Iron-modulated Ni3S2 derived from a Ni-MOF-based Prussian blue analogue for a highly efficient oxygen evolution reaction.

Developing efficient, environmentally friendly and cost-effective non-precious metal electrocatalysts for the oxygen evolution reaction (OER) is essential to alleviate the energy crisis and environmental pollution. Herein, we report a simple and practical method to prepare non-precious metal catalysts, namely iron-modulated Ni3S2 (Fe-Ni3S2/NF) on nickel foam, by growing a Ni-MOF directly on 3D porous conductive nickel foam, followed by the formation of Ni-MOF-based Prussian blue analogs (Ni-MOF@PBA) via in situ cation exchange reactions, which are further sulfidated to iron-modulated Ni3S2. Based on a series of characterization results, it is confirmed that iron acts as a modulator at the Ni active site, leading to electron depletion, thereby modulating the electron spin state and optimizing the binding energy of key reaction intermediates, resulting in highly exposed active sites and acceleration of OER reaction kinetics. The synthesized Fe-Ni3S2/NF exhibits excellent activity in alkaline media, which needs overpotentials of only 232 mV and 287 mV to drive current densities of 10 mA cm-2 and 50 mA cm-2, respectively. Additionally, Fe-Ni3S2/NF exhibits excellent stability for at least 24 h during the OER process. This work presents a rational design and synthesis of transition metal-based catalysts with nanocone structures, providing a new strategy for assembling advanced materials and insights for exploring various energy storage and conversion systems.

Prussian blue analogue assisted formation of iron doped CoNiSe2 nanosheet arrays for efficient oxygen evolution reaction.

Electrochemical water splitting is a promising approach to produce hydrogen gas, but sluggish four-electron transfer of the oxygen evolution reaction (OER) severely limits the overall energy conversion efficiency of water splitting. Herein, as an excellent OER electrocatalyst, a technique of synthesizing Fe doped CoNiSe2 nanosheet (Fe-CoNiSe2) whole series using CoFe prussian blue analog produced by Co-ZIF-L reaction as a template is proposed here. The introduction of iron ions promotes the redistribution of the cobalt-nickel charge density, which enhances the OER kinetics. In view of the abovementioned points, Fe-CoNiSe2/NF has excellent activity, electrocatalytic properties and excellent stability in alkaline media, which only demands a lower overpotential of 244 mV and 271 mV to deliver a current density of 10 mA cm-2 and 50 mA cm-2, respectively. The material also exhibits excellent stability for at least 24 h during the OER process. This work may provide some new insights into the assembly of advanced and highly-active materials for a variety of other energy conversion applications.

Preparation of a novel functionalized magnesium-based curing agent as an intrinsic flame retardant for epoxy resin.

In this study, a novel organic-inorganic hybrid flame retardant 10-(1,4-dicarboxylic acid magnesium salt)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DMMH) was synthesized via neutralization and addition reaction of maleic acid, magnesium hydroxide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and subsequently used in an intrinsic flame retardant epoxy resin. The chemical structure and morphology of DMMH were analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Further, the prepared DMMH was combined with ammonium polyphosphate (APP) to form an intumescent flame retardant system. The thermal stability and flame retardance were evaluated by thermogravimetric analysis (TG), UL-94 vertical burning test, limiting oxygen index (LOI) and cone calorimetry. It was observed that the addition of 1.7% DMMH and 5.3% APP led EP-7 to acquire UL-94 V-0 rating, with the limiting oxygen index of 26.0%. As compared with pure EP, the peak heat release rate, total heat release, smoke production rate and total smoke production of the sample was noted to decrease by 54.5%, 35.1%, 43.6% and 38.1%, respectively. In addition, the introduction of DMMH did not negatively impact the mechanical properties of the epoxy resin.

Iron ion irradiated Bi2Te3 nanosheets with defects and regulated hydrophilicity to enhance the hydrogen evolution reaction.

The introduction of defects can enhance the active sites on transition metal dichalcogenides, which can cause changes in crystal structures, and then lead to a change in the original catalytic performance. Herein, an efficient method of introducing defects was reported. In this method, high-energy iron ions were irradiated on the surface of Bi2Te3 nanosheets by ion irradiation technology, which resulted in the generation of a variety of defects. Compared to the original Bi2Te3 nanosheets, the Bi2Te3 nanosheets irradiated by iron ions showed significant improvement in the hydrogen evolution reaction performance in acidic solution. After the iron ion irradiation, the electric double layer capacitance of the Bi2Te3 nanosheets increased significantly, which indicated an increase in the number of active sites on the surface of Bi2Te3. Analysis of high-resolution transmission electron microscopy images reveals the occurrence of various defects on the surface of Bi2Te3 after the iron ion irradiation, which increased the active sites. Moreover, the conductivity of the iron ion-irradiated Bi2Te3 nanosheets was also significantly improved. It is noteworthy that iron ion irradiation changed the characteristic of the Bi2Te3 surface from hydrophobic to hydrophilic, which facilitated the release of hydrogen bubbles from the catalyst surface and exposed the active sites in time. At the same time, the damage caused by the large bubbles to the electrode material could be avoided, and the stability of the material was improved. This efficient iron ion irradiation method provides an innovative idea for the design of other high-efficient catalysts.

