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A facile, ultralow-cost, and up-scalable printable manufacturing process of flexible, multifunctional sensors that respond to more than one external stimulus could have a pivotal role in low-cost wearables and portable systems for Industry 4.0. Herein, using a low capex, in-house spray coating system, the fabrication of a low-cost photodetector that is tuneable by mechanical strain exploiting the piezo-phototronic nature of defect-free 2D In2Se3 nanosheets is reported. Moreover, force sensors that respond to different levels of applied force are spray-coated by using In2Se3 nanosheets. Regarding the photodetector, a nonmonotonic and asymmetric effect of strain on photocurrent response is shown exhibiting a local maximum at the 23°–32° compressive angle range and a slight hysteresis. Forward compressive bending leads to a photocurrent enhancement by 27% at 32° and reverse by 31% at 23°, while tensile strain leads to a current suppression by 8–10% at 23°–32° angle. The resulting force sensor repeatably demonstrates discrete piezoelectric voltages in the millivolt scale upon different mass loads, opening the path for force and tactile sensing applications. Applying industrially compatible materials for the underlying flexible substrate and electrodes, combined with spray coating, removes manufacturing complexities that engage costly and energy intensive fabrication.

Charge transport through a randomly oriented multilayered network of two-dimensional (2D) Ti3C2Tx (where Tx is the surface termination and corresponds to O, OH and F) was studied using time-of-flight photoconductivity (TOFP) method, which is highly sensitive to the distribution of charge carrier velocities. We prepared samples comprising Ti3C2Tx with thickness of 12 nm or 6-monolayers. MXene flakes of size up to 16 μm were randomly deposited on the surface by spin-coating from water solution. Using TOFP, we have measured electron mobility that reached values up to 279 cm2/Vs and increase with electric-field in a Poole-Frenkel manner. These values are approximately 50 times higher than previously reported field-effect mobility. Interestingly, our zero-electric-field extrapolate approaches electron mobility measured using terahertz absorption method, which represents intra-flake transport. Our data suggest that macroscopic charge transport is governed by two distinct mechanisms. The high mobility values are characteristic for the intra-flake charge transport via the manifold of delocalized states. On the other hand, the observed Poole-Frenkel dependence of charge carrier mobility on the electric field is typical for the disordered materials and suggest the existence of an important contribution of inter-flake hopping to the overall charge transport.

Transition metal carbides and nitrides (MXenes) are an emerging class of 2D materials, which are attracting ever-growing attention due to their remarkable physicochemical properties. The presence of various surface functional groups on MXenes’ surface, e.g., –F, –O, –OH, –Cl, opens the possibility to tune their properties through chemical functionalization approaches. However, only a few methods have been explored for the covalent functionalization of MXenes and include diazonium salt grafting and silylation reactions. Here, an unprecedented two-step functionalization of Ti3C2Tx MXenes is reported, where (3-aminopropyl)triethoxysilane is covalently tethered to Ti3C2Tx and serves as an anchoring unit for subsequent attachment of various organic bromides via the formation of C–N bonds. Thin films of Ti3C2Tx functionalized with linear chains possessing increased hydrophilicity are employed for the fabrication of chemiresistive humidity sensors. The devices exhibit a broad operation range (0–100% relative humidity), high sensitivity (0.777 or 3.035), a fast response/recovery time (0.24/0.40 s ΔH−1, respectively), and high selectivity to water in the presence of saturated vapors of organic compounds. Importantly, our Ti3C2Tx-based sensors display the largest operating range and a sensitivity beyond the state of the art of MXenes-based humidity sensors. Such outstanding performance makes the sensors suitable for real-time monitoring applications.

