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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Ecol. Evol.</journal-id>
<journal-title>Frontiers in Ecology and Evolution</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Ecol. Evol.</abbrev-journal-title>
<issn pub-type="epub">2296-701X</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.3389/fevo.2022.897410</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Ecology and Evolution</subject>
<subj-group>
<subject>Original Research</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Effective Air Purification <italic>via</italic> Pt-Decorated N<sub>3</sub>-CNT Adsorbent</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name><surname>Yang</surname> <given-names>Yinli</given-names></name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
<xref ref-type="author-notes" rid="fn002"><sup>&#x2020;</sup></xref>
</contrib>
<contrib contrib-type="author">
<name><surname>Liu</surname> <given-names>Sitong</given-names></name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
<xref ref-type="author-notes" rid="fn002"><sup>&#x2020;</sup></xref>
</contrib>
<contrib contrib-type="author">
<name><surname>Guo</surname> <given-names>Kai</given-names></name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
</contrib>
<contrib contrib-type="author">
<name><surname>Chen</surname> <given-names>Liang</given-names></name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
<xref ref-type="aff" rid="aff2"><sup>2</sup></xref>
<uri xlink:href="http://loop.frontiersin.org/people/826254/overview"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name><surname>Xu</surname> <given-names>Jing</given-names></name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
<xref ref-type="corresp" rid="c002"><sup>&#x002A;</sup></xref>
<uri xlink:href="http://loop.frontiersin.org/people/985558/overview"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name><surname>Liu</surname> <given-names>Wei</given-names></name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
<xref ref-type="corresp" rid="c001"><sup>&#x002A;</sup></xref>
<uri xlink:href="http://loop.frontiersin.org/people/1722039/overview"/>
</contrib>
</contrib-group>
<aff id="aff1"><sup>1</sup><institution>Department of Optical Engineering, College of Optical, Mechanical and Electrical Engineering, Zhejiang A&#x0026;F University</institution>, <addr-line>Hangzhou</addr-line>, <country>China</country></aff>
<aff id="aff2"><sup>2</sup><institution>School of Physical Science and Technology, Ningbo University</institution>, <addr-line>Ningbo</addr-line>, <country>China</country></aff>
<author-notes>
<fn fn-type="edited-by"><p>Edited by: Shupeng Zhu, University of California, Irvine, United States</p></fn>
<fn fn-type="edited-by"><p>Reviewed by: Lei Zhao, Southwest Petroleum University, China; Haifeng Zheng, State Key Laboratory of Rare Earth Resources Utilization, Changchun Institute of Applied Chemistry (CAS), China</p></fn>
<corresp id="c001">&#x002A;Correspondence: Wei Liu, <email>weiliu@zafu.edu.cn</email></corresp>
<corresp id="c002">Jing Xu, <email>jingxu@zafu.edu.cn</email></corresp>
<fn fn-type="equal" id="fn002"><p><sup>&#x2020;</sup>These authors have contributed equally to this work</p></fn>
<fn fn-type="other" id="fn004"><p>This article was submitted to Interdisciplinary Climate Studies, a section of the journal Frontiers in Ecology and Evolution</p></fn>
</author-notes>
<pub-date pub-type="epub">
<day>26</day>
<month>04</month>
<year>2022</year>
</pub-date>
<pub-date pub-type="collection">
<year>2022</year>
</pub-date>
<volume>10</volume>
<elocation-id>897410</elocation-id>
<history>
<date date-type="received">
<day>16</day>
<month>03</month>
<year>2022</year>
</date>
<date date-type="accepted">
<day>06</day>
<month>04</month>
<year>2022</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#x00A9; 2022 Yang, Liu, Guo, Chen, Xu and Liu.</copyright-statement>
<copyright-year>2022</copyright-year>
<copyright-holder>Yang, Liu, Guo, Chen, Xu and Liu</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/"><p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p></license>
</permissions>
<abstract>
<p>Effectively removal of air pollutants using adsorbents is one of the most important methods to purify the air. In this work, we proposed for the first time that PtN<sub>3</sub>-CNT is an effective adsorbent for air purification. Its air purification performance was studied by calculating the adsorption behaviors and electronic structures of 12 gas molecules, including the main components of air (N<sub>2</sub>, O<sub>2</sub>, H<sub>2</sub>O, CO<sub>2</sub>) and the most common air pollutants (NO, NO<sub>2</sub>, SO<sub>3</sub>, SO<sub>2</sub>, CO, O<sub>3</sub>, NH<sub>3</sub>, H<sub>2</sub>S), on the surface of PtN<sub>3</sub>-CNT using first-principles calculations. The results showed that these gases were adsorbed stably <italic>via</italic> the coordination between Pt and the coordinated atoms (C, N, O, and S atoms) in the gas molecules, and the adsorption energies vary in the range of &#x2212;0.81&#x223C;&#x2212;4.28 eV. The obvious chemical interactions between PtN<sub>3</sub>-CNT and the adsorbed gas molecules are mainly determined by the apparent overlaps between the Pt <italic>5d</italic> orbitals and the outmost <italic>p</italic> orbitals of the coordination atoms. PtN<sub>3</sub>-CNT has strong adsorption capacity for the toxic gas molecules, while relatively weaker adsorption performance for the main components of the air except oxygen. The recovery time of each adsorbed molecule calculated at different temperatures showed that, CO<sub>2</sub>, H<sub>2</sub>O, and N<sub>2</sub> can be desorbed gradually at 298&#x223C;498 K, while the toxic gases are always adsorbed stably on the surface of PtN<sub>3</sub>-CNT. Considering the excellent thermal stability of PtN<sub>3</sub>-CNT at up to 1000 K proved by AIMD, PtN<sub>3</sub>-CNT is very suitable to act as an adsorbent to remove toxic gases to achieve the purpose of air purification. Our findings in this report would be beneficial for exploiting possible carbon-based air purification adsorbents with excellent adsorbing ability and good recovery performance.</p>
