CoOOH ultrathin nanoflake arrays grown on nickel foam (NF) have been fabricated by a two-step soft chemical procedure. The ultrathin nanoflakes with a thickness of about 2.7 nm were interconnected with each other and formed a loose and open 3D network structure, providing sufficient exposure of the active sites to an electrolyte. Moreover, the growth mechanism was also investigated. Furthermore, as a supercapacitor material, the CoOOH/NF electrode exhibited ultrahigh specific capacitance (2550 F g−1 at 1.25 A g−1) and good cycling stability (83% of its initial capacitance value was preserved after 5000 charge/discharge cycles at 10 A g−1). Meanwhile, an asymmetric supercapacitor device was assembled with CoOOH/NF as the positive electrode and reduced graphene oxide (rGO) as the negative electrode, displaying an energy density of 49.8 W h kg−1 at a power density of 435 W kg−1. Furthermore, the capacitance retention of the asymmetric supercapacitor after 3000 cycles of charge–discharge at a current density of 7.7 A g−1 is 86%, showing good stability of the asymmetric pseudocapacitor.

•A series of hybrids metal hydroxides nanoarray with hollow tubular structure is fabricated.•The Ni-Co hydroxide/Cu(OH)2/CF electrode exhibits ultrahigh specific capacity.•Hybrid supercapacitor device composed of Ni-Co hydroxide/Cu(OH)2/CF battery-type electrode and rGO capacitor-type electrode.•High energy density of 58.61 Wh kg−1 at a power density of 359.33 W kg−1.In this work, we have developed a versatile method for hybrid Ni–Co hydroxide array fabricated on copper foam (CF). Starting from commercial copper foam, the process involves sequential solution immersion and electrolytic deposition steps, both of which are simple and rapid to carry out and potentially scalable. The resulting Ni–Co hydroxide/Cu(OH)2/CF has a hierarchical and the nanoarray has a hollow structure, and exhibits outstanding electrochemical performance as battery-type electrode material for hybrid supercapacitors with excellent specific capacity (849.6 C g−1, at 5 mA cm−2) and good cycling stability (81.03% of its initial capacity value was preserved after 5000 charge/discharge cycles at 100 mA cm−2). Furthermore, an asymmetric supercapacitor was fabricated with the Ni-Co hydroxide/Cu(OH)2/CF as positive electrode while the rGO as negative electrode. The hybrid device exhibits excellent energy density of 58.61 Wh kg−1 at a power density of 359.33 W kg−1. Furthermore, we demonstrated that the process is also scalable in practice, by fabricating a large-size (20 cm × 30 cm) Ni–Co hydroxide/Cu(OH)2/CF which retains excellent specific capacity.Hybrid Ni-Co hydroxide nanoarrays with hollow tubular structure were prepared by a facile method. The prepared Ni-Co hydroxide/Cu(OH)2/CF exhibits outstanding electrochemical performance as a battery-type electrode material for hybrid supercapacitors with ultrahigh specific capacity. Furthermore, an asymmetric supercapacitor (ASC) was fabricated with the Ni-Co hydroxide/Cu(OH)2/CF as battery-type electrode while the rGO as the capacitor-type electrode, exhibiting a high energy density and can easy lighting the red LED.

Three-dimensional (3D) potassium niobate nanoarray/vermiculite (KNbO3/VMT) was synthesized by an in situ hydrothermal method using niobium chloride as the niobium resource. Scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, Fourier transform infrared and X-ray photoelectron spectroscopy tests were used to confirm that KNbO3 nanoneedles have been grown both on the outer and inner surfaces of natural layered VMT and the growth mechanism of the well-aligned KNbO3 nanoarray grown on mineral VMT was attributed to the existence of Nb species. The photocatalytic performance of the as-prepared composite was investigated using the photodegradation of methylene blue (MB) under illumination. MB was removed from aqueous solution by fully taking advantage of the good absorption property of VMT and photocatalytic property of KNbO3, and visible light was used in the process. After illumination for 105 min, the removal rate of MB in aqueous solution could be higher than 81%. The removal of MB via adsorption–degradation synergy of the structured composite was much better than that of pristine VMT and KNbO3 powder with the same amount of addition, respectively. Moreover, the environmentally friendly KNbO3/VMT material is easy to synthesize and is expected to be a promising structured photocatalyst for the removal of dyes.

