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By virtue of high theoretical sodium storage capacities and low cost, FeP is a prospective anode material for sodium-ion batteries (SIBs). Nevertheless, poor cycling and rate performance greatly limit the application of FeP in practice. Herein, a facile template-engaged method is employed to synthesize copper and carbon-incorporated yolk-shelled FeP (denoted as YS-Cu-FeP@C) spheres. The copper is doped into FeP, while the carbon layer with N-doping is coated on the surface of yolk-shelled FeP spheres. Aided by the unique compositional and structural advantages, the as-synthesized YS-Cu-FeP@C spheres exhibit enhanced electrochemical performance for SIBs, including excellent rate capability (145 mAh g−1 at 10 A g−1) and remarkable long-term cycle performance (up to 900 cycles at 1 A g−1). This work provides a rational design and synthetic strategy to boost the sodium storage properties of metal phosphide-based electrode materials.

Nanosized transition metal oxides (TMOs) are one class of the most potential candidates for supercapacitors due to their short electron transport channels and reversible redox reactions. However, their easy-aggregation characteristics and volume shrinkage/expansion during the charge/discharge process seriously limit the practical application. To address this issue, in this work, a two-step thermal conversion different from traditional approaches is reported to synthesize tightly aligned Co3O4/carbon materials. The architecture of cross-linked nanosheets and uniformly distributed Co3O4 nanoparticles (NPs) is obtained by in-situ reduction of cobalt cations in flake-like zeolitic imidazolate frameworks (ZIFs) within inert gas at 500 °C and subsequent mild oxidation of metallic cobalt NPs to Co3O4 NPs (Co3O4@C-500). As a result, this strategy effectively prevents structural collapse and defect formation, which are usually caused by direct oxidation of ZIF-67 nanosheets. In supercapacitor tests, Co3O4@C-500 shows an appreciable specific capacitance (703.3 F g−1 at 1 A g−1) and excellent cycling stability with the capacitance retention of 100% after 10,000 cycles at 10 A g−1. Moreover, the Co3O4@C-500//reduced graphene oxide (RGO) asymmetric supercapacitor (ASC) exhibits an energy density of 43.99 Wh kg−1 at a power density of 824.8 W kg−1, and excellent cycling performance with a capacity retention of 88% after 10,000 cycles. Such excellent performance might benefit from the rational composition control and unique structure of Co3O4 NPs embedded in the carbon skeleton, which results in short electrolyte diffusion channels as well as electron transport distance and effectively reduce negative effect of volume change of electrode materials during the charge/discharge process.

Xylene molecules are a class of volatile organic compounds (VOCs) in the air that are harmful to human health. It is difficult to selectively capture xylenes from the air using existing porous sorbents, due to unspecific and insufficient sorbent/sorbate interactions. We herein report a series of covalent-triazine frameworks (CTFs) that enable selectively capturing of xylene compounds with high adsorption capacities at low pressure. The best-performing CTF material (CTF-2-400), which is comprised of biphenyl and triazine motifs, can adsorb a remarkable amount of o-xylene (358 mg g−1), m-xylene (392 mg g−1) and p-xylene (523 mg g−1) at 25 °C, outperforming most of emerging porous adsorbents. Its ability to capture low-concentration xylenes from the air has been demonstrated using a column breakthrough measurement. The column packed with CTF-2-400 (1 g) continuously captured xylene from the flowing air (~1300 ppm; 10 mL min−1) for 192 h; by contrast, the commercial activated carbon lost its xylene capture capability after only 35 h under the same conditions. We find that the xylene adsorption capacities of the evaluated CTF adsorbents are unrelated to their pore widths or surface areas, and infer that the multiple C-H…π interactions between the CTF framework and xylene molecules account for the observed excellent xylene capture performance.

Developing the transition metal-based electrocatalysts for hydrogen evolution reaction (HER) under large-current-density is crucial for industrial electrolysis of water. However, most of reported HER electrocatalysts in alkaline solution are tested under the current density of less than 100 mA cm−2. In this work, CoFe Prussian blue analogues (PBA) supported on iron foam (IF) as precursor can (has been) be utilized to construct the fluorine-doped cobalt-iron phosphides (F-Co2P/Fe2P/IF). At the large-current-density at 100, 500, 1000 and 2000 mA cm−2, we systematically investigate the HER performance of F-Co2P/Fe2P/IF. Compared to the electrocatalyst without F− doping, F-Co2P/Fe2P/IF only need the low overpotential of 229.8, 260.5, 292.2 and 304.4 mV, respectively, when reaching the large current of 500, 1000, 2000 and 3000 mA cm−2. The F doping may induce the valence state and electronic structure of Co and Fe ions for enhanced HER activity. The role of F doping is furtherly analyzed by introducing barium ions as precipitation agent. At the same time, it can maintain for a long-term stability in 1.0 and 6.0 M KOH at the different high current density. The stableF-Co2P/Fe2P/IF may bear the high current density and high temperature during industrial water electrolysis. This work enables it possible at the large current density for industrial water splitting.

