Unveiling the power of MXenes: Solid lubrication perspectives and future directions

The interaction between two surfaces leads to the generation of friction and wear of material. Friction and wear are some of the major challenges that may readily be overcome by the third part of tribology called lubrication. Utilizing solid lubricants including polymers, carbon-based materials, soft metals, transition metal dichalcogenides, along with their potential benefits and drawbacks in dry environments can reduce friction. Recently, an emerging class of two-dimensional (2D) transition metal nitrides, carbides or carbonitrides commonly known as MXenes have emerged as an attractive alternative for solid lubrication because of their ability to establish wear-resistant tribo layers and well as low friction and shear strength. Furthermore, the inherent hydrophilic nature of these substances has led to limited dispersion stability and phase compatibility when combined with pure base oils. As a result, their potential use as solid lubricants and lubricant additives has been impeded. To address this issue and enhance the applicability of MXenes as solid lubricants, their surface modification can be an attractive tool. Therefore, this review provides a succinct summary of the current state-of-the-art in surface functionalization of MXenes, a subject that has not yet been thoroughly addressed. Further, the mechanical behavior of MXenes and composites has been discussed, followed by the potential of MXenes as a solid lubricant at micro- and macro-scale. Finally, the existing opportunities and challenges of the research area have been discussed with possible future research directions. We believe, this article will be a valuable resource for MXenes and opens the door to improve the chemical, physical and mechanical properties of MXenes in various applications, such as solid lubrication.

Electrochemical Biosensor for Detection of the CYP2C19*2 Allele Based on Exonuclease Ⅲ

Currently, the therapeutic effect of clopidogrel differs considerably among individuals and is thought to be closely related to the genetic polymorphism of CYP2C19. The CYP2C19*2 gene can reduce the antiplatelet aggregation effect of clopidogrel, which increases the risk of major cardiovascular adverse events in patients. In this research, we report a new type of biosensor for the highly sensitive detection of the CYP2C19*2 gene based on exonuclease III assisted electric signal amplification and the use of calixarene to enrich electrical signal substances. Specifically, under the best conditions, the logarithmic concentrations of the analytes have a good linear relationship with the peak current in the range of 0.01 fM to 100 pM and the detection limit is 13.49 aM. The results have also shown that this method has good selectivity, high sensitivity, and stability, etc., and will provide a very promising application for the detection of the CYP2C19*2 gene and other biological molecules by replacing corresponding nucleic acid sequences.

MXenes Functionalized with Macrocyclic Hosts: From Molecular Design to Applications

Two-dimensional (2D) MXene has aroused wide attention for its excellent physical and chemical properties. The interlayer engineering formed by layer-by-layer stacking of MXene nanosheets can be employed for molecular sieving and water purification by incorporating specific groups onto the exterior surface of MXene. Macrocyclic hosts exhibiting unique structural features and recognition ability can construct smart devices for external stimuli with reversible features between macrocycles and guests. On that basis, macrocyclic hosts can be anchored to MXene to provide numerous insights into their compositions and intercalation states. In this review, the MXene prepared based on macrocyclic hosts from molecular design to applications is highlighted. Various MXenes functionalized with macrocyclic hosts are empowered in functional membrane (including water purification, organic solvent nanofiltration, and electromagnetic shielding), photocatalysis, sensing, and adsorption (interactions with specific guest). Hopefully, this review can bring new inspiration to the design of multifunctional MXene-based materials and improving its practical applications.

Advances in Studies of Boron Nitride Nanosheets and Nanocomposites for Thermal Transport and Related Applications

Hexagonal boron nitride (h-BN) and exfoliated nanosheets (BNNs) not only resemble their carbon counterparts graphite and graphene nanosheets in structural configurations and many excellent materials characteristics, especially the ultra-high thermal conductivity, but also offer other unique properties such as being electrically insulating and extreme chemical stability and oxidation resistance even at elevated temperatures. In fact, BNNs as a special class of 2-D nanomaterials have been widely pursued for technological applications that are beyond the reach of their carbon counterparts. Highlighted in this article are significant recent advances in the development of more effective and efficient exfoliation techniques for high-quality BNNs, the understanding of their characteristic properties, and the use of BNNs in polymeric nanocomposites for thermally conductive yet electrically insulating materials and systems. Major challenges and opportunities for further advances in the relevant research field are also discussed.