Engineered neural tissues serve as models for studying neurological conditions and drug screening. Besides observing the cellular physiological properties, in situ monitoring of neurochemical concentrations with cellular spatial resolution in such neural tissues can provide additional valuable insights in models of disease and drug efficacy. In this work, we demonstrate the first three-dimensional (3D) tissue cultures with embedded optical dopamine (DA) sensors. We developed an alginate/Pluronic F127 based bio-ink for human dopaminergic brain tissue printing with tetrapodal-shaped-ZnO microparticles (t-ZnO) additive as the DA sensor. DA quenches the autofluorescence of t-ZnO in physiological environments, and the reduction of the fluorescence intensity serves as an indicator of the DA concentration. The neurons that were 3D printed with the t-ZnO showed good viability, and extensive 3D neural networks were formed within one week after printing. The t-ZnO could sense DA in the 3D printed neural network with a detection limit of 0.137 μM. The results are a first step toward integrating tissue engineering with intensiometric biosensing for advanced artificial tissue/organ monitoring.

Controllable rapid expansion and activation of gases is important for a variety of applications, including combustion engines, thrusters, actuators, catalysis, and sensors. Typically, the activation of macroscopic gas volumes is based on ultra-fast chemical reactions, which require fuel and are irreversible. An “electrically powered explosion”, i.e., the rapid increase in temperature of a macroscopic relevant gas volume induced by an electrical power pulse, is a feasible repeatable and clean alternative, providing adaptable non-chemical power on demand. Till now, the fundamental problem was to find an efficient transducer material that converts electrical energy into an immediate temperature increase of a sufficient gas volume. To overcome these limitations, we developed electrically powered repeatable air explosions (EPRAE) based on free-standing graphene layers of nanoscale thickness in the form of microtubes that are interconnected to a macroscopic framework. These low-density and highly permeable graphene foams are characterized by heat capacities comparable to air. The EPRAE process facilitates cyclic heating of cm3-sized air volumes to several 100 °C for more than 100,000 cycles, heating rates beyond 300,000 K s−1 and repetition rates of several Hz. It enables pneumatic actuators with the highest observed output power densities (>40 kW kg−1) and strains ∼100%, as well as tunable microfluidic pumps, gas flowmeters, thermophones, and micro-thrusters.

To obtain high-quality two-dimensional (2D) materials from the bulky crystals, delamination under an externally controlled stimulus is crucial. Electrochemical exfoliation of layered materials requires simple instrumentation yet offers high-quality exfoliated 2D materials with high yields and features straightforward upscalability; therefore, it represents a key technology for advancing fundamental studies and industrial applications. Moreover, the solution processability of functionalized 2D materials enables the fabrication of (opto)electronic and energy devices via different printing technologies such as inkjet printing and 3D printing. This paper presents the electrochemical exfoliation protocol for the synthesis of black phosphorus (BP), one of the most promising emerging 2D materials, from its bulk crystals in a step-by-step manner, namely, cathodic electrochemical exfoliation of BP in the presence of N(C4H9)4∙HSO4 in propylene carbonate, dispersion preparation by sonication and subsequent centrifugation for the separation of flakes, and morphological characterization by scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM).

Graphene and related materials have been widely studied due to their superior properties in a wide range of applications. However, large-scale production remains a critical challenge to enable commercial acceptance. Here, we present a facile, scalable, one-step electrochemical method for producing hybrid transition metal oxide (V, Fe, Ti, or Mn)/graphene materials (TMO-EGs) as active materials for supercapacitors. Therein, we have designed and developed a continuous flow reactor with a high production rate (>4 g h−1) of TMO-EGs, where the TMO accounts for 36 weight%. TMO-EG flakes demonstrate a moderate lateral size of up to 5 μm and a specific surface area of 64 m2 g−1. Notably, TMO-EGs present a capacitance of up to 188 F g−1 as single electrodes in 4 M LiCl. The most promising material, MnOx-EG, has been used for the large-scale production of thin-film supercapacitor devices (40 × 40 × 0.25 mm) in a commercial pilot line. Using 1 M Na2SO4 as the electrolyte, the as-fabricated devices deliver a capacitance of 52 mF cm−2, with 83% capacitance retention after 6000 charge–discharge cycles, comparable to recent reports of similar devices. The simplicity, scalability, and versatility of our method are highly promising to promote the commercial applications of graphene-based materials and can be further developed for the upscalable production of other 2D materials, such as transition metal dichalcogenides and MXenes.

