Layer-by-Layer Assembly and Infrared Emissivity of(LDH/DNA/LDH/LTO)nHybrid Films

WANG Yong-Juan ZHOU Yu-Ming HE Man HE Qiang ZHONG Yang-Yang

(School of Chemistry and Chemical Engineering,Southeast University,Jiangsu Optoelectronic Functional Materials and Engineering Laboratory,Nanjing 211189,China)

Abstract:Herein,by using sequentially electrostatic layer-by-layer(LBL)deposition method,the artificialdesigned hybrid films were fabricated through the alternatively assemble of negatively charged layered titanium oxide(LTO)nanosheets and DNA molecules with positively charged layered double hydroxide(LDH)nanosheets.The infrared emissivity values at the wavelength of 8～14 μm of the as-synthesized samples were investigated.The X-ray diffraction(XRD)results demonstrate that the(LDH/DNA/LDH/LTO)nhybrid films were orderly stacked on the substrate in the normal direction,in which the DNA molecules and LTO nanosheets were accommodated as monolayer between the LDH nanosheets layers,respectively.It can be seen from the scanning electron microscope(SEM)and atomic force microscope(AFM)images that the surface morphology of the film was uniform and continuous.The energy dispersive X-ray spectroscopy(EDS)and X-ray photoelectron spectroscopy(XPS)analysis verify the composition,the homogenous element distribution,and the well-ordered structure in the multilayer films.This multilayered hybrid film with tetra-layer units possessed a low infrared emissivity value of 0.419 based on the synergistic effect of its multi-components,the interfacial interaction between different layers and the uniform and smooth surface.These results clearly demonstrate that the ordered LBL assembly of the artificial designed hybrid film is quite effective in decreasing the infrared emissivity value.

Keywords:LDH;DNA;layered titanium oxide;layer-by-layer;organic-inorganic hybrid composites;infrared emissivity

0 Introduction

In recent years,infrared stealth technology has been attracted more and more attention,thus the rapid development of infrared stealth materials is required urgently[1-2]. Relatively, extensive works on lowemissive materials for camouflage in the IR region have been devoted[3-7].Among them,thin films with smooth surface and few interfacial deficiencies are favorable for decreasing the infrared emissivity value,which can be assembled directly on the surface of the objectives without binders and additives.In this way,many kinds of low infrared emissivity thin films,such as Ag and Au films,have been investigated[8-9].For the fabrication of these low-emissive thin films,the physical method of direct current magnetron sputtering is currently the main method.But unfortunately,physical method usually requires the complicated processing and special equipment.In addition,the film thickness and surface roughness,which could be affected by the sputtering distance,pressure,sputtering power and so on,are crucial for infrared emissivity but hardly controlled preciously.In order to overcome these problems,sequential layer-by-layer(LBL)assembly technique is considered as one of the most powerful methods for fabricating nanostructured multilayer films at a nanometer scale with precisely controlled composition,thickness and architecture[10].This method may provide new insights in current film-growth techniques for room-temperature fabrication of multilayer films with the elimination of the encountered integration problems.

Layered double hydroxides(LDH)have been reported to have potential applications in infrared stealth due to their ordered structure and tunable properties[11-13].LDH(represented as[MⅡMⅢ(OH)]x+(An-)1-xx2x/n·yH2O)are one family of anionic clays consisting of positively charged brucite-like layers and exchangeable interlayer anions[14-15].The tunability of metal ions and intercalated anions in LDH,which would give rise to special and outstanding chemical,physical and mechanical characteristics of LDH,are beneficial to reduce the infrared emissivity.Based on the layered structure,with unique ion-exchange properties as well as good biocompatibility,LDH materials have been widely used as host matrices for various guest species[16-18].However,the ion-exchange reaction provides only intercalation of guest species,which may be restricted by the geometry size and orientation of the intercalated anion.Recently,the delamination of LDH to single nanosheet as a building block for various nanostructures has been reported[19-21].It is even possible to tailor super lattice-like assemblies by incorporating into the nanosheet galleries with a wide range of materials.Layer structured ultrathin films with sophisticated functionalities may be designed through the selection of nanosheets and combining materials,and precise controlling over their arrangement at the molecular scale by sequential LBL assembly method.In previous work,cationic LDH nanosheets were singly assembled with anionic polymers or biomolecules such as poly(sodium styrene-4-sulfonate)[22],hemoglobin[23]and DNA[24].Some studies have even been dedicated to the direct combination of positively charged LDH nanosheets and negatively charged inorganic nanosheets such as layered titanates,perovskites,and manganese oxides nanosheets[20,25].However,as far as we known,no research has been devoted to the assembly of positive charged LDH nanosheets alternatively with both anionicmacromoleculesand negatively charged inorganic nanosheets.Besides,due to the diversified multi-compositions and ordered structure of the multilayer hybrid structure,it is highly possible that drastic changes can occur in physical properties such as infrared emissivity.

