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Preparation and Tribological Properties of Lanthanum Trifluoride Nanoparticles-Decorated Graphene Oxide Nanosheets Xiao Hou,† Cuizhen Yang,† Jie He,‡ Zhiwei Li,*,† and Zhijun Zhang† †

Key Laboratory of Ministry of Education for Special Functional Materials, Henan University, Kaifeng 475004, P.R. China School of Life Science, Henan University, Kaifeng 475004, P.R. China

‡

ABSTRACT: Graphene oxide (GO) nanosheets were decorated with lanthanum trifluoride (LaF3) nanoparticles by a simple solution method to afford LaF3−GO nanohybrids, with which ammonium fluoride and lanthanum nitrate were used as raw materials to synthesize LaF3 nanoparticles. As-prepared LaF3−GO nanohybrids were characterized by X-ray diffraction, Raman spectrometry, transmission electron microscopy, and Fourier transform infrared spectrometry. Moreover, the thermal stability of the as-prepared LaF3−GO nanohybrids was evaluated by thermogravimetric analysis, and their tribological properties as an additive of distilled water were evaluated with a four-ball friction and wear tester. It was found that LaF3 nanoparticles are integrated with the GO nanosheets through electrostatic interaction thereby affording LaF3−GO nanohybrids. In addition, when the as-prepared LaF3−GO nanohybrid was added into distilled water at an optimum mass fraction of 1.5%, it was able to significantly improve the tribological properties of distilled water. This is because LaF3−GO nanohybrids can be deposited on rubbed steel surfaces to form protective and lubricious layers consisting of GO, LaF3, Fe2O3, and FeF3, thereby significantly reducing the friction and wear of the steel−steel contact under water lubrication.

1. INTRODUCTION Graphene, a two-dimensional material composed of layers of carbon atoms tightly packed into a honeycomb lattice, has attracted extensive attention owing to its excellent properties such as high thermal conductivity, high Young’s modulus, good electron transport ability, large specific surface area, and ease of functionalization.1−4 Besides, the special lamellar structure of graphene allows it to easily enter into the contact zone of a frictional pair and reduce the shear stress at the contact interface during sliding, thereby preventing the direct contact of the rough surfaces and suppressing wear of material.5−12 For instance, Kim et al. demonstrated that graphene films fabricated via chemical vapor deposition can effectively reduce the adhesion and friction forces.13 Berman et al. found that graphene layers can form a conformal protective coating on sliding contact interfaces thereby slowing down tribo-corrosion and drastically reducing wear.14 They also provided a survey of graphene from the nanoscale to macroscale saying that graphene can be used as a self-lubricating solid or as an additive for lubricating oils.15 Li et al. prepared graphene oxide and reduced graphene oxide layers on Ti or its alloy substrates by the way of self-assembly and found that as-prepared layers can be used as effective antifriction and antiwear coatings for the substrates.16,17 The fabrication of various graphene-based composites is of particular significance in terms of their application as lubricating additives, because the composites usually exhibit excellent tribological properties attributed to the synergistic effect among two or more components.18 In this respect, the researches conducted by Bai et al. and Zhang et al. are worth special attention. Namely, Bai et al. prepared graphene decorated with well-dispersed CeO2 and found that the decorated graphene exhibits better tribological properties than graphene or CeO2 nanoparticles alone.19 Zhang et al. synthesized reduced © XXXX American Chemical Society

graphene oxide/Cu nanoparticle composites and investigated their tribological properties as a lubricating oil additive.20 These researches primarily demonstrate that graphene-based composites are promising lubricant additives. With a view to the tribological application of graphene-based composites, we anticipate that the composites made of graphene oxide (GO) and lanthanum fluoride nanoparticles would be of extraordinary significance, because GO contains many functional C−O species which are favorable for its dispersion in water21,22 while lanthanum fluoride nanoparticles have promising applications as lubricating oil additives.23−26 For instance, Zhang et al. found that a surface-capped LaF3 nanocluster is able to effectively improve the lubricating performance of liquid paraffin.23 Zhou et al. reported that LaF3 nanoparticles surface-capped by S- and P-containing organic compounds can greatly improve the load-carrying capacity and antiwear ability of fluoro-silicone oil.24 We also found in previous researches that surface-modified LaF3 nanoparticles exhibit good tribological properties in fluorosilicone oil and liquid paraffin.25,26 Unfortunately, few data are currently reported on the tribological properties of LaF3 nanoparticles as water-based lubricant additives, largely because LaF3 nanoparticles have poor dispersibility and stability in water.27 Bearing those perspectives in mind, in the present research we use LaF3 nanoparticles to decorate GO nanosheets via electrostatic interaction, hoping to obtain LaF3−GO nanohybrids as a potential water-based lubricant additive with desired aqueous dispersibility and tribological properties. Such Received: February 9, 2015 Revised: April 1, 2015 Accepted: April 14, 2015

