Next Article in Journal
Dynamometer Testing of Energy Efficient Hydraulic Fluids and Fuel Savings Analysis for US Army Construction and Material Handling Equipment
Next Article in Special Issue
Comparative Study of Tribological Properties of Modified and Non-modified Graphene-Oil Nanofluids under Heated and Non-heated Conditions
Previous Article in Journal
Activated Carbon Nano-Particles from Recycled Polymers Waste as a Novel Nano-Additive to Grease Lubrication
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Lubricants
Volume 10
Issue 9
10.3390/lubricants10090215
lubricants-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Graphene-Family Lubricant Additives: Recent Developments and Future Perspectives

by
Yanfei Liu
1,2,
Shengtao Yu
1,
Qiuyu Shi
3,
Xiangyu Ge
1,* and
Wenzhong Wang
1
1
School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China
2
State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, Beijing 100084, China
3
State Grid Smart Grid Research Institute Co., Ltd., Beijing 102209, China
*
Author to whom correspondence should be addressed.
Lubricants 2022, 10(9), 215; https://doi.org/10.3390/lubricants10090215
Submission received: 1 August 2022 / Revised: 21 August 2022 / Accepted: 31 August 2022 / Published: 6 September 2022
(This article belongs to the Special Issue Tribology of 2D Nanomaterials)
Browse Figures
Versions Notes

Abstract

:
Graphene-family materials have been investigated by researchers as promising additives for various lubrication systems due to their unique physical-chemical properties. It has been proven that graphene-family materials can lead to enhanced lubrication and wear-resistance performance, which have potential to reduce the energy losses and carbon emissions, and the wear of machines for industrial applications. Experimental, theoretical, and simulation studies have been performed to investigate the tribological behaviors of graphene-family materials as additives. The tribological properties of graphene-family materials, including graphene, reduced graphene oxide, functionalized graphene, and the combination of graphene-family materials and other materials as additives, and the fundamental mechanism are systematically reviewed and concluded. The authors also discuss the potential engineering applications of graphene-family materials as lubricating additives, and the unsolved issues and optimistic outlooks in the near future.

Graphical Abstract

1. Introduction

The friction and wear of machine parts usually cause huge carbon emissions and economic losses, restricting the sustainable development of human society [1]. Under such a background, advanced lubrication techniques have been proposed by researchers to reduce energy dissipation and enhance durability [2,3,4,5,6,7,8,9,10]. Additives are usually added to lubricants to enhance the lubrication performance, viscosity under high temperature, antioxidation, wear-reduction properties, and so on. Among all the lubricant additives, carbon nanomaterials have attracted a lot of attention due to the low cost, eco-friendliness, and significant improvement in lubrication and anti-wear performances [11,12,13].
Graphene, as an atomically thin carbon material, exhibits extremely high mechanical strength, high thermal and electronic conductivities, and other unique properties, which make it highly attractive for numerous applications [14,15]. Graphene also exhibits excellent tribological performance. Even single-layer graphene can lead to a significant reduction in coefficient of friction (COF) and wear between friction pairs [16,17]. At the nanoscale or microscale, superlubricity (COF < 0.01) can be achieved between graphene layers with incommensurate contact [18,19,20,21]. Although graphene shows great potential for various applications, it should also be noticed that graphene has some inherent properties including zero bandgaps and chemical inertness, restricting the application of graphene. That is one of the reasons for researchers investigating the functionalization of graphene through the reaction with inorganic or organic molecules, chemical modification of the surface of graphene, and the noncovalent interaction with graphene [22,23,24,25,26,27]. Functionalized graphene (Figure 1) also exhibits different dispersion properties and tribological behaviors [28,29,30]. The excellent tribological behaviors and the feasible functional design of graphene-family materials make them promising additives for different lubrication systems. Within this work, the authors aim to review the recent achievements that have been realized with graphene-family materials as lubricating additives; and the functional mechanisms are also discussed in detail. Moreover, the unsolved issues and the optimistic outlooks for the graphene-family materials as additives are also discussed.

2. Tribological Behaviors of Graphene-Family Additives

Graphene-family materials have great potential as lubrication additives due to the atomic thin structure and high strength of graphene. Researchers have developed various lubricants containing graphene-family materials as additives, proving that graphene-family materials can effectively enhance lubrication and wear-resistance performances. However, different from the studies using graphene-family materials as solid lubricants, the detailed functional mechanisms of graphene-family materials as additives have not been elucidated due to the complexity of liquid-based lubricants. Hence, systematic studies are important for a better understanding of the tribological behaviors and the functional mechanisms of graphene-family materials as lubrication additives.

2.1. Pristine Graphene and Reduced Graphene Oxide (rGO)

Oil-based lubricants, including non-synthetic lubricating oils, synthetic lubricating oils, grease, and most recently, bio-based lubricating oil, are widely used as lubricants in both the market and the scientific research field. Typically, additives are needed for oil-based lubricants to improve the rheological, lubrication, anti-wear, and antioxidation behaviors. Different from traditional additives, nanomaterials have been used as additives due to the environmentally friendly, easy-processing properties and significantly improved lubrication and anti-wear performances [33]. Recently, graphene-family materials have attracted much attention from researchers as lubrication additives; and the performances of graphene-family materials as additives have been widely investigated. Among all the graphene-family materials, pristine graphene and reduced graphene oxide are ideal model materials for the understanding of the unique properties of graphene-family materials as lubrication additives. Eswaraiah et al. [34] prepared ultra-thin graphene through the exfoliation of graphite oxide. Different from the graphite oxide as starting material, the as-prepared ultra-thin graphene has a low concentration of oxide. Ultra-thin graphene nanoflakes were added to engine oil to prepare nanofluids with graphene concentration of 0.0125–0.0625 mg/mL (Figure 2a). It was found that the optimized graphene concentration of nanofluids is 0.0250 mg/mL, which can significantly reduce the COF by 80% (Figure 2b) and wear scar diameter of friction pairs. The performance of graphene as additive was attributed to the nano-bearing effect of graphene and the ultrahigh mechanical strength of graphene. It was found that the concentration of graphene as an additive has an important influence on tribological behaviors. Guo et al. [35] prepared PAO2 oil with graphene concentration from 0.05–0.5 wt%, finding that the lowest COF can be achieved with the lowest graphene concentration of 0.05 wt%. Cai et al. [36] found that even a low graphene concentration of 0.01 wt% can effectively reduce the COF by 78% and wear rate by 90% with textured bronze plates as friction pairs. The function mechanism of graphene nanoflakes was attributed to the nano-bearing effect and the formation of protective film on the friction pairs. Sanes et al. [37] investigated the influence of graphene nanoflakes and the ionic liquid (1-octyl-3-methylimidazolium tetrafluoroborate) as additives on the tribological behaviors of additive-free isoparaffinic base oil and formulated motor oil. It was found that the addition of 0.005 wt% of graphene nanoflakes can lead to a 70% reduction of COF of motor oil at the temperature of 150 °C, while for the additive-free base oil, ionic liquid dispersed with graphene nanoflakes can significantly reduce the friction and wear at room temperature. It has also been found the tribological behaviors of PAO6 [38,39,40], hydraulic oil [41], 4010 AL base oil [42], vegetable oil [43], cashew nut shells liquid [44], wax extracted from Codonopsis pilosula [45], or lithium complex and polypropylene-thickened greases [46] can be also improved with graphene as additives. However, there is still room for the improvement of graphene as a lubrication additive. The structure of the sliding interface has significant influence on the lubrication performance of graphene or other 2D materials as solid lubricants, which has been widely investigated at the nanoscale [47,48,49] or macroscale [5,50,51]. For graphene as an additive, Jin et al. [52] regulated the structure of graphene through ball-milling treatment, suppressing the commonly observed wrinkles and curved edge-site (Figure 3). With the ultra-flat graphene as additive, the COF and wear depth can be reduced by 49% and 93% at high contact pressure of 2.5 GPa, respectively.

