Synergistic Coupling of Charge Extraction and Sinking in Cu5FeS4/Ni3S2@NF for Photoassisted Electrocatalytic Oxygen Evolution.

Exploring low-cost and high-performance oxygen evolution reaction (OER) catalysts has attracted great attention due to their crucial role in water splitting. Here, a bifunctional Cu5FeS4/Ni3S2@NF catalyst was in situ formed on a nickel (Ni) foam toward efficient photoassisted electrocatalytic (P-EC) OER, which displays an ultralow overpotential of 260 mV at 30 mA cm-2 in alkaline solution, outperforming most previously reported Ni-based catalysts. It also shows great potential in degradation of antibiotics as an alternative anode reaction to OER owing to the prompt transfer of photogenerated holes. The photocurrent test and transient photovoltage spectroscopy indicate that the synergistic coupling of charge extraction and sinking effects in Cu5FeS4 and Ni3S2 is critical for boosting the OER activity via photoassistance. Electrochemical active surface area and electrochemical impedance spectroscopy tests further prove that the photogenerated electromotive force can effectively compensate the overpotential of OER. This work not only provides a good guidance for integrating photocatalysis and electrocatalysis, but also indicates the key role of synergistic extraction and utilization of photogenerated charge carriers in P-EC.

Quasi-type-II Cu-In-Zn-S/Ni-MOF heterostructure with prolonged carrier lifetime for photocatalytic hydrogen production.

Visible-driven photocatalytic hydrogen production using narrow-bandgap semiconductors has great potential for clean energy development. However, the widespread use of these semiconductors is limited due to problems such as severe charge recombination and slow surface reactions. Herein, a quasi-type-II heterostructure was constructed by combining bifunctional Ni-based metal-organic framework (Ni-MOF) nanosheets with BDC (1,4-benzenedicarboxylic acid) linker coupled with Cu-In-Zn-S quantum dots (CIZS QDs). This heterostructure exhibited a prolonged charge carrier lifetime and abundant active sites, leading to significantly improved hydrogen production rate. The optimized rate achieved by the CIZS/Ni-MOF heterostructure was 2642 µmol g-1 h-1, which is 5.28 times higher than that of the CIZS QDs. This improved performance can be attributed to the quasi-type-II band alignment between the CIZS QDs and Ni-MOF, which facilitates effective delocalization of the photogenerated electrons within the system. Additional photoelectrochemical tests confirmed the well-maintained photoluminescence and prolonged charge carrier lifetime of the CIZS/Ni-MOF heterostructure. This study provides valuable insights into the use of multifunctional MOFs in the development of highly efficient composite photocatalysts, extending beyond their role in light harvesting and charge separation.

Well-defined diatomic catalysis for photosynthesis of C2H4 from CO2.

Owing to the specific electronic-redistribution and spatial proximity, diatomic catalysts (DACs) have been identified as principal interest for efficient photoconversion of CO2 into C2H4. However, the predominant bottom-up strategy for DACs synthesis has critically constrained the development of highly ordered DACs due to the random distribution of heteronuclear atoms, which hinders the optimization of catalytic performance and the exploration of actual reaction mechanism. Here, an up-bottom ion-cutting architecture is proposed to fabricate the well-defined DACs, and the superior spatial proximity of CuAu diatomics (DAs) decorated TiO2 (CuAu-DAs-TiO2) is successfully constructed due to the compact heteroatomic spacing (2-3 Å). Owing to the profoundly low C-C coupling energy barrier of CuAu-DAs-TiO2, a considerable C2H4 production with superior sustainability is achieved. Our discovery inspires a novel up-bottom strategy for the fabrication of well-defined DACs to motivate optimization of catalytic performance and distinct deduction of heteroatom synergistically catalytic mechanism.

Controllable synthesis of bifunctional magnetic carbon dots for rapid fluorescent detection and reversible removal of Hg2.

Mercury is one of the most toxic heavy metals, whose identification and separation are crucial for environmental remediation. Till now, it remains a significant challenge upon simultaneous detection and removal of Hg2+. Herein, bifunctional probe magnetic carbon dots were synthesized and optimized via systematic structure manipulation of the carbon and iron precursors towards fluorescence, Hg2+ adsorption and magnetic separation. The probe exhibited blue emission at 440 nm with high quantum yield of 55 % and a high paramagnetism with the saturation magnetization value of 22.70 emu/g. Furthermore, the fluorescent detection of Hg2+ with limit of 5.40 nM and high selectivity were achieved through surface structure manipulation with moderate -NH2, -SH and Fe contents. As a result, the magnetic removal of Hg2+ was consecutively effectuated with high removal efficiency of 98.30 %. The detection and recovery of Hg2+ in real samples were further verified and demonstrated the excellent environmental tolerance of probe. The reusability was viable with recycling at least three turns by external magnet. This work not only provides a promising approach for simultaneous detection and removal of heavy metal pollution, but also provides an excellent example as a versatile platform for multifunction integration via the structure manipulation for other applications.

