Search

Electroreduction of N2 is a highly promising route for NH3 production. The lack of efficient catalysts that can activate and then reduce N2 into NH3 limits this as a pragmatic application. In this work, a 2D layered group IV-V material, silicon phosphide (SiP), is evaluated as a suitable substrate for the electrochemical nitrogen reduction reaction (ENRR). To capture N2, one phosphorus (P) defect was introduced on the plane of SiP. DFT calculations found that the defective SiP monolayer (D1-SiP, which is defined by the P-defect on SiP) exhibits enormous prospects towards the ENRR because of enhanced electron conductivity, good activation on N2, lower limiting potential (UL = -0.87 V) through the enzymatic pathway, smooth charge transfer between the catalyst and the reaction species, and robust thermal stability. Importantly, D1-SiP demonstrates the suppressed activities on producing of H2 and N2H4 side-products. This research demonstrates the potential of 2D metal-free Si-based catalysts for nitrogen fixation and further enriches the study of group IV-V materials for the ENRR.

Cyanopyridone-based oligothiophene donors with both hydrophobic and hydrophilic characters have been evaluated as active layers within simple capacitive devices for humidity sensing at room temperature. Surface studies using atomic force microscopy revealed a self-assembled nanofibrous network with a thin needle-like structure for the terminal hydroxy example (CP6), devoid in the methyl example (CP1). The sensing performance of each sensor was investigated over a broad range of relative humidity levels as a function of capacitance at room temperature. The sensor CP6 demonstrated favourable features such as high sensitivity (12.2 pF/%RH), quick response/recovery (13 s/20.7 s), wide working range of relative humidity (10%–95% RH), low hysteresis (0.57%), outstanding recyclability, and excellent long-term stability. From the results obtained, hydrophilicity and hydrogen bonding appear to play a vital role in enhancing humidity sensing performance, leading to possible new design directions for simple organic semiconductor-based sensors.

We report for the first-time the development of capacitive type humidity sensors employing naphthalene diimide derivatives (NDI) as sensing layer. Three different naphthalene diimide derivatives bearing imide side chains of different hydrophilicity were designed, synthesised and characterised. X-ray diffraction and thermogravimetric analyses gave useful information about structural and thermal behaviour of the newly developed materials, indicating their crystallinity and stability. Atomic force microscopy analysis revealed a variety of morphologies in thin films as a result of the structural properties of the NDIs. Devices bearing NDI layers were fabricated on ceramic substrates with gold interdigitated electrodes spaced 200 µm apart. Humidity sensing performance, as a change in capacitance, was studied upon exposure to a wide range of relative humidity levels (0–95%) at ambient temperature. Importantly, an increase in the capacitance of the sensors was recorded with an increase in relative humidity. The developed sensors exhibited high sensitivity, good long-term stability, excellent reproducibility, and low hysteresis. The sensor performance was also tested against different operating frequencies (250 Hz–2 kHz) to improve linearity, illustrating directions for optimised performance. These results confirm that sensors based on NDIs possess better sensing performance to other types of reported capacitive humidity sensors.

This review provides an update on advances in the area of electrical mode sensors using organic small molecule n-type semiconductors based on perylene. Among small organic molecules, perylene diimides (PDIs) are an important class of materials due to their outstanding thermal, chemical, electronic, and optical properties, all of which make them promising candidates for a wide range of organic electronic devices including sensors, organic solar cells, organic field-effect transistors, and organic light-emitting diodes. This is mainly due to their electron-withdrawing nature and significant charge transfer properties. Perylene-based sensors of this type show high sensing performance towards various analytes, particularly reducing gases like ammonia and hydrazine, but there are several issues that need to be addressed including the selectivity towards a specific gas, the effect of relative humidity, and operating temperature. In this review, we focus on the strategies and design principles applied to the gas-sensing performance of PDI-based devices, including resistive sensors, amperometric sensors, and operating at room temperature. The device properties and sensing mechanisms for different analytes, focusing on hydrazine and ammonia, are studied in detail, and some future research perspectives are discussed for this promising field. We hope the discussed results and examples inspire new forms of molecular engineering and begin to open opportunities for other rylene diimide classes to be applied as active materials.

This work reports synthesis, thin film characterizations, and study of an organic semiconductor 2-aminoanthraquinone (AAq) for humidity and temperature sensing applications. The morphological and phase studies of AAq thin films are carried out by scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD) analysis. To study the sensing properties of AAq, a surface type Au/AAq/Au sensor is fabricated by thermally depositing a 60 nm layer of AAq at a pressure of ~10&minus, 5 mbar on a pre-patterned gold (Au) electrodes with inter-electrode gap of 45 &micro, m. To measure sensing capability of the Au/AAq/Au device, the variations in its capacitance and resistance are studied as a function of humidity and temperature. The Au/AAq/Au device measures and exhibits a linear change in capacitance and resistance when relative humidity (%RH) and temperature are varied. The AAq is a hydrophobic material which makes it one of the best candidates to be used as an active material in humidity sensors, on the other hand, its high melting point (575 K) is another appealing property that enables it for its potential applications in temperature sensors.

The positive impact of self-assembly on the photovoltaic properties of a donor-π-acceptor oligothiophene molecule coded as CP3, which contains a barbituric acid as a terminal acceptor unit and triphenylamine as donor, enabling hydrogen-bonded spherulites to assemble in its films is described. The hydrogen-bonded supramolecular array of barbiturated-oligothiophene molecules were directly visualized by scanning electron microscopy. Bulk-heterojunction solar cells comprising CP3 and the fullerene PC61BM show a power conversion efficiency of 6.31%, which is markedly higher than a structural analogue CP4, which comprises a N-ethylrhodanine terminal acceptor unit incapable of participating in the same degree of self-assembly, supporting the impact of self-assembly in BHJ devices.

Through the molecular engineering of cyanopyrid-2,6-dione functionality, herein we report the design and synthesis of a novel, small molecule electron donor, (Z)-5-((5'-(4-(diphenylamino)phenyl)-[2,2′-bithiophen]-5-yl)methylene)-1-(4-(hexyloxy)phenyl)-4-methyl-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-carbonitrile (coded as CP2), which exhibits improved optoelectronic and photovoltaic properties when compared with its structural analogue (E)-5-((5'-(4-(diphenylamino)phenyl)-[2,2′-bithiophen]-5-yl)methylene)-1-(2-ethylhexyl)-4-methyl-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-carbonitrile (coded as CP1). The molecular engineering helps to achieve more desirable energy levels together with bathochromic shift in the absorption spectrum, which improves the short-circuit current density. A high conversion efficiency of 6.28% was obtained in simple devices (CP2: PC61BM 1: 1) which is one of the best results in the current literature for cyanopyrid-2,6-dione-based small molecule donors.

Parent isoquinoline diimide (IQDI) and phthalazine diimide (PTDI), as two new heterocyclic analogues of naphthalene diimides (NDIs), have been synthesized through an oxidative strategy in 35-79 % yield. X-ray crystallography has been used to support the formation of IQDI, which also show fluorescence quantum yields of 3.5 %. The electrochemical and electrical properties of these molecules have been studied. The electrochemical results show an interesting trend in first reduction potential PTDI

A simple one pot hydrothermal procedure for the synthesis of cobalt selenide (CoSe) decorated reduced graphene oxide (rGO) is reported along with the application of this hybrid material as a new electrocatalyst for glucose oxidation. In alkaline media, glassy carbon electrodes modified with CoSe–rGO composite dispersed in chitosan display excellent reproducibility for the determination of glucose along with a high sensitivity of 480 μA mM−1 cm−2, a linear dynamic range of up to 10 mM, a lower limit of detection of 2.5 μM and an exceptionally high maximum current density of 5.41 ± 0.03 mA cm−2. Bulk electrolysis measurements carried out with the CoSe–rGO/chitosan modified glassy carbon plate revealed that the oxidation of glucose can proceed beyond the formation of gluconolactone with formate detected by 1H-NMR and CO2 detected by gas chromatography; the latter result showing the ability to achieve complete oxidation of glucose. Studies with ascorbic and uric acid showed that their interference with respect to glucose measurement either is negligible or can be overcome.

Bioanodes for fuel cell applications require highly efficient oxidation reactions to achieve a sufficiently large current density. In this study, gold nanoparticles have been synthesized using branched polyethylenimine (bPEI), a well-known polymer that forms a hydrogel in water, as the stabilizer. Primary amine groups available in bPEI provide active sites for further conjugation with ferrocene propionic acid via the 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide coupling reaction, with the enzyme glucose oxidase, using glutaraldehyde as linkers. This composite material was then used for the fabrication of glucose oxidase electrodes by drop casting of aqueous solutions onto glassy carbon electrodes. The three-dimensional structure offered by the new hydrogel facilitates communication between the enzyme and the electrode through the redox mediator ferrocene. This allows the glucose oxidase electrode to exhibit excellent activity towards electrocatalytic oxidation of glucose in phosphate buffer solutions at pH 7 with a maximum current density of approximately 800 μA cm−2, one of the highest values reported so far for redox hydrogel based glucose oxidase electrodes. Over a wide glucose concentration range, the enzyme response follows that predicted by the Michaelis-Menten equation with a Michaelis constant of 8.4 mM. In the sensing context, this electrode also exhibits a wide linear dynamic glucose concentration range of 0.5–10 mM with a limit of detection of 0.04 mM.

The fabrication of increasingly smaller machines to the nanometer scale can be achieved by either a “top-down” or “bottom-up” approach. While the former is reaching its limits of resolution, the latter is showing promise for the assembly of molecular components, in a comparable approach to natural systems, to produce functioning ensembles in a controlled and predetermined manner. In this review we focus on recent progress in molecular systems that act as molecular machine prototypes such as switches, motors, vehicles and logic operators.

The photophysics and excited-state dynamics of two dyads consisting of either a free-base or a zinc-tetraphenylporphyrin linked through a rigid bridge to a core-substituted naphthalenediimide (NDI) have been investigated by femtosecond-resolved spectroscopy. The absorption and fluorescence spectra differ substantially from those of the individual units, pointing to a substantial coupling and to a delocalisation of the excitation over the whole molecule, as confirmed by quantum chemistry calculations. A strong dependence of their excited-state dynamics on the solvent polarity has been observed. In toluene, the fluorescence quantum yield of the dyads is of the order of a few percent and the main decay channel of the emitting state is proposed as intersystem-crossing to the triplet state. However, in a medium polarity solvent like dichloromethane, the emitting state undergoes charge separation from the porphyrin to the NDI unit within 1-3 ps, and the ensuing charge-separated state recombines in about 10-20 ps. This solvent dependence can be explained by the weak driving force for charge separation in polar solvents and the large electronic coupling between the porphyrin and NDI moieties, making charge separation a solvent-controlled adiabatic process.

Micro-Raman spectra of hemozoin encapsulated within the food vacuole of a Plasmodium falciparum-infected erythrocyte are presented. The spectrum of hemozoin is identical to the spectrum of β-hematin at all applied excitation wavelengths. The unexpected observation of dramatic band enhancement of A1g modes including ν4 (1374 cm−1) observed when applying 780 nm excitation enabled Raman imaging of hemozoin in the food vacuole. This unusual enhancement, resulting from excitonic coupling between linked porphyrin moieties in the extended porphyrin array, enables the investigation of hemozoin within its natural environment for the first time.