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Space-confined growth of defect-rich molybdenum disulfide nanosheets within graphene: application in the removal of smoke particles and toxic volatiles Dong Wang, Weiyi Xing, Lei Song, and Yuan Hu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b09548 • Publication Date (Web): 29 Nov 2016 Downloaded from http://pubs.acs.org on November 30, 2016

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ACS Applied Materials & Interfaces

Space-Confined Growth of Defect-Rich Molybdenum Disulfide Nanosheets Within Graphene: Application in The Removal of Smoke Particles and Toxic Volatiles

Dong Wang a, 1, Weiyi Xing a, 1, Lei Song*a and Yuan Hu*a, b

a

State Key Laboratory of Fire Science, University of Science and Technology of

China, 96 Jinzhai Road, Hefei, Anhui 230026, P. R. China b

USTC-CityU Joint Advanced Research Center, Suzhou Key Laboratory of Urban

Public Safety, Suzhou Institute for Advanced Study, University of Science and Technology of China, Suzhou, Jiangsu 215123, PR China

Corresponding Author *Tel./Fax: +86-551-63600081. E-mail: [email protected]. (Lei Song) *Tel./Fax: +86-551-63606463. E-mail: [email protected]. (Yuan Hu)

ACS Paragon Plus Environment


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Abstract In the paper, molybdenum disulfide/reduced graphene oxide (MoS2/RGO) hybrids are synthesized by a spatially confined reaction to insert the growth of defect-rich MoS2 nanosheets within graphene and incorporated into polymer matrix for the application in the removal of smoke particles and toxic volatiles. The steady state tube furnace result demonstrates that MoS2/RGO hybrid could considerably reduce the yield of CO and smoke particles. TG-IR coupling technique was utilized to identify species of toxic volatiles including aromatic compounds, CO and hydrocarbons, and investigate the removal effect of MoS2/RGO hybrids on reducing toxic volatiles. The removal of smoke particles and toxic volatiles was attributed to the adsorption capacity derived from edges sites of MoS2 and honeycomb lattice of graphene, and the inhibition of nano-barrier resulting from two-dimension structure. The work will offer a strategy for fabricating graphene-based hybrids by the space-confined synthesis, and exploit the application of space-confined graphene-based hybrid.

Keywords: space-confined synthesis; molybdenum disulfide; graphene; unsaturated polyester resin composite; removal of smoke particles and toxic volatiles


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1. Introduction Polymer materials have been broadly applied in modern-day life, while most of them are organic and thus flammable that easily triggers fire accident.1 Smoke and combustion gas including carbon monoxide result in most of the deaths.2 Compared to aliphatic polymers, aromatic polymers are cracked to polybenzenoid intermediates that likely induce cancer, and tend to produce more smoke particles that increase the difficulty of fire rescues during combustion.3-4 Up to now, numerous methods to lower smoke and toxic gas have generally covered the use of smoke suppressant additives and structural modification of polymer backbones.5-7 Polymer molecules with aliphatic backbones have a trend toward decreasing smoke generation, but polyenic and aromatic polymers often lead to more smoke generation. However, structural modification is difficult to achieve and may deteriorate excellent properties of polymer itself. In contrast, the use of smoke suppressant additives are easy to realize but the type of additives has great effect on the removal of smoke and toxic gas. Organic additives containing phosphorus and nitrogen elements are environmental friendly, but has low efficiency in the removal of toxic gas and usually deteriorate mechanical properties of polymer matrix. Inorganic additives including metal oxide and hydroxide takes a lot of amount (up to 20 wt%) to reduce smoke and toxic gas. The low efficiency of metal oxide and hydroxide was primarily ascribed to low specific surface area. With the rise of two dimensional structure, graphene nanosheets exhibit tremendous potential ability of the removal of smoke particles and toxic gas because of the strong absorption originated from high specific surface area,



