Assembling carbon nitride quantum dots into hollow fusiformis and loading CoP for photocatalytic hydrogen evolution.

The self-assembled carbon nitride quantum dots (CNQDs) has been largely advanced owing to the structure-relative photocatalytic activities, especially its electronic structure, which can be regulated by defects, functional groups, and doping. However, there are still issues such as wide band gaps for the assembles and severe recombination of photoinduced charges. Herein, we demonstrate the self-assembly of CNQDs into fusiform hollow superstructures (CNFHs), induced by hydrogen bonding between the terminal functional groups (-OH, -COOH, and -NH2). During the top-down assembly process, the hydrogen bonding dominates and initiates lateral cross-linking between adjacent CNQDs, which further twist into fusiform hollow structures. Benefitted greatly from the ultrathin and hollow nature of the superstructure that provides more exposed active sites, coupled with the introduction of phosphorus doping atoms into the framework induced narrowed band gap, CNFHs exhibits an 18-fold higher activity than the bulk counterpart toward photocatalytic hydrogen evolution after loading the CoP co-catalyst. This work presents a new platform to design and manipulate carbon nitride superstructures.

Streamlined synthesis of superstructure Ni-benzimidazole MOFs: Glucose electrochemical analysis.

The design and synthesis of efficient electrochemical sensors are crucial transformation technologies in electrochemistry. We successfully synthesize a three-dimensional Ni-metal-organic framework (MOF) nanostructured material with a superior architecture using benzimidazole and nickel nitrate as precursors at room temperature which is being applied in glucose electrochemical sensors. The reaction mechanism of M-6 during glucose detection is thoroughly studied using various characterization techniques, such as in situ Raman spectroscopy, in situ ultraviolet-visible spectrophotometry, synchrotron radiography, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The research findings demonstrate that the M-6 material exhibits high sensitivity for glucose detection, with a sensitivity of 2199.88 mA M-1 cm-2. This study provides an important reference for designing more efficient electrochemical reaction systems and optimizing material performance. Furthermore, the superstructural design offers new ideas and possibilities for the development and application of similar materials.

Tailoring coordination environments of single-atom electrocatalysts for hydrogen evolution by topological heteroatom transfer.

The rational design of carbon-supported transition-metal single-atom catalysts requires the precise arrangement of heteroatoms within the single-atom catalysts. However, achieving this design is challenging due to the collapse of the structure during the pyrolysis. Here, we introduce a topological heteroatom-transfer strategy to prevent the collapse and accurately control the P coordination in carbon-supported single-atom catalysts. As an illustration, we have prepared self-assembled helical fibers with encapsulated cavities. Within these cavities, adjustable functional groups can chelate metal ions (Nx···Mn+···Oy), facilitating the preservation of the structure during the pyrolysis based phosphidation. This process allows for the transfer of heteroatoms from the assembly into single-atom catalysts, resulting in the precise coordination tailoring. Notably, the Co-P2N2-C catalyst exhibits electrocatalytic performance as a non-noble metal single-atom catalyst for alkaline hydrogen evolution, attaining a current density of 100 mA cm-2 with an overpotential of only 131 mV.

Tuning the Electronic Property of Reconstructed Atomic Ni-CuO Cluster Supported on N/O-C for Electrocatalytic Oxygen Evolution.

Electrochemical activation usually accompanies in situ atom rearrangement forming new catalytic sites with higher activity due to reconstructed atomic clusters or amorphous phases with abundant dangling bonds, vacancies, and defects. By harnessing the pre-catalytic process of reconstruction, a multilevel structure of CuNi alloy nanoparticles encapsulated in N-doped carbon (CuNi nanoalloy@N/C) transforms into a highly active compound of Ni-doped CuO nanocluster supported on (N/O-C) co-doped C. Both the exposure of accessible active sites and the activity of individual active sites are greatly improved after the pre-catalytic reconstruction. Manipulating the Cu/Ni ratios of CuNi nanoalloy@N/C can tailor the electronic property and d-band center of the high-active compound, which greatly optimizes the energetics of oxygen evolution reaction (OER) intermediates. This interplay among Cu, Ni, C, N, and O modifies the interface, triggers the active sites, and regulates the work functions, thereby realizing a synergistic boost in OER.