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DOI: 10.1021/acs.iecr.5b00576 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

XRD. Figure 1 shows the XRD patterns of LaF3−GO, GO, and the standard spectrum of LaF3 powders. It is clear that the

a synthetic strategy could be feasible, because on the one hand, GO possessing abundant surface C−O functional groups is able to provide LaF3 with good dispersibility in water. On the other hand, LaF3 nanoparticles possessing excellent friction-reducing, antiwear, and extreme pressure properties could have tribological synergistic effects with GO thereby adding to the tribological properties of as-prepared LaF3−GO nanohybrids. This article reports the fabrication of LaF3−GO nanohybrids and their tribological properties as water-based lubricant additives. Up to date, the present research could be the first one to deal with the preparation of LaF3−GO nanohybrids and their application as water-based lubricant additives

2. EXPERIMENTAL SECTION 2.1. Preparation of GO Nanosheets. Purified natural graphite was used as the starting material to fabricate GO nanosheets by a modified Hummers method.28,29 2.2. Preparation of LaF3−GO Nanohybrids. Ammonium fluoride and lanthanum nitrate were employed as the reactants to synthesize LaF3 nanoparticles. Briefly, 5.56 g of ammonium fluoride was dissolved in the mixed solvent of distilled water (130 mL) and absolute ethanol (20 mL) with a beaker under magnetic stirring. Into the resultant solution was added 200 mg of as-obtained GO nanosheets, followed by 30 min of ultrasonic vibration. As-formed mixed solution was transferred to a 250 mL flask and slowly heated to 70 °C under magnetic stirring, followed by dropwise addition of 50 mL of 0.4 mol/L lanthanum nitrate solution. The reactant system was held at 70 °C for 3 h and finally cooled to ambient temperature. The crude target product was isolated by filtration and repeatedly washed with distilled water and absolute ethanol several times to remove remaining impurities. As-washed crude product was dried at 80 °C in air for 12 h to afford the ready-for-use LaF3− GO nanohybrids target product. 2.3. Apparatus and Experimental Method. X-ray powder diffraction (XRD) patterns were collected with an X’ Pert Pro diffractometer (Cu Kα radiation, λ = 0.15418 nm). Transmission electron microscopy (TEM) pictures were obtained with a JEM-2010 microscope. A confocal microscopic Raman spectrometer (RM-1000, Renishaw; excitation source, 632.8 nm laser) was performed to record the Raman scattering spectra. Fourier transform infrared (FT-IR) spectra of the target products pressed in KBr pellet were measured with an AVATAR360 FT-IR spectrometer. A DSC6200 thermal analyzer was performed for thermogravimetric analysis (TGA) at a scanning rate of 10 °C/min in ambient air flow. An MSR-10A four-ball friction and wear tester was conducted to evaluate the tribological properties of assynthesized LaF3−GO nanohybrids in distilled water. The sliding tests were run at a rotary speed of 1450 rpm (abridged as rev/min) and an ambient temperature of about 25 °C for 30 min. The surface analyses of worn steel surfaces were observed with a scanning electron microscope (SEM; Nova Nano SEM 450) equipped with an energy dispersive spectrometer (EDS) attachment. An AXIS ULTRA multifunctional X-ray photoelectron spectroscope (XPS; Mg Kα radiation; C 1s: 284.8 as reference) was used to further study tribological mechanism.