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sp2-bonded aromatic structure, and so on.8-10 Thus, it is very promising to develop a novel graphene-based smoke suppressant additives for the effective elimination of smoke particles and toxic gas during polymer combustion. Molybdenum disulfide (MoS2), consisting of hexagonal planes of S and Mo atoms in a trigonally prismatic structure, has been widely applied in the field of gas adsorption because of the various active sites (sulfur defect, vacancy and edge sites).11-12 Density functional study has studied the attachment of aromatic and conjugated substances on the basal plane of MoS2 mainly relies on van der Waals interaction.13 In addition, MoS2 with the edge sites has high d-orbital electronic density that could cause intense coupling interaction between the gas molecules and the MoS2.14 A mass of researches have reported that MoS2 has outstanding catalytic activity of char formation, which contributes to the reduction of smoke particles and toxic volatiles.15 Recently, amorphous MoS2 has been regarded as an efficient catalyst because it owns numerous lively unsaturated sulfur atoms, indicating the association of the catalytic ability of the S-Mo-S layers with active edge sites.16 Generally, the exposed basal planes of MoS2 nanosheets are the thermodynamically stable (002) compared to the active edge planes.17-18 For improving the absorption storage and catalytic ability, engineering defect-triggered cracks on the basal planes of MoS2 holds great promise to expose active edge sites. Restriction of nanoparticles within fullerene,19 carbon nanotubes,20 and graphene 21

could effectively limit the measure of nanoparticles, which results in extraordinary

performance. Graphene, consisting of sp2-bonded carbon sheets, are usually used as


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the promising substrate to disperse and restrict nanoparticles, causing better properties such as catalytic ability,22 electrical transport,23 and so on.24-28 Graphene oxide (GO) was regarded as a prominent matrix to assisting nucleation and subsequent growth because of the binding interactions between nanoparticles precursors and oxygen groups onto GO sheets.29-33 Li et al. have synthesized MoS2/RGO hybrids, possessing few-layer MoS2 nanosheets adhered onto graphene, compared to the growth of seriously aggregated MoS2 particles without GO substrate.34-37 Few-layered graphene is an intermediate state between graphite and mono-layered graphene, suiting for the interlayer growth of nanoparticles.38 So far, limited literatures have reported the confinement of defect-rich MoS2 nanosheets within graphene layers yet.39-40 Hence, the synthesis of space-restricted and defect-rich MoS2 nanosheets have a great significance for basic research and actual practice. In term of graphene itself, it has the graphitic structure like carbon nanotube and fullerene to scavenge free radicals through high electron affinity,41 and 2D structure with large specific surface area to serve as gas barriers.42 Jonas et al. have studied the adsorption of aromatic and anti-aromatic substances onto graphene via π-π stacking.43 The team of Michal et al. has experimentally and theoretically quantified the adsorption of small organic molecules on graphene.44 Herein, we report a spatially confined reaction to insert the growth of defect-rich MoS2 nanosheets synthesized by designing a reaction with appropriate sodium molybdate and excess amount of thiourea into the interlayers of partially reduced graphene oxide (RGO). The partially RGO nanosheets have dual effects in the



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synthesis of MoS2/RGO hybrid, providing oxygen-containing groups of the interlayers for strong coupling interaction between RGO nanosheets and MoS2 precursor, and a confined space to assisting the nucleation and growth of MoS2 nanosheets. As expected, the resulting MoS2/RGO hybrid shows remarkable removal of smoke and toxic gas during the burning of polymer composites. Moreover, the paper also investigates the effect of the size of partially RGO on the removal of smoke and toxic gas of unsaturated polyester resin (UPR) with abundant aromatic monomers. The detailed research of MoS2/RGO hybrid would provide a deep insight into the space-confined method to design graphene-based materials for the elimination of smoke particles and toxic volatiles.

2. Experimental 2.1. Materials Graphite powder (325 and 8000 mesh, chemical purity (CP)), hydrazine hydrate (85%, analytical reagent (AR)), sodium molybdate (Na2MnO4·2H2O, CP), thiourea (CP) were bought from Sinopharm Chemical Reagent Co., Ltd. 2.2. Synthesis of space-confined MoS2/RGO hybrid Scheme 1 demonstrates the idea of the space-confined preparation of MoS2/RGO hybrid. The synthesis begins with graphene oxide by partial reduction, resulting in the reduction of interlayer spacing and restoration of graphitic structure. Then the decreased space and remaining oxygen-containing groups within interlayers allows MoS2 precursors to intercalate and form coupling interaction. At last, MoS2