Dispersant-assisted liquid-phase exfoliation of 2D materials beyond graphene

The extensive research on liquid-phase exfoliation (LPE) performed in the last 10 years has enabled a low cost and mass scalable approach to the successful production of a range of solution-processed 2-dimensional (2D) materials suitable for many applications, from composites to energy storage and printed electronics. However, direct LPE requires the use of specific solvents, which are typically toxic and expensive. Dispersant-assisted LPE allows us to overcome this problem by enabling production of solution processed 2D materials in a wider range of solvents, including water. This approach is based on the inclusion of an additive, typically an amphiphilic molecule, designed to interact with both the nanosheet and the solvent, enabling exfoliation and stabilization at the same time. This method has been extensively used for the LPE of graphene and has been discussed in many reviews, whilst little attention has been given to dispersant-assisted LPE of 2D materials beyond graphene. Considering the increasing number of 2D materials and their potential in many applications, from nanomedicine to energy storage and catalysis, this review focuses on the dispersant-assisted LPE of transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN) and less studied 2D materials. We first provide an introduction to the fundamentals of LPE and the type of dispersants that have been used for the production of graphene, we then discuss each class of 2D material, providing an overview on the concentration and properties of the nanosheets obtained. Finally, a perspective is given on some of the challenges that need to be addressed in this field of research.

Calixarene-mediated assembly of water-soluble C60-attached ultrathin graphite hybrids for efficient activation of reactive oxygen species to treat neuroblastoma cells

Unprecedented nano-carbon hybrids consisting of exfoliated ultrathin graphite (or single-walled carbon nanotubes) with pristine C₆₀ molecules attached on the surfaces have been produced in water in the presence of p-phosphonic acid calix[8]arene. The amphiphilic calixarene plays multiple roles in these processes to provide water dispersibility and π-π interactions with flexible conformations complementing curvatures of the carbon surfaces. The significantly increased water solubility and area of exposure of C₆₀ enable efficient activation of reactive oxygen species for enhanced phototoxicity to SH-SY5Y human neuroblastoma cell line under laser irradiation.

Exfoliation of 2D Materials for Energy and Environmental Applications

The fascinating properties of single-layer graphene isolated by mechanical exfoliation have inspired extensive research efforts toward two-dimensional (2D) materials. Layered compounds serve as precursors for atomically thin 2D materials (briefly, 2D nanomaterials) owing to their strong intraplane chemical bonding but weak interplane van der Waals interactions. There are newly emerging 2D materials beyond graphene, and it is becoming increasingly important to develop cost-effective, scalable methods for producing 2D nanomaterials with controlled microstructures and properties. The variety of developed synthetic techniques can be categorized into two classes: bottom-up and top-down approaches. Of top-down approaches, the exfoliation of bulk 2D materials into single or few layers is the most common. This review highlights chemical and physical exfoliation methods that allow for the production of 2D nanomaterials in large quantities. In addition, remarkable examples of utilizing exfoliated 2D nanomaterials in energy and environmental applications are introduced.

A novel fluorescence assay for resveratrol determination in red wine based on competitive host-guest recognition

A label-free fluorescence assay for resveratrol determination is presented for the first time. The approach was based on fluorescence resonance energy transfer (FRET), via competitive supramolecular recognition, between p-sulfonated calix[6]arene (CX6)-modified reduced graphene oxide (CX6@RGO) and a probe-resveratrol complex. The probe molecule (Rhodamine B or rhodamine 123) had a strong fluorescence signal, and its fluorescence was quenched by CX6@RGO, based on FRET. When the target molecule was added to CX6@RGO, the probe molecule was displaced by resveratrol, and a host-guest complex, CX6@RGO-resveratrol formed, turning-on the fluorescence signal. Fluorescence intensity of the CX6@RGO-probe complex increased linearly with increased resveratrol concentrations (2.0-40.0 μM). The proposed approach was used to determine resveratrol in red wine with satisfactory detection limits and recoveries. Compared with traditional determination methods, our procedure is advantageous because it saves time, is easy to operate, and does not require sample pretreatment.

p-Phosphonic acid calix[8]arene mediated synthesis of ultra-large, ultra-thin, single-crystal gold nanoplatelets

Large, ultrathin, single-crystal gold platelets are produced in the presence of p-phosphonic acid calix[8]arene as both a catalyst and stabiliser.

The Effect of Agglomeration Reduction on the Tribological Behavior of WS2 and MoS2 Nanoparticle Additives in the Boundary Lubrication Regime

This study investigates the impact of different surfactants and dispersion techniques on the friction and wear behavior of WS2 and MoS2 nanoparticles additives in a Polyalphaolefin (PAO) base oil under boundary lubrication conditions. The nanoparticles were dispersed using Oleic acid (OA) and Polyvinylpyrrolidone (PVP) to investigate their impact on particle agglomeration. The size distribution of the dispersed nanoparticles in PAO was measured by dynamic light scattering. The nanoparticles treated using PVP resulted in the most stable particle size. Friction studies showed that nanoparticle agglomeration reduction and the homogeneity of the suspension did not significantly impact the friction reduction behavior of the lubricant. Reciprocating wear experiments showed that, for our test conditions, both WS2 and MoS2 nano additives exhibited maximum wear depth reduction (45%) when using the PVP surface treatment compared to base oil. The wear results confirmed the significance of minimizing agglomeration and promoting high dispersion in promoting favorable wear resistance under boundary lubricant conditions. Analysis of the wear surfaces showed that a tribofilm formation was the primary wear reduction mechanism for WS2 particles treated by PVP while, in the case of MoS2 treated by PVP, the mechanism was load sharing via particles rolling and/or sliding at the interface.

Molecular chemistry approaches for tuning the properties of two-dimensional transition metal dichalcogenides

Two-dimensional (2D) semiconductors, such as ultrathin layers of transition metal dichalcogenides (TMDs), offer a unique combination of electronic, optical and mechanical properties, and hold potential to enable a host of new device applications spanning from flexible/wearable (opto)electronics to energy-harvesting and sensing technologies. A critical requirement for developing practical and reliable electronic devices based on semiconducting TMDs consists in achieving a full control over their charge-carrier polarity and doping. Inconveniently, such a challenging task cannot be accomplished by means of well-established doping techniques (e.g. ion implantation and diffusion), which unavoidably damage the 2D crystals resulting in degraded device performances. Nowadays, a number of alternatives are being investigated, including various (supra)molecular chemistry approaches relying on the combination of 2D semiconductors with electroactive donor/acceptor molecules. As yet, a large variety of molecular systems have been utilized for functionalizing 2D TMDs via both covalent and non-covalent interactions. Such research endeavours enabled not only the tuning of the charge-carrier doping but also the engineering of the optical, electronic, magnetic, thermal and sensing properties of semiconducting TMDs for specific device applications. Here, we will review the most enlightening recent advancements in experimental (supra)molecular chemistry methods for tailoring the properties of atomically-thin TMDs - in the form of substrate-supported or solution-dispersed nanosheets - and we will discuss the opportunities and the challenges towards the realization of novel hybrid materials and devices based on 2D semiconductors and molecular systems.