2.2. Functionalized Graphene

Pristine graphene or reduced graphene oxide exhibits excellent tribological behaviors as additives in the oil-based lubricant. However, those graphene-family materials are hard to be dispersed in water-based lubricants, restricting their application. In addition, the frictional and wear-resistant behaviors of graphene-family materials can be also regulated by functionalization. Hence, researchers have focused on the functionalization of graphene-family materials; and the tribological behaviors of functionalized graphene have also been systematically investigated. Wang et al. found that GO as an additive can effectively enhance the lubrication and wear-resistance performance of hexadecane-based oil [53]. Zhao et al. [38] compared the tribological behaviors of rGO and GO as additives in PAO6. It was found that PAO6 with GO exhibited much larger and unstable COF compared to that with rGO, which was attributed to the hindered interlayer sliding between lattice layers by oxygen-containing groups. For the achievement of better tribological behaviors, Fan et al. [54] prepared fluorinated graphene through direct fluorination with F2. Fluorinated graphene with different concentrations of F was added into liquid paraffin oil as additives. It was found that fluorination with C/F ratio of 1.0 can reduce friction and wear by 50.4% and 90.9%, respectively. The formation of tough tribofilm was believed the dominant mechanism for the friction and wear reduction properties. Paul et al. [55] prepared dodecylamine functionalized graphene nanosheets as an additive, which can reduce the COF by up to 40% compared to the base engine oil. Li et al. [56] prepared graphene oxide grafted with titanate coupling agent (T-GO) as an additive to hydraulic oil. With 0.08 wt% of T-GO, the COF and wear can be reduced by up to 50% and 20%, and better extreme pressure performance compared to the original hydraulic oil. Fu et al. [57] prepared ionic liquid-modified graphene. The excellent tribological behaviors of the ionic liquid-modified graphene as an additive can be attributed to the adsorption of modified graphene and tribochemical reaction of contact surfaces. The alkylated graphene [58] and graphene oxide [59,60], phosphonium-organophosphate-modified graphene [61], CuAAC-modified graphene oxide [62], 3,5-ditert-butyl-4-hydroxybenzaldehyde-grafted graphene [63], octadecylamine- and dicyclohexylcarbodiimide-modified GO [64], octadecylamine-functionalized rGO [65], rGO doped with N and B species and polyisobutylene succinimide-grafted graphene [66] also exhibit excellent dispersibility and tribological behaviors as additives of oil-based lubricants.
Despite oil-based lubricants, functionalized graphene has been widely used as an additive to water-based lubricants due to its better dispersibility and stability [67,68,69,70,71]. Kinoshita et al. [72] found that with GO as an additive in pure water, the COF between tungsten carbide ball and stainless steel plate can be significantly reduced from around 0.4 to 0.05; and the wear of friction pairs can be also significantly suppressed. Adsorbed GO was found on the surface of friction pairs, which was believed to act as a protective coating for the lubrication and wear-resistance properties. He et al. [73] investigated the influence of pH value on the tribological behaviors of GO as an additive to water. It was found that the GO sheets can be broken down and chemically reduced under high pH value, leading to a higher COF. Wei et al. found that better lubrication behavior can be achieved with graphene oxide/polysaccharide copolymer nanohybrids [74]. With the nanohybrid as an additive in pure water, the COF can be reduced by 40% and 84% compared with pristine GO and individual copolymer as additives, respectively. Researchers have also designed various functionalized graphene to further enhance tribological behaviors. Fan et al. [75] prepared ionic liquids modified graphene oxide as an additive of multialkylated cyclopentanes, finding that the ionic liquids-modified GO can lead to a reduction of COF and wear by 27% and 74%, respectively. GO modified by imidazolyl dinitrile amine also exhibited improved tribological performance [76]. Liu et al. [77] prepared graphene grafted with polyethyleneimine and polyacrylic acid, which improves the multiple adsorption effects of graphene on the counterparts’ surfaces, leading to the formation of tough and stable tribofilms. Researchers found that fluorinated graphene exhibits better tribological performance compared to pristine graphene at the macroscale [54,78], but the hydrophobic nature of fluorinated graphene makes it difficult to be used as an additive for water-based lubrication systems. Targeting this problem, Ye et al. [79] developed hydrophilic urea-modified fluorinated graphene. Using urea-modified fluorinated graphene as an additive to water with a concentration of 1 mg/mL, wear can be reduced by 64.4% compared to that lubricated by pure water. Min et al. [80] prepared fluorinated graphene oxide using hydrothermal reaction, obtaining excellent dispersibility in water and tremendous abrasion resistance performance. Fan et al. [81] prepared fluorinated graphene with relatively low F content under mild temperature conditions. The as-prepared fluorinated graphene oxide as an additive of water led to a 47% and 31% lower wear rate compared to that with the lubrication of pure water and water suspension of GO, respectively. Later, urea-modified fluorinated graphene oxide was also prepared as the additive for water lubrication [82].
With traditional lubricants, the COFs are usually in the range of 0.02–0.1 [81,83,84,85,86]. Under the background of energy saving and emission reduction, the concept of superlubricity (COF < 0.01) has attracted a lot of attention [1,87,88]. Ge et al. [89] found that macroscale superlubricity can be achieved by ethylene glycol water solution containing GO as an additive. The achievement of superlubricity was attributed to the synergy between hydrodynamic effect and boundary lubrication provided by GO tribofilm. Even better lubrication and wear-reduction performances were achieved with the combination of GO nanosheets and an ionic liquid as additives [90] (Figure 4). Superlubricity can be also achieved by GO and lithium salts as an additive for dihydric alcohol aqueous solutions [91]. The adsorbed GO and tribochemical reaction are both important for the achievement of superlubricity. The functional groups have a potential influence on the superlubricity behaviors with graphene-family as additives. Recently, GO-OH, GO–COOH, and GO–NH2 were added to dihydric alcohols as additives [92]. It was found that robust superlubricity can be achieved using GO–NH2 as an additive, which was believed attributed to the formation of the adsorption layer due to the high adhesion between GO–NH2 and SiO2 substrate. The achievement of superlubricity usually needs a running-in process with high COF and severe wear. Recently, Liu et al. [93] used GO quantum dots as nano-additive of ethylene glycol water solution. A superlubricity state with COF of 0.0068 can be achieved with an extremely short running-in process of 6 s. The tribofilms with adsorbed GOQDs were believed to be critical for the reduced running-in process, and the achievement of a superlubricity state at relatively high contact pressure, which was confirmed by the in-situ friction tests and surface characterization results. Graphene-family as additives can provide lubrication and wear-resistance performance. Superlubricity with high contact pressure and the extremely short running-in process can be achieved with water-based lubricants with graphene-family materials as additives. However, the choice of graphene-family materials for water-based superlubricity systems is largely restricted by dispersibility and stability. GO is commonly used for water-based lubrication systems, but the interlayer shearing strength of GO is higher than the pristine graphene and other functionalized graphene such as fluorinated graphene [94,95]; and the interlayer sliding can be further influenced by the adsorbed water molecules, leading to higher COF in the environments with the presence of water molecules [96,97]. Targeting the above-mentioned problems, Liu et al. [98] proposed a novel strategy to achieve superlubricity with water-based lubricant and hydrophobic graphene, where the coatings with different graphene-family coatings were firstly deposited on the SiO2 substrate and the glycerol aqueous solution was then added on the coatings for lubrication. The performances of pristine graphene, GO, and fluorinated graphene was compared. All the deposited graphene coatings led to lower COF and wear of friction pairs. Among the graphene-family materials, pristine graphene coating exhibited the best lubrication performance at a sliding speed of 0.1 m/s, where macroscale superlubricity with COF of 0.004 can be achieved. The superlubricity behavior can be attributed to the hydrodynamic effect and the boundary lubrication provided by the tribofilm containing graphene nanoflakes (Figure 5). Combining graphene-family materials as additives and lubrication coatings is also a strategy to realize superlubricity. An extremely small COF of 0.002 was achieved on silicon-doped hydrogenated amorphous carbon film with the lubrication of ethylene glycol containing GO as an additive [99].

2.3. Synergy between Graphene-Family and Other Nanomaterials

Researchers also combined graphene-family materials and other nanomaterials including other kinks of 2D materials, carbon nanomaterials, metal or metal oxide nanoparticles, and silica nanoparticles as additives for further improved tribological behaviors. Xu et al. [100] investigated the synergetic effect between graphene and MoS2 as additives for esterified bio-oil. The tribological behaviors of the bio-oil added with 0.5 wt% graphene, 0.5 wt% MoS2, and 0.3 wt% graphene, and 0.2 wt% MoS2 were compared, finding that the nanofluid with 0.3 wt% graphene and 0.2 wt% MoS2 exhibited lower COF and wear rate comparing to other samples. The formation of tribofilm is critical for enhanced tribological behaviors. With the combination of graphene and MoS2 nanoflakes, it was found that the oxidation and degradation of MoS2 can be suppressed by graphene nanoflakes, and the structure of graphene and MoS2 can be better maintained through the synergetic effect (Figure 6). Farsadi et al. [101] added functionalized GO and MoS2 into petroleum-based oil as an additive, achieving improved tribological performances. MoS2 can be also directly synthesized on graphene or GO through calcination [102] and hydrothermal reaction [103,104,105]. The obtained composited nanomaterials can effectively enhance the lubrication and wear resistance performance of polyalkylene glycol [102,104] and based oil [103,105]. The intrinsic incommensurate between graphene and MoS2 was believed to be one of the reasons for the enhanced lubrication performance [105]. Graphene-family materials were also mixed with h-BN [106], or grafted with APTMS-modified h-BN to improve the tribological properties as additives [107].
The synergetic lubrication performance between graphene-family materials and nanoparticle or nanotubes was also investigated. A lubricant with GO and nanodiamonds as additives in pure water was developed by Wu et al. [108] to improve tribological performance. The low friction of approximately 0.03 can be obtained with 0.1 wt.% and 0.5 wt.% for GO and ND, respectively. Nanostructured tribofilm was found on the surface of friction pairs (Figure 7). The low shearing strength between graphene layers and the possible nano-bearing effect of ND was believed to be the mechanism for the remarkable lubrication performance. In addition ND, functionalized carbon spheres were also used combined with graphene, which led to an 18% reduction of COF compared to the CASTROL-20 W 40 engine oil [109]. Graphene-family materials have been combined with WS2 [110], onion-like carbon [111], metal [112,113,114,115,116,117,118,119,120] or metal oxide [121,122,123,124,125,126,127,128,129] nanoparticles, silica nanoparticles [130,131,132,133,134,135], or carbon nanotubes [136,137,138] as additives for oil-based or water-based lubricants to provide better lubrication and wear-resistance performance.

2.4. Lubrication Mechanisms of Graphene-Family Materials as Additives

The friction behavior with graphene-family materials as additives is a complex physical-chemical process, especially at the macroscale, leading to different tribological behaviors reported in the literature (Table 1). Various lubrication mechanisms have been proposed.
For the graphene-family additives, well-accepted lubrication and wear-resistance mechanism is the formation of graphene-containing tribofilm, which has been observed in both oil-based [38,39,40,41,42,43] and water-based lubrication systems [72,89]. However, the investigation of the formation and function of adsorbed graphene-family during friction is still at an early stage. There are still many opening questions to be solved. It was proven that the graphene-containing tribofilms can effectively reduce friction and wear, but the studies related to the formation of graphene-containing tribofilms are still insufficient. Ge et al. [92] found that the GO-NH2 exhibited better lubrication performance compared to GO with -OH and -COOH groups, which was attributed to the better robustness of GO-NH2 tribofilm arising from the larger adhesive force between functional groups of GO-NH2 and contact surfaces. In addition to the adhesion force, tribochemical reactions between graphene-family materials also have potential influence on the tribofilm formation, thus the tribological behaviors. For fluorinated graphene, the formation of metal-F bonds during friction is believed to be an important mechanism for the formation of robust tribofilm and better macroscale lubrication performance [28]. In addition to the functional groups, it was found that the size of graphene-family materials also influences the formation of tribofilm and the lubrication behavior. Li et al. [148] investigated the influence of flake size and concentration of graphene as additive of linear alpha olefin on the lubrication behaviors using molecular dynamics simulation. It was found that when the size of graphene flakes is larger than 40 carbon atoms, the graphene flakes can be anchored on the surface of friction pairs to form a protective tribofilm, leading to a passivated and smoothened sliding interface and ultralow COF (Figure 8).
In addition to the formation of graphene-containing tribofilm, understanding how the graphene-containing tribofilms perform lubrication performance is also important. With the protection of graphene-containing tribofilm, the direct contact between asperities under boundary or mixed lubrication conditions can be prevented by the tribofilms, providing a low shear strength, and thus enhancing lubrication and wear-resistance performance. In addition, the wear interaction between graphene-containing tribofilm and lubricant molecules is also believed to be an important mechanism for the lubrication performance of graphene-family additives. A new strategy was proposed by Li et al. [149] to investigate the interaction between water molecules and graphene surfaces. A highly hydrophobic surface of self-assembled fluoroalkyl monolayers was prepared on the SiO2 tip for the friction tests conducted using AFM. A superlubricity state with an extremely low COF of 0.0003 was obtained between the modified SiO2 tip and graphene surface in a water environment, where the weak interaction between graphene surface and water molecules contributed to the achievement of superlubricity (Figure 9). The influence of weak interaction between graphene and liquid molecules on the lubrication performance was also verified by molecular dynamics simulations. It was found that the graphene tribofilm can promote the mobility of water molecules [150] or oil molecules [151,152], leading to a lower COF. In addition to those mechanisms, the nano-ball bearing [153], self-repairing [154], the micro-polishing effect [155], tribochemical reaction [57], and the incommensurate contact between graphene-family materials and other nanomaterials were also proposed as lubrication mechanisms for the graphene-family materials as additives.