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nanosheets are grown within RGO interlayers by in-situ hydrothermal method. In addition, excess amount of thiourea absorbed onto primary nano-crystallites of MoS2 could hinder the oriented crystal growth and result in a defect-rich structure with quasiperiodic configuration. Experimental steps are as follows: 0.1 g graphene oxide powders prepared by modified Hummers' method45 were homo-dispersed in the mixed aqueous solution of 100 mL water and 0.1 mL hydrazine hydrate, heated to 100 °C for 1h, and then cooled to room temperature. 1 mmol sodium molybdate and 5 mmol thiourea were incorporated into the aforesaid solution under ultrasonication for 3 h to enter into graphene interlayers. Then the mixture was transferred into an reaction kettle and held at 200 °C for 12 h. Afterwards, MoS2/RGO hybrid was gathered by centrifugal separation, then cleaned with distilled water, and completely dried overnight. Moreover, graphene oxide in the synthesis of MoS2/RGO1 hybrids were prepared by using graphite power with average particle size of 8000 mesh as raw material and graphene oxide in the synthesis of MoS2/RGO2 hybrids were prepared by using graphite powder with average particle size of 325 mesh as raw material. 2.3. Fabrication of MoS2/RGO/UPR composite The preparative route of 2 wt% MoS2/RGO/UPR composite was performed as follows: the calculated amount of MoS2/RGO1 or MoS2/RGO2 hybrid was incorporated into 60 g UPR matrix and stirred under ultrasonication for 24 h to get the homogenous mixture. Benzoyl peroxide (BPO) with accurate quality was added into the above mixture and sequentially stirred under ultrasonication for 2 h. Then it was degassed until bubbles disappeared, poured in the 100 × 100 mm teflon mould, cured at 70 °C



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for 3 h and post-cured at 120 °C for 4 h. For comparison, MoS2/UPR, RGO1/UPR and RGO2/UPR composites were prepared by the same route. 2.4. Characterization X-ray diffraction (XRD) measurements were implemented on a Japan Rigaku D Max-Ra rotating anode X-ray diffractometer. The scanning speed and range were 4°/min and 5-60°, respectively. Laser Raman spectroscopy measurements were performed using a SPEX-1403 laser Raman spectrometer (SPEX Co., USA) with excitation provided in back-scattering geometry by a 514.5 nm argon laser line. Transmission electron microscopy (TEM) (JEM-2100F, Japan Electron Optics Laboratory Co., Ltd.) and PHILIPS XL30E scanning electron microscope (SEM) were applied to investigate the morphology of MoS2/RGO hybrid. X-ray photoelectron spectrometer (XPS) spectra were recorded using a Kratos Axis Ultra DLD spectrometer employing a monochromatic Al Kα X-ray source (hν = 1486.6 eV). The steady state tube furnace (SSTF) (BS 7790 and ISO TS 19700)46 used in the paper is both a standard test apparatus and research tool that can provide building engineers and designers with valuable data of fire hazard. The significant advantage of this apparatus over other techniques is its capability to replicate each stage of fire development.47

The

thermogravimetric

analysis/infrared

spectroscopy/mass

spectroscopy (TG-IR-MS) was performed using the TL-9000 instrument (Perkin Elmer Co., USA) successively coupled with thermogravimetric analyzer, FT-IR spectrophotometer and Mass Spectroscopy. The temperature was increased from room temperature to 800 °C at a linear heating rate of 20 °C·min−1.


