Interface Amorphization of Two-Dimensional Black Phosphorus upon Treatment with Diazonium Salts.

Two-dimensional (2D) black phosphorus (BP) represents one of the most appealing 2D materials due to its electronic, optical, and chemical properties. Many strategies have been pursued to face its environmental instability, covalent functionalization being one of the most promising. However, the extremely low functionalization degrees and the limitations in proving the nature of the covalent functionalization still represent challenges in many of these sheet architectures reported to date. Here we shine light on the structural evolution of 2D-BP upon the addition of electrophilic diazonium salts. We demonstrated the absence of covalent functionalization in both the neutral and the reductive routes, observing in the latter case an unexpected interface conversion of BP to red phosphorus (RP), as characterized by Raman, 31 P-MAS NMR, and X-ray photoelectron spectroscopies (XPS). Furthermore, thermogravimetric analysis coupled to gas chromatography and mass spectrometry (TG-GC-MS), as well as electron paramagnetic resonance (EPR) gave insights into the potential underlying radical mechanism, suggesting a Sandmeyer-like reaction.

Covalent Bisfunctionalization of Two-Dimensional Molybdenum Disulfide.

Covalent functionalization of two-dimensional molybdenum disulfide (2D MoS2 ) holds great promise in developing robust organic-MoS2 hybrid structures. Herein, for the first time, we demonstrate an approach to building up a bisfunctionalized MoS2 hybrid structure through successively reacting activated MoS2 with alkyl iodide and aryl diazonium salts. This approach can be utilized to modify both colloidal and substrate supported MoS2 nanosheets. We have discovered that compared to the adducts formed through the reactions of MoS2 with diazonium salts, those formed through the reactions of MoS2 with alkyl iodides display higher reactivity towards further reactions with electrophiles. We are convinced that our systematic study on the formation and reactivity of covalently functionalized MoS2 hybrids will provide some practical guidance on multi-angle tailoring of the properties of 2D MoS2 for various potential applications.

Spatially Resolved Bottom-Side Fluorination of Graphene by Two-Dimensional Substrate Patterning.

Patterned functionalization can, on the one hand, open the band gap of graphene and, on the other hand, program demanding designs on graphene. The functionalization technique is essential for graphene-based nanoarchitectures. A new and highly efficient method was applied to obtain patterned functionalization on graphene by mild fluorination with spatially arranged AgF arrays on the structured substrate. Scanning Raman spectroscopy (SRS) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) were used to characterize the functionalized materials. For the first time, chemical patterning on the bottom side of graphene was realized. The chemical nature of the patterned functionalization was determined to be the ditopic scenario with fluorine atoms occupying the bottom side and moieties, such as oxygen-containing groups or hydrogen atoms, binding on the top side, which provides information about the mechanism of the fluorination process. Our strategy can be conceptually extended to pattern other functionalities by using other reactants. Bottom-side patterned functionalization enables utilization of the top side of a material, thereby opening up the possibilities for applications in graphene-based devices.

Lattice Opening upon Bulk Reductive Covalent Functionalization of Black Phosphorus.

The chemical bulk reductive covalent functionalization of thin-layer black phosphorus (BP) using BP intercalation compounds has been developed. Through effective reductive activation, covalent functionalization of the charged BP by reaction with organic alkyl halides is achieved. Functionalization was extensively demonstrated by means of several spectroscopic techniques and DFT calculations; the products showed higher functionalization degrees than those obtained by neutral routes.

Isomerically Pure Star-Shaped Triphenylene-Perylene Hybrids Involving Highly Extended π-Conjugation.

The synthesis and characterization of a new type of a highly conjugated heterocyclic π-chromophore, consisting of a central triphenylene core fused with three perylene monoimide units (star-shaped molecules), is described. By judicious bay functionalization with tert-butylphenoxy substituents, aggregation was completely prevented by using 1,1,2,2-tetrachloroethane, allowing for a straightforward purification and, for the very first time, the complete separation of the constitutional isomers by HPLC. Both isomers can be easily distinguished by means of several conventional spectroscopic techniques. Furthermore, we have illustrated the absence of supramolecular aggregates and enhanced processability by noncovalent functionalization of graphene substrates, showing an outstanding homogeneity and demonstrating a different doping behavior in both isomers, making it possible to distinguish them by Raman spectroscopy.