Phosphorus-doped CoTe2/C nanoparticles create new Co-P active sites to promote the hydrogen evolution reaction.

Doping has been widely recognized as an effective method for adjusting the performance of electrocatalysts. It can cause changes in the electronic structure of substances. Thereby, it can affect the intrinsic catalytic performance. Herein, we report a facile doping method in which phosphorus can be simultaneously doped into both CoTe2 and C. In the acidic solution, the hydrogen evolution reaction (HER) performance of the obtained P-CoTe2/C nanoparticles was significantly improved compared with that of undoped nanoparticles. At a current density of 10 mA cm-2, the overpotential decreased from 430 mV to 159 mV. Density functional theory (DFT) calculations show that phosphorus doping can produce new high activity Co-P catalytic sites. In addition, phosphorus can be doped into the carbon in the composite at the same time, which enhances the electrical conductivity of the composite. Moreover, in the process of calcination and doping, the electric double layer capacitance (Cdl) of the composite is significantly increased, which helps in exposing more active sites. This work has developed a multi-effect doping method that simultaneously increases the intrinsic activity, conductivity and active sites of the material. This method provides a new strategy for the performance regulation of other electrocatalysts.

Superhydrophobic meshes that can repel hot water and strong corrosive liquids used for efficient gravity-driven oil/water separation.

Oil-polluted water has become a worldwide problem due to increasing industrial oily wastewater as well as frequent oil-spill pollution. Compared with underwater superoleophobic (water-removing) filtration membranes, superhydrophobic/superoleophilic (oil-removing) materials have advantages as they can be used for the filtration of heavy oil or the absorption of floating oil from water/oil mixtures. However, most of the superhydrophobic materials used for oil/water separation lose their superhydrophobicity when exposed to hot (e.g. >50 °C) water and strong corrosive liquids. Herein, we demonstrate superhydrophobic overlapped candle soot (CS) and silica coated meshes that can repel hot water (about 92 °C) and strong corrosive liquids, and were used for the gravity driven separation of oil-water mixtures in hot water and strong acidic, alkaline, and salty environments. To the best of our knowledge, we are unaware of any previously reported studies on the use of superhydrophobic materials for the separation of oil from hot water and corrosive aqueous media. In addition, the as-prepared robust superhydrophobic CS and silica coated meshes can separate a series of oils and organic solvents like kerosene, toluene, petroleum ether, heptane and chloroform from water with a separation efficiency larger than 99.0%. Moreover, the as-prepared coated mesh still maintained a separation efficiency above 98.5% and stable recyclability after 55 cycles of separation. The robust superhydrophobic meshes developed in this work can therefore be practically used as a highly efficient filtration membrane for the separation of oil from harsh water conditions, benefiting the environment and human health.

Growth of cedar-like Au nanoparticles coating on an etched stainless steel wire and its application for selective solid-phase microextraction.

A novel cedar-like Au nanoparticles (AuNPs) coating was fabricated on an etched stainless steel (SS) wire by direct chemical deposition and used as an efficient and unbreakable solid phase microextraction (SPME) fiber. The etched SS wire offers a rough surface structure for subsequent growth of AuNPs in chloroauric acid solution. As a result, the uniform cedar-like AuNPs coating with larger surface area was tightly attached to the etched SS wire substrate. The AuNPs coated etched SS fiber (AuNPs/SS) was examined for SPME of ultraviolet (UV) filters, phthalate esters and aromatic hydrocarbons coupled to high-performance liquid chromatography with UV detection. The fabricated fiber exclusively exhibited excellent extraction efficiency and selectivity for some aromatic hydrocarbons. Influential parameters of extraction and desorption time, temperature, stirring rate and ionic strength were investigated and optimized. The limits of detection ranged from 0.008 µg L(-1) to 0.037 µg L(-1). The single fiber repeatability varied from 3.90% to 4.50% and the fiber-to-fiber reproducibility ranged from 5.15% to 6.87%. The recovery of aromatic hydrocarbons in real water samples spiked at 2.0 µg L(-1) and 20 µg L(-1) ranged from 94.38% to 106.2% with the relative standard deviations below 6.44%. Furthermore the growth of the cedar-like AuNPs coating can be performed in a highly reproducible manner. This fabricated fiber exhibits good stability and withstands at least 200 extraction and desorption replicates.

Electrodeposition of gold nanoparticles onto an etched stainless steel wire followed by a self-assembled monolayer of octanedithiol as a fiber coating for selective solid-phase microextraction.