Natural lignocellulosic kapok fiber/MXene constructed hydrogel evaporators for high efficiency solar steam generation.

Solar-driven interfacial evaporation (SDIE) is a green and sustainable technique for desalination. Hydrogel composite evaporators have been widely used for SDIE, but it is still challenging for the hydrogel evaporators to achieve uniform distribution of the light absorbing nanomaterials and at the same time possess satisfactory evaporation rate, durability and environmental applicability. We developed a 3D hydrogel evaporator with an asymmetric structure for high-efficiency SDIE. Natural kapok fibers, an important lignocellulosic plant fiber with a hollow structure, are decorated with MXene nanosheets for construction of one-dimensional photothermal conversion network. The top composite hydrogel serves as the light-absorption layer where MXene-modified kapok fibers are evenly dispersed in PVA hydrogel, while the bottom PVA hydrogel with an oriented structure acts as water delivery path. The evaporator exhibits a high solar evaporation rate and efficiency (2.49 kg·m-2·h-1 and 91.5 %, respectively) under one sun irradiation (1 kW·m-2). Even in a high salinity brine, emulsion and corrosive solutions, the evaporator can work normally with a slightly decreased evaporation rate. The 3D hydrogel evaporator with long-term stability and durability shows promising applications in purification of seawater and different waste water.

Water vapor assisted aramid nanofiber reinforcement for strong, tough and ionically conductive organohydrogels as high-performance strain sensors.

Conductive organohydrogels have gained increasing attention in wearable sensors, flexible batteries, and soft robots due to their exceptional environment adaptability and controllable conductivity. However, it is still difficult for conductive organohydrogels to achieve simultaneous improvement in mechanical and electrical properties. Here, we propose a novel "water vapor assisted aramid nanofiber (ANF) reinforcement" strategy to prepare robust and ionically conductive organohydrogels. Water vapor diffusion can induce the pre-gelation of the polymer solution and ensure the uniform dispersion of ANFs in organohydrogels. ANF reinforced organohydrogels have remarkable mechanical properties with a tensile strength, stretchability and toughness of up to 1.88 ± 0.04 MPa, 633 ± 30%, and 6.75 ± 0.38 MJ m-3, respectively. Furthermore, the organohydrogels exhibit great crack propagation resistance with the fracture energy and fatigue threshold as high as 3793 ± 167 J m-2 and ∼328 J m-2, respectively. As strain sensors, the conductive organohydrogel demonstrates a short response time of 112 ms, a large working strain and superior cycling stability (1200 cycles at 40% strain), enabling effective monitoring of a wide range of complex human motions. This study provides a new yet effective design strategy for high performance and multi-functional nanofiller reinforced organohydrogels.

Nanofiber Composite Reinforced Organohydrogels for Multifunctional and Wearable Electronics.

Composite organohydrogels have been widely used in wearable electronics. However, it remains a great challenge to develop mechanically robust and multifunctional composite organohydrogels with good dispersion of nanofillers and strong interfacial interactions. Here, multifunctional nanofiber composite reinforced organohydrogels (NCROs) are prepared. The NCRO with a sandwich-like structure possesses excellent multi-level interfacial bonding. Simultaneously, the synergistic strengthening and toughening mechanism at three different length scales endow the NCRO with outstanding mechanical properties with a tensile strength (up to 7.38 ± 0.24 MPa), fracture strain (up to 941 ± 17%), toughness (up to 31.59 ± 1.53 MJ m-3) and fracture energy (up to 5.41 ± 0.63 kJ m-2). Moreover, the NCRO can be used for high performance electromagnetic interference shielding and strain sensing due to its high conductivity and excellent environmental tolerance such as anti-freezing performance. Remarkably, owing to the organohydrogel stabilized conductive network, the NCRO exhibits superior long-term sensing stability and durability compared to the nanofiber composite itself. This work provides new ideas for the design of high-strength, tough, stretchable, anti-freezing and conductive organohydrogels with potential applications in multifunctional and wearable electronics.