Fundamental Insights into the Degradation and Stabilization of Thin Layer Black Phosphorus.

Herein, we have developed a systematic study on the oxidation and passivation of mechanically exfoliated black phosphorus (BP). We analyzed the strong anisotropic behavior of BP by scanning Raman microscopy providing an accurate method for monitoring the oxidation of BP via statistical Raman spectroscopy. Furthermore, different factors influencing the environmental instability of the BP, i.e., thickness, lateral dimensions or visible light illumination, have been investigated in detail. Finally, we discovered that the degradation of few-layer BP flakes of <10 nm can be suppressed for months by using ionic liquids, paving the way for the development of BP-based technologies.

Exploring the Formation of Black Phosphorus Intercalation Compounds with Alkali Metals.

Black phosphorus intercalation compounds (BPICs) with alkali metals (namely: K and Na) have been synthesized in bulk by solid-state as well as vapor-phase reactions. By means of a combination of in situ X-ray diffraction, Raman spectroscopy, and DFT calculations the structural behavior of the BPICs at different intercalation stages has been demonstrated for the first time. Our results provide a glimpse into the very first steps of a new family of intercalation compounds, with a distinct behavior as compared to its graphite analogues (GICs), showing a remarkable structural complexity and a dynamic behavior.

Topology-Driven Reductive Silylation of Synthetic Carbon Allotropes.

Herein, the combined application of characterization tools, such as Raman spectroscopy, thermal gravimetric analysis coupled with mass spectrometry, and optical and atomic force microscopy, confirms the reductive silylation of synthetic carbon allotropes as a new covalent functionalization strategy for the formation of heteroatom-carbon bonds. In particular, our study gives interesting insights into the topology-driven retrofunctionalization of nanotubide and graphenide derivatives.

Noncovalent Functionalization of Black Phosphorus.

Black phosphorus (BP) was functionalized with organic moieties on the basis of liquid exfoliation. The treatment of BP with electron-withdrawing 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) led to electron transfer from BP to the organic dopant. On the other hand, the noncovalent interaction of BP with a perylene diimide was mainly due to van der Waals interactions but also led to considerable stabilization of the BP flakes against oxygen degradation.

Few-layer black phosphorus enables nitrogen fixation under ambient conditions.

Nitrogen (N2) fixation is a key reaction in biological and industrial chemistry, which does not occur spontaneously under ambient conditions but often depends on very specific catalysts and harsh reaction processes. Here we show that exposing exfoliated black phosphorus to the open air triggers, concomitantly, the oxidation of the two-dimensional (2D) material and the fixation of up to 100 parts per million (0.01%) of N2 on the surface. The fixation also occurs in pristine non-exfoliated material. Besides, other allotropic forms of phosphorus, like red P, also fixes N2 during ambient oxidation, suggesting that the N2 fixation process is intrinsic with phosphorus oxidation and does not depend on the chemical structure or the dimensionality of the solid. Despite the low amounts of N2 fixed, this serendipitous discovery could have fundamental implications on the chemistry and environmental stability of phosphorous and the design of related catalysts for N2 fixation.

Acid Catalysis with Alkane/Water Microdroplets in Ionic Liquids.

Ionic liquids are composed of an organic cation and a highly delocalized perfluorinated anion, which remain tight to each other and neutral across the extended liquid framework. Here we show that n-alkanes in millimolar amounts enable a sufficient ion charge separation to release the innate acidity of the ionic liquid and catalyze the industrially relevant alkylation of phenol, after generating homogeneous, self-stabilized, and surfactant-free microdroplets (1-5 µm). This extremely mild and simple protocol circumvents any external additive or potential ionic liquid degradation and can be extended to water, which spontaneously generates microdroplets (ca. 3 µm) and catalyzes Brönsted rather than Lewis acid reactions. These results open new avenues not only in the use of ionic liquids as acid catalysts/solvents but also in the preparation of surfactant-free, well-defined ionic liquid microemulsions.