</abstract>
<kwd-group>
<kwd>air pollution</kwd>
<kwd>gas separation</kwd>
<kwd>carbon nanotube</kwd>
<kwd>transition metal doping</kwd>
<kwd>density functional theory</kwd>
</kwd-group>
<contract-num rid="cn001">LQ20B030002</contract-num>
<contract-num rid="cn002">12075211</contract-num>
<contract-num rid="cn002">11975206</contract-num>
<contract-num rid="cn002">11875236</contract-num>
<contract-num rid="cn002">U1832150</contract-num>
<contract-sponsor id="cn001">Natural Science Foundation of Zhejiang Province<named-content content-type="fundref-id">10.13039/501100004731</named-content></contract-sponsor>
<contract-sponsor id="cn002">National Natural Science Foundation of China<named-content content-type="fundref-id">10.13039/501100001809</named-content></contract-sponsor>
<counts>
<fig-count count="6"/>
<table-count count="1"/>
<equation-count count="3"/>
<ref-count count="50"/>
<page-count count="9"/>
<word-count count="5675"/>
</counts>
</article-meta>
</front>
<body>
<sec id="S1" sec-type="intro">
<title>Introduction</title>
<p>In recent years, more and more attention has been paid to the impact of air pollution on human health. The effective purification of the air has become a research hotspot in both academia and industry (<xref ref-type="bibr" rid="B48">Zhao and Yang, 2003</xref>; <xref ref-type="bibr" rid="B29">Ren et al., 2017</xref>). One of the most important ways to purify the air is to adsorb the pollutants through adsorbents (<xref ref-type="bibr" rid="B7">DeCoste and Peterson, 2014</xref>; <xref ref-type="bibr" rid="B26">Perreault et al., 2015</xref>; <xref ref-type="bibr" rid="B20">Liu et al., 2020</xref>). The rapid development of low-dimensional carbon materials provides more options for the detection and separation of atmospheric pollutants (<xref ref-type="bibr" rid="B30">Samaddar et al., 2018</xref>; <xref ref-type="bibr" rid="B35">Teng et al., 2018</xref>; <xref ref-type="bibr" rid="B3">Cai et al., 2021</xref>). Single-walled carbon nanotubes (CNTs) are often used as adsorbents to adsorb certain harmful gases due to their unique tubular structures, huge effective surfaces, high thermal stability and high chemical stability (<xref ref-type="bibr" rid="B17">Li et al., 2018</xref>; <xref ref-type="bibr" rid="B27">Poudel and Li, 2018</xref>). However, the pristine CNTs have some disadvantages of few detection gas types, poor recovery performance, low sensitivity, and poor selectivity (<xref ref-type="bibr" rid="B33">Tabtimsai et al., 2020</xref>). Therefore, a variety of methods have been proposed to improve the adsorption performance of CNTs, mainly including functional group modification (<xref ref-type="bibr" rid="B12">Guo et al., 2021</xref>; <xref ref-type="bibr" rid="B19">Lim et al., 2021</xref>), metal doping (<xref ref-type="bibr" rid="B49">Zhou X. et al., 2010</xref>; <xref ref-type="bibr" rid="B5">Cui et al., 2018</xref>), non-metal doping (<xref ref-type="bibr" rid="B8">Esrafili and Heydari, 2019</xref>; <xref ref-type="bibr" rid="B21">Liu et al., 2019</xref>), plasma treatment (<xref ref-type="bibr" rid="B1">Babu et al., 2013</xref>; <xref ref-type="bibr" rid="B6">Cui et al., 2020</xref>; <xref ref-type="bibr" rid="B32">Sun et al., 2021</xref>), molecular sieve treatment, and so on (<xref ref-type="bibr" rid="B22">Niimura et al., 2012</xref>; <xref ref-type="bibr" rid="B14">Hou et al., 2018</xref>).</p>
<p>Noble metals are commonly used catalysts in chemical reactions (<xref ref-type="bibr" rid="B39">Zhang et al., 2021</xref>), and they can also serve as active centers for interaction with gas molecules (<xref ref-type="bibr" rid="B34">Tabtimsai et al., 2018</xref>). Novel gas sensors have been fabricated and reported by doping metal atoms on the surfaces of transition metal dichaldogenides (<xref ref-type="bibr" rid="B41">Zhang D. et al., 2017</xref>; <xref ref-type="bibr" rid="B42">Zhang et al., 2019</xref>, <xref ref-type="bibr" rid="B40">2020</xref>). When noble metals are embedded on the surfaces of CNTs, the physical and chemical properties of CNTs will be significantly changed, thus enhancing the adsorption capacity of CNTs to various gas molecules (<xref ref-type="bibr" rid="B44">Zhang et al., 2014</xref>). However, the binding of metal atoms with CNTs is often weak and the anchored metal atoms are easy to desorb. Due to the strong coordination interaction between nitrogen atoms and many metal atoms (<xref ref-type="bibr" rid="B36">Wang H. et al., 2021</xref>; <xref ref-type="bibr" rid="B37">Wang L. et al., 2021</xref>) N<sub><italic>x</italic></sub> (x = 3 or 4) groups have been introduced into the surfaces of CNTs to stabilize the adsorption of metal atoms (<xref ref-type="bibr" rid="B9">Feng et al., 2010</xref>). The doping of N atoms in CNTs will also introduce novel states near the Fermi level, thus improving the adsorption selectivity and sensitivity of CNTs to gas molecules (<xref ref-type="bibr" rid="B50">Zhou Y. et al., 2010</xref>; <xref ref-type="bibr" rid="B10">Gao et al., 2018</xref>; <xref ref-type="bibr" rid="B33">Tabtimsai et al., 2020</xref>). Hence, the combination of the electron-donating properties of noble metals and electron-attracting properties of N<sub><italic>x</italic></sub> groups will result in significant electron localization, which is helpful to promote the stable chemisorption behavior of gas molecules on the surfaces of CNTs (<xref ref-type="bibr" rid="B23">Peng and Cho, 2003</xref>; <xref ref-type="bibr" rid="B18">Li et al., 2009</xref>).</p>
