Functional Group Modification and Bonding Characteristics of Ti3C2 MXene-Organic Composites from First-Principles Calculations

The unique physical structure and abundant surface functional groups of MXene make the grafted organic molecules exhibit specific electrical and optical properties. This work reports the results of first-principles calculations to investigate the composite systems formed by different organic molecular monomers, namely acrylic acid (AA), acrylamide (AM), 1-aziridineethanol (1-AD) and glucose, and Ti₃C₂ MXene saturated with different functional groups, namely −OH, −O and −F. The results show that the interaction between organic molecules and the MXene surface depends on the type of functional groups of the organic molecules, while the strength of the interaction is determined by the type of surface functional groups and the number of hydrogen bonds. The bare Ti₃C₂ and Ti₃C₂(OH)₂ can readily form strong chemical and hydrogen bonds with AA and AM molecules, leading to strong adsorption energy and a large amount of charge transfer, while the interaction between organic molecules and MXene saturated by −F or −O groups mainly exhibits physical interactions, accompanied by low adsorption energy and a small amount of charge transfer. This research provides theoretical guidance for the synthesis of high-performance MXene organic composite systems.     

Mussel‐inspired decoration of Ni(OH)2 nanosheets on 2D MoS2 towards enhancing thermal and flame retardancy properties of poly(lactic acid)

In the present work, a facile and environmental method was developed to fabricate the novel functionalized MoS₂ hybrid. Firstly, MoS₂ nanosheets were coated with polydopamine (PDA) through the self‐polymerization of dopamine (MoS₂‐PDA) in a buffer solution. Then the decoration of Ni(OH)₂ on the MoS₂‐PDA was synthesized because of the strong affinity of Ni²⁺ with hydroxyl groups in PDA. Finally, the as‐synthesized MoS₂‐PDA@Ni(OH)₂ was introduced into poly(lactic acid) (PLA) matrix to explore flame retardancy, thermal stability, and crystalline property of the composites. As confirmed by X‐ray diffraction (XRD), Fourier‐transform infrared spectrometer (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), the MoS₂ nanosheets were dually modified with PDA and Ni(OH)₂ without destroying the original structures. The thermal degradation of PLA with MoS₂‐PDA@Ni(OH)₂ generated a notably higher yield of char. Moreover, the crystallization rate of composites is higher than neat PLA. The cone calorimeter test revealed that the introduction of 3% MoS₂‐PDA@Ni(OH)₂ resulted in lower Peak Heat Release Rate (PHRR) (decreased by 21.7%). Thus, the research provided an innovative functionalization method for manufacturing PLA composites with high performances.     

Understanding how Lewis acids dope organic semiconductors: a “complex” story

We report on computational studies of the potential of three borane Lewis acids (LAs) (B(C₆F₅)₃ (BCF), BF₃, and BBr₃) to form stable adducts and/or to generate positive polarons with three different semiconducting π-conjugated polymers (PFPT, PCPDTPT and PCPDTBT). Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations based on range-separated hybrid (RSH) functionals provide insight into changes in the electronic structure and optical properties upon adduct formation between LAs and the two polymers containing pyridine moieties, PFPT and PCPDTPT, unravelling the complex interplay between partial hybridization, charge transfer and changes in the polymer backbone conformation. We then assess the potential of BCF to induce p-doping in PCPDTBT, which does not contain pyridine groups, by computing the energetics of various reaction mechanisms proposed in the literature. We find that reaction of BCF(OH₂) to form protonated PCPDTBT and [BCF(OH)]⁻, followed by electron transfer from a pristine to a protonated PCPDTBT chain is highly endergonic, and thus unlikely at low doping concentration. The theoretical and experimental data can, however, be reconciled if one considers the formation of [BCF(OH)BCF]⁻ or [BCF(OH)(OH₂)BCF]⁻ counterions rather than [BCF(OH)]⁻ and invokes subsequent reactions resulting in the elimination of H₂.

Here we report on DFT calculations investigating the mechanistic aspects in doping organic semiconductors by the use of Lewis acids. Our results highlight the role played by the formation of diboron-containing bridged anions in the doping mechanism.     

Structural isomers of 2-(2,3 and 4-substituted-phenyl)-1,2-benzisoselenazol-3(2H)-one: A Theoretical Study

A series of 2-(2,3 and 4-substituted-phenyl)-1,2-benzisoselenazol-3(2H)-one molecules were theoretically investigated by the use of density functional theory (DFT) calculations at the B3LYP/6-311++G^∗∗ level of the theory. The substituents studied in this work are X = H; CH₃; NH₂; OH; OCH₃; F, Cl; Br; NO₂; CN; COCH₃; CO₂H; CO₂Me; SH; BH₂. We have selected these functional groups to be placed in the 2, 3 and 4 positions with relation to the benzisoselenazol moiety in order to show the effect of these structural modifications on the electronic properties of the molecules.     

