Synthesis of novel nitrogen-doped carbon dots for highly selective detection of iron ion.

Herein, we report an eco-friendly and simple fluorescent nitrogen-doped carbon quantum dot (N-CQD) biosensor which was synthesized via a hydrothermal method using erhanediamine (EDA) and citric acid (CA) as precursors. The surface functionalization of N-CQDs exhibited a bright blue emission under the excitation wavelength of 350 nm. The obtained N-CQDs were characterized by atomic force microscopy (AFM), Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy. It was found that the surface of the CQDs was successfully functionalized. After that, as-prepared N-CQDs were further applied in Fe(III) detection. Spectroscopic data indicated that fluorescent carbon-based nanomaterials displayed a sensitive response to Fe3+ in the range of 0.5-1000 µM as a fluorescence sensor in real environmental samples. Furthermore, the results also showed that a novel N-CQD nanomaterial could be employed as an ideal fluorescent Fe(III) probe.

Preparation of Pd/Bacterial Cellulose Hybrid Nanofibers for Dopamine Detection.

Palladium nanoparticle-bacterial cellulose (PdBC) hybrid nanofibers were synthesized by in-situ chemical reduction method. The obtained PdBC nanofibers were characterized by a series of analytical techniques. The results revealed that Pd nanoparticles were evenly dispersed on the surfaces of BC nanofibers. Then, the as-prepared PdBC nanofibers were mixed with laccase (Lac) and Nafion to obtain mixture suspension, which was further modified on electrode surface to construct novel biosensing platform. Finally, the prepared electrochemical biosensor was employed to detect dopamine. The analysis result was satisfactory, the sensor showed excellent electrocatalysis towards dopamine with high sensitivity (38.4 µA·mM(-1)), low detection limit (1.26 µM), and wide linear range (5-167 µM). Moreover, the biosensor also showed good repeatability, reproducibility, selectivity and stability and was successfully used in the detection of dopamine in human urine, thus providing a promising method for dopamine analysis in clinical application.

Decoupling Activation and Transport by Electron-Regulated Atomic-Bi Harnessed Surface-to-Pore Interface for Vanadium Redox Flow Battery.

Vanadium redox flow battery (VRFB) promises a route to low-cost and grid-scale electricity storage using renewable energy resources. However, the interplay of mass transport and activation processes of high-loading catalysts makes it challenging to drive high-performance density VRFB. Herein, a surface-to-pore interface design that unlocks the potential of atomic-Bi-exposed catalytic surface via decoupling activation and transport is reported. The functional interface accommodates electron-regulated atomic-Bi catalyst in an asymmetric Bi─O─Mn structure that expedites the V3+ /V2+ conversion, and a mesoporous Mn3 O4 sub-scaffold for rapid shuttling of redox-active species, whereby the site accessibility is maximized, contrary to conventional transport-limited catalysts. By in situ grafting this interface onto micron-porous carbon felt (Bi1 -sMn3 O4 -CF), a high-performance flow battery is achieved, yielding a record high energy efficiency of 76.72% even at a high current density of 400 mA cm-2 and a peak power density of 1.503 W cm-2 , outdoing the battery with sMn3 O4 -CF (62.60%, 0.978 W cm-2 ) without Bi catalyst. Moreover, this battery renders extraordinary durability of over 1500 cycles, bespeaking a crucial breakthrough toward sustainable redox flow batteries (RFBs).

N-P covalent bond regulation of mesoporous carbon-based catalyst for lowered oxygen reduction overpotential and enhanced zinc-air battery performance.

