Synergistic Enhancement of Water-Splitting Performance Using MOF-Derived Ceria-Modified g-C3N4 Nanocomposites: Synthesis, Performance Evaluation, and Stability Prediction with Machine Learning.

Diminishing the charge recombination rate by improving the photoelectrochemical (PEC) performance of graphitic carbon nitride (g-C3N4) is essential for better water oxidation. In this concern, this research explores the competent approach to enhance the PEC performance of g-C3N4 nanosheets (NSs), creating their nanocomposites (NCs) with metal-organic framework (MOF)-derived porous CeO2 nanobars (NBs) along with ZnO nanorods (NRs) and TiO2 nanoparticles (NPs). The synthesis involved preparing CeO2 NBs and g-C3N4 NSs through the calcination of respective precursors, while the sol-gel method is employed for ZnO NRs and TiO2 NPs. Following the subsequent analysis of the physicochemical properties of the materials, the binder-free brush-coating method is deployed to fabricate NC-based photoanodes, followed by an evaluation of the PEC performance through various electrochemical techniques. Remarkably, the binary g-C3N4/CeO2 NCs with 20 wt % CeO2 NBs (gC20 NCs) exhibited a significantly enhanced current density of 0.460 mA/cm2 at 1.23 V vs reversible hydrogen electrode, which is 2.3 times greater than that of bare g-C3N4 NSs (0.195 mA/cm2). Further improvements are observed with ternary gC20/TiO2 (gCT50) and gC20/ZnO (gCZ50) NCs, achieving current densities of 1.810 and 1.440 mA/cm2, respectively. These enhanced current densities are attributed to increased donor densities, reduced charge transfer resistances, and efficient charge transport within the NCs. In addition, higher surface areas with beneficial instinctive defects are perceived for gCT50 and gCZ50 NCs, as revealed by Brunauer-Emmett-Teller and electron spin resonance analysis. Finally, the stability of gCZ50 and gCT50 NC-based photoanodes is predicted and forecasted with the help of the recurrent neural network-based long short-term memory technique. Overall, this study demonstrates the efficacy of organic-inorganic hybrids for efficient photoanodes, facilitating advancements in water-splitting studies.

Inkjet-printed sub-zero temperature sensor for real-time monitoring of cold environments.

Real-time monitoring of low temperatures (usually below 0 °C) or cold environments is a specific requirement that finds its high demand in the aerospace, pharmaceutical, food, and beverage industries to maintain the temperature at high altitudes or in refrigerators and cold storage. In general, this purpose is achieved by using a sub-zero temperature sensor coupled with a control system. However, the market available such temperature sensors are very expensive, and bulky, thus not being suitable for portable operation, and also they suffer from poor accuracy. Therefore, the development of high-performance, low-cost, lightweight, and portable sub-zero temperature sensors is highly desired. In our recent work, we developed such sensors and integrated them with auxiliary electronics to demonstrate their wireless operation for the continuous and real-time monitoring of cold environments. So, in order to obtain low-cost sensors a cost-effective inkjet printing technology was employed for the fabrication of devices. A lightweight polydimethylsiloxane (PDMS) was used as the substrate and an electrically conducting graphene nanocomposite was used as the temperature-sensing material. To obtain a functional graphene nanocomposite film with a thickness of 530 nm and a conductivity of ~189 S m-1, the printed graphene nanocomposite was photonically sintered using a xenon flash lamp. This step was crucial for obtaining a sensor on the soft PDMS platform. The graphene nanocomposite film exhibited a positive temperature coefficient resistance value of approximately 0.119 %/°C, and its resistance values varied almost linearly (with an Adjusted R2 value (model accuracy) of 0.99) with temperature within the operating range of -30 °C to 80 °C. The sensor was properly encapsulated for protection without significantly affecting its performance. The sensors demonstrated sufficient flexibility, with a bending radius of 20 mm, and sustained 500 continuous bending cycles. Finally, the real-time operation of the sensors was demonstrated by wirelessly transmitting and monitoring the temperature over a smartphone platform.