Extremely Electron-Withdrawing Lewis-Paired CN Groups for Organic p-Dopants

P-type chemical doping (p-doping) is a key technique to modulate the optical, electrical, and electronic properties of organic semiconductors. However, typical functional groups in organic p-dopants have insufficient electron-withdrawing strength, and the inevitable diffusion of dopants in host matrices degrades doping stabilities. Herein, we utilize extremely electron-withdrawing Lewis-paired CN groups as a new class of building blocks for designing unprecedentedly strong organic p-dopants with excellent doping stability. Various Lewis acids are paired with CN-functionalized conjugated molecules in the solution state, which strengthens the electron-withdrawing properties of CN groups almost twofold. The large dopants afford outstanding doping stability against continuous heating and long-term atmospheric exposure, which is promising for practical applications in devices. Given the broad applicability of this simple combinatorial approach, it may impact many fields of (opto)electronics.     

Electronic structure of niobium-doped molybdenum disulfide nanotubes

The effect of doping transition metal disulfide nanotubes on their structural and electronic properties was studied for the first time using self-consistent band-structure calculations by the density functional tight-binding method (DFTB). The influence of partial Nb → Mo substitution in the walls of MoS₂ nanotubes of various diameters and atomic configurations (armchair and zigzag) on their electronic structure, structural parameters, and relative stability is exemplified by a series of “mixed” Mo_0.9Nb_0.1S₂ nanotubes. The electronic properties of Mo_0.9Nb_0.1S₂ nanotubes are discussed as a function of the possible types of distribution of doping Nb atoms in the tubes.     

Precise Tuning of the Charge Transfer Kinetics and Catalytic Properties of MoS2 Materials via Electrochemical Methods

MoS₂ has become particularly popular for its catalytic properties towards the hydrogen evolution reaction (HER). It has been shown that the metallic 1T phase of MoS₂, obtained by chemical exfoliation after lithium intercalation, possesses enhanced catalytic activity over the semiconducting 2H phase due to the improved conductivity properties which facilitate charge‐transfer kinetics. Here we demonstrate a simple electrochemical method to precisely tune the electron‐transfer kinetics as well as the catalytic properties of both exfoliated and bulk MoS₂‐based films. A controlled reductive or oxidative electrochemical treatment can alter the surface properties of the film with consequently improved or hampered electrochemical and catalytic properties compared to the untreated film. Density functional theory calculations were used to explain the electrochemical activation of MoS₂. The electrochemical tuning of electrocatalytic properties of MoS₂ opens the doors to scalable and facile tailoring of MoS₂‐based electrochemical devices.     

Metal-like Charge Transport in PEDOT(OH) Films by Post-processing Side Chain Removal from a Soluble Precursor Polymer

Herein, a route to produce highly electrically conductive doped hydroxymethyl functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) films, termed PEDOT(OH) with metal-like charge transport properties using a fully solution processable precursor polymer is reported. This is achieved via an ester-functionalized PEDOT derivative [PEDOT(EHE)] that is soluble in a range of solvents with excellent film-forming ability. PEDOT(EHE) demonstrates moderate electrical conductivities of 20–60 S cm⁻¹ and hopping-like (i.e., thermally activated) transport when doped with ferric tosylate (FeTos₃). Upon basic hydrolysis of PEDOT(EHE) films, the electrically insulative side chains are cleaved and washed from the polymer film, leaving a densified film of PEDOT(OH). These films, when optimally doped, reach electrical conductivities of ≈1200 S cm⁻¹ and demonstrate metal-like (i.e., thermally deactivated and band-like) transport properties and high stability at comparable doping levels.     

Designing new donor materials based on functionalized DCCnT with different electron-donating groups: A density functional theory (DFT) and time dependent density functional theory (TDDFT)-based study

Finding a promising donor/acceptor material of organic solar cells is one of the most important ways to improve their power conversion efficiency. Extensive studies have focused on designing and synthesizing new and suitable materials. Small organic molecule materials, different from polymers, have many merits, such as easy synthesis and modification, less by-products, and crystallinity. In the present work, we theoretically design a series of new donor materials based on 1-(1,1-dicyanomethylene)-cyclohex-2-ene-substituted oligothiophenes, that is, DCCnT (n = 1-4) series. Furthermore, we model and predict photoelectric properties of functionalized DCCnT with different electron-donating groups (─CH₃/─CHCH₂/─OCH₃/─NH₂/─OH). The calculated results, based on density functional theory and time-dependent functional theory, show that DCCnT-X (X = OH, NH₂, and OCH₃) series show odd-even effect of dipole moments when n varies from 1 to 4, whereas DCCnT-CH₃ and DCCnT-CHCH₂ do not. Finally, we find that DCC3T-X (X = OH, OCH₃, and NH₂) may be better candidates of donor materials because of their larger dipole moments, stronger electron donating ability, and smaller exciton binding energy with respect to prototype DCCnT molecules.     

