analysis 16 2.4 Calculation scheme 17 Chapter RESULTS AND DISCUSSION 20 3.1 Adsorbent characteristics 20 3.2 Energetically favorable configurations 21 3.2.1 CO - borophene 21 3.2.2 CO2 - borophene 22 3.2.3 NH3 - borophene 23 3.2.4 NO2 - borophene 24 3.2.5 NO - borophene 25 3.3 Adsorption energy and reaction length 26 3.3.1 Adsorption energy and adsorption distance in comparison of vdWemployed functionals 26 3.3.2 Comparison of adsorption energy among gases 30 3.4 Potential energy surface 31 3.5 Electronic characteristic 36 3.6 Charge transfer characteristic 39 ii 3.6.1 Charge analysis of the (CO – borophene) system .39 3.6.2 Charge analysis of the (CO2 - borophene) system 40 3.6.3 Charge analysis of the (NO - borophene) system .42 3.6.4 Charge analysis of the (NO2 - borophene) system 43 3.6.5 Charge analysis of the (NH3 - borophene) system 44 CONCLUSION 47 FUTURE PLANS 48 REFERENCES 49 iii LIST OF TABLES Page Table 1.1 The adsorption energy of CO, CO2, NO2, NO, and NH3 on different twodimensional materials (eV) Table 3.1 Calculated lattice constants of β12 borophene vs experimental data .20 Table 3.2 Bader charge analysis of the (CO - borophene) system 39 Table 3.3 Bader charge analysis of the (CO2 – borophene) system 41 Table 3.4 Bader charge analysis of the (NO – borophene) system 42 Table 3.5 Bader charge analysis of the (NO2 – borophene) system 43 Table 3.6 Bader charge analysis of the (NH3 – borophene) system 44 iv LIST OF FIGURES Page Figure 1.1 Elements predicted to be precursors of synthetic elemental 2D materials and their synthetic methods Figure 1.2 Borophene assumed to be synthesized on Ag (111) substrate (a) buckled triangular borophene, (b) β12 borophene, and (c) χ3 borophene .4 Figure 2.1 The flow chart of gas absorbing calculations 19 Figure 3.1 The calculated supercell of β12 boron sheet after optimization 20 Figure 3.2 Band structure and DOS of the unit cell of β12 borophene 21 Figure 3.3 Top view and side view of the most stable configurations of CO on borophene 22 Figure 3.4 Top view and side view of the most stable configurations of CO2 on borophene 23 Figure 3.5 Top view and side view of the most stable configurations of NH3 on borophene 23 Figure 3.6 Top view and side view of the most stable configurations of NO2 on borophene 24 Figure 3.7 Top view and side view of the most stable configurations of NO on borophene using different vdW functionals 25 Figure 3.8 Adsorption energy change accordingly to the distance of the (a) CO and (b) CO2 molecule and borophene in comparison 26 Figure 3.9 Adsorption energy change accordingly to the distance of the (a) NH3 and (b) NO2 molecule and borophene .28 Figure 3.10 Adsorption energy change accordingly to the distance between NO molecule and borophene 29 Figure 3.11 Comparison among gases of the shortest distance between gas molecules and substrate (dz), the distance from the massed center of gas molecules to the substrate (dc), and the adsorption energy (Ea) using optPBE-vdW functional 30 Figure 3.12 Potential energy surface of CO adsorbed borophene 31 Figure 3.13 Potential energy surface of CO2 adsorbed borophene 32 Figure 3.14 The projected binding energy of NH3 along the surface of borophene 33 Figure 3.15 Potential energy surface of borophene-NO 34 Figure 3.16 Potential energy surface of NO2 – borophene .35 Figure 3.17 Band structure and DOS of CO - borophene .36 Figure 3.18 Band structure and DOS of CO2 - borophene 37 v Figure 3.19 Band structure and DOS of NH3 - borophene .38 Figure 3.20 Band structure and DOS of NO - borophene .38 Figure 3.21 Band structure and DOS of NO2 - borophene .39 Figure 3.22 Charge density difference after CO adsorption illustrated using isosurface (isosurface level = 0.00034) 40 Figure 3.23 Charge density difference after CO2 adsorption illustrated using isosurface (isosurface level = 0.00054) 42 Figure 3.24 Charge density difference after NO adsorption (isosurface level = 0.003) .43 Figure 3.25 Charge density difference after NO2 adsorption illustrated using isosurface (isosurface level = 0.01) 44 Figure 3.26 Charge density difference after adsorbing NH3 (isosurface level = 0.0012) .45 Figure 3.27 Charge transfer of CO, CO2, NH3, NO, NO2, and SO2 and borophene 45 vi LIST OF ABBREVIATIONS 2D Two-dimensional DFT Density Functional Theory VASP Vienna Ab initio Software Package vdW van der Waals DOS Density of state KS Kohn-Sham MO Molecular orbital HF Hartree-Fock 3D Three-dimensional PAW Projector Augmented Wave vii ABSTRACT 2D materials have attracted significant research interest due to their