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Herein, organic–inorganic hybrid sulfur-containing carbon nanospheres (SCNs) were successfully prepared by one-pot chemical oxidation polymerization of a thiophene monomer and then rigorous carbonization. On account of the good structural strength and organic phase derived from the precursor polythiophene, the as-prepared SCNs manifested remarkable oil-dispersing and tribological properties as lubricant nanoadditives. Subsequently, the friction mechanism of SCNs was deduced; the as-prepared SCNs had the capacity to take the shape of a strong protective film on the surface of friction pairs by intricate physical deposition and tribochemical reaction. So, the SCNs exhibited excellent tribological performance, including a high extreme pressure (950 N), an ultralow friction coefficient of less than 0.06, and a significant reduction in abrasion by 90%. [ABSTRACT FROM AUTHOR]

Thiadiazole compounds and their derivatives have good carrying capacity and lubricating properties. Herein, polydopamine can be in situ self-assembled onto gallium-based liquid metal (GLM) nanoparticles via ultrasound treatment of bulk GLM nanoparticles in dopamine-containing Tris aqueous solution followed by covalent bonding with a thiadiazole dimer (DMCT) through Michael addition reactions. The as-prepared thiadiazole dimer-functionalized liquid metal (GLM-DMCT) nanoparticles, with an average particle size of 380 nm, can be used as nanoadditives in the base oil (500SN). The tribological properties of GLM-DMCT as additives were evaluated under various loads, temperatures, and frequencies, and the results showed that GLM-DMCT additives have improved anti-friction and anti-wear performances of 500SN. The coefficient of friction can be reduced to 0.092 from 0.147 after adding 2 wt % GLM-DMCT, the wear volume reduces by 89.7%, and the load-carrying capacity is increased from 150 to 1050 N. The improved tribological performance is credited to the formation of a stable, protective layer on the friction pair via the complex tribo-chemical reaction of Ga, In, and S elements of GLM-DMCT. Furthermore, the as-prepared GLM-DMCT exhibits good anti-corrosion performance, which is attributed to the breaking of the disulfide bond of DMCT, releasing the corrosion inhibitor DMTD during the corrosion process. [ABSTRACT FROM AUTHOR]

Surface modification can be used as an effective tool for designing functionalized 2D nanomaterial-based lubricant additives with desirable properties. In this paper, Ti3C2Tx-based nanoadditives are prepared via surface modification with a tannic acid (TA)–Fe3+ complex and then by introducing commercial lubricating additive dialkyl dithiophosphate (DDP) via Michael addition. TA and FeCl3 solutions are used to form a TA–metal complex as the adhesion layer to anchor Ti3C2Tx nanosheets and then modification with a commercial lubricating additive DDP molecule via Michael addition, resulting in the formation of DDP-functionalized MXene nanosheets (DDP-Ti3C2Tx). The experimental results show that the dispersive stability of the as-prepared DDP-Ti3C2Tx in 500SN base oil is greatly improved for more than 1 week. Furthermore, the tribological properties of the DDP-Ti3C2Tx nanosheet additive are evaluated. The results show that the as-prepared DDP-Ti3C2Tx exhibits significant anti-wear and friction reduction abilities with a low coefficient of friction not exceeding 0.11, reduction in the corresponding wear volume by about 87%, and a high load-carrying capacity up to 500 N as a lubricating additive. The tribological properties may be attributable to the good dispersion and the shape of the small sheet, which ensure their entry into the contact area of the friction pair and the formation of a continuous chemical protective film that prevents direct contact and seizure. [ABSTRACT FROM AUTHOR]

The exceptional semiconducting properties of two-dimensional (2D) transition metal dichalcogenides (TMDs) have made them highly promising for the development of future electronic and optoelectronic devices. Extensive studies of TMDs are partly associated with their ability to generate 2D-confined hot carriers above the conduction band edges, enabling potential applications that rely on such transient excited states. In this work, room-temperature spatiotemporal hot carrier dynamics in monolayer MoS 2 is studied by transient absorption microscopy (TAM), featuring an initial ultrafast expansion followed by a rapid negative diffusion, and ultimately a slow long-term expansion of the band edge C-excitons. We provide direct experimental evidence to identify the abnormal negative diffusion process as a spatial contraction of the hot carriers resulting from spatial variation in the hot phonon bottleneck effect due to the Gaussian intensity distribution of the pump laser beam.

