Conventional adsorbents were usually subject to problems such as low adsorption capacity, poor single performance, and difficulty in recovery and processing when they confronted the anfractuous highly toxic wastewater containing abundant cations and anions. To overcome these problems, a fascinating regular honeycomb-like structure of a Ag2O/reduced graphene oxide (Ag2O/rGO) aerogel was skillfully fabricated via self-assembly/reduction of graphene oxide and in situ deposition of Ag2O nanoparticles. Herein, the introduced Ag2O provided rGO with the ability to selectively adsorb anions; due to this ability of rGO, the resultant Ag2O/rGO aerogels possessed the potential to safely and efficiently co-purify toxic anions/cations. To our delight, the resulting Ag2O/rGO aerogels not only exhibited a fast co-removal kinetic rate and superior co-capture performance towards several kinds of cationic/anionic pairs (Sr2+ ≈ 1.75 and Br− ≈ 4.32 mmol g−1, Cs+ ≈ 0.86 and I− ≈ 5.24 mmol g−1, etc.), but also showed an additional excellent visible light photocatalytic activity towards MB (90% of 15 mg ml−1 MB was degraded within 60 min). Furthermore, the Ag2O/rGO aerogels with moldable shapes solved the problem of easy loss and difficult post-processing of adsorbents. Additionally, the as-fabricated Ag2O/rGO compounds possess an outstanding adsorption capacity to other cations or anions, such as Pb2+, Cu2+, Rb2+, Cr3+, S2−, SO42−, SO32−, and PO43−. Therefore, the Ag2O/rGO aerogels could serve as efficient and practical adsorbents for hyper-complex water remediation.

The development of advanced adsorbents with high adsorption capacity and fast adsorption rates is one of the most important issues for water treatment. Herein, oxygen vacancy-rich WOx/C inorganic–organic hybrid nanowire networks were prepared by a one-pot and high yield solvothermal method. With their unique intercrossed hierarchical structure and abundant active sites, the WOx/C networks exhibited high adsorption capacities of ∼1224.7 and 1188.3 mg g−1 for the removal of Pb2+ and MB, respectively. Moreover, the adsorption equilibriums of Pb2+ and MB onto WOx/C networks can be achieved within only ∼1 min, which were among the fastest of those previously reported for Pb2+ and MB adsorbents. These unexpected ultrafast and high adsorption capacities are attributed not only to the unique network nanostructure, but also to the enriched oxygen vacancies onto which small carbonaceous molecules can attach with high affinities, which may serve as anchoring sites for Pb2+ ions or dyes. The removal mechanism of Pb2+ and MB on WOx/C can be attributed to ion exchange, π–π interaction, hydrogen bonding and/or electrostatic attraction. This study not only provides a new strategy to design inorganic–organic hybrid adsorbents, but also demonstrates its prospective application in adsorptive removal and/or recovery of heavy metals and organic pollutants on a large scale.

The core–shell structure has been extensively utilized to develop new functional materials and become a research focus in materials science recently. Over the past decades, the requirements of high-capacity, high-rate, long cycle-life and superior safety have been the main driving force for the advance of cathode materials for lithium-ion batteries (LIBs). Correspondingly, the concept of the core–shell structure is introduced to prepare the above desired cathodes. After that, the concentration-gradient structure is further exploited to overcome the drawbacks of the core–shell structure. The co-precipitation route is more suitable for synthesizing core–shell and concentration-gradient structures compared with other methods, such as sol–gel and spray-drying. More importantly, it is capable of producing large-scale cathodes in the domain of LIBs. In this review, we first illustrate the design principles and formation mechanism of core–shell and concentration-gradient cathode materials; then the recent advances in co-precipitation preparation core–shell and concentration-gradient cathodes for high-energy, high-power, long-life and safe LIBs are summarized. Moreover the structural evolution during cycles to uncover the origin of these improved performances is also analysed. Based on these achievements thus gained, we propose a new strategy to enhance the performances of cathodes. Finally, the remaining challenges including fundamental investigation, commercialized application and present possible solutions are also discussed.