In this work,the(LDH/DNA/LDH/LTO)nmultilay-er hybrid films were constructed through the electrostatic LBL assembly method,and an obvious change was obtained in the infrared emission properties.Specifically,the positively charged LDH nanosheets as building blocks were assembled alternately with both negatively charged DNA and layered titanium oxide nanosheets.The structure of the hybrid films composed of biomolecule-inorganic multi-components was discussed in detail.The infrared emissivity values at the wavelength of 8～14 μm were investigated.This work provides an efficient strategy for the fabrication of the multilayer thin films with low infrared emissivity.

1 Experimental

1.1 Materials

Nickel hydroxide,indium hydroxide,titanium（Ⅳ）isopropoxide,cesium carbonate,citric acid anhydrous,tetrabutyl ammonium hydroxide,polyetherimide(PEI)and poly(styrene sulfonic acid)(PSS)were obtained from Aladdin Reagent,Shanghai,China.Acetic acid,sodium hydroxide,methyl alcohol,ethylene glycol and hydrochloric acid were purchased from Sinopharm Chemical reagent Co.Ltd.,Shanghai,China.Salmon sperm DNA(D1626,approximately 2 000 bp)was purchased from the Sigma Chemical Co.All the reagents above were analytical reagent grade and were used without further purification.Deionized and decarbonated water was used in all solutions.

1.2 Synthesis of exfoliated Ni-In LDH nanosheets

The Ni-In LDH nanosheets were prepared according to the reported method[26].Firstly,acetate intercalated Ni-In LDH were prepared by co-precipitation method.After centrifugation and washing,the wet gel was suspended in deionized water directly for delamination.The content of LDH nanosheets in the colloidal solution was estimated to be 1 mg·mL-1.

1.3 Synthesis of layered titanium oxide nanosheets

The starting material CsxTi(2-x/4)□x/4O4(x=0.76)was prepared by the complex polymerization method[27].The protonated form HxTi(2-x/4)□x/4O4·H2O was derived through the repeated ion exchange(three cycles)of the cesium form with 1 mol·L-1HCl[28].The protonated form powders were exfoliated in an aqueous tetrabutyl ammonium solution.The reaction was allowed to take place for 7 days under continuous stirring to obtain a reasonable amount of exfoliation.Subsequent centrifugation under 2 000 r·min-1for 30 min yielded colloidal suspensions having exfoliated LTO nanosheets(TiO6layers).

1.4 Assembly of(LDH/DNA/LDH/LTO)nhybrid films

Prior to assembly,Si wafer and quartz glass substrates were cleaned by treatment in a bath of methanol/HCl(12 mol·L-1)(1∶1,V/V)and then concentrated H2SO4(18.4 mol·L-1)for 30 min each,followed by rinsing in deionized water and drying with a N2flow.The cleaned Si wafer and quartz substrates were firstly dipped into a cationic PEI solution(1 mg·mL-1),and then anionic PSS solution(1 mg·mL-1)for 20 min,respectively,and then washed thoroughly and dried with a N2flow after each deposition.After these processes,the substrates were modified with a PEI/PSS precursor film,resulting in a negatively charged surface.

The fabrication of the(LDH/DNA/LDH/LTO)nfilms were carried out by alternate immersion of the PEI/PSS coated substrates in LDH nanosheets colloidal suspension,DNA solution(1 mg·mL-1in 0.05 mol·L-1Tri-HCl,pH=8.0),LDH nanosheets colloidal and LTO nanosheets colloidal,respectively,for 15 min each time.Water rinsing and N2drying were performed after each deposition step.Similarly,the respective(LDH/DNA/LDH/DNA)nand(LDH/LTO/LDH/LTO)nfilms were also prepared for comparison.The resulting films were finally rinsed,dried and stored in 4℃before use.