Developing sustainable metal-free carbon-based electrocatalysts is essential for the deployment of metal-air batteries such as zinc-air batteries (ZABs), among which doping of heteroatoms has attracted tremendous interest over the past decade. However, the effect of the heteroatom covalent bonds in carbon matrix on catalysis was neglected in most studies. Here, an efficient metal-free oxygen reduction reaction (ORR) catalyst is demonstrated by the N-P bonds anchored carbon (termed N,P-C-1000). The N,P-C-1000 catalyst exhibits superior specific surface area of 1362 m2 g-1 and ORR activity with a half-wave potential of 0.83 V, close to that of 20 wt% Pt/C. Theoretical computations reveal that the p-band center for C-2p orbit in N,P-C-1000 has higher interaction strength with the intermediates, thus reducing the overall reaction energy barrier. The N,P-C-1000 assembled primary ZAB can attain a large peak power density of 121.9 mW cm-2 and a steady discharge platform of ∼1.20 V throughout 120 h. Besides, when served as the cathodic catalyst in a solid-state ZAB, the battery shows flexibility, conspicuous open circuit potential (1.423 V), and high peak power density (85.8 mW cm-2). Our findings offer a strategy to tune the intrinsic structure of carbon-based catalysts for improved electrocatalytic performance and shed light on future catalysts design for energy storage technologies beyond batteries.

Nano-sphere RuO2 embedded in MOF-derived carbon arrays as a dual-matrix anode for cost-effective electrochemical wastewater treatment.

The electrodes' activity, surface area and cost hinder the deployment of electrochemical wastewater treatment. Using an economical microfiber-based carbon felt (CF) substrate, we design RuO2 nanospheres confined by CoxO cooperated carbon nanoarrays (RuO2-CoxO@TCF) to augment noble metal utilization and thus reduce the catalyst cost. RuO2-CoxO@TCF anode with vertical diffusion channels exhibits rapid generation ability of oxidizing species particularity in the presence of Cl- ions, which play a crucial role in azo bond cleavage and benzene ring chlorination of methyl orange. As a result, the catalyst shows 99.5 % color removal and ∼ 70 % mineralization efficiency at a concentration of 60 ppm. In synthetic dyeing wastewater, RuO2-CoxO@TCF delivers a stable total organic carbon (TOC) removal throughout ten cycling tests. Moreover, the electricity consumption of RuO2-CoxO@TCF is far below the reference anode, showing great promise for dye degradation and remediation of industrial wastewater.

Asymmetric Chemical Potential Activated Nanointerfacial Electric Field for Efficient Vanadium Redox Flow Batteries.

Constructing active sites with enhanced intrinsic activity and accessibility in a confined microenvironment is critical for simultaneously upgrading the round-trip efficiency and lifespan of all-vanadium redox flow battery (VRFB) yet remains under-explored. Here, we present nanointerfacial electric fields (E-fields) featuring outstanding intrinsic activity embodied by binary Mo2C-Mo2N sublattice. The asymmetric chemical potential on both sides of the reconstructed heterogeneous interface imposes the charge movement and accumulation near the atomic-scale N-Mo-C binding region, eliciting the configuration of an accelerator-like E-field from Mo2N to Mo2C sublattice. Supported with theoretical calculations and intrinsic activity tests, the improved vanadium ion adsorption behavior and charge-transfer process at the nanointerfacial sites were further substantiated, hence expediting the electrochemical kinetics. Accordingly, the pronounced promotion is achieved in the resultant flow battery, yielding an energy efficiency of 77.7% and an extended lifespan of 1000 cycles at 300 mA cm-2, outperforming flow cells with conventional single catalysts in most previous reports.

Biomechanical Energy Harvesters Based on Ionic Conductive Organohydrogels via the Hofmeister Effect and Electrostatic Interaction.

The recent use of cryoprotectant replacement method for solving the easy drying problem of hydrogels has attracted increasing research interest. However, the conductivity decrease of organohydrogels due to the induced insulating solvent limited their electronic applications. Herein, we introduce the Hofmeister effect and electrostatic interaction to generate hydrogen and sodium bonds in the hydrogel. Combined with its double network, an effective charge channel that will not be affected by the solvent replacement, is therefore built. The developed organohydrogel-based single-electrode triboelectric nanogenerator (OHS-TENG) shows low conductivity decrease (one order) and high output (1.02-1.81 W/m2), which is much better than reported OHS-TENGs (2-3 orders, 41.2-710 mW/m2). Moreover, replacing water with glycerol in the hydrogel enables the device to exhibit excellent long-term stability (four months) and temperature tolerance (-50-100 °C). The presented strategy and mechanism can be extended to common organohydrogel systems aiming at high performance in electronic applications.

MOF-Derived Sulfide-Based Electrocatalyst and Scaffold for Boosted Hydrogen Production.