Scalable exfoliation and dispersion of two-dimensional materials - an update

The preparation of dispersions of single- and few-sheet 2D materials in various solvents, as well as the characterization methods applied to such dispersions, is critically reviewed. Motivating factors for producing single- and few-sheet dispersions of 2D materials in liquids are briefly discussed. Many practical applications are expected for such materials that do not require high purity formulations and tight control of donor and acceptor concentrations, as required in conventional Fab processing of semiconductor chips. Approaches and challenges encountered in exfoliating 2D materials in liquids are reviewed. Ultrasonication, mechanical shearing, and electrochemical processing approaches are discussed, and their respective limitations and promising features are critiqued. Supercritical and more conventional liquid and solvent processing are then discussed in detail. The effects of various types of stabilizers, including surfactants and other amphiphiles, as well as polymers, including homopolymeric electrolytes, nonionic polymers, and nanolatexes, are discussed. Consideration of apparent successes of stabilizer-free dispersions indicates that extensive exfoliation in the absence of dispersing aids results from processing-induced surface modifications that promote stabilization of 2D material/solvent interactions. Also apparent paradoxes in "pristineness" and optical extinctions in dispersions suggest that there is much we do not yet quantitatively understand about the surface chemistry of these materials. Another paradox, emanating from modeling dilute solvent-only exfoliation by sonication using polar components of solubility parameters and surface tension for pristine graphene with no polar structural component, is addressed. This apparent paradox appears to be resolved by realizing that the reactivity of graphene to addition reactions of solvent radicals produced by sonolysis is accompanied by unintended polar surface modifications that promote attractive interactions with solvent. This hypothesis serves to define important theoretical and experimental studies that are needed. We conclude that the greatest promise for high volume and high concentration processing lies in applying methods that have not yet been extensively reported, particularly wet comminution processing using small grinding media of various types.

Colloidal 2D nanosheets of MoS2 and other transition metal dichalcogenides through liquid-phase exfoliation

This review focuses on the exfoliation of transition metal dichalcogenides MQ₂ (TMD, M=Mo, W, etc., Q=S, Se, Te) in liquid media, leading to the formation of 2D nanosheets dispersed in colloids. Nowadays, colloidal dispersions of MoS₂, MoSe₂, WS₂ and other related materials are considered for a wide range of applications, including electronic and optoelectronic devices, energy storage and conversion, sensors for gases, catalysts and catalyst supports, biomedicine, etc. We address various methods developed so far for transferring these materials from bulk to nanoscale thickness, and discuss their stabilization and factors influencing it. Long-time known exfoliation through Li intercalation has received renewed attention in recent years, and is recognized as a method yielding highest dispersed concentrations of single-layer MoS₂ and related materials. Latest trends in the intercalation/exfoliation approach include electrochemical lithium intercalation, experimenting with various intercalating agents, multi-step intercalation, etc. On the other hand, direct sonication in solvents is a much simpler technique that allows one to avoid dangerous reagents, long reaction times and purifying steps. The influence of the solvent characteristics on the colloid formation was closely investigated in numerous recent studies. Moreover, it is being recognized that, besides solvent properties, sonication parameters and solvent transformations may affect the process in a crucial way. The latest data on the interaction of MoS₂ with solvents evidence that not only solution thermodynamics should be employed to understand the formation and stabilization of such colloids, but also general and organic chemistry. It appears that due to the sonolysis of the solvents and cutting of the MoS₂ layers in various directions, the reactive edges of the colloidal nanosheets may bear various functionalities, which participate in their stabilization in the colloidal state. In most cases, direct exfoliation of MQ₂ into colloidal nanosheets is conducted in organic solvents, while a small amount of works report low-concentrated colloids in pure water. To improve the dispersion abilities of transition metal dichalcogenides in water, various stabilizers are often introduced into the reaction media, and their interactions with nanosheets play an important role in the stabilization of the dispersions. Surfactants, polymers and biomolecules usually interact with transition metal dichalcogenide nanosheets through non-covalent mechanisms, similarly to the cases of graphene and carbon nanotubes. Finally, we survey covalent chemical modification of colloidal MQ₂ nanosheets, a special and different approach, consisting in the functionalization of MQ₂ surfaces with help of thiol chemistry, interaction with electrophiles, or formation of inorganic coordination complexes. The intentional design of surface chemistry of the nanosheets is a very promising way to control their solubility, compatibility with other moieties and incorporation into hybrid structures. Although the scope of the present review is limited to transition metal dichalcogenides, the dispersion in colloids of other chalcogenides (such as NbS₃, VS₄, Mo₂S₃, etc.) in many ways follows similar trends. We conclude the review by discussing current challenges in the area of exfoliation of MoS₂ and its related materials.