1.5 Characterization

X-ray diffraction(XRD)data were collected by PAN alytical X′Pert Pro instrument(Cu Kα radiation,λ=0.154 05 nm,40 kV,30 mA,2°～8°).UV-Vis spectra were measured on a Shimadzu UV-2450 spectropolarimeter.The morphologies and the EDS(energy dispersive X-ray spectroscopy)element maps of the samples were examined by scanning electron microscopy(SEM)at 5 kV/10 μA(Hitachi S-3400N).Tapping mode atomic force microscopic images were acquired at room tem-perature in air by using Dimension Icon system(Bruker AXS)with NanoScope software(tip radius＜5 nm,nominal resonant frequency of 300～400 kHz,nominal spring constant of 42 N·m-1).X-ray photoelectron spectra(XPS)were recorded on a Physical Electronics XPS-5700 spectrometer with Al Kα X-ray line(1 486.6 eV).A depth profile was obtained by etching the films with Ar+gun(3.0 kV).Infrared emissivity values of the samples were carried out on an IR-2 Double Band Infrared Emissometer of Shanghai Institute of Technology and Physics,China.

2 Results and discussion

The structure of LDH nanosheets(Ni0.75In0.25(OH)2)is corresponded to the single layer of the parent brucite-like layered double hydroxides(Fig.1a).The metal cations occupy the centers of edge sharing octahedra,whose vertexes contain hydroxide ions that connect to form infinite 2D sheets.The synthesized LDH nanosheets in this paper are comparable to our previous studies[26],which are confirmed to be unilamellar with a thickness of about 1.2 nm and a lateral dimension of 100～200 nm by AFM observation;two-dimensional unit cell parameter(a)was refined to be 0.305 0 nm for Ni-In LDH nanosheets.The LTO nanosheet of Ti0.91O2is corresponding to the individual host layer of the parent titanate CsxTi(2-x/4)□x/4O4,as shown in Fig.1b.Titanium atom is coordinated with six oxygen atoms and the resulted octahedra are joined via edge sharing to produce the two-dimensional crystallite.And thus the thickness of LTO nanosheet,which is consisted of two edge-shared TiO6octahedra,is well below 1 nm.Here,the LTO nanosheets were synthesized by the intercalation-exfoliation procedure and the morphology and size of the exfoliated nanosheets were examined by TEM and AFM.Fig.2a shows the TEM images of the LTO nanosheets,allowing the identification of individual nanosheet crystallites.The lateral size of the nanosheets was in the range of 0.1～1 μm,which is smaller than the dimension of the parent layered microcrystals,indicating the breakage or fracture of sheets during the delamination process.As can be seen from TEM images,the obtained nanosheets had very faint but homogeneous contrast,reflecting their ultrathin nature and uniform thickness.The selected area electron diffraction(SAED)pattern of individual nanosheet exhibits orthogonal arranged spots,confirming the single-crystal nature as well as the high crystallinity of the LTO nanosheets.The unit cell parameters of the orthogonal lattice were estimated to be a=0.376 8 nm,c=0.297 8 nm for the LTO nanosheets which is compatible with the values investigated previously[29].A tapping-mode AFM image(Fig.2b)shows thin sheet-like objects with similar lateral dimensions as those detected by TEM observations.The height profile demonstrates that the nanosheets had a fairly flat terrace with an average thickness of 1.2 nm.This value is very similar to that previously observed[29],which has been explained as the sum of crystallographic thickness(0.7 nm)of the LTO layer and the adsorbed monolayers of water molecules(0.25 nm×2)on both side of the nanosheets.Such a thickness of 1.2 nm unambiguously indicates the unilamellar nature of the delaminated LTO nanosheets.

Fig.1 Top views of nanosheets:(a)Ni0.75In0.25(OH)2and(b)Ti0.91O2;(c)3D model for DNA helix chain

Fig.2 (a)TEM image and SAED pattern and(b)AFM images and height profile of LTO nanosheet

Fig.3 UV-Vis absorption spectra of(LDH/DNA/LDH/LTO)nfilms with tetra-layer number(n)ranging from 1～6