Charge Transport across Proteins inside Proteins: Tunneling across Encapsulin Protein Cages and the Effect of Cargo Proteins.

Charge transport across proteins can be surprisingly efficient over long distances-so-called long-range tunneling-but it is still unclear as to why and under which conditions (e.g., presence of co-factors, type of cargo) the long-range tunneling regime can be accessed. This paper describes molecular tunneling junctions based on an encapsulin (Enc), which is a large protein cage with a diameter of 24 nm that can be loaded with various types of (small) proteins, also referred to as "cargo". We demonstrate with dynamic light scattering, transmission electron microscopy, and atomic force microscopy that Enc, with and without cargo, can be made stable in solution and immobilized on metal electrodes without aggregation. We investigated the electronic properties of Enc in EGaIn-based tunnel junctions (EGaIn = eutectic alloy of Ga and In that is widely used to contact (bio)molecular monolayers) by measuring the current density for a large range of applied bias of ±2.5 V. The encapsulated cargo has an important effect on the electrical properties of the junctions. The measured current densities are higher for junctions with Enc loaded with redox-active cargo (ferritin-like protein) than those junctions without cargo or redox-inactive cargo (green fluorescent protein). These findings open the door to charge transport studies across complex biomolecular hierarchical structures.

Smart Eutectic Gallium-Indium: From Properties to Applications.

Eutectic gallium-indium (EGaIn), a liquid metal with a melting point close to or below room temperature, has attracted extensive attention in recent years due to its excellent properties such as fluidity, high conductivity, thermal conductivity, stretchability, self-healing capability, biocompatibility, and recyclability. These features of EGaIn can be adjusted by changing the experimental condition, and various composite materials with extended properties can be further obtained by mixing EGaIn with other materials. In this review, not only the are unique properties of EGaIn introduced, but also the working principles for the EGaIn-based devices are illustrated and the developments of EGaIn-related techniques are summarized. The applications of EGaIn in various fields, such as flexible electronics (sensors, antennas, electronic circuits), molecular electronics (molecular memory, opto-electronic switches, or reconfigurable junctions), energy catalysis (heat management, motors, generators, batteries), biomedical science (drug delivery, tumor therapy, bioimaging and neural interfaces) are reviewed. Finally, a critical discussion of the main challenges for the development of EGaIn-based techniques are discussed, and the potential applications in new fields are prospected.

Dynamic molecular switches with hysteretic negative differential conductance emulating synaptic behaviour.

To realize molecular-scale electrical operations beyond the von Neumann bottleneck, new types of multifunctional switches are needed that mimic self-learning or neuromorphic computing by dynamically toggling between multiple operations that depend on their past. Here, we report a molecule that switches from high to low conductance states with massive negative memristive behaviour that depends on the drive speed and number of past switching events, with all the measurements fully modelled using atomistic and analytical models. This dynamic molecular switch emulates synaptic behavior and Pavlovian learning, all within a 2.4-nm-thick layer that is three orders of magnitude thinner than a neuronal synapse. The dynamic molecular switch provides all the fundamental logic gates necessary for deep learning because of its time-domain and voltage-dependent plasticity. The synapse-mimicking multifunctional dynamic molecular switch represents an adaptable molecular-scale hardware operable in solid-state devices, and opens a pathway to simplify dynamic complex electrical operations encoded within a single ultracompact component.

Synthesis, Self-Aggregation, Surface Characteristics, Electrochemical Property, Micelle Size, and Antimicrobial Activity of a Halogen-Free Picoline-Based Surface-Active Ionic Liquid.