The synthesis of gold nanoclusters with high stability and their application in fluorometric detection for Hg2+ and cell imaging.

Sensing Hg2+ is significant to protecting human health and environmental ecosystems, for its toxicity and genotoxicity. Here, highly stable fluorescent folic acid (FA)-protected Au nanoclusters (FA-AuNCs) were synthesized by optimizing the reactive parameters with high quantum yield of 34.7%. Main components of Au4L were confirmed by MALDI-TOF, and the electron-rich residues of FA shell enabled FA-AuNCs excellent photostability. FA-AuNCs exhibited sensitive response behavior to Hg2+ with a minimum detectability of 1.3 nM, and presented extreme effect to the detection of Hg2+ in real water. Notably, the cellular imaging and in-situ detection of Hg2+ in cells can be achieved visually. The high selectivity was attributed to the chemical bond formed between Au+ (4f145d10) and Hg2+ (4f145d10). And the internal filter effect and static quenching effect were proved triggering the quenching of FA-AuNCs. The ultra-stable FA-AuNCs provide a potential promising opportunity for the in-situ tracing Hg2+ from environmental and biological samples.

Portable smartphone-integrated AuAg nanoclusters electrospun membranes for multivariate fluorescent sensing of Hg2+, Cu2+ and l-histidine in water and food samples.

Detection of heavy metals have been pivotal due to their non-biodegradability and food chain accumulation. Herein, a multivariate ratiometric sensor was developed by in situ integrating AuAg nanoclusters (NCs) into electrospun cellulose acetate nanofibrous membranes (AuAg-ENM) for visual detection of Hg2+, Cu2+ and consecutive sensing of l-histidine (His), which was integrated into a smartphone platform for quantitative on-site detection. AuAg-ENM achieved multivariate detection of Hg2+ and Cu2+ by fluorescence quenching, and subsequent selective recovery of the Cu2+-quenched fluorescence by His, which distinguished Hg2+ and Cu2+ and fulfilled determination of His simultaneously. Notably, AuAg-ENM achieved selective monitoring of Hg2+, Cu2+ and His in water, food and serum samples with high accuracy comparable to ICP and HPLC tests. A logic gate circuit was devised to further explain and promote the application of AuAg-ENM detection by smartphone App. This portable AuAg-ENM provides a promising reference for fabricating intelligent visual sensors for multiple detection.

Surface modified silver/magnetite nanocomposite activating hydrogen peroxide for efficient degradation of chlorophenols.

The mixed-valent magnetite (Fe3O4) played a critical role in H2O2-based Fenton-like system for the removal of chlorophenols, but high activity and cycle stability of the Fe3O4-based catalysts are still a huge challenge. Herein, a series of surface hydroxyl- and carboxyl-modified Ag0/Fe3O4 nanocomposite catalysts were prepared and used to activate H2O2 for degradation chlorophenols pollutants. Under the optimized condition, nearly 100% degradation ratio were achieved within 2-30 min for 2,4-dichlorophenol, 2,3-dichlorophenol, 3,4-dichlorophenol, 2,4,6-trichlorophenol, p-nitrophenol, and 98% degradation ratio for 2,5-dichlorophenol, 2,6-dichlorophenol and 3,5-dichlorophenol,. Moreover, wide pH applicability was obtained for the Ag0/Fe3O4-H2O2 system, where 95% degradation ratio of 2,4-dichlorophenol was still obtained at pH 6.0. The excellent activity of Ag0/Fe3O4 catalyst can be ascribed to the incorporation of Ag0 nanoparticles that accelerated the Fe(III)/Fe(II) transformation with the assistance of surface hydroxyl and carboxyl groups. Detailed mechanism study indicated a pseudo-second-order kinetic model, where the oxidative degradation and reductive degradation pathways coexisted in the system. The surface-modified Ag0/Fe3O4-H2O2 provide a practical catalyst system for the removal of phenol contaminants with high reaction rate, wide pH adaptability, and validity for a series of chlorophenols.

Ag-In-Zn-S Quantum Dot-Dominated Interface Kinetics in Ag-In-Zn-S/NiFe LDH Composites toward Efficient Photoassisted Electrocatalytic Water Splitting.

