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C: Surfaces, Interfaces, Porous Materials, and Catalysis

DFT Insight into Interfacial Chemical Behavior of Hybrid LDH/GO Nanocomposities Qiuwei Jiang, Yanan Guo, Zhijun Xu, and Xiaoning Yang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b08481 • Publication Date (Web): 30 Dec 2018 Downloaded from http://pubs.acs.org on January 4, 2019

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The Journal of Physical Chemistry

DFT Insight into Interfacial Chemical Behavior of Hybrid LDH/GO Nanocomposites

Qiuwei Jiang, Yanan Guo*, Zhijun Xu*, Xiaoning Yang*

State Key Laboratory of Material-Orientated Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing Tech University, Nanjing 210009, China

* Corresponding Author

ACS Paragon Plus Environment

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ABSTRACT: Hybrid layered double hydroxides (LDHs)/graphene oxide (GO) nanocomposites

are novel two-dimensional materials applied in extensive fields, which take advantages of the synergistic effect of LDH and GO at the composite interface. However, the interfacial interaction mechanism determining the LDH/GO nanocomposites properties is still remaining to be explored. Herein, we used density functional theory to comprehensively illustrate interfacial interactions, as well as structural and electronic properties of MgAl LDH/GO nanocomposites. Our results, for the first time, reveal there exists unique water-generated chemical interaction during the LDH/GO combining process. The generated interfacial water molecules play a key role in maintaining the nanocomposites by forming complicated and diverse interfacial hydrogen bond structures. Moreover, the transfer of hydrogen atom from LDH to the epoxy group resulting in hydroxyl was also observed. The results provide hints for interpreting previous experimental observations. There is interfacial charge transfer from LDH to GO and water molecules. The electrical properties of the LDH component in the composite can be modulated by properly varying the epoxy: hydroxyl ratio on GO. The current results might prove to be instrumental in the design of two-dimensional heterostructural LDH/GO composites.


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INTRODUCTION Combining various building blocks together to form a well-designed hierarchical composite structure is a popular method of designing new materials with improved physical and chemical properties in materials science areas.1-3 Layered double hydroxides (LDHs) and graphene oxide (GO) are two promising and extensively studied building blocks both with two-dimensional (23+ x+ nD) lamellar structures. LDH has a chemical composition of [M2+ 1-xMx (OH)2] Ax/nꞏnH2O, where

M2+, M3+ and An- represent divalent metal cation, trivalent metal cation and interlayer anion, respectively.4, 5 The LDH bulk flakes can be easily delaminated into single-layer structures.1, 6-8 The single-layer LDH is positively charged due to the substitution of divalent cations by trivalent cations, which makes it easy to restack9. GO single sheet is negatively charged because of the various oxygen-containing functional groups on its basal plane.10, 11 It has become a promising support material to tackle the restacking problem of LDH by combining LDH and GO, furthermore yielding LDH/GO nanocomposite.12 LDH/GO nanocomposite has great potential applications in various fields such as energy storage,13 catalysis,14 environment protection15, 16 and biological medicine,17 which benefits from the synergistic effect of LDH and GO at the composite interface. For example, LDH/GO composites show better CO2 adsorption capacity than the isolated LDH, which is attributed to the fact that GO support can improve the particle dispersion of LDH.6, 12, 15 Moreover, LDH/GO composites have been applied as adsorbents to remove heavy metal ions from wastewater.18 In addition, the synergy of well-defined LDH/GO composites can increase the photoelectron catalytic performance on account of a combination of charge separation efficiency facilitated by charge transfer between LDH and GO and excellent catalytic ability of LDH.14 From another


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perspective, the steady formation of LDH/GO composite could eliminate the cytotoxicity of GO by increasing GO coagulation .19 Further efforts are needed to develop a wide variety of LDH/GO composites with excellent properties and promising applications, which greatly depend on the interaction at the interface of building blocks.20 Therefore, it is essential to have a thorough understanding of the molecular interaction mechanism at the LDH/GO composite interface. GO sheets are decorated with various functional groups and exhibit abundant surface chemical properties. It is speculated that the combination between GOs and LDHs will present unique interfacial performances, accordingly providing tuning strategies for improving various applications. Unfortunately, the interfacial interaction of LDH/GO composites is very complicated, and there are still some open questions to be resolved, including the geometric and electronic structure evolution of each building block, as well as the electron transfer properties between two blocks upon combining. Inspired of these considerations, in this work, we employed density functional theory (DFT) calculations to get deeper insight into the interfacial behavior between LDH and GO. The interfacial interaction and the underlying mechanism for LDH/GO composites have been comprehensively investigated. The interfacial water formation has been firstly revealed in the unique chemical interaction between LDH and GO, which is critical to control the stability and functions of the LDH/GO assembly. It is further shown that the electrical properties of LDH component in the composite can be modulated by combining with GO. SIMULATION MODELS AND METHODS Models: The two dimensional GO models were constructed by randomly adding epoxy and hydroxyl groups on the graphene basal plane according to the widely accepted Lerf−Klinowski rules.10, 21 The C/O ratio on the graphene plane was controlled to be 16.7%. Five GO models