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3. Results and discussion 3.1 Characterization of MoS2/RGO hybrids The structural information of MoS2/RGO hybrids was characterized by XRD and Raman spectra. As observed in XRD spectrum of synthetic MoS2 (Fig. 1), four broad and weak peaks located at 2θ = 14.1°, 32.5°, 36.8° and 57.5° are ascribed to (002), (100), (103) and (110) planes of hexagonal MoS2 with poor crystallized structure.48 Except the characteristic diffraction peaks of MoS2 with decreased intensity, a fresh wide peak at 2θ = 25.0° emerges in the XRD spectra of MoS2/RGO1 and MoS2/RGO2 hybrid, ascribed to (002) plane of RGO. Compared to the (002) planes at 2θ = 23.8° in the XRD spectra of RGO1 and RGO2 (Fig. S1, Supporting Information), the postponed (002) peaks in MoS2/RGO1 and MoS2/RGO2 hybrid demonstrate the further reduced interlayer spacing of RGO during the hydrothermal process, because of the reduction of excess thiourea under high temperature. In addition, the characteristic diffraction peaks of MoS2 with decreased intensity in MoS2/RGO1 and MoS2/RGO2 hybrid indicates the intervention of RGO has successfully inhibit the stack of as-synthesized MoS2 nanosheets.49 As exhibited in Fig. 2a, Raman spectra of MoS2/RGO1 and MoS2/RGO2 hybrid show three dominant peaks centered at 1348, 1587 and 2690 cm-1 ascribed to D, G and 2D bands of graphene50 and two weak peaks ascribed to in-plane E12g and out-of-plane A1g vibrational modes of the hexagonal MoS2.51 Generally, the level of disorder in graphene is characterized by the ratio of the relative intensity of D and G bands (ID/IG).52 Compared to GO1 and GO2, the ID/IG



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values of MoS2/RGO1 and MoS2/RGO2 hybrid are decreased, also indicating the restoration of graphene structure in hydrothermal process. As reported, the peak frequency difference between E12g and A1g is positively correlated to the numbers of MoS2 monolayers.53 Fig. 2c exhibits the lower frequency difference of MoS2/RGO2 than MoS2/RGO1, indicating thinner MoS2 nanosheets grown within RGO2 interlayers. Fig. 3 shows the morphologies of pure MoS2, MoS2/RGO1 and MoS2/RGO2 hybrid observed by SEM and TEM. SEM and TEM pictures of pure MoS2 exhibits free MoS2 nanosheets with the lateral size in the range of 80-100 nm are tightly aggregated together to form flower-analogous microspheres. As observed in Fig. S2 (Supporting Information), RGO1 shows wrinkled nanosheets with several hundred nanometers size, and RGO2 exhibits more folded nanosheets with larger size. HRTEM of pure MoS2 reveals MoS2 nanosheets with interlayer spacing of 0.63 nm comprises more than dozens of layers. As observed in SEM image of MoS2/RGO1 hybrid, several layers of MoS2 nanosheets are grown within graphene nanosheets. Its HRTEM image also confirms the typical lamellar MoS2 nanosheets with interlamellar spacing of 0.63 nm germinated within graphene nanosheets with interlayer spacing of 0.35 nm. It is worth noticed that the crystal fringes along the curled edge are discontinuous, attributed to the existence of rich defects, as marked in the image. The HRTEM image of MoS2/RGO2 hybrid shows monolayer MoS2 nanosheets with discontinuous crystal fringes with graphene nanosheets as well, indicating the existence of rich defects. Combined with SEM image of MoS2/RGO2 hybrid, it is concluded that MoS2


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nanosheets grown within RGO2 nanosheets are almost monolayer, probably because RGO2 nanosheets have plenty of interlayer space enough to satisfy the growth of monolayer MoS2 nanosheets. To obtain the composition and chemical status of various elements in MoS2/RGO1 and MoS2/RGO2 hybrid, XPS technology was carried out. The relative atomic ratios of C, O, Mo and S elements in MoS2/RGO1 and MoS2/RGO2 hybrid are listed in Table 1. The calculated atomic ratios of S to Mo elements in MoS2/RGO1 and MoS2/RGO2 hybrid are 2.09 and 2.04 respectively, closing to theoretical values of MoS2, indicating the formation of MoS2 nanosheets with high purity. Fig. 4 exhibits C 1s, Mo 3d and S 2p spectra of MoS2/RGO1 and MoS2/RGO2 hybrid. Two peaks located at 284.7 and 286.7 eV in the C 1s spectra of MoS2/RGO1 and MoS2/RGO2 hybrid are ascribed to C=C/C-C and C-O respectively.54 As observed in the Mo 3d spectra of MoS2/RGO1 and MoS2/RGO2 hybrid, the four deconvoluted peaks centered at 226.5, 229.1, 232.7 and 235.9 eV are corresponding to S 2s, Mo 3d5/2, Mo 3d3/2 and Mo6+, respectively. The intense characteristic bands of Mo 3d5/2 and Mo 3d3/2 indicates the existence of Mo4+ in MoS2/RGO1 and MoS2/RGO2 hybrid, suggesting the successful growth of MoS2. The weak peak of Mo6+ is attributed to a small amount of MoO4- or MoO3 within MoS2/RGO1 and MoS2/RGO2 hybrid. In the high resolution S 2p spectrum of MoS2/RGO1 hybrid, the two intense peaks at 162.2 and 163.4 eV correspond to S 2p3/2 and S 2p1/2 of MoS2.55 The peaks at 164.7 eV indicates the synthesis of S22- and/or apical S22-, resulting in the defect structure in as-grown MoS2 nanosheets.56 The high energy peak at 168.8 eV is assigned to S4+ species in