In the present study, a novel approach for rapid electrodeposition on an etched stainless steel (SS) wire followed by self-assembled monolayer (SAM) was proposed for the fabrication of solid-phase microextraction (SPME) fiber. The etched SS wire offers a rough surface structure for subsequent electrochemical deposition of gold nanoparticles (AuNPs). As a result, uniform AuNPs coating was tightly attached to the etched SS wire substrate. After SAM of 1,8-octanedithiol onto AuNPs coating via Au-S bonding, a unique floccular structure with extremely large surface area was obtained for the fabricated fiber. The mercaptooctyl groups modified AuNPs coated etched SS fiber (C8-S-AuNPs/SS) was then assessed for SPME of phthalate esters (PAEs), polychlorinated biphenyls (PCBs), chlorophenols (CPs), ultraviolet (UV) filters, polycyclic aromatic hydrocarbons (PAHs) and substituted anilines coupled to high-performance liquid chromatography with UV detection. This fiber exhibits higher extraction capability and better selectivity for some PCBs, CPs, UV filters and PAHs. Extraction conditions were investigated and optimized for SPME performance of UV filters. Under the optimized conditions, the developed method showed good linearity between 0.10 and 400µgL-1 with corresponding coefficients in the range of 0.9989-0.9998. The limits of detection ranged from 0.025 to 0.056µgL-1. The relative standard deviation for fiber-to-fiber reproducibility of five fabricated fibers was less than 9.4%. The developed method was successfully applied to the preconcentration and determination of trace UV filters from environmental water samples. Furthermore the fabrication of the C8-S-AuNPs/SS fiber can be performed in a highly reproducible manner. This fabricated fiber exhibits good stability and long lifetime, and could be a potential alternative for the conventional fused silica fiber.

Electrochemical in situ fabrication of titanium dioxide-nanosheets on a titanium wire as a novel coating for selective solid-phase microextraction.

A novel TiO2-nanosheets coated fiber for solid-phase microextraction (SPME) was fabricated by anodization of Ti wire substrates in ethylene glycol with concentrated NH4F. The in situ fabricated TiO2-nanosheets were densely embedded into Ti substrates with about 1µm long, 300nm wide and 80nm thick. The as-fabricated TiO2-nanosheets coating was employed to extract polycyclic aromatic hydrocarbons, phthalates and ultraviolet (UV) filters in combination with high performance liquid chromatography-UV detection (HPLC-UV). It was found that the TiO2-nanosheets coating exhibited high extraction capability and good selectivity for some UV filters frequently used in cosmetic sunscreen formulations. The main parameters affecting extraction performance were investigated and optimized. Under the optimized conditions, the calibration graphs were linear in the range of 0.1-400µgL(-1). The limits of detection of the proposed method were between 0.026µgL(-1) and 0.089µgL(-1) (S/N=3). The single fiber repeatability varied from 4.50% to 8.76% and the fiber-to-fiber reproducibility ranged from 7.75% to 9.64% for the extraction of spiked water with 50µgL(-1) UV filters (n=5). The SPME-HPLC-UV method was successfully established for the selective preconcentration and sensitive detection of target UV filters from real environmental water samples. Recovery of UV filters spiked at 10µgL(-1) and 25µgL(-1) ranged from 88.8% to 107% and the relative standard deviations were less than 9.8%. Furthermore the in situ growth of the TiO2-nanosheets coating was performed in a highly reproducible manner and the TiO2-nanosheets coated fiber has high mechanical strength, good stability and long service life.

Facile spray-coating process for the fabrication of tunable adhesive superhydrophobic surfaces with heterogeneous chemical compositions used for selective transportation of microdroplets with different volumes.

In this paper, tunable adhesive superhydrophobic ZnO surfaces have been fabricated successfully by spraying ZnO nanoparticle (NP) suspensions onto desired substrates. We regulate the spray-coating process by changing the mass percentage of hydrophobic ZnO NPs (which were achieved by modifying hydrophilic ZnO NPs with stearic acid) in the hydrophobic/hydrophilic ZnO NP mixtures to control heterogeneous chemical composition of the ZnO surfaces. Thus, the water adhesion on the same superhydrophobic ZnO surface could be effectively tuned by controlling the surface chemical composition without altering the surface morphology. Compared with the conventional tunable adhesive superhydrophobic surfaces, on which there were only three different water sliding angle values: lower than 10°, 90° (the water droplet is firmly pinned on the surface at any tilted angles), and the value between the two ones, the water adhesion on the superhydrophobic ZnO surfaces has been tuned effectively, on which the sliding angle is controlled from 2 ± 1° to 9 ± 1°, 21 ± 2°, 39 ± 3°, and 90°. Accordingly, the adhesive force can be adjusted from extremely low (∼2.5 µN) to very high (∼111.6 µN). On the basis of the different adhesive forces of the tunable adhesive superhydrophobic surfaces, the selective transportation of microdroplets with different volumes was achieved, which has never been reported before. In addition, we demonstrated a proof of selective transportation of microdroplets with different volumes for application in the droplet-based microreactors via our tunable adhesive superhydrophobic surfaces for the quantitative detection of AgNO3 and NaOH. The results reported herein realize the selective transportation of microdroplets with different volumes and we believe that this method would potentially be used in many important applications, such as selective water droplet transportation, biomolecular quantitative detection and droplet-based biodetection.