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with different epoxy:hydroxyl (E:OH) ratios (8:0, 5:3, 4:4, 3:5 and 0:8) were considered. The constructed GO models have a rectangular shape with the size of 17.22 Å×12.78 Å. The monolayer Mg/Al LDH shows the typical sandwich-like structure, in which the metal layer intercalates between two hydroxyl layers. Two LDH models with the Mg:Al ratios of 2 and 3 were built. The rectangular LDH monolayers have a size of 16.31 Å×12.56 Å. As shown in Figure S1, the GO/LDH complex was constructed by matching one LDH monolayer in parallel to the above GO layer, resulting in the hybrid LDH/GO nanocomposite models (Figure S1). In the combining LDH/GO structure, a slight (< 3%) lattice deformation occurred. This is consistent with the previous XRD result,22 which shows GO/LDH has a minor change in the complex structure. The hybrid LDH/GO complex structure with the size of 16.31 Å×12.56 Å2 was adopted as the supercell in the following simulation. The periodic boundary conditions in x, y and z directions were taken into account. A vacuum layer of 25 Å in z direction was added to avoid the interactions between adjacent images. In order to obtain the initial configuration with suitable spacing between the LDH monolayer and GO layer, we selected the vertical LDH-GO distance with the minimal interaction energies in each GO/LDH complex. Methods: All quantum chemistry calculations were performed using the band module of Amsterdam Density Functional (ADF) program (version 2017) 23 under the condition of periodic boundary condition. The constructed periodic GO/LDH complexes were geometrically optimized.24,

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The electron exchange-correlation was taken into account using the Perdew-

Burke-Ernzerhof (PBE) functional26 within the generalized gradient approximation (GGA).27 The double zeta basis set plus polarization function (DZP) was employed in the structure optimization. The optimized structures were then utilized to study the energetic and electronic properties of the GO/LDH complex. All single point calculations were conducted using the PBE-


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D3 functional which includes the dispersion correction through the Grimme approach.28 The triple zeta basis set plus polarization function (TZP) 25 was employed. The k-point mesh over the Brillouin zone for all structures was set to 3×3×3, which was sampled based on the Wiesenekker-Baerends scheme.29 RESULTS AND DISCUSSION Stability of the Nanocomposites To quantitatively evaluate the interfacial properties, the cohesion energy between LDH and GO is calculated 30 as  E coh  E comp  E LDH  E GO , where Ecomp, ELDH and EGO are energies of the nanocomposite, the isolated LDH and the isolated GO, respectively. Figure 1 (a) and (b) shows the cohesion energies for the LDH/GO composites with various E:OH ratios. The negative value of  E coh indicates that LDH and GO can combine spontaneously. The more negative  E coh , the larger stability of the nanocomposite. The stabilities of the nanocomposites with the same Mg:Al ratio are quite similar under various E:OH ratios of GO sheets. However, the nanocomposite with Mg:Al = 2 is more stable than that with Mg:Al = 3 under the same E:OH ratio. Thus, the Mg:Al ratio has more important influence on the stability of LDH/GO nanocomposite than the GO E:OH ratio.


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Figure 1.

(a, b) The decomposition terms of cohesion energies for different systems, including

deformation energy (red bars, ∆Eprep), interaction energy between GO and LDH (orange bars, E Int ), the contribution from the interfacial H2O molecules (green bars,  E env ). The total cohesion energies (  E coh ) are denoted by striped bars. (c, d) The interaction energy between interfacial H2O molecules and LDH/GO and the corresponding decomposing parts. The navy, orange, green and red bars refer to Pauli interaction energy, dispersion interaction energy, electrostatic interaction energy and orbital interaction energy, respectively.