Probing the interfacial interaction between monolayer molybdenum disulfide and Au nanoclusters

Coupling of plasmonic metal nanostructures on two‐dimensional materials represents one promising approach to improve their optoelectronic device performance. In this article, we systematically investigated the interfacial interactions between Au nanoclusters and monolayer molybdenum disulfide (MoS₂) and the effect of Au decoration on the electrical transport and optical properties of MoS₂, through the combination of in situ MoS₂ field‐effect transistor device evaluation and in situ ultraviolet photoelectron spectroscopy and X‐ray photoelectron spectroscopy measurements. The in situ X‐ray photoelectron spectroscopy/ultraviolet photoelectron spectroscopy experiments revealed a weak interfacial coupling between Au nanoclusters and monolayer MoS₂. The absence of strong charge transfer between Au nanoclusters and MoS₂ was further confirmed by the photoluminescence and Raman measurements. It was also found that the electron charge‐carrier concentration in monolayer MoS₂ weakly depended on the coverage of Au nanoclusters. Copyright © 2017 John Wiley & Sons, Ltd.     

DFT Theoretical Calculation of the Site Selectivity of Dihydroxylated (5, 0) Zigzag Carbon Nanotube

Functionalization is an important method to change electrical and thermodynamic properties of carbon nanotubes. In this study, the effect of functionalization of a single-walled carbon nanotube (SWCNT) was investigated with the aid of density functional theory. For this case, a (5, 0) zigzag SWCNT model containing 60 C atoms with 10 hydrogen atoms added to the dangling bonds of the perimeter carbons was used. To model hydroxyl CNT two terminal H atoms were replaced by two –OH groups. All the functionalized CNTs are thermodynamically more stable and have higher dipole moment with respect to the pristine CNT. Depending on the positions of hydroxyl groups on CNT five isomers of C₆₀H₈(OH)₂ were obtained. The structure of these five isomers and molecular properties such as the HOMO–LUMO gaps, the dipole moments, and the density of state were calculated. Our results indicate that the HOMO–LUMO gap strongly depends on the placement of the hydroxyl groups on the nanotubes. The isomers were hydroxyl groups locate on the anti-position show the highest distortions in the structure of the CNT.

     

Top‐Down and Bottom‐Up Approaches in Engineering 1 T Phase Molybdenum Disulfide (MoS2): Towards Highly Catalytically Active Materials

The metallic 1 T phase of MoS₂ has been widely identified to be responsible for the improved performances of MoS₂ in applications including hydrogen evolution reactions and electrochemical supercapacitors. To this aim, various synthetic methods have been reported to obtain 1 T phase‐rich MoS₂. Here, the aim is to evaluate the efficiencies of the bottom‐up (hydrothermal reaction) and top‐down (chemical exfoliation) approaches in producing 1 T phase MoS₂. It is established in this study that the 1 T phase MoS₂ produced through the bottom‐up approach contains a high proportion of 1 T phase and demonstrates excellent electrochemical and electrical properties. Its performance in the hydrogen evolution reaction and electrochemical supercapacitors also surpassed that of 1 T phase MoS₂ produced through a top‐down approach.     

A glassy carbon electrode modified with a nanocomposite consisting of molybdenum disulfide intercalated into self-doped polyaniline for the detection of bisphenol A

Thin-layered molybdenum disulfide (MoS₂) was intercalated, via ultrasonic exfoliation, into self-doped polyaniline (SPAN). This material, when placed on a glassy carbon electrode (GCE), exhibits excellent electrical conductivity and synergistic catalytic activity with respect to the detection of bisphenol A (BPA). The electrochemical response of the modified GCE to BPA was investigated by cyclic voltammetry and differential pulse voltammetry. Under optimal conditions, the oxidation peak current (measured best at 446 mV vs. SCE) is related to the concentration of BPA in the range from 1.0 nM to 1.0 μM, and the detection limit is 0.6 nM.