Figure 1. XRD pattern of the LaF3−GO nanohybrids and GO nanosheets.

prominent XRD peaks of LaF3−GO can be indexed as the hexagonal structure phase of LaF3 (JCPDS No. 32-0483). No obvious signal of GO is detected in LaF3−GO nanohybrids, possibly because the growth of LaF3 crystal between the interlayer of GO destroys the regular layer stacking of GO and shields the diffraction peak of GO while LaF3 possessing good crystallinity provides strong reflections to cover the GO signal in LaF3−GO nanohybrids. Raman scattering was used to document the existence of GO. As shown in Figure 2, the strong peaks at 1350 and 1576 cm−1

Figure 2. Raman spectra of LaF3−GO nanohybrids and GO nanosheets.

are attributed to the D band and G band of GO. This, in combination with the above-mentioned XRD data, proves that GO nanosheets are successfully decorated by LaF3 nanoparticles affording LaF3−GO nanohybrids. Figure 3 shows the TEM images of GO nanosheets and LaF3−GO nanohybrids. GO nanosheets are of high transparency and seem to fold at the edges (Figure 3a), which implies that they are quite thin. Because GO nanosheets have a large specific surface area, they tend to aggregate and form a

3. RESULTS AND DISCUSSION 3.1. Analyses of LaF3−GO Nanohybrids by XRD, Raman, TEM, FT-IR, and TGA. The composition and crystalline phase of the as-prepared samples were analyzed by B


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Figure 3. TEM images of (a) GO and LaF3−GO nanohybrids obtained by the different weight ratio of LaF3 nanoparticles/GO nanosheets: (b) 50:1 (c) 100:1; (d) 10:1.

stacked graphitic structure after the complete evaporation of alcohol. Besides, GO nanosheets are well decorated by LaF3 nanoparticles to afford LaF3−GO nanohybrids (Figure 3b); and the LaF3 nanoparticles, without sign of obvious aggregation, are uniformly distributed on GO nanosheets. Moreover, although LaF3 nanoparticles well cover the surface of the GO nanosheets, they do not influence the morphology of the nanosheets. Naturally, the decoration of LaF3 nanoparticles on GO nanosheets is visibly influenced by the initial mass ratio of inorganic nanoparticles to GO nanosheets. When the mass ratio of LaF3 nanoparticles to GO nanosheets increases from 50:1 to 100:1, more LaF3 nanoparticles are decorated on the GO nanosheets (Figure 3c), and a small amount of LaF3 nanoparticles seems to be slightly aggregated, due to the saturated concentration thereat. When a higher content of GO nanosheets is adopted (corresponding to decreased mass ratio of LaF3 nanoparticles/GO sheets), the LaF3 nanoparticles (average diameter, 20 nm) exhibit a lower loading percentage (Figure 3d), and in this case some free GO nanosheets are found. These observations demonstrate that LaF3 nanoparticles are successfully incorporated onto the surface of GO nanosheets by a simple liquid-phase reaction route, and the coverage density of the LaF3 nanoparticles on the decorated GO nanosheets can be well manipulated by tuning the weight ratio of LaF3 nanoparticles to GO nanosheets during the preparation process. Figure 4 shows the FT-IR spectra of GO nanosheets and LaF3−GO nanohybrids. The prominent absorption band at 3400 cm−1 is assigned to the O−H stretching vibration. The absorption peak of GO nanosheets around 1622 cm−1 is due to the CC stretching vibration, the one at 1395 cm−1 is

Figure 4. Typical FTIR spectra of LaF3−GO nanohybrids and GO nanosheets.

attributed to the tertiary C−OH group, and those at 1261 and 1067 cm−1 are ascribed to the C−O stretching vibrations of −COOH and C−OH groups situated at the edges of the GO nanosheets. Besides, LaF 3−GO nanohybrids retain the stretching vibration bands of the −COOH and C−OH groups at the edges of GO nanosheets, and they exhibit an additional stretching vibration band of a La−F bond around 546 cm−1. These FT-IR data also support the conclusion that LaF3 nanoparticles are decorated on the surface of GO nanosheets via electrostatic interaction thereby affording LaF3−GO nanohybrids. C


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Industrial & Engineering Chemistry Research 3.2. Thermogravimetric Analysis of LaF3−GO Nanohybrids. The TG curves of LaF3 nanoparticles, GO nanosheets, and LaF3−GO nanohybrids are shown in Figure 5. LaF3