2.5. Engineering Applications of Graphene-Family Materials as Additives

With decades of development, researchers have also focused on the commercialization and engineering applications of graphene-family materials [156,157]. The function of graphene-family materials as lubrication additives for engineering applications was also investigated. Rasheed et al. [158] investigated the heat transfer and tribological performance of engine oil with graphene as nano-additive using an internal combustion engine. It was found that with 0.01 wt.% of graphene, COF can be reduced by 21%, and the thermal conductivity of lubricant can be enhanced by 23%. In addition, heat transfer rate of the engine can be also enhanced by 70%. The wear of engine can be also suppressed with graphene nanoflakes as additives. The potential applications of graphene-family additives for machining process were also investigated. Baldin et al. [159] studied the effect of graphene addition in cutting fluids applied by minimum quantity lubrication (MQL) for end milling of AISI 1045 steel. It was found that the addition of graphene nanoflakes can enhance the lubrication performance of cutting fluids. For some cutting fluid, the addition of graphene nanoflakes leads to increased tool life, while for some cutting fluid, the addition of graphene nanoflakes can leads to reduced tool life. Li et al. [160] investigated the performance of vegetable oil-based cutting fluid dispersed with graphene nanoparticles for the MQL milling of Ti6Al4V. It was found that the graphene additive could enhance the cooling and lubrication performances of the oil film formed at the milling zone, leading to reduced milling temperature, milling force, tool wear, and enhanced tool life. The influence of graphene-family additive for drilling [161] and hard-turning [162] was also investigated, finding that graphene-family materials as additives could provide excellent lubrication, and improved surface roughness. Graphene-family additives have also been added into drilling fluid for the petroleum industry [157] to enhance the fluid loss control, rheology properties, and lubrication and wear-resistance performances. Those studies indicate that graphene-family materials are promising for various industrial applications.

3. Conclusions and Perspectives

Graphene-family materials have been investigated by researchers as promising additives for various lubrication systems due to the unique physical-chemical properties. It has been proven that graphene-family materials can lead to enhanced lubrication and wear-resistance performance. Experimental, theoretical, and simulation studies have been performed to investigate the tribological behaviors of graphene-family materials as additives, and various function mechanisms have been proposed. Over the years, many breakthroughs have been achieved, but there are still problems for both scientific research and engineering applications.
  • For graphene-family additives, dispersion stability is an important issue related to the instability in oil or water-based lubrication systems. However, the high temperature introduced wear debris, and the material degradation all have potential influence on the long-term stability of graphene-family additives, which still need further investigation.
  • The cost of graphene-family materials is still high for industrial applications. Developing a large-scale, low-cost preparation process is important for the practical application of graphene-family materials as additives.
  • There is still a lack of widely accepted criteria for the designing of graphene-family materials as additives. For example, the optimized parameters such as particle size, layer numbers, types, and concentration of functional groups for specified application condition are still unclear. An in-depth investigation of the fundamental mechanisms and advanced techniques [163,164,165] for the guidance of designing and application of graphene-family materials as additives is needed in the future.