The new generation of three roll mills is able to monitor occurring process loads while dispersion. This paper focuses on the interpretation of the gathered data to find criteria quantifying the dispersion state online. The aim is process time reduction. We used impedance spectroscopy to identify the dispersion state and correlated it with the occurring process loads. The dispersion process of a wide spectrum of carbon based nano particles, namely carbon black, single walled carbon nanotubes, multi walled carbon nanotubes, a few-layer graphene powder, electrochemically exfoliated graphite and a functionalized electrochemically exfoliated graphite was investigated. The filler content was varied along the material’s electrical percolation threshold. The criteria found led to a reduction of processing time and revealed the prevalent mechanisms during dispersion.

Dual-ion batteries are considered to be an emerging viable energy storage technology owing to their safety, high power capability, low cost, and scalability. Intercalation of anions into a graphite positive electrode provides high operating voltage and improved energy density to such dual-ion batteries. In this work, we have performed a combinatorial study of graphite intercalation compounds considering four anions, namely hexafluorophosphate (PF 6 − ), perchlorate (ClO 4 − ), bis(fluorosulfonyl)imide (FSI−), and bis(trifluoromethanesulfonyl)imide (TFSI−), via first-principles calculations. The structural properties and energetics of the intercalation compounds are compared based on different sizes, geometries, and the physical and chemical properties of the intercalated anions. The staging mechanism of anion intercalation into graphite and the specific capacities, and voltage profiles of the intercalated compounds are investigated. A comparison regarding battery electrochemistry is also done with available experimental observations. Our calculated intercalation energies and voltage profiles show that the initial anion intercalation into graphite is less favorable than subsequent ones for all the anions considered in this study. Although the effect of the size of anions in a graphite cathode on various properties of the intercalated compounds is not as significant as the size of cations in a graphite anode, some distinction between the studied anions can still be made. Among the studied anions, the intercalation compounds based on PF 6 − are the most stable ones. These PF 6 − anions cause relatively small structural deformations of the graphite and have the highest oxidative ability, highest onset voltage, and highest diffusion barrier along the graphene sheets. The overall small diffusion barriers of the anions within graphite explain the high rate capability of dual-ion batteries.

MXene (e.g., Ti3C2) represents an important class of two‐dimensional (2D) materials owing to its unique metallic conductivity and tunable surface chemistry. However, the mainstream synthetic methods rely on the chemical etching of MAX powders (e.g., Ti3AlC2) using hazardous HF or alike, leading to MXene sheets with fluorine termination and poor ambient stability in colloidal dispersions. Here, we demonstrate a fluoride‐free, iodine (I2) assisted etching route for preparing 2D MXene (Ti3C2Tx, T=O, OH) with oxygen‐rich terminal groups and intact lattice structure. More than 71 % of sheets are thinner than 5 nm with an average size of 1.8 μm. They present excellent thin‐film conductivity of 1250 S cm−1 and great ambient stability in water for at least 2 weeks. 2D MXene sheets with abundant oxygen surface groups are excellent electrode materials for supercapacitors, delivering a high gravimetric capacitance of 293 F g−1 at a scan rate of 1 mV s−1, superior to those made from fluoride‐based etchants (, An iodine‐assisted method has been developed for etching bulk Ti3AlC2 in anhydrous acetonitrile (CH3CN), resulting in 2D MXene sheets (Ti3C2Tx, T=O, OH) with intact lattice, high yield (71 %), large size (1.8 μm) and ultimate thickness (

Nano letters 21(8), 3690 - 3697 (2021). doi:10.1021/acs.nanolett.0c04375, The fabrication of electrically conductive hydrogels is challenging as the introduction of an electrically conductive filler often changes mechanical hydrogel matrix properties. Here, we present an approach for the preparation of hydrogel composites with outstanding electrical conductivity at extremely low filler loadings (0.34 S m$^{–1}$, 0.16 vol %). Exfoliated graphene and polyacrylamide are microengineered to 3D composites such that conductive graphene pathways pervade the hydrogel matrix similar to an artificial nervous system. This makes it possible to combine both the exceptional conductivity of exfoliated graphene and the adaptable mechanical properties of polyacrylamide. The demonstrated approach is highly versatile regarding porosity, filler material, as well as hydrogel system. The important difference to other approaches is that we keep the original properties of the matrix, while ensuring conductivity through graphene-coated microchannels. This novel approach of generating conductive hydrogels is very promising, with particular applications in the fields of bioelectronics and biohybrid robotics., Published by ACS Publ., Washington, DC