Thin-layered molybdenum disulfide (MoS₂) was intercalated into self-doped polyaniline (SPAN) via ultrasonic exfoliation. The special conjugated structure and functional groups of MoS₂-SPAN composite help to adsorb BPA easily. MoS₂-SPAN has a synergistic effect for catalyzing the oxidation of BPA. The BPA electrochemical sensor based on MoS₂-SPAN has a high sensitivity and low detection limit.

     

Surface Modulation of Iron-doped MoS2 Nanosheets by Phytic Acid for Enhanced Water Oxidation

Surface modulation and heteroatom doping are important approaches for boosting the electrocatalytic performances of MoS₂ nanosheets. As a molecular electrocatalyst, the natural organic phytic acid (PA) offer attractive intermediate for oxygen evolution reaction (OER). Here, a surface modulation strategy is demonstrated through the decoration of PA onto the basal plane of iron (Fe)-doped MoS₂ nanosheets supported on nickel foam (NF) for boosted OER activity. Experimental results indicate that the PA modification and Fe doping could effectively boost the charge transfer and mass transport during the OER process. Specially, PA2-Fe−MoS₂ grown on NF (PA2-Fe−MoS₂/NF) exhibits excellent OER activity (218 mV@20 mA cm⁻²) and durability, even superior to RuO₂ and many other previously reported OER catalysts. This natural organic molecule modification provides a facile strategy to designing low-cost and efficient electrocatalytic materials.     

Selective Reduction of Nitroarenes with Molybdenum Disulfide

Commercial MoS₂ was found to be a highly selective catalyst for the reduction of nitrobenzenes to the corresponding anilines with hydrazine under mild conditions. MoS₂ is not only much cheaper, but also more selective than noble metal catalysts for the reduction of functional nitrobenzenes to the corresponding anilines. Nitrobenzenes with halides (F, Cl, Br and I) were reduced selectively, and the corresponding anilines were obtained in excellent yields, and no dehalogenation was detected. Functional groups such as NH₂, OH, alkene groups were tolerated during the reduction of the nitro compounds. The reduction of p‐chloronitrobenzene was studied over MoS₂ and Pd/C respectively with hydrazine. The yield of p‐chloroaniline was much higher with MoS₂ than that with Pd/C at full conversion.     

Water-Assisted Concerted Proton-Electron Transfer at Co(II)-Aquo Sites in Polyoxotungstates With Photogenerated RuIII(bpy)33+ Oxidant

The cobalt substituted polyoxotungstate [Co₆(H₂O)₂(α-B-PW₉O₃₄)₂(PW₆O₂₆)]¹⁷⁻ ( Co6 ) displays fast electron transfer (ET) kinetics to photogenerated Ru^III(bpy)₃³⁺, 4 to 5 orders of magnitude faster than the corresponding ET observed for cobalt oxide nanoparticles. Mechanistic evidence has been acquired indicating that: (i) the one-electron oxidation of Co6 involves Co(II) aquo or Co(II) hydroxo groups (abbreviated as Co6(II) −OH ₂ and Co6(II) −OH, respectively, whose speciation in aqueous solution is associated to a pK_a of 7.6), and generates a Co(III)−OH moiety ( Co6(III) −OH), as proven by transient absorption spectroscopy; (ii) at pH>pK_a, the Co6(II) −OH→Ru^III(bpy)₃³⁺ ET occurs via bimolecular kinetics, with a rate constant k close to the diffusion limit and dependent on the ionic strength of the medium, consistent with reaction between charged species; (iii) at pH <pK_a, the process involves Co6(II) − OH₂ → Co6(III)−OH transformation and proceeds via a multiple-site, concerted proton electron transfer (CPET) where water assists the transfer of the proton, as proven by the absence of effect of buffer base concentrations on the rate of the ET and by a H/D kinetic isotope in a range of 1.2–1.4. The reactivity of water is ascribed to its organization on the surface of the polyanionic scaffold through hydrogen bond networking involving the Co(II)−OH₂ group.     

Synthesis, thermal behavior, and spectral properties of mixed-metal Cu(I)-VO(IV)-thiourea coordination polymers

Abstract  

The heterometallic complexes [Cu(VO)₂(CSN₂H₄)₃Cl(OH)₄]·H₂O, [Cu₂(VO)₂(CSN₂H₄)₂(C₂H₃O₂)₂·(OH)₄], and [Cu₂(VO)₃(CSN₂H₄)₄(C₂H₃O₂)₄(OH)₄] were prepared and characterized in terms of their molecular electrical conductivity, electronic and IR spectra, and thermal behavior. A polymeric structure is proposed in which a thiourea ligand is bonded via a sulfur atom to the tetracoordinated copper(I) and via amino groups to the oxovanadium(IV) ion. The polymeric nature of the complexes is due to bridging via the OH, thiourea, and/or acetate moieties between oxovanadium(IV) coordination centers.     