Photoassisted electrocatalysis (P-EC) emerges as a rising star for hydrogen production by embedding photoactive species in electrocatalysts, for which the interfacial structure design and charge transfer kinetics of the multifunctional catalysts remain a great challenge. Herein, Zn-AgIn5S8 quantum dots (ZAIS QDs) were embedded into 2D NiFe layered double hydroxide nanosheets through a simple hydrothermal treatment to form 0D/2D composite catalysts for P-EC. With evidence from transient photovoltage spectroscopy, we acquired a clear and fundamental understanding on the kinetics of charge extraction time and extraction amount in the 0D/2D heterojunctions that was proved to play a key role in P-EC. Upon light illumination, for HER, the optimized NiFe-ZAIS exhibits obviously reduced overpotentials of 129 and 242 mV at current densities of 10 and 50 mA cm-2, which are 22 and 33 mV lower than those of dark electrocatalysis, respectively. For OER, the NiFe-ZAIS electrode also shows low overpotentials of 220 and 268 mV at current densities of 10 and 50 mA cm-2, respectively, under light illumination, which were able to almost double the intrinsic activity. Finally, with NF@NiFe-ZAIS as both the cathode and the anode, the assembled electrolyzer only requires 1.62 V to reach the overall water splitting current density of 10 mA cm-2 under P-EC. This work provides a useful example for the profound understanding of the design and the kinetics study of multifunctional P-EC catalysts.

One-Step Nickel Foam Assisted Synthesis of Holey G-Carbon Nitride Nanosheets for Efficient Visible-Light Photocatalytic H2 Evolution.

Graphitic carbon nitride (g-C3N4) with layered structure represents one of the most promising metal-free photocatalysts. As yet, the direct one-step synthesis of ultrathin g-C3N4 nanosheets remains a challenge. Here, few-layered holey g-C3N4 nanosheets (CNS) were fabricated by simply introducing a piece of nickel foam over the precursors during the heating process. The as-prepared CNS with unique structural advantages exhibited superior photocatalytic water splitting activity (1871.09 µmol h-1 g-1) than bulk g-C3N4 (BCN) under visible light (λ > 420 nm) (≈31 fold). Its outstanding photocatalytic performance originated from the high specific surface area (240.34 m2 g-1) and mesoporous structure, which endows CNS with more active sites, efficient exciton dissociation, and prolonged charge carrier lifetime. Moreover, the obvious upshift of the conduction band leads to a larger thermodynamic driving force for photocatalytic proton reduction. This methodology not only had the advantages for the direct and green synthesis of g-C3N4 nanosheets but also paved a new avenue to modify molecular structure and textural of g-C3N4 for advanced applications.

Core-shell structured ZnCo2O4@ZnWO4 nanowire arrays on nickel foam for advanced asymmetric supercapacitors.

One of the most effective tactics to promote the electrochemical performance of supercapacitors is to design and synthesize hybrid binder-free electrodes with core-shell structures. In this work, hierarchical ZnCo2O4@ZnWO4 core-shell nanowire arrays grown on nickel foam are successfully fabricated via a facile two-step hydrothermal route and subsequent thermal treatment. The ZnCo2O4 nanowire arrays supported on nickel foam serve as the backbone for anchoring ZnWO4 nanosheets. When tested as binder-free electrodes for supercapacitors, the as-prepared ZnCo2O4@ZnWO4 hybrid electrode exhibits an ultrahigh specific areal capacitance of 13.4 F cm-2 at a current density of 4 mA cm-2 and superb cycling stability (98.5% retention after 5000 continuous cycles at a current density of 100 mA cm-2). Furthermore, an asymmetric supercapacitor based on ZnCo2O4@ZnWO4//active carbon is successfully designed. The as-designed asymmetric supercapacitor can achieve a maximum energy density of 24 Wh kg-1 at a power density of 400 W kg-1. Moreover, two as-prepared asymmetric supercapacitor devices in a series connection are able to light up a white light-emitting diode over 30 min. The outstanding electrochemical properties of the hybrid electrode demonstrate that it holds great potential for next generation energy storage applications.

Nickel foam derived nitrogen doped nickel sulfide nanowires as an efficient electrocatalyst for the hydrogen evolution reaction.

