•3D ultrathin NiFe-LDH nanosheets were prepared on Ni foam.•The specific capacitance of NiFe-LDH-based electrode is 2708 F/g at 5 A/g.•The asymmetric supercapacitor exhibited a high energy density and power density.•The asymmetric supercapacitors can power two LED more than 5 min after charging for 1 min.Layered double hydroxide materials with sheet-like morphologies (i.e., LDH nanosheets) have been proposed to use in supercapacitors. However, the practical application of LDH nanosheets has been inhibited by the notorious inter-particle aggregation and poor charge transport between active materials and current collectors. In this work, 3D nickel-iron layered double hydroxide (NiFe-LDH) nanosheet films with porous nanostructures were synthesized using a hydrothermal method. The ultrathin nanosheets are homogeneously and vertically aligned on the surface of Ni foam. The pseudocapacitors assembled using NiFe-LDH nanosheets exhibit a superior specific capacitance of 2708 F g−1 at 5 A g−1, higher than the previously reported LDHs. The effect of growth concentration and Ni/Fe mole ratio on the electrochemical properties was also investigated. Asymmetric supercapacitors with the NiFe-LDH nanosheets film as the positive electrode and active carbon as the negative electrode display a high energy density of 52 Wh kg−1 at an average power density of 800 W kg−1. When two aqueous asymmetric supercapacitors were assembled in series and charged for only 1 min, the stored energy was capable of powering two green light-emitting-diodes for more than 5 min, indicating the great potential of these 3D NiFe-LDH nanosheets for high-performance energy storage.Download high-res image (366KB)Download full-size image

•Robust superhydrophobic PPS-PTFE/SiO2 coatings were fabricated by a simple spray method.•The PPS-PTFE/SiO2 (4 g/l)coating displays superior hydrophobic after 10-m sand paper abraded.•The PPS-PTFE/SiO2 coatings showed markedly enhanced corrosion resistance to AZ31 Mg alloy.Composite coatings consisting of polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE) and 40 nm silicon dioxide (SiO2) nanoparticles (PPS-PTFE/SiO2) with SiO2 in the range of 0–4 g/l were successfully prepared on AZ31 Mg alloys by a simple spray process. The morphology, composition, water contact angle (WCA), wear behavior and corrosion properties of the composite coatings were measured by using SEM, FT-IR, OCA20, sandpaper abrasion and electrochemical workstation, respectively. Effects of SiO2 content on the wear behavior and corrosion properties of the coatings were studied. It is found that micro-sized protrusions distribute on the surface of the coatings, and a fibrous-network structure of PTFE arranges on the protrusions. WCAs of the PPS-PTFE/SiO2 (0–4 g/l) coating are in the range of (152°–145.5°) ± 0.3° and the sliding angles (SAs) are less than 5°. The WCAs of the un-abraded and 10 m-abraded-on-sandpaper PPS-PTFE/SiO2 (4 g/l) coating are 145.5°±0.3° and 142.5°±0.3°, respectively, implying the PPS-PTFE/SiO2 coating is a robust superhydrophobic one with good wear resistance. Due to the superhydrophobic characteristics, the PPS-PTFE-based coatings show superior corrosion resistance in 3.5 wt% NaCl solution to pristine AZ31 Mg alloys. Owing to the excellent superhydrophobicity, wear resistance and corrosion resistance properties, the robust PPS-PTFE/SiO2 coating is regarded to possess great potential to be applied in automobiles and navigation industries in future.

•Bi2Te3 nanotubes were synthesized by a two-step solution phase reaction.•Bi2Te3/ZnO composite photoanode was applied to improve DSSCs performance.•The composite photoanode can convert both thermal and photo energy simultaneously.•The Bi2Te3 nanotubes provide a direct pathway for electrons transport in photoanode.•The highest η of 4.27% was achieved in a DSSC with Bi2Te3 content of 1.5 wt.%.Ultralong and highly crystalline rhombohedral Bi2Te3 nanotubes were fabricated by a two-step solution phase reaction. A novel photoanode architecture has been fabricated by embedding 0–2.5 wt.% Bi2Te3 nanotubes into ZnO nanoparticles. The photocurrent density-voltage (J-V) characteristics reveal that the dye sensitized solar cells (DSSCs) with Bi2Te3/ZnO composite photoanode exhibit significantly enhanced photovoltaic performance. Notably, the DSSC incorporating 1.5 wt.% Bi2Te3 in the ZnO photoanode demonstrates an energy conversion efficiency (η) of 4.27%, which is 44.3% higher than that of the bare ZnO photoanode. The electrochemical impedance spectroscopy (EIS) analysis shows that the Bi2Te3 nanotubes can provide a direct pathway for electron transportation, prolong the lifetime of electrons, suppress the charge recombination and improve the electron collection efficiency. The thermoelectric effect analysis indicates that with the increase of irradiation time, Bi2Te3/ZnO composite photoanode could convert both heat and photon energies to electrical energy simultaneously and slow down the decline of η. The calculated electron density (ns) further proves that the increment of short-circuit current density (Jsc) is attributed to Seebeck effect in the composite photoanode. These results suggest that compositing 1D thermoelectric nano-materials in photoanode is a promising route to improve the performance of DSSCs.The Bi2Te3/ZnO composite photoanode could convert both heat and photo energies to electrical energy simultaneously.