We present a new approach toward the design of a halogen-free picoline-based surface-active ionic liquid (SAIL) (1-octyl-4-methyl pyridinium dodecyl sulfate) [C8γPic]DS consisting of long dodecyl sulfate (DS) as an anion. The surface properties, micellization behavior, and antimicrobial activity in an aqueous solution were investigated using tensiometry, conductometry, and ultraviolet (UV) spectroscopy. Incorporating the DS group in SAIL leads to lower critical micellar concentration (CMC) and enhanced adsorption at the air/water interface of the functionalized ionic liquid compared to the C8-alkyl chain-substituted pyridine ionic liquids. The antimicrobial activity was evaluated against a representative Gram-negative and Gram-positive bacteria panel. Antibacterial activities increased with the alkyl chain length, C8 being the homologous most effective antimicrobial agent. The micelle size of [C8γPic]DS was determined by the dynamic light-scattering (DLS) study. Cyclic voltammetry (CV) measurements have been employed to evaluate the interaction between the SAIL micelle and working electrode, diffusion coefficient, and micelle size of the SAIL solution. The diffusion coefficient explored the correlation of surface properties and the antimicrobial activity of [C8γPic]DS. This halogen-free SAIL is the future of wetting agents and emulsion studies in agriculture due to its small micelle size and surface characteristics.

Empirical Parameter to Compare Molecule-Electrode Interfaces in Large-Area Molecular Junctions.

This paper describes a simple model for comparing the degree of electronic coupling between molecules and electrodes across different large-area molecular junctions. The resulting coupling parameter can be obtained directly from current-voltage data or extracted from published data without fitting. We demonstrate the generalizability of this model by comparing over 40 different junctions comprising different molecules and measured by different laboratories. The results agree with existing models, reflect differences in mechanisms of charge transport and rectification, and are predictive in cases where experimental limitations preclude more sophisticated modeling. We also synthesized a series of conjugated molecular wires, in which embedded dipoles are varied systematically and at both molecule-electrode interfaces. The resulting current-voltage characteristics vary in nonintuitive ways that are not captured by existing models, but which produce trends using our simple model, providing insights that are otherwise difficult or impossible to explain. The utility of our model is its demonstrative generalizability, which is why simple observables like tunneling decay coefficients remain so widely used in molecular electronics despite the existence of much more sophisticated models. Our model is complementary, giving insights into molecule-electrode coupling across series of molecules that can guide synthetic chemists in the design of new molecular motifs, particularly in the context of devices comprising large-area molecular junctions.

Synergistic 2D MoSe2@WSe2 nanohybrid heterostructure toward superior hydrogen evolution and flexible supercapacitor.

Two-dimensional (2D) transition metal dichalcogenide (TMDC) heterostructure is a new age strategy to achieve high electrocatalytic activity and ion storage capacity. The less complex and cost-effective applicability of the large-area TMDC heterostructure (HS) for energy applications require more research. Herein, we report the MoSe2@WSe2 nanohybrid HS electrocatalyst prepared using liquid exfoliated nanocrystals, followed by direct electrophoretic deposition (EPD). The improved catalytic activity is attributed to the exposure of catalytic active sites on the edge of nanocrystals after liquid exfoliation and the synergistic effect arises at HS interfaces between the MoSe2 and WSe2 nanocrystals. As predicted, the HS catalyst achieves a lower overpotential of 158 mV, a smaller Tafel slope of 46 mV dec-1 for a current density of 10 mA cm-2, and is stable for a long time. The flexible symmetric supercapacitor (FSSC) based on the HS catalyst demonstrates the excellent specific capacitance (Csp) of 401 F g-1 at 1 A g-1, 97.20% capacitance retention after 5000 cycles and high flexible stability over 1000 bending cycles. This work presents a less complex and solution-processed efficient catalyst for future electrochemical energy applications.

Real-time photovoltaic parameters assessment of carbon quantum dots showing strong blue emission.

The need for replacing conventional sources of energy with renewable ones has been on a swift rise since the last couple of decades. In this context, the progress in third-generation solar cells has taken a good leap in the last couple of years with increasing prospects of high efficiency, stability, and lifetime. Quite recently, a new form of carbon has been discovered accidentally in the form of carbon quantum dots (C QD), which is being pursued actively owing to its chemical stability and luminescent properties. In the current work, we report highly luminescent C QD prepared via a simple hydrothermal route. Transmission electron microscopy revealed an average particle size of 3.4 nm. The prepared C QD were used in a co-sensitized solar cell, where an improvement in the device characteristics was observed. The enhancement in the device characteristics is supported by impedance and electron life-time analysis. Further, the time-dependent analysis of the current and voltage revealed the functioning of the solar cell in real-time condition.

