Structure-directing Reagent Research Articles

In-situ constructing hetero-structured Mo2C-Mo2N embedded in carbon nanosheet as an efficient separator modifier for high-performance lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are promising electrochemical energy storage devices. However, the shuttle effects and slow conversion kinetics of lithium polysulfides (LiPSs) still impede the practical application of LSBs. Herein, with the assistance of g-C3N4, a hetero-structured Mo2C-Mo2N embedded in the nitrogen-doped carbon sheets composite (Mo2C-Mo2N/C) is facilely in-situ synthesized. The g-C3N4 not only acts as the nitriding reagent for the heterostructure formation, but also is the structure-directing reagent for the formation of two-dimensional structures. More interestingly, Mo2C-Mo2N/C is also employed as a modifier of separators for LSBs. As evidenced experimentally and theoretically, the hetero-structured Mo2C-Mo2N exhibits a strong adsorption ability to LiPSs and concurrently offers a built-in electric field inside the heterostructure that ensures the fast conversion of LiPSs, thus significantly suppressing the shuttle effect and accelerating the electrochemical kinetics of LSBs. Therefore, the prepared LSBs with the Mo2C-Mo2N/C modified separator deliver a discharge specific capacity of 1404 mAh/g at 0.1 C and 660 mAh/g at 4 C, and achieve 1000 stable cycles at 1 C, with a capacity decay rate of only 0.028% per cycle. This study not only provides an efficient strategy for synthesizing hetero-structured materials but also sheds new light on the design of functional separators for high-performance and long-life cycle LSBs.

Visible light-assisted hydrogen generation over platinum-loaded tungsten trioxide nanorods with the hexagonal and triclinic phases

Visible light-assisted hydrogen (H2) generation was attempted for tungsten trioxide (WO3) nanorods (NRs) loaded with platinum (Pt). WO3 NRs were synthesized with a simple hydrothermal method using sodium tungstate as a precursor and oxalic acid as a structure-directing reagent. A variety of structural analyses clarify that both the end parts of a single hexagonal WO3 NR are transformed into triclinic WO3 when oxalic acid is added during the NR synthesis. The WO3 NR synthesized without oxalic acid (WO3(0)) displayed site-selective photodeposition of Pt cocatalysts on the (100) plane, whereas the Pt photodeposition occurred preferentially at the end (triclinic) parts of the WO3 NR synthesized with 0.05 M of oxalic acid (WO3(0.05)). These site-selective Pt deposition allows us to consider an inversion of the redox reaction field in WO3(0) and WO3(0.05) sample. Pt-loaded WO3(0.05) showed better photocatalytic activity ascertained in both methylene blue decomposition and H2 generation from water and methanol mixture, which can be brought about by a direct Z-scheme formed at heterojunctions between hexagonal and triclinic WO3 in a single NR. Finally, photoassisted H2 generation from water including ammonia borane with Pt-loaded WO3(0.05) was demonstrated, where a H2 generation rate under visible light irradiation was about 2.7 times higher than that in the dark. This result suggests a new strategy of efficient H2 generation based on synergetic effects of the WO3 NR photocatalysis and the Pt catalysis.

Co2P nanorods with exposure of high-index facets for efficient photochemical reduction of CO2 by promoting the directional transfer of electrons

Herein, Co2P nanorods (NRs) with exposure to high-index facets (HIFs) were prepared by a special assembly-calcination method using thioacetamide (TAA) as a structure-directing reagent. The analysis of adsorption energies of S atoms on different facets as well as the surface energies of Co2P indicate that the HIFs become more stable after adsorbing S atoms. With rich unsaturated sites on HIFs, the photochemical reduction rate of CO2 over Co2P NRs is 14.5 mmol h−1 g−1 for the production of CO within 3 h. The analysis of electron transfer, bond lengths, bond angles and adsorption energies indicate that the CO2 molecules are more easily adsorbed and activated on the HIFs. The free energy calculations and d band theory demonstrate that the HIFs are conducive to reducing the formation energy barriers as well as improving the stability of the intermediate *COOH, then enhancing the catalytic performance of CO2 reduction.

Shape selective flower-like ZnO nanostructures prepared via structure-directing reagent free methods for efficient photocatalytic performance

Zinc oxides (ZnO) nanoflowers have gained enormous attention in photocatalytic applications, despite of the fact that optimization of explicitly designed nanoflower for effective application is still underexplored. In this work, a variety of ZnO nanoflowers were successfully synthesized without using structure directing reagents. ZnO nanoflowers with different morphologies (viz., sea urchin, southern cone marigold and rose flowers) were synthesized through controlling the growth direction by concentrating on synthesis process alone. The photocatalytic performance of ZnO nanoflowers follow order of sea urchin > rose > southern cone marigold flower. These results suggest that optimal ZnO nanoflower (sea urchin) with improved physicochemical parameters such as specific surface area; reduced charge carrier recombination; high aspect ratio and uniform growth along c-axis etc. holds the significant advantage over other morphology. The effective separation and transportation of photogenerated charge carriers were boosted by the existence of high aspect ratio flower like structure, which is confirmed through the detailed photoelectrochemical study. The photocatalysis results substantiated that ZnO nanoflowers display the performance in a morphology-dependent manner and confirms that difference in the intrinsic morphology and the physical accessibility act as a deciding factor in optimizing the best performing ZnO nanoflower. Subsequently, a probable mechanism of optimal flower formation is also discussed.

Graphene oxide @ nickel phosphate nanocomposites for photocatalytic hydrogen production

The graphene oxide @nickel phosphate (GO:NPO) nanocomposites (NCs) are prepared by using a one-pot in-situ solar energy assisted method by varying GO:NPO ratio i.e. 0.00, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, and 2.00 without adding any surfactant or a structure-directing reagent. As produced GO:NPO nanosheets exhibited an improved photocatalytic activity due to the spatial seperation of charge carriers through interface, where photoinduced electrons transferred from NiPO4 to the GO sheets without charge-recombination. Out of the series, the system 1.00 GO:NPO NC show the optimum hydrogen production activity (15.37 μmol H2 h−1) towards water splitting under the visible light irradiation. The electronic environment of the nanocomposite GO-NiO6/NiO4-PO4 elucidated in the light of advance experimental analyses and theoretical DFT spin density calculations. Structural advanmcement of composites are well correlated with their hydrogen production activity.

Ethylenediamine-assisted phase engineering of 1T/2H–MoS2/graphene for efficient and stable electrocatalytic hydrogen evolution

1T-MoS2 exhibits superior eletroconductivity and electrocatalytic activity in hydrogen evolution reaction (HER) over 2H–MoS2. But its thermodynamic instability severely hinders its practical application. This paper develops a highly active and stable triphasic 1T/2H–MoS2/graphene heterostructure through a facile one-step hydrothermal route with the assistance of a small organic molecule, ethylenediamine, as the structure-directing reagent. The novel triphasic heterostructure is fabricated by vertically stacking lateral 1T/2H–MoS2 heterojuctions on graphene. The stability of the 1T phase is associated with the strain effects in the lateral 1T/2H–MoS2 heterojunctioned nanosheets and the electron coupling effects in the vertical 1T/2H–MoS2/graphene 2D/2D heterostructure. The content of 1T phase in 1T/2H–MoS2/graphene can be regulated by adjusting the preparation temperature. The optimized 1T/2H–MoS2/graphene hybrid contains 40.5% 1T phase and exhibits outstanding HER performance with a low overpotential of 143 mV at current density of 10 mA cm-2, a small Tafel slope of 64 mV dec-1 and excellent durability in acid electrolyte. This work highlights a new strategy to utilize structure-directing reagents for fabricating highly efficient MoS2-based electrocatalysts.

Ethylenediamine-assisted hydrothermal synthesis of NiCo2O4 absorber with controlled morphology and excellent absorbing performance

In recent years, developing excellent electromagnetic wave (EMW) absorbers with small thickness and large bandwidth is an effective strategy to deal with the seriously EMW interferes in military and civil field. The morphology of absorbers has profound effects on their EMW absorption performance. Herein, ethylenediamine (EDA) was applied to EMW absorbing field as morphology control agent for the first time (as far as we know) for the synthesis of nickel cobaltate (NiCo2O4) absorber, and the effect of EDA content on the morphology and EMW absorbing performance was also investigated elaborately. As a bidentate ligand and structure-directing reagent, EDA controlled the morphology of NiCo2O4 by reducing the rate of nucleation and crystal growth through the complexation with metal ions, and adjusting the growth rate of different facets through the selective binding of amino to certain surfaces. The study found that the morphology of NiCo2O4 changed from three-dimensional urchin-like structures to two-dimensional nanosheets with the increase of EDA content, and meanwhile the dielectric loss property decreased, which led to decline in EMW attenuation properties. The urchin-like NiCo2O4 absorber at a molar ratio of 0.5 (EDA: metal ions) exhibited optimum absorption properties with a small thickness of 1.70 mm and large effective absorption bandwidth (EAB) of 5.81 GHz (12.19–18 GHz). The excellent EMW absorbing properties mainly originate from remarkable dipole polarization induced by oxygen vacancies and lattice defects, interface polarization stemming from the interfaces of NiCo2O4 fibers, and multiple reflections and scattering in its unique urchin-like structures. This work provides a simple method for absorber with controlled morphologies, and also expands the family members of Co-based ferrite with outstanding absorbing performance.

Deep eutectic solvent synthesis of a 3D hierarchical porous NaTi2(PO4)3/C as a high-performance anode for sodium-ion batteries

A 3D hierarchical porous NaTi2(PO4)3/C was successfully synthesized by using choline chloride/triethanolamine-based deep eutectic solvent (DES), which act as both solvent and template. The as-synthesized sample consisted of carbon-coated nanosized NaTi2(PO4)3 with abundant macropores. When this sample is used as an anode material for sodium-ion batteries, it exhibits excellent rate capability (116 mAh g−1 at 5 C and 113 mAh g−1 at 20 C) and superior long-term cyclic stability (capacity retention of over 99% after 1000 cycles at 5 and 20 C). The improved performance can be ascribed to the high Na+ transport and its high structural stability. The excellent electrochemical results indicate that the prepared 3D hierarchical porous NaTi2(PO4)3/C could be used as a promising anode material for SIBs. The finding of this work opens a new way to design porous electrode materials by using DESs as structure-directing reagent.

CuGeO3 micro-nanomaterial as Electrocatalyst for hydrogen evolution reaction

Novel broom-like copper germanate (CuGeO3) micro-nanomaterials were synthesized by a facile one-step hydrothermal method with ethylenediamine (En) acting as structure-directing reagent. In acidic electrolyte, the broom-like CuGeO3 micro-nanomaterials have a hydrogen evolution reaction (HER) overpotential of 135 mV at 10 mA cm−2, a small Tafel slope of 98 mV dec−1 and good stability over 80 h. The improved activity in HER could be attributed to the more active sites for the unique broom-like morphology of CuGeO3.

Hierarchical cobalt phenylphosphonate nanothorn flowers for enhanced electrocatalytic water oxidation at neutral pH

Cobalt-based phosphate/phosphonates are a class of promising water oxidation catalysts at neutral pH. Herein, we reported a facile hydrothermal synthesis of various nanostructured cobalt phenylphosphonates. It is found that the number of hydroxyl group of structure-directing reagent is crucial for the construction of 3D hierarchical structures including hierarchical nanosheet flower-like assemblies and nanothorn microsphere. These samples were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, infrared, and X-ray photoelectron spectroscopy techniques. They can act as highly efficient electrocatalysts for the oxygen evolution reaction at neutral pH. Among these, hierarchical cobalt phenylphosphonate nanothorn flowers present excellent performance, affording a current density of 1 mA cm−2 required a small overpotential of 393 mV. This work offers a new clue to develop high-performance metal phosphonate/phosphate catalysts toward electrochemical water oxidation.

Influence of Synthesis Conditions on Microstructure and NO₂ Sensing Properties of WO₃ Porous Films Synthesized by Non-Hydrolytic Sol⁻Gel Method.