Along with extending reaction time, LaF3 nanocrystals grow into LaF3−GO nanohybrids under the driving force of surface energy minimization. 3.3. Tribological Properties of LaF3−GO Nanohybrids As Additives in Distilled Water. Figure 7 shows the wear scar diameters (WSD) and friction coefficients of the steel− steel pair lubricated by distilled water containing different concentrations of LaF3−GO nanohybrids (load, 50 N; speed, 1450 rev/min; time, 30 min; room temperature). The friction coefficient and WSD of the steel−steel sliding pair gradually decrease with the increase LaF3−GO nanohybrids concentration in distilled water, and higher concentrations of LaF3− GO nanohybrids correspond to a larger friction coefficient and WSD. For instance, when 1.5% (mass fraction; the same hereafter) of LaF3−GO nanohybrids is added in water, the best antiwear performance is obtained. Namely, the WSD under the lubrication of water with 1.5% LaF3−GO nanohybrids is reduced by 19% as compared with that under the lubrication of water (from 0.85 mm to 0.69 mm) and it slightly rises with further increase of additive concentration above 1.5%. Meanwhile, the lowest friction coefficient is achieved with distilled water containing 1.5% LaF3−GO nanohybrids. Thus, the optimal concentration of LaF3−GO nanohybrids as an additive in distilled water is suggested as 1.5%. Figure 8 shows the variations in the WSD and friction coefficient with load under the lubrication of distilled water, distilled water containing 1.5% of GO nanosheet, and distilled water containing 1.5% of LaF3−GO nanohybrids (speed, 1450 rev/min; time, 30 min; room temperature). It is seen that LaF3−GO nanohybrids as an additive in distilled water can effectively improve the antiwear ability and load-carrying capacity of distilled water. Namely, the WSD reduces from 0.85 mm under the lubrication of distilled water alone to 0.69 mm under the lubrication of distilled water containing 1.5% of LaF3−GO nanohybrids. The load-carrying capacity of the distilled water containing 1.5% of LaF3−GO nanohybrid is up to 400 N, much higher than that of distilled water (100 N; distilled water undergoes lubrication failure at an applied load of 100 N). Besides, LaF3−GO nanohybrid as a water-based lubricant additive exhibits better tribological properties than GO nanosheets, and it could effectively reduce the friction coefficient and WSD of the steel−steel sliding pair. Moreover, LaF3−GO nanohybrids exhibit excellent friction-reducing ability above 200 N. This could be because LaF3−GO nanohybrids can form a stable suspension in distilled water, and the resultant suspension can be easily transferred onto the contact zone of the rubbing steel surfaces and deposited thereon, thereby forming a protective and lubricious layer consisting of LaF3 nanocores and GO nanosheets to reduce friction coefficient and WSD. 3.4. SEM-EDS and XPS Analyses of Worn Steel Surfaces. Figure 9 shows the SEM images of worn steel

Figure 5. TGA curves of LaF3 nanoparticles, LaF3−GO nanohybrids, and GO nanosheets.

nanoparticles are relatively stable and show a slight weight loss of about 7%, possibly due to vaporization of physically adsorbed water and impurity. The major mass loss of GO (32%) emerges in the range of 100−300 ◦C (corresponding to the decomposition of labile oxygen functional groups), which well conforms to what is reported elsewhere. In the meantime, GO undergoes a mass loss of 6% below 100 °C, due to the removal of adsorbed water; and its slow and steady mass loss (56%) over the range of 400−600 °C is ascribed to the removal of more stable O-containing functional groups. LaF3−GO nanohybrids present a total weight loss of 11% within 25−800 °C, which indicates that incorporating LaF3 nanoparticles on the surface of GO is beneficial to retarding the thermal degradation of GO thereby affording LaF3−GO nanohybrids with improved thermal stability. According to the above-mentioned characterization data and TGA results, the synthetic process of LaF3−GO nanohybrids is schematically shown in Figure 6. On the one hand, GO nanosheets contain a large amount of surface functional groups including carboxyl and hydroxyl. On the other hand, the pH of the ammonium fluoride solution is less than 7, which means there exists a large amount of H+ on the surface of the GO nanosheets. The H+ ions on a GO nanosheet surface can catch and strongly bond with F− ions through electrostatic attraction in NH4F solution, and LaF3 nanocrystals tend to nucleate by way of the chemical reaction between the La3+ cation and the F− anion upon the addition of the lanthanum nitrate solution.