•The relationship of band gap (Eg) and stress (σ) in BZO is deduced.•XPS and PL illustrate B doping can promote the formation of Zni and VO in BZO.•The lowest resistivity (1.58 × 10−3 Ω cm) is obtained at 2 at.% B content.Boron doped ZnO (BZO) films with B content in the range of 0–6 at.% were deposited on quartz glass substrates by RF magnetron sputtering technique. The effects of B doping content on microstructure, optical and electrical properties of BZO films were systematically investigated by XRD, SEM, AFM, XPS, PL, UV–vis–near infrared spectrophotometer and Hall-effect measurement, respectively. It is found that the crystal quality of ZnO films can be improved as B doping content increases to no larger than 4 at.% and will be deteriorated at higher B doping content. The grain size and surface roughness of the films reduce with the increase of B doping content. The BZO films exhibit tensile stress and the stress increases with B content. The transmittance of the BZO films is revealed to be 90% in the visible region. As the B doping content increases from 0 to 6 at.%, the optical band gap of BZO films enhances from 3.28 to 3.57 eV, which is found to increase linearly with the tensile stress in the films. The lowest resistivity of 1.58 × 10−3 (Ω cm) is obtained at 2 at.% B doping content. XPS and PL analyses demonstrated that B doping can promote the formation of defects of zinc interstitials (Zni) and oxygen vacancies (VO).

•Novel sorbents, CoFe-LDH for the removal of MO and Cr(VI) were prepared.•Adsorption kinetics and isothermals of MO and Cr(VI) were studied.•The adsorption mechanisms were discussed in detail.•High adsorption amount of MO and fast removal of Cr(VI) were obtained in CoFe-LDHs.CoFe-nitrate-layered double hydroxides (LDHs) with Co2+/Fe3+ molar ratios of 2, 3 and 4 were synthesized by a simple co-precipitation method. The as-prepared CoFe-LDHs exhibited a high adsorption activity to the methyl orange (MO) dye and Cr(VI). The adsorption characteristics including adsorption kinetics and isothermals were investigated. Structure analysis of the as-synthesized LDHs before and after adsorption revealed that adsorption proceeds in two processes: external surface adsorption and interlayer anion exchange. The results of MO adsorption experiments showed that LDHs with Co2+/Fe3+ molar ratios of 4 worked best with the largest MO adsorption amount up to 1290 mg/g at an initial concentration of 300 mg/L due to the porous structures. We have also noted that Cr(VI) in a range of 2–25 mg/L can be quickly removed with the maximum adsorption capacity of 27.62 mg/g in the initial 5 min, much faster than other LDH materials. Therefore, CoFe-LDHs are potential cost-effective adsorbents for both MO dye and Cr(VI).

•NZO films with different Na contents were grown on quartz glass using sol–gel method.•An increase in crystallinity of NZO film was observed with the increasing Na content.•The violet emission centered at 424 nm appeared in the PL spectra of 30 at.% NZO.•Low Na doping concentration contributed to the enhancement of INBE/IDLE.In this paper, Na-doped ZnO (NZO) thin films with doping contents of 3–30 at.% were synthesized on quartz glass substrates by sol–gel spin coating method. The structure, morphology, optical transmittance and photoluminescence properties of NZO films were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), atomic force microscope (AFM), UV–VIS spectrometer and fluorescence spectrophotometer, respectively. The results showed that all the NZO thin films exhibit a strong preferential c-axis orientation with a hexagonal polycrystalline structure. An apparent increase in crystallinity was observed with the increasing Na content. The surface of the heavily Na doped samples (30 at.%) exhibits nanorods morphology. The RMS roughness changed from 16.219 nm to 53.072 nm with the increase of Na concentrations. As Na doping content increases to 24 at.%, the average transmittance was still larger than 62% in the visible range. The optical band gap initially increased and then decreased nearly linearly with the increase of Na content. The refractive index of NZO films in the visible range was found to increase gradually with increasing Na dopants. Room temperature photoluminescence (PL) spectra showed sharp ultraviolet emissions centered at 388 nm and broad green–yellow emissions (450–650 nm). The violet emission centered at 424 nm appeared in the spectra of 30 at.% NZO. In addition, it was found that the low Na doping concentration contributed to the enhancement of INBE/IDLE.