Enhanced Superhydrophobic Performance of BN-MoS2 Heterostructure Prepared via a Rapid, One-Pot Supercritical Fluid Processing

Fabrication of highly crystalline BN-MoS₂ heterostructure with >95% yield was demonstrated using one-pot supercritical fluid processing within 30 min. The existence of 20-50 layers of BN-MoS₂ in the prepared heterostructure was confirmed by AFM analysis. The HR-TEM imaging and mapping analysis revealed the well-melded BN and MoS₂ nanosheets in the heterostructure. The drastic reduction in XRD line intensities corresponding to the (002) plane and broadening of the peaks for the BN system over MoS₂ indicated the effective exfoliation and lateral size reduction in BN nanosheets during SCF processing. Also, the exfoliated MoS₂ nanosheets are preferentially exposed rather than BN nanosheets; consequently, the MoS₂ nanosheets sturdily covered BN nanosheets in the heterostructure. The exfoliated BN and MoS₂ nanosheets with nanoscale roughness make the surface highly hydrophobic in nature. As a result, the BN-MoS₂ heterostructure showed superior superhydrophobic performance with high water contact angle of 165.9°, which is much higher than the value reported in the literature.

Aqueous Exfoliation of Transition Metal Dichalcogenides Assisted by DNA/RNA Nucleotides: Catalytically Active and Biocompatible Nanosheets Stabilized by Acid-Base Interactions

The exfoliation and colloidal stabilization of layered transition metal dichalcogenides (TMDs) in an aqueous medium using functional biomolecules as dispersing agents have a number of potential benefits toward the production and practical use of the corresponding two-dimensional materials, but such a strategy has so far remained underexplored. Here, we report that DNA and RNA nucleotides are highly efficient dispersants in the preparation of stable aqueous suspensions of MoS₂ and other TMD nanosheets at significant concentrations (up to 5-10 mg mL^-1). Unlike the case of common surfactants, for which adsorption on 2D materials is generally based on weak dispersive forces, the exceptional colloidal stability of the TMD flakes was shown to rely on the presence of relatively strong, specific interactions of Lewis acid-base type between the DNA/RNA nucleotide molecules and the flakes. Moreover, the nucleotide-stabilized MoS₂ nanosheets were shown to be efficient catalysts in the reduction of nitroarenes (4-nitrophenol and 4-nitroaniline), thus constituting an attractive alternative to the use of expensive heterogeneous catalysts based on noble metals, and exhibited an electrocatalytic activity toward the hydrogen evolution reaction that was not impaired by the possible presence of nucleotide molecules adsorbed on their active sites. The biocompatibility of these materials was also demonstrated on the basis of cell proliferation and viability assays. Overall, the present work opens new vistas on the colloidal stabilization of 2D materials based on specific interactions that could be useful toward different practical applications.

p-Phosphonated Calix[n]arene Stabilizes Superparamagnetic Nanoparticles for Nitrate and Phosphate Uptake

Highly faceted superparamagnetic magnetite nanoparticles roughly 11 nm in diameter are readily accessible in the presence of p-phosphonated calix[n]arenes of different ring sizes (n=4, 5 and 6), through the use of a simple co-precipitation technique. In contrast, the larger calix[8]arene affords spherical particles of comparable size. The maximum magnetization is 70-60 emu g^-1 , which decreases with increasing size of the calixarene macrocycle, and the evidence indicates that the calixarenes bind to the surface of the nanoparticles via the phosphonate head groups rather than the phenolic oxygen centers. The stabilized nanoparticles show dual functionality: they remove up to 62 % of nitrate nitrogen and 48 % of phosphate from an aqueous effluent after 24 hours at concentrations of only 1 g L^-1 of calixarene-coated nanoparticles.