The ∆Ecoh for all systems in our study was calculated to be in the range of -0.140 to -0.104 eV/Å2, which is smaller than the value (-0.075 eV/Å2) between NiFe LDH and graphene.13 The smaller ∆Ecoh between MgAl LDH and GO in the current study is possibly ascribed to the existence of oxygen-containing functional groups on GO. Hua et al.31 systematically explored the interactions between monolayer MoS2 and GO with various oxygen concentrations, finding


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that the binding energy increases with the oxidation degree of GO. This demonstrates the importance of the oxygenated functional groups in the formation of composites. Gillespie et al.32 reported the weak interaction energy (-0.0086 eV/Å2) between TiO2 and graphene, designating physical interaction mechanism. Thus, the relatively stronger interaction between MgAl LDH and GO in our study implies that there exists chemical interaction between single-layer MgAl LDH and GO sheet. It should be noted that in the optimization computation, we did not consider the dispersion correction due to the concern of computation resource. However, our additional test computation indeed shows that the dispersion does not have influence on the MgAl LDH/GO nanocomposite geometries. Water Plays a Key Role in Maintaining the Nanocomposite In the combining process of LDH and GO, we observed the dissociation of OH groups from GO, and the dissociated OH group can combine the hydrogen atom on LDH to form H2O molecule (Figure 2a). This was confirmed by our ab initio MD simulation (see Figure S2 for the details). As shown in Figure 2d, H2O molecules can be formed at ca. 0.1 ps through the binding of the dissociated OH with the hydrogen from LDH. We further performed the potential energy surface (PES) scanning of H2O formation (see supporting information for the details). The obtained PES (Figure S3) shows that the H2O formation process has no energy barrier. Ghaderi et al.

33

studied the OH groups on graphene, finding that the binding strength of OH groups on

perfect graphene is weak and they can easily aggregate to form H2O. Therefore, the formation of H2O molecules in the current simulations is theoretically reliable. However, the previous experimental FT-IR spectra34 did not show obvious change of surface functional groups on MgAl LDH after the coagulation of GO. The discrepancy is probably due to the different and miscellaneous structures of LDHs or GOs between simulation


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and experiments. These diverse results further indicate the interfacial complexity in the LDH/GO nanocomposites. As shown in Figure 2b, the number of generated H2O molecules has a positive relationship with the number of OH groups on GO, signifying that OH groups are robustly involved in the LDH/GO interfacial interaction. In the experimental study35 on GO and La-doped MgAl LDH interaction, the authors reported apparent reduction of the characteristic OH XPS peak upon the formation of the LDH/GO nanocomposite, and they speculated that the OH groups dominated the reaction process. Unfortunately, the way how OH functions in this process was not explained35. Our result suggests that forming H2O molecule is perhaps one of the ways that OH conducts the combining of LDH and GO. Interestingly, the transfer of H atom(s) from LDH to the E group(s) of GO resulting in OH was also observed in some cases. This phenomenon might provide a hint for interpreting the experimental observation that OH groups increase after GO coagulation on CaAl LDH.34


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Figure 2. (a) Representative geometrically optimized structure of the LDH/GO nanocomposite. The Al, Mg, C, O, H, H2O are marked in orange, cyan, grey, red and white. For clarity, the H atoms in H2O are labeled in green color, and the O atom is labeled in dark blue. (b) The number of the interfacial H2O molecules in the nanocomposites with different E:OH ratios. (c) The center of mass distance between LDH and GO in nanocomposites with different E:OH ratios. (d) Representative configurations along simulation time in ab initio MD simulation. At 0.08ps, OH groups were dissociated from GO; at 0.1ps, H2O molecules are formed.

The contribution of the consequential H2O molecules and the transferred H atoms to the nanocomposite stability can be approximately examined through  E env   E coh   E Int   E prep ， where E Int is the interaction energy between GO after OH dissociation (or H atom acceptation) and LDH after H atom dissociation, ∆Eprep the deformation energy of LDH and GO forming the distor distor distor  E GO  E LDH  E GO , where E LDH and nanocomposite. ∆Eprep was obtained by  E prep  E LDH