Brain implants are promising instruments for a broad variety of nervous tissue diseases with a wide range of applications, e.g. for stimulation, signal recording or local drug delivery. Recently, graphene-based scaffold materials have emerged as attractive candidates as neural interfaces, 3D scaffolds, or drug delivery systems due to their excellent properties like flexibility, high surface area, conductivity, and lightweight. To date, however, there is a lack of appropriate studies of the foreign body response, especially by glial cells, towards graphene-based materials. In this work, we investigated the effects of macroscopic, highly porous (>99.9%) graphene oxide (GO) and reduced graphene oxide (rGO) (conductivity ∼1 S m−1) scaffolds with tailorable macro- and microstructure on human astrocyte and microglial cell viability and proliferation as well as expression of neuroinflammation and astrogliosis associated genes in an indirect contact approach. In this in vitro model, as well as ex vivo in organotypic murine brain slices, we could demonstrate that both GO and rGO based 3D scaffolds exert slight effects on the glial cell populations which are the key players of glial scar formation. These effects were in most cases completely abolished by curcumin, a known anti-inflammatory and anti-fibrotic drug that could in perspective be applied to brain implants as a protectant.

2D conjugated metal-organic frameworks (2D c-MOFs) are emerging as a novel class of conductive redox-active materials for electrochemical energy storage. However, developing 2D c-MOFs as flexible thin-film electrodes have been largely limited, due to the lack of capability of solution-processing and integration into nanodevices arising from the rigid powder samples by solvothermal synthesis. Here, the synthesis of phthalocyanine-based 2D c-MOF (Ni2[CuPc(NH)8]) nanosheets through ball milling mechanical exfoliation method are reported. The nanosheets feature with average lateral size of ≈160 nm and mean thickness of ≈7 nm (≈10 layers), and exhibit high crystallinity and chemical stability as well as a p-type semiconducting behavior with mobility of ≈1.5 cm2 V−1 s−1 at room temperature. Benefiting from the ultrathin feature, the nanosheets allow high utilization of active sites and facile solution-processability. Thus, micro-supercapacitor (MSC) devices are fabricated mixing Ni2[CuPc(NH)8] nanosheets with exfoliated graphene, which display outstanding cycling stability and a high areal capacitance up to 18.9 mF cm−2; the performance surpasses most of the reported conducting polymers-based and 2D materials-based MSCs.

Because of its thickness-dependent direct bandgap and exceptional optoelectronic properties, indium(III) selenide (In2 Se3 ) has emerged as an important semiconductor for electronics and optoelectronics. However, the scalable synthesis of defect-free In2 Se3 flakes remains a significant barrier for its practical applications. Here, a facile electrochemical strategy is presented for the ultrafast delamination of bulk layered In2 Se3 crystals in nonaqueous media, resulting in high-yield (83%) production of defect-free In2 Se3 flakes with large lateral size (up to 26 µm). The intercalation of tetrahexylammonium (THA+ ) ions mainly creates stage-3 intercalated compounds in which every three layers of In2 Se3 are occupied by one layer of THA molecules. The subsequent exfoliation leads to a majority of trilayer In2 Se3 nanosheets. As a proof of concept, solution-processed, large-area (400 µm × 20 µm) thin-film photodetectors embedded with the exfoliated In2 Se3 flakes reveal ultrafast response time with a rise and decay of 41 and 39 ms, respectively, and efficient responsivity (1 mA W-1 ). Such performance surpasses most of the state-of-the-art thin-film photodetectors based on transition metal dichalcogenides.