•Assembled MgAl–LDH on the surface of VMT is achieved via in situ growing technique.•The growth mechanism was attributed to lattice match between the VMT and MgAl–LDH.•Shows high adsorption capacity and excellent regeneration property for Cr(VI).•The transfer channel and mass diffusion of MgAl–LDH/VMT are highly enhanced.Hierarchical MgAl–layered double hydroxide (MgAl–LDH) was fabricated both on the external and interlayer surfaces of natural mineral vermiculite (VMT) via in situ epitaxial growing technique. The fabrication of the MgAl–LDH/VMT was achieved by lattice match of VMT with MgAl–LDH, which indicates MgAl–LDH can adopt a tilted orientation to the VMT surface. Compared with traditional MgAl–LDH, the hierarchically structured MgAl–LDH/VMT exhibits higher sorption-regeneration performance for Cr(VI), since the specific surface area and transfer channel are significantly enhanced due to its porous 3D framework. The 3D hierarchical MgAl–LDH/VMT can be potentially used as a structured adsorbent in waste water treatment.

NiAl-layered double hydroxide (NiAl-LDH) platelets were uniformly grown on a porous Ni foam substrate by a facile in situ hydrothermal method. By subsequent calcination, the three-dimensional (3D) structured adsorbent, a calcined NiAl-layered double hydroxide film/Ni foam (NiAl-LDO/NF) was obtained. Batch experiments were carried out to investigate the selective adsorption performance of the obtained material for thiosulfate and thiocyanate anions in water, compared with the powder NiAl-LDO adsorbent. The results show that the NiAl-LDO/NF has highly selective adsorption for S2O32− in the mixture solution with a maximum adsorptive capacity of about 209.4 mg g−1 at room temperature, while the removal capacity for SCN− was only about 15.9 mg g−1. At the same time, the resultant 3D structured adsorbent exhibited higher preferential adsorption and easier separation performance from the solution than the corresponding NiAl-LDO powder. It was found that the adsorbability and selectivity of this material was well maintained after more than 10 regeneration cycles. Therefore, the obtained 3D hierarchical NiAl-LDO/NF can be considered as a potential structured adsorbent in environmental applications for the selective removal of S2O32− from SCN−-containing aqueous solution.

The performances of pseudocapacitors usually depend heavily on their hierarchical architectures and composition. Herein, we report a three-dimensional hierarchical NiAl layered double hydroxide/multiwalled carbon nanotube/nickel foam (NiAl–LDH/MWCNT/NF) electrode prepared by a facile three-step fabrication method: in situ hydrothermal growth of NiAl–LDH film on a Ni foam, followed by direct chemical vapor deposition growth of dense MWCNTs onto the NiAl–LDH film, and finally the growth of NiAl–LDH onto the surface of the MWCNTs via an in situ hydrothermal process in the presence of surfactant sodium dodecyl sulfate. The MWCNT surface was fully covered by NiAl–LDH hexagonal platelets, and this hierarchical architecture led to a much enhanced capacitance. The NiAl–LDH/MWCNT/NF electrode has an areal loading mass of 5.8 mg of LDH per cm2 of MWCNT/NF surface. It also possesses exceptional areal capacitance (7.5 F cm–2), specific capacitance (1293 F g–1), and cycling stability (83% of its initial value was preserved after 1000 charge–discharge cycles). The NiAl–LDH/MWCNT/NF material is thus a highly promising electrode with potential applications in electrochemical energy storage.Keywords: layered double hydroxide; multiwalled carbon nanotube; nickel foam; pseudocapacitor

A NiAl layered double hydroxide (NiAl-LDH) film was grown on the surface of a three-dimensional (3D) nickel foam by an in situ hydrothermal method using a nickel foam substrate as a nickel source, and boehmite (AlOOH) sol as an aluminium source. The 3D NiAl-mixed metal oxide (NiAl-MMO) film was obtained by calcining a NiAl-LDH film at 400 °C. The structure and surface morphology of the film samples were studied by X-ray diffraction, elemental analysis, room temperature Fourier transform infrared spectra and electron microscopy analysis. The results showed that NiAl-LDH nanoplatelets densely covered the surface of the nickel foam substrate. The 3D NiAl-MMO film obtained by calcining the NiAl-LDH film was used as capacitive deionization (CDI) electrode for electrosorption of NaCl in water. Under static test conditions, the electrosorption ratio for 0.01 mol L−1 NaCl is above 37.5%, while the electrosorptive capacity of the electrode is ultrahigh at about 81.2 mg g−1 electrode. For 15 rounds of electrosorption and desorption cycling, the decrease of the electrosorption ratio is very minimal, and the desorption ratio of NaCl is above 87.7%. It is shown that the NiAl-MMO film electrode can be used for the removal of NaCl in water.

The performance of pseudocapacitors usually depends largely on careful manipulation of nano-architectures and suitable composition of the active materials. Herein, NiTi layered double hydroxide (LDH) thin films with uniform density were synthesized by a process including two hydrothermal treatment steps and the composition of the hexagonal NiTi-LDH nanosheets was tunable in a relatively wide range. The obtained NiTi-LDH films on nickel foam show a high areal capacitance of 10.37 F cm−2 at 5 mA cm−2, and good cycling stability (86% of its initial value was preserved after 1000 charge–discharge cycles), much better than β-Ni(OH)2 and basic nickel hydroxides carbonate {Ni2(OH)2CO3·4H2O} films. It is indicated that NH3·H2O in the reaction solution played some important roles including enlarging the particle size, focusing the size distribution, and regulating the stacking modes of NiTi-LDH on nickel foam. This work demonstrated the importance of homogeneous dispersion of Ti atoms in layered nanostructures used in supercapacitors.