Determination of ribavirin by molecularly imprinted electrochemical sensors using pyrro-1-propionyl-alaninoyl-chitooligosaccharide and pyrrole as bifunctional monomers on Prussian blue-gold nanocomposite films.

Herein, we developed a highly sensitive imprinted electrochemical sensor for the trace detection of ribavirin (RBV) using pyrrole (PYR) and pyrro-1-propionyl-alaninoyl-chitooligosaccharides (PPACO) as bifunctional monomers on Prussian blue-gold nanocomposite films. PPACO had strong molecular effect on RBV molecule and was selected by quantitative calculations. After the deposition of the Prussian blue-gold nanocomposite on a glassy carbon electrode (GCE) surface, a 4-aminothiophenol layer successfully self-assembled on the surface. Subsequently, the molecularly imprinted membrane (MIM) was subjected to electrochemical polymerization on the electrode surface using RBV as the template and PPACO and PYR as the two monomers. After eluting the RBV molecules from the MIM, the fabricated RBV-MIM/Fn-Au-PB/GCE exhibited the specific adsorption of RBV. Under optimal conditions, differential pulse voltammetry (DPV) was used to measure the performance of the synthesized sensor, which exhibited a linear relationship between the decreasing peak current and RBV concentration from 0.015 to 3.5 µM with a low detection limit of 3 nM (S/N = 3). As a proof of concept, RBV-MIM/Fn-Au-PB/GCE was also applied to monitor the RBV content in RBV granules. It showed a satisfactory recovery (96.5-99.2%) with a relative standard deviation of less than 3.5% (n = 5), and thus, we believe it has potential for practical applications.

Carbon nanofiber reinforced carbon aerogels for steam generation: Synergy of solar driven interface evaporation and side wall induced natural evaporation.

Solar-based interface evaporation (SIE) is a green, efficient and cost-effective technique to harvest fresh water. 3D solar evaporators show their unique advantages in gaining energy from environment and hence possess a higher evaporation rate than 2D evaporators. However, much effort is still required to develop mechanically robust and superhydrophilic 3D evaporators with strong water transportation capability and salt-rejection performance, and at the same time reveal how they gain energy from environment via the natural evaporation. In this work, a novel carbon nanofiber reinforced carbon aerogel (CNFA) is prepared for the SIE. The CNFA has a high light absorption up to 97.2% and outstanding photothermal conversion performance. The heteroatom doping and hierarchically porous structure endow the CNFA with superhydrophilicity and thus powerful water transportation capability and salt rejection performance. Benefiting from synergy of the SIE and side wall induced natural evaporation, the CNFA evaporator exhibits a high evaporation rate and efficiency (as high as 3.82 kg m-2h-1 and 95.5%, respectively) with long-term stability and durability. The CNFA can also work normally in high-salinity and corrosive seawater. This study demonstrates a new method to fabricate all-carbon aerogel solar evaporators and provides insights for the effective thermal management during the interface evaporation.

Oxygen Vacancy-Dependent Photocatalytic Selective Synthesis of an Unsaturated Amide on Spinel CuFe2O4.

Oxygen vacancies can change the physical and chemical properties of oxide semiconductors, which is applied to the field of ph otocatalysis, including water splitting, carbon dioxide reduction, and organic synthesis. However, the mechanism of oxygen vacancies in photocatalytic organic synthesis is still unclear. Herein, oxygen vacancies constructed on spinel CuFe2O4 nanoparticles were found to trigger the photocatalytic synthesis of an unsaturated amide with high conversion and selectivity. Such superior performance was attributed to the fact that the enriched surface oxygen vacancies could increase the charge separation efficiency and optimize the reaction path, which has been demonstrated both experimentally and theoretically.