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distor are energies of distorted LDH and GO in the LDH/GO nanocomposite, respectively. The E GO

detailed numerical values for each energetic part were listed in Table S1. As shown in Figure 1b, in the nanocomposites with Mg:Al = 2, the relative smaller values of  E env with respect to  E int indicate that the H2O molecules and the transferred H atoms have larger contribution to the composite stability than the direct interaction between LDH and GO. This phenomenon becomes more prominent with the increase of OH groups on GO. This can be ascribed to formation of more water molecules in the high OH:E ratio. The H2O molecules usually occupy the interlayer interaction sites between LDH and GO, eliminating the direct contact between LDH and GO and leading to decreased interaction between LDH and GO. In addition, a larger interlayer separation is generally required to accommodate more interlayer H2O molecules, which has been revealed by the increasing center of mass (COM) distance between LDH and GO with the number of formed H2O molecules (Figure 2c). In the nanocomposites with Mg:Al = 3, when GO contains more E groups than OH groups (E:OH = 8:0, 5:3), it is the interaction between LDH and GO mainly contributes to the composite stability (Figure 1a). This discrepancy with respect to Mg:Al = 2 might be due to the fact that the number of formed H2O molecules is less in the current composites (Mg:Al = 3). When GO contains more OH groups than E groups (E:OH = 3:5, 0:8), the H2O molecules and the H atoms transfer become the main contributors to the nanocomposite stability. According to our simulation, H2O molecules in the interlayer can modulate the composite stability. In the fabrication of LDH/GO nanocomposite, high concentration of epoxy groups on GO can facilitate the direct contact between LDH and GO. To get a deeper insight into the interfacial water-related interactions, we divided the nanocomposite into two fragments, i.e. all H2O molecules as one fragment and LDH and GO


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together as the other one. The interaction energy between two fragments (  E wat  slab ) was given by  E wat  slab  E elstat  E orb  E disp  E pauli through the periodic energy decomposition analysis (pEDA) method,36,37 where the four terms on the right side are the energies of electrostatic interaction, orbitals interaction, vdW dispersion interaction and Pauli repulsive interaction, respectively. The energy decomposition of  E wat  slab (Figure 1 (c) and (d)) shows that electrostatic interaction, orbitals attractive interaction and vdW interaction can stabilize the nanocomposite, while Pauli repulsive interaction destabilize the system. The relatively smaller value of E elstat among the first three terms indicates that the electrostatic interaction arising from H2O molecules plays a predominant role at the LDH/GO interface. The slightly larger Eorb implies that there is charge transfer, revealing the existence of chemical interaction between H2O molecules and LDH or GO in the system. These results are in agreement with the experimental study by Zou et al., in which GO coagulation on LDH is mainly driven by electrostatic interaction and hydrogen bonds (HBs).38 There is hydrogen bond (HB) network formation in the interlayer of MgAl LDH/GO nanocomposites (Figure S5), suggesting that HBs play a significant role in maintaining the nanocomposite stability. All HBs appear in the systems were categorized into six types (see Figure 3a): Type-1, the epoxy breaks one C-O bond and serves as the H atom acceptor for LDHOH; Type-2, the intact epoxy serves as the H atom acceptor for LDH-OH; Type-3, the hydroxyl serves as the H atom donor for LDH-O; Type-4, the hydroxyl serves as the H atom acceptor for LDH-OH; Type-5, the H2O molecule serves as the H atom donor for LDH-OH; Type-6, the H2O molecule serves as the H atom acceptor for LDH-OH. Figure 3b shows the number of HBs in each LDH/GO nanocomposite for Mg:Al = 3. The data for the nanocomposites with Mg:Al = 2 were shown in Figure S6(a). When there are more E


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groups than OH groups on GO (E:OH = 8:0, 5:3), it is the direct HBs between LDH and GO (Type-1, Type-4) that stabilize the composites. With an increase of OH on GO, the number of HBs between LDH (or H2O) and GO decreases, which is ascribed to the dissociation of OH groups. As a result, the number of HBs between LDH and H2O (type-5 and type-6) increases. It should be noted that the exposure of sp2 hybridized C atoms on GO along with OH dissociation might lead to the formation of HO…π interaction between H2O molecule and GO, which can play a key role in the stabilization of the interacting system.39 In this case, H2O molecules play an essential role in maintaining the nanocomposites, i.e. on the one hand they form HBs with LDH, on the other hand they have the HO…π interaction with GO. The bonding natures of various types of HBs were analyzed through the theory of Atoms in Molecules (AIM) (Please see the details in the Supporting Information). As shown in Table 1, the Laplacian of electron density (∇ 𝜌 ) at the bond critical point (BCP) is in the range of 0.024-0.150 au, and the electron density (𝜌 ) at the BCP is in the range of 0.002-0.100 au for all six types of HBs, all of which satisfy the criteria for the existence of HB.40


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Figure 3. (a) Six types of hydrogen bonds denoted by red dashed lines. (b) The number of hydrogen bonds in each LDH/GO nanocomposite with Mg:Al = 3 under different E:OH ratios. (c) The total energy of hydrogen bonds in each LDH/GO nanocomposite with Mg:Al = 3 under different E:OH ratios.