Graphene hydrophobic coatings paved the way towards a new generation of optoelectronic and fluidic devices. Nevertheless, such hydrophobic thin films rely only on graphene non-polar surface, rather than taking advantage of its surface roughness. Furthermore, graphene is typically not self-standing. Differently, carbon aerogels have high porosity, large effective surface area due to their surface roughness, and very low mass density, which make them a promising candidate as a super-hydrophobic material for novel technological applications. However, despite a few works reporting the general super-hydrophobic and lipophilic behavior of the carbon aerogels, a detailed characterization of their wetting properties is still missing, to date. Here, the wetting properties of graphene aerogels are demonstrated in detail. Without any chemical functionalization or patterning of their surface, the samples exhibit a super-lipophilic state and a stationary super-hydrophobic state with a contact angle up to $150\pm15^{\deg}$ and low contact angle hysteresis $\approx15^{\deg}$, owing to the fakir effect. In addition, the adhesion force of the graphene aerogels in contact with the water droplets and their surface tension are evaluated. For instance, the unique wettability and enhanced liquid absorption of the graphene aerogels can be exploited for reducing contamination from oil spills and chemical leakage accidents., Comment: 7 pages, 4 figures

Electrochemical energy storage (EES) devices integrated with smart functions are highly attractive for powering the next‐generation electronics in the coming era of artificial intelligence. In this regard, exploiting functional electrolytes represents a viable strategy to realize smart functions in EES devices. In this review, recent advances in the development of functional electrolytes for smart EES devices like rechargeable batteries and supercapacitors are presented. Various stimulus‐responsive electrolytes are first summarized, including temperature‐, mechanical force‐, voltage‐, magnetism‐, and light‐responsive electrolytes. Emphasis is placed on the working principles of stimulus‐responsive electrolytes and their specific problem‐solving functions in EES devices. Then, the latest advances in electrochromic and self‐healing electrolytes used for smart EES devices are discussed. Finally, key challenges and research opportunities related to functional electrolyte design and smart EES device development are envisioned, with the goal of accelerating further research in this thriving field.

One of the most important applications of graphene-based materials is the formation of nanocomposite materials, where graphene in the bulk-polymer matrix transfers its properties onto the polymeric material. Control of the polymer/graphene interface by attached polymeric interlayers is essential to generate nanocomposites, thus avoiding the aggregation of graphene nanoparticles. Among all graphene materials graphene oxide (GO) and reduced graphene oxide (r-GO) can be prepared on large scales useful for mass production graphene/polymer composites. The direct use of graphene materials as both, the polymerization initiator or catalyst and additive not only diminishes the agglomeration of particles in composites but also reduces the process of composite production to one facile step, which in turn avoids further purification regarding to strong acid initiators and metal particles catalysts. Here, literature activities within the past ∼10 years using graphene-based materials either as initiator or catalyst in different polymerization reactions are reviewed.

2D materials are important building blocks for the upcoming generation of nanostructured electronics and multifunctional devices due to their distinct chemical and physical characteristics. To this end, large-scale production of 2D materials with high purity or with specific functionalities represents a key to advancing fundamental studies as well as industrial applications. Among the state-of-the-art synthetic protocols, electrochemical exfoliation of layered materials is a very promising approach that offers high yield, great efficiency, low cost, simple instrumentation, and excellent up-scalability. Remarkably, playing with electrochemical parameters not only enables tunable material properties but also increases the material diversities from graphene to a wide spectrum of 2D semiconductors. Here, a succinct and critical survey of the recent progress in this research direction is presented, comprising the strategic design, exfoliation principles, underlying mechanisms, processing techniques, and potential applications of 2D materials. At the end of the discussion, the emerging trends, challenges, and opportunities in real practice are also highlighted.