Author Contributions

Writing—original draft preparation, Y.L.; funding acquisition, Y.L.; writing—review and editing, Y.L., S.Y., Q.S., X.G. and W.W. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the National Natural Science Foundation of China (grant number 52005287), Beijing Institute of Technology Research Fund Program for Young Scholars, Tribology Science Fund of State Key Laboratory of Tribology in Advanced Equipment (SKLT) (No. SKLTKF21B14), and the Fund of the Key Laboratory of Advanced Materials of the Ministry of Education (No. ADV21-4).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Luo, J.; Liu, M.; Ma, L. Origin of friction and the new frictionless technology—Superlubricity: Advancements and future outlook. Nano Energy 2021, 86, 106092. [Google Scholar] [CrossRef]
  2. Li, J.; Zhang, C.; Luo, J. Superlubricity Behavior with Phosphoric Acid–Water Network Induced by Rubbing. Langmuir 2011, 27, 9413–9417. [Google Scholar] [CrossRef] [PubMed]
  3. Liu, Y.-F.; Liskiewicz, T.; Yerokhin, A.; Korenyi-Both, A.; Zabinski, J.; Lin, M.; Matthews, A.; Voevodin, A.A. Fretting wear behavior of duplex PEO/chameleon coating on Al alloy. Surf. Coat. Technol. 2018, 352, 238–246. [Google Scholar] [CrossRef]
  4. Chen, X.; Zhang, C.; Kato, T.; Yang, X.-A.; Wu, S.; Wang, R.; Nosaka, M.; Luo, J. Evolution of tribo-induced interfacial nanostructures governing superlubricity in a-C:H and a-C:H:Si films. Nat. Commun. 2017, 8, 1675. [Google Scholar] [CrossRef]
  5. Liu, Y.; Li, J.; Yi, S.; Ge, X.; Chen, X.; Luo, J. Enhancement of friction performance of nanocomposite fluorinated graphene and molybdenum disulfide coating by microdimple array. Carbon 2020, 167, 122–131. [Google Scholar] [CrossRef]
  6. Berman, D.; Deshmukh, S.A.; Sankaranarayanan, S.K.R.S.; Erdemir, A.; Sumant, A.V. Macroscale superlubricity enabled by graphene nanoscroll formation. Science 2015, 348, 1118–1122. [Google Scholar] [CrossRef]
  7. Liu, Y.; Yu, S.; Wang, W. Nanodiamond plates as macroscale solid lubricant: A “non-layered” two-dimension material. Carbon 2022, 198, 119–131. [Google Scholar] [CrossRef]
  8. Liu, Y.; Li, J.; Li, J.; Yi, S.; Ge, X.; Zhang, X.; Luo, J. Shear-Induced Interfacial Structural Conversion Triggers Macroscale Superlubricity: From Black Phosphorus Nanoflakes to Phosphorus Oxide. ACS Appl. Mater. Interfaces 2021, 13, 31947–31956. [Google Scholar] [CrossRef]
  9. Xie, Z.; Jiao, J.; Yang, K.; He, T.; Chen, R.; Zhu, W. Experimental and numerical exploration on the nonlinear dynamic behaviors of a novel bearing lubricated by low viscosity lubricant. Mech. Syst. Signal Process. 2023, 182, 109349. [Google Scholar] [CrossRef]
  10. Xie, Z.; Zhu, W. Theoretical and experimental exploration on the micro asperity contact load ratios and lubrication regimes transition for water-lubricated stern tube bearing. Tribol. Int. 2021, 164, 107105. [Google Scholar] [CrossRef]
  11. Xue, S.; Li, H.; Guo, Y.; Zhang, B.; Li, J.; Zeng, X. Water lubrication of graphene oxide-based materials. Friction 2022, 10, 977–1004. [Google Scholar] [CrossRef]
  12. Kumar, V.B.; Sahu, A.K.; Rao, K.B. Development of Doped Carbon Quantum Dot-Based Nanomaterials for Lubricant Additive Applications. Lubricants 2022, 10, 144. [Google Scholar] [CrossRef]
  13. Bai, Y.; Yu, Q.; Zhang, J.; Cai, M.; Liang, Y.; Zhou, F.; Liu, W. Soft-nanocomposite lubricants of supramolecular gel with carbon nanotubes. J. Mater. Chem. A 2019, 7, 7654–7663. [Google Scholar] [CrossRef]
  14. Novoselov, K.S.; Fal’ko, V.I.; Colombo, L.; Gellert, P.R.; Schwab, M.G.; Kim, K. A roadmap for graphene. Nature 2012, 490, 192–200. [Google Scholar] [CrossRef] [PubMed]
  15. Liu, Y.; Ge, X.; Li, J. Graphene lubrication. Appl. Mater. Today 2020, 20, 100662. [Google Scholar] [CrossRef]
  16. Berman, D.; Deshmukh, S.A.; Sankaranarayanan, S.K.R.S.; Erdemir, A.; Sumant, A.V. Extraordinary Macroscale Wear Resistance of One Atom Thick Graphene Layer. Adv. Funct. Mater. 2014, 24, 6640–6646. [Google Scholar] [CrossRef]
  17. Kim, K.-S.; Lee, H.-J.; Lee, C.; Lee, S.-K.; Jang, H.; Ahn, J.-H.; Kim, J.-H.; Lee, H.-J. Chemical Vapor Deposition-Grown Graphene: The Thinnest Solid Lubricant. ACS Nano 2011, 5, 5107–5114. [Google Scholar] [CrossRef]
  18. Zheng, X.; Gao, L.; Yao, Q.; Li, Q.; Zhang, M.; Xie, X.; Qiao, S.; Wang, G.; Ma, T.; Di, Z.; et al. Robust ultra-low-friction state of graphene via moiré superlattice confinement. Nat. Commun. 2016, 7, 13204. [Google Scholar] [CrossRef]
  19. Feng, X.; Kwon, S.; Park, J.Y.; Salmeron, M. Superlubric Sliding of Graphene Nanoflakes on Graphene. ACS Nano 2013, 7, 1718–1724. [Google Scholar] [CrossRef] [PubMed]
  20. Li, J.; Gao, T.; Luo, J. Superlubricity of Graphite Induced by Multiple Transferred Graphene Nanoflakes. Adv. Sci. 2018, 5, 1700616. [Google Scholar] [CrossRef] [Green Version]
  21. Li, J.; Li, J.; Luo, J. Superlubricity of Graphite Sliding against Graphene Nanoflake under Ultrahigh Contact Pressure. Adv. Sci. 2018, 5, 1800810. [Google Scholar] [CrossRef] [PubMed]
  22. Ohta, T.; Bostwick, A.; Seyller, T.; Horn, K.; Rotenberg, E. Controlling the Electronic Structure of Bilayer Graphene. Science 2006, 313, 951–954. [Google Scholar] [CrossRef] [PubMed]
  23. Elias, D.C.; Nair, R.R.; Mohiuddin, T.M.G.; Morozov, S.V.; Blake, P.; Halsall, M.P.; Ferrari, A.C.; Boukhvalov, D.W.; Katsnelson, M.I.; Geim, A.K.; et al. Control of Graphene’s Properties by Reversible Hydrogenation: Evidence for Graphane. Science 2009, 323, 610–613. [Google Scholar] [CrossRef] [PubMed]
  24. Wang, Q.H.; Hersam, M.C. Room-temperature molecular-resolution characterization of self-assembled organic monolayers on epitaxial graphene. Nat. Chem. 2009, 1, 206–211. [Google Scholar] [CrossRef]
  25. Bostwick, A.; Ohta, T.; Seyller, T.; Horn, K.; Rotenberg, E. Quasiparticle dynamics in graphene. Nat. Phys. 2007, 3, 36–40. [Google Scholar] [CrossRef]
  26. Bai, H.; Xu, Y.; Zhao, L.; Li, C.; Shi, G. Non-covalent functionalization of graphene sheets by sulfonated polyaniline. Chem. Comm. 2009, 13, 1667–1669. [Google Scholar] [CrossRef]
  27. Georgakilas, V.; Otyepka, M.; Bourlinos, A.B.; Chandra, V.; Kim, N.; Kemp, K.C.; Hobza, P.; Zboril, R.; Kim, K.S. Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications. Chem. Rev. 2012, 112, 6156–6214. [Google Scholar] [CrossRef]
  28. Liu, Y.; Li, J.; Chen, X.; Luo, J. Fluorinated Graphene: A Promising Macroscale Solid Lubricant Under Various Environments. ACS Appl. Mater. Interfaces 2019, 11, 40470–40480. [Google Scholar] [CrossRef]
  29. Liu, Y.; Chen, X.; Li, J.; Luo, J. Enhancement of friction performance enabled by synergetic effect between graphene oxide and molybdenum disulfide. Carbon 2019, 154, 266–276. [Google Scholar] [CrossRef]
  30. Wang, M.; Zhou, M.; Li, X.; Luo, C.; You, S.; Chen, X.; Mo, Y.; Zhu, H. Research progress of surface-modified graphene-based materials for tribological applications. Mater. Res. Express 2021, 8, 042002. [Google Scholar] [CrossRef]
  31. Pei, S.; Wei, Q.; Huang, K.; Cheng, H.-M.; Ren, W. Green synthesis of graphene oxide by seconds timescale water electrolytic oxidation. Nat. Commun. 2018, 9, 145. [Google Scholar] [CrossRef] [PubMed]
  32. Robinson, J.T.; Burgess, J.S.; Junkermeier, C.E.; Badescu, S.C.; Reinecke, T.L.; Perkins, F.K.; Zalalutdniov, M.K.; Baldwin, J.W.; Culbertson, J.C.; Sheehan, P.E.; et al. Properties of Fluorinated Graphene Films. Nano Lett. 2010, 10, 3001–3005. [Google Scholar] [CrossRef]
  33. Esquivel-Gaon, M.; Nguyen, N.H.A.; Sgroi, M.F.; Pullini, D.; Gili, F.; Mangherini, D.; Pruna, A.I.; Rosicka, P.; Sevcu, A.; Castagnola, V. In vitro and environmental toxicity of reduced graphene oxide as an additive in automotive lubricants. Nanoscale 2018, 10, 6539–6548. [Google Scholar] [CrossRef]
  34. Eswaraiah, V.; Sankaranarayanan, V.; Ramaprabhu, S. Graphene-Based Engine Oil Nanofluids for Tribological Applications. ACS Appl. Mater. Interfaces 2011, 3, 4221–4227. [Google Scholar] [CrossRef] [PubMed]
  35. Guo, Y.-B.; Zhang, S.-W. The Tribological Properties of Multi-Layered Graphene as Additives of PAO2 Oil in Steel–Steel Contacts. Lubricants 2016, 4, 30. [Google Scholar] [CrossRef]
  36. Cai, Z.B.; Zhao, L.; Zhang, X.; Yue, W.; Zhu, M.H. Combined Effect of Textured Patterns and Graphene Flake Additives on Tribological Behavior under Boundary Lubrication. PLoS ONE 2016, 11, e0152143. [Google Scholar] [CrossRef] [PubMed]
  37. Sanes, J.; Avilés, M.-D.; Saurín, N.; Espinosa, T.; Carrión, F.-J.; Bermúdez, M.-D. Synergy between graphene and ionic liquid lubricant additives. Tribol. Int. 2017, 116, 371–382. [Google Scholar] [CrossRef]
  38. Zhao, J.; Li, Y.; Wang, Y.; Mao, J.; He, Y.; Luo, J. Mild thermal reduction of graphene oxide as a lubrication additive for friction and wear reduction. RSC Adv. 2017, 7, 1766–1770. [Google Scholar] [CrossRef]
  39. Ouyang, T.; Shen, Y.; Lei, W.; Xu, X.; Liang, L.; Waqar, H.S.; Lin, B.; Tian, Z.Q.; Shen, P.K. Reduced friction and wear enabled by arc-discharge method-prepared 3D graphene as oil additive under variable loads and speeds. Wear 2020, 462–463, 203495. [Google Scholar] [CrossRef]
  40. Gu, W.; Chu, K.; Lu, Z.; Zhang, G.; Qi, S. Synergistic effects of 3D porous graphene and T161 as hybrid lubricant additives on 316 ASS surface. Tribol. Int. 2021, 161, 107072. [Google Scholar] [CrossRef]
  41. Mao, J.; Zhao, J.; Wang, W.; He, Y.; Luo, J. Influence of the micromorphology of reduced graphene oxide sheets on lubrication properties as a lubrication additive. Tribol. Int. 2018, 119, 614–621. [Google Scholar] [CrossRef]
  42. Wu, L.; Gu, L.; Jian, R. Lubrication mechanism of graphene nanoplates as oil additives for ceramics/steel sliding components. Ceram. Int. 2021, 47, 16935–16942. [Google Scholar] [CrossRef]