Hierarchically Porous Metal-Organic Gel Hosting Catholyte for Limiting Iodine Diffusion and Self-Discharge Control in Sustainable Aqueous Zinc-I2 Batteries.

Rechargeable aqueous zinc-iodine batteries (AZIBs) represent excellent zinc-iodine redox chemistry and emerged as a promising aspirant due to their high safety, low cost, ease of fabrication, and high energy density. Nevertheless, the high-dissolution-induced iodide diffusion toward the zinc anode brings the self-discharge, which governs the capacity fading and poor cycling life of the battery. Herein, a multipurpose sponge-like porous matrix of a metal-organic gel to host a substantial amount of an iodine-based catholyte and uniform distribution of iodine with controlled iodide diffusion is introduced. Limiting the iodine diffusion due to increased viscosity provides superior electrochemical performance of this promising cathode for solid-state AZIBs. As a result, AZIBs delivering high performance and long-term stability are fabricated with a capacity of 184.9 mA h g-1 with a superior capacity retention of 95.8% even after 1500 cycles at 1 C rate. The unique concept of self-discharge protection is successfully evaluated. Prototype flexible band-aid-type AZIBs were fabricated, which delivered 166.4 mA h g-1 capacity in the bending state, and applied to real-scale wearable applications.

Intermolecular Effects on Tunneling through Acenes in Large-Area and Single-Molecule Junctions.

This paper describes the conductance of single-molecules and self-assembled monolayers comprising an oligophenyleneethynylene core, functionalized with acenes of increasing length that extend conjugation perpendicular to the path of tunneling electrons. In the Mechanically Controlled Break Junction (MCBJ) experiment, multiple conductance plateaus were identified. The high conductance plateau, which we attribute to the single molecule conformation, shows an increase of conductance as a function of acene length, in good agreement with theoretical predictions. The lower plateau is attributed to multiple molecules bridging the junctions with intermolecular interactions playing a role. In junctions comprising a self-assembled monolayer with eutectic Ga-In top-contacts (EGaIn), the pentacene derivative exhibits unusually low conductance, which we ascribe to the inability of these molecules to pack in a monolayer without introducing significant intermolecular contacts. This hypothesis is supported by the MCBJ data and theoretical calculations showing suppressed conductance through the PC films. These results highlight the role of intermolecular effects and junction geometries in the observed fluctuations of conductance values between single-molecule and ensemble junctions, and the importance of studying molecules in both platforms.

Immobilization of Agrobacterium tumefaciensd-psicose 3-epimerase onto titanium dioxide for bioconversion of rare sugar.

d-Psicose (d-ribo-2-hexulose or d-allulose) is the Carbon-3 epimer of d-fructose sugar and considered as an unnatural (rare) sugar found in low amount in nature. It has about 70% of the relative sweetness but 0.3% of the energy of sucrose, which is suggested as the most suitable sucrose substitute for food additives. Enzymatic biosynthesis using ketose 3-epimerases is a necessary procedure for the production of d-Psicose from d-fructose. However, significant drawbacks in the application of ketose 3-epimerases at industrial scale observe lower thermal stability as well as bioconversion efficiency, reusability and recovery of the enzyme. We have attempted immobilization of ketose 3-epimerases from Agrobacterium tumefaciens (agtu) d-psicose 3-epimerase (DPEase) on titanium dioxide. Further, Scanning electron microscopy (SEM), inverted microscopy, Fourier transform infrared spectroscopy (FTIR) and UV-vis spectroscopy showed that the enzyme was successfully immobilized on the titanium dioxide (TiO2) surface. Titanium dioxide immobilized agtu-DPEase (TiO2-agtu-DPEase) shows pH optima at 6.0 and 60 °C as a higher working temperature. TiO2-agtu-DPEase showed a half-life of 180 min at 60 °C, which is higher as compared to Agrobacterium tumefaciens (agtu) DPEase (3.99 min at 50 °C). At equilibrium, 36:64 (D-psicose: d-fructose), the bioconversion efficiency was accounted for titanium dioxide immobilized DPEase, which is higher than the agtu-DPEase. Titanium dioxide immobilized DPEase showed bioconversion efficiency up to 9 cycles of reusability.