<p>In this work, the air purification performance of Pt-decorated N<sub>3</sub>-CNT as adsorbent was studied using first-principles calculations. The adsorption behaviors and electronic structures of 12 gas molecules on the surface of PtN<sub>3</sub>-CNT were investigated. The calculated results confirmed that the N<sub>3</sub> group could effectively enhance the adsorption performance of metal-doped CNTs toward gas molecules through the improvement of electron mobility and chemical activity. The adsorption capacity of PtN<sub>3</sub>-CNT to common air pollutants and the main components of the air varies greatly. The recovery time for the gas molecules to desorb from the PtN<sub>3</sub>-CNT surface were further calculated at different temperatures.</p>
</sec>
<sec id="S2" sec-type="methods">
<title>Computational Methods</title>
<p>The Vienna Ab initio Simulation Package (VASP) (<xref ref-type="bibr" rid="B16">Kresse and Furthm&#x00FC;ller, 1996</xref>) based on density functional theory was used for all the first-principles calculations. The Perdew-Burke-Ernzerhof (PBE) (<xref ref-type="bibr" rid="B25">Perdew et al., 1996</xref>) functional in generalized gradient approximation (GGA) (<xref ref-type="bibr" rid="B15">Kohn and Sham, 1965</xref>) was used to describe the exchange-correlation interactions. The kinetic energy cutoff was set to 550 eV. The convergence criteria for energy and force in all the calculations were 1 &#x00D7; 10<sup>&#x2013;5</sup> eV and &#x2212;0.01 eV/&#x00C5;, respectively. The first Brillouin zone was represented using the Monkhorst-Pack scheme (<xref ref-type="bibr" rid="B4">Chadi, 1977</xref>) with a 1 &#x00D7; 1 &#x00D7; 2 K-point mesh. Vacuum layers of 25&#x00C5; were set in the radial directions of the CNTs to avoid interactions between adjacent structures. The Gaussian smearing method and a denser K-point mesh (1 &#x00D7; 1 &#x00D7; 8) were used in all the electronic properties calculations. In addition, the van der Waals interaction was considered using DFT-D3 correction method of <xref ref-type="bibr" rid="B11">Grimme et al. (2010)</xref>. Ab initio molecular dynamics (AIMD) simulations in the canonical ensemble (NVT) with the Nos&#x00E9;-Hoover thermostat (<xref ref-type="bibr" rid="B13">Hoover, 1985</xref>) were performed for 5.0 ps with a time-step of 1.0 fs at 1000 K. The stress tensor was calculated every time-step.</p>
<p>To evaluate the adsorption behaviors of gas molecules, we use the adsorption energy (<italic>E</italic><sub><italic>ad</italic></sub>) as the descriptor which is defined as follows:</p>
<disp-formula id="S2.E1"><label>(1)</label><mml:math id="M1"><mml:mrow><mml:mpadded width="+3.3pt"><mml:msub><mml:mi>E</mml:mi><mml:mrow><mml:mi>a</mml:mi><mml:mi>d</mml:mi></mml:mrow></mml:msub></mml:mpadded><mml:mo rspace="5.8pt">=</mml:mo><mml:mrow><mml:msub><mml:mi>E</mml:mi><mml:mrow><mml:mrow><mml:mi>P</mml:mi><mml:mi>t</mml:mi><mml:msub><mml:mi>N</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow><mml:mo>-</mml:mo><mml:mrow><mml:mrow><mml:mrow><mml:mi>C</mml:mi><mml:mi>N</mml:mi><mml:mi>T</mml:mi></mml:mrow><mml:mo>/</mml:mo><mml:mi>g</mml:mi></mml:mrow><mml:mi>a</mml:mi><mml:mi>s</mml:mi></mml:mrow></mml:mrow></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>E</mml:mi><mml:mrow><mml:mrow><mml:mi>P</mml:mi><mml:mi>t</mml:mi><mml:msub><mml:mi>N</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow><mml:mo>-</mml:mo><mml:mrow><mml:mi>C</mml:mi><mml:mi>N</mml:mi><mml:mi>T</mml:mi></mml:mrow></mml:mrow></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>E</mml:mi><mml:mrow><mml:mi>g</mml:mi><mml:mi>a</mml:mi><mml:mi>s</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mrow></mml:math></disp-formula>
<p>where <italic>E</italic><sub><italic>PtN</italic><sub>3</sub>&#x2013;<italic>CNT/gas</italic></sub>, <italic>E</italic><sub><italic>PtN</italic><sub>3</sub>&#x2013;<italic>CNT</italic></sub>, <italic>E</italic><sub><italic>gas</italic></sub> represent the total energy of the adsorption system, PtN<sub>3</sub>-CNT and isolated gas molecules, respectively. In addition, the bader charge (<xref ref-type="bibr" rid="B2">Bader and Beddall, 1972</xref>) is used to analyze the charge transfer between the gas molecules and the modified surface. The charge transfer can be defined as the number of electrons carried by the gas molecules after adsorption, because the electron value carried by the molecule is always zero before adsorption. Positive values indicate charge transfer from PtN<sub>3</sub>-CNT to gas molecules, while negative values indicate the reverse charge transfer path.</p>
</sec>
<sec id="S3" sec-type="results">
<title>Results</title>
<sec id="S3.SS1">
<title>Geometric and Electronic Structures of PtN<sub>3</sub>-CNT</title>