  43. Kiu, S.S.K.; Yusup, S.; Soon, C.V.; Arpin, T.; Samion, S.; Kamil, R.N.M. Tribological investigation of graphene as lubricant additive in vegetable oil. J. Phys. Sci. 2017, 28, 257. [Google Scholar]
  44. Bhaumik, S.; Paleu, V.; Pathak, R.; Maggirwar, R.; Katiyar, J.K.; Sharma, A.K. Tribological investigation of r-GO additived biodegradable cashew nut shells liquid as an alternative industry lubricant. Tribol. Int. 2019, 135, 500–509. [Google Scholar] [CrossRef]
  45. Xie, M.; Cheng, J.; Huo, C.; Zhao, G. Improving the lubricity of a bio-lubricating grease with the multilayer graphene additive. Tribol. Int. 2020, 150, 106386. [Google Scholar] [CrossRef]
  46. Larsson, E.; Westbroek, R.; Leckner, J.; Jacobson, S.; Rudolphi, Å.K. Grease-lubricated tribological contacts—Influence of graphite, graphene oxide and reduced graphene oxide as lubricating additives in lithium complex (LiX)- and polypropylene (PP)-thickened greases. Wear 2021, 486–487, 204107. [Google Scholar] [CrossRef]
  47. Lee, C.; Li, Q.; Kalb, W.; Liu, X.-Z.; Berger, H.; Carpick, R.W.; Hone, J. Frictional Characteristics of Atomically Thin Sheets. Science 2010, 328, 76–80. [Google Scholar] [CrossRef]
  48. Li, S.; Li, Q.; Carpick, R.W.; Gumbsch, P.; Liu, X.Z.; Ding, X.; Sun, J.; Li, J. The evolving quality of frictional contact with graphene. Nature 2016, 539, 541. [Google Scholar] [CrossRef]
  49. Zhang, S.; Hou, Y.; Li, S.; Liu, L.; Zhang, Z.; Feng, X.-Q.; Li, Q. Tuning friction to a superlubric state via in-plane straining. Proc. Natl. Acad. Sci. USA 2019, 116, 24452–24456. [Google Scholar] [CrossRef] [PubMed]
  50. Li, R.; Sun, C.; Yang, X.; Wang, Y.; Gao, K.; Zhang, J.; Li, J. Toward high load-bearing, ambient robust and macroscale structural superlubricity through contact stress dispersion. Chem. Eng. J. 2021, 431, 133548. [Google Scholar] [CrossRef]
  51. Li, P.; Ju, P.; Ji, L.; Li, H.; Liu, X.; Chen, L.; Zhou, H.; Chen, J. Toward Robust Macroscale Superlubricity on Engineering Steel Substrate. Adv. Mater. 2020, 32, 2002039. [Google Scholar] [CrossRef] [PubMed]
  52. Jin, B.; Zhao, J.; He, Y.; Chen, G.; Li, Y.; Zhang, C.; Luo, J. High-quality ultra-flat reduced graphene oxide nanosheets with super-robust lubrication performances. Chem. Eng. J. 2022, 438, 135620. [Google Scholar] [CrossRef]
  53. Wang, W.; Zhang, G.; Xie, G. Ultralow concentration of graphene oxide nanosheets as oil-based lubricant additives. Appl. Surf. Sci. 2019, 498, 143683. [Google Scholar] [CrossRef]
  54. Fan, K.; Chen, X.; Wang, X.; Liu, X.; Liu, Y.; Lai, W.; Liu, X. Toward Excellent Tribological Performance as Oil-Based Lubricant Additive: Particular Tribological Behavior of Fluorinated Graphene. ACS Appl. Mater. Interfaces 2018, 10, 28828–28838. [Google Scholar] [CrossRef] [PubMed]
  55. Paul, G.; Shit, S.; Hirani, H.; Kuila, T.; Murmu, N.C. Tribological behavior of dodecylamine functionalized graphene nanosheets dispersed engine oil nanolubricants. Tribol. Int. 2019, 131, 605–619. [Google Scholar] [CrossRef]
  56. Li, X.; Gan, C.; Han, Z.; Yan, H.; Chen, D.; Li, W.; Li, H.; Fan, X.; Li, D.; Zhu, M. High dispersivity and excellent tribological performance of titanate coupling agent modified graphene oxide in hydraulic oil. Carbon 2020, 165, 238–250. [Google Scholar] [CrossRef]
  57. Fu, H.; Fan, X.; Li, W.; Zhu, M.; Peng, J.; Li, H. In situ modified multilayer graphene toward high-performance lubricating additive. RSC Adv. 2017, 7, 24399–24409. [Google Scholar] [CrossRef]
  58. Zhang, L.; He, Y.; Zhu, L.; Yang, C.; Niu, Q.; An, C. In Situ Alkylated Graphene as Oil Dispersible Additive for Friction and Wear Reduction. Ind. Eng. Chem. Res. 2017, 56, 9029–9034. [Google Scholar] [CrossRef]
  59. Mungse, H.P.; Gupta, K.; Singh, R.; Sharma, O.P.; Sugimura, H.; Khatri, O.P. Alkylated graphene oxide and reduced graphene oxide: Grafting density, dispersion stability to enhancement of lubrication properties. J. Colloid Interface Sci. 2019, 541, 150–162. [Google Scholar] [CrossRef]
  60. Yin, S.; Ye, C.; Chen, Y.; Jin, C.; Wu, H.; Wang, H. Dependence of the lubrication enhancement of alkyl-functionalized graphene oxide and boric acid nanoparticles on the anti-oxidation property. Colloids Surf. A Physicochem. Eng. Asp. 2022, 649, 129521. [Google Scholar] [CrossRef]
  61. Gan, C.; Liang, T.; Chen, D.; Li, W.; Fan, X.; Tang, G.; Lin, B.; Zhu, M. Phosphonium-organophosphate modified graphene gel towards lubrication applications. Tribol. Int. 2020, 145, 106180. [Google Scholar] [CrossRef]
  62. Ismail, N.A.; Bagheri, S. Highly oil-dispersed functionalized reduced graphene oxide nanosheets as lube oil friction modifier. Mater. Sci. Eng. B 2017, 222, 34–42. [Google Scholar] [CrossRef]
  63. Chouhan, A.; Mungse, H.P.; Sharma, O.P.; Singh, R.K.; Khatri, O.P. Chemically functionalized graphene for lubricant applications: Microscopic and spectroscopic studies of contact interfaces to probe the role of graphene for enhanced tribo-performance. J. Colloid Interface Sci. 2018, 513, 666–676. [Google Scholar] [CrossRef] [PubMed]
  64. Wu, P.; Chen, X.; Zhang, C.; Zhang, J.; Luo, J.; Zhang, J. Modified graphene as novel lubricating additive with high dispersion stability in oil. Friction 2021, 9, 143–154. [Google Scholar] [CrossRef]
  65. 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, 14394–14402. [Google Scholar] [CrossRef]
  66. Bao, T.; Wang, Z.; Zhao, Y.; Wang, Y.; Yi, X. Long-term stably dispersed functionalized graphene oxide as an oil additive. RSC Adv. 2019, 9, 39230–39241. [Google Scholar] [CrossRef]
  67. Chouhan, A.; Mungse, H.P.; Khatri, O.P. Surface chemistry of graphene and graphene oxide: A versatile route for their dispersion and tribological applications. Adv. Colloid Interface Sci. 2020, 283, 102215. [Google Scholar] [CrossRef]
  68. Gan, C.; Liang, T.; Li, X.; Li, W.; Li, H.; Fan, X.; Zhu, M. Ultra-dispersive monolayer graphene oxide as water-based lubricant additive: Preparation, characterization and lubricating mechanisms. Tribol. Int. 2021, 155, 106768. [Google Scholar] [CrossRef]
  69. Hu, Y.; Wang, Y.; Zeng, Z.; Zhao, H.; Ge, X.; Wang, K.; Wang, L.; Xue, Q. PEGlated graphene as nanoadditive for enhancing the tribological properties of water-based lubricants. Carbon 2018, 137, 41–48. [Google Scholar] [CrossRef]
  70. Song, H.-J.; Li, N. Frictional behavior of oxide graphene nanosheets as water-base lubricant additive. Appl. Phys. A 2011, 105, 827–832. [Google Scholar] [CrossRef]
  71. Kinoshita, H.; Kondo, M.; Nishina, Y.; Fujii, M. Anti-Wear Effect of Graphene Oxide in Lubrication by Fluorine-Containing Ionic Liquid for Steel. Tribol. Online 2015, 10, 91–95. [Google Scholar] [CrossRef] [Green Version]
  72. Kinoshita, H.; Nishina, Y.; Alias, A.A.; Fujii, M. Tribological properties of monolayer graphene oxide sheets as water-based lubricant additives. Carbon 2014, 66, 720–723. [Google Scholar] [CrossRef]
  73. He, A.; Huang, S.; Yun, J.-H.; Jiang, Z.; Stokes, J.; Jiao, S.; Wang, L.; Huang, H. The pH-dependent structural and tribological behaviour of aqueous graphene oxide suspensions. Tribol. Int. 2017, 116, 460–469. [Google Scholar] [CrossRef]
  74. Wei, Q.; Fu, T.; Yue, Q.; Liu, H.; Ma, S.; Cai, M.; Zhou, F. Graphene oxide/brush-like polysaccharide copolymer nanohybrids as eco-friendly additives for water-based lubrication. Tribol. Int. 2021, 157, 106895. [Google Scholar] [CrossRef]
  75. Fan, X.; Wang, L. High-performance lubricant additives based on modified graphene oxide by ionic liquids. J. Colloid Interface Sci. 2015, 452, 98–108. [Google Scholar] [CrossRef] [PubMed]
  76. Han, Z.; Gan, C.; Li, X.; Feng, P.; Ma, X.; Fan, X.; Zhu, M. Electrochemical preparation of modified-graphene additive towards lubrication requirement. Tribol. Int. 2021, 161, 107057. [Google Scholar] [CrossRef]
  77. Liu, J.; Wang, X.; Liu, Y.; Liu, X.; Fan, K. Bioinspired three-dimensional and multiple adsorption effects toward high lubricity of solvent-free graphene-based nanofluid. Carbon 2022, 188, 166–176. [Google Scholar] [CrossRef]
  78. Matsumura, K.; Chiashi, S.; Maruyama, S.; Choi, J. Macroscale tribological properties of fluorinated graphene. Appl. Surf. Sci. 2018, 432, 190–195. [Google Scholar] [CrossRef]
  79. Ye, X.; Ma, L.; Yang, Z.; Wang, J.; Wang, H.; Yang, S. Covalent Functionalization of Fluorinated Graphene and Subsequent Application as Water-based Lubricant Additive. ACS Appl. Mater. Interfaces 2016, 8, 7483–7488. [Google Scholar] [CrossRef]
  80. Min, C.; He, Z.; Song, H.; Liang, H.; Liu, D.; Dong, C.; Jia, W. Fluorinated graphene oxide nanosheet: A highly efficient water-based lubricated additive. Tribol. Int. 2019, 140, 105867. [Google Scholar] [CrossRef]
  81. Fan, K.; Liu, J.; Wang, X.; Liu, Y.; Lai, W.; Gao, S.; Qin, J.; Liu, X. Towards enhanced tribological performance as water-based lubricant additive: Selective fluorination of graphene oxide at mild temperature. J. Colloid Interface Sci. 2018, 531, 138–147. [Google Scholar] [CrossRef] [PubMed]
  82. Zhu, W.; Wu, C.; Chang, Y.; Cheng, H.; Yu, C. Solvent-free preparation of hydrophilic fluorinated graphene oxide modified with amino-groups. Mater. Lett. 2019, 237, 1–4. [Google Scholar] [CrossRef]
  83. Zhang, G.; Xu, Y.; Xiang, X.; Zheng, G.; Zeng, X.; Li, Z.; Ren, T.; Zhang, Y. Tribological performances of highly dispersed graphene oxide derivatives in vegetable oil. Tribol. Int. 2018, 126, 39–48. [Google Scholar] [CrossRef]
  84. Jaiswal, V.; Kalyani; Umrao, S.; Rastogi, R.B.; Kumar, R.; Srivastava, A. Synthesis, Characterization, and Tribological Evaluation of TiO2-Reinforced Boron and Nitrogen co-Doped Reduced Graphene Oxide Based Hybrid Nanomaterials as Efficient Antiwear Lubricant Additives. ACS Appl. Mater. Interfaces 2016, 8, 11698–11710. [Google Scholar] [CrossRef]
  85. Zhao, F.; Zhang, L.; Li, G.; Guo, Y.; Qi, H.; Zhang, G. Significantly enhancing tribological performance of epoxy by filling with ionic liquid functionalized graphene oxide. Carbon 2018, 136, 309–319. [Google Scholar] [CrossRef]
  86. Wu, L.; Xie, Z.; Gu, L.; Song, B.; Wang, L. Investigation of the tribological behavior of graphene oxide nanoplates as lubricant additives for ceramic/steel contact. Tribol. Int. 2018, 128, 113–120. [Google Scholar] [CrossRef]
  87. Luo, J.; Zhou, X. Superlubricitive engineering—Future industry nearly getting rid of wear and frictional energy consumption. Friction 2020, 8, 643–665. [Google Scholar] [CrossRef]
  88. Chen, X.; Li, J. Superlubricity of carbon nanostructures. Carbon 2020, 158, 1–23. [Google Scholar] [CrossRef]
  89. Ge, X.; Li, J.; Luo, R.; Zhang, C.; Luo, J. Macroscale Superlubricity Enabled by the Synergy Effect of Graphene-Oxide Nanoflakes and Ethanediol. ACS Appl. Mater. Interfaces 2018, 10, 40863–40870. [Google Scholar] [CrossRef]
  90. Ge, X.; Li, J.; Wang, H.; Zhang, C.; Liu, Y.; Luo, J. Macroscale superlubricity under extreme pressure enabled by the combination of graphene-oxide nanosheets with ionic liquid. Carbon 2019, 151, 76–83. [Google Scholar] [CrossRef]
  91. Ge, X.; Chai, Z.; Shi, Q.; Liu, Y.; Tang, J.; Wang, W. Liquid Superlubricity Enabled by the Synergy Effect of Graphene Oxide and Lithium Salts. Materials 2022, 15, 3546. [Google Scholar] [CrossRef]
  92. Ge, X.; Chai, Z.; Shi, Q.; Li, J.; Tang, J.; Liu, Y.; Wang, W. Functionalized graphene-oxide nanosheets with amino groups facilitate macroscale superlubricity. Friction 2022, 1–14. [Google Scholar] [CrossRef]
  93. Liu, Y.; Yu, S.; Li, J.; Ge, X.; Zhao, Z.; Wang, W. Quantum dots of graphene oxide as nano-additive triggers macroscale superlubricity with an extreme short running-in period. Mater. Today Nano 2022, 18, 100219. [Google Scholar] [CrossRef]
  94. Wang, L.-F.; Ma, T.-B.; Hu, Y.-Z.; Wang, H. Atomic-scale friction in graphene oxide: An interfacial interaction perspective from first-principles calculations. Phys. Rev. B 2012, 86, 125436. [Google Scholar] [CrossRef]
  95. Wang, L.-F.; Ma, T.-B.; Hu, Y.-Z.; Wang, H.; Shao, T.-M. Ab Initio Study of the Friction Mechanism of Fluorographene and Graphane. J. Phys. Chem. C 2013, 117, 12520–12525. [Google Scholar] [CrossRef]
  96. Arif, T.; Colas, G.; Filleter, T. Effect of Humidity and Water Intercalation on the Tribological Behavior of Graphene and Graphene Oxide. ACS Appl. Mater. Interfaces 2018, 10, 22537–22544. [Google Scholar] [CrossRef] [PubMed]
  97. Saravanan, P.; Selyanchyn, R.; Tanaka, H.; Darekar, D.; Staykov, A.; Fujikawa, S.; Lyth, S.M.; Sugimura, J. Macroscale Superlubricity of Multilayer Polyethylenimine/Graphene Oxide Coatings in Different Gas Environments. ACS Appl. Mater. Interfaces 2016, 8, 27179–27187. [Google Scholar] [CrossRef]
  98. Liu, Y.; Li, J.; Ge, X.; Yi, S.; Wang, H.; Liu, Y.; Luo, J. Macroscale Superlubricity Achieved on the Hydrophobic Graphene Coating with Glycerol. ACS Appl Mater Interfaces 2020, 12, 18859–18869. [Google Scholar] [CrossRef]
  99. Yi, S.; Chen, X.; Li, J.; Liu, Y.; Ding, S.; Luo, J. Macroscale superlubricity of Si-doped diamond-like carbon film enabled by graphene oxide as additives. Carbon 2021, 176, 358–366. [Google Scholar] [CrossRef]
  100. Xu, Y.; Peng, Y.; Dearn, K.D.; Zheng, X.; Yao, L.; Hu, X. Synergistic lubricating behaviors of graphene and MoS2 dispersed in esterified bio-oil for steel/steel contact. Wear 2015, 342–343, 297–309. [Google Scholar] [CrossRef]
  101. Farsadi, M.; Bagheri, S.; Ismail, N.A. Nanocomposite of functionalized graphene and molybdenum disulfide as friction modifier additive for lubricant. J. Mol. Liq. 2017, 244, 304–308. [Google Scholar] [CrossRef]
  102. Gong, K.; Wu, X.; Zhao, G.; Wang, X. Nanosized MoS2 deposited on graphene as lubricant additive in polyalkylene glycol for steel/steel contact at elevated temperature. Tribol. Int. 2017, 110, 1–7. [Google Scholar] [CrossRef]
  103. Ismail, N.A.; Chowdhury, Z.Z.; Johan, M.R.; Zulkifli, N.W.M. MoS2-Functionalized Graphene Composites—Potential Replacement for Lubricant Friction Modifier and Anti-Wear Additives. Adv. Eng. Mater. 2021, 23, 2100030. [Google Scholar] [CrossRef]
  104. Gong, K.; Lou, W.; Zhao, G.; Wu, X.; Wang, X. MoS2 nanoparticles grown on carbon nanomaterials for lubricating oil additives. Friction 2021, 9, 747–757. [Google Scholar] [CrossRef]
  105. Hou, K.; Wang, J.; Yang, Z.; Ma, L.; Wang, Z.; Yang, S. One-pot synthesis of reduced graphene oxide/molybdenum disulfide heterostructures with intrinsic incommensurateness for enhanced lubricating properties. Carbon 2017, 115, 83–94. [Google Scholar] [CrossRef]
  106. Qi, S.; Geng, Z.; Lu, Z.; Zhang, G.; Wu, Z. Synergistic Lubricating Behaviors of 3D Graphene and 2D Hexagonal Boron Nitride Dispersed in PAO4 for Steel/Steel Contact. Adv. Mater. Interfaces 2020, 7, 1901893. [Google Scholar] [CrossRef]
  107. Samanta, S.; Sahoo, R.R. Covalently Linked Hexagonal Boron Nitride-Graphene Oxide Nanocomposites as High-Performance Oil-Dispersible Lubricant Additives. ACS Appl. Nano Mater. 2020, 3, 10941–10953. [Google Scholar] [CrossRef]
  108. Wu, P.; Chen, X.; Zhang, C.; Luo, J. Synergistic tribological behaviors of graphene oxide and nanodiamond as lubricating additives in water. Tribol. Int. 2019, 132, 177–184. [Google Scholar] [CrossRef]
  109. Radhika, P.; Sobhan, C.B.; Chakravorti, S. Improved tribological behavior of lubricating oil dispersed with hybrid nanoparticles of functionalized carbon spheres and graphene nano platelets. Appl. Surf. Sci. 2021, 540, 148402. [Google Scholar] [CrossRef]
  110. Zheng, D.; Wu, Y.-p.; Li, Z.-y.; Cai, Z.-b. Tribological properties of WS2/graphene nanocomposites as lubricating oil additives. RSC Adv. 2017, 7, 14060–14068. [Google Scholar] [CrossRef]
  111. Su, F.; Chen, G.; Huang, P. Lubricating performances of graphene oxide and onion-like carbon as water-based lubricant additives for smooth and sand-blasted steel discs. Friction 2020, 8, 47–57. [Google Scholar] [CrossRef] [Green Version]
  112. Meng, Y.; Su, F.; Chen, Y. Au/Graphene Oxide Nanocomposite Synthesized in Supercritical CO2 Fluid as Energy Efficient Lubricant Additive. ACS Appl. Mater. Interfaces 2017, 9, 39549–39559. [Google Scholar] [CrossRef] [PubMed]
  113. Song, H.J.; Wang, Z.Q.; Yang, J.; Jia, X.H.; Zhang, Z.Z. Facile synthesis of copper/polydopamine functionalized graphene oxide nanocomposites with enhanced tribological performance. Chem. Eng. J. 2017, 324, 51–62. [Google Scholar] [CrossRef]
  114. Wang, L.; Gong, P.; Li, W.; Luo, T.; Cao, B. Mono-dispersed Ag/Graphene nanocomposite as lubricant additive to reduce friction and wear. Tribol. Int. 2020, 146, 106228. [Google Scholar] [CrossRef]
  115. Gan, C.; Liang, T.; Li, W.; Fan, X.; Zhu, M. Amine-terminated ionic liquid modified graphene oxide/copper nanocomposite toward efficient lubrication. Appl. Surf. Sci. 2019, 491, 105–115. [Google Scholar] [CrossRef]
  116. Zhang, Y.; Tang, H.; Ji, X.; Li, C.; Chen, L.; Zhang, D.; Yang, X.; Zhang, H. Synthesis of reduced graphene oxide/Cu nanoparticle composites and their tribological properties. RSC Adv. 2013, 3, 26086–26093. [Google Scholar] [CrossRef]
  117. White, D.; Chen, M.; Xiao, C.; Huang, W.; Sundararajan, S. Microtribological behavior of Mo and W nanoparticle/graphene composites. Wear 2018, 414–415, 310–316. [Google Scholar] [CrossRef]
  118. Meng, Y.; Su, F.; Chen, Y. Supercritical Fluid Synthesis and Tribological Applications of Silver Nanoparticle-decorated Graphene in Engine Oil Nanofluid. Sci. Rep. 2016, 6, 31246. [Google Scholar] [CrossRef]
  119. Jia, Z.; Chen, T.; Wang, J.; Ni, J.; Li, H.; Shao, X. Synthesis, characterization and tribological properties of Cu/reduced graphene oxide composites. Tribol. Int. 2015, 88, 17–24. [Google Scholar] [CrossRef]
  120. Meng, Y.; Su, F.; Chen, Y. Synthesis of nano-Cu/graphene oxide composites by supercritical CO2-assisted deposition as a novel material for reducing friction and wear. Chem. Eng. J. 2015, 281, 11–19. [Google Scholar] [CrossRef]
  121. Meng, Y.; Su, F.; Li, Z. Boundary and Elastohydrodynamic Lubrication Behaviors of Nano-CuO/Reduced Graphene Oxide Nanocomposite as an Efficient Oil-Based Additive. Langmuir 2019, 35, 10322–10333. [Google Scholar] [CrossRef]
  122. Huang, S.; He, A.; Yun, J.-H.; Xu, X.; Jiang, Z.; Jiao, S.; Huang, H. Synergistic tribological performance of a water based lubricant using graphene oxide and alumina hybrid nanoparticles as additives. Tribol. Int. 2019, 135, 170–180. [Google Scholar] [CrossRef]
  123. Zhou, Q.; Huang, J.; Wang, J.; Yang, Z.; Liu, S.; Wang, Z.; Yang, S.J.R.A. Preparation of a reduced graphene oxide/zirconia nanocomposite and its application as a novel lubricant oil additive. RSC Adv. 2015, 5, 91802–91812. [Google Scholar] [CrossRef]
  124. Zhao, J.; Li, Y.; He, Y.; Luo, J. In Situ Green Synthesis of the New Sandwichlike Nanostructure of Mn3O4/Graphene as Lubricant Additives. ACS Appl. Mater. Interfaces 2019, 11, 36931–36938. [Google Scholar] [CrossRef] [PubMed]
  125. Wang, J.; Zhuang, W.; Yan, T.; Liang, W.; Li, T.; Zhang, L.; Wei, X. Tribological performances of copper perrhenate/graphene nanocomposite as lubricating additive under various temperatures. J. Ind. Eng. Chem. 2021, 100, 296–309. [Google Scholar]
  126. Ren, B.; Gao, L.; Xie, B.; Li, M.; Zhang, S.; Zu, G.; Ran, X. Tribological properties and anti-wear mechanism of ZnO@graphene core-shell nanoparticles as lubricant additives. Tribol. Int. 2020, 144, 106114. [Google Scholar] [CrossRef]
  127. Alghani, W.; Karim, M.S.A.; Bagheri, S.; Amran, N.A.M.; Gulzar, M. Enhancing the Tribological Behavior of Lubricating Oil by Adding TiO2, Graphene, and TiO2/Graphene Nanoparticles. Tribol. Trans. 2019, 62, 452–463. [Google Scholar] [CrossRef]
  128. Sun, J.; Ge, C.; Wang, C.; Li, S. Tribological behavior of graphene oxide-Fe3O4 nanocomposites for additives in water-based lubricants. Fuller. Nanotub. Carbon Nanostruct. 2022, 30, 863–872. [Google Scholar] [CrossRef]
