Graphene has demonstrated great potential in next-generation electronics due to its unique two-dimensional structure and properties including a zero-gap band structure, high electron mobility, and high electrical and thermal conductivity. The integration of atom-thick graphene into a device always involves its interaction with a supporting substrate by van der Waals forces and other intermolecular forces or even covalent bonding, and this is critical to its real applications. Graphene films on different surfaces are expected to exhibit significant differences in their properties, which lead to changes in their morphology, electronic structure, surface chemistry/physics, and surface/interface states. Therefore, a thorough understanding of the surface/interface properties is of great importance. In this review, we describe the major "graphene-on-surface" structures and examine the roles of their properties and related phenomena in governing the overall performance for specific applications including optoelectronics, surface catalysis, anti-friction and superlubricity, and coatings and composites. Finally, perspectives on the opportunities and challenges of graphene-on-surface systems are discussed.

was also recognized. [2] In addition to these forces, one intriguing noncovalent interaction: cation-π interaction, has emerged as an intermolecular force of great significance in chemistry, biology, and materials science. [3] The cation-π interactions basically refers to the interplay between cations and the π electron cloud of an aromatic system. It plays a great role in biological systems for molecular recognition, protein-protein interactions, and the maintenance of macromolecular structures. It also occurs in protein-ligand interactions and protein-DNA complexes. In structural biology, the positively charged amino acids interact with aromatic amino acids, which contribute to the formation of complex protein structures. The amide NHs are in close contact with the aromatic ring of another amino acid in the protein crystal structures. [4] The cation-π interactions are of great importance to protein stability. There is at least one intermolecular cation-π interaction in half of proteins and one third of homodimers, [5] making significant contributions to the tertiary and quaternary protein structures caused by protein folding. In addition, metallic cations, such as Na + , K + , Cu 2+ , Fe 2+ , Ca 2+ , exist in many enzymes. Their interactions with the π systems in protein structures cannot be ignored. In molecular neurobiology, many studies have proved that receptors bind the neurotransmitters through cation-π interactions. [6] The cation-π interaction is electrostatic in nature because the major contributions arise from the electrostatic attractions between cations and the quadrupole moment of the aromatics. [7] As a result, the strength of cation-π interactions can be the strongest among the noncovalent interactions, several times greater than others. It can also be regulated to be weak, depending on the type of cations and the nature of the π system. The adjustability of cation-π interaction offers a potential strategy to modify the neighboring environment where it is involved.Graphene, a 2D carbon network, with carbon atoms jointed together in a hexagonal honeycomb matrix, can be taken as a novel aromatic macromolecule from certain points of view. The unique structure endows it with excellent physicochemical, electronic, optical, thermal, and mechanical properties, leading to its potential applications in broad fields. [8] The interplay between cations and the delocalized polarizable π electrons of graphene, would alter the intrinsic characteristics of graphene-based structures and impart influences on the performance of graphene-based devices.Cation-π interactions are common in nature, especially in organisms. Their profound influences in chemistry, physics, and biology have been continuously investigated since they were discovered in 1981. However, the importance of cation-π interactions in materials science, regarding carbonaceous nanomaterials, has just been realized. The interplay between cations and delocalized polarizable π electrons of graphene would bring about significant changes to the intrinsic...

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Graphene oxide (GO) has been demonstrated as the most promising candidate for surface modification of polymer separation membranes for durable filtration applications. However, the adhesion between GO coating and polymer substrate, as the most essential issue for reliable applications, has been little explored. Herein, we developed a facile high-pressure assisted deposition method to physically anchor GO sheets on microfiltration (MF) and reverse osmosis (RO) membranes, and established a tape test procedure for assessing the adhesion of GO coating to polymer substrates based on the ASTM D3359. Through regulating the GO sources and coating process, we demonstrated that the adhesion depends sensitively on the GO flake size and deposition pressure, whereas the adhesion level dramatically improved from 0B to 5B, with decrease in the lateral size of GO and increase in the coating deposition pressure. The strong GO coatings showed evidently higher water flux than that of weak counterparts. The underlying mechanism was further analyzed and verified. Nanosize of GO and high deposition pressure favor the formation of the conformal morphologies of GO coatings on both MF and RO membranes, which allow strong interfacial van der Waals interaction because of the large contact areas and result in the strong GO coatings on membranes. These results potentially open up a versatile pathway to develop the strong graphene-based coatings on separation membranes.