<p>Zigzag (8,0) single-walled carbon nanotube was chosen as the substrate to construct the PtN<sub>3</sub>-CNT structure by firstly deleting one carbon atom to form a single-vacancy defect, secondly substitutional doping of three carbon atoms possessing dangling bonds with nitrogen atoms, and finally adsorbing one Pt atom at the center of the N<sub>3</sub> group. The geometric and electronic structures of PtN<sub>3</sub>-CNT were investigated. <xref ref-type="fig" rid="F1">Figure 1A</xref> shows the top and side views of the geometric configuration of the optimized PtN<sub>3</sub>-CNT. The Pt atom is captured by the N<sub>3</sub> group, and the lengths of Pt-N bonds are 1.96 and 2.08&#x00C5;, respectively. The binding energies (<italic>E</italic><sub><italic>b</italic></sub>) for one Pt atom on the surface of CNTs were calculated using the following formula:</p>
<disp-formula id="S3.E2"><label>(2)</label><mml:math id="M2"><mml:mrow><mml:mpadded width="+3.3pt"><mml:msub><mml:mi>E</mml:mi><mml:mi>b</mml:mi></mml:msub></mml:mpadded><mml:mo rspace="5.8pt">=</mml:mo><mml:mrow><mml:msub><mml:mi>E</mml:mi><mml:mrow><mml:mrow><mml:mi>P</mml:mi><mml:mi>t</mml:mi><mml:msub><mml:mi>N</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow><mml:mo>-</mml:mo><mml:mrow><mml:mi>C</mml:mi><mml:mi>N</mml:mi><mml:mi>T</mml:mi></mml:mrow></mml:mrow></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>E</mml:mi><mml:mrow><mml:msub><mml:mi>N</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:mrow><mml:mi>C</mml:mi><mml:mi>N</mml:mi><mml:mi>T</mml:mi></mml:mrow></mml:mrow></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>E</mml:mi><mml:mrow><mml:mi>P</mml:mi><mml:mi>t</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mrow></mml:math></disp-formula>
<p>where <italic>E</italic><sub><italic>PtN</italic><sub>3</sub>&#x2013;<italic>CNT</italic></sub>, <italic>E</italic><sub><italic>N</italic><sub>3</sub>&#x2013;<italic>CNT</italic></sub>, <italic>E</italic><sub><italic>Pt</italic></sub> represent the energies of PtN<sub>3</sub>-CNT, pure N<sub>3</sub>-CNT and Pt atom, respectively. The obtained negative <italic>E</italic><sub><italic>b</italic></sub> (&#x2212;3.20 eV) value demonstrates that the binding of Pt atom on the surface of CNT <italic>via</italic> N<sub>3</sub> groups is thermodynamically preferable. Furthermore, to investigate the thermal stability of PtN<sub>3</sub>-CNT, ab initio molecular dynamics (AIMD) simulations were performed at 1000 K. The obtained results were shown in <xref ref-type="supplementary-material" rid="FS1">Supplementary Figure 1</xref>. No reconstruction of the PtN<sub>3</sub>-CNT structure was found, implying that PtN<sub>3</sub>-CNT can withstand temperatures up to 1000 K.</p>
<fig id="F1" position="float">
<label>FIGURE 1</label>
<caption><p><bold>(A)</bold> The top and side views of the optimized geometries of PtN<sub>3</sub>-CNT; <bold>(B)</bold> Deformation charge distribution of PtN<sub>3</sub>-CNT. The yellow area and cyan area represent the accumulation and consumption of electrons, respectively. The value of the isosurface level is 0.0011 e/&#x00C5;<sup>3</sup>. <bold>(C)</bold> DOS and PDOS of PtN<sub>3</sub>-CNT; <bold>(D)</bold> <italic>d</italic>-band centers of PtN<sub>3</sub>-CNT and PtC<sub>3</sub>-CNT. Brown, blue, gray balls represent C, N, and Pt atoms, respectively.</p></caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fevo-10-897410-g001.tif"/>
</fig>
<p>The result of deformation charge distribution (DCD) of PtN<sub>3</sub>-CNT are shown in <xref ref-type="fig" rid="F1">Figure 1B</xref>, which indicates that the N<sub>3</sub> group could act as the electron active center to withdraw electrons from the carbon nanotube and Pt atom. The Pt atom acts as an electron donor to release 0.52 <italic>e</italic> to N<sub>3</sub>-CNT, and the three N atoms obtain 0.14 <italic>e</italic>, 0.13 <italic>e</italic> and 0.12 <italic>e</italic>, respectively. This is because the lone pair electrons and non-bonded electrons carried on the <italic>sp</italic><sup>2</sup> orbitals of the three N atoms produce highly localized acceptor-like states at the Fermi level (<xref ref-type="bibr" rid="B28">Rangel and Sansores, 2014</xref>), and the strong electron withdrawing properties of the N<sub>3</sub> center further enhance the electron distribution.</p>
<p>Next, the density of states (DOS) and the projected density of states (PDOS) of PtN<sub>3</sub>-CNT and PtC<sub>3</sub>-CNT were calculated to further understand the electronic behaviors and the effect of the N<sub>3</sub> group. As shown in <xref ref-type="fig" rid="F1">Figure 1C</xref>, the partial DOS curve of the metal dopant and the N<sub>3</sub> group are in good agreement with the total DOS curve of PtN<sub>3</sub>-CNT, especially in the region close to the Fermi level. In the PtN<sub>3</sub>-CNT system, it can be seen that due to the doping of N atoms in carbon nanotubes, the electron-donating properties of Pt are combined with the electron-absorbing properties of N<sub>3</sub> group, leading to significant electron localization, thus forming a new state near the Fermi level, which will improve the adsorption selectivity and sensitivity of carbon nanotubes to gas molecules. The contribution of the Pt dopant to the total DOS in PtN<sub>3</sub>-CNT is greater than that in PtC<sub>3</sub>-CNT (shown in <xref ref-type="supplementary-material" rid="FS1">Supplementary Figure 2</xref>), which endows the doped Pt atom a greater regulatory effect on the electronic behavior of PtN<sub>3</sub>-CNT. From the PDOS, it is shown that there exists a large-area overlap between the Pt 5<italic>d</italic> orbital and the N 2<italic>p</italic> orbital. This means that the Pt atom chemically interacts with N<sub>3</sub>-CNT, leading to significant electron transfer and making PtN<sub>3</sub>-CNT more active (<xref ref-type="bibr" rid="B47">Zhao and Wu, 2018</xref>).</p>