  129. Bai, G.; Wang, J.; Yang, Z.; Wang, H.; Wang, Z.; Yang, S. Preparation of a highly effective lubricating oil additive–ceria/graphene composite. RSC Adv. 2014, 4, 47096–47105. [Google Scholar] [CrossRef]
  130. Guo, Y.; Guo, L.; Li, G.; Zhang, L.; Zhao, F.; Wang, C.; Zhang, G. Solvent-free ionic nanofluids based on graphene oxide-silica hybrid as high-performance lubricating additive. Appl. Surf. Sci. 2019, 471, 482–493. [Google Scholar] [CrossRef]
  131. Guo, P.; Chen, L.; Wang, J.; Geng, Z.; Lu, Z.; Zhang, G. Enhanced Tribological Performance of Aminated Nano-Silica Modified Graphene Oxide as Water-Based Lubricant Additive. ACS Appl. Nano Mater. 2018, 1, 6444–6453. [Google Scholar] [CrossRef]
  132. Shen, Y.; Lei, W.; Tang, W.; Ouyang, T.; Liang, L.; Tian, Z.Q.; Shen, P.K. Synergistic friction-reduction and wear-resistance mechanism of 3D graphene and SiO2 nanoblend at harsh friction interface. Wear 2022, 488–489, 204175. [Google Scholar] [CrossRef]
  133. Song, W.; Yan, J.; Ji, H. Tribological Performance of an Imidazolium Ionic Liquid-Functionalized SiO2@Graphene Oxide as an Additive. ACS Appl. Mater. Interfaces 2021, 13, 50573–50583. [Google Scholar] [CrossRef] [PubMed]
  134. Xiong, S.; Zhang, B.; Luo, S.; Wu, H.; Zhang, Z. Preparation, characterization, and tribological properties of silica-nanoparticle-reinforced B-N-co-doped reduced graphene oxide as a multifunctional additive for enhanced lubrication. Friction 2021, 9, 239–249. [Google Scholar] [CrossRef]
  135. Singh, V.K.; Elomaa, O.; Johansson, L.-S.; Hannula, S.-P.; Koskinen, J. Lubricating properties of silica/graphene oxide composite powders. Carbon 2014, 79, 227–235. [Google Scholar] [CrossRef]
  136. Mohamed, A.; Tirth, V.; Kamel, B.M. Tribological characterization and rheology of hybrid calcium grease with graphene nanosheets and multi-walled carbon nanotubes as additives. J. Mater. Res. Technol. 2020, 9, 6178–6185. [Google Scholar] [CrossRef]
  137. Kamel, B.M.; El-Kashif, E.; Hoziefa, W.; Shiba, M.S.; Elshalakany, A.B. The effect of MWCNTs/GNs hybrid addition on the tribological and rheological properties of lubricating engine oil. J. Dispers. Sci. Technol. 2021, 42, 1811–1819. [Google Scholar] [CrossRef]
  138. Ouyang, T.; Tang, W.; Pan, M.; Tang, J.; Huang, H. Friction-reducing and anti-wear properties of 3D hierarchical porous graphene/multi-walled carbon nanotube in castor oil under severe condition: Experimental investigation and mechanism study. Wear 2022, 498–499, 204302. [Google Scholar] [CrossRef]
  139. Paul, G.; Hirani, H.; Kuila, T.; Murmu, N.C.J.N. Nanolubricants dispersed with graphene and its derivatives: An assessment and review of the tribological performance. Nanoscale 2019, 11, 3458–3483. [Google Scholar] [CrossRef]
  140. Senatore, A.; D’Agostino, V.; Petrone, V.; Ciambelli, P.; Sarno, M. Graphene oxide nanosheets as effective friction modifier for oil lubricant: Materials, methods, and tribological results. J. ISRN Tribol. 2013, 2013, 425809. [Google Scholar] [CrossRef]
  141. Cheng, Z.-L.; Li, W.; Liu, Z. Preparation, characterization, and tribological properties of oleic diethanolamide-capped zinc borate-coated graphene oxide composites. J. Alloy. Compd. 2017, 705, 384–391. [Google Scholar] [CrossRef]
  142. Lin, J.; Wang, L.; Chen, G. Modification of Graphene Platelets and their Tribological Properties as a Lubricant Additive. Tribol. Lett. 2011, 41, 209–215. [Google Scholar] [CrossRef]
  143. Fan, X.; Xia, Y.; Wang, L.; Li, W. Multilayer Graphene as a Lubricating Additive in Bentone Grease. Tribol. Lett. 2014, 55, 455–464. [Google Scholar] [CrossRef]
  144. Liang, S.; Shen, Z.; Yi, M.; Liu, L.; Zhang, X.; Ma, S. In-situ exfoliated graphene for high-performance water-based lubricants. Carbon 2016, 96, 1181–1190. [Google Scholar] [CrossRef]
  145. Marchetto, D.; Restuccia, P.; Ballestrazzi, A.; Righi, M.C.; Rota, A.; Valeri, S. Surface passivation by graphene in the lubrication of iron: A comparison with bronze. Carbon 2017, 116, 375–380. [Google Scholar] [CrossRef]
  146. Wu, Y.; Zeng, X.; Ren, T.; de Vries, E.; van der Heide, E. The emulsifying and tribological properties of modified graphene oxide in oil-in-water emulsion. Tribol. Int. 2017, 105, 304–316. [Google Scholar] [CrossRef]
  147. Zheng, D.; Cai, Z.-b.; Shen, M.-x.; Li, Z.-y.; Zhu, M.-h. Investigation of the tribology behaviour of the graphene nanosheets as oil additives on textured alloy cast iron surface. Appl. Surf. Sci. 2016, 387, 66–75. [Google Scholar] [CrossRef]
  148. Li, X.; Zhang, D.; Xu, X.; Lee, K.-R. Tailoring the Nanostructure of Graphene as an Oil-Based Additive: Toward Synergistic Lubrication with an Amorphous Carbon Film. ACS Appl. Mater. Interfaces 2020, 12, 43320–43330. [Google Scholar] [CrossRef]
  149. Li, J.; Cao, W.; Li, J.; Ma, M.; Luo, J. Molecular Origin of Superlubricity between Graphene and a Highly Hydrophobic Surface in Water. J. Phys. Chem. Lett. 2019, 10, 2978–2984. [Google Scholar] [CrossRef]
  150. Li, C.; Tang, W.; Tang, X.-Z.; Yang, L.; Bai, L. A molecular dynamics study on the synergistic lubrication mechanisms of graphene/water-based lubricant systems. Tribol. Int. 2022, 167, 107356. [Google Scholar] [CrossRef]
  151. Li, X.; Xu, X.; Zhou, Y.; Lee, K.-R.; Wang, A. Insights into friction dependence of carbon nanoparticles as oil-based lubricant additive at amorphous carbon interface. Carbon 2019, 150, 465–474. [Google Scholar] [CrossRef]
  152. Li, X.; Xu, X.; Qi, J.; Zhang, D.; Wang, A.; Lee, K.-R. Insights into Superlow Friction and Instability of Hydrogenated Amorphous Carbon/Fluid Nanocomposite Interface. ACS Appl. Mater. Interfaces 2021, 13, 35173–35186. [Google Scholar] [CrossRef] [PubMed]
  153. Dou, X.; Koltonow, A.R.; He, X.; Jang, H.D.; Wang, Q.; Chung, Y.-W.; Huang, J. Self-dispersed crumpled graphene balls in oil for friction and wear reduction. Proc. Natl. Acad. Sci. USA 2016, 113, 1528. [Google Scholar] [CrossRef]
  154. Kong, L.; Sun, J.; Bao, Y. Preparation, characterization and tribological mechanism of nanofluids. RSC Adv. 2017, 7, 12599–12609. [Google Scholar] [CrossRef]
  155. Zin, V.; Agresti, F.; Barison, S.; Colla, L.; Fabrizio, M. Influence of Cu, TiO2 Nanoparticles and Carbon Nano-Horns on Tribological Properties of Engine Oil. J. Nanosci. Nanotechnol. 2015, 15, 3590–3598. [Google Scholar] [CrossRef]
  156. Zurutuza, A.; Marinelli, C. Challenges and opportunities in graphene commercialization. Nat. Nanotechnol. 2014, 9, 730–734. [Google Scholar] [CrossRef]
  157. Neuberger, N.; Adidharma, H.; Fan, M. Graphene: A review of applications in the petroleum industry. J. Pet. Sci. Eng. 2018, 167, 152–159. [Google Scholar] [CrossRef]
  158. Rasheed, A.K.; Khalid, M.; Javeed, A.; Rashmi, W.; Gupta, T.C.S.M.; Chan, A. Heat transfer and tribological performance of graphene nanolubricant in an internal combustion engine. Tribol. Int. 2016, 103, 504–515. [Google Scholar] [CrossRef]
  159. Baldin, V.; da Silva, L.R.R.; Houck, C.F.; Gelamo, R.V.; Machado, Á.R. Effect of Graphene Addition in Cutting Fluids Applied by MQL in End Milling of AISI 1045 Steel. Lubricants 2021, 9, 70. [Google Scholar] [CrossRef]
  160. Li, M.; Yu, T.; Zhang, R.; Yang, L.; Li, H.; Wang, W. MQL milling of TC4 alloy by dispersing graphene into vegetable oil-based cutting fluid. Int. J. Adv. Manuf. Technol. 2018, 99, 1735–1753. [Google Scholar] [CrossRef]
  161. Yi, S.; Li, G.; Ding, S.; Mo, J. Performance and mechanisms of graphene oxide suspended cutting fluid in the drilling of titanium alloy Ti-6Al-4V. J. Manuf. Processes 2017, 29, 182–193. [Google Scholar] [CrossRef]
  162. Singh, R.K.; Sharma, A.K.; Dixit, A.R.; Tiwari, A.K.; Pramanik, A.; Mandal, A. Performance evaluation of alumina-graphene hybrid nano-cutting fluid in hard turning. J. Clean. Prod. 2017, 162, 830–845. [Google Scholar] [CrossRef] [Green Version]
  163. Kałużny, J.; Świetlicka, A.; Wojciechowski, Ł.; Boncel, S.; Kinal, G.; Runka, T.; Nowicki, M.; Stepanenko, O.; Gapiński, B.; Leśniewicz, J.; et al. Machine Learning Approach for Application-Tailored Nanolubricants’ Design. Nanomaterials 2022, 12, 1765. [Google Scholar] [CrossRef] [PubMed]
  164. Ryu, B.; Wang, L.; Pu, H.; Chan, M.K.Y.; Chen, J. Understanding, discovery, and synthesis of 2D materials enabled by machine learning. Chem. Soc. Rev. 2022, 51, 1899–1925. [Google Scholar] [CrossRef]
  165. Hasan, M.S.; Kordijazi, A.; Rohatgi, P.K.; Nosonovsky, M. Machine learning models of the transition from solid to liquid lubricated friction and wear in aluminum-graphite composites. Tribol. Int. 2022, 165, 107326. [Google Scholar] [CrossRef]
Lubricants 10 00215 g001 550
Figure 1. Functionalization of graphene-family materials including (a) oxidation [31] and (b) fluorination [32]. Reprinted with permission from Ref. [32]. American Chemical Society, 2010.
Figure 1. Functionalization of graphene-family materials including (a) oxidation [31] and (b) fluorination [32]. Reprinted with permission from Ref. [32]. American Chemical Society, 2010.
Lubricants 10 00215 g001
Lubricants 10 00215 g002 550
Figure 2. (a) Fourier transform infrared spectrum of as-prepared ultrathin graphene nanoflakes, where the insets are the photographs of the engine oil nanofluids with different concentrations of graphene, and the water droplet on graphene film; (b) COF versus time curves with engine oil and nanofluids. Reprinted with permission from Ref. [34]. American Chemical Society, 2011.
Figure 2. (a) Fourier transform infrared spectrum of as-prepared ultrathin graphene nanoflakes, where the insets are the photographs of the engine oil nanofluids with different concentrations of graphene, and the water droplet on graphene film; (b) COF versus time curves with engine oil and nanofluids. Reprinted with permission from Ref. [34]. American Chemical Society, 2011.
