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Black phosphorus (BP) has extraordinary properties, but its ambient instability remains a critical challenge. Functionalization has been employed to overcome the sensitivity of BP to ambient conditions while preserving its properties. Herein, a simultaneous exfoliation–functionalization process is reported that functionalizes BP flakes during exfoliation and thus provides increased protection, which can be attributed to minimal exposure of the flakes to ambient oxygen and water. A tetrabutylammonium salt was employed for intercalation of BP, resulting in the formation of flakes with large lateral dimensions. The addition of an aryl iodide or an aryl iodonium salt to the exfoliation solvent creates a scalable strategy for the production of functionalized few‐layer BP flakes. The ambient stability of functionalized BP was prolonged to a period of one week, as revealed by STEM, AFM, and X‐ray photoelectron spectroscopy.

Two-dimensional (2D) layered antimony (Sb) and antimony telluride (Sb2 Te3 ) are two valuable materials for optoelectronic devices and thermoelectric applications. Preparing high-quality sheets of these materials is the initial phase to promote their expected issues. Herein, micrometer-sized few-to-multilayered sheets of Sb and Sb2 Te3 have been obtained by electrochemical exfoliation. The layered rhombohedral Sb was exfoliated in Na2 SO4 and Li2 SO4 electrolytes by anodic-cationic intercalation, and Sb2 Te3 was exfoliated in Na2 SO4 . These findings are important contributions for the solution-based room-temperature electrochemical exfoliation, which is stable under glove-box-free conditions, to further improve the production of high-quality exfoliated sheets.

Efficient exfoliation and downsizing of Sb2 S3 and Bi2 S3 layered compounds by using scalable bipolar electrochemistry on their suspensions in aqueous media are here demonstrated. The resulting samples were characterized in detail by transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy; their electrochemistry toward hydrogen evolution was also investigated. Hydrogen evolution ability of exfoliated Sb2 S3 and Bi2 S3 was investigated and compared to the bulk counterparts.

An electroadsorption technique similar to the ultrafast charging mechanism in supercapacitors is utilized to remove metals with different sizes and hydrophilicities from contaminated water using self-propelled microswimmers. The swimmers carry graphite fibre or bismuth with a layered crystal structure providing high electrostatic double-layer capacitances. Unlike previous methods, this electrochemical technique does not only utilize the surface of the swimmers, but due to the interlayer spacing of the graphite and bismuth, it is able to store metals in ≈400 layers, allowing removal and recovery of >50 ppm lithium in only 5 min. A larger interlayer distance between bismuth sheets allows the removal of bigger cations (sodium and calcium), expanding the application of this method to a large variety of natural elements. Finally, magnetic navigation of charged swimmers to an oxygen-saturated media causes oxidation and thus immediate release of the metal ions from the swimmers.

Advanced materials 34(15), 2108682 (2022). doi:10.1002/adma.202108682, Published by Wiley-VCH, Weinheim

The application of enzymes is a crucial issue for current biotechnological application in pharmaceutical, as well as food and cosmetic industry. Effective platforms for enzyme immobilization are necessary for their industrial use in various biosynthesis procedures. Such platforms must provide high yield of immobilization and retain high activity at various conditions for their large-scale applications. Graphene derivatives such as hydrogenated graphene (graphane) and fluorographene can be applied for enzyme immobilization with close to 100 % yield that can result to activities of the composites significantly exceeding activity of free enzymes. The hydrophobic properties of graphene stoichiometric derivatives allowed for excellent non-covalent bonding of enzymes and their use in various organic solvents. The immobilized enzymes retain their high activities even at elevated temperatures. These findings show excellent application potential of enzyme biocatalysts immobilized on graphene stoichiometric derivatives.

Fluorographene is an excellent precursor for the synthesis of graphene derivatives. Relative to pure graphene, fluorographene possesses higher reactivity and, in comparison with graphene oxide, is also homogenous in composition, which enables the preparation of well-defined materials. Recently, it has been shown that several graphene derivatives can be synthesized from fluorographene, thus yielding various products such as graphene acid or alkylated graphene. This study focuses on the hydrogenation of fluorographene by using various hydrogenation reactions, including the use complex hydrides and solvated electrons in different media. In addition, a comparison of these reactions shows that fluorinated graphite has significantly lower reactivity than fluorographene. The conversion rates of these reactions are higher when fluorographene is used relative to fluorographite. These reactions can be used to tune the hydrogen/fluorine composition on a graphene backbone.