Lateral Versus Vertical Growth of Two-Dimensional Layered Transition-Metal Dichalcogenides: Thermodynamic Insight into MoS2

Unprecedented interest has been spurred recently in two-dimensional (2D) layered transition metal dichalcogenides (TMDs) that possess tunable electronic and optical properties. However, synthesis of a wafer-scale TMD thin film with controlled layers and homogeneity remains highly challenging due mainly to the lack of thermodynamic and diffusion knowledge, which can be used to understand and design process conditions, but falls far behind the rapidly growing TMD field. Here, an integrated density functional theory (DFT) and calculation of phase diagram (CALPHAD) modeling approach is employed to provide thermodynamic insight into lateral versus vertical growth of the prototypical 2D material MoS2. Various DFT energies are predicted from the layer-dependent MoS2, 2D flake-size related mono- and bilayer MoS2, to Mo and S migrations with and without graphene and sapphire substrates, thus shedding light on the factors that control lateral versus vertical growth of 2D islands. For example, the monolayer MoS2 flake in a small 2D lateral size is thermodynamically favorable with respect to the bilayer counterpart, indicating the monolayer preference during the initial stage of nucleation; while the bilayer MoS2 flake becomes stable with increasing 2D lateral size. The critical 2D flake-size of phase stability between mono- and bilayer MoS2 is adjustable via the choice of substrate. In terms of DFT energies and CALPHAD modeling, the size dependent pressure-temperature-composition (P-T-x) growth windows are predicted for MoS2, indicating that the formation of MoS2 flake with reduced size appears in the middle but close to the lower T and higher P "Gas + MoS2" phase region. It further suggests that Mo diffusion is a controlling factor for MoS2 growth owing to its extremely low diffusivity compared to that of sulfur. Calculated MoS2 energies, Mo and S diffusivities, and size-dependent P-T-x growth windows are in good accord with available experiments, and the present data provide quantitative insight into the controlled growth of 2D layered MoS2.

p-sulfonated calix[8]arene functionalized graphene as a "turn on" fluorescent sensing platform for aconitine determination

This work reports a novel method for the determination of aconitine through the competitive host-guest interaction between p-sulfonated calix[8]arene (SCX8) and signal probe/target molecules by using SCX8 functionalized reduced graphene oxide (SCX8-RGO) as a receptor. Three dyes (ST, RhB, BRB) and aconitine were selected as the probe and target molecules, respectively. The formation of SCX8-RGO·ST, SCX8-RGO·RhB, and SCX8-RGO·BRB complexes greatly decreases the fluorescence emission of ST, RhB, and BRB. The aconitine/SCX8 complex possesses a higher binding constant than ST/SCX8, RhB/SCX8, and BRB/SCX8 complexes, thus the dye in the SCX8 cavity can be replaced by aconitine to revert the fluorescence emission of SCX8-RGO·dye, leading to a "switch-on" fluorescence response. The fluorescence intensity of SCX8-RGO·ST, SCX8-RGO·RhB, and SCX8-RGO·BRB complexes increased linearly with increasing concentration of aconitine ranging from 1.0 to 14.0μM, 2.0-16.0μM, and 1.0-16.0μM, respectively. Based on the competitive host-guest interaction, the proposed detection method for aconitine showed detection limits of 0.28μM, 0.60μM, and 0.37μM, respectively, and was successfully applied for the determination of aconitine in human serum samples with good recoveries from 95.1% to 104.8%. The proposed method showed high selectivity for aconitine beyond competitive binding analytes. In addition, the inclusion complex of the SCX8/aconitine was studied by the molecular docking and molecular dynamics simulation, which indicated that the phenyl ester group of the aconitine molecule was included into the SCX8 cavity.