Figure 6. Possible formation process of LaF3−GO nanohybrids. D


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Figure 7. Variations of WSD and friction coefficient with LaF3−GO nanohybrids concentration.

Figure 8. Variations of WSD and friction coefficient with load.

Figure 9. SEM micrographs of worn steel ball surfaces lubricated by distilled water (load, 50 N; speed, 1450 rpm; time, 30 min; room temperature).

Figure 10. SEM micrographs of worn steel ball surfaces lubricated by distilled water containing 1.5% of LaF3−GO nanohybrids (load, 50 N; speed, 1450 rpm; time, 30 min; room temperature).

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Figure 11. EDS spectra of wear scar of the steel bar surface lubricated by distilled water containing 1.5% of LaF3−GO nanohybrids.

Figure 12. XPS spectra of worn steel ball surfaces lubricated by distilled water containing 1.5% LaF3−GO nanohybrids.

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4. CONCLUSIONS A simple liquid-phase reaction route has been established to realize the largescale synthesis of LaF3−GO nanohybrids. Asprepared LaF3−GO nanohybrids as a water-based lubricant additive contain LaF3 nanoparticles with a diameter of about 10−30 nm and can effectively improve the tribological properties of distilled water. During the friction process under the lubrication of distilled water containing LaF3−GO nanohybrids, the deposited film consisting of GO and LaF3 and the tribochemical reaction film consisting of Fe2O3 and FeF3 are formed on the rubbed steel surface to significantly reduce the friction and wear of the steel−steel contact.

surfaces lubricated with distilled water (load, 50 N; speed, 1450 rev/min; time, 30 min; room temperature). Under water lubrication, the worn surfaces of the steel balls show signs of severe scuffing and adhesion in association with deep grooves and rough wear scar, possibly because water causes erosion during the sliding. Under the lubrication of distilled water containing 1.5% of LaF3−GO nanohybrids, the worn steel surface shows hints of mild scuffing and seems to be free of adhesion (Figure 10; load, 50 N; speed, 1450 rev/min; time, 30 min; room temperature). In the meantime, the worn steel surface lubricated with distilled water containing 1.5% of LaF3− GO nanohybrids is smooth and appears to be coated by a protective layer. Figure 11 shows the EDS spectra of the wear scars of the steel balls lubricated by distilled water containing 1.5% of LaF3−GO nanohybrids as the examples (load, 50 N; speed, 1450 rev/min; time, 30 min; room temperature). It is seen that F, C, O, Fe, and La elements are present on the worn steel surface, which indicates that tribochemical reactions take place during the sliding process which generate tribolayers on the rubbing steel surfaces thereby preventing the direct steel−steel contact and reducing the friction and wear. Under contact stress, GO nanosheets decorated with LaF3 nanoparticles can fill up the nanogaps of the rubbing surfaces and prevent direct contact,8 while LaF3 nanoparticles can form a deposited film on the sliding steel surfaces, thereby improving the tribological properties of distilled water. To know more about the tribochemical reactions, we conducted XPS analysis of the worn surfaces of the upper steel ball lubricated by distilled water containing LaF3−GO nanohybrids (load, 200 N, speed, 1450 rev/min; time, 30 min; room temperature; additive concentration, 1.5%. At the end of the sliding tests, the steel balls were ultrasonically washed in ethanol for 15 min). The high-resolution XPS spectra of C 1s, O 1s, Fe 2p, F 1s, and La 3d on the rubbed steel surfaces are shown in Figure 12 as examples. The C 1s peaks at 285.0 and 288.4 eV are assigned to GO and CO on the surface of GO, respectively.30 The weak Fe 2p2/3 peaks emerge at 710.8 and 713.9 eV, and they correspond to Fe2O3 (in association with the O 1s peak at 530 eV) and FeF3 (in combination with the F 1s peak at 687.3 eV), respectively. FeF3 is detected on the worn steel surface, possibly because LaF3 is partly decomposed during the friction process to generate HF that can react with the steel balls. Besides, the La 3d5/2 peak at 835.9 eV, in association with the F 1s peak at 684.1 eV, gives clear evidence that La is present in the La(III) state, that is, LaF3. In combination with the aforementioned EDS results, we can stipulate that metallic La and GO are released from the LaF3− GO nanohybrid to comprise the deposited film and tribochemical reaction film on the sliding surfaces of the steel. Because of the lamellar structure and good dispersibility in water, the LaF3−GO nanohybrid can easily enter the interface of the frictional pair and form a protective and lubricious film, thereby preventing the direct contact between asperities, while the LaF3 nanoparticles released from the LaF3−GO nanohybrids are able to strengthen graphene and can fill up the micropits and grooves on the steel sliding surfaces. Subsequently, the protective and lubricious film composed of GO, FeF3, and LaF3 accounts for the effective reduction in the friction and wear of the steel−steel sliding contact.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 37123881358. Fax: +86 37123881358. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge the financial support provided by National Basic Research Program of China, Grant No. 2015CB654700 (2015CB674703), and National Natural Science Foundation of China, Grant No. 21371050.