Layered transition-metal dichalcogenides (TMDs) are valued for their electrocatalytic properties toward the hydrogen-evolution reaction (HER) and oxygen-reduction reaction (ORR). One effective strategy to activate the electrocatalytic properties of TMDs is through doping. The optimistic outlook of doped-MoS2 as an electrocatalyst witnessed in previous reports spurred us to examine the effect of doping WSe2 with Group 5 transition-metal species, namely V, Nb, and Ta, in aspects of inherent electroactivities and catalysis. Apart from the mild reduction signal unique to the Group 5 transition-metal dopants, the Group 5 transition-metal-doped WSe2 materials are found to possess largely identical inherent electrochemistry to the undoped WSe2 with a characteristic anodic peak. Living up to expectations, the Group 5 transition-metal-doped WSe2 materials exhibit improved electrocatalytic HER efficiency, as evident by the lower HER overpotentials and Tafel slopes relative to undoped WSe2 . After doping with V, Nb, or Ta species, an increased number of active sites is observed given the distinct changes in morphology from thick bulky pieces in undoped WSe2 to thinner fragments in doped WSe2 . Although undoped WSe2 exists in the semiconducting 2H phase, the Group 5 transition-metal-doped WSe2 materials are dominated by the metallic 1T phase. Doping WSe2 with V, Nb, or Ta stabilizes the catalytic 1T phase and appears to induce the transition from the 2H to 1T phase. In contrast to the enhanced HER performance of WSe2 upon doping, Group 5 transition-metal dopants proved futile in activating the ORR electrocatalytic behavior of WSe2 , for which the ORR efficiency is unchanged. Therefore, these findings facilitate the understanding of the role of Group 5 transition-metal dopants in the electrochemical and catalytic properties of WSe2 relative to their morphological features and provide an evaluation of the efficacy of doping TMDs in electrocatalytic applications.

The chemistry of graphene and its derivatives is one of the hottest topics of current material science research. The derivatisation of graphene is based on various approaches, and to date functionalization with halogens, hydrogen, various functional groups containing oxygen, sulfur, nitrogen, phosphorus, boron, and several other elements have been reported. Most of these functionalizations are based on sp3 hybridization of carbon atoms in the graphene skeleton, which means the formation of out-of-plane covalent bonds. Several elements were also reported for substitutional modification of graphene, where the carbon atoms are substituted with atoms like nitrogen, boron, and several others. From tens of functional groups, for only two of them were reported full functionalization of graphene skeleton and formation of its stoichiometric counterparts, fluorographene and hydrogenated graphene. The functionalization of graphene is crucial for most of its applications including energy storage and conversion devices, electronic and optic applications, composites, and many others.

The natural occurring Palaeoproterozoic carbon mineral shungite is a complex raw carbon microporous matrix, loaded with a wide range of elements. Shungite.exhibits disordered and amorphous structure with highly irregular building blocks. Shungite incorporates metals in its structure, typically catalytic elements such Fe and Ni are also present, as well as, the toxic elements Pb and As at mg/g level. We show here that incorporation of the metals in the carbon matrix of shungite leads into synergiustic catalytic effect. We investigate the application of the shungite in energy related electrochemical catalytic reaction, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). All elements have a synergetic effect, thus contributing for shungite interesting catalytic performance towards a different range of electrochemical reactions, outperforming other tested carbon allotropes, such as carbon black, metal loaded carbon nanotubes, fullerene and glassy carbon. These findings have profound impact on the application of the natural carbon materials for catalysis.

Graphene oxide (GO) is an important material used as precursor for the synthesis of graphene, its derivatives and various graphene based composite materials. In this paper we would like to demonstrate that highly-oxidized graphene oxide can be prepared much faster and, moreover, it has almost identical chemical composition compared to the previously published and currently broadly used standard procedures. We prepared two samples: one using the usual Tour's method and the other one using the novel method. The main advantage of this improved method is the shorter synthesis time which can be reduced six times allowing scaling and speeding up of large scale production. Oxidation shortening also led to reduction of defect concentration. Both graphene oxides were characterized in detail showing almost identical structure as well as chemical composition and concentration of oxygen functionalities typical for graphene oxide prepared by permanganate methods. In addition the sorption capacity towards heavy metals (zinc, cadmium and lead) was also studied showing a comparable sorption capacity with standard graphene oxide prepared by Tour method. Graphene oxide prepared by rapid oxidation can form mechanically stable transparent membranes. Our developed method of graphene oxide synthesis is time-efficient, cost-efficient and can help to introduce graphene oxide to industrial scale production.