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sulfate groups which are still absorbed on the defect-rich MoS2 nanosheets after cleaning with soluble salts.57 Compared to MoS2/RGO1 hybrid, MoS2/RGO2 hybrid shows the similar XPS S 2p spectrum except the S4+ peak, demonstrating the defect-less MoS2 nanosheets grown within MoS2/RGO2 hybrid.58

3.2 Smoke particles and toxic volatiles evaluated by SSTF and TG-IR The SSTF was utilized to measure the output of toxic volatiles such as CO, smoke particles in a real fire accident.59 Fig. 5a shows the curve of CO yield versus time, reflecting the real-time CO yield. Incorporation of MoS2/RGO1 or MoS2/RGO2 hybrid into UPR matrix can cause a significant decrease of CO yield, compared with pure UPR. The integral curves of CO yield (Fig.5b) demonstrates total CO yields of MoS2/RGO1/UPR and MoS2/RGO2/ UPR are reduced by 60.2% and 44.66%, respectively. The nano-barrier effect originated from the large specific surface area of graphene and the high absorption derived from defects in defect-rich MoS2 nanosheet are responsible for the reduced CO yield.60-61 Interestingly, MoS2/RGO1 hybrid exhibits the slight advantage in reducing CO yield of UPR composite over MoS2/RGO2 hybrid. Generally, smoke density performs negative correlation with smoke extinction coefficient. The lower smoke extinction coefficient, the higher smoke particles yield. The addition of MoS2/RGO1 or MoS2/RGO2 hybrid into UPR matrix can obviously reduce the smoke density as well. Fig. 5d exhibits 14.5% and 26.8%

decrement

in

total

smoke

production

of

MoS2/RGO1/UPR

and

MoS2/RGO2/UPR, respectively. The absorption of aromatic compounds in the basal


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plane of MoS2 nanosheet through van der Waals interaction, and the strong absorption of aromatic compounds in the basal plane of graphene nanosheet through π-π stacking mainly take charge of reducing the yield of smoke particles. Although phosphorus flame-retardants with more than 10wt% addition could significantly decrease smoke production, they usually cause the increased CO yield due to incomplete combustion.62-63 Wang et al. have demonstrated the slight effect of metal oxide with less than 5wt% addition on the removal of smoke particles and CO yield.64 Compared to other graphene-based flame-retardants,59,

65

MoS2/RGO hybrids exhibit more

excellent removal of smoke particles and CO yield. During combustion process, polymer pyrolysis liberates inflammable gas to support combustion, accompanying with smoke particles and toxic volatiles. In the article, TG-IR coupling technique was utilized to investigate the thermal degradation process and identify the pyrolysis products. As observed in Fig. 6, pure UPR and its composite have two thermal degradation stages including the thermal decomposition of molecular chains along with char formation induced by the agglomeration of aromatic compounds and hydrocarbons, and subsequent char oxidation. The temperatures at the weight loss of 5 wt% and the maximum weight loss rate are defined as the onset temperature (Tonset) and Tmax, respectively. At the initial stage, the good thermal-conductivity of graphene would promote UPR matrix pyrolysis, whereas the nano-barrier effect of graphene could inhibit the escape of pyrolysis products. Notably, compared with pure UPR, MoS2/RGO2/UPR composite shows the lower Tonset, but MoS2/RGO1/UPR composite exhibits the higher Tonset, probably