As discussed above,the LTO nanosheets,which are dispersed in a colloidal suspension,would have the negatively charged and extremely high 2D anisotropy crystallites.Besides,DNA has an isoelectric point(pI)of 4.5,making it also negatively charged in Tris-HCl buffer at pH=8.0.Thus,both of the LTO nanosheets and DNA can be used as building blocks for assembly with positively charged LDH nanosheets via electrostatic interaction.In this case,the multilayer films were prepared by sequentially adsorbing positively charged LDH nanosheets and negatively charged DNA molecular and LTO nanosheets alternatively on a Si wafer or quartz glass substrates.The growth of the(LDH/DNA/LDH/LTO)nhybrid films under the optimized conditions was monitored by UV-Vis absorption spectra mea-sured immediately after each deposition cycle(Fig.3).The absorption spectra of the hybrid films show progressive enhancement as a function of the tetra-layer number.It happened to be that the UV-Vis absorption peaks of DNA[12,30]and titania nanosheet[31]are both around 260 nm,as have been reported previously.The LDH nanosheets do not show substantial absorption in the energy region shown.In this way,the absorption bands centered at around 260 nm of the hybrid films are attributed to superimposing of the typical absorption of DNA and the excitonic transition characteristic of titania nanosheet.Consequently,the nearly liner growth of the absorption band indicates that the DNA and LTO nanosheets are deposited for each tetra-layer assembly in an approximately equal amount,providing persuasive evidence for a stepwise and uniform film growth procedure.

Fig.4 displays the small-angle XRD patterns of the obtained(LDH/DNA/LDH/LTO)nhybrid films.A narrow and strong Bragg diffraction peak is observed at 2θ=2.2°.Notably,the peak intensity of each sample was increased gradually upon increasing the tetra-layer number,further verifying the successful multilayer buildup in the obtained hybrid films.The diffraction feature can be attributed to the so-called superlattice reflection of the inorganic/organic periodic nanostructure,indicating that the long range stacking order of the films is in the normal direction of the substrate.The average thickness of each LDH/DNA/LDH/LTO tetra-layer unit was about 4.0 nm.By subtracting the thickness of two LDH host layer(2×0.48 nm[32]),the gallery height for the summation of DNA and LTO nanosheets in the normal direction was about 3.04 nm.Based on the diameter size of the DNA helix chain(2 nm)and the thickness of the LTO nanosheets(0.7 nm),it is relatively proposed that DNA and LTO nanosheets are accommodated respectively as a monolayer arrangement between LDH nanosheets.

Fig.4 Small-angel XRD patterns of(LDH/DNA/LDH/LTO)nfilms with different tetra-layers

The surface morphology of the(LDH/DNA/LDH/LTO)15multilayer films is monitored by SEM and AFM images.A top-view of SEM image for(LDH/DNA/LDH/LTO)15film is shown in Fig.5a.As illustration,the film is densely covered with plate-like nanosheets to form a continuous and uniform surface.The cross-sectional SEM image(Fig.5b)shows clearly the multilayered structure with the building blocks parallel to the substrate.The thickness of the(LDH/DNA/LDH/LTO)15multilayer films was estimated to be about 63 nm.Thus,one tetra-layer unit thickness was calculated to be 4.2 nm in approximately accordance with the result obtained by XRD(4 nm).However,the actual film thickness of the(LDH/DNA/LDH/LTO)15film is comparably larger than the calculated value(15×(0.48+2.1+0.48+0.7)=56.4 nm).This is probably because that the real structure effects as opposed to an ideal ordered structure composed of infinitely extended layers.The real layers may have significant degree of flexibility and bending around defects such as sheet terminations,which lead to voids and overlaps in the assembly.The top-view AFM image(Fig.5c)displays a continuous coverage and arrangement of the nanosheets on the surface of the film in accordance with the SEM image.The side-view AFM image(Fig.5d)confirms the continuous and uniform surface with the RMS roughness of the surface of about 2 nm.The presence of all the components of Ni0.75In0.25(OH)2,Ti0.91O2and DNA in the assembly is verified based on EDS mapping of the LDH-,DNA-and LTO-specific elements,respectively(Fig.6).The signals of the Ni Kα,In Lα,P Kα,and Ti Kα peaks from EDS mappings show the evidence of a homogeneous distribution throughout the multilayer,thus confirming the formation of a hybrid nanostructure featuring layered componentsintimately mixed atthe nanoscale.