The changing behavior of HB type in the LDH/GO interface is compatible with the corresponding HB energies. As exhibited in Figure 3c, in the nanocomposites with Mg:Al=3, the HB energy between LDH and GO shows a reducing trend while that between LDH and H2O displays an increase trend with the OH group on GO. The corresponding HBs energy for the Mg:Al=2 are shown in Figure S6(b). We can see that, at the same E:OH ratio, the HBs energy with Mg:Al = 2 is larger than that with Mg:Al = 3. A comparison of Figure 1a and Figure 3c shows that the LDH-GO interaction energy ( E int ) follows the same tendency with the HB energy of LDH-GO. The above results confirm that HBs have an important contribution to the LDH-GO interfacial interaction. Additionally, the interfacial H2O molecules can be robustly involved in forming the HB network at the composite interface. This new finding needs to be further verified through more experimental and theoretical studies. Table 1. Topological parameters of the bond critical points for different types of HBs.


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Deformations of MgAl LDH and GO The positive deformation energies  E prep of LDH and GO (Figure 1) reveal that it is difficult to form the composite. However, the E prep is largely offset by the Eenv . In the distor distor deformation energy of LDH/GO composites, E LDH is much smaller than E GO . This means

that LDH main structures are not changed much, compared with GO structure (Figure S4). Wang et al.34 observed the same phenomenon after GO aggregation on MgAl LDH or CaAl LDH through XRD measurement. From Figure 1 (a) and (b), we can see that  E prep increases with the number of OH groups on GO, indicating that the deformation energy is greatly associated with the dissociation of OH groups. In the nanocomposites with Mg:Al = 2, more OH groups were dissociated (i.e. more H2O molecules were formed), thereby leading to higher ∆Eprep values than the case with Mg:Al = 3. Electronic Properties of the Nanocomposites We examined the charge transfer involved in the combining of LDH and GO. The charge density difference was calculated as,      comp   LDH   GO   H

2O

, where   comp ,  LDH ,

 GO and  H O are charge densities of the nanocomposite, isolated LDH, isolated GO, and H2O 2

molecule(s), respectively. Figure 4a shows the representative   isosurfaces for the LDH/GO systems with Mg:Al = 3. It can be seen that the H and the metal atoms of LDH show charge depletion, whereas the O atoms of H2O molecules and functional groups of GO show charge accumulation. The quantitative average electron difference of each element is shown in Figure S7. These indicate that there is charge transfer from LDH to H2O molecules and GO. In Figure 4b, the Hirshfeld charge analysis further quantitatively verifies this point of view. The amount of charges lost by LDH is almost the sum of that gained by H2O molecules and GO. Such charge


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transfer might enhance the interfacial interaction and lead to a built-in electric field, which has been similarly reported between monolayer MoS2 and GO by Hua et al.31

Figure 4. (a) Calculated charge density difference maps (isovalue = 0.008 e Å-3) of LDH/GO nanocomposites, in which the violet and green regions represent charge accumulation and depletion, respectively. (b) The charge differences of LDH, GO and H2O molecules upon the formation of the nanocomposites with different E:OH ratios. The negative and positive values represent charge loss and gain, respectively.

Work function can be applied to characterize the charge transport of two different materials upon contact.30 The calculated work functions of isolated MgAl LDH are ca. 2.00 eV, and the values of isolated GO are 5.00-5.35 eV. Kumar et al.41 reported that the work function of GO with oxidation degree of 10%-20% is in the range of 5.00-5.50 eV. Our results are in good