Despite tremendous efforts toward fabrication of three-dimensional macrostructures of two-dimensional (2D) materials, the existing approaches still lack sufficient control over microscopic (morphology, porosity, pore size) and macroscopic (shape, size) properties of the resulting structures. In this work, a facile fabrication method for the wet-chemical assembly of carbon 2D nanomaterials into macroscopic networks of interconnected, hollow microtubes is introduced. As demonstrated for electrochemically exfoliated graphene, graphene oxide, and reduced graphene oxide, the approach allows for the preparation of highly porous (> 99.9%) and lightweight (-3) aeromaterials with tailored porosity and pore size as well as tailorable shape and size. The unique tubelike morphology with high aspect ratio enables ultralow-percolation-threshold graphene composites (0.03 S m-1, 0.05 vol%) which even outperform most of the carbon nanotube-based composites, as well as highly conductive aeronetworks (8 S m-1, 4 mg cm-3). On top of that, long-term compression cycling of the aeronetworks demonstrates remarkable mechanical stability over 10;000 cycles, even though no chemical cross-linking is employed. The developed strategy could pave the way for fabrication of various macrostructures of 2D nanomaterials with defined shape, size, as well as micro- and nanostructure, crucial for numerous applications such as batteries, supercapacitors, and filters.

Because of its thickness-dependent direct bandgap and exceptional optoelectronic properties, indium(III) selenide (In

A trade-off between enhancement of physical properties of the final part and the processability during manufacturing always exists for the application of nanocarbon materials in thermoset-based composites. For different epoxy resins, this study elaborates the impact of nanocarbon particle type, functionalization, and filler loading on the resulting properties, i.e., rheological, electrical, thermo-mechanical, as well as the fracture toughness in mode I and mode II loading. Therefore, a comprehensive set of carbon nanoparticles, consisting of carbon black (CB), single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), few layer graphene (FLG), and electrochemically expanded graphite (ExG), in purified or functionalized configuration was introduced in various epoxy resins, with different molecular weight distributions. A novel technique to introduce sharp cracks into single-edge notched bending (SENB) fracture toughness specimens led to true values. SWCNT show highest potential for increasing electrical properties without an increase in viscosity. Functionalized MWCNT and planar particles significantly increase the fracture toughness in mode I by a factor of two.

The excellent gas sensing performance of metal oxide based nano- and microstructures, including a fast response time and good sensitivity, is typically limited by their low selectivity. Therefore, novel approaches and strategies are required to gain a precise control of the selectivity. Here, we introduce a nanoporous few-layer graphene oxide (GO) membrane with permeability only to specific gas molecules to improve the selectivity of individual zinc oxide microwires (ZnO MWs) toward hydrogen (H2) gas. The fabricated GO-covered ZnO MWs showed ultra-low power consumption (60−200 nW) and an excellent room temperature H2 gas sensing properties with fast response (114 s) and recovery (30 s) times, and a low detection limit of ∼4 ppm, while no gas response was measured to all other tested gases. As proposed, the gas sensing mechanism is based on selective sieving of H2 gas molecules through the GO membrane and further diffusion to the Schottky contacts, resulting in a decreased barrier height. Being based on a bottom-up fabrication approach, the presented results could have great potential for further technological applications such as high-performance and highly selective ultra-low power metal oxide-based gas sensors, opening new opportunities for the design of nanosensors and their integration in wireless and portable devices.

The generation of graphene nanocomposites by curing of a new resin material via the Cu(I) catalyzed azide-alkyne click reaction (CuAAC) has been investigated by using graphene supported copper nanoparticles (TRGO-Cu 2 O) as catalyst directly embedded into the curing resin. Low molecular weight trivalent azide and alkyne were used as resin-components for “click” crosslinking by graphene supported copper nanoparticles (TRGO-Cu 2 O) in comparison to different commercially available homo- and heterogeneous copper catalysts. The kinetics of the crosslinking process were investigated by differential scanning calorimetry (DSC) and melt rheology, proving the superior performance of the (TRGO-Cu 2 O). Additionally the physical and mechanical properties of the finally cured resins were studied via melt-rheology, broadband dielectric spectroscopy (BDS) and thermogravimetric analysis (TGA), proving the outstanding catalytic activity of the TRGO-Cu 2 O catalyst performing “click” crosslinking without addition of base or oxidizing/reducing agents. Along with its catalytic performance, TRGO-Cu 2 O acts as reinforcing filler, significantly improving the mechanical and physical properties, as well as the conductivity and the thermal stability of the final resin material.