Fig.5 (a)Top-view and(b)side-view SEM images of(LDH/DNA/LDH/LTO)15films;(c)Top-view and(d)side-view AFM images of(LDH/DNA/LDH/LTO)15film

Fig.6 EDS element mappings and(center)SEM image of(LDH/DNA/LDH/LTO)15film

XPS survey scans were used to identify the composition of the assembled multilayer film(Fig.7).The(LDH/DNA/LDH/LTO)15film exhibits various peaks which can be assigned to Ni,In,Ti,P,N and O elements from the film components.The binding energies at 855.6,861.1,873.3,879.5,444.8 and 452.3 eV in the spectrum are attributed to Ni2p3/2,Ni2p3/2sat.,Ni2p1/2,Ni2p1/2sat.,In3d5/2and In3d3/2of Ni and In elements in their hydroxides[33-34],indicating the exis-tence of the Ni-In LDH nanosheets.The binding energies at 458.6 and 464.3 eV are assigned to Ti2p and Ti2p1/2of Ti in its oxides confirming that the LTO nanosheets are present in the hybrid structure[35].The binding energy of P2p at 132.5 eV is attributed to phosphate backbone of DNA helix chain[36],demonstrating the presence of DNA.The N1s(399.25 eV)spectra for DNA and O1s(530.5 eV)spectra for the titanium oxides and metal hydroxides further verify the existenceoftheLDH nanosheets,DNA and LTO nanosheets in the hybrid film[36].

Fig.7 (A)Survey XPS spectra of(LDH/DNA/LDH/LTO)15film;(B)XPS data for(a)Ni2p,(b)In3d,(c)Ti2p,(d)P2p,(e)N1s and(f)O1s

Fig.8 XPS depth profile for(LDH/DNA/LDH/LTO)15 film

In the XPS depth analysis(Fig.8),the relatively steady plateaus were reached after a sputtering time of 3 min.At the very surface,carbon was found to be the main component,which might be explained as the carbon pollution on the surface of the film.Thus,its content drastically dropped to a constant level after a short sputtering time.The carbon element in the inner part of the film is mainly attributed to the DNA molecules in the film.The Ni,In,Ti and P contents can be regarded as reflecting the intrinsic chemical composition of the film.Atomic ratio of Ni to In was roughly in consistent with the expected value of 3 for the LDH nanosheets,illustrating the validity of the analysis.Considering the high reliability of XPS quantitative analysis,the Ti and P elements are taken as measures of real compositions.Accordingly,the average molar ratio of Ni0.75In0.25(OH)2to Ti0.91O2and DNA base pair(bp)in the multilayer hybrid film was estimated to be 1∶0.51∶0.05 for(LDH/DNA/LDH/LTO)15film.

Two plausible models involving charge balance and area balance may be theoretically considered for the formation of these hybrid sandwich layered materials,which are composed of the oppositely charged layers.In the charge-balance model,LDH nanosheets,DNA molecules and LTO nanosheets are combined in a ratio to attain the charge neutrality for the total system.However,the total areas of LDH nanosheets,DNA molecules and LTO nanosheets deviate from each other due to an intrinsic difference in layer charge density.On the other hand,the area-balance model assumes a mixing ratio,which provides equal area of three kinds of layer components in the stacked systems.It is important to discuss which model is followed in the real process.

The two-dimensional unit cell of Ni0.75In0.25(OH)2nanosheets had an area of 0.088 nm2(0.305 02×sin120°)containing a net positive charge of 0.25.On the other hand,the unit cell area of Ti0.91O2nanosheets was estimated to be 0.112 nm2(0.376 8×0.297 8),containing two formula units with a net negative charge of 0.76.For the DNA helix chain,the average unit crosssectional area of one base pair in the double helix chain was 0.68 nm2(2×0.34)with a net negative charge of 2.Assuming that the charge balance is followed,the molar ratio of Ni0.75In0.25(OH)2to Ti0.91O2nanosheets and DNA base pair is calculated to be 1∶0.33∶0.063.For the area balance,a molar ratio yield should be 1∶0.78∶0.065.Determined by XPS analysis above,the molar ratio of Ni0.75In0.25(OH)2nanosheets to Ti0.91O2nanosheets falls just between theoretical values of charge balance and area balance.On the other hand,the molar ratio of Ni0.75In0.25(OH)2nanosheets to DNA base pair is lower than the theoretical values since the theoretical values of charge balance and area balance are similar.Considering the existence of LDH as an acetate form in the sample,a practical content of Ni0.75In0.25(OH)2nanosheets combined with Ti0.91O2nanosheets and DNA bp is less than the measured value.Thus,the effective molar ratio of Ni0.75In0.25(OH)2nanosheets to Ti0.91O2nanosheets and DNA bp may be smaller than 1∶0.51 and 1∶0.05,respectively.In this way,the yield molar ratio of Ni0.75In0.25(OH)2nanosheets to Ti0.91O2nanosheets may be somewhat closer to the theoretical value of area balance,and for DNA bp,the value is close to both of the theoretical ones.