Metal-organic frameworks (MOFs) can act as precursors or templates to a myriad of nanostructured materials that are difficult to prepare. In this study, Co-MOF nanorods (NRs) were prepared at room temperature followed by a calcination and hydrothermal sulfurization strategy to transform the MOF into CoS NRs on carbon cloth (CoS/CC). Intriguingly, the resultant 3D sulfide NRs can serve as scaffolds to electrodeposit layered double hydroxides (LDHs) on the surfaces. Through combining the advantages of structure and composition, the as-fabricated CoS@CoNi-LDH/CC exhibits remarkable electrocatalytic activity for the hydrogen evolution reaction (HER). An overpotential of 124 mV is needed to reach a current density of 10 mA cm-2 with a Tafel slope of only 89 mV dec-1, which is superior to that of pure CoS/CC (141 mV along with 103 mV dec-1) and other reported cobalt-based catalysts. Notably, after the chronopotentiometry test for 50 h, the overpotential of CoS@CoNi-LDH/CC increased by 17 mV only.

MoS2 Coexisting in 1T and 2H Phases Synthesized by Common Hydrothermal Method for Hydrogen Evolution Reaction.

Molybdenum disulfide has been one of the most studied hydrogen evolution catalyst materials in recent years, but its disadvantages, such as poor conductivity, hinder its further development. Here, we employ the common hydrothermal method, followed by an additional solvothermal method to construct an uncommon molybdenum disulfide with two crystal forms of 1T and 2H to improve catalytic properties. The low overpotential (180 mV) and small Tafel slope (88 mV/dec) all indicated that molybdenum disulfide had favorable catalytic performance for hydrogen evolution. Further conjunctions revealed that the improvement of performance was probably related to the structural changes brought about by the 1T phase and the resulting sulfur vacancies, which could be used as a reference for the further application of MoS2.

C@TiO2 /MoO3 Composite Nanofibers with 1T-Phase MoS2 Nanograin Dopant and Stabilized Interfaces as Anodes for Li- and Na-Ion Batteries.

Integrating layered nanostructured MoS2 with a structurally stable TiO2 backbone to construct reciprocal MoS2 /TiO2 -based nanocomposites is an effective strategy. C@TiO2 /MoO3 composite nanofibers doped with 1T-phase MoS2 nanograins were fabricated by partially sulfurizing MoOx /TiO2 precursors. By controlling a suitable preoxidation temperature before severe thermolysis of polyvinylpyrrolidone (PVP), the MoOx /TiO2 precursors formed a polymer-embedded array through coordination of the Mo source and pyrrolidyl groups of PVP. Sulfidation under water/solvent hydrothermal conditions led to partial formation of metallic 1T-phase MoS2 from the MoOx precursor with preoxidation at 200 °C. After carbonization, the TiO2 /MoO3 /MoS2 nanograins were encapsulated in a carbon backbone in a vertical pattern, providing both chemical contact for confined electron transport and sufficient space to adapt to volume changes. The obtained carbon-based platform not only has the advantages of an integral structure, but also exhibited ultrastable specific capacities of 540 and 251 mAh g-1 for Li-ion batteries and Na-ion batteries, respectively, after 100 cycles.

Sol-Gel Synthesis of Carbon Xerogel-ZnO Composite for Detection of Catechol.

Carbon xerogel-zinc oxide (CXZnO) composites were synthesized by a simple method of sol-gel condensation polymerization of formaldehyde and resorcinol solution containing zinc salt followed by drying and thermal treatment. ZnO nanoparticles were observed to be evenly dispersed on the surfaces of the carbon xerogel microspheres. The as-prepared CXZnO composites were mixed with laccase (Lac) and Nafion to obtain a mixture solution, which was further modified on an electrode surface to construct a novel biosensing platform. Finally, the prepared electrochemical biosensor was employed to detect the environmental pollutant, catechol. The analysis result was satisfactory, the sensor showed excellent electrocatalysis towards catechol with high sensitivity (31.2 µA·mM-1), a low detection limit (2.17 µM), and a wide linear range (6.91-453 µM). Moreover, the biosensor also displayed favorable repeatability, reproducibility, selectivity, and stability besides being successfully used in the trace detection of catechol existing in lake water environments.