Lubricants 10 00215 g002
Lubricants 10 00215 g003 550
Figure 3. SEM and HRTEM images of (a) ultra-flat reduced graphene oxide, (b) curly edge reduced graphene oxide, and (c) internal wrinkle reduced graphene oxide; (d) COF versus time curves with different nanomaterials as additives. Reprinted with permission from Ref. [52]. Elsevier, 2022.
Figure 3. SEM and HRTEM images of (a) ultra-flat reduced graphene oxide, (b) curly edge reduced graphene oxide, and (c) internal wrinkle reduced graphene oxide; (d) COF versus time curves with different nanomaterials as additives. Reprinted with permission from Ref. [52]. Elsevier, 2022.
Lubricants 10 00215 g003
Lubricants 10 00215 g004 550
Figure 4. Superlubricity is achieved with the combination of GO nanosheets and an ionic liquid as additives in ethylene glycol water solution. Adsorbed GO can be observed onto the wear surface, which is critical for the achievement of superlubricity. Reprinted with permission from Ref. [90]. Elsevier, 2019.
Figure 4. Superlubricity is achieved with the combination of GO nanosheets and an ionic liquid as additives in ethylene glycol water solution. Adsorbed GO can be observed onto the wear surface, which is critical for the achievement of superlubricity. Reprinted with permission from Ref. [90]. Elsevier, 2019.
Lubricants 10 00215 g004
Lubricants 10 00215 g005 550
Figure 5. Superlubricity is achieved with the hydrophobic graphene coating and the glycerol aqueous solution. (a) COF versus time curves with different lubricants and the (b) long duration result with pristine graphene coating; (c) TEM and (d) HRTEM images of the tribofilm after the friction test with deposited pristine graphene coating; (e) schematic diagram of the superlubricity mechanism with hydrophobic graphene and water-based lubricant. Reprinted with permission from Ref. [98]. American Chemical Society, 2020.
Figure 5. Superlubricity is achieved with the hydrophobic graphene coating and the glycerol aqueous solution. (a) COF versus time curves with different lubricants and the (b) long duration result with pristine graphene coating; (c) TEM and (d) HRTEM images of the tribofilm after the friction test with deposited pristine graphene coating; (e) schematic diagram of the superlubricity mechanism with hydrophobic graphene and water-based lubricant. Reprinted with permission from Ref. [98]. American Chemical Society, 2020.
Lubricants 10 00215 g005
Lubricants 10 00215 g006 550
Figure 6. A proposed synergetic effect between graphene and MoS2 nanoflakes as an additive in bio-oil. Schematic diagram of the structural evolution and chemical changes with graphene, MoS2, and graphene combined with MoS2 additives during friction process. Reprinted with permission from Ref. [100]. Elsevier, 2015.
Figure 6. A proposed synergetic effect between graphene and MoS2 nanoflakes as an additive in bio-oil. Schematic diagram of the structural evolution and chemical changes with graphene, MoS2, and graphene combined with MoS2 additives during friction process. Reprinted with permission from Ref. [100]. Elsevier, 2015.
Lubricants 10 00215 g006
Lubricants 10 00215 g007 550
Figure 7. (a–d) Structure of the tribofilm containing GO and ND; (e,f) COFs with the lubrication of pure water, GO, ND, and the GO-ND suspensions. Reprinted with permission from Ref. [108]. Elsevier, 2019.
Figure 7. (a–d) Structure of the tribofilm containing GO and ND; (e,f) COFs with the lubrication of pure water, GO, ND, and the GO-ND suspensions. Reprinted with permission from Ref. [108]. Elsevier, 2019.
Lubricants 10 00215 g007
Lubricants 10 00215 g008 550
Figure 8. Effect of size and concentration of the graphene as additive on the COFs. (a) Change of COF with size and concentration of graphene; (b) interfacial structures containing graphene with different sizes and concentrations (the molecules of base oil are neglected for better observation of the structure of graphene). Reprinted with permission from Ref. [148]. American Chemical Society, 2020.
Figure 8. Effect of size and concentration of the graphene as additive on the COFs. (a) Change of COF with size and concentration of graphene; (b) interfacial structures containing graphene with different sizes and concentrations (the molecules of base oil are neglected for better observation of the structure of graphene). Reprinted with permission from Ref. [148]. American Chemical Society, 2020.
Lubricants 10 00215 g008
Lubricants 10 00215 g009 550
Figure 9. Superlubricity achieved by self-assembled fluoroalkyl monolayers and graphene surfaces in a water environment. Reprinted with permission from Ref. [149]. American Chemical Society, 2019.
Figure 9. Superlubricity achieved by self-assembled fluoroalkyl monolayers and graphene surfaces in a water environment. Reprinted with permission from Ref. [149]. American Chemical Society, 2019.
Lubricants 10 00215 g009
Table
Table 1. Statistical data of studies related to graphene-family additives in liquid lubrication. Reproduced with permission. [15,139].
Table 1. Statistical data of studies related to graphene-family additives in liquid lubrication. Reproduced with permission. [15,139].
Additive (Fraction),
in Base Liquid		Test ModeSpecimen DetailsTest ParametersResultsLubrication Mechanisms
COF ReductionWear Reduction
GO (0.1 wt%),
in 150 SN		Upper disk on the lower ball,
Rotary		Ball: X45Cr13 steel, 52−54 HRC, Φ8 mm.
Disk: X155CrVMo12-1 steel, 60 HRC, Ra 0.5 μm, Φ105 mm,		0.05−2.1 m/s;
30, 60, 90 N;
25, 50, 80 °C		30%27%Deposited GO protective layer
[140]
Zinc borate/GO composite (2 wt%),
in 500 SN		Four-ball—1200 rpm;
147 N;
Test 2 h		48.2%40%Protective layer
[141]
Cu nanoparticles decorated on polydopamine functionalized GO (0.1 wt%),
in soybean oil		Ball on diskBall: GCr15 steel, Φ9.525 mm, 62 HRC.
Disk: 45#steel		100−500 rpm;
1−12 N;
Test 0.5 h		57%27%Tribolayer
[113]
Modified graphene (0.075 wt%),
in 350 SN		Four-ballGCr15A steel,
Φ12.7 mm, 61 HRC, Test standard: ASTM D4172-82		1200 rpm;
147 N;
75 ± 2 °C;
Test 1 h		37%—Protective layer
[142]
Single layer GO (0.06%),
in water		Ball on three disksBall: Cr alloy steel, Ra 11.1 ± 0.4 nm, 64 HRC.
Disk: AISI304 stainless steel, Ra 37.0 ± 6.2 nm, 92 HRB		50 mm/s;
20 N;
sliding 7.5 m		44.4%17.1%Tribolayer
[73]
Multilayer graphene (0.1 wt%),
in benton grease		Ball on disk, reciprocationBall: AISI52100 steel, Φ10 mm, 710 HV.
Disk: AISI52100, 664 HV		100−500 N;
10−50 Hz;
Test 0.5 h		10.4%25−50%Tribolayer
[143]
Graphene (0.01 wt%),
in PAO4		Ball on diskBall: GCr15 steel, Φ9.525 mm.
Disk: Bronze contained elliptical dimple (area ratios: 0, 5%, 10%, 20%)		5 mm/s;
5 N;
Sliding 8 mm;
25, 60, 100, 150 °C
Test 1.67 h		78%90%Tribolayer and texturing
[36]
CeO2-decorated graphene (0.06 wt%),
in paraffin oil		Reciprocation,
test method: ASTM D6425-05		Ball: GCr15 steel, Φ10 mm, Ra 20 nm, 62 HRC.
Disk: GCr15 steel, 792 HV, Ra: 50 nm		6 cm/s;
15 Hz;
50 N;
17% RH;
Test 0.5 h		52%1.5%Transfer layer and nanoparticle spacer between graphene sheets
[129]
ZrO2/rGO composite (0.06 wt%),
in paraffin oil		Reciprocation,
test method: ASTM D6425-05,		Ball: GCr15 steel, Φ10 mm, Ra 20 nm, 62 HRC.
Disk: GCr15 steel, 790−820 HV, Ra 50 nm		6 cm/s;
50−450 N;
25 ± 5% RH;
Test 0.5 h		56%6.4%Protective layer and ball bearing
[123]
Graphene (23.8−110 μg/mL),
in water		Ball on disk, rotaryBall: GCr15 steel, Φ9.53 mm.
Disk: GCr15 steel		62.8−251.2 mm/s;
2−15 N;
25 ± 5% RH;
Test 0.5 h		81.3%61.8%Fluid adhesive layer and graphene protective layer
[144]
Single layer graphene (1 mg/mL),
in ethanol		Ball on diskBall: 100Cr6 steel, Φ4 mm.
Disk: Iron (99.98% pure) and bronze (98% Cu and 2% Sn), Ra 30 nm		100 mm/s;
1 N;
50% RH		48%—Chemical passivation of iron by graphene
[145]
Silica/GO composite (0.125 wt%),
in EG		Pin on disk,
rotary		Ball: AISI420 steel, Φ12.7 mm.
Disk: AISI52100 steel, Φ40 mm, Ra < 0.1 μm		0.008 m/s;
68.9 N;
50% RH;
Test 1 h		38%31%Tribolayer and ball bearing
[135]
Modified GO,
in oil/water emulsion		Ball on ringBall: bearing steel, Φ25.4 mm, 65 HRC, Ra 30 ± 10 nm.
Ring: AISI52100 steel, 65 HRC, Ra 100 ± 50 nm		20−200 mm/s;
0.5 N;
25 ± 5% RH;
sliding 100 m		18%48%Transfer layer, adsorption layer, and tribolayer; and the lubricity of emulsion droplets [146]
Graphene (0.01 wt%),
in Span-80/PAO4		Ball on disk, reciprocationBall: GCr15 steel, Φ4 mm, 766 HV.
Disk: RTCr2 alloy cast iron, 220 HV, Ra ≤ 0.03 μm		——50% on normal surface, 90% on textured surfacePolishing, self-repairing, and tribolayer [147]
GO (2 mg/mL) in ethylene glycol aqueous solutionBall on disk, rotaryBall: Si3N4, Φ4 mm,
Disk: SiO2		0.1 m/s;
3 N; 10−25% RH		Superlubricity with COF ≈ 0.00499.5% compared to ethylene glycol aqueous solutionAdsorbed GO; low shear stress between GO layers and the interface between GO and ethylene glycol aqueous solution, and the formation of hydrated networks [89]
GO quantum dots (1 mg/mL) in ethylene glycol aqueous solutionBall on disk, rotaryBall: Si3N4, Φ20 mm,
Disk: sapphire		0.1 m/s;
15 N; 10−25% RH		Superlubricity with COF of 0.006890%Formation of tribofilm containing GO quantum dots [93]
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Liu, Y.; Yu, S.; Shi, Q.; Ge, X.; Wang, W. Graphene-Family Lubricant Additives: Recent Developments and Future Perspectives. Lubricants 2022, 10, 215. https://doi.org/10.3390/lubricants10090215

AMA Style

Liu Y, Yu S, Shi Q, Ge X, Wang W. Graphene-Family Lubricant Additives: Recent Developments and Future Perspectives. Lubricants. 2022; 10(9):215. https://doi.org/10.3390/lubricants10090215

Chicago/Turabian Style

Liu, Yanfei, Shengtao Yu, Qiuyu Shi, Xiangyu Ge, and Wenzhong Wang. 2022. "Graphene-Family Lubricant Additives: Recent Developments and Future Perspectives" Lubricants 10, no. 9: 215. https://doi.org/10.3390/lubricants10090215

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop