Highly Reversible Molecular Photoswitches with Transition Metal Dichalcogenides Electrodes.

The molecule-electrode coupling plays an essential role in photoresponsive devices with photochromic molecules, and the strong coupling between the molecule and the conventional electrodes leads to/ the quenching effect and limits the reversibility of molecular photoswitches. In this work, we developed a strategy of using transition metal dichalcogenides (TMDCs) electrodes to fabricate the thiol azobenzene (TAB) self-assembled monolayers (SAMs) junctions with the eutectic gallium-indium (EGaIn) technique. The current-voltage characteristics of the EGaIn/GaOx //TAB/TMDCs photoswitches showed an almost 100% reversible photoswitching behavior, which increased by ∼28% compared to EGaIn/GaOx //TAB/AuTS photoswitches. Density functional theory (DFT) calculations showed the coupling strength of the TAB-TMDCs electrode decreased by 42% compared to that of the TAB-AuTS electrode, giving rise to improved reversibility. our work demonstrated the feasibility of 2D TMDCs for fabricating SAMs-based photoswitches with unprecedentedly high reversibility.

Conductance Growth of Single-Cluster Junctions with Increasing Sizes.

Quantum-tunneling-based nanoelectronics has the potential for the miniaturization of electronics toward the sub-5 nm scale. However, the nature of phase-coherent quantum tunneling leads to the rapid decays of the electrical conductance with tunneling transport distance, especially in organic molecule-based nanodevices. In this work, we investigated the conductance of the single-cluster junctions of a series of atomically well-defined silver nanoclusters, with varying sizes from 0.9 to 3.0 nm, using the mechanically controllable break junction (MCBJ) technique combined with quantum transport theory. Our charge transport investigations of these single-cluster junctions revealed that the conductance grows with increasing cluster size. The conductance decay constant was determined to be ∼-0.4 nm-1, which is of opposite sign to that of organic molecules. Comparison between experiment and theory reveals that although charge transport through the silver single-cluster junctions occurs via phase-coherent tunneling, this is compensated by a rapid decrease in the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO gap) with size and the increase in the electrode-cluster coupling, which results in their conductance increase up to lengths of ∼3.0 nm. These results demonstrate that such families of nanoclusters provide unique bottom-up building blocks for the fabrication of nanodevices in the sub-5 nm size range.

Electric Field-Induced Assembly in Single-Stacking Terphenyl Junctions.

Molecular assembly is crucial in functional molecular materials and devices. Among the molecular interactions that can form assemblies, stacking among π-conjugated molecular backbones plays an essential role in charge transport through organic materials and devices. The single-molecule junction technique allows for the application of an electric field of approximately 108 V/m to the nanoscale junctions and to investigate the electric field-induced assembly at the single-stacking level. Here, we demonstrate an electric field-induced stacking effect between two molecules using the scanning tunneling microscope break junction (STM-BJ) technique and we found an increase in the stacking probability with increasing intensity of the electric field. The combined density functional theory (DFT) calculations suggest that the molecules become more planar under the electric field, leading to the energetically preferred stacking configuration. Our study provides a new strategy for tuning molecular assembly by employing a strong electric field.

Light-Driven Reversible Intermolecular Proton Transfer at Single-Molecule Junctions.

Photoresponsive molecular systems are essential for molecular optoelectronic devices, but most molecular building blocks are non-photoresponsive. Employed here is a photoinduced proton transfer (PIPT) strategy to control charge transport through single-molecule azulene junctions with visible light under ambient conditions, which leads to a reversible and controllable photoresponsive molecular device based on non-photoresponsive molecules and a photoacid. Also demonstrated is the application of PIPT in two single-molecule AND gate and OR gate devices with electrical signal as outputs.

A high-performance electrochemical supercapacitor based on a polyaniline/reduced graphene oxide electrode and a copper(ii) ion active electrolyte.