Indicator displacement assay for cholesterol electrochemical sensing using a calix[6]arene functionalized graphene-modified electrode

Indicator displacement assay for cholesterol (Cho) sensing using CX6–Gra against MB.

Fluorescent Detection of Tadalafil Based on Competitive Host-Guest Interaction Using p-Sulfonated Calix[6]arene Functionalized Graphene

A competitive fluorescence method toward tadalafil detection has been developed based on host-guest recognition by selecting rhodamine B (RhB) and p-sulfonated calix[6]arene functionalized graphene (CX6-Gra) as the "reporter pair". Upon the presence of tadalafil to the performed CX6-Gra-RhB complex, the RhB molecules are displaced by tadalafil, leading to a "switch-on" fluorescence signal. The observed fluorescence signal can be used for quantitative detection of tadalafil ranging from 1.00 to 50.00 μM with a detection limit of 0.32 μM (S/N = 3). The inclusion complex of tadalafil and CX6 was studied by molecular docking and the results indicated that a 1:1 host-guest stoichiometry had the lowest ΔG value of -7.18 kcal/mol. The docking studies demonstrated that the main forces including π-π interactions, electrostatic interactions, and hydrophobic interactions should be responsible for the formation of this inclusion compound. The mechanism of the competitive host-guest interaction was clarified. The binding constant (K) of the tadalafil/CX6 complex was more than 5 times greater than that of RhB/CX6.

Towards aryl C-N bond formation in dynamic thin films

C-N bond forming reactions are important in organic chemistry. A thin film microfluidic vortex fluidic device (VFD) operating under confined mode affords N-aryl compounds from 2-chloropyrazine and the corresponding amine, without the need for a transition metal catalyst.

Lateral assembly of oxidized graphene flakes into large-scale transparent conductive thin films with a three-dimensional surfactant 4-sulfocalix[4]arene

Graphene is a promising candidate material for transparent conductive films because of its excellent conductivity and one-carbon-atom thickness. Graphene oxide flakes prepared by Hummers method are typically several microns in size and must be pieced together in order to create macroscopic films. We report a macro-scale thin film fabrication method which employs a three-dimensional (3-D) surfactant, 4-sulfocalix[4]arene (SCX), as a lateral aggregating agent. After electrochemical exfoliation, the partially oxidized graphene (oGr) flakes are dispersed with SCX. The SCX forms micelles, which adsorb on the oGr flakes to enhance their dispersion, also promote aggregation into large-scale thin films under vacuum filtration. A thin oGr/SCX film can be shaved off from the aggregated oGr/SCX cake by immersing the cake in water. The oGr/SCX thin-film floating on the water can be subsequently lifted from the water surface with a substrate. The reduced oGr (red-oGr) films can be as thin as 10−20 nm with a transparency of >90% and sheet resistance of 890 ± 47 kΩ/sq. This method of electrochemical exfoliation followed by SCX-assisted suspension and hydrazine reduction, avoids using large amounts of strong acid (unlike Hummers method), is relatively simple and can easily form a large scale conductive and transparent film from oGr/SCX suspension.

Electrocatalytic activity of molybdenum disulfide nanosheets enhanced by self-doped polyaniline for highly sensitive and synergistic determination of adenine and guanine

Recently, easy, green, and low-cost liquild exfoliation of bulk materials to obtain thin-layered nanostructure significantly emerged. In this work, thin-layered molybdenum disulfide (MoS2) nanosheets were fabricated through intercalation of self-doped polyaniline (SPAN) to layer space of bulk MoS2 by ultrasonic exfoliating method to effectively prevent reaggregation of MoS2 nanosheets. The obtained hybrid showed specific surface area, a large number of electroactive species, and open accessible space, accompanied by rich negative charged and special conjugated structure, which was applied to adopt positively charged guanine and adenine, based on their strong π-π* interactions and electrostatic adsorption. Also, the SPAN-MoS2 interface exhibited the synergistic effect and good electrocatalytic activity compared with the sole SPAN or MoS2 modified electrode.