Few-layer Black Phosphorous Catalyzes Radical Additions to Alkenes Faster than Low-valence Metals.

The substitution of catalytic metals by p-block main elements has a tremendous impact not only in the fundamentals but also in the economic and ecological fingerprint of organic reactions. Here we show that few-layer black phosphorous (FL-BP), a recently discovered and now readily available 2D material, catalyzes different radical additions to alkenes with an initial turnover frequency (TOF0) up to two orders of magnitude higher than representative state-of-the-art metal complex catalysts at room temperature. The corresponding electron-rich BP intercalation compound (BPIC) KP6 shows a nearly twice TOF0 increase with respect to FL-BP. This increase in catalytic activity respect to the neutral counterpart also occurs in other 2D materials (graphene vs. KC8) and metal complex catalysts (Fe0 vs. Fe2- carbon monoxide complexes). This reactive parallelism opens the door for cross-fertilization between 2D materials and metal catalysts in organic synthesis.

Lumbatex: A Wearable Monitoring System Based on Inertial Sensors to Measure and Control the Lumbar Spine Motion.

Measuring the curvature of the lumbar spine is an important challenge in disciplines related to physical therapy, rehabilitation, and sports medicine seeking to solve the incidence of the low back pain and other spinal disorders in the population. In clinical practice, most of the methods used are manual or depend on the trained eye of the specialist who is measuring. We have developed Lumbatex: an integrated system based on inertial sensors integrated into a wearable textile device. This device is connected via Bluetooth to software, which interprets data from the sensors and provides real-time biofeedback to users in a graphical way and also a quantitative measure of the curvature and spinal motion. The system is tested in two ways: first, checking the accuracy detecting changes in curvatures; second, evaluating the usability and comfort from the user standpoint. The accuracy is checked through a static method getting curvature values from the device placed on curved platforms and a dynamic validation with volunteers performing different exercises. The results obtained showed a high accuracy measuring changes in curvature with an error lower than 1° in the static test and good usability and comfort according to the opinion of the volunteers.

Liquid phase exfoliation of carbonate-intercalated layered double hydroxides.

Direct exfoliation of a carbonate layered double hydroxide (LDH) has been achieved by using a novel horn-probe sonic tip, avoiding the development of time-consuming anion-exchange reactions. The most suitable solvents were chosen based on the Hildebrand solubility parameters and the thickness of the exfoliated nanosheets confirmed unambiguously the successful delamination.

Monolayer black phosphorus by sequential wet-chemical surface oxidation.

We report a straightforward chemical methodology for controlling the thickness of black phosphorus flakes down to the monolayer limit by layer-by-layer oxidation and thinning, using water as solubilizing agent. Moreover, the oxidation process can be stopped at will by two different passivation procedures, namely the non-covalent functionalization with perylene diimide chromophores, which prevents the photooxidation, or by using a protective ionic liquid layer. The obtained flakes preserve their electronic properties as demonstrated by fabricating a BP field-effect transistor (FET). This work paves the way for the preparation of BP devices with controlled thickness.

Few layer 2D pnictogens catalyze the alkylation of soft nucleophiles with esters.

Group 15 elements in zero oxidation state (P, As, Sb and Bi), also called pnictogens, are rarely used in catalysis due to the difficulties associated in preparing well-structured and stable materials. Here, we report on the synthesis of highly exfoliated, few layer 2D phosphorene and antimonene in zero oxidation state, suspended in an ionic liquid, with the native atoms ready to interact with external reagents while avoiding aerobic or aqueous decomposition pathways, and on their use as efficient catalysts for the alkylation of nucleophiles with esters. The few layer pnictogen material circumvents the extremely harsh reaction conditions associated to previous superacid-catalyzed alkylations, by enabling an alternative mechanism on surface, protected from the water and air by the ionic liquid. These 2D catalysts allow the alkylation of a variety of acid-sensitive organic molecules and giving synthetic relevancy to the use of simple esters as alkylating agents.