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because few-layer MoS2 nanosheets as-grown within RGO1 nanosheet significantly decrease the thermal-conductivity of RGO1. In contrast to pure UPR, the addition of MoS2/RGO1 hybrid into UPR matrix results in an obvious decrease of the maximum weight loss rate, and the incorporation of MoS2/RGO2 hybrid causes a more reduction. In addition, their Tmaxs are slightly higher than pure UPR. In the case of the maximum char oxidation rate, MoS2/RGO2 hybrid leads to the highest value, verifying the most char residues in the thermal decomposition stage of molecular chains of MoS2/RGO2/ UPR composite. Compared to pure UPR, the slightly higher char oxidation rate of MoS2/RGO2/UPR composite demonstrates a little more char yield in the thermal decomposition. When the samples undergo pyrolysis process, the pyrolysis volatiles were then transported to half-qualitatively distinguish pyrolysis components via the location of their infrared characteristic bands and half-quantitatively contrast pyrolysis concentration by the intensity of their infrared characteristic bands. Fig. 7 exhibits the total pyrolysis products, aromatic compounds, CO and hydrocarbons versus

temperature

curves

of

UPR,

MoS2/UPR,

RGO1/UPR,

RGO2/UPR,

MoS2/RGO1/UPR and MoS2/RGO2/UPR composites, respectively. It is clearly observed that the total pyrolysis volatiles of UPR composites are reduced compared to pure UPR. From FTIR spectra (Fig. S3, Supporting Information), it is observed that aromatic compounds (1596 cm-1), CO (2180 cm-1)and hydrocarbons (2954 cm-1) are released during pyrolysis process. In contrast to pure UPR, aromatic compounds of MoS2/RGO1/UPR and MoS2/RGO2/UPR composites are decreased by 53.7 and 67.9%, primarily attributed to the strong adsorption of aromatic compounds on the basal


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plane of graphene nanosheet with large specific surface through π-π stacking. In addition, hydrocarbons of MoS2/RGO1/UPR and MoS2/RGO2/UPR composites are reduced by 31.4 and 52.4%, mainly ascribed to van der Waals interaction of graphene and MoS2 nanosheet with hydrocarbon molecules. Interestingly, MoS2/RGO1/UPR composite exhibit the best elimination of CO, probably because defect-rich MoS2 nanosheet has good affinity for CO molecules. 3.3 Removal mechanism of smoke particles and toxic volatiles Based on the above results and analysis, scheme 2 shows the possible removal mechanism of smoke particles and toxic pyrolysis volatiles of MoS2/RGO1/UPR and MoS2/RGO2/UPR composite during combustion. In fire scene, underlying UPR firstly starts pyrolysis under heat, and then literates inflammable volatiles including hydrocarbons, aromatic compounds to support combustion.66 Moreover, hydrocarbons and aromatic compounds are inclined to unite into smoke particles, reducing the visibility and increasing the difficulty of fire rescues.5,

67

As two-dimensional

nanosheet composed of sp2 hybridized carbon, graphene can capture hydrocarbons and aromatic compounds through varying degrees of van der Waals interaction,68-69 and serve as gas nano-barriers to inhibit the release of toxic volatiles.70-71 This dual-effects also enhance the collision chance of smoke particles to united into char residues which subsequently are accumulated into char layers by using graphene nanosheet as grown substrates.72 Generally, larger the size of graphene nanosheet, stronger the ability of capture and the inhibition of nano-barrier.73-74 This interprets MoS2/RGO2 hybrid exhibits more excellent removal ability of hydrocarbons and



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aromatic compounds. Previous literatures have studied the adsorption of gas guests on the basal plane of MoS2 nanosheet via weak van der Waals interaction and the stronger binding interaction between gas guests and MoS2 nanosheet with the increase of edge sites of MoS2 containing high d-orbital electron density.14, 75-76 Defect-rich MoS2 nanosheets grown within RGO1 or RGO2 nanosheets could strongly absorb CO, hydrocarbons and aromatic compounds on the edge sites of MoS2. MoS2/RGO1/UPR composite liberates less CO amount than MoS2/RGO1/UPR composite, demonstrating that edge sites of MoS2 have excellent adsorption of CO molecules, Furthermore, nano-barrier effect of two-dimensional MoS2 nanosheets somewhat restrains the liberation of toxic volatiles as well.15 In summary, RGO nanosheets play the crucial role in the removal of hydrocarbons and aromatic compounds, and defect-rich MoS2 nanosheets act the decisive effect on the elimination of CO.

