Tunable Optical Transition in 2H-MoS2 via Direct Electrochemical Engineering of Vacancy Defects and Surface S-C Bonds

Clicking beyond suspensions: understanding thiol-ene chemistry on solid-supported MoS2

Molecular functionalization of MoS2 has attracted a lot of attention due to its potential to afford fine-tuned hybrid materials that benefit from the power of synthetic chemistry and molecular design. Here, we report on the on-surface reaction of maleimides on bulk and molecular beam epitaxy grown single-layer MoS2, both in ambient conditions as well as ultrahigh vacuum using scanning probe microscopy.

The Covalent Functionalization of Surface-Supported Graphene: An Update

In the last decade, the use of graphene supported on solid surfaces has broadened its scope and applications, and graphene has acquire a promising role as a major component of high-performance electronic devices. In this context, the chemical modification of graphene has become essential. In particular, covalent modification offers key benefits, including controllability, stability, and the facility to be integrated into manufacturing operations. In this Review, we critically comment on the latest advances in the covalent modification of supported graphene on substrates. We analyze the different chemical modifications with special attention to radical reactions. In this context, we review the latest achievements in reactivity control, tailoring electronic properties, and introducing active functionalities. Finally, we extended our analysis to other emerging 2D materials supported on surfaces, such as transition metal dichalcogenides, transition metal oxides, and elemental analogs of graphene.

Covalent photofunctionalization and electronic repair of 2H-MoS2via nitrogen incorporation

A route towards covalent functionalization of chemically inert 2H-MoS₂ exploiting sulfur vacancies is explored by means of (TD)DFT and GW/BSE calculations. Functionalization via nitrogen incorporation at sulfur vacancies is shown to result in more stable covalent binding than via thiol incorporation. In this way, defective monolayer MoS₂ is repaired and the quasiparticle band structure as well as the remarkable optical properties of pristine MoS₂ are restored. Hence, defect-free functionalization with various molecules is possible. Our results for covalently attached azobenzene, as a prominent photo-switch, pave the way to create photoresponsive two-dimensional (2D) materials.

Molecular Functionalization of 2H-Phase MoS2 Nanosheets via an Electrolytic Route for Enhanced Catalytic Performance

The molecular functionalization of two-dimensional MoS₂ is of practical relevance with a view to, for example, facilitating its liquid-phase processing or enhancing its performance in target applications. While derivatization of metallic 1T-phase MoS₂ nanosheets has been relatively well studied, progress involving their thermodynamically stable, 2H-phase counterpart has been more limited due to the lower chemical reactivity of the latter. Here, we report a simple electrolytic strategy to functionalize 2H-phase MoS₂ nanosheets with molecular groups derived from organoiodides. Upon cathodic treatment of a pre-expanded MoS₂ crystal in an electrolyte containing the organoiodide, water-dispersible nanosheets derivatized with acetic acid or aniline moieties (∼0.10 molecular groups inserted per surface sulfur atom) were obtained. Analysis of the functionalization process indicated it to be enabled by the external supply of electrons from the cathodic potential, although they could also be sourced from a proper reducing agent, as well as by the presence of intrinsic defects in the 2H-phase MoS₂ lattice (e.g., sulfur vacancies), where the molecular groups can bind. The acetic acid-functionalized nanosheets were tested as a non-noble metal-based catalyst for nitroarene and organic dye reduction, which is of practical utility in environmental remediation and chemical synthesis, and exhibited a markedly enhanced activity, surpassing that of other (1T- or 2H-phase) MoS₂ materials and most non-noble metal catalysts previously reported for this application. The reduction kinetics (reaction order) was seen to correlate with the net electric charge of the nitroarene/dye molecules, which was ascribed to the distinct abilities of the latter to diffuse to the catalyst surface. The functionalized MoS₂ catalyst also worked efficiently at realistic (i.e., high) reactant concentrations, as well as with binary and ternary mixtures of the reactants, and could be immobilized on a polymeric scaffold to expedite its manipulation and reuse.

Substrate Materials for Biomolecular Immobilization within Electrochemical Biosensors

Electrochemical biosensors have potential applications for agriculture, food safety, environmental monitoring, sports medicine, biomedicine, and other fields. One of the primary challenges in this field is the immobilization of biomolecular probes atop a solid substrate material with adequate stability, storage lifetime, and reproducibility. This review summarizes the current state of the art for covalent bonding of biomolecules onto solid substrate materials. Early research focused on the use of Au electrodes, with immobilization of biomolecules through ω-functionalized Au-thiol self-assembled monolayers (SAMs), but stability is usually inadequate due to the weak Au-S bond strength. Other noble substrates such as C, Pt, and Si have also been studied. While their nobility has the advantage of ensuring biocompatibility, it also has the disadvantage of making them relatively unreactive towards covalent bond formation. With the exception of Sn-doped In2O3 (indium tin oxide, ITO), most metal oxides are not electrically conductive enough for use within electrochemical biosensors. Recent research has focused on transition metal dichalcogenides (TMDs) such as MoS2 and on electrically conductive polymers such as polyaniline, polypyrrole, and polythiophene. In addition, the deposition of functionalized thin films from aryldiazonium cations has attracted significant attention as a substrate-independent method for biofunctionalization.

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.

Covalent functionalization of molybdenum disulfide by chemically activated diazonium salts

Covalent functionalization is one of the most efficient ways to tune the properties of layered materials in a highly controlled manner. However, molecular chemisorption on semiconducting transition metal dichalcogenides remains a delicate task due to the inertness of their surface. Here we perform covalent modification of bulk and single layer molybdenum disulfide (MoS₂) using chemical activation of diazonium salts. A high level of control over the grafting density and yield on MoS₂ basal plane can be achieved by this approach. Using scanning probe microscopies and X-ray photoelectron spectroscopy we prove the covalent functionalization of MoS₂.