•ZnO nanorods were grown on Ga-doped ZnO seed layers using hydrothermal method.•Using the ZnO nanorods as photoanodes for fabricated dye-sensitized solar cells.•The highest η of 1.23% can be achieved in a DSSC with 3 at.% Ga-doped in seeds.•The effects of ZnO seed layers on electron transport properties were investigated.•The enhancement performance of DSSCs contributed to higher dye loading and ηcc.Zinc oxide (ZnO) nanorod arrays were grown on FTO substrates with a Ga-doped ZnO (GZO) seed layer by a hydrothermal method. GZO seed layers were obtained via sol–gel technology with Ga concentration in the range of 0–4 at.%. The dye sensitized solar cells (DSSCs) using ZnO nanorod arrays as the photoanode layers were prepared. The effect of Ga dopant concentrations in ZnO seed layer on the morphology features of ZnO nanorod arrays and the performance of DSSCs were systematically investigated. Results indicate that the average diameter and density of ZnO nanorod arrays decrease with increasing Ga concentration, but their length shows an opposite trend. The photocurrent density–voltage (J–V) characteristics reveal that the DSSCs with GZO seed layer exhibit significantly improved photovoltaic performance. In particular, the highest energy conversion efficiency (η) of 1.23% can be achieved in a DSSC with 3 at.% Ga doping, which is increased by 86.36% compared with that of the undoped DSSC. The external quantum efficiency (EQE) spectra and electrochemical impedance spectroscopy (EIS) were employed to explore the photon-to-electron conversion process in DSSCs. It is demonstrated that the performance enhancement of DSSCs based on GZO seed layer can be attributed to higher amount of dye loading, more efficient electron transportation and better electrons collection efficiency.

•RTFM was firstly observed in Ag–N codoped ZnO thin films.•A large number of VO are present in ZnO:(Ag, N) thin films.•The MS of ZnO:(Ag, N) thin films is strongly correlated with VO concentration.•The observed RTFM in ZnO:(Ag, N) thin films is induced by VO defects.Room temperature ferromagnetism (RTFM) was firstly observed in Ag–N codoped ZnO [ZnO:(Ag,N)] thin films prepared on quartz substrates by radio frequency (RF) magnetron sputtering. Typical ferromagnetic saturation behavior was clearly demonstrated by magnetization loops in all the ZnO:(Ag,N) films, and the saturated magnetization significantly decreases under both the Ag-rich and N-rich conditions. The defect analysis based on X-ray photoelectron spectroscopy and photoluminescence confirms that a large number of oxygen vacancies (VO) are present in ZnO:(Ag,N) films and the saturated magnetization of the films was found to be strongly correlated with the variation of VO concentration. It is suggested that the observed FM in ZnO:(Ag,N) films is neither directly induced by Ag nor N ions, but by VO defects. Therefore, our work provides a facile way to establish and mediate the RTFM in ZnO:(Ag,N) films by tuning the VO defects, which are regulated by the incorporation of Ag and N dopants.

We employ density-functional theory within the generalized-gradient approximation to study the structural and electronic properties of Ag–N codoped ZnO. The calculations show a strong tendency towards formation of the nearest-neighbor AgZn–NO pairs shown to be in the spin polarized state with a total magnetic moment of 2.02 μB. Compared with the isolated Ag or N doped ZnO, it is found that Ag–N codoping can obviously enhance the local magnetic moment of Ag and N atoms due to strong p–d hybridization. However, Ag–N codoping system shows non-ferromagnetic behavior, which is other than Cu–N codoping system, where robust ferromagnetism is confirmed by both experimental and theoretical research. It is demonstrated that the atomic relaxation is responsible for diminishing the magnetic moments of Ag–N codoped ZnO. We therefore suggest that Ag–N codoped ZnO is unsuitable for spintronics applications.