4. Conclusion In the work, MoS2/RGO hybrids were synthesized via a spatially confined reaction to insert the growth of defect-rich MoS2 nanosheets within graphene nanosheets. The structural characterizations of MoS2/RGO hybrids reveals that few-layers MoS2 nanosheets with more edge sites were grown within small-sized graphene nanosheets, yet almost mono-layer MoS2 nanosheets with less edge sites were developed within large-sized graphene nanosheets. SSTF result demonstrates that MoS2/RGO hybrid could considerably reduce the yield of CO and smoke particles. TG-IR coupling technique was utilized to investigate the thermal degradation process, identify


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pyrolysis components and contrast pyrolysis concentration, demonstrating pyrolysis volatiles including CO, aromatic compounds and hydrocarbons are significantly removed by MoS2/RGO hybrid. In addition, MoS2/RGO1 hybrid exhibits better elimination of CO, and MoS2/RGO2 hybrid shows better removal of hydrocarbons and aromatic compounds. Finally, it is reasonably proposed that the adsorption capacity derived from edges sites of MoS2 and honeycomb lattice of graphene and the inhibition of nano-barrier resulting from two-dimension structure are responsible for the removal of smoke particles and toxic volatiles. As expected, the paper will provide graphene-based hybrids with theoretical basis of the removal of smoke particles and toxic volatiles.

Acknowledgements The work was financially supported by National Basic Research Program of China (973 Program) (2014CB931804), National Natural Science Foundation of China (51473154) and Fundamental Research Funds for the Central Universities (WK2320000032)

ASSOCIATED CONTENT Supporting Information Available: XRD patterns of RGO1 and RGO2, TEM images of RGO1 and RGO2, FTIR spectra of pyrolysis volatiles of UPR samples. This material is available free of charge via the Internet at http://pubs.acs.org.



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Notes and references 1.

Mouritz, A.; Mathys, Z.; Gibson, A., Heat release of polymer composites in fire.

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Table. 1 Relative atomic ratios of various elements in MoS2/RGO1 and MoS2/RGO2 hybrid.

Samples

C (at. %)

O (at. %)

Mo (at. %)

S (at. %)

MoS2/RGO1

77.72

14.30

2.58

5.40

MoS2/RGO2

76.71

15.98

2.40

4.91

Scheme 1. Space-confined synthesis route of defect-rich MoS2/RGO hybrid.

Scheme 2. Schematic illustration of the flaming MoS2/RGO/UPR composite.



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Fig. 1. XRD patterns of MoS2, MoS2/RGO1 and MoS2/RGO2 hybrid.

Fig. 2. Raman spectra of MoS2/RGO1 and MoS2/RGO2 hybrid (a); Raman spectra of GO1, GO2, MoS2/RGO1 and MoS2/RGO2 hybrid (b); Raman spectra of MoS2/RGO1 and MoS2/RGO2 hybrid between 350 and 450 cm-1(c).


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Fig.3. TEM, SEM and HRTEM images of pure MoS2, MoS2/RGO1 and MoS2/RGO2 hybrid.

Fig.4. High resolution C 1s, Mo 3d and S 2p spectra of MoS2/RGO1 and MoS2/RGO2 hybrid.



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Fig.5. CO yield (a), total CO yield (b), smoke extinction coefficient (c) and total smoke coefficient (d) of pure UPR and its composites.

Fig.6. TGA (a) and DTG (b) curves of pure UPR, MoS2/RGO1/UPR and MoS2/RGO2/UPR composite.


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Fig.7. The intensity curves of (a) total volatiles (Gram-Schmidt), (b) aromatic compounds, (c) CO and (d) hydrocarbons of pure UPR and its composites.



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Table Of Contents (TOC) graphic


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Space-Confined Growth of Defect-Rich ... - ACS Publications

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