In this paper, we demonstrate the effects of Cd-doping ZnMn2O4 on structural and electrochemical performance. Cd-doped ZnMn2O4 spheres with diameters of about 2 μm were successfully synthesized by a facile hydrothermal method at 200 °C for 18 h. The fabricated Cd-doped ZnMn2O4 samples were characterized by X-ray diffraction, scanning electron microscopy, Brunauer Emmett Teller surface area analyzer and X-ray photoelectron spectroscopy. The electrochemical performance was investigated by cyclic voltammetry and electrochemical impedance spectrometry. The experimental results show that the synthesized spherical Cd-doped ZnMn2O4 exhibit far better rate capability and cyclic stability than that of pure spinel porous ZnMn2O4 microspheres. The result of cyclic voltammetry measurement indicates that the obtained Cd-doped ZnMn2O4 microspheres exhibited the high specific capacitance of 364 Fg−1 at 2 mV/s.

Ni0.5Co0.5(OH)2 nanosheets coated CuCo2O4 nanoneedles arrays were successfully designed and synthesized on carbon fabric. The core/shell nanoarchitectures directly served as the binder-free electrode with a superior capacity of 295.6 mAh g−1 at 1 A g−1, which still maintained 220 mAh g−1 even at the high current density of 40 A g−1, manifesting their enormous potential in hybrid supercapacitor devices. The as-assembled CuCo2O4@Ni0.5Co0.5(OH)2//AC hybrid supercapacitor device exhibited favorable properties with the specific capacitance as high as 90 F g−1 at 1 A g−1 and the high energy density of 32 Wh kg−1 at the power density of 800 W kg−1. Furthermore, the as-assembled device also delivered excellent cycling performance (retaining 91.9% of the initial capacitance after 12,000 cycles at 8 A g−1) and robust mechanical stability and flexibility, implying the huge potential of present hierarchical electrodes in energy storage devices.

•MnO2 nanoflakes@PPy nanowire core/shell nanoarchitectures were designed and synthesized.•Synergetic effects of MnO2 shell and PPy core are responsible for the high power density.•Ultra-flexible and high energy density asymmetrical supercapacitors were achieved.Hierarchically porous polypyrrole nanowires/manganese oxides nanoflakes (MnO2 NFs@PPy NWs) core/shell nanostructures were successfully constructed through a simple, convenient and environmentally friendly method by using PPy nanowires as the core buffer and K-Birnessite type MnO2 as the shell. The core/shell nanostructures effectively increase active surface areas and decrease the ion transmission distance, which is conducive to the efficient transfer of ions. The MnO2 NFs@PPy NWs core/shell nanostructures exhibited not only high specific capacitance (276 F g−1 at 2 A g−1) but also excellent capacitance retained ratio of 72.5% under extreme charge/discharge conditions (200 F g−1 at 20 A g−1) due to the synergistic effect by combining the merits of MnO2 and PPy. Using such hierarchical nanostructure as the positive electrode, we further demonstrate that ultra-flexible asymmetrical supercapacitors (AFSCs) (MnO2@PPy//AC) possess excellent cycling stability (90.3% after 6000 cycles at 3 A g −1), mechanical flexibility, large voltage operation window (1.8–2.0 V vs. SCE) and high energy densities at all charge/discharge conditions (25.8 W h kg−1 at the power density of 901.7 W kg−1, and 17.1 W h kg−1 at the power density of 9000 W kg−1, respectively).Download high-res image (262KB)Download full-size image

The development of advanced functional materials for catalytic reduction and gas sensing is one of the most important issues for the detection and prevention of environmental pollution. Herein, hierarchical peony-like metal/metal oxide (Co/Al2O3 and Co3O4/Al2O3) composites assembled with uniform nanosheets were successfully synthesized using CoAl layered double hydroxides as self-sacrificial templates. Co/Al2O3 composites exhibited high surface dispersions and low metal–support interactions which can be confirmed by a series of structure and morphology characterizations. With the above advantages, Co/Al2O3 composites showed remarkable catalytic ability and stability towards 4-nitrophenol (4-NP) reduction with a nearly 100% conversion within 3 minutes and a conversion efficiency over 98% after 10 successive recycles. After that, Co/Al2O3 composites with different Co/Al ratios were fabricated to investigate the optimal Co content in the catalytic reduction of 4-NP. The results indicated that when the Co/Al ratio reaches 4 : 1, the fabricated composites have the best catalytic reduction abilities. Furthermore, the fabricated Co3O4/Al2O3 gas sensors exhibited a superior response time of 1 s towards 50 ppm ethanol with a sensing response of 8.9. These excellent catalytic reduction and gas sensing abilities could be attributed to the unique peony-like hierarchical structure which could provide large surface areas and abundant active sites. More importantly, this work provided a new synthesis strategy to design materials with enhanced catalytic reduction and gas sensing abilities, which will be beneficial to the development of highly effective catalysts and gas sensing materials.