Ni3S2 has been validated as an effective electrocatalyst for the oxygen evolution reaction, attributable to its suitable electronic configuration. However, pure Ni3S2 towards the hydrogen evolution reaction (HER) exhibits relatively low catalytic activity. Herein, a one-step annealing strategy is demonstrated for the synthesis of Ni3S2 nanowires on nickel foam (NF) through N doping towards vigorous HER performance both in acid and alkaline solution. The 1D N-Ni3S2 nanowires, integrated onto a 3D NF electrode, show a high catalytic current density of 10 mA cm-2 at a low overpotential of 196 mV and a small Tafel slope of 63 mV dec-1 in an acid electrolyte. In an alkaline medium, the N-Ni3S2 NWs exhibit a low overpotential of 105 mV at the current density of 10 mA cm-2, which is lower than other reported Ni3S2-based HER catalysts. The superior HER catalytic performance is attributed to its unique structural features, both the morphology and electronic structure. Our work provides profound guidance for the design and optimization of electrocatalysts for an efficient HER.

Facile and controllable synthesis of polyoxometalate nanorods within polyelectrolyte matrix.

Well dispersed polyoxometalate nanorods have been selectively and controllably synthesized within the polyelectrolyte (PE) films via a layer-by-layer (LbL) adsorption-precipitation method. The PE matrix was fabricated by LbL self-assembly technology and then the multilayer films containing polyoxometalate nanorods were constructed by repetitive adsorption of polyanions and subsequent precipitation with counter ions-tetraethylammonium bromide (TEAB). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to observe the variation of size and morphology of the nanorods. The growth process and composition of the multilayer films containing nanorods were also studied.

Enhanced photoelectrochemical water oxidation performance of a hematite photoanode by decorating with Au-Pt core-shell nanoparticles.

It is well known that bimetallic nanomaterials usually exhibit unique catalytic, optical, electric and magnetic properties due to the synergistic effect between different metals. In this work, we reported on a scalable method to fabricate an AuPt bimetallic core-shell nanoparticles loaded hematite (α-Fe2O3) photoanode for solar-driven photoelectrochemical water oxidation. Compared to single metal-modified α-Fe2O3 photoanodes, the AuPt bimetallic core-shell nanoparticles loaded α-Fe2O3 photoanodes exhibited a synergistic effect for photoelectrochemical water oxidation. The photocurrent density of AuPt0.2/α-Fe2O3 was boosted to 0.83 mA cm-2 at 1.23 V versus a reversible hydrogen electrode in a neutral electrolyte (0.5 M Na2SO4 aqueous solution) under 45 W xenon lamp irradiation. The incident photon-to-photocurrent efficiency value of optimum AuPt0.2/α-Fe2O3 was estimated to be 58%, which was significantly higher than the single metal-modified α-Fe2O3 and pristine α-Fe2O3 photoanodes (<10%). Electrochemical impedance spectroscopy and Mott-Schottky analysis confirmed that the Schottky junction formed by the AuPt bimetallic nanoparticles and α-Fe2O3 led to enhanced charge separation and band bending, resulting in a negative shift of onset potential. Based on the experimental and characterized results, a possible mechanism was proposed. This work provides an important reference for the design of other bimetallic-modified photoanodes for application in energy conversion.

Precisely tunable thickness of graphitic carbon nitride nanosheets for visible-light-driven photocatalytic hydrogen evolution.

Graphitic carbon nitride (GCN) nanosheets with unique physicochemical properties have received increasing attention in the area of photocatalysis, yet tunable thickness for the straightforward production of this graphite-like two-dimensional (2D) nanomaterial remains a challenge. In this work, GCN nanosheets with different thicknesses were firstly prepared by a direct calcination of melamine supramolecular aggregates (MSA) obtained from a hydrochloric acid (HCl)-induced hydrothermal assembly approach. The resultant nanosheets over nanometer scale thickness could be precisely controlled via simply adjusting the HCl concentration. Compared to the bulk GCN (BGCN), the thinner nanosheets possessed a high specific surface area, a large electronic-band structure, and fast charge separation ability. The thinnest nanosheets with a thickness of approximately 4 nm exhibited excellent visible-light-driven photocatalytic water splitting performance in hydrogen evolution (524 µmol h-1 g-1), which is over 9-fold higher than the BGCN powder. This work provides a thickness-dependent strategy for the preparation of metal-free GCN nanosheets and develops a promising 2D photocatalyst for application in solar energy conversion.

New Insight of Water-Splitting Photocatalyst: H2O2-Resistance Poisoning and Photothermal Deactivation in Sub-micrometer CoO Octahedrons.