The ordered mesoporous carbon (SBA-C) with parallel channels, synthesized using mesoporous silicon (SBA-15) as a hard template, is decorated with nanoflowers assembled by porous nickel cobalt sulfide (NiCoS) nanosheets with Al leaching through an oil bath following by a hydrothermal method. The nickel cobalt aluminum layered double hydroxide (NiCoAl LDH) precursor is successfully in-situ transformed into NiCoS nanosheets with Al leaching due to the replace of OH− and CO32− ions of the NiCoAl LDH precursor by S2− and the Kirkendall effects to etch and dissolve Al hydroxide. The NiCoS@SBA-C electrode shows surprising electrochemical performance, such as an excellent specific supercapacitance of 1757 F g−1 at a current density of 1 A g−1, superior rate capacity of 79.68% retention at 20 A g−1, and good cycling stability. An asymmetric supercapacitor (ASC) is assembled employing NiCoS@SBA-C as positive electrode and SBA-C as negative electrode, which delivers a high energy density of 38.8 Wh kg−1 at a power density of 800 W kg−1. The above results revel that incorporating ordered mesoporous carbon with transition metal sulfides is a candidate electrode material for application of energy storage devices.

CoSe2 is a potential anode material for sodium-ion batteries in terms of their high sodium storage capacity and tunable properties. However, structural degradation and unstable interphase during the reversible sodiation and de-sodiation lead to fast capacity decay. In this work, we develop a nanocomposite architecture based on CoSe2 nanoparticles embedded in N-doped carbon matrix with conformal TiO2 coating (CoSe2@NC@TiO2) by using a metal-organic framework-assisted strategy. The small CoSe2 nanoparticles and N-doped carbon matrix facilitate charge transport and suppress the structural degradation, while the redox-active TiO2 shell further strengthens the structural and interfacial stability without decreasing the capacity. The as-prepared CoSe2@NC@TiO2 nanocomposite particles deliver a reversible sodium storage capacity of 520 mAh g−1 at 0.1 A g−1 with a capacity retention of 78% after 200 cycles, in contrast to the rapid capacity fading after 50 cycles of the pristine CoSe2@NC particles without TiO2 shell.

Natroalunite microtubes and spheres were synthesized and characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption–desorption isotherms. The volume ratio of water and ethylene glycol play key roles in the formation of natroalunite microtubes and spheres. The growth process of the natroalunite microtubes and spheres was investigated. Batch experiments were performed to study the influence of various experimental parameters such as contact time, initial fluoride concentration, temperature, pH value and the presence of competing anions on the adsorption of fluoride on natroalunite microtubes. The kinetic data was well fitted to pseudo-second-order model. The fluoride adsorption on natroalunite microtubes can be well described by the Langmuir model, and the maximum adsorption capacity was 85.84 mg g −1 at pH 7.0. Thermodynamic parameters including the Gibbs free energy, standard enthalpy and standard entropy were calculated, and the results suggested that the adsorption of fluoride on the natroalunite microtubes was a feasible, spontaneous and exothermic process. The co-existing bicarbonate and phosphate anions have great influence on fluoride removal. The adsorption mechanism was revealed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy analysis and zeta potential study. The point of zero charge (pH PZC ) was 8.37. With the solution pH higher than the pH PZC , both of the surface hydroxyl groups and sulfate anions were participated in the fluoride removal process. When the solution pH was lower than the pH PZC , the electrostatic attraction and the ion-exchange based on the sulfate anions played important role in the fluoride removal.

This research was undertaken to evaluate the fluoride removal performance of 2-line ferrihydrite/bayerite composites (LFBC), which was prepared by a simple coprecipitation method. Batch experiments were performed to study the influence of various experimental parameters such as contact time, initial fluoride concentration, temperature, pH value and the presence of competing anions on the adsorption of fluoride on LFBC. The experiment data of adsorption kinetic and isotherm were fitted by nonlinear regression approach. With the low initial concentration of fluoride, the kinetic data were well fitted to pseudo-first-order model. In the case of high initial concentration, the kinetic data can be described by pseudo-second-order model. The Langmuir maximum adsorption capacity was 123.03 mg g −1 at pH 7.0. Thermodynamic parameters including the Gibbs free energy, standard enthalpy and standard entropy revealed that adsorption of fluoride on the LFBC was a feasible, spontaneous and exothermic process. Furthermore, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis revealed that the surface sulfate anions played important roles in the fluoride removal process, which was also confirmed by the investigation of the released sulfate anions in kinetic process. Findings of this work demonstrate the potential utility of the LFBC as an effective adsorbent for fluoride removal from water.

In this study, adsorption potential of a typical aluminum-based metal–organic frameworks (MOFs), Al 12 O(OH) 18 (H 2 O) 3 (Al 2 (OH) 4 )(BTC) 6 ·24H 2 O (referred as MIL-96), was investigated for defluoridation of drinking water using batch experiment. The effects of different parameters such as pH, contact time, initial fluoride concentration, and competing anions were studied to understand the adsorption behavior of the adsorbent under various conditions. Optimum removal of fluoride ions occurred in a pH range of 3–10. The results indicated that the defluoridation efficiency and aluminum residual of MIL-96 were far superior to that of activated alumina (AA) or nano-alumina (NA). The Langmuir equilibrium model was found to be suitable for describing the fluoride sorption on MIL-96. The maximum fluoride uptake capacity for MIL-96 was calculated to be 31.69 mg g −1 at the temperature of 298 K. Moreover, there were no significant influence on fluoride removal by MIL-96 in the presence of chloride, nitrate, sulfate, bicarbonate and phosphate. Temperature study was carried out at 298 K, 308 K and 318 K revealed that the adsorption process was endothermic reactions. In column tests using real groundwater as influent, about 140 bed volumes (BVs) of groundwater were treated before breakthrough was reached under space velocities (SVs) of 4 h −1 . Results from this study demonstrated the MIL-96 is a promising adsorbent that can be potentially used into drinking water processes.