Unexpected optical limiting properties from MoS2 nanosheets modified by a semiconductive polymer

We have developed a facile method for exfoliation of MoS₂ with the assistance of P3HT to synthetize a P3HT–MoS₂ nanohybrid which shows unexpected optical limiting properties compared with the individual compartments.

p-Phosphonic acid calix[8]arene assisted dispersion and stabilisation of pea-pod C60@multi-walled carbon nanotubes in water

Pristine C₆₀ and MWCNTs are non-covalently stabilised in water by p-phosphonic acid calix[8]arene, additionally with ‘pea-pod’ encapsulation of C₆₀ inside the MWCNTs.

Amphiphilic graphene oxide stabilisation of hexagonal BN and MoS2 sheets

A simple and scalable method has been developed for directly forming water-dispersible heterolaminar solids involving mixing aqueous solution of amphiphilic graphene oxide with hexagonal boron nitride or molybdenum disulphide in N-methylpyrrolidone.

Hydrogen induced p-phosphonic acid calix[8]arene controlled growth of Ru, Pt and Pd nanoparticles

Monodispersed Ru, Pt and Pd nanoparticles with narrow size distributions (2, 12 and 20 nm respectively) have been synthesised via bubbling hydrogen gas into aqueous solutions of the noble metal ions in the presence of p-phosphonic acid calix[8]arene, at room temperature. Molecular modelling of the Ru nanoparticles provides insight into the role of the calixarene in controlling the size and stabilisation of the metal nanoparticles.

Self-assembled calixarene aligned patterning of noble metal nanoparticles on graphene

Patterns of noble metal nanoparticles (NMNPs) of ruthenium and platinum are formed on p-phosphonic acid calix[8]arene stabilised graphene in water. This involves hydrogen gas induced reduction of metal ions absorbed on the stabilised graphene, with TEM revealing the patterns being comprised of domains of parallel arrays of NMNPs ∼7 nm apart. The domains are orientated in three directions on each graphene sheet at an angle of ∼60° or ∼120° with respect to each other. AFM of self-assembled p-phosphonic acid calix[8]arene on the surface of a highly ordered pyrolytic graphite (HOPG) revealed a similar pattern, implying that the orientation of the assembly of p-phosphonic acid calix[8]arene is governed by the hexagonal motif of graphite/graphene.

Antioxidant phospholipid calix[4]arene mimics as micellular delivery systems

Amphiphilic calix[4]arenes were designed as phospholipid mimics by incorporating PO3H2 or NMe3(+) head groups. Using PC12 cells and three stressors (H2O2, menadione and glutamate), we established safe calix[4]arene levels that are able not only to deliver antioxidant payloads of curcumin, but intriguingly also have inherent antioxidant properties. The calix[4]arenes appear to be potent synthetic antioxidants that could be used as nano-carriers for drug delivery.

Nitrate uptake by p-phosphonic acid or p-(trimethylammonium)methyl calix[8]arene stablized laminar materials

Graphite, BN, MoS₂ and WS₂ are exfoliated and stablized in water with positively or negatively charged non-toxic calix[8]arenes. All 2D materials adsorb nitrate from waste effluent, precipitating once nitrate is bound, and can be regenerated.

Production of aqueous dispersions of inorganic graphene analogues by exfoliation and stabilization with non-ionic surfactants

The production of stable aqueous suspensions of several inorganic graphene analogues was performed by exfoliation of the corresponding bulk layered materials via sonication using non-ionic surfactants as dispersing agents.