Hydrogen production by photocatalytic overall water-splitting represents an ideal pathway for clean energy harvesting, for which developing high-efficiency catalysts has been the central scientific topic. Nanosized CoO with high solar-to-hydrogen efficiency (5%) is one of the most promising catalyst candidates. However, poor understanding of this photocatalyst leaves the key issue of rapid deactivation unclear and severely hinders its wide application. Here, we report a sub-micrometer CoO octahedron photocatalyst with high overall-water-splitting activity and outstanding ability of H2O2-resistance poisoning. We show that the deactivation of CoO catalyst originates from the unintended thermoinduced oxidation of CoO during photocatalysis, with coexistence of oxygen and water. We then demonstrate that introduction of graphene, as a heat conductor, largely enhanced the photocatalytic activity and stability of the CoO. Our work not only provides a new insight of CoO for photocatalytic water splitting but also demonstrates a new concept for photocatalyst design.

Fabrication of high quality carbon nanotubes with a simple ethanol-assisted arc discharge process.

In this paper, a simplified ethanol-assisted arc discharge method was developed for the fabrication of multi-wall carbon nanotubes in high quality. Carbon nanotubes with high purity (80-90%) were obtained through controlling the current (15-25 V, 10-25 A) and ethanol concentration (70-100%). The products were characterized using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectrometry.

Layer-by-layer assembly of polyoxometalates into microcapsules.

The polyoxometalate (POM) chemistry world has been experiencing an unparalleled development of rapid synthesis of new compounds and slow development of POM-based functional materials and devices. Meanwhile, researchers in the microcapsule world, encouraged by the introduction of the layer-by-layer method, are pursuing good components for constructing functional capsule devices. Here, in view of the versatile properties that POM-based microcapsules may possess, various types of POM-polyelectrolyte composite microcapsules were constructed using the layer-by-layer method. Microscopy reveals that polyoxometalates form nanoparticles on the shell in the presence of cationic polyelectrolytes. These nanoparticles connected with polyelectrolytes constitute the shell and support the microcapsule from collapse after drying, and this is an interesting characteristic different from those of common composite and polyelectrolyte capsules. Fourier transform infrared (FTIR), UV-vis absorption, and X-ray photoelectron spectroscopy (XPS) were used to examine the properties of the POMs in the microcapsules. The obtained microcapsules exhibit higher thermal stability than polyelectrolyte microcapsules. Furthermore, the functions of POMs were maintained when they were assembled into microcapsules. It is proved that microcapsules bearing POMs with redox activity can provide a reduction environment, which can lead to the realization of in situ synthesis of materials, and that microcapsules with photoluminescent POMs as a component can also have a photoluminescent property, providing a way to develop functional capsule devices. This work may provide an opportunity to enrich both the polyoxometalate chemistry and the capsule field.

Visible-light-driven reversible and switchable hydrophobic to hydrophilic nitrogen-doped titania surfaces: correlation with photocatalysis.

Visible-light-responsive nitrogen-doped titanium dioxide nanorods have been synthesized by a hydrothermal method at low temperature. X-Ray diffraction, scanning electron microscopy, UV-vis spectroscopy, and contact angle measurements were used to obtain the crystal structures, morphologies, visible-light absorbance, and hydrophobicity, respectively, of the prepared nanorods. The surface wettability of the samples could be reversibly tuned from hydrophobic to hydrophilic upon visible-light illumination. This switchable surface wettability is crucial since the photocatalytic activity of this nanoscaled catalyst for the decomposition of organic molecules exhibits a strong dependence on the surface wettability.

'One-step' controllable synthesis of Ag and Ag(2)S nanocrystals on a large scale.

Ag and Ag(2)S nanocrystals (NCs) were synthesized by a simple 'one-step' process. Dodecanethiol played three important roles in the synthesis: as the capping reagent, reducer (for the synthesis of Ag) and S(2-) source (for the synthesis of Ag(2)S). Due to the multifunctional characteristic of dodecanethiol, only two reactants (silver nitrate and dodecanethiol) are needed in the synthesis, avoiding the use of toxic organic solvents and a complex reaction procedure. X-ray powder diffraction and transmission electron microscopy studies indicated that both the phase (Ag or Ag(2)S) and the particle size were controlled by reaction parameters. The infrared spectra studies indicated that the nanoparticles were stabilized by dodecanethiol. As a result, the particles were stable (no irreversible conglomeration) in the solid state and in solution for several months. In addition, a large quantity of Ag and Ag(2)S NCs could be readily obtained. A possible formation and size evolution mechanism for Ag and Ag(2)S NCs was proposed.

Controllable fabrication of carbon nanotube and nanobelt with a polyoxometalate-assisted mild hydrothermal process.

Carbon nanotubes, carbon nanobelts, and carbon nanoparticles can be prepared directly from active carbon powders by a polyoxometalates (POMs)-assisted mild hydrothermal process. After the hydrothermal reaction the POMs are changed into heteropoly blues, which can be converted into the POMs by a small amount of H2O2 solution.