Two members of the transition metal ditelluride family, CoTe2 and NiTe2, exist in multiple structures encompassing marcasite-, pyrite- and CdI2 related structures. The allotrope modification is influenced by weak changes in stoichiometry and synthesis. It is crucial to emphasize that the CdI2 structure type is manifested by NiTe2 while the CoTe2 adopts a related structure for a non-stoichiometric composition with ratio below 1:1.8. The obtained structure is based on LiTiS2 which is derived from CdI2 structure, however contains a polymeric cobalt network. Despite the atypical nature of their layered structure, layered phases of CoTe1.8 and NiTe2 are rarely cast into the spotlight. Here, layered CoTe1.8 and NiTe2 are investigated for their electrochemical and electrocatalytic properties. In electrocatalytic aspects, layered CoTe1.8 and NiTe2 demonstrate low overpotentials and small Tafel slopes that are quintessential features of hydrogen evolution electrocatalysts. These findings impart fundamental insights to the transition metal ditelluride family and affirm the prospective use of layered CoTe1.8 and NiTe2 in electrochemical applications.

Halogenated graphenes have been attracting great attention in the recent years. The currently used methods are usually non-specific, and halogen groups are randomly distributed over the graphene. Here we demonstrate a selective graphene functionalization based on a well known reaction mechanism-Hunsdiecker reaction-applied on selective bromination of graphene oxide. The chemical analysis using various spectroscopic methods proved a high efficiency of this functionalization method. Bromination can be carried out under mild conditions without any high temperature or high pressure treatment. The chemical modification led to introduction of up to 20 wt.% of bromine covalently bonded to the graphene skeleton. The modified graphene was characterized in detail using a broad range of microscopic and spectroscopic methods and no significant contamination by reaction by-products was detected.

In comparison to the extensive research and great success attained by Group 6 transition metal dichalcogenides (TMDs) as hydrogen evolution reaction (HER) electrocatalysts, there is limited research focused on metallic Group 5 TMDs for use as electrocatalysts for hydrogen evolution. Density functional theory calculations have pointed out that Group 5 TMDs are highly favorable for HER, especially vanadium disulfide. In this work, nanocomposites of graphene and Group 5 TMDs were synthesized by thermal exfoliation of graphene oxide/TMD precursors in an H2S atmosphere or in a H2 atmosphere as a control. Graphene oxide was prepared by the Hummers method while vanadium tetrachloride, niobium pentachloride, and tantalum pentachloride were utilized as TMD precursors. Then the potential of these nanocomposites as electrocatalysts towards HER was explored. Although these nanocomposites do not have comparable HER performance to Group 6 TMDs, they exhibit higher electrocatalytic activity in comparison with thermally reduced graphene oxide (TRGO) in the absence of TMD modification. In addition, the capacitive performance of these materials was also investigated in consideration of the high capacitance of graphene. It was indicated that the presence of TMDs on graphene actually suppress the capacitance performance of graphene itself.

Tremendous attention is paid to renewable sources of energy. Transition metal dichalcogenides (TMDs) are intensively studied for their promising catalytic activities in hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). In this fundamental work, we explore the catalytic properties of TMDs family members: 2H TaS2 and 1T TaS2. Our findings reveal that both polytypes exhibit poor HER performance which is even more pronounced when subjected to electrochemical treatment with reduction/oxidation. Our experimental data show that 1T TaS2 has a lower overpotential at a current density of -10 mA.cm-1, despite our theoretical density functional theory (DFT) calculations indicating that more favorable free energy of hydrogen adsorption should make perfect 2H TaS2 a better HER catalyst. By a thorough characterization, it is shown that the higher conductivity of 1T TaS2 and a slightly higher surface oxidation of 2H TaS2 explains this discrepancy. Moreover the changes in catalytic activity after electrochemical treatment are addressed here. For the oxygen reduction reaction (ORR) the electrochemical treatment leads to an improvement of catalytic properties. With onset potentials similar to that of Pt/C catalyst, TaS2 is found to be an efficient catalyst for oxygen reduction, rather than for proton reduction, in opposite to the behaviour of group VIB layered TMDs.