<p>We also calculated the <italic>d</italic>-band center structures and positions of PtN<sub>3</sub>-CNT and PtC<sub>3</sub>-CNT to evaluate whether the N<sub>3</sub> group has enhanced the gas adsorption ability of Pt-decorated CNT (shown in <xref ref-type="fig" rid="F1">Figure 1D</xref>). The result illustrates that the <italic>d</italic>-band center value of the PtC<sub>3</sub>-CNT system is &#x2212;4.26 eV, while the value of the PtN<sub>3</sub>-CNT system is &#x2212;2.67 eV, which is closer to the Fermi level than the PtC<sub>3</sub>-CNT system. As the position of the <italic>d</italic>-band center increases, the anti-bonding orbital formed by the system to adsorb gas molecules will be pushed up. The higher the anti-bonding orbital position is, the more stable the system is after adsorbing gas molecules. Therefore, the PtN<sub>3</sub>-CNT system is more favorable for gas adsorption than the PtC<sub>3</sub>-CNT system, and the adsorption ability of Pt-decorated CNT toward gas molecules is effectively enhanced.</p>
</sec>
<sec id="S3.SS2">
<title>Adsorption of Gas Molecules on the Surface of PtN<sub>3</sub>-CNT</title>
<p>The adsorption of 12 kinds of gas molecules on the surface of PtN<sub>3</sub>-CNT were investigated, including the main components of the air (N<sub>2</sub>, O<sub>2</sub>, H<sub>2</sub>O, and CO<sub>2</sub>), the most common air pollutants nitrous oxides (NO, NO<sub>2</sub>), sulfur oxides (SO<sub>2</sub>, SO<sub>3</sub>), CO, O<sub>3</sub>, NH<sub>3</sub>, and H<sub>2</sub>S. For each adsorbed gas molecule, a variety of different adsorption structures were obtained and only the most stable geometric structures are discussed in the following sections. These 12 gas molecules are divided into three categories for discussion, namely the oxides, the hydrides and the elemental gases.</p>
<p>The optimized structures for the oxides adsorption on PtN<sub>3</sub>-CNT and the DCD figures are shown in <xref ref-type="fig" rid="F2">Figure 2</xref>. CO, NO, NO<sub>2</sub>, and SO<sub>2</sub> molecules interact with the dopant Pt atoms through a single atom forming new Pt-C (1.82&#x00C5;), Pt-N (1.74&#x00C5; for NO, and 2.21&#x00C5; for NO<sub>2</sub>), and Pt-S (2.10&#x00C5;) bonds while CO<sub>2</sub> and SO<sub>3</sub> are adsorbed on the surface by forming two bonds. The newly formed Pt-C, Pt-N, and Pt-S bonds in the adsorption structures of CO, NO, and SO<sub>2</sub> are shorter than the sum of the covalent bond radius of Pt and C (1.98&#x00C5;), Pt and N (1.94&#x00C5;), Pt and S (2.26&#x00C5;), indicating that the noble metal dopant (Pt) has a strong binding force to CO, NO, and SO<sub>2</sub> molecules, resulting in the chemisorption properties of these systems. The adsorption energies of these oxides vary in the range of &#x2212;0.81&#x223C;&#x2212;4.28 eV, and 0.15&#x223C;0.89 electrons are transferred from the adsorbent surfaces to the gas molecules. Among these oxides, the adsorption of CO<sub>2</sub> on the surface of PtN<sub>3</sub>-CNT is the weakest.</p>
<fig id="F2" position="float">
<label>FIGURE 2</label>
<caption><p>Adsorption structures and deformation charge distribution of <bold>(A)</bold> CO@PtN<sub>3</sub>-CNT system; <bold>(B)</bold> CO<sub>2</sub>@PtN<sub>3</sub>-CNT system; <bold>(C)</bold> NO@PtN<sub>3</sub>-CNT system; <bold>(D)</bold> NO<sub>2</sub>@PtN<sub>3</sub>-CNT system; <bold>(E)</bold> SO<sub>3</sub>@PtN<sub>3</sub>-CNT system; and <bold>(F)</bold> SO<sub>2</sub>@PtN<sub>3</sub>-CNT system. In the middle of the side views are the adsorption energies of the gas molecules. Yellow and red balls represent S and O atoms, respectively. The yellow area and cyan area represent the accumulation and consumption of electrons, respectively.</p></caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fevo-10-897410-g002.tif"/>
</fig>
<p>As shown in <xref ref-type="fig" rid="F3">Figure 3</xref>, the three hydrides (NH<sub>3</sub>, H<sub>2</sub>O, and H<sub>2</sub>S) are adsorbed stably on PtN<sub>3</sub>-CNT with adsorption energies of &#x2212;1.85, &#x2212;1.03, and &#x2212;1.93 eV, respectively. The adsorption of H<sub>2</sub>O has the smallest adsorption energy in the considered hydrides. In the adsorption structures, Pt atoms coordinate with the N, O, and S atoms as in the adsorption of oxides, and the newly formed Pt-N, Pt-O, and Pt-S bonds are 2.10, 2.19, and 2.21&#x00C5;, respectively. Moreover, unlike the adsorption of oxides, 0.23, 0.09, and 0.17 e are transferred from the gas molecules to the adsorbent PtN<sub>3</sub>-CNT, which is because that the electronegativity of hydrogen atoms is much weaker.</p>
<fig id="F3" position="float">
<label>FIGURE 3</label>
<caption><p>Adsorption structures and deformation charge distribution of <bold>(A)</bold> NH<sub>3</sub>@PtN<sub>3</sub>-CNT system; <bold>(B)</bold> H<sub>2</sub>O@PtN<sub>3</sub>-CNT system; <bold>(C)</bold> H<sub>2</sub>S@PtN<sub>3</sub>-CNT system. Light pink ball represents H atom. The yellow area and cyan area represent the accumulation and consumption of electrons, respectively.</p></caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fevo-10-897410-g003.tif"/>