Solvent-Exchange-Assisted Wet Annealing: A New Strategy for Superstrong, Tough, Stretchable, and Anti-Fatigue Hydrogels.

Hydrogels are widely used in tissue engineering, soft robots, wearable electronics, etc. However, it remains a great challenge to develop hydrogels possessing simultaneously high strength, large stretchability, great fracture energy, and good fatigue threshold to suit different applications. Herein, a novel solvent-exchange-assisted wet-annealing strategy is proposed to prepare high performance poly(vinyl alcohol) hydrogels by extensively tuning the macromolecular chain movement and optimizing the polymer network. The reinforcing and toughening mechanisms are found to be "macromolecule crystallization and entanglement". These hydrogels have large tensile strengths up to 11.19 ± 0.27 MPa and extremely high fracture strains of 1879 ± 10%. In addition, the fracture energy and fatigue threshold can reach as high as 25.39 ± 6.64 kJ m-2 and ≈1233 J m-2 , respectively. These superb mechanical properties compare favorably to those of other tough hydrogels, organogels, and even natural tendons and synthetic rubbers. This work provides a new and effective method to fabricate superstrong, tough, stretchable, and anti-fatigue hydrogels with potential applications in artificial tendons and ligaments.

Design of Uniform Hollow Carbon Nanoarchitectures: Different Capacitive Deionization between the Hollow Shell Thickness and Cavity Size.

Carbon-based materials with high capacitance ability and fast electrosorption rate are ideal electrode materials in capacitive deionization (CDI). However, traditional carbon materials have structural limitations in electrochemical and desalination performance due to the low capacitance and poor transmission channel of the prepared electrodes. Therefore, reasonable design of electrode material structure is of great importance for achieving excellent CDI properties. Here, uniform hollow carbon materials with different morphologies (hollow carbon nanospheres, hollow carbon nanorods, hollow carbon nano-pseudoboxes, hollow carbon nano-ellipsoids, hollow carbon nano-capsules, and hollow carbon nano-peanuts) are reasonably designed through multi-step template method and calcination of polymer precursors. Hollow carbon nanospheres and hollow carbon nano-pseudoboxes exhibit better capacitance and higher salt adsorption capacity (SAC) due to their stable carbonaceous structure during calcination. Moreover, the effects of the thickness of the shell and the size of the cavity on the CDI performance are also studied. HCNSs-0.8 with thicker shell (≈20 nm) and larger cavity (≈320 nm) shows the best SAC value of 23.01 mg g-1 due to its large specific surface area (1083.20 m2  g-1 ) and rich pore size distribution. These uniform hollow carbon nanoarchitectures with functional properties have potential applications in electrochemistry related fields.

Dual-ligand and hard-soft-acid-base strategies to optimize metal-organic framework nanocrystals for stable electrochemical cycling performance.

Most metal-organic frameworks (MOFs) hardly maintain their physical and chemical properties after exposure to acidic, neutral, or alkaline aqueous solutions, resulting in insufficient stability, therefore limiting their applications. Thus, the design and synthesis of stable size/morphology-controlled MOF nanocrystals is critical but challenging. In this study, dual-ligand and hard-soft-acid-base strategies were used to fabricate a variety of 3D pillared-layer [Ni(thiophene-2,5-dicarboxylate)(4,4'-bipyridine)]n MOF nanocrystals (1D nanofibers, 2D nanosheets and 3D aggregates) with controllable morphology by varying the concentration of 4,4'-bipyridine and thus controlling the crystal growth direction. Owing to the shorter ion diffusion length, enhanced electron/ion transfer and strong interactions between thiophene-2,5-dicarboxylate and 4,4'-bipyridine, the 2D nanosheets showed much larger specific capacitance than 1D nanofibers and 3D aggregates. A single device with an output voltage as high as 3.0 V and exceptional cycling performance (95% of retention after 5000 cycles at 3 mA cm-2) was realized by configuring two aqueous asymmetric supercapacitive devices in series. The excellent cycling property and charge-discharge mechanism are consistent with the hard-soft-acid-base theory.