Fluorinated graphene can be prepared directly by thermal exfoliation of fluorographite. The exfoliation was performed in a dynamic nitrogen atmosphere at various temperatures and the exfoliation products were analysed in detail by GC-MS. The structure and properties of all prepared fluorinated graphenes with various contents of fluorine were characterized by a number of analytical techniques. The results show both the dependence of fluorine concentration on exfoliation temperature and the suitability of this method for the synthesis of graphene with controlled concentration of fluorine. The high-temperature exfoliated fluorographite exhibits a high heterogeneous electron transfer rate and excellent catalytic properties towards the oxygen reduction reaction. These synthetic procedures can open a simple way for the synthesis of fluorinated graphene-based devices with tailored properties.

A new member of the family of graphene derivatives, namely, graphene acid with a composition close to C1(COOH)1, was prepared by oxidation of graphene oxide. The synthetic procedure is based on repeated oxidation of graphite with potassium permanganate in an acidic environment. The oxidation process was studied in detail after each step. The multiple oxidations led to oxidative removal of other oxygen functional groups formed in the first oxidation step. Detailed chemical analysis showed only a minor amount of other oxygen-containing functional groups such as hydroxyl and the dominant presence of carboxyl groups in a concentration of about 30 wt %. Further oxidation led to complete decomposition of graphene acid. The obtained material exhibits unique sorption capacity towards metal ions and carbon dioxide. The highly hydrophilic nature of graphene acid allowed the assembly of ultrathin free-standing membranes with high transparency.

Graphane, the hydrogenated counterpart of graphene, was shown to exhibit properties such as tunable band gaps through varied degrees of hydrogenation, fluorescence, or ferromagnetism. Graphane nanostripe properties have also been theoretically predicted. Herein, we show that graphane nanostripes can be prepared by opening carbon nanotubes using Birch reduction in liquid ammonia utilizing potassium as a reducing agent and water as a proton donor. The prepared graphane nanostripes exhibit several exceptional properties when coupled with trace metal dopants. The interplay of metallic nanoparticles and defects lead to a spin polarization and induction of ferromagnetic moment, as well as to enhanced electrocatalytic properties in the hydrogen evolution reaction when compared to non-hydrogenated carbon nanotubes.

The chemical functionalization of hydrogenated graphene can modify its physical properties and lead to better processability. Herein, we describe the chemical functionalization of hydrogenated graphene through a dehydrogenative cross-coupling reaction between an allylic C-H bond and the α-C-H bond of tetrahydrothiophen-3-one using Cu(OTf)2 as the catalyst and DDQ as the oxidant. The chemical functionalization was confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy and visualized by scanning electron microscopy. The functionalized hydrogenated graphene material demonstrated improved dispersion stability in water, bringing new quality to the elusive hydrogenated graphene (graphane) materials. Hydrogenated graphene provides broad possibilities for chemical modifications owing to its reactivity.

It is well established that graphene oxide can be prepared by the oxidation of graphite using permanganate or chlorate in an acidic environment. Recently, however, the synthesis of graphene oxide using potassium ferrate(VI) ions has been reported. Herein, we critically replicate and evaluate this new ferrate(VI) oxidation method. In addition, we test the use of potassium ferrate(VI) for the synthesis of graphene oxide under various experimental routes. The synthesized materials are analyzed by a number of analytical methods in order to confirm or disprove the possibility of synthesizing graphene oxide by the ferrate(VI) oxidation route. Our results confirm the unsuitability of using ferrate(VI) for the oxidation of graphite on graphene oxide because of its high instability in an acidic environment and low oxidation power in neutral and alkaline environments.

MoS2 and WS2 have been prepared on a conductive graphene support by thermal reduction of tetrathiotungstate/tetrathiomolybdate and graphite oxide. Whereas the catalytic properties towards hydrogen evolution are strongly influenced by the Magnéli phases formed as a byproduct during the synthesis, the catalytic activity towards oxygen reduction of these composite materials is not affected by this phenomenon and these materials exhibit high catalytic activity towards this industrially important reaction.