</fig>
<p>The adsorption structures of the three elemental gases (O<sub>3</sub>, O<sub>2</sub>, N<sub>2</sub>) on PtN<sub>3</sub>-CNT are shown in <xref ref-type="fig" rid="F4">Figure 4</xref>. The adsorption energies of O<sub>3</sub> and O<sub>2</sub> (&#x2212;3.59 and &#x2212;3.24 eV, respectively) on PtN<sub>3</sub>-CNT are much larger than that of N<sub>2</sub> (&#x2212;1.36 eV), which may be due to the fact that two oxygen atoms are coordinated with the dopant Pt in the adsorption structures of O<sub>3</sub> and O<sub>2</sub>. The newly formed Pt-O bonds in O<sub>3</sub>@PtN<sub>3</sub>-CNT and O<sub>2</sub>@PtN<sub>3</sub>-CNT are 1.99, 1.95, and 2.07&#x00C5;, respectively. The newly formed Pt-N bond in N<sub>2</sub>@PtN<sub>3</sub>-CNT (1.89&#x00C5;) is smaller than the sum of the covalent bond radius of Pt and N (1.94&#x00C5;), indicating that the adsorption of N<sub>2</sub> molecules on the surface of PtN<sub>3</sub>-CNT is chemical adsorption. 0.70, 0.59, and 0.22 e are transferred from the elemental gas molecules to the adsorbent surfaces, respectively.</p>
<fig id="F4" position="float">
<label>FIGURE 4</label>
<caption><p>Adsorption structures and deformation charge distribution of <bold>(A)</bold> O<sub>3</sub>@PtN<sub>3</sub>-CNT system; <bold>(B)</bold> O<sub>2</sub>@PtN<sub>3</sub>-CNT system; <bold>(C)</bold> N<sub>2</sub>@PtN<sub>3</sub>-CNT system. The yellow area and cyan area represent the accumulation and consumption of electrons, respectively.</p></caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fevo-10-897410-g004.tif"/>
</fig>
<p>In all the adsorption structures discussed above, the chemical Pt-N bonds in PtN<sub>3</sub>-CNT are stretched by 0.01&#x2013;0.29&#x00C5; after adsorption, and one Pt-N is even broken in some adsorption structures (CO, NO<sub>2</sub>, NH<sub>3</sub>, H<sub>2</sub>O, H<sub>2</sub>S, O<sub>2</sub>, and N<sub>2</sub>). After adsorption, the chemical bonds in the gas molecules are all elongated relative to free molecules, indicating that these gas molecules are activated after adsorption on the PtN<sub>3</sub>-CNT surfaces. Moreover, the adsorption energies of some gas molecules on Pt-CNT (&#x2212;1.73 eV for CO, &#x2212;3.53 eV for NO, &#x2212;1.37 eV for NH<sub>3</sub>, &#x2212;1.06 eV for N<sub>2</sub>, respectively) have been reported previously. These <italic>E</italic><sub><italic>ad</italic></sub> are 0.30&#x223C;1.16 eV smaller than the corresponding adsorption energies on PtN<sub>3</sub>-CNT, confirming that the N<sub>3</sub> dopant have effectively improved the reactivity of CNTs, thereby enhancing the adsorption performance of the system for gas molecules.</p>
<p>Next, the electronic structures of gas@PtN<sub>3</sub>-CNT systems are investigated. From the above discussion, it can be found that the gas molecules are adsorbed on the surface of PtN<sub>3</sub>-CNT through the coordination of Pt with C, N, O, and S atoms, respectively. The DOS and PDOS of the gas molecules with the largest <italic>E</italic><sub><italic>ad</italic></sub> (CO, NO, O<sub>3</sub>, and H<sub>2</sub>S) in each coordination mode are shown in <xref ref-type="fig" rid="F5">Figure 5</xref>, and those of the other gases are shown in <xref ref-type="supplementary-material" rid="FS1">Supplementary Figure 3</xref>. Generally, the total DOS curves of gas@PtN<sub>3</sub>-CNT are very similar with that of isolated PtN<sub>3</sub>-CNT, except that the total DOS curves of the adsorbed systems shift to the high energy region. This could be attributed to the electron-withdrawing behavior of PtN<sub>3</sub>-CNT that results in an increase of the effective Coulomb potential (<xref ref-type="bibr" rid="B43">Zhang et al., 2018</xref>). The adsorbed gas molecules contribute dramatically to the total DOS in some specific areas (for CO, near 3.75, &#x2212;5.82, and &#x2212;6.85 eV; for NO, near 2.01, &#x2212;1.15, and &#x2212;7.42 eV; for O<sub>3</sub>, near 4.25, 3.45, &#x2212;4.15, &#x2212;6.75, and &#x2212;7.71 eV; for H<sub>2</sub>S, near 2.85 and &#x2212;7.68 eV), which are derived from the outermost <italic>p</italic> orbitals of the coordinated atoms in the gas molecules. And obvious deformations have taken place at these areas in the total DOS curves. Meanwhile, there exist apparent overlaps between the Pt <italic>5d</italic> and the outmost <italic>p</italic> orbitals of the coordination atoms, indicating the obvious chemical interactions between PtN<sub>3</sub>-CNT and the adsorbed gas molecules. It can also be concluded that these outermost <italic>p</italic> orbitals of the coordinated atoms in the adsorbed gas molecules play an important role in the adsorption of gases on PtN<sub>3</sub>-CNT.</p>
<fig id="F5" position="float">
<label>FIGURE 5</label>
<caption><p>DOS and PDOS of <bold>(A)</bold> CO@PtN<sub>3</sub>-CNT system; <bold>(B)</bold> NO@PtN<sub>3</sub>-CNT system; <bold>(C)</bold> O<sub>3</sub>@PtN<sub>3</sub>-CNT system; and <bold>(D)</bold> H<sub>2</sub>S@PtN<sub>3</sub>-CNT system. The dashed line represents the Fermi level.</p></caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fevo-10-897410-g005.tif"/>
</fig>
</sec>
<sec id="S3.SS3">
<title>Application of PtN<sub>3</sub>-CNT in Air Purification</title>