Bifunctional monomer oligomers-based composite molecularly imprinted membranes for the electrochemical monitoring of Sudan I.

Herein, we developed a highly sensitive electrochemical sensor for the trace detection of Sudan I (SDI) dye based on composite molecularly imprinted membranes (MIMs). The pentenyl (lipoic acyl)-isoleucyl-chitosan oligosaccharide (P(L)ICO) and pentenyl-asparaginyl-chitosan oligosaccharide (PASCO) served as bifunctional monomer oligomers. After deposition of gold nanoparticles on a glassy carbon electrode (GCE) surface, a P(L)ICO layer successfully self-assembled on the surface. Subsequently, the primary MIM was polymerised on the electrode surface by using SDI as a template, PASCO as a functional monomer oligomer, and ethylene glycol dimethacrylate as a cross-linking agent. Electrochemical polymerisation was then conducted in an N,N'-methylenebisacrylamide solution. After eluting the SDI molecules from the composite MIMs, the fabricated SDI-MIM(PM)/Fn-Au/GCE demonstrated specific adsorption of SDI. Under optimal conditions, the constructed sensor exhibited a linear relationship between decreasing peak current and SDI concentration from 0.02 to 3.5 µM with a low detection limit of 4 nM (S/N = 3). As a proof of concept, SDI-MIM(PM)/Fn-Au/GCE was also applied to detect SDI in chili powder samples, with recoveries ranging from 96.8 to 106.6%.

Hollow mesoporous carbon nanospheres space-confining ultrathin nanosheets superstructures for efficient capacitive deionization.

In this work, we propose a novel strategy to fabricate nickel silicate nanoflakes inside hollow mesoporous carbon spheres (Ni3Si2O5(OH)4/C). Hollow mesoporous carbon spheres (HMCSs) can well regulate and limit the growth of Ni3Si2O5(OH)4 nanosheets, which obviously enhance the structural stability and conductivity of the composites. The core-shell Ni3Si2O5(OH)4/C superstructure has been proven to possess an extremely excellent electrosorption capacity of 28.7 mg g-1 at 1.2 V under a NaCl concentration of 584 mg L-1 for capacitive deionization (CDI). This outstanding property can be attributed to the core-shell superstructure with ultrathin Ni3Si2O5(OH)4 nanosheets as the stable core and mesoporous carbon as the conductive shell. This work will provide a direction for the application of core-shell superstructure carbon-based nanomaterials as high-performance electrode materials for CDI.

Electrochemical activation-induced surface-reconstruction of NiOx microbelt superstructure of core-shell nanoparticles for superior durability electrocatalysis.

The tailoring of intrinsic electronic structures and extrinsic hierarchical morphologies is widely recognized as a promising strategy to enhance the oxygen evolution reaction (OER) performance of electrocatalysts. It is generally accepted that the surface of the transition metal-based electrocatalyst exposed to the alkaline electrolyte is highly oxidized and reconstructed, forming an amorphous layer during the electrochemical process. This amorphous active phase is favorable for OER due to its abundant dangling bonds, vacancies and defects, which is tricky to be rationally prepared by conventional methods. Herein, a facile access to crystalline / amorphous NiOx microbelt superstructure of core-shell nanoparticles is presented, which is assembled of crystalline NiO nanoparticles coated with amorphous Ni3+/Ni2+ oxide layer. Electrochemical activation induces the in-situ surface reconstruction of the NiOx microbelt superstructure, resulting in a thicker outer amorphous Ni3+/Ni2+ layer further facilitating OER. Owing to the optimization of the in-situ surface reconstruction, the NiOx microbelt superstructure with crystalline / amorphous dual phases exhibited both high electrocatalytic activity and superior durability for OER, with the original microbelt superstructure retained after 50000 s I-t test.