excellent characteristics Borophene, a new member of the 2D material family, was proven that it has a unique structure and promising properties by both empirical and theoretical studies In this study, the adsorption configuration, adsorption energy of toxic gas molecules (CO, NO, CO2, NH3, and NO2) on 12 – borophene was investigated by first – principle calculations using three van der Waals correlation functionals: revPBE-vdW, optPBE-vdW, and vdW-DF2 The most stable configurations and diffusion possibilities of the gas molecules on the 12 – borophene surface were determined visually by using Computational DFT-based Nanoscope [10] The nature of bonding and interaction between gas molecules and 12 – borophene are also disclosed by using the density of states analysis and Bader charge analysis The obtained results are not only considerable for understanding gas molecules on borophene but also useful for technological applications of borophene in very near future Keywords: 12 – borophene, DFT, adsorption, toxic gases viii Table 3.3 Bader charge analysis of the (CO2 – borophene) system Atom index B … B B 12 B … B 32 B 35 B … B 45 B 56 B O O C Charge of complex Charge of isolated Charge difference system (qe) system (qe) (qe) … … … 2.7062 2.6996 0.0067 2.7045 2.6994 0.0051 … … … 2.9344 2.9324 0.0021 2.9370 2.9325 0.0045 … … … 3.4215 3.4297 -0.0082 3.3460 3.3573 -0.0113 … … … 7.0176 7.0045 0.0130 7.0383 7.0239 0.0145 1.9709 1.9716 -0.0006 Charge transfer (qe) -0.0268 +0.0268 In analogy to CO, in the case of adsorbing CO2 on borophene, generally, borophene gives its electrons to the gas molecule In other words, electrons transfer from adsorbent to CO molecule As a result, the adsorbent is slightly positively charged Also, this interaction is not significant, which is somewhat stronger than CO and borophene interaction The charge density different after adsorption is illustrated in Figure 3.23, where the yellow color means the increase of electron density, and the blue color means decreasing electron density Regarding borophene substrate, two boron atoms B56 and B45 nearest to oxygen atoms of gas molecule lose their charge most considerably Notably, the substrate‘s charge density at the area surrounding and parallel with CO2 molecule increase despite the decreasing trend of the whole substrate It can be explained by Pauli repulsion, when gas molecule approaching borophene surface, electrons under gas molecule is repulsed to the surrounding area Regarding the gas molecule, there is a little decrease in carbon‘s electron density while the charge density of oxygen atoms increases Similar to CO, this weak 41 interaction may reflect the physical adsorbed behavior It is also in agreement with the quite low adsorption energy of -0.24 eV Figure 3.23 Charge density difference after CO2 adsorption illustrated using isosurface (isosurface level = 0.00054) 3.6.3 Charge analysis of the (NO - borophene) system The Bader charge analysis shows the change of charge for each atom of the system after adsorption of NO on borophene described particularly in Table 3.4 Table 3.4 Bader charge analysis of the (NO – borophene) system Atom index B … B 20 B 29 B … B 52 B 59 B … O N Charge of complex system (qe) … 3.4557 2.9608 … 2.8771 2.7338 … 6.2618 3.9696 Charge of isolated system (qe) … 3.3522 2.8600 … 2.7263 2.8163 … 6.4792 4.5208 Charge difference (qe) … 0.1035 0.1009 … 0.1508 -0.0825 … -0.2174 -0.5512 Charge transfer (qe) +0.7686 -0.7686 As mentioned above, the binding energy of borophene and NO gas is three times larger than CO Interestingly, the charge transfer between NO gas and borophene also larger than CO2 case, however, more than 30 times larger It shows an excellent sensitivity of borophene toward NO gas Moreover, oppositely, the gas molecule 42 here is electron donator, and borophene acts like electron acceptor As a result, there is a large blue area surrounding the NO molecule illustrated in Figure 3.24 below Figure 3.24 Charge density difference after NO adsorption (isosurface level = 0.003) 3.6.4 Charge analysis of the (NO2 - borophene) system The Bader charge analysis shows the change of charge for each atom of the system after the adsorption of NO2 on borophene described particularly in Table 3.5 Table 3.5 Bader charge analysis of the (NO2 – borophene) system Atom index B B B … B 25 B … B 51 B … O O N Charge of complex Charge of isolated system (qe) system (qe) 3.4382 3.4014 3.4633 3.3789 … … 2.6375 2.8891 … … 2.5476 2.7959 … … 6.4156 6.3424 6.5589 6.2653 4.7777 4.3923 Charge difference (qe) 0.0367 