<p>Previous calculated results show that PtN<sub>3</sub>-CNT has strong adsorption capacity for the toxic gas molecules (NO, NO<sub>2</sub>, SO<sub>3</sub>, SO<sub>2</sub>, CO, NH<sub>3</sub>, H<sub>2</sub>S, and O<sub>3</sub>) with <italic>E</italic><sub><italic>ad</italic></sub> in the range of &#x2212;1.85&#x223C;&#x2212;4.28 eV, while relatively weaker adsorption performance for the main components of the air except oxygen (N<sub>2</sub>, H<sub>2</sub>O, and CO<sub>2</sub>) with <italic>E</italic><sub><italic>ad</italic></sub> in the range of &#x2212;0.81&#x223C;&#x2212;1.36 eV. If these gas molecules were adsorbed on the surface of PtN<sub>3</sub>-CNT, it would be very difficult for the toxic gas molecules to desorb, but the main components of the air may be desorbed by heating. Therefore, we assume that PtN<sub>3</sub>-CNT possess the potential as an excellent gas adsorbent for the air purification.</p>
<p>To prove this hypothesis, the recovery time for the gas molecules to desorb from the PtN<sub>3</sub>-CNT surface was investigated based on the transition state theory and van&#x2019;t Hoff-Arrhenius expression (<xref ref-type="bibr" rid="B46">Zhang et al., 2009</xref>) as below:</p>
<disp-formula id="S3.E3"><label>(3)</label><mml:math id="M3"><mml:mrow><mml:mpadded width="+3.3pt"><mml:mi mathvariant="normal">&#x03C4;</mml:mi></mml:mpadded><mml:mo rspace="5.8pt">=</mml:mo><mml:mrow><mml:msup><mml:mtext>A</mml:mtext><mml:mrow><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mo>-</mml:mo><mml:mrow><mml:mrow><mml:msub><mml:mi>E</mml:mi><mml:mi>a</mml:mi></mml:msub><mml:mo>/</mml:mo><mml:msub><mml:mi>K</mml:mi><mml:mi>B</mml:mi></mml:msub></mml:mrow><mml:mi>T</mml:mi></mml:mrow></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:mrow></mml:math></disp-formula>
<p>where A, <italic>K</italic><sub><italic>B</italic></sub>, and T represent the attempt frequency (10<sup>12</sup> s<sup>&#x2013;1</sup>) (<xref ref-type="bibr" rid="B24">Peng et al., 2004</xref>), the Boltzmann constant [8.318 &#x00D7; 10<sup>&#x2013;3</sup> kJ (mol K)<sup>&#x2013;1</sup>] and the temperature, respectively. <italic>E</italic><sub><italic>a</italic></sub> is the desorption potential barrier and can be considered the same as <italic>E</italic><sub><italic>ad</italic></sub>. From Equation (3), it can be concluded that the recovery time increases exponentially with the increase of <italic>E</italic><sub><italic>ad</italic></sub>. The larger the <italic>E</italic><sub><italic>ad</italic></sub> is, the more difficult the gas desorption process is. And increasing the temperature can effectively accelerate this process (<xref ref-type="bibr" rid="B31">Schedin et al., 2007</xref>; <xref ref-type="bibr" rid="B38">Yang et al., 2017</xref>; <xref ref-type="bibr" rid="B45">Zhang X. et al., 2017</xref>). According to the previously obtained <italic>E</italic><sub><italic>ad</italic></sub> as shown in <xref ref-type="table" rid="T1">Table 1</xref>, the recovery time for the desorption of all the gas molecules from the PtN<sub>3</sub>-CNT surface at 298, 398, 498 K were calculated (listed in <xref ref-type="supplementary-material" rid="TS1">Supplementary Table 1</xref>) and plotted in <xref ref-type="fig" rid="F6">Figure 6</xref>. The results showed that the desorption of all the gas molecules is very unrealistic at room temperature, except for CO<sub>2</sub> which requires only 42.10 s to desorb from the surface of PtN<sub>3</sub>-CNT. The good adsorption performance and short recovery time at ambient temperature make PtN<sub>3</sub>-CNT an excellent candidate for CO<sub>2</sub> sensing. When the temperature is increased by 100&#x2013;398 K, H<sub>2</sub>O can be desorbed with a recovery time of 9.38 s. When the temperature is increased again by 100&#x2013;498 K, N<sub>2</sub> will be desorbed with a recovery time of 1.62 h, while all the toxic gas molecules and O<sub>2</sub> are still adsorbed stably on the surface of PtN<sub>3</sub>-CNT. Therefore, considering the excellent thermal stability of PtN<sub>3</sub>-CNT at up to 1000 K proved by AIMD previously, and the adsorption and desorption behavior at different temperature, PtN<sub>3</sub>-CNT structure is very suitable to act as an adsorbent to remove toxic gases to achieve the purpose of air purification.</p>
<table-wrap position="float" id="T1">
<label>TABLE 1</label>
<caption><p>Adsorption energies (<italic>E</italic><sub><italic>ad</italic></sub>), distances between Pt and the coordinated atoms (D), and the charge transferred between PtN<sub>3</sub>-CNT and the gas molecules for Gas@PtN<sub>3</sub>-CNT systems (Q<sub><italic>T</italic></sub>).</p></caption>
<table cellspacing="5" cellpadding="5" frame="hsides" rules="groups">
<thead>
<tr>
<td valign="top" align="left">Gas</td>
<td valign="top" align="center"><italic>E</italic><sub><italic>ad</italic></sub> (eV)</td>
<td valign="top" align="center">D (&#x00C5;)</td>
<td valign="top" align="center">Q<sub><italic>T</italic></sub> (e)</td>
<td valign="top" align="center">Gas</td>
<td valign="top" align="center"><italic>E</italic><sub><italic>ad</italic></sub> (eV)</td>
<td valign="top" align="center">D (&#x00C5;)</td>
<td valign="top" align="center">Q<sub><italic>T</italic></sub> (e)</td>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">CO</td>
<td valign="top" align="center">&#x2212;2.89</td>
<td valign="top" align="center">1.82</td>
<td valign="top" align="center">0.15</td>
<td valign="top" align="center">NH<sub>3</sub></td>
<td valign="top" align="center">&#x2212;1.85</td>
<td valign="top" align="center">2.10</td>
<td valign="top" align="center">&#x2212;0.23</td>
</tr>
<tr>
<td valign="top" align="left">CO<sub>2</sub></td>