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REFERENCES

(1) Xiang, Q. J.; Yu, J. G.; Jaroniec, M. Graphene-based semiconductor photocatalysts. Chem. Soc. Rev. 2012, 41, 782. (2) Castro Neto, A. H.; Guinea, F.; Preres, N. M. R.; Novoselov, K. S.; Geim, A. K. The electronic properties of graphene. Rev. Mod. Phys. 2009, 81, 109. (3) Bai, S.; Shen, X. P. Graphene−inorganic nanocomposites. RSC Adv. 2012, 2, 64. (4) Azizi, M.; Hosseini, M.; Zafarnak, S.; Shanbedi, M.; Amiri, A. Experimental analysis of thermal performance in a two-phase closed thermosiphon using graphene/water nanofluid. Ind. Eng. Chem. Res. 2013, 52, 10015. (5) Li, H. P.; Chen, L.; Zhang, Y.; Ji, X. R.; Chen, S.; Song, H. J.; Li, C. S.; Tang, H. Synthesis of MoSe2/reduced graphene oxide composites with improved tribological properties for oil-based additives. Cryst. Res. Technol. 2014, 49, 204. (6) Mungse, H. P.; Khatri, O. P. Chemically functionalized reduced graphene oxide as a novel material for reduction of friction and wear. J. Phys. Chem. C 2014, 118, 14394. (7) Wang, S. R.; Zhang, Y.; Abidi, N.; Cabrales, L. Wettability and surface free energy of graphene films. Langmuir 2009, 25, 11078. (8) Chen, T. D.; Xia, Y. Q.; Jia, Z. F.; Liu, Z. L.; Zhang, H. B. Synthesis, characterization, and tribological behavior of oleic acid capped graphene oxide. J. Nanomater. 2014, 2014, 1. (9) Singh, V. K.; Elomaa, O.; Johansson, L.; Hannula, S.; Koskinen, J. Lubricating properties of silica/graphene oxide composite powders. Carbon 2014, 79, 227. (10) Eswaraiah, V.; Sankaranarayanan, V.; Ramaprabhu, S. Graphenebased engine oil nanofluids for tribological applications. ACS Appl. Mater. Interfaces 2011, 3, 4221. (11) Liang, H. Y.; Bu, Y. F.; Zhang, J. Y.; Cao, Z. Y.; Liang, A. M. Graphene oxide film as solid lubricant. ACS Appl. Mater. Interfaces 2013, 5, 6369. (12) Lee, C.; Li, Q. Y.; Kalb, W.; Liu, X. Z.; Berger, H.; Carpick, R. W.; Hone, J. Frictional characteristics of atomically thin sheets. Science 2010, 328, 76. (13) Kim, K. S.; Lee, H. J.; Lee, C.; Lee, S. K.; Jang, H.; Ahn, J. H.; Kim, J. H.; HJ, L. Chemical vapor deposition-grown graphene: The thinnest solid lubricant. ACS Nano 2011, 5, 5107. G


