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Abstract Viologen, as a type of strong electron acceptor, is prone to undergo electron transfer (ET) and change color under external stimuli. However, due to the easy aggregation of viologen molecules, they usually suffer from poor fluorescence emission in the condensed phase. Herein, a new viologen derivative of VioCl2·2Cl (12+·2Cl) was designed and synthesized, in which the fluorescence was enhanced by introducing Me‐β‐CD to weaken the interactions between viologen molecules. Then a viologen‐based host–guest supramolecule of 12+@Me‐β‐CD was obtained by electrostatic interactions. Photo‐/chemo‐responded guest 12+ supplies 12+@Me‐β‐CD, a green and dark purple caused by intramolecular and intermolecular ET. Furthermore, 12+@Me‐β‐CD displays an additional thermal responsive purple color. The triple chromic behaviors all exhibit excellent reversibility and cycling stability. As expected, 12+@Me‐β‐CD exhibits strong photoluminescence (PL) in solid–liquid dual states, presenting an improved quantum yield (Φ) from 12+ (Φs = 0.37%, Φl = 16.74%) to 12+@Me‐β‐CD (Φs = 10.45%, Φl = 25.86%), and the fluorescence intensity can be dynamically modulated by light, heat, and acid/base vapors. The multi‐responsive chromism and tunable fluorescence of 12+@Me‐β‐CD allow for potential applications in information security and smart windows.

Highlights Feedback-regulation system is established between single Pt sites and MoS2 supports The Pt1-MoS2-def can expand the electron transfer path from single Pt sites to whole Pt-MoS2 supports in SO2 gas atmosphere. The Pt1-MoS2-def sensors exhibit high SO2 responses and extremely low limit of detection (3.14% to 500 ppb SO2) at room temperature. The Pt1-MoS2-def sensors array can realize real-time monitoring of SO2 for plant growth.

Supercapacitors are a kind of energy storage device that lie between traditional capacitors and batteries, characterized by high power density, long cycle life, and rapid charging and discharging capabilities. The energy storage mechanism of supercapacitors mainly includes electrical double-layer capacitance and pseudocapacitance. In addition to constructing multi-level pore structures to increase the specific surface area of electrode materials, defect engineering is essential for enhancing electrochemical active sites and achieving additional extrinsic pseudocapacitance. Therefore, developing a simple and efficient method for defect engineering is essential. Atomic layer deposition (ALD) technology enables precise control over thin film thickness at the atomic level through layer-by-layer deposition. This capability allows the intentional introduction of defects, such as vacancies, heteroatom doping, or misalignment, at specific sites within the material. The ALD process can regulate the defects in materials without altering the overall structure, thereby optimizing both the electrochemical and physical properties of the materials. Its self-limiting surface reaction mechanism also ensures that defects and doping sites are introduced uniformly across the material surface. This uniform defect distribution is particularly profitable for high surface area electrodes in supercapacitor applications, as it promotes consistent performance across the entire electrode. This review systematically summarizes the latest advancements in defect engineering via ALD technology in supercapacitors, including the enhancement of conductivity and the increase of active sites in supercapacitor electrode materials through ALD, thereby improving specific capacitance and energy density of the supercapacitor device. Furthermore, we discuss the underlying mechanisms, advantages, and future directions for ALD in this field.

Abstract Carbon dots (CDs) and their composites as energy storage materials and electrocatalysts have emerged as new types of quasi‐zero‐dimensional carbon materials. CDs can provide a large specific surface area, numerous electron–electron hole pairs, adjustable heteroatom doping, rich surface functional groups, and so on. However, the roles and functional mechanisms of CDs and their composite materials in the enhancement of electrochemical performance remain unclear and need to be understood in depth. Based on the most recent literature, this paper comprehensively reviews the synthesis methods and applications of various categories of CDs and their composites as electrode materials of supercapacitors, lithium‐ion batteries, sodium‐ion batteries, and potassium‐ion batteries, and as electrocatalysts for hydrogen evolution, oxygen evolution, and oxygen reduction reactions in metal–air batteries, fuel cells, and water electrolysis. To facilitate further research and development, several important aspects related to CDs and their composite materials are summarized with analysis of the technical challenges in practical applications and discussion of the possible development perspectives.