strategy to produce fresh water from seawater and polluted water, without generating harmful by-products. [3] Among them, thin-film composite nanofiltration (TFC NF) membranes are an important component. They can produce higher water flux with lower energy consumption compared with reverse osmosis membranes. They are efficient in removal of both conventional and emerging contaminants from water. In addition, the higher rejection of divalent ions compared with monovalent ones makes them promising in the application of water softening. [4][5][6] Generally TFC NF membranes are prepared through the interfacial polymerization (IP) method, forming a structure of an ultrathin polyamide (PA) selective layer on the surface of a porous substrate. The structure and physiochemical properties of the PA selective layer and the underlying substrate can be individually modified to improve the overall membrane performance. [7] However, the trade-off between water permeability and salt rejection, a so-called "upper bound" relation, is one of the key problems faced by TFC membranes. [8][9][10] It is highly desirable that we can fabricate TFC PA NF membranes with improved water permeability and salt/dye rejection for promoting both energy effectiveness and water quality.Incorporating hydrophilic nanoparticles (NPs), such as TiO 2 , [11] SiO 2 , [12,13] Al 2 O 3 , [14] Ag, [15] nanozeolite, [16,17] and graphene oxide quantum dots (GO QDs), [18] into the top PA selective layer to form thin-film nanocomposite (TFN) membranes has been demonstrated as an effective strategy to improve the water permeability of membranes. The improvement is resulted from the increased membrane hydrophilicity and additional water pathways introduced by the NPs. However, NPs tend to interfere the IP process of the PA selective layer, leading to undesired changes in pore structure, thickness, and surface roughness of membranes. [19,20] Besides, the incompatibility between inorganic NPs and the organic polymer matrix results in microporous defects. [21,22] Both of them account for the decrease in membrane salt rejection. Additionally, NPs are mainly embedded inside the polymer matrix, so that they are not effectively available for surface-based interactions.A physically bound coating of graphene oxide quantum dots (GO QDs) on thin-film composite polyamide nanofiltration (NF) membranes is prepared through a pressure-assisted filtration method to simultaneously improve the membranes' water permeability and salt/dye rejection. It is the first attempt to use carbon-based nanoparticles as surface coating to improve the efficiency of water filtration membranes. Influences of the GO QDs' coating on the hydrophilicity and surface charge of the membranes are investigated by water contact angle and zeta potential measurements. With the GO QDs' coating, the surface roughness and hydrophilicity of the membranes increase, and the membrane surface becomes more negatively charged. Water permeability and salt/dye rejection of GO QD-coated NF membranes increase simultaneously ...

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Graphene oxide (GO) has shown enormous potential in applications for improving crop yield and soil cultivation quality. However, in heavy metal contaminated soil, the effect of GO on heavy metals and the indirect toxicity of GO to plants remain unclear. In this work, we reveal the GO-promoted cadmium (Cd) uptake by rice in a Cd-contaminated soil system. The oxygen-rich functional groups and the large specific surface area of monolayer GO result in strong Cd­(II) adsorption (with a maximum adsorption capacity of 265.8 mg/g), which significantly change the existing forms of Cd­(II) in the soil. In particular, GO converts the inorganic-bound form Cd­(II) that is not readily absorbed by plants into the exchangeable form that is more available for plant absorption. As a result, Cd­(II) content in rice seedlings is increased by 12.5% with the application of GO. Therefore, it can be concluded that GO exhibited indirect toxicity to plants in heavy metal-enriched soil.

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