The dispersion stability of nanomaterials in lubricants significantly influences tribological performance, yet their addition as lubricant additives often presents challenges in secondary dispersion. Here, we present a straightforward method for in situ preparation of N,S-codoped CDs (N,S-CDs)-based lubricants using heterocyclic aromatic hydrocarbons containing N/S elements in poly(ethylene glycol) (PEG) base oil by a directional ultrasound strategy. Two types of N,S-CDs were successfully prepared via the directional ultrasound treatment of PEG with benzothiazole (BTA) and benzothiadiazole (BTH) separately. The resultant N,S-CDs have a uniform distribution of N and S elements and maintain good colloidal dispersion stability in PEG even after 9 months of storage. The N,S-CDs can enter the surface gap of the friction pairs and then induce a tribochemical reaction. Benefiting from the synergistic effect of N and S activating elements, a robust and stable protective film consisting of iron sulfides, iron oxides, carbon nitrides, and amorphous carbonaceous compounds is formed, thus endowing N,S-CDs-based lubricants with improved antiwear and friction-reducing performance. Compared with pure PEG, the coefficient of friction (COF) of the N,S-CDs(BTH)-based lubricant decreased to 0.108 from 0.292, accompanied by a 91.2% reduction in wear volume, and the maximum load carrying capacity increased to 450 from 150 N.

Vertical van der Waals heterostructures composed of graphene (Gr) and transition metal dichalcogenides (TMDs) have created a fascinating platform for exploring optical and electronic properties in the two-dimensional limit. Numerous studies have focused on Gr/TMDs heterostructures to elucidate the underlying mechanisms of charge-energy transfer, quasiparticle formation, and relaxation following optical excitation. Nevertheless, a comprehensive understanding of interfacial charge separation and subsequent dynamics in graphene-based heterostructures remains elusive. Here, we have investigated the carrier dynamics of Gr-MoS 2 heterostructures (including Gr/MoS 2 and MoS 2 /Gr stacking sequences) grown on a fused silica substrate under varying photoexcitation energies by comprehensive ultrafast means, including time-resolved terahertz (THz) spectroscopy, THz emission spectroscopy, and transient absorption spectroscopy. Our findings highlight the impact of the substrate electric field on the efficiency of modulating the interfacial charge transfer (CT). Specifically, the optical excitation in Gr/MoS 2 generates thermal electron injection from the graphene layer into the MoS 2 layer with photon energy well below A-exciton of MoS 2 , whereas the interfacial CT in the MoS 2 /Gr is blocked by the electric field of the substrate. In turn, photoexcitation of the A exciton above leads to hole transfer from MoS 2 to graphene, which occurs for both Gr-MoS 2 heterostructures with opposite stacking orders, resulting in the opposite orientations of the interfacial photocurrent, as directly demonstrated by the out-of-phase THz emission. Moreover, we demonstrate that the recombination time of interfacial exciton is approximately ∼18 ps, whereas the defect-assisted interfacial recombination occurs on a time scale of ∼ns. This study provides valuable insights into the interplay between interfacial CT, substrate effects, and defect engineering in Gr-TMDs heterostructures, thereby facilitating the development of next-generation optoelectronic devices.

Low interlaminar shear stress, high mechanical strength, and tunable structure make Ti 3 C 2 T x MXene a burgeoning star as solid lubricants and lubricant additives. Although surface modification strategy can improve its compatibility with base oils, it will eventually settle due to gravity. Additionally, base oils are prone to leakage, creep, and volatilization, which limit their application. To address these issues, supramolecular gels with surface-modified Ti 3 C 2 T x were conceived. Apart from the lubrication effect, the high thermal conductivity of Ti 3 C 2 T x MXene accelerated the phase transition rate of supramolecular gels. The thermal-reversible and creep-resistant properties distinguish them from other conventional lubricants. The tribological tests showed that the 500 solvent neutral (SN) supramolecular gel with 0.10 wt % Ti 3 C 2 T x -octadecylphosphonic acid (Ti 3 C 2 T x -ODPA) reduced the coefficient of friction (COF) by 46.32% and wear volume by 81.18% compared with pure 500SN oil. Moreover, they also performed well in load-carrying capacity, temperature tolerance, and speed adaptability. This work puts forward a new approach to prepare MXene-based lubricants tailored for some severe lubrication conditions. These exceptional features enable their application in rolling bearings, some gears, and other low maintenance mechanisms.

Heterostructures constructed from graphene and transition metal dichalcogenides (TMDs) have established a new platform for optoelectronic applications. After a large number of studies, one intriguing debate is the existence of the interfacial exciton in graphene/TMDs. Hereby, by combined optical pump-terahertz probe spectroscopy and transient absorption spectroscopy, we report the observation of the interfacial exciton in graphene/MoS 2 heterostructure. With the photon energy well below the band gap of monolayer MoS 2 , the hot electrons of graphene are transferred to MoS 2 within 0.5 ps; subsequently, the relaxation of the holes in graphene and electrons in MoS 2 shows an identical time scale of 15-18 ps, which manifests the formation and relaxation of the interfacial exciton in the heterostructure following photoexcitation. Moreover, a model of the carrier heating and photogating effect in graphene is proposed to estimate the amount of transferred charge, which agrees well with the experimental results. Our study provides insights into the dynamics of graphene-based heterostructure interfacial non-equilibrium carriers.

Inspired by Namib Desert beetle and leaf venation, a wettability-integrated system consisting of wettability-hybrid coatings and venation-like patterns was designed and successfully fabricated via a simple, low-cost, and eco-friendly route. The as-prepared surface can construct a 3D topography with a water layer and efficiently drain through the venation-like patterns. The combination of multiple mechanisms enhances the fog harvesting ability significantly. Meanwhile, the synergistic mechanisms of fog harvesting enhancement by a wettability-integrated surface were further studied and discussed.

In the field of space mechanical lubrication, to improve the reliability and life of space lubrication, solid lubricating film-liquid lubricant composite lubrication has been used in recent years. This lubrication method can improve the durability of sliding friction mating surfaces, reduce equipment wear, and extend the service life of motion mechanisms. However, due to unstable factors such as volatilization and creeping of liquid lubricants in microgravity and ultra-high-vacuum environments, the solid lubricating film wears out after long-term use and produces wear debris and other unfavorable factors. To solve the above problems, this study proposes a novel composite lubrication system constituting a MoS 2 film in combination with a supramolecular gel. The tribological performance of this lubrication system establishes an extended service life with a lower wear rate compared to the MoS 2 film, regardless of functioning in vacuum or atmospheric conditions. More importantly, the results of the irradiation experiment demonstrate that MoS 2 -gel exhibits better anticreep performance as compared to MoS 2 -oil when exposed to atomic oxygen and ultraviolet light for 4 h. The analysis of this composite lubrication mechanism also reveals the formation of a continuous transfer film on the surface of the friction pairs by virtue of the outstanding synergistic effect between the MoS 2 film and the gel. MoS 2 debris is present in the gel as an additive, and the gel is capable of replenishing automatically once the MoS 2 film is depleted. Moreover, the strong anticreep properties of the gel are attributable to the multialkylated cyclopentane oil being trapped by the intricate reassembling of the gelator network. It is firmly believed that this novel MoS 2 -gel composite lubrication system may have good prospective applications in space and special machinery domains.