0.0844 … -0.2517 … -0.2483 … 0.0732 0.2936 0.3854 Charge transfer (qe) -0.7522 +0.7522 In the same order of charge transferred magnitude with NO gas, however, NO2 gas, inversely, is electron acceptor and borophene is electron donator In this case, borophene also exhibits strong interaction with NO2 molecule Considering to the 43 charge difference visualized in the below Figure 3.25, the accumulation of electron in space between N atom and B25 atom as well as between O2 atom and B51 atom can be considered as an evidence of chemical bond within those atoms It is consistent with the high binding energy, which is almost -1.5 eV Figure 3.25 Charge density difference after NO2 adsorption illustrated using isosurface (isosurface level = 0.01) 3.6.5 Charge analysis of the (NH3 - borophene) system The Bader charge analysis shows the change of charge for each atom of the system after the adsorption of NH3 on borophene, described particularly in Table 3.6 Table 3.6 Bader charge analysis of the (NH3 – borophene) system Atom index Charge of complex Charge of isolated system (qe) system (qe) Charge Charge difference (qe) transfer (qe) B B B B B B B B 10 … 46 48 … 60 2.8169 … 2.8151 … 3.4130 3.3924 … 3.4293 2.8112 … 2.8096 … 3.4071 3.4105 … 3.4557 0.0057 … 0.0055 … +0.0066 0.0059 -0.0181 … -0.0263 H H H N 0.6089 0.6098 0.6361 6.1386 0.6155 0.6145 0.6377 6.1323 -0.0066 -0.0047 -0.0066 -0.0017 0.0064 44 In the same order of binding energy adsorption with CO and CO2, however, the charge transferring behavior of NH3 with borophene is even weaker than those of CO and CO2 Overall, electrons move from NH3 molecule to borophene; however, the amount of charge is not significant It can be interpreted that borophene is quite inert with ammonia gas This slight interaction is illustrated in Figure 3.26 Figure 3.26 Charge density difference after adsorbing NH3 (isosurface level = 0.0012) Charge transfer to gas molecule ∆Q (e) 0.7522 0.8 0.6 0.4 0.2 0.0236 0.0268 -0.0066 -0.2 -0.4 -0.6 -0.8 -0.7686 -1 CO CO2 CO2 NH3 NH NO NO2 NO Figure 3.27 Charge transfer between gas molecules and borophene 45 From the obtained results depicted in Figure 3.27, we can conclude that borophene has high selectivity regard to NO and NO2 gases While borophene expresses its inert features to CO, CO2, especially for NH3 cases with the charge transfer much less than 0.1 electrons, it has a great interaction with NO, and NO2, proven by the large charge transfer around 0.7 electrons This data shows an impressive adsorbing performance of borophene toward these gases in comparison with other 2D materials For example, in the case of phosphorene, NO2 also has the greatest electronics interaction with adsorbent, but the charge transfer is only 0.185 e [6] The charge transfers between WS2 and CO, and NO gas are also smaller than those of borophene, at 0.0078 and 0.0096 e, respectively [5] Hence, it opens promising potential applications for borophene as a new adsorbent 46 CONCLUSION In this work, the adsorbability of borophene was examined throughout firstprinciples calculation of the energy configuration, the adsorption potential energy, the density of state for five poisonous gases i.e., CO, CO2, NO, NH3, and NO2 The charge transfer and Bader charge analysis were also given for analyzing the adsorption mechanism Remarkably, CO, CO2, and NH3 are physically adsorbed on β12 borophene, while NO and NO2 are chemically adsorbed on β12 borophene Regarding charge transferring behaviors, CO, CO2 and NO2 are electron acceptors, whereas NO and NH3 are electron donators when being absorbed on the surface of borophene In short, borophene expresses as a material with high selectivity, which is much more sensitive to NO and NO2 gases Considerably, although the adsorption energy of NO on borophene is just in weak chemical adsorption range, which is neither too weak nor too strong for borophene as an adsorbent, NO has a great charge transfer with borophene It is very potential characteristic, facilitating favorable conditions for borophene to be an excellent sensing material i.e., to fabricate a sensitive and recyclable sensor 47 FUTURE PLANS There are many rooms to explore in the field of the gas adsorbability of borophene which has huge applications in the future With great potential, β12 borophene as well as other types of boron nanosheets or nanoribbons are worth to be intensively studied For further works, we want to carry out calculations for gas adsorption on borophene with other research subjects: - 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