Incorporation of two‐dimensional nanomaterials into silk fibroin nanofibers for cardiac tissue engineering

Mimicking the extracellular matrix to have a similar nanofibrous structure regarding electrical conductivity and mechanical properties would be highly beneficial for cardiac tissue engineering. The molybdenum disulfide, MoS₂, and reduced graphene oxide, rGO, nanosheets are two‐dimensional nanomaterials which can be considered as great candidates for enhancing the electrical and mechanical properties of biological scaffolds for cardiac tissue engineering applications. In this study, MoS₂ and rGO nanosheets were synthesized and incorporated into silk fibroin nanofibers, SF, via electrospinning method. Then, the human iPSCs transfected with TBX‐18 gene, TBX18‐hiPSCs, were seeded on these scaffolds for in vitro studies. The MoS₂ and rGO nanosheets were studied by Raman spectroscopy. After incorporation of the nanosheets into SF nanofibers, the associated characterizations were carried out including scanning electron microscopy, transmission electron microscopy, water contact angle, and mechanical test. Furthermore, SF, SF/MoS₂, and SF/rGO scaffolds were used for in vitro studies. Herein, the scaffolds exhibited acceptable biocompatibility and considerable attachment to TBX18‐hiPSCs confirmed by 3‐(4, 5‐dimethylthiazol‐2‐yl)‐2, 5‐diphenyl tetrazolium bromide, MTT, assay, and scanning electron microscopy. Also, the real‐time PCR and immunostaining studies confirmed the maturity and upregulation of cardiac functional genes, including GATA‐4, c‐TnT, and α‐MHC in the SF/MoS₂ and SF/rGO scaffolds compared with the bare SF one. Therefore, the reinforcement of these SF‐based scaffolds with MoS₂ and rGO endues them as a suitable candidate for cardiac tissue engineering.     

Engineering Chemically Exfoliated Large‐Area Two‐Dimensional MoS2 Nanolayers with Porphyrins for Improved Light Harvesting

Molybdenum disulfide (MoS₂) is a promising candidate for electronic and optoelectronic applications. However, its application in light harvesting has been limited in part due to crystal defects, often related to small crystallite sizes, which diminish charge separation and transfer. Here we demonstrate a surface‐engineering strategy for 2D MoS₂ to improve its photoelectrochemical properties. Chemically exfoliated large‐area MoS₂ thin films were interfaced with eight molecules from three porphyrin families: zinc(II)‐, gallium(III)‐, iron(III)‐centered, and metal‐free protoporphyrin IX (ZnPP, GaPP, FePP, H₂PP); metal‐free and zinc(II) tetra‐(N‐methyl‐4‐pyridyl)porphyrin (H₂T4, ZnT4); and metal‐free and zinc(II) tetraphenylporphyrin (H₂TPP, ZnTPP). We found that the photocurrents from MoS₂ films under visible‐light illumination are strongly dependent on the interfacial molecules and that the photocurrent enhancement is closely correlated with the highest occupied molecular orbital (HOMO) levels of the porphyrins, which suppress the recombination of electron–hole pairs in the photoexcited MoS₂ films. A maximum tenfold increase was observed for MoS₂ functionalized with ZnPP compared with pristine MoS₂ films, whereas ZnT4‐functionalized MoS₂ demonstrated small increases in photocurrent. The application of bias voltage on MoS₂ films can further promote photocurrent enhancements and control current directions. Our results suggest a facile route to render 2D MoS₂ films useful for potential high‐performance light‐harvesting applications.     

In Situ Formation of a MoS2‐Based Inorganic–Organic Nanocomposite by Directed Thermal Decomposition

Nanocomposites based on molybdenum disulfide (MoS₂) and different carbon modifications are intensively investigated in several areas of applications due to their intriguing optical and electrical properties. Addition of a third element may enhance the functionality and application areas of such nanocomposites. Herein, we present a facile synthetic approach based on directed thermal decomposition of (Ph₄P)₂MoS₄ generating MoS₂ nanocomposites containing carbon and phosphorous. Decomposition at 250 °C yields a composite material with significantly enlarged MoS₂ interlayer distances caused by in situ formation of Ph₃PS bonded to the MoS₂ slabs through Mo?S bonds and (Ph₄P)₂S molecules in the van der Waals gap, as was evidenced by ³¹P solid‐state NMR spectroscopy. Visible‐light‐driven hydrogen generation demonstrates a high catalytic performance of the materials.