Chitosan assisted MXene decoration onto polymer fabric for high efficiency solar driven interfacial evaporation of oil contaminated seawater.

The solar-driven interfacial evaporation (SDIE) is now a promising way to solve the shortage of fresh water. However, high performance SDIE for the oil contaminated seawater remains challenging. Here, we propose a facile "chitosan assisted MXene decoration" strategy to prepare a superhydrophilic and underwater superoleophobic Chitosan/MXene/fabric (CMF) for highly efficient SDIE. Benefiting from the superhydrophilicity and excellent photo-thermal conversion performance, the CMF is served as both the solar absorber and the water transportation path. Under the light illumination with one sun intensity (1 kW·m-2), a high evaporation rate of 1.50 kg·m-2·h-1 and efficiency of 88.05% are achieved. The strong interfacial interaction and outstanding salt rejection behavior of the CMF ensure the SDIE long-term stability and durability. In addition, the underwater superoleophobic CMF can effectively and quickly repel different oils and is hence suitable for high performance SDIE of the oil-in-water emulsion and the crude oil contaminated seawater. This work provides a rational design and optimization for the SDIE system, which holds great potential in practical desalination applications.

Pillared-layer Ni-MOF nanosheets anchored on Ti3C2 MXene for enhanced electrochemical energy storage.

The poor conductivity, unsatisfactory stability and easy aggregation of metal-organic framework (MOF) nanomaterials have been recognized as the main reasons that prevent their practical application. Here, we report the highly conductive and cyclic-stable Ti3C2 MXene@pillared-layer [Ni(thiophene-2,5-dicarboxylate)(4,4'-bipyridine)]n MOF composites (MXene@Ni-MOF). Based on the hard-soft-acid-base principle, the pillared-layer Ni-MOF porous structure with Ni-N coordination bonds confer better structural stability. The Ni-MOF nanosheets are immobilized by the MXene, leading to fast charge transfer between the Ni-MOF and MXene, solving the problem of poor conductivity of Ni-MOF, while avoiding the agglomeration of Ni-MOF nanosheets. Moreover, the strong interaction between the organic ligands of Ni-MOF and surface functional groups of MXene plays a key role: it reduces the exposure of surface groups of MXene, limits the oxidation of MXene, and increases its layer spacing, thus facilitating the rapid ion transport. The MXene@Ni-MOF exhibits a high specific capacitance (979 F g-1 at 0.5 A g-1) and the new aqueous asymmetric supercapacitor device displays an excellent cycling property with only 2% decay after 5000 cycles.

Mechanically robust Janus nanofibrous membrane with asymmetric wettability for high efficiency emulsion separation.

Water pollution caused by oil leakage or oily sewage has seriously threatened the ecological environment and human health. It remains a tough task for scientists to develop versatile materials to purify different kinds of oily wastewater. In this study, we propose a facile "carbon nanotubes (CNTs) decoration and nanofibrous membrane integration" method to prepare a mechanical robust Janus membrane (JM) composed of a superhydrophilic nanofiber composite layer and a hydrophobic nanofiber composite layer. The asymmetric wettability can be controlled by tuning the thickness of the hydrophobic layer. The nanofiber composite in both two layers possesses a core-shell structure, guaranteeing the excellent flexibility and stretchability of the JM. In addition, the strong interfacial compatibility between the two layers ensures the stability and durability of the JM even after multiple stretching. More importantly, the JM could realize on-demand separation of different kinds of oily wastewater with high separation flux and separation efficiency, including oil/water mixtures with different oil densities, oil-in-water emulsions and water-in-oil emulsions. Furthermore, the JM exhibits cycling stability and long-term serviceability for the emulsion separation. The mechanically robust and stretchable JM has promising applications in purification of various oil contaminated wastewater.