Table 1 Infrared emissivity values of different samples

The infrared emissivity values of the samples at wavelength of 8～14 μm are listed in Table 1.The factors that influence the infrared emissivity of the film are including the infrared emissivity value of each pristine component,the surface roughness,the microstructure of the film and the synergistic effect between the different components in the film as we have investigated in our previous work[12-13,37]. The pristine Ni-In-CH3COO--LDHs and DNA have the infrared emissivity values of 0.705 and 0.802 respectively as discussed in our previous work[12].The infrared emissivity value of the layered titanium oxide is 0.728,which is lower than the value of particle TiO2(0.925[38]).The different results between layer structural and particle titanium oxide should mainly be explained by two different reasons:particle size dependent scattering and surface structure/shape dependent scattering.If the surface area is increased due to an irregular surface structure,the emissivity will increase.Consequently,the layer titanium oxide,which has a lower surface area with ordered layer structure,possesses lower infra-red emissivity.

The infrared emissivity value of(LDH/DNA/LDH/LTO)15multilayer film with tetra-layer units was 0.419,which is lower than that of the pristine components.On one hand,the surface roughness as mentioned previously in this paper may have effective influence on the infrared emissivity.When the negatively charged LTO nanosheetsand DNA moleculesare alternatively assembled with positively charged LDH nanosheets by LBL method to fabricate the hybrid films,the obtained multilayer films have smoother surfaces than the pristine LDH,LTO and DNA powders.According to the Kirchhoff′s law and the Principle of Conservation of Energy,the relationship between the infrared emissivity(ε)and reflection(r)of non-transparent material can be expressed as ε=1-r.Therefore,the smooth surface with low surface roughness would result in high reflection thus lead to the decreasing of the infrared emissivity.In this way,the assembled hybrid multilayer film with smooth and continuous surface with few deficiencies will have lower infrared emissivity than the native LDH,LTO and DNA powders.On the other hand,the decrease of the infrared emissivity may be attributed to interfacial interaction such as hydrogen bonds or electrostatic interactions between the layer ingredients[39-42],which is strengthened by the construction of the ordered layer structure.When LTO nanosheets and DNA are assembled with the exfoliated LDH nanosheets,as discussed above,the LTO nanosheets and the backbone of the DNA chain are oriented parallel to the basal plane of the LDHs host layer,and thus the ordered layered structure is well-formed.The interfacial interaction is reinforced by the construction of the ordered layer structure.The geometrically constrained environment supplied by LDHs host alters the vibration mode of the atoms or pendant groups on the interface among DNA,LTO and LDH host layers,which would directly reduce the infrared emissivity value of the material.

However,the infrared emissivity values of(LDH/DNA/LDH/DNA)15and(LDH/LTO/LDH/LTO)15films were 0.657 and 0.602,respectively.Compared with these films composed of two components,the(LDH/DNA/LDH/LTO)15multilayer film with three components had the lowest values of 0.419.It can be proposed that a synergistic effect among different components does exist.The interfacial synergism forces among DNA,LTO and LDH nanosheets would be strengthened by the formation of tetra-layer units,and therefore,make the decrease of the infrared emissivity in the hybrid film.Hence,the(LDH/DNA/LDH/LTO)15multilayer film with tetra-layer units is promising candidate for low infrared emissivity materials.

3 Conclusions

The hybrid multilayer thin films have been successfully fabricated based on the alternate assembly of DNA moleculesandLTO nanosheetswithLDH nanosheets via LBL technique.Structural characterizations show that the(LDH/DNA/LDH/LTO)nfilms exhibit long range stacking order resulting from a super lattice nanostructure,in which DNA helix chain and LTO nanosheets are formed as a monolayer arrangement in the LDH gallery.The hybrid films exhibit remarkable low infrared emissivity values derived from the synergistic effect of the multi-components,interfacial interaction among different layers and the uniform and smooth surface.The methodology reported in this work can be conveniently extended to the designed fabrication of other multi-functional hybrid films.