•Ag–N dual-doped p-type ZnO films were grown on quartz substrate.•The p-type behavior of ZnO:(Ag, N) film is not stable.•The instability of p-ZnO is due to the presence of Ag aggregation and Ni in the film.Silver and nitrogen codoped ZnO films [ZnO:(Ag, N)] were grown on quartz substrates by radio frequency magnetron sputtering deposition followed by ion-implantation technique. Room-temperature (RT) Hall-effect measurements confirm that Ag–N codoped ZnO film is converted to p-type ZnO under optimum post-annealing conditions. The p-type conductivity of ZnO:(Ag, N) is attributed to the formation of the AgZn–NO pairs and/or NO–AgZn–NO triangles, which can create impurity bands above the VBM of ZnO due to the p–d interaction between accepters and hence offer improved incorporation and activation of acceptors. The sample exhibited a stable conductivity-type over four month period after post-annealing, but apparent degradation of p-type characteristic was observed. It is demonstrated that the Ag aggregation (metallic Ag and/or Ag2O) can be stable in the film and metastable interstitial nitrogen is easy to diffuse and be trapped by acceptor NO to form double-donor (N2)O at RT, resulting in a decrease in the conductivity and stability of p-type ZnO:(Ag, N) film.

•In and N doped thin ZnO:Mn films were fabricated.•All samples possess typical wurtzite structure and have no other impurity phase.•Both Mn doped and Mn–In codoped ZnO films show paramagnetic behavior.•Room-temperature ferromagnetism in ZnO:Mn + N was observed.•Magnetic interactions were also studied by GGA + U.In this paper, indium (In) and nitrogen (N) doped ZnO:Mn thin films were fabricated and their structural and magnetic properties were investigated. X-ray diffraction and X-ray photoelectron spectroscopy measurements show that the samples possess typical wurtzite structure and have no other impurity phase. Magnetic measurements reveal that both Mn mono-doped and Mn–In codoped ZnO films show paramagnetic behavior, while room temperature ferromagnetism is achieved in weak p-type ZnO:Mn films by codoping with N. First-principles calculations further indicate that N codoping can change the ground state of ZnO:Mn system from antiferromagnetic to ferromagnetic while the Mn–In codoped ZnO is favored antiferromagnetic in energy. Therefore, N codoping is expected to be a promising technique to realize ferromagnetic ZnO:Mn semiconductors with high Curie temperature.

•Well-aligned ZnO nanorod films were prepared onto a spin-coated ZnO seed layer.•The growth time has effect on the structure and morphology.•The effect of growth time on the hydrophobicity of ZnO nanorod films was analyzed.•The contact angle and sliding angle of the superhydrophobic surface are 161.7° and 6°.ZnO nanowire films have been prepared by chemical process at 90 °C for different growth time varied from 4 h to 12 h. The effect of growth time on the structure, morphology, and the hydrophobicity of ZnO nanowire films were investigated. The results indicate that all of the films exhibit the hexagonal wurtzite phase with growth direction perpendicular to the substrate surface. The scanning election microscopy images of ZnO nanowire films show that prolonging the growth time results in longer nanowires with uneven diameter. The influence of the diameter of nanowires on the wettability of the film was analyzed. Typically, the film prepared for 4 h exhibits a high water contact angle of about 161.7 ± 0.3° with the advancing contact angle of 157.2 ± 0.5° and receding contact angle of 163.2 ± 0.5° and a small sliding angle of 6° after hydrophobic treatment. Based on the Cassie theory, the analysis results reveal that only about 6% of the water surface contacts with the ZnO films and the remaining 94% contacts with the air cushion, which is reasonable for the hydrophobicity of a ZnO nanowire films.Superhydrophobic ZnO surfaces with tunable high water adhesion have been fabricated by combining both a simple solution chemistry approach and ethanol solution of triethoxyoctylsilane.

Indium and nitrogen codoped ZnCdO films [ZCO:(In, N)] have been grown on quartz substrates by radio frequency magnetron sputtering deposition followed by ion-implantation technique. The room-temperature Hall measurements confirm that a stable p-type ZCO:(In, N) film is obtained by optimizing postimplantation annealing temperature (Tann) and time (tann). The Raman measurements reveal that the concentration of NO acceptors in stable p-type film is higher than unstable p-type films and much higher than n-type films, which indicates that choosing appropriate annealing window plays a key role in stabilizing the NO acceptors to obtain the stable p-type ZCO:(In, N). Both theory and experiment indicate that the stable p-type conductivity of ZCO:(In, N) is attributed to the formation of passive complexes (-Cd-O-In-N-), which can form an impurity band above the valence band maximum, resulting in a decrease in the ionization energy of the acceptor and an improvement in the stability of p-type ZCO:(In, N). The Hall measurements also confirm that the p-type films would convert to n-type conductivity under both higher Tann and longer tann. Combined with the transition state calculations, the possible reasons of such phenomenon are discussed in detail at the end of the article.