Superlubricity of graphite and graphene has aroused increasing interest in recent years. Yet how to obtain a long-lasting superlubricity between graphene layers, under high applied normal load in ambient atmosphere still remains a challenge but is highly desirable. Here, we report a direct measurement of sliding friction between graphene and graphene, and graphene and hexagonal boron nitride (h-BN) under high contact pressures by employing graphene-coated microsphere (GMS) probe prepared by metal-catalyst-free chemical vapour deposition. The exceptionally low and robust friction coefficient of 0.003 is accomplished under local asperity contact pressure up to 1 GPa, at arbitrary relative surface rotation angles, which is insensitive to relative humidity up to 51% RH. This ultralow friction is attributed to the sustainable overall incommensurability due to the multi-asperity contact covered with randomly oriented graphene nanograins. This realization of microscale superlubricity can be extended to the sliding between a variety of two-dimensional (2D) layers.

Natural vascular plants leaves rely on differences in osmotic pressure, transpiration and guttation to produce tons of clean water, powered by sunlight. Inspired by this, we report a sunlight-driven purifier for high-efficiency water purification and production. This sunlight-driven purifier is characterized by a negative temperature response poly(N-isopropylacrylamide) hydrogel (PN) anchored onto a superhydrophilic melamine foam skeleton, and a layer of PNIPAm modified graphene (PG) filter membrane coated outside. Molecular dynamics simulation and experimental results show that the superhydrophilicity of the relatively rigid melamine skeleton significantly accelerates the swelling/deswelling rate of the PNPG-F purifier. Under one sun, this rational engineered structure offers a collection of 4.2 kg m⁻² h⁻¹ and an ionic rejection of > 99% for a single PNPG-F from brine feed via the cooperation of transpiration and guttation. We envision that such a high-efficiency sunlight driven system could have great potential applications in diverse water treatments.

The relationship between a low interlayer lateral force constant and ultrasmall potential energy corrugation in a graphene/MoS₂ heterostructure provides another viewpoint to the origin of superlubricity.

Two-dimensional (2D) materials possess outstanding lubrication property with their thicknesses down to a few atomic layers, but they are easily susceptible to sliding induced degradation or ubiquitous chemical modification. Maintaining the superior lubricating performance of 2D materials in a harsh working environment is highly desirable yet grandly challenging. Here we show that by proper alignment of graphene on a Ge(111) substrate, friction of graphene could be well preserved at an ultra-low level even after fluorination or oxidation. This behaviour is experimentally found to be closely related to the suppression of molecular-level deformation of graphene within the moiré superlattice structure. Atomistic simulations reveal that the formation of an interconnected meshwork with enhanced interfacial charge density imposes a strong anchoring effect on graphene even under chemical modification. Modulating molecular-level deformation by interfacial confinements may offer a unique strategy for tuning the mechanical or even chemical properties of 2D materials.

Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials.