Facile in situ Electrosynthesis and High Electrocatalytic Performance of Interconnected Layered Double Hydroxides/Graphene Hybrids for Dopamine Oxidation: A Comparative Study

We are reporting a facile in situ electrodeposition approach to prepare a rational design of M?Al (M: Ni, Co) layered double hydroxide (LDH)/reduced graphene oxide (G) hybrids and its superior electrocatalytic activity towards the electrooxidation of dopamine. Comparatively, the worm like interconnected nano‐chain networks of as‐prepared NiAl‐LDH/G hybrid modified electrode exhibits better performance than the CoAl‐LDH/G hybrid modified electrode. The enhanced electrocatalytic activity is because of its morphological evolution, which is due to its enhanced reduction rate, attachment pathway and incorporation or heterogeneous combination of Al³⁺ in the bimetallic LDHs/G hybrid. The satisfactory results are obtained for modified electrodes for the real‐time quantitative detection of dopamine in the real injectable medicine as well as human blood serum samples and it has also shown good reproducibility, stability and anti‐interference. This cost‐effective and facile in situ electrodeposition approach will give insights to design high performing hybrid materials and its application to non‐invasive electrochemical sensing which will be useful for daily diagnosis of neurological disorder.     

Utilization of Active Ni to Fabricate Pt–Ni Nanoframe/NiAl Layered Double Hydroxide Multifunctional Catalyst through In Situ Precipitation

Integration of different active sites into metallic catalysts, which may impart new properties and functionalities, is desirable yet challenging. Herein, a novel dealloying strategy is demonstrated to decorate nickel–aluminum layered double hydroxide (NiAl–LDH) onto a Pt–Ni alloy surface. The incorporation of chemical etching of Pt–Ni alloy and in situ precipitation of LDH are studied by joint experimental and theoretical efforts. The initial Ni‐rich Pt–Ni octahedra transform by interior erosion into Pt₃Ni nanoframes with enlarged surface areas. Furthermore, owing to the basic active sites of the decorated LDH together with the metallic sites of Pt₃Ni, the resulting Pt–Ni nanoframe/NiAl–LDH composites exhibit excellent catalytic activity and selectivity in the dehydrogenation of benzylamine and hydrogenation of furfural.     

Preparation of NiAl double hydroxide@polypyrrole materials for high‐performance supercapacitors

A novel NiAl double hydroxide@polypyrrole (LDH@PPy) core–shell material was designed and fabricated by a facile in situ oxidative polymerization of pyrrole (Py) monomer. The microstructure and morphology of the LDH@PPy composites were determined by X‐ray diffractometer, Fourier transform infrared (FTIR), scanning electron microscopy/transmission electron microscopy, and thermogravimetric and differential thermal, revealing that the polypyrrole (PPy) was successfully coated onto the surface of the NiAl‐LDH (LDH) core and the loading amount of PPy impacted the thickness and the dispersion of the conductive PPy shell. The electrochemical performances of the LDH@PPy composites were also evaluated by cyclic voltammogram, electrochemical impedance spectroscopy, and galvanostatic charge–discharge measurements. The results indicated that the supercapacitor performances were attributed to the synergy of unique core–shell heterostructure and each individual component, where the LDH core provided the high‐energy storage capacity and the PPy shell with networks had high electronic conductivity. These shorted the ion diffusion pathway and made electrolyte ions more easily accessible for faradic reactions to enhance the electrochemical performance of the LDH@PPy composites. It was found that the LDH@PPy composite (LDH@PPy₇) fabricated at 7 mL?L^?1 of Py monomer feed exhibiting the best electrochemical performances with high specific capacitance of 437.5 F?g^?1 at 2 A?g^?1 and excellent capacitance retention of about 91% after 1000 cycles. The work provides a simple approach for designing organic–inorganic core–shell materials with potential application in supercapacitors. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1653–1662     

Research on WPU‐RGO/ATP‐Fe3O4/chitosan composites with excellent electrical and magnetic properties

First, attapulgite‐Fe₃O₄ magnetic filler (ATP‐Fe₃O₄) was prepared by using a chemical precipitation method. Subsequently, graphite oxide (GO) was prepared through Hummer method, and then reduced GO (RGO) was prepared through GO reduced by chitosan (CS). Finally, a series of WPU‐RGO/ATP‐Fe₃O₄/CS composites were prepared by introduced RGO/ATP‐Fe₃O₄/CS to waterborne polyurethane. The structure and properties were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), X‐ray diffraction (XRD), vibrating sample magnetometry (VSM), thermogravimetric analysis TGA, conductivity test, and tensile test. The experimental results indicated that thermal stability and tensile strength of nanocomposites were improved with the increase of the content of RGO/ATP‐Fe₃O₄/CS. Meanwhile, with the increase of the RGO/ATP‐Fe₃O₄/CS content, the electrical and magnetic properties of WPU‐RGO/ATP‐Fe₃O₄/CS composites were improved. When the content of RGO/ATP‐Fe₃O₄/CS was 8 wt%, the electrical conductivity and the saturation magnetic strength of WPU‐RGO/ATP‐Fe₃O₄/CS composites were 3.1 × 10^?7 S·cm^?1 and 1.38 emu/g, respectively. WPU‐RGO/ATP‐Fe₃O₄/CS composites have excellent electrical and magnetic properties.     

Effects of flower-like ZnO nanowhiskers on the mechanical, thermal and antibacterial properties of waterborne polyurethane

A novel waterborne polyurethane/flower-like ZnO nanowhiskers (WPU/f-ZnO) composite with different f-ZnO content (0-4.0 wt%) was synthesized by an in-situ copolymerization process. The f-ZnO consisting of uniform nanorods was prepared via a simple hydrothermal method. In order to disperse and incorporate f-ZnO into WPU matrix, f-ZnO was modified with γ-aminopropyltriethoxysilane. Morphology of f-ZnO in WPU matrix was characterized by scanning electron microscope. The properties of WPU/f-ZnO composites such as mechanical strength, thermal stability as well as water swelling were strongly influenced by the f-ZnO contents. It was demonstrated that appropriate amount of f-ZnO with good dispersion in the WPU matrix significantly improved the performance of the composites. The mechanical property was enhanced with an increase of f-ZnO content up to the optimum content (1 wt%) and then declined. Incorporation of f-ZnO enhanced the water resistance of the composites remarkably. It was amazing to observe that the thermal degradation temperatures of the composites initially decreased significantly and then leveled off with content increase of f-ZnO, which was different from the results of other WPU composite systems reported. Antibacterial activity of WPU/f-ZnO composite films against Escherichia coli and Staphylococcus aureus was also tested. The results revealed that the antibacterial activity enhanced with the increasing f-ZnO content, and the best antibacterial activity was obtained at the loading level of 4.0 wt% f-ZnO.     

The effect of OCoAl‐LDH and OCoFe‐LDH on the combustion behaviors of polyvinyl chloride

The effects of the modified layered double hydroxide (LDH) of Co/Al (OCoAl‐LDH) and the modified LDH of Co/Fe (OCoFe‐LDH) on the combustion behaviors of polyvinyl chloride (PVC) during pyrolysis processes were compared and investigated. The thermal degradation and combustion behavior of the PVC composites were investigated by thermogravimetric analysis (TGA), microscale combustion calorimetry (MCC), and cone calorimetry (CONE). The results indicate that the incorporation of LDHs brought about the improved thermal stability and reduced heat release of PVC composites at a high temperature. The smoke‐suppression properties of the composites are investigated by steady‐state tube furnace (SSTF), and the results indicated that the toxic gases such as CH₄, CO, and N_xO were inhibited by both of the two LDHs, but the OCoFe‐LDH has a better effect on the smoke suppression. Subsequently, the char layer was investigated by scanning electron microscopy–energy‐dispersive spectrometry (SEM‐EDS) and Raman analysis. The results indicate that the LDHs can promote the dechlorination of PVC during the thermal oxidation process and can inhibit the production of HCl in inert gas. Generally, OCoAl‐LDH and OCoFe‐LDH can be potential catalysts for waste disposal and can improve the fire safety of PVC.     

Facile Fabrication of Highly‐Dispersed Nickel Nanoparticles with Largely Enhanced Electrocatalytic Activity

Supported nickel nanoparticles with high dispersion have been prepared by partial reduction of NiAl‐layered double hydroxide (NiAl‐LDH) precursors, which exhibit significant electrocatalytic behavior towards glucose. XRD and XPS results confirm that the nickel nanoparticles are successfully synthesized. TEM images reveal that the nickel nanoparticles are highly dispersed in the NiAl‐LDH matrix with a size of 6±0.3 nm. The resulting nanocomposite modified electrode displays significant electrocatalytic performance to glucose with a broad linear response range (8.0×10^?5–2.0×10^?3 M), low detection limit (3.6 µM), high sensitivity (339.2 µA/mM), selectivity and excellent reproducibility as well as repeatability.     

Synergistic effects of zinc oxide with layered double hydroxides in EVA/LDH composites

The synergistic effects of zinc oxide (ZnO) with layered double hydroxides (LDH) in ethylene vinyl acetate copolymer/LDH (EVA/LDH) composites have been studied using thermal analysis (TG), limiting oxygen index (LOI), UL-94 tests, and cone calorimeter test (CCT). The results from the UL-94 tests show that the ZnO can also act as flame retardant synergistic agents in the EVA/LDH composites. The CCT data indicated that the addition of ZnO in EVA/LDH system can greatly reduce the heat release rate. The TG data show that the ZnO can increase the thermal degradation temperature and the charred residues after burning.     

Optical and mechanical properties of polyurethane/surface-modified nanocrystalline cellulose composites

in order to improve the optical and mechanical performances of waterborne polyurethane （WPU）, nanocrystalline cellulose （NCC）/WPU composites were synthesized in this study. NCC （prepared by acid hydrolysis of cotton fiber） was modified by （3-aminopropyl）triethoxysilane （APTES） to enhance its compatibility with WPU, and the surface-modified NCC was characterized by grafting ratio, crystallinity and contact angle （CA）. NCC/WPU composites were examined by scanning electron microscopy （SEM）, X-ray powder diffraction （XRD） and thermogravimetric analysis （TG）. The anti-yellowing property, specular gloss, pencil hardness, and abrasion resistance of NCC/WPU composites were investigated by the methods of Chinese National Standards GB/T 23999-2009, GB/T 9754-2007, GB/T 6739-2006 and GB/T 1768-2006, respectively. The results showed that the grafting ratio of NCC modified by 6% APTES was 36.01% and the crystallinity of modified NCC was decreased with the enhancement of APTES. CA of the modified NCC was decreased by 28.8% and the nanoparticles were homogeneously dispersed in the WPU matrix. The XRD patterns of the NCC/WPU composites were relatively steady, while the thermal stability of the composites was enhanced by 6.7% with 1.0 wt% modified NCC. Modified NCC affected the specular gloss of NCC/WPU composites more obviously than the anti-yellowing property. The pencil hardness of NCC/WPU composites was increased from 2H to 4H by addition of NCC and the abrasion resistance of the composites was enhanced significantly. In general, NCC/WPU composites showed significant improvements in the optical and mechanical performances.     

Self-assembled fabrication and flame-retardant properties of reduced graphene oxide/waterborne polyurethane nanocomposites

The graphite oxide (GO) was prepared from expandable graphite by the pressurized oxidation method, and samples were characterized using XRD, UV–Vis, and TEM. GO is reduced in situ emulsion using hydrazine to achieve reduced graphene oxide/waterborne polyurethane (rGO/WPU) nanocomposites. The effect of rGO content on the stability, fracture morphologies, mechanical performance, thermal degradation, and flame-retardant properties of rGO/WPU composites was investigated by zeta potential analyzer, TEM, SEM, universal testing machine, TG, and Cone Calorimeter. The results of zeta potential, TEM, and SEM analysis indicate that rGO has a good stability and dispersibility in rGO/WPU nanocomposites. The results of mechanical tests showed that the mechanical properties of rGO/WPU nanocomposites increased consistently with increasing rGO content up to 2 mass%, and TG showed that the thermostability of rGO/WPU nanocomposites decreased slightly compared to pure WPU, but carbon residue increased from 0.99 to 1.99 % when the mass fraction of rGO in WPU is 2 %. Cone Calorimeter test indicated that the flame-retardant and smoke suppression properties of rGO/WPU composites showed significant improvement compared to the WPU alone. When the mass fraction of rGO is 1 %, the total smoke release and smoke factor decreased by 25 and 38 %, respectively, compared to those of pure WPU.     

Binary Au/MWCNT and Ternary Au/ZnO/MWCNT Nanocomposites: Synthesis,Characterisation and Catalytic Performance

Gold nanoparticles of 10–24 and 5–8 nm in size were obtained by chemical citrate reduction and UV photoreduction, respectively, on acid‐treated multiwalled carbon nanotubes (MWCNTs) and on ZnO/MWCNT composites. The shape and size of the deposited Au nanoparticles were found to be dependent upon the synthetic method used. Single‐crystalline, hexagonal gold particles were produced in the case of UV photoreduction on ZnO/MWCNT, whereas spherical Au particles were deposited on MWCNT when the chemical citrate reduction method was used. In the UV photoreduction route, n‐doped ZnO serves as the e^? donor, whereas the solvent is the hole trap. All materials were fully characterised by UV/Vis spectroscopy, scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, Raman spectroscopy and BET surface analysis. The catalytic activity of the composites was studied for the selective hydrogenation of α,β‐unsaturated carbonyl compound 3,7‐dimethyl‐2,6‐octadienal (citral). The Au/ZnO/MWCNT composite favours the formation of unsaturated alcohols (selectivity=50 % at a citral conversion of 20 %) due to the presence of single‐crystalline, hexagonal gold particles, whereas saturated aldehyde formation is favoured in the case of the Au/MWCNT nanocomposite that contains spherical gold particles.     

Highly Selective Photoreduction of CO2 with Suppressing H2 Evolution over Monolayer Layered Double Hydroxide under Irradiation above 600 nm

Although progress has been made to improve photocatalytic CO₂ reduction under visible light (λ>400 nm), the development of photocatalysts that can work under a longer wavelength (λ>600 nm) remains a challenge. Now, a heterogeneous photocatalyst system consisting of a ruthenium complex and a monolayer nickel‐alumina layered double hydroxide (NiAl‐LDH), which act as light‐harvesting and catalytic units for selective photoreduction of CO₂ and H₂O into CH₄ and CO under irradiation with λ>400 nm. By precisely tuning the irradiation wavelength, the selectivity of CH₄ can be improved to 70.3 %, and the H₂ evolution reaction can be completely suppressed under irradiation with λ>600 nm. The photogenerated electrons matching the energy levels of photosensitizer and m‐NiAl‐LDH only localized at the defect state, providing a driving force of 0.313 eV to overcome the Gibbs free energy barrier of CO₂ reduction to CH₄ (0.127 eV), rather than that for H₂ evolution (0.425 eV).     

Preparation of Antibacterial Waterborne Polyurethane/silver Nanocomposite

Stable aqueous dispersions of silver (Ag) nanoparticles were prepared by reducing silver nitrate solutions with sodium borohydride (NaBH₄) in the presence of waterborne polyurethane as a stabilizing agent. WPU/Ag nanocomposites were obtained after evaporating water. Transmission electron microscope (TEM) shows nanoscale Ag particles are well dispersed in WPU matrix at a lower concentration, while particles exhibit a little aggregation at a higher concentration. UV‐visible spectra, X‐ray powder diffraction, and energy dispersive X‐ray spectrometer (EDS) confirm the existence of Ag particle in WPU matrix. The WPU/Ag composite films show good antibiotic ability.     