Active electrolyte enhanced supercapacitors (AEESCs) have received increasing attention because of their large specific capacitance and easy fabrication process. The better matching between the active electrolyte and the counter electrode and the slow self-discharge rate are the challenges of this type of supercapacitor. In this paper, a novel AEESC with polyaniline/reduced graphene oxide hydrogel (PANI/RGOHG) as the anode and Cu(ii) ions as the cathodic active electrolyte is constructed. Experimental results demonstrate that the electrode potentials of PANI and Cu(ii) can match perfectly, thus the device has a wide working voltage range. Because of the large specific capacitance of both PANI and Cu(ii), a high average specific capacitance of a single electrode of 1120 F g-1 at 2.6 A g-1 is achieved. Meanwhile, self-discharge is also suppressed because the reduction product of Cu(ii) is immobilized on the electrode. These results demonstrate that the performance of AEESCs strongly depends on the choice of a suitable electrode material, and also reveal that Cu(ii) is a promising cathodic active electrolyte for AEESCs.

Gating of Quantum Interference in Molecular Junctions by Heteroatom Substitution.

To guide the choice of future synthetic targets for single-molecule electronics, qualitative design rules are needed, which describe the effect of modifying chemical structure. Here the effect of heteroatom substitution on destructive quantum interference (QI) in single-molecule junctions is, for the first time experimentally addressed by investigating the conductance change when a "parent" meta-phenylene ethylene-type oligomer (m-OPE) is modified to yield a "daughter" by inserting one nitrogen atom into the m-OPE core. We find that if the substituted nitrogen is in a meta position relative to both acetylene linkers, the daughter conductance remains as low as the parent. However, if the substituted nitrogen is in an ortho position relative to one acetylene linker and a para position relative to the other, destructive QI is alleviated and the daughter conductance is high. This behavior contrasts with that of a para-connected parent, whose conductance is unaffected by heteroatom substitution. These experimental findings are rationalized by transport calculations and also agree with recent "magic ratio rules", which capture the role of connectivity in determining the electrical conductance of such parents and daughters.

Effects of the fungicide trifloxystrobin on the structure and function of soil bacterial community.

Trifloxystrobin has been widely applied to prevent fungal diseases because of its high efficiency and desirable safety characteristics. In the present study, the effects of trifloxystrobin on soil microorganisms were integrally investigated. The results showed that trifloxystrobin inhibited urease activity, promoted dehydrogenase activity. Downregulated expressions of the nitrifying gene (amoA), denitrifying genes (nirK and nirS), and carbon fixation gene (cbbL) were also observed. Soil bacterial community structure analysis showed that trifloxystrobin changed the abundance of bacteria genera related to nitrogen and carbon cycle in soil. Through the comprehensive analysis of soil enzymes, functional gene abundance, and soil bacterial community structure, we concluded that trifloxystrobin inhibited both nitrification and denitrification of soil microorganisms, and also diminished the carbon-sequestration ability. Integrated biomarker response analysis showed that dehydrogenase and nifH were the most sensitive indicators of trifloxystrobin exposure. It provides new insights about trifloxystrobin environmental pollution and its influence on soil ecosystem.

Plasmon-Molecule Interactions in Single-Molecule Junctions.

Single-molecule optoelectronics offers opportunities for advancing integrated photonics and electronics, which also serves as a tool to elucidate the underlying mechanism of light-matter interaction. Plasmonics, which plays pivotal role in the interaction of photons and matter, have became an emerging area. A comprehensive understanding of the plasmonic excitation and modulation mechanisms within single-molecule junctions (SMJs) lays the foundation for optoelectronic devices. Consequently, this review primarily concentrates on illuminating the fundamental principles of plasmonics within SMJs, delving into their research methods and modulation factors of plasmon-exciton. Moreover, we underscore the interaction phenomena within SMJs, including the enhancement of molecular fluorescence by plasmonics, Fano resonance and Rabi splitting caused by the interaction of plasmon-exciton. Finally, by emphasizing the potential applications of plasmonics within SMJs, such as their roles in optical tweezers, single-photon sources, super-resolution imaging, and chemical reactions, we elucidate the future prospects and current challenges in this domain.

Effect of flumetsulam alone and coexistence with polyethylene microplastics on soil microbial carbon and nitrogen cycles: Elucidation of bacterial community structure, functional gene expression, and enzyme activity.

Flumetsulam (FLU) is a new class of broad-spectrum herbicides. With the widespread use of plastic products, polyethylene (PE) microplastics (MPs) may remain in the soil. It is possible for these two novel contaminants to co-exist in the soil environment. In the present study, we used brown soil as the test soil and determined the toxicity of FLU at 0.05, 0.5 and 2.5 mg kg-1 alone and in combination with PE MPs (1%) on soil microorganisms. The obtained results demonstrated that the exposure of FLU and FLU+MPs had an inhibitory effect on the numbers of bacteria and fungi. In addition, FLU and FLU+MPs caused changes in the relevant functional bacterial genera, favored nitrogen fixation and denitrification, and promoted soil carbon fixation, but inhibited nitrification. Compared to FLU exposure alone, exposure to FLU+MPs gave rise to significant differences in soil bacterial community composition, but did not affect carbon and nitrogen cycling. The integrated biomarker response results indicated that the toxicity of FLU and FLU+MPs to soil microorganisms increased with increasing concentrations of FLU. The present experiment clarified the toxicological effects of co-exposure of FLU and MPs on microorganisms and filled the toxicological data gap of FLU.

Polyethylene mulch film-derived microplastics enhance the bioaccumulation of atrazine in two earthworm species (Eisenia fetida and Metaphire guillelmi) via carrier effects.

Microplastics (MPs) may significantly affect the bioavailability of coexisting pollutants in soil by adsorption-desorption behavior. However, the mechanisms underlying these interaction remain unclear. Herein, the influence of unused polythylene mulch film-derived MPs (MFMPs) and farmland residual polyethylene mulch film-derived MPs (MFMPs-aged) on the adsorption-desorption behavior and bioavailability of atrazine (ATZ) in soil were investigated. The adsorption kinetics and the adsorption isotherms of ATZ on soil, MFMPs, and MFMPs-aged fitted well by the pseudo-second-order model and the Langmuir model, respectively. ATZ were easier to desorb from soil, MFMPs, and MFMPs-aged in the simulated earthworm digestive fluid than that in the CaCl2 solution. The adsorption and desorption capacities of MFMPs and MFMPs-aged for ATZ were higher than those of soil, especially for MFMPs-aged. The existence of MPs in soil strengthened the adsorption and desorption capacities of ATZ, and the strengthened effects were promoted by the addition amount and aging process of MPs. Moreover, the occurrence of MPs significantly increased the bioaccumulation of ATZ in earthworms, especially for MFMPs-aged. This study deepens the knowledge of the interaction mechanisms of mulch film-derived MPs and pesticide pollution.

σ-σ Stacked supramolecular junctions.

Intermolecular charge transport plays an essential role in organic electronic materials and biological systems. To date, experimental investigations of intermolecular charge transport in molecular materials and electronic devices have been restricted to conjugated systems in which π-π stacking interactions are involved. Herein we demonstrate that the σ-σ stacking interactions between neighbouring non-conjugated molecules offer an efficient pathway for charge transport through supramolecular junctions. The conductance of σ-σ stacked molecular junctions formed between two non-conjugated cyclohexanethiol or single-anchored adamantane molecules is comparable to that of π-π stacked molecular junctions formed between π-conjugated benzene rings. The current-voltage characteristics and flicker noise analysis demonstrate the existence of stacked molecular junctions formed between the electrode pairs and exhibit the characteristics of through-space charge transport. Density functional theory calculations combined with the non-equilibrium Green's function method reveal that efficient charge transport occurs between two molecules configured with σ-σ stacking interactions.

Determination of Ag[I] and NADH Using Single-Molecule Conductance Ratiometric Probes.

The sensing platform based on single-molecule measurements provides a new perspective for constructing ultrasensitive systems. However, most of these sensing platforms are unavailable for the accurate determination of target analytes. Herein, we demonstrate a conductance ratiometric strategy combing with the single-molecule conductance techniques for ultrasensitive and precise determination. A single-molecule sensing platform was constructed with the 3,3',5,5'-tetramethylbenzidine (TMB) and oxidized TMB (oxTMB) as the conductance ratiometric probes, which was applied in the detection of Ag[I] and nicotinamide adenine dinucleotide (NADH). It was found that the charge transport properties of TMB and oxTMB were distinct with more than an order of magnitude change of the conductance, thus enabling conductance ratiometric analysis of the Ag[I] and NADH in the real samples. The proposed method is ultrasensitive and has an anti-interference ability in the complicated matrix. The limit of detection can be as low as attomolar concentrations (∼34 aM). We believe that the proposed conductance ratiometric approach is generally enough to have a promising potential for broad and complicated analysis.

Electric field-induced switching among multiple conductance pathways in single-molecule junctions.

Here, we report the switching among multiple conductance pathways achieved by sliding the scanning tunneling microscope tip among different binding sites under different electric fields. With an increase in the electric field, high molecular conductance states appear, suggesting the formation of different configurations in single-molecule junctions. The switch can be operated in situ and reversibly, which is also confirmed by the apparent conductance conversion in I-V measurements. Theoretical simulations also agree well with the experimental results, which implies that the electric field enables the possibility to trigger switching in single-molecule junctions.

Cross-plane transport in a single-molecule two-dimensional van der Waals heterojunction.

Two-dimensional van der Waals heterojunctions (2D-vdWHs) stacked from atomically thick 2D materials are predicted to be a diverse class of electronic materials with unique electronic properties. These properties can be further tuned by sandwiching monolayers of planar organic molecules between 2D materials to form molecular 2D-vdWHs (M-2D-vdWHs), in which electricity flows in a cross-plane way from one 2D layer to the other via a single molecular layer. Using a newly developed cross-plane break junction technique, combined with density functional theory calculations, we show that M-2D-vdWHs can be created and that cross-plane charge transport can be tuned by incorporating guest molecules. The M-2D-vdWHs exhibit distinct cross-plane charge transport signatures, which differ from those of molecules undergoing in-plane charge transport.

A rapid and scalable integrated membrane separation process for purification of polysaccharides from Enteromorpha prolifera.

An integrated membrane separation process combining the tubular ceramic microfiltration (MF) membrane and the flat-sheet ultrafiltration (UF) membrane was developed to purify polysaccharides from Enteromorpha prolifera. The effects of membrane pore size, molecular weight cut-off (MWCO), transmembrane pressure (TMP) and adding-water multiples on membrane performance were in-depth studied. The results indicated that the optimal membrane pore size and TMP of the tubular ceramic MF process were found to be 1.2 µm and 0.225 MPa, and the optimal MWCO and TMP of the flat-sheet UF process were found to be 100 kDa and 0.3 MPa. The yields of polysaccharides were increased and optimized while the adding-water multiples was 1 during the diafiltration procedure. Furthermore, the water fluxes could be completely recovered using the specialized membrane cleaning methods, which ensured the reuse of membrane elements and satisfied the demands of industrial production. After purification by this integrated membrane separation process, the content of polysaccharides reached to 96.3%. The purified polysaccharides exhibited the superior moisture absorption and moisture retention properties compared to glycerol, polyethylene glycol (PEG) and luffa water.

Atomically defined angstrom-scale all-carbon junctions.