<td valign="top" align="center">&#x2212;0.81</td>
<td valign="top" align="center">2.00 2.10</td>
<td valign="top" align="center">0.45</td>
<td valign="top" align="center">H<sub>2</sub>S</td>
<td valign="top" align="center">&#x2212;1.93</td>
<td valign="top" align="center">2.21</td>
<td valign="top" align="center">&#x2212;0.17</td>
</tr>
<tr>
<td valign="top" align="left">NO</td>
<td valign="top" align="center">&#x2212;4.28</td>
<td valign="top" align="center">1.74</td>
<td valign="top" align="center">0.32</td>
<td valign="top" align="center">H<sub>2</sub>O</td>
<td valign="top" align="center">&#x2212;1.03</td>
<td valign="top" align="center">2.19</td>
<td valign="top" align="center">&#x2212;0.09</td>
</tr>
<tr>
<td valign="top" align="left">NO<sub>2</sub></td>
<td valign="top" align="center">&#x2212;3.06</td>
<td valign="top" align="center">2.21</td>
<td valign="top" align="center">0.45</td>
<td valign="top" align="center">O<sub>3</sub></td>
<td valign="top" align="center">&#x2212;3.59</td>
<td valign="top" align="center">1.99</td>
<td valign="top" align="center">0.70</td>
</tr>
<tr>
<td valign="top" align="left">SO<sub>3</sub></td>
<td valign="top" align="center">&#x2212;2.18</td>
<td valign="top" align="center">2.01</td>
<td valign="top" align="center">0.89</td>
<td valign="top" align="center">O<sub>2</sub></td>
<td valign="top" align="center">&#x2212;3.24</td>
<td valign="top" align="center">1.95 2.07</td>
<td valign="top" align="center">0.59</td>
</tr>
<tr>
<td valign="top" align="left">SO<sub>2</sub></td>
<td valign="top" align="center">&#x2212;1.89</td>
<td valign="top" align="center">2.10</td>
<td valign="top" align="center">0.28</td>
<td valign="top" align="center">N<sub>2</sub></td>
<td valign="top" align="center">&#x2212;1.36</td>
<td valign="top" align="center">1.89</td>
<td valign="top" align="center">0.22</td>
</tr>
</tbody>
</table>
</table-wrap>
<fig id="F6" position="float">
<label>FIGURE 6</label>
<caption><p>Recovery time for the Gas@PtN<sub>3</sub>-CNT systems at various temperatures.</p></caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fevo-10-897410-g006.tif"/>
</fig>
</sec>
</sec>
<sec id="S4" sec-type="conclusion">
<title>Conclusion</title>
<p>In summary, we proposed that PtN<sub>3</sub>-CNT is an excellent adsorbent for air purification in this work. The adsorption of four main components of the air (N<sub>2</sub>, O<sub>2</sub>, H<sub>2</sub>O, CO<sub>2</sub>) and eight common air pollutants (NO, NO<sub>2</sub>, SO<sub>3</sub>, SO<sub>2</sub>, CO, O<sub>3</sub>, NH<sub>3</sub>, H<sub>2</sub>S) on the surface of PtN<sub>3</sub>-CNT were studied using first-principles calculations. The calculation results about <italic>d</italic>-band centers and adsorption energies confirmed that the N<sub>3</sub> dopant have effectively improved the reactivity of CNTs, thereby enhancing the adsorption performance of PtN<sub>3</sub>-CNT for gas molecules. All the considered gases can be adsorbed stably on PtN<sub>3</sub>-CNT, and the adsorption energies for the toxic gas molecules (&#x2212;1.85&#x223C;&#x2212;4.28 eV) are larger than those for the main components of the air except oxygen (&#x2212;0.81&#x223C;&#x2212;1.36 eV). The recovery time for the desorption of all the gas molecules from the PtN<sub>3</sub>-CNT surface at 298, 398, 498 K were calculated. The obtained results showed that CO<sub>2</sub>, H<sub>2</sub>O, and N<sub>2</sub> can be desorbed at 298, 398, and 498 K, respectively, while all the air pollutants and O<sub>2</sub> are always adsorbed stably. Therefore, PtN<sub>3</sub>-CNT can be used to purify the air by firstly adsorbing the gas mixture and then gradually releasing the air by heating.</p>
</sec>
<sec id="S5" sec-type="data-availability">
<title>Data Availability Statement</title>
<p>The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.</p>
</sec>
<sec id="S6">
<title>Author Contributions</title>
<p>WL, JX, YY, and SL conceived the research. YY, KG, and SL performed the calculations and analyzed the data. WL, JX, and YY wrote the manuscript. LC helped to revise the manuscript. All authors discussed and commented on the manuscript and approved the submitted version.</p>
</sec>
<sec id="conf1" sec-type="COI-statement">
<title>Conflict of Interest</title>
<p>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.</p>
</sec>
<sec id="pudiscl1" sec-type="disclaimer">
<title>Publisher&#x2019;s Note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
</body>
<back>
<sec id="S7" sec-type="funding-information">
<title>Funding</title>
<p>This work was supported by the Zhejiang Provincial Natural Science Foundation of China (No. LQ20B030002) and the National Natural Science Foundation of China (Nos. 12075211, 11975206, 11875236, and U1832150).</p>
</sec>
<sec id="S8" sec-type="supplementary-material">
<title>Supplementary Material</title>
<p>The Supplementary Material for this article can be found online at: <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fevo.2022.897410/full#supplementary-material">https://www.frontiersin.org/articles/10.3389/fevo.2022.897410/full#supplementary-material</ext-link></p>
<supplementary-material xlink:href="Presentation_1.pdf" id="FS1" mimetype="application/pdf" xmlns:xlink="http://www.w3.org/1999/xlink"/>
<supplementary-material xlink:href="Table_1.DOCX" id="TS1" mimetype="application/vnd.openxmlformats-officedocument.wordprocessingml.document" xmlns:xlink="http://www.w3.org/1999/xlink"/>
</sec>
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