Oriented dense thin films of CuZnAl–NO3 layered double hydroxide (CuZnAl–NO3 LDH) have been grown on the surface of copper foil by an in situ hydrothermal method with Cu substrate as Cu source, boehmite sol as Al source, and Zn(NO3)2 aqueous solution as Zn source. The structure and morphology of the as-prepared CuZnAl–NO3 LDH films were studied by X-ray diffraction, elemental analysis, room temperature Fourier transform infrared spectra, and scanning electron microscopy analysis. The results showed that the [00l] direction (or ab plane) of CuZnAl–NO3 LDH platelets was parallel to the surface of the Cu substrate. By a facial immersion method, intercalation of laurate anions by ion exchange with the CuZnAl–NO3 LDH film precursors endowed hydrophobic properties on Cu substrate. Moreover, the corrosion behavior of the hydrophobic laurate intercalated LDH films was then investigated by detecting the contact angle, potentiodynamic polarization, and electrochemical impedance properties, which showed that the corrosion resistance of the pristine Cu was highly improved due to the “hydrophobic interaction” and “anion exchange” effects. Therefore, this work provides an effective way to develop a new type of ternary LDH films with potential application as hydrophobic and long-term anticorrosive materials.

Enhancing the capacity and selectivity of adsorbent materials was critical for removing the sulfur-containing pollutants from industrial effluents and fuels. CO32– and dodecylsulfate intercalated ZnAl layered double hydroxides (denoted as CO3-LDH and DDS-LDH, respectively) were used as functional adsorbents for thiophene removal, and they show better absorption properties. The adsorption behavior of thiophene on them was significantly different. The first difference focused on pH dependence. The adsorption behavior onto CO3-LDH was obviously influenced by initial pH; the removal percentage of thiophene reached a maximum value at pH ∼7. However, the adsorption capacity of DDS-LDH was influenced indistinctively by initial pH and the removal percentage of thiophene was practically constant at various pH. The second difference was the effect of initial thiophene concentration. As the thiophene concentration increased, the curve of adsorption capacity became S-type onto CO3-LDH but linear onto DDS-LDH, indicating two different adsorption processes. The adsorption behavior for DDS-LDH was proposed by the dissolution of thiophene in a three-dimensional hydrophobic interlayer region (i.e., adsolubilization), induced by the intercalated DDS, rather than a simple surface adsorption. The results suggested that DDS-LDH could be applied as a potential adsorbent for thiophene removal in a wide range of pH.

The performance of pseudocapacitors usually depends largely on careful manipulation of nano-architectures and suitable composition of the active materials. Herein, NiTi layered double hydroxide (LDH) thin films with uniform density were synthesized by a process including two hydrothermal treatment steps and the composition of the hexagonal NiTi-LDH nanosheets was tunable in a relatively wide range. The obtained NiTi-LDH films on nickel foam show a high areal capacitance of 10.37 F cm−2 at 5 mA cm−2, and good cycling stability (86% of its initial value was preserved after 1000 charge–discharge cycles), much better than β-Ni(OH)2 and basic nickel hydroxides carbonate {Ni2(OH)2CO3·4H2O} films. It is indicated that NH3·H2O in the reaction solution played some important roles including enlarging the particle size, focusing the size distribution, and regulating the stacking modes of NiTi-LDH on nickel foam. This work demonstrated the importance of homogeneous dispersion of Ti atoms in layered nanostructures used in supercapacitors.

CoOOH ultrathin nanoflake arrays grown on nickel foam (NF) have been fabricated by a two-step soft chemical procedure. The ultrathin nanoflakes with a thickness of about 2.7 nm were interconnected with each other and formed a loose and open 3D network structure, providing sufficient exposure of the active sites to an electrolyte. Moreover, the growth mechanism was also investigated. Furthermore, as a supercapacitor material, the CoOOH/NF electrode exhibited ultrahigh specific capacitance (2550 F g−1 at 1.25 A g−1) and good cycling stability (83% of its initial capacitance value was preserved after 5000 charge/discharge cycles at 10 A g−1). Meanwhile, an asymmetric supercapacitor device was assembled with CoOOH/NF as the positive electrode and reduced graphene oxide (rGO) as the negative electrode, displaying an energy density of 49.8 W h kg−1 at a power density of 435 W kg−1. Furthermore, the capacitance retention of the asymmetric supercapacitor after 3000 cycles of charge–discharge at a current density of 7.7 A g−1 is 86%, showing good stability of the asymmetric pseudocapacitor.