As a volatile air pollutant, formaldehyde can enter people’s living environment through interior decoration, furniture and paint, causing serious harm to human health. Therefore, it is necessary to develop a sensor for the real-time detection of formaldehyde in low concentrations. According to the chemical interaction between amino groups and formaldehyde, a MIL-101(Cr) aminated-material-based formaldehyde cantilever sensor was prepared, of which ethylenediamine- functionalized MIL-101(Cr) named ED-MIL-101(Cr)) showed the best gas sensing performance. Using quasi-in situ infrared spectroscopy, ED-MIL-101(Cr) was found bound to formaldehyde through a Schiff base. The adsorption enthalpy of formaldehyde-bound ED-MIL-101(Cr) was −52.6 kJ/mol, which corresponds to weak chemical adsorption, so the material showed good selectivity. In addition, ED-MIL-101(Cr) has the most active sites, so its response value to formaldehyde is larger and it takes longer to reach saturation adsorption than bare MIL-101(Cr). Through the research on the gas sensing performance of functionalized MIL-101(Cr) material, we found that it has a strong application potential in the field of formaldehyde monitoring, and the material performance can be quantitatively and accurately evaluated through combining calculation and experimentation for understanding the gas sensing mechanism.

In this work, a facile synthesis method was adopted to synthesize MOF-14 with mesoporous structure. The physical properties of the samples were characterized by PXRD, FESEM, TEM and FT-IR spectrometry. By coating the mesoporous-structure MOF-14 on the surface of a quartz crystal microbalance (QCM), the fabricated gravimetric sensor exhibits high sensitivity to p-toluene vapor even at trace levels. Additionally, the limit of detection (LOD) of the sensor obtained experimentally is lower than 100 ppb, and the theoretical detection limit is 57 ppb. Furthermore, good gas selectivity and fast response (15 s) and recovery (20 s) abilities are also illustrated along with high sensitivity. These sensing data indicate the excellent performance of the fabricated mesoporous-structure MOF-14-based p-xylene QCM sensor. On the basis of temperature-varying experiments, an adsorption enthalpy of −59.88 kJ/mol was obtained, implying the existence of moderate and reversible chemisorption between MOF-14 and p-xylene molecules. This is the crucial factor that endows MOF-14 with exceptional p-xylene-sensing abilities. This work has proved that MOF materials such as MOF-14 are promising in gravimetric-type gas-sensing applications and worthy of future study.

For the energy supply of smart and portable equipment, high performance supercapacitor electrode materials are drawing more and more concerns. Conductive Ni-MOF is a class of materials with higher conductivity compared with traditional MOFs, but it continues to lack stability. Specifically, MXene (Ti3C2Tx) has been employed as an electrochemical substrate for its high mechanical stability and abundant active sites, which can be combined with MOFs to improve its electrochemical performance. In this paper, a novel Ni-MOF nanorods array/Ti3C2Tx nanocomposite was prepared via a facile hydrothermal reaction, which makes good use of the advantages of conductive Ni-MOF and high strength Ti3C2Tx. The high density forest-like Ni-MOF array in situ grown on the surface of Ti3C2Tx can provide abundant active electrochemical sites and construct a pathway for effective ion transport. The formation of a “Ti-O···Ni” bond accomplished during an in situ growth reaction endows the strong interfacial interaction between Ni-MOF and Ti3C2Tx. As a result, the Ni-MOF/Ti3C2Tx nanocomposite can achieve a high specific capacitance of 497.6 F·g−1 at 0.5 A·g−1 and remain over 66% of the initial capacitance when the current density increases five times. In addition, the influence of the Ti3C2Tx concentration and reaction time on the morphology and performance of the resultant products were also investigated, leading to a good understanding of the formation process of the nanocomposite and the electrochemical mechanism for a supercapacitive reaction.

Aggregation-induced quenching (ACQ) is a hard problem in fluorescence material, leading to a poor utilization rate of fluorophores. In this work, 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) was synthesized and used as a precursor to build two kinds of fluorescence polymer. The TFFPy molecule with D2h symmetry can easily form polymers with C3 symmetry amines through the Schiff base reaction, making the resulting polymer a 3D amorphous material. Thus, ACQ of fluorophore can be reduced to minimum, making the most usage of the fluorescence of pyrene core. Fluorescence titration and DFT calculation can clearly prove this conclusion. The resulting CPs showed a highly sensitivity to picric acid, down to 3.43 ppm in solution, implying its potential in explosive detection.

The capture and separation of CO2 is an important means to solve the problem of global warming. MOFs (metal–organic frameworks) are considered ideal candidates for capturing CO2, where the adsorption enthalpy is a crucial indicator for the screening of materials. For this purpose, we propose a new minimalist solution using QCM (quartz crystal microbalance) to extract the CO2 adsorption enthalpy on MOFs. Three kinds of MOFs with different properties, sizes and morphologies were employed to study the adsorption enthalpy of CO2 using a QCM platform and a commercial gas sorption analyzer. A Gaussian simulation calculation and previously data reported were used for comparison. It was found that the measuring errors were between 5.4% and 6.8%, proving the reliability and versatility of our new method. This low-cost, easy-to-use, and high-accuracy method will provide a rapid screening solution for CO2 adsorption materials, and it has potential in the evaluation of the adsorption of other gases.

As an n-type semiconductor material, tungsten oxide (WO3) has good application prospects in the field of gas sensing. Herein, using oxalic acid (OA), citric acid (CA) and tartaric acid (TA) as auxiliary agents, three homogeneous tungsten oxide nanosheets were prepared by the rapid microwave-assisted hydrothermal method. The potential exhaled gases of various diseases were screened for the gas sensitivity test. Compared with WO3-OA and WO3-TA, WO3-CA exhibits significant sensitivity to formaldehyde, acetone and various alkanes. Photoluminescence (PL) chromatography and photoelectric properties show that its excellent gas sensitivity is due to its abundant oxygen vacancies and high surface charge migration rate, which can provide more preferential reaction sites with gas molecules. The experiment is of great significance for the sensor selection of the large disease exhaled gas sensor array.

In recent years, two-dimensional layered material MXene has attracted extensive attention in the fields of sensors due to its large specific surface area and rich active sites. So, we employed multilayer Ti3C2TX and SnO2 microspheres to prepare SnO2/MXene composites for enhancing gas-sensing properties of pristine SnO2. The composite was brushed on a microelectromechanical system (MEMS) platform to make resistance-type gas sensors with low power consumption. The gas-sensing results show that the SnO2/MXene sensor with the best composite ratio (SnO2: MXene mass ratio is 5:1, named SM-5) greatly improves gas sensitivity of SnO2 sensor, among which the sensitivity to ethanol gas is the highest. At the same time, the composite also speeds up the response recovery speed of the sensor. When the SM-5 sensor worked at its optimal temperature 230 °C, its response value to 10 ppm ethanol reaches 5.0, which is twice that of the pristine SnO2 sensor. Its response and recovery time are only 14 s and 26 s, respectively. The sensing mechanism of the composite is discussed according to the classical the space charge or depletion layer model. It is concluded that the Schottky barrier of composites and the metal properties of Ti3C2Tx are responsible for improvement of the gas-sensing properties of the composite.

The construction of heterojunctions in composite materials to optimize the electronic structures and active sites of energy materials is considered to be the promising strategy for the fabrication of high-performance electrochemical energy devices. In this paper, a one-step, easy processing and cost-effective technique for generating composite materials with heterojunctions was successfully developed. The composite containing Ni _3 S _4 , NiS, and N-doped amorphous carbon (abbreviated as Ni _3 S _4 /NiS/NC) with multiple heterojunction nanosheets are synthesized via the space-confined effect of molten salt interface of recrystallized NaCl. Several lattice matching forms of Ni _3 S _4 with cubic structure and NiS with hexagonal structure are confirmed by the detailed characterization of heterogeneous interfaces. The C–S bonds are the key factor in realizing the chemical coupling between nickel sulfide and NC and constructing the stable heterojunction. Density functional theory calculations further revealed that the electronic interaction on the heterogeneous interface of Ni _3 S _4 /NiS can contribute to high electronic conductivity. The heterogeneous interfaces are identified to be the good electroactive region with excellent electrochemical performance. The synergistic effect of abundant active sites, the enhanced kinetic process and valid interface charge transfer channels of Ni _3 S _4 /NiS/NC multiple heterojunction can guarantee high reversible redox activity and high structural stability, resulting in both high specific capacitance and energy/power densities when it is used as the electrode for supercapacitors. This work offers a new avenue for the rational design of the heterojunction materials with improved electrochemical performance through space-confined effect of NaCl.

In this paper, the precursor Ni0.8Co0.1Mn0.1(OH)2 is prepared by a co-precipitation method. By mixing this material with LiOH in proportion and sintering twice under 500 and 800°C, respectively, the cathode material of LiNi0.8Co0.1Mn0.1O2 (NCM811) for lithium ion batteries (LIBs) is synthesized. To improve the performance of this NCM811 material, Al2O3, ZrO2, and LBO (Li2O-2B2O3) are, respectively, used to coat it by a wet chemical method. The effects of Al2O3, ZrO2, and LBO thin coating layers (~20–200 nm) on the morphology, structure and electrochemical property of NCM811 are studied using XRD, SEM, TEM, XPS, and electrochemical measurements. Coin LIBs are assembled with the uncoated, Al2O3-coated, ZrO2-coated, and LBO-coated NCM811 cathode materials for performance validation. The experiment results confirm that the charge-discharge specific capacity, Coulomb efficiency, water absorption stability, cycle characteristics, and resistance stability of the NCM811 cathode material can be significantly improved by coating it with LBO particularly. Therefore, the surface coating to the particles of cathode materials using LBO is expected to be an effective and practical modification method to improve the electrochemical performance of LIBs.

The flocculation of small surficial groups on pristine CNCs (carbon nanocoils) bundles limit their application. In this study, we designed and fabricated novel array CNCs with a surficial decoration of polyaniline (PANI) using in situ methods. Atomic layer deposition (ALD) and chemical vapor deposition (CVD) methods were employed to fabricate the highly pure array CNCs. The array CNCs decorated with ultra-thin PANI were confirmed by different characterizations. Furthermore, this material displayed a good performance in its detection of formaldehyde. The detection results showed that the CNCs coated with PANI had a low limit of detection of HCHO, as low as 500 ppb, and the sensor also showed good selectivity for other interfering gases, as well as good repeatability over many tests. Furthermore, after increasing the PANI loading on the surface of the CNCs, their detection performance exhibited a typical volcanic curve, and the value of the enthalpy was extracted by using the temperature-varying micro-gravimetric method during the process of detection of the formaldehyde molecules on the CNCs. The use of array CNCs with surficial decoration offers a novel method for the application of CNCs and could be extended to other applications, such as catalysts and energy conversion.

In recent years, bimetallic nanocrystals have attracted great interest from many researchers. Bimetallic nanocrystals are expected to exhibit improved physical and chemical properties due to the synergistic effect between the two metals, not just a combination of two monometallic properties. More importantly, the properties of bimetallic nanocrystals are significantly affected by their morphology, structure, and atomic arrangement. Reasonable regulation of these parameters of nanocrystals can effectively control their properties and enhance their practicality in a given application. This review summarizes some recent research progress in the controlled synthesis of shape, composition and structure, as well as some important applications of bimetallic nanocrystals. We first give a brief introduction to the development of bimetals, followed by the architectural diversity of bimetallic nanocrystals. The most commonly used and typical synthesis methods are also summarized, and the possible morphologies under different conditions are also discussed. Finally, we discuss the composition-dependent and shape-dependent properties of bimetals in terms of highlighting applications such as catalysis, energy conversion, gas sensing and bio-detection applications.

Tin(II) monosulfide (SnS) nanosheets were synthesized using SnCl4•5H2O and S powders as raw materials in the presence of H2O via a facile chemical bath method. Orthorhombic phase SnS nanosheets with a thickness of ~100 nm and lateral dimensions of 2~10 μm were obtained by controlling the synthesis parameters. The formation of a SnO2 intermediate is key to the valence reduction of Sn ions (from IV to II) and the formation of SnS. The gas sensors fabricated from SnS nanosheets exhibited an excellent response of 14.86 to 100 ppm ethanol vapor when operating at 160 °C, as well as fast response and recovery times of 23 s and 26 s, respectively. The sensors showed excellent selectivity for the detection of ethanol over acetone, methanol, and ammonia gases, which indicates the SnS nanosheets are promising for high-performance ethanol gas sensing applications.

Weight aggregation is the key process to solve a multiple-attribute group decision-making (MAGDM) problem. This paper is trying to propose a possible approach to objectivize subjective information and to aggregate information from attribute values themselves and decision-makers’ judgment. An MAGDM problem without information about decision-makers’ and attributes’ weight is considered. In order to define decision-makers’ subjective preference, their utility function is introduced. The attributes value matrix is converted into a subjective attributes value matrix based on their subjective judgment on attribute values. By utilizing the entropy weighting technique, decision-maker’s subjective weight on attributes and objective weight on attributes are determined individually based on the subjective attributes value matrix and attributes value matrix. Based on the principle of minimum cross-entropy, all decision-makers’ subjective weights are integrated into a single weight vector that is closest to all decision-makers’ judgment without any extra information added. Then, by applying the principle of minimum cross-entropy again, a weight aggregation method is proposed to combine the subjective and objective weight of attributes. Finally, an MAGDM example of project choosing is presented to illustrate the procedure of the proposed method.

Novel bimetallic nanoparticles have been synthesized via rapid microwave irradiation, leading to an improved sensitivity and a highly anti-interference property for amperometric biosensor in H2O2 detection. The material characterizations were performed by TEM, XRD, and EDX, which show the bimetallic formation of Pt-based catalysts and well-dispersed nanoparticles of 2–5 nm. The sensitivities for the detection of H2O2 of PtRu, PtAu, and PtIr as the biosensor working electrode catalysts are 539.01 (R2=0.99), 415.46 (R2=0.99), and 404.52 (R2=0.97) μA mM−1 cm-2, respectively, nearly twice higher than the pure Pt catalyst (221.77 μA mM−1 cm−2, R2=0.98), at a low applied potential of +0.25 V versus Ag/AgCl. Furthermore, Pt-Ru and Pt-Ir show a highly sensitive response and a promising anti-interference capability to ascorbic acid, a major interferent, by reducing the interferent current as low as 7-8% significantly lower than that of Pt (30% change). The enhancement of both sensitivity and selectivity in the bimetallic catalysts can be found practical applications in biosensing.

A bimetallic Pt-Ru nanoparticle catalyst was prepared and characterized for the enhancement of hydrogen peroxide (H2O2) detection in biosensing applications. The particles were synthesized via sodium borohydride reduction, with low heat treatment, and characterized by TEM and HRTEM. The chemical composition analyses were performed by EDX. The bimetallic particle diameters ranged from 2 to 12 nm, with an average of 4.5 nm. The Pt-Ru catalyst exhibited an improved performance at low overpotential (+0.2 V versus Ag/AgCl reference electrode) in H2O2 detection, suggesting a sensitivity value of 78.95 μA⋅mM-1 (or 402.1 μA⋅mM-1⋅cm-2) which was 30% higher than that for the single Pt catalyst. The major contribution of this enhancement comes from the stronger oxygen adsorption on Ru metal. The Pt-Ru catalyst also showed a more stable signal at the high overpotential (+0.4 V versus Ag/AgCl), providing better accuracy in the detection of H2O2.