Article

Industrial & Engineering Chemistry Research (14) Berman, D.; Erdemir, A.; Sumant, A. V. Few layer graphene to reduce wear and friction on sliding steel surfaces. Carbon 2013, 54, 454. (15) Berman, D.; Erdemir, A.; Sumant, A. V. Graphene: A new emerging lubricant. Mater. Today 2014, 17, 31. (16) Li, P. F.; Zhou, H.; Cheng, X. H. Nano/micro tribological behaviors of a self-assembled graphene oxide nanolayer on Ti/titanium alloy substrates. Appl. Surf. Sci. 2013, 285, 937. (17) Li, P. F.; Zhou, H.; Cheng, X. H. Investigation of a hydrothermal reduced graphene oxide nano coating on Ti substrate and its nano-tribological behavior. Surf. Coat. Technol. 2014, 254, 298. (18) Song, H. J.; Jia, X. H.; Li, N.; Yang, X. F.; Tang, H. Synthesis of α-Fe2O3 nanorod/graphene oxide composites and their tribological properties. J. Mater. Chem. 2012, 22, 895. (19) Bai, G. Y.; Wang, J. Q.; Yang, Z. G.; Wang, H. G.; Wang, Z. F.; Yang, S. R. Preparation of a highly effective lubricating oil additiveceria/graphene composite. RSC Adv. 2014, 4, 47096. (20) Zhang, Y.; Tang, H.; Ji, X. R.; Li, C. S.; Chen, L.; Zhang, D.; Yang, X. F.; Hang, H. T. Synthesis of reduced graphene oxide/Cu nanoparticle composites and their tribological properties. RSC Adv. 2013, 3, 26086. (21) Kinoshita, H.; Nishina, Y.; Alias, A. A.; Fujii, M. Tribological properties of monolayer graphene oxide sheets as water-based lubricant additives. Carbon 2014, 66, 720. (22) Song, H. J.; Li, N. Frictional behavior of oxide graphene nanosheets as water-based lubricant additive. Appl. Phys. A, Mater. 2011, 105, 827. (23) Zhang, Z. F.; Yu, L. G.; Liu, W. M.; Xue, Q. J. The effect of LaF3 nanocluster modified with succinimide on the lubricating performance of fluoro silicone oil for steel-on-steel system. Tribol. Int. 2001, 34, 83. (24) Zhou, J. F.; Wu, Z. S.; Zhang, Z. J.; Liu, W. M.; Dang, H. X. Study on an antiwear and extreme pressure additive of surface coated LaF3 nanoparticles in liquid paraffin. Wear 2001, 249, 333. (25) Hou, X.; He, J.; Yu, L. G.; Li, Z. W.; Zhang, Z. J.; Zhang, P. Y. Preparation and tribological properties of fluorosilane surface-modified lanthanum trifluoride nanoparticles as additive of fluoro silicone oil. Appl. Surf. Sci. 2014, 316, 515. (26) Li, Z. W.; Hou, X.; Yu, L. G.; Zhang, Z. J.; Zhang, P. Y. Preparation of lanthanum trifluoride nanoparticles surface-capped by tributyl phosphate and evaluation of their tribological properties as lubricant additive in liquid paraffin. Appl. Surf. Sci. 2014, 292, 971. (27) Zhang, J.; Zhang, Y. J.; Zhang, S. M.; Yu, L. G.; Zhang, P. Y.; Zhang, Z. J. Preparation of water-soluble lanthanum fluoride nanoparticles and evaluation of their tribological properties. Tribol. Lett. 2013, 52, 305. (28) Hummers, W. S.; Offeman, R. E. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958, 80, 1339. (29) Becerril, H. A.; Mao, J.; Liu, Z.; Stoltenberg, R. M.; Bao, Z.; Chen, Y. Evaluation of solution-processed reduced graphene oxide films as transparent conductors. ACS Nano 2008, 2, 463. (30) Jiang, S. D.; Bai, Z. M.; Tang, G.; Hu, Y.; Song, L. Synthesis of ZnS decorated graphene sheets for reducing fire hazards of epoxy composites. Ind. Eng. Chem. Res. 2014, 53, 6708.

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