Full-carbon electronics at the scale of several angstroms is an expeimental challenge, which could be overcome by exploiting the versatility of carbon allotropes. Here, we investigate charge transport through graphene/single-fullerene/graphene hybrid junctions using a single-molecule manipulation technique. Such sub-nanoscale electronic junctions can be tuned by band gap engineering as exemplified by various pristine fullerenes such as C60, C70, C76 and C90. In addition, we demonstrate further control of charge transport by breaking the conjugation of their π systems which lowers their conductance, and via heteroatom doping of fullerene, which introduces transport resonances and increase their conductance. Supported by our combined density functional theory (DFT) calculations, a promising future of tunable full-carbon electronics based on numerous sub-nanoscale fullerenes in the large family of carbon allotropes is anticipated.

Facile Synthesis of Silver Nanoparticles with High Antibacterial Activity.

We report on a reverse microemulsion method for the synthesis of silver nanocrystals and examine their antibacterial activities. As the molar ratio of water to sodium bis(2-ethylhexyl) sulfosuccinate (AOT) increases to 25, a morphology transition from a sphere-like nanocrystal to a wire-like one was observed. For both the gram-negative and gram-positive bacteria, the wire-like silver nanocrystal showed higher antibacterial activities. We conclude that the morphology of silver nanocrystals dominates their antibacterial activity.

Three-Dimensional Printing of Polyaniline/Reduced Graphene Oxide Composite for High-Performance Planar Supercapacitor.

We apply direct ink writing for the three-dimensional (3D) printing of polyaniline/reduced graphene oxide (PANI/RGO) composites with PANI/graphene oxide (PANI/GO) gel as printable inks. The PANI/GO gel inks for 3D printing are prepared via self-assembly of PANI and GO in a blend solvent of N-methyl-2-pyrrolidinone and water, and offer both shaping capability, self-sustainability, and electrical conductivity after reduction of GO. PANI/RGO interdigital electrodes are fabricated with 3D printing, and based on these electrodes, a planar solid-state supercapacitor is constructed, which exhibits high performance with an areal specific capacitance of 1329 mF cm-2. The approach developed in this work provides a simple, economic, and effective way to fabricate PANI-based 3D architectures, which leads to promising application in future energy and electric devices at micro-nano scale.

Electrical and SERS detection of disulfide-mediated dimerization in single-molecule benzene-1,4-dithiol junctions.

We applied a combination of mechanically controllable break junction (MCBJ) and in situ surface enhanced Raman spectroscopy (SERS) methods to investigate the long-standing single-molecule conductance discrepancy of prototypical benzene-1,4-dithiol (BDT) junctions. Single-molecule conductance characterization, together with configuration analysis of the molecular junction, suggested that disulfide-mediated dimerization of BDT contributed to the low conductance feature, which was further verified by the detection of S-S bond formation through in situ SERS characterization. Control experiments demonstrated that the disulfide-mediated dimerization could be tuned via the chemical inhibitor. Our findings suggest that a combined electrical and SERS method is capable of probing chemical reactions at the single-molecule level.

One-Pot Synthesis of Hierarchical Flower-Like Pd-Cu Alloy Support on Graphene Towards Ethanol Oxidation.

The synergetic effect of alloy and morphology of nanocatalysts play critical roles towards ethanol electrooxidation. In this work, we developed a novel electrocatalyst fabricated by one-pot synthesis of hierarchical flower-like palladium (Pd)-copper (Cu) alloy nanocatalysts supported on reduced graphene oxide (Pd-Cu(F)/RGO) for direct ethanol fuel cells. The structures of the catalysts were characterized by using scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectrometer (XPS). The as-synthesized Pd-Cu(F)/RGO nanocatalyst was found to exhibit higher electrocatalytic performances towards ethanol electrooxidation reaction in alkaline medium in contrast with RGO-supported Pd nanocatalyst and commercial Pd black catalyst in alkaline electrolyte, which could be attributed to the formation of alloy and the morphology of nanoparticles. The high performance of nanocatalyst reveals the great potential of the structure design of the supporting materials for the future fabrication of nanocatalysts.