Nanostructured tungsten trioxide porous films were prepared by a non-hydrolytic sol–gel method following the inorganic route in which ethanol and PEG were used as the oxygen-donor and structure-directing reagent, respectively. The effects of aging time of the precursor solution, PEG content, and calcination temperature on the structure, morphology, and NO2 sensing properties of WO3 films were systematically investigated by using the techniques of X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and gas sensing measurements. The results demonstrated that a series of WO3 films with different microstructures could be obtained by manipulating the synthesis parameters. Furthermore, a suitable synthesis condition of WO3 films for NO2 sensing application was determined.

Fabrication of cobalt aluminate nanopigments by coprecipitation method in threonine waterborne solution

A novel cobalt aluminate (CoAl2O4) nanopigments with bright blue color and good dispersibility was fabricated via a coprecipitation process of threonine. Threonin acts as coordination and structure-directing reagents for the nucleation and assembly of hydroxide precursor, limitation of the CoAl2O4 nanoparticle growth during calcination process, and fine-tuning the molar ratio of Co/Al in final products. The products were characterized with XRD, FESEM, TEM, FTIR, DLS, EDX, ICP-AES and UV-vis. The particle size, colorimetric values and printing ink of CoAl2O4 nanopigments with different amount of threonine and without threonine were investigated. The study exhibited that the CoAl2O4 nanopigments with 0.1–0.2 mol/L threonine showed a smaller size of 10–20 nm, better dispersion and color property than other test samples. The coloration mechanism of the CoAl2O4 nanopigments is also discussed.

Reaction time dependent investigation on the properties of the Bi2S3 nanoparticles: Photocatalytic application

Different morphologies of the Bi2S3 nanostructures (nanorods and nanoparticles) were successfully synthesized with a facile reflux method with small reaction time (10 min, 20 min and 30 min) at 120°C. The morphology was transformed from nanorods to nanoparticles when the reaction time is increased. The effect of reaction time on the morphology, particle size, band gap and photocatalytic performance of the Bi2S3 products have been investigated. The Bi2S3 nanostructures have been formed with bismuth nitrate and thiourea as starting reactants, ethylene glycol as the reaction medium and polyvinylpyrrolidone (PVP) as the structure-directing reagent. The obtained products are characterized by Powder X-Ray Diffraction, SEM, EDAX, UV-Vis Spectroscopy and FT-IR. XRD patterns show that the Bi2S3 nanoparticles obtained are of orthorhombic structure. The Scanning electron microscopic images confirm the formation of nanoparticles. The results of the energy dispersive analysis of X-ray (EDAX), UV-Visible spectroscopy (UV-Vis), FT-IR studies are compared and discussed. The photocatalytic activity studies reveal that the synthesized Bi2S3 nanorods exhibit excellent photocatalytic performance in degrading methylene blue dye solution under UV irradiation.

Polyvinyl pyrrolidone-assisted synthesis of flower-like nickel-cobalt layered double hydroxide on Ni foam for high-performance hybrid supercapacitor

Nickel-cobalt layered double hydroxides (NiCo-LDH) were successfully deposited on nickel foam by a facile hydrothermal method using polyvinyl pyrrolidone (PVP) as the structure-directing reagent. The effect of PVP on the morphology and electrochemical performance of binder-free NiCo-LDH electrode for supercapacitor were investigated in detail. The prepared NiCo-LDH presented good dispersivity and appeared different flower-like structure via the addition of PVP. Specially, the NiCo-LDH electrode using 1 g of PVP exhibited a superior performance with a high-specific capacity of 724.9 C g−1 at a current density of 1 A g−1 and 577.1 C g−1 at 10 A g−1. In addition, a hybrid supercapacitor (HSC) based on the optimized NiCo-LDH as positive electrode and activated carbon as negative electrode was assembled with 6 M KOH as the electrolyte. The HSC device can deliver an energy density of 32.3 Wh kg−1 at the power density of 387.1 W kg−1. Moreover, the HSC device exhibited a good cycling stability with a retention rate of 94.0% after 2000-cycle charge-discharge test at 3 A g−1.

Morphological tunable three-dimensional flower-like zinc oxides with high photoactivity for targeted environmental Remediation: Degradation of emerging micropollutant and radicals trapping experiments

Abstract Zinc oxide (ZnO) with a high potentiality for tunable morphology is gaining immense research interests for targeted environmental remediation of emerging micropollutants in source waters. Various three-dimensional (3D) flower-like nanostructures of ZnO were synthesized by following a facile and low-temperature hydrothermal synthesis approach, using Zn(CH3COO)2∙2H2O as the starting precursor reagent, in the presence of different bases at varying concentrations as the structure-directing reagents. BET studies indicated that the ZnO-flowers 1 were more superior than ZnO-flowers 2 and 3, as it possessed the highest specific surface area (10.83 m2/g), pore volume (0.054 cm3/g) and pore size (23.52 nm). Subsequently, the photoactivities of ZnO-flowers on the degradation of emerging salicylic acid micropollutant under UV-A illumination were examined. Batch studies suggested that the ZnO-flowers were photoactive and photocatalysed optimally under neutral pH condition that are aligned with the cost-effective and practical implementation for water/wastewater treatment. ZnO-flowers 1 demonstrated the highest photoactivity according to its reaction rate constant, where the kinetics data was well-fitted using the pseudo-first order Langmuir-Hinshelwood rate equation. This finding was well correlated to the BET studies, where the high photoactivity in ZnO-flowers 1 could be ascribed to its exceptional surface morphology that maximises the surface contact area with salicylic acid during photodegradation. Finally, the radicals trapping experiments were carried out in order to validate the role of primary photogenerated holes (h+) and various secondary reactive oxygen species (ROS) in the photodegradation of salicylic acid using ZnO-flowers photocatalysts. It was confirmed that the active species of photogenerated h+, •OH, and •O2− were responsible for the photodegradation process. The plausible mechanistic pathways for the reaction between scavenging reagents and the reactive transitory species to form by-products and intermediates were also proposed.

Iodide-Switched Deposition for the Synthesis of Segmented Pd-Au-Pd Nanorods: Crystal Facet Matters.

Segmented metallic nanorods with well-defined shapes and controllable components play an important role on the systematic investigation of their shape-dependent catalytic, electric, and plasmonic properties of metal nanostructures. Unfortunately, the shape and composition of segmented nanorods are difficult to be precisely controlled via colloidal methods. Here, we reported the growth of Pd-Au-Pd bimetallic heterostructures by using Au 5-fold twinned bipyramids (BPs) as seeds, with KI as a structure-directing reagent. Through a series of control experiments we revealed that two parameters were identified as critical factors for the growth of segmented Pd-Au-Pd nanorods. First, 5-fold twinned Au BPs with low-index end facets and high-index side facets function as a unique template for directed growth. Second, iodide can switch the deposition of Pd on the Au BPs. A high concentration of iodide is believed to block the high-index facets of the Au BPs and lower the reaction kinetics to promote the selective growth of two Pd segments on the Au BPs. As a result, uniformed segmented Pd-Au-Pd nanorods were obtained. The segmented nanorods exhibit intense extinction in the near-IR range and could be a potential candidate for plasmon-based biological applications such as thermal therapy.

One-step solvothermal synthesis, a worm-shaped morphology and luminescence properties of green-emitting Y2O2S:Tb3+ nanophosphors

The worm-shaped Y2O2S:Tb3+ nanophosphors have been successfully prepared via one-step solvothermal synthesis, using ethanediamine as the main solvent and sublimed sulfur powder as the source of sulfur without adding additional structure-directing reagents. XRD, FT-IR, FESEM, PL and CIE chromaticity diagram were used to characterize the obtained products. XRD results demonstrate that all diffraction peaks of the sample can be well indexed to pure hexagonal phase of Y2O2S with optimal condition, i.e. the molar ration of S/Y3+m=10, solvothermal temperature T=220°C and synthetic time t=24h. When t varies from 2h to 24h, the morphology of Y2O2S transforms from cauliflower-like structure to worm-shaped nanoparticles with the length of ∼80nm. The formation mechanism depending on t has also been proposed. Upon 250nm ultraviolet (UV) light excitation, the worm-shaped Y2O2S:Tb3+ nanophosphors exhibit green emissions, corresponding to the 5D4→7FJ (J=6, 5, 4, 3) transitions of Tb3+ions. The quenching concentration is 7% and its corresponding lifetime is 1216μs. The CIE chromaticity coordinates show the tuneable emission shifting from yellow green to yellowish green with increasing concentration of Tb3+ions from 1% to 7%. Those results suggest that the worm-shaped Y2O2S:Tb3+ nanophosphors may have potential applications in X-ray intensifying screens, fluorescence and biomedical fields.

3D Pt-Ni Nanosponges Wrapped with Graphene-Dots and Their Application to Effective Catalysts for Oxygen Reduction Reaction

In this study, we first report how to synthesize 3D PtNi nanosponges without using surfactants. A 3D PtNi nanosponge wrapped with graphene dots was synthesized at room temperature using formic acid as a reducing agent and N-doped carbon dot as a structure-directing reagent. 3D PtNi nanosponge was formed only in the presence of carbon dots in the reaction solution. During the reaction, the N-doped carbon dots were reduced and exfoliated to graphene dots, which encapsulated PtNi nanocrystals. The composition of the developed nanosponge can be easily controlled by adjusting the reaction temperature. The prepared material exhibited excellent catalytic activity and durability for oxygen reduction reaction as compared with commercially available Pt/C. This is due to the self-supporting structure of interconnected nanosponge and the role of the graphene shell wrapping around the PtNi nanosponge. The proposed strategy has the potential to synthesize other multi-metal nanocrystals with 3D nano sponge structures that are expected to provide high catalytic performance in other electrocatalyses such as hydrogen evolution reaction and oxygen evolution reaction.

3 D Co3 (PO4 )2 -Reduced Graphene Oxide Flowers for Photocatalytic Water Splitting: A Type II Staggered Heterojunction System.

The design, synthesis, and photoelectrochemical characterization of Co3 (PO4 )2 , a hydrogen evolving catalyst modified with reduced graphene oxide (RGO), is reported. The 3 D flowerlike Co3 (PO4 )2 heterojunction system, consisting of 3 D flowerlike Co3 (PO4 )2 and RGO sheets, was synthesized by a one-pot in situ photoassisted method under visible-light irradiation, which was achieved without the addition of surfactant or a structure-directing reagent. For the first time, Co3 (PO4 )2 is demonstrated to act as a hydrogen evolving catalyst rather than being used as an oxygen evolving photoanode. In particular, 3 D flowerlike Co3 (PO4 )2 anchored to RGO nanosheets is shown to possess dramatically improved photocatalytic activity. This enhanced photoactivity is mainly due to the staggered type II heterojunction system, in which photoinduced electrons from 3 D flowerlike Co3 (PO4 )2 transfer to the RGO sheets and result in decreased charge recombination, as evidenced by photoluminescence spectroscopy. The band gap of Co3 (PO4 )2 was calculated to be 2.35 eV by the Kubelka-Munk method. Again, the Co3 (PO4 )2 semiconductor displays n-type behavior, as observed from Mott-Schottky measurements. These RGO-Co3 (PO4 )2 conjugates are active in the visible range of solar light for water splitting and textile dye degradation, and can be used towards the development of greener and cheaper photocatalysts by exploiting solar light.

Mesostructured zinc oxide architectures with high photocatalytic activity

Several photocatalysts with different architectures were synthesized via a facile hydrothermal approach in the presence of diverse structure-directing reagents at varied concentrations. It was found that the concentration of the directing reagents played a crucial role in the architecture of the obtained products. Flower-like ZnO architectures were synthesized at a high concentration of PVP, while pencil-like mesocrystals (MCs) at a low concentration. The flower shaped assembly was composed of leaf-like ZnO MCs. More interestingly, the MCs were assembled with ZnO nanocrystals aligned along [111] direction. The photocatalytic activities of the samples were examined by photocatalytic degradation of methylene blue, and the results indicated that the flower-like architectures exhibited highest performance, compared with those of ZnO nanocrystals, pencil shaped ZnO mesocrystal, and the sheet-like ZnO MCs. This could be attributed to not only the hierarchical architecture of the assembly, high crystallinity, and large surface area, but also the unique mesoscopic structure of ZnO MCs.