The miniaturization of energy storage microcapacitors to develop portable electronic devices has been of high recent interest. Here, microsupercapacitors microrobot is fabricated using membrane template-assisted electrodeposition of WS2 nanoparticles (WS2NPs)/polyaniline (PANI) and platinum (Pt) layers. The microrobot navigates in the microchannel and attaches itself as part of the electrical circuit. The attached WS2NPs-PANI/Pt microrobots enhance the capacitive behavior of the circuit significantly. The results presented in this work open the door for the development of smart and miniaturized functional micromotors that are able to self-assemble to on-demand circuits. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore)

Partially hydrogenated graphene materials, synthesized by the chemical reduction/hydrogenation of two different graphene oxides using zinc powder in acidic environment or aluminum powder in alkaline environment, exhibit high electrocatalytic activities, as well as electrochemical sensing properties. The starting graphene oxides and the resultant hydrogenated graphenes were characterized in detail. Their electrocatalytic activity was examined in the oxygen reduction reaction, whereas sensing properties towards explosives were tested by using picric acid as a redox probe. Findings indicate that the high electrocatalytic performance originates not only from the hydrogenation of graphene, but also from unintentional contamination of graphene with manganese and other metals during synthesis. A careful evaluation of the obtained data and a detailed chemical analysis are necessary to identify the origin of this anomalous electrocatalytic activity.

WS2 nanoparticles are prepared using bipolar electrochemistry. Obtained material exhibits high activity for hydrogen evolution reaction (HER) and it is used as a label in standard magneto-immunosandwich assay for protein detection through HER. This new system shows high analytical performance in terms of a wide range, selectivity, sensitivity, and reproducibility. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore)

Presently, research in layered transition metal dichalcogenides (TMDs) for numerous electrochemical applications have largely focused on Group 6 TMDs, especially MoS2 and WS2, whereas TMDs belonging to other groups are relatively unexplored. This work unravels the electrochemistry of Group 10 TMDs: specifically PtS2, PtSe2, and PtTe2. Here, the inherent electroactivities of these Pt dichalcogenides and the effectiveness of electrochemical activation on their charge transfer and electrocatalytic properties are thoroughly examined. By performing density functional theory (DFT) calculations, the electrochemical and electrocatalytic behaviors of the Pt dichalcogenides are elucidated. The charge transfer and electrocatalytic attributes of the Pt dichalcogenides are strongly associated with their electronic structures. In terms of charge transfer, electrochemical activation has been successful for all Pt dichalcogenides as evident in the faster heterogeneous electron transfer (HET) rates observed in electrochemically reduced Pt dichalcogenides. Interestingly, the hydrogen evolution reaction (HER) performance of the Pt dichalcogenides adheres to a trend of PtTe2 > PtSe2 > PtS2 whereby the HER catalytic property increases down the chalcogen group. Importantly, the DFT study shows this correlation to their electronic property in which PtS2 is semiconducting, PtSe2is semimetallic, and PtTe2 is metallic. Furthermore, Pt dichalcogenides are effectively activated for HER. Distinct electronic structures of Pt dichalcogenides account for their different responses to electrochemical activation. Among all activated Pt dichalcogenides, PtS2 shows most accentuated improvement as a HER electrocatalyst with an exceptional 50% decline in HER overpotential. Knowledge on Pt dichalcogenides provides valuable insights in the field of TMD electrochemistry, in particular, for the currently underrepresented Group 10 TMDs.

Layered elemental materials, such as black phosphorus, exhibit unique properties originating from their highly anisotropic layered structure. The results presented herein demonstrate an anomalous anisotropy for the electrical, magnetic, and electrochemical properties of black phosphorus. It is shown that heterogeneous electron transfer from black phosphorus to outer- and inner-sphere molecular probes is highly anisotropic. The electron-transfer rates differ at the basal and edge planes. These unusual properties were interpreted by means of calculations, manifesting the metallic character of the edge planes as compared to the semiconducting properties of the basal plane. This indicates that black phosphorus belongs to a group of materials known as topological insulators. Consequently, these effects render the magnetic properties highly anisotropic, as both diamagnetic and paramagnetic behavior can be observed depending on the orientation in the magnetic field.