Correlating the Influence of Disulfides in Monolayers across Photoelectron Spectroscopy Wettability and Tunneling Charge-Transport.

Despite their ubiquity, self-assembled monolayers (SAMs) of thiols on coinage metals are difficult to study and are still not completely understood, particularly with respect to the nature of thiol-metal bonding. Recent advances in molecular electronics have highlighted this deficiency due to the sensitivity of tunneling charge-transport to the subtle differences in the overall composition of SAMs and the chemistry of their attachment to surfaces. These advances have also challenged assumptions about the spontaneous formation of covalent thiol-metal bonds. This paper describes a series of experiments that correlate changes in the physical properties of SAMs to photoelectron spectroscopy to unambiguously assign binding energies of noncovalent interactions to physisorbed disulfides. These disulfides can be converted to covalent metal-thiolate bonds by exposure to free thiols, leading to the remarkable observation of the total loss and recovery of length-dependent tunneling charge-transport. The identification and assignment of physisorbed disulfides solve a long-standing mystery and reveal new, dynamic properties in SAMs of thiols.

Understanding the Role of Parallel Pathways via In-Situ Switching of Quantum Interference in Molecular Tunneling Junctions.

This study describes the modulation of tunneling probabilities in molecular junctions by switching one of two parallel intramolecular pathways. A linearly conjugated molecular wire provides a rigid framework that allows a second, cross-conjugated pathway to be effectively switched on and off by protonation, affecting the total conductance of the junction. This approach works because a traversing electron interacts with the entire quantum-mechanical circuit simultaneously; Kirchhoff's rules do not apply. We confirm this concept by comparing the conductances of a series of compounds with single or parallel pathways in large-area junctions using EGaIn contacts and single-molecule break junctions using gold contacts. We affect switching selectively in one of two parallel pathways by converting a cross-conjugated carbonyl carbon into a trivalent carbocation, which replaces destructive quantum interference with a symmetrical resonance, causing an increase in transmission in the bias window.

Above 800 mV Open-Circuit Voltage in Solid-State Photovoltaic Devices Using Phosphonium Cation-Based Solid Ionic Conductors.

Here, we report phosphonium-based two solid ionic conductors (SICs), namely, triphenylphosphonium methyl iodide (TPPMeI) and triphenylphosphonium iodide (TPPHI), prepared via simple protocol at room temperature and were used as an electrolyte for solid-state photovoltaic devices (ss-PVDs) with open-circuit voltage (Voc) exceeding 800 mV. Here, for the first time, detailed electrochemical investigations with theoretical aspects of phosphonium electrolytes were conducted, where PVDs prepared from these SICs, TPPMeI, showed the highest power conversion efficiency (PCE) of 4.08% with a Voc of 810 mV. However, this performance was further improved up to the PCE of 6.71% with 824 mV of Voc in the presence of additives like LiI and tert-butyl pyridine. This work leads to find the best alternative of liquid and quaternary ammonium ion-based electrolytes that suffers from problems like lower Voc (<800 mV) and stability, leakage, etc.

Eliminating Fatigue in Surface-Bound Spiropyrans.

This paper describes an experimental approach to eliminating the loss of reversibility that surface-bound spiropyrans exhibit when switched with light. Although such fatigue can be controlled in other contexts, on surfaces, the photochromic compounds are held in close proximity to each other and relatively few molecules modulate the properties of a device, leading to a loss of functionality after only a few switching cycles. The switching process was characterized by photoelectron spectroscopy and differences in tunneling currents in the spiropyran and merocyanine forms using eutectic Ga-In. Self-assembled monolayers comprising only the photochromic compounds degraded rapidly, while mixed monolayers with hexanethiol showed different behaviors depending on the relative humidity. Under dry conditions, no chemical degradation was observed and the switching process was reversible over at least 100 cycles. Under humid conditions, no degradation occurred, but the switching process became irreversible. The absence of degradation observed in mixed monolayers is ascribed to the lack of solvation, which increases the barrier to a key bond rotation past the available thermal energy. These results highlight important differences in the contexts in which photochromic compounds are utilized and demonstrate that they can be leveraged to extract device-relevant functionality from surface-bound switches by suppressing fatigue and irreversibility.