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agreement with this previous computation. The calculated work function of GO is larger than that of LDH, confirming that the electrons can flow from LDH to GO at the interface, which has been demonstrated through the preceding analysis of charge density difference. The charge transfer from LDH to GO in our study coincides with the previous theoretical and experimental observations in the combination of LDH and carbon materials.13, 42 The electronic band structures of the LDH/GO nanocomposites and the isolated GO and LDH are shown in Figure S8. The Fermi energies of equilibrated LDH/GO nanocomposites are between the values of isolated LDH and GO, meaning that the Fermi levels of LDH shift downward and those of GO shift upward until they are equal upon the formation of the nanocomposite. The band structures of the nanocomposites near the Fermi levels are quite different from those of the isolated LDH and GO. Ma et al.43 reported that the band structure of monolayer MoS2/graphene composite is a simple sum of MoS2 and graphene, which is ascribed to the fact that the interaction involved in the interface is mainly the weak vdW interaction. However, there appears obvious charge transfer in the MgAl LDH/GO interface; as a result, the band structures of the MgAl LDH/GO composites are far more complicated than the simple sum of each component. This result implies that the interactions at the interface between GO and MgAl LDH significantly affect the electronic properties of both components. The DOS plots for the isolated LDH, LDH in the composite (E:OH = 4:4), GO in the composite (E:OH = 4:4) and H2O in the composite (E:OH = 4:4) are shown in Figure 5. The DOS plots for all the other systems are shown in Figure S9. It can be seen that, the DOS value is not zero at Fermi level for isolated LDH, meaning that the isolated monolayer MgAl LDH is metallic. The DOS plot for LDH in the composites with E:OH = 8:0, 5:3, 4:4, 3:5 shows a gap within ~2.0 eV, indicating that LDH transforms from being metallic to being semiconductive


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after combining with GO. However, a clear inspection of Figure S9 for E:OH = 0:8 shows a slight DOS around Fermi level, implicating LDH is still conductor.

Figure 5. The density of states of isolated LDH and LDH, GO and H2O components of the representative hybrid systems (E:OH = 4:4 with Mg:Al=2 and 3). The Fermi levels are normalized to zero eV, denoted by dashed lines. There is a band gap in the LDH of composite marked in blue region.

Meanwhile, the conductive band positions of GO are lower than those of MgAl LDH, allowing the migrating of photoexcited electrons in the LDH component into the unoccupied electronic level of the GO component, resulting in the spatial separation of electrons and holes. This is just the prerequisite for the good photocatalytic activity of 2-D nanostructured material,31,44,45 e.g. for light-induced oxygen molecule generation.46 The above results suggest a way of regulating the properties of monolayer MgAl LDH, i.e. combining with GO, to fulfil specific application requirement. If the semiconductive LDH is required (e.g. in photocatalysis), it is perhaps a good choice to combine it with GO covering with more E groups than OH groups. Figure 5 and Figure S9 also show the partial DOS of each system. The valence band and conductive band edges mainly consist of the GO states. The overlapping region between the GO-


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O states and the LDH-H states decreases with the increasing of OH groups on GO, indicating that the direct LDH-GO interaction declines with the increasing of OH groups. In the nanocomposites, in which H2O molecules were formed, there is an overlap between H2O states and LDH states, implying the interaction between H2O and LDH. These results are all in consistent with our analysis in the above sections. CONCLUSION Interfacial

interactions,

structural

and

electronic

properties

of

MgAl

LDH/GO

nanocomposites were thoroughly investigated through DFT method. After the formation of the nanocomposites, there is less change in LDH structures, while the GO sheets exhibit large distortion. The Mg:Al ratio is more important than the E:OH ratio in determining the nanocomposite stability. We can observe the formation of H2O molecules in the interface during the combining between LDH and GO, in which the dissociated OH groups can combine the hydrogen atom on LDH to form interfacial H2O molecules. Moreover, the transfer of hydrogen atom from LDH to the epoxy group resulting in hydroxyl was also observed. The as-formed H2O molecules play a key role in maintaining the nanocomposites: In the case where E groups are more than OH groups on GO, the interaction between LDH and GO provides the main role in stabilizing the composite system and the H2O molecules only has weak contribution. In the case where E groups are less than OH groups, H2O molecules play an essential role in maintaining the nanocomposites. Our simulation suggests that high concentration of epoxy groups on GO can facilitate the direct contact between LDH and GO in the fabrication of LDH/GO nanocomposite. In the LDH/GO interfaces, the charge transfer from LDH to GO and H2O molecules leads to the change of the electrical properties of building components. This demonstrates chemical interaction between LDH and GO and further makes the band structures of the nanocomposites


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very complicated. From the band structure, the hybrid materials in most cases show metallic behavior. However, the metallic monolayer MgAl LDH in the isolated state can become semiconductive by combining with GOs that carry more E groups than OH groups. Our study proposes the application potential of monolayer MgAl LDH/GO nanocomposite in the relevant photocatalysis field.

ASSOCIATED CONTENT Supporting Information Some supplementary figures. This material is available free of charge via the Internet at http://pubs.acs.org.

Notes The authors declare no competing financial interest.

AKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China under Grants 21676136, 21606122 and A PAPD Project of Jiangsu Higher Education Institution. The computational resources generously provided by High Performance Computing Center of Nanjing Tech University are greatly appreciated.

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