四甲基苯二甲基二异氰酸酯基水性聚氨酯的合成和性能

采用四甲基苯二甲基二异氰酸酯、聚酯二元醇和二羟甲基丙酸为原料,合成了一系列具有不同异氰酸根与羟基摩尔比（n(-NCO)/n(-OH)）的聚氨酯乳液。 研究了n(-NCO)/n(-OH)对水性聚氨酯性能的影响。 结果表明,当该比值增加时,乳液的粒径增大,分布变宽,结晶性降低,耐热性下降,耐水性能呈现降低的趋势。 当异氰酸根与羟基摩尔比为3时,四甲基苯二甲基二异氰酸酯基水性聚氨酯的乳液粒径为10～30 nm,膜的分解温度达到275 ℃,24 h吸水率低于10%。     

喜树碱插层的镁铝型层状双金属氢氧化物的合成及表征

采用共沉淀法把抗癌药物喜树碱（Camptothecin, CPT）插入层状双金属氢氧化物(layered double hydroxide, LDH)层间, 合成了CPT-LDH纳米杂化物。结果表明,在CPT-LDH纳米杂化物中,CPT在层间的排布方式有两种,即平行于层板的单层排列和垂直于层板的双层排列;缓释研究表明,CPT-LDH在pH 7.5的磷酸缓冲液中具有明显的缓释效果,其释放速率较相同pH值时CPT和LDH物理混合物的释放速率明显降低;考察了CPT-LDH的药物释放机理,在 pH 7.5的缓冲溶液中,释放过程受粒内扩散过程控制;CPT-LDH纳米杂化物的释放动力学符合准一级动力学过程。     

Effect of Molecular Weight of WPU on the Heterogenic PUA Composite Latex Prepared by Soap-Free Emulsion Polymerization

Aqueous acrylic-polyurethane (PUA) composite emulsion was prepared by soap-free seeded emulsion copolymerization. Waterborne polyurethane (WPU) was used as the seeded emulsion and functioned as surfactant. The effect of molecular weight of WPU on the heterogenic was investigated. The molecular weight of WPU was controlled by varying the NCO/OH mole ratio. The GPC results confirmed that the molecular weight of WPU presented double distribution. And the molecular weight of WPU decreased with the increasing NCO/OH mole ratio. Surface tension test indicated that the molecular weight had little influence on the surface activity of WPU. However, after emulsion copolymerization of acrylic monomers, the morphology and properties of the PUA composite were impacted markedly by the molecular weight of WPU. With an increase in the NCO/OH mole ratio, the morphology of PUA composite latex changed from core-shell structures to fish bowl structure, and the mechanical properties of PUA films changed correspondingly.     

Electrochemical Characterization of (ZnO/dsDNA)n Layer-by-layer Films and Detection of Natural DNA Oxidative Damage

The positively charged nano‐ZnO and negatively charged natural DNA were alternately adsorbed on the surface of a gold electrode, forming (ZnO/dsDNA)_nlayer‐by‐layer films. Valuable dynamic information for controlling the formation and growth of the films was obtained by cyclic voltammetry and electrochemical impedance spectroscopy. Differential pulse voltammetric (DPV) measurements showed that the electroactive probe methylene blue (MB) could be loaded in the (ZnO/dsDNA)_nfilms from its solution, and then released from the films into Britton‐Robinson (B‐R) buffer. The complete reloading of MB in the films could be realized by immersing the films in MB solution again. However, after incubation in the solution of carcinogenic metal nickel, the damaged (ZnO/dsDNA)_n films could not return to their original and fully‐loaded state, and showed smaller DPV peak currents. The results demonstrated that the DNA damage induced by the hydroxyl radical could be achieved by electrochemistry.     

Synthesis of a novel polyphosphazene/triazine bi‐group flame retardant in situ doping nano zinc oxide and its application in poly (lactic acid) resin

A novel polyphosphazene/triazine bi‐group flame retardant in situ doping nano ZnO (A4‐d‐ZnO) was synthesized and applied in poly (lactic acid) (PLA). Fourier transform infrared (FTIR), solid state nuclear magnetic resonance (SSNMR), X‐ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and energy dispersive spectrometer (EDS) were used to confirm the chemical structure of A4‐d‐ZnO. The thermal stability and the flame‐retardant properties of the PLA composites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), limiting oxygen index (LOI), vertical burning test (UL‐94), and micro combustion calorimeter (MCC) test. The results of XPS showed that A4‐d‐ZnO has been synthesized, and the doping ratio of ZnO was 7.2% in flame‐retardant A4‐d‐ZnO. TGA results revealed that A4‐d‐ZnO had good char forming ability (40 wt% at 600°C). The results of LOI, vertical burning test, and MCC showed that PLA/5%A4‐d‐ZnO composite acquired a higher LOI value (24%), higher UL94 rating, and lower pk‐HRR (501 kW/m²) comparing with that of pure PLA. It indicated that a small amount of flame‐retardant A4‐d‐ZnO could achieve great flame‐retardant performance in PLA composites. The catalytic chain scission effect of A4‐d‐ZnO could make PLA composites drip with flame and go out during combustion, which was the reason for the good flame‐retardant property. Moreover, after the addition of A4‐d‐ZnO, the impaired mechanical properties of PLA composites are minimal enough.     