Systematic experimental study of quantum interference effects in anthraquinoid molecular wires.

In order to translate molecular properties in molecular-electronic devices, it is necessary to create design principles that can be used to achieve better structure-function control oriented toward device fabrication. In molecular tunneling junctions, cross-conjugation tends to give rise to destructive quantum interference effects that can be tuned by changing the electronic properties of the molecules. We performed a systematic study of the tunneling charge-transport properties of a series of compounds characterized by an identical cross-conjugated anthraquinoid molecular skeleton but bearing different substituents at the 9 and 10 positions that affect the energies and localization of their frontier orbitals. We compared the experimental results across three different experimental platforms in both single-molecule and large-area junctions and found a general agreement. Combined with theoretical models, these results separate the intrinsic properties of the molecules from platform-specific effects. This work is a step towards explicit synthetic control over tunneling charge transport targeted at specific functionality in (proto-)devices.

Electrophoretically Deposited MoSe2/WSe2 Heterojunction from Ultrasonically Exfoliated Nanocrystals for Enhanced Electrochemical Photoresponse.

The solar response ability and low-cost fabrication of the photoanode are important factors for the effective output of the photoelectrochemical system. Modification of the photoanode by which its ability to absorb irradiation can be manipulated has gained tremendous attention. Here, we demonstrated the MoSe2, WSe2, and MoSe2/WSe2 nanocrystal thin films prepared by the liquid-phase exfoliated and electrophoresis methods. Atomic force microscopy and high-resolution transmission electron microscopy show that the liquid exfoliated nanocrystals have a few layered dimensions with good crystallinity. Scanning electron microscopy demonstrated uniform distribution and randomly oriented nanocrystals, having a homogeneous shape and size. X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectra confirm the equal contribution of MoSe2 and WSe2 nanocrystals in the formation of the MoSe2/WSe2 heterojunction. Because of superior absorption of MoSe2/WSe2 heterojunction in the visible region and type-II heterojunction band alignment, in situ measurement of heterojunction electrode shows almost 1.5 times incident photo-to-current conversion efficiency and photoresponsivity in comparison to individual material electrodes. Our result clearly indicates the influence of heterojunction formation between liquid exfoliated nanocrystals on effective separation of photogenerated exciton and enhances charge carrier transfer, which leads to the improvement in photoelectrochemical performance. Liquid exfoliated nanosheet-based heterojunction is attractive as efficient photoanodes for the photoelectrochemical systems.

Correction: Systematic experimental study of quantum interference effects in anthraquinoid molecular wires.

[This corrects the article DOI: 10.1039/C8NA00223A.].

Tunneling Probability Increases with Distance in Junctions Comprising Self-Assembled Monolayers of Oligothiophenes.

Molecular tunneling junctions should enable the tailoring of charge-transport at the quantum level through synthetic chemistry but are hindered by the dominance of the electrodes. We show that the frontier orbitals of molecules can be decoupled from the electrodes, preserving their relative energies in self-assembled monolayers even when a top-contact is applied. This decoupling leads to the remarkable observation of tunneling probabilities that increase with distance in a series of oligothiophenes, which we explain using a two-barrier tunneling model. This model is generalizable to any conjugated oligomers for which the frontier orbital gap can be determined and predicts that the molecular orbitals that dominate tunneling charge-transport can be positioned via molecular design rather than by domination of Fermi-level pinning arising from strong hybridization. The ability to preserve the electronic structure of molecules in tunneling junctions facilitates the application of well-established synthetic design rules to tailor the properties of molecular-electronic devices.