Enhanced Photocatalytic Performance of ZnO Nanorods Coupled by Two‐Dimensional α‐MoO3 Nanoflakes under UV and Visible Light Irradiation

We exploit the utilization of two‐dimensional (2D) molybdenum oxide nanoflakes as a co‐catalyst for ZnO nanorods (NRs) to enhance their photocatalytic performance. The 2D nanoflakes of orthorhombic α‐MoO₃ were synthesized through a sonication‐aided exfoliation technique. The 2D MoO₃ nanoflakes can be further converted to substoichiometric quasi‐metallic MoO_3?x by using UV irradiation. Subsequently, 1D–2D MoO₃/ZnO NR and MoO_3?x/ZnO NR composite photocatalysts have been successfully synthesized. The photocatalytic performances of the novel nanosystems in the decomposition of methylene blue are studied by using UV‐ and visible‐illumination setup. The incorporated 2D nanoflakes show a positive influence on the photocatalytic activity of the ZnO. The obtained rate constant values follow the order of pristine ZnO NR<MoO₃/ZnO NR<MoO_3?x/ZnO NR composites. The enhancement of the photocatalytic efficiency can be ascribed to a fast charge carrier separation and transport within the heterojunctions of the MoO₃/ZnO NRs. In particular, the best photocatalytic performance of the MoO_3?x/ZnO NR composite can be additionally attributed to a quasi‐metallic conductivity and substoichiometry‐induced mid‐gap states, which extend the light absorption range. A tentative photocatalytic degradation mechanism was proposed. The strategy presented in this work not only demonstrates that coupling with nanoscale molybdenum oxide nanoflakes is a promising approach to significantly enhance the photocatalytic activity of ZnO but also hints at new type of composite catalyst with extended applications in energy conversion and environmental purification.     

Binder Free Modification of Glassy Carbon Electrode by Employing Reduced Graphene Oxide/ZnO Composite for Voltammetric Determination of Certain Nitroaromatics

Reduced Graphene oxide/ZnO nanoflowers ( rGO/ZnO‐NFs ) composite has been synthesized in‐situ using asymmetric Zn complex ( 1 ) as a single‐source molecular precursor (SSMP) with GO at 150 °C. The rGO/ZnO‐NFs composite was characterized by PXRD, UV‐vis, SEM, EDX mapping, TEM and SAED pattern to confirm its purity and morphology. The rGO/ZnO‐NFs composite shows uniform distribution of nanoflowers on graphene sheets. The modified glassy carbon electrode ( GCE ) was fabricated by drop wise layering of the rGO/ZnO‐NFs composite at the surface of the GCE without using binder. The binder free modified electrode ( GCE‐rGO/ZnO ) was explored for detection of nitroaromatics such as p‐nitro‐phenol ( p ‐NP ), 2,4‐dinitrophenol ( 2,4‐DNP ), 2,4‐dinitrotoluene ( 2,4‐DNT ) and 2,4,6‐trinitrophenol ( 2,4,6‐TNP ). The fabricated sensor showed remarkable response for the both toxicants and explosives. The LOD, sensitivity and linear range for the studied toxicants and explosives were found to be in a good range: p ‐NP= 0.93 μM, 240 μA mM⁻¹ cm⁻² and 0.2–0.9 mM; 2,4‐DNP= 6.2 μM, 203 μA mM⁻¹ cm⁻² and 0.1–0.9 mM; 2,4‐DNT= 10 μM, 371 μA mM⁻¹ cm⁻² and 0.2–0.9 mM; 2,4,6‐TNP= 16 μM, 514 μA mM⁻¹ cm⁻² and 0.2–0.9 mM, respectively.