Abstract3D-networked, ultrathin, and porous Ni3S2/CoNi2S4 on Ni foam (NF) is successfully designed and synthesized by a simple sulfidation process from 3D Ni–Co precursors. Interestingly, the edge site-enriched Ni3S2/CoNi2S4/NF 3D-network is realized by the etching-like effect of S2− ions, which made the surfaces of Ni3S2/CoNi2S4/NF with a ridge-like feature. The intriguing structural/compositional/componental advantages endow 3D-networked-free-standing Ni3S2/CoNi2S4/NF electrodes better electrochemical performance with specific capacitance of 2435 F g−1 at a current density of 2 A g−1 and an excellent rate capability of 80% at 20 A g−1. The corresponding asymmetric supercapacitor achieves a high energy density of 40.0 W h kg−1 at an superhigh power density of 17.3 kW kg−1, excellent specific capacitance (175 F g−1 at 1A g−1), and electrochemical cycling stability (92.8% retention after 6000 cycles) with Ni3S2/CoNi2S4/NF as the positive electrode and activated carbon/NF as the negative electrode. Moreover, the temperature dependences of cyclic voltammetry curve polarization and specific capacitances are carefully investigated, and become more obvious and higher, respectively, with the increase of test temperature. These can be attributed to the components' synergetic effect assuring rich redox reactions, high conductivity as well as highly porous but robust architectures. This work provides a general, low-cost route to produce high performance electrode materials for portable supercapacitor applications on a large scale.

Manganese dioxide (MnO2) nanoarchitectures including microspheres assembled by nanosheets and hollow urchins assembled by nanorods have been successfully synthesized using a facile and efficient hydrothermal method at 150 °C. The effects of concentrations of the reactants and reaction time on the structures and morphologies of MnO2 were systematically investigated. The experimental results showed that the morphologies of MnO2 transformed into nanosheet-assembled microspheres (10 min) from nanorod-assembled hollow urchins (5 min) by tuning the suitable reaction time. The nanorod-assembled hollow urchins experienced the morphology transformation cycle from urchin to a disordered structure to urchin with the extension of the reaction time. Furthermore, the nanorods with different diameters and lengths were formed with different concentrations of reactants at the same reaction time (8 h). The MnO2 nanorods fabricated with 0.59 g KMnO4 showed a maximum specific capacitance (198 F g−1) with a good rate capability and excellent cycling stability (maintained 94% after 2000 cycles). Furthermore, the nanosheet-assembled microspheres exhibited the higher specific capacitance of 131 F g−1 at 1 A g−1 with a long-term cycling stability for the samples at different reaction times. These results indicated their promising applications as high-performance supercapacitor electrodes and provided a generic guideline in developing different nanostructured electrode materials for electrochemical energy storage.

A hierarchical structure composed of porous TiO2:Al2O3:Eu3+ nanoparticles (NPs) and vertically grown one-dimensional TiO2:Er3+,Yb3+ nanorods (NRs) on fluorine doped tin oxide (FTO) substrates coated with a TiO2:graphene (G) seed layer was investigated for use in photoanodes for dye sensitized solar cells (DSSCs). The DSSCs assembled with this hierarchical structure exhibit an outstanding power conversion efficiency of 4.58%, which is superior to that of the devices based on pure TiO2. This high performance can be attributed to the spectrum modifications achieved by utilizing the upconversion (UC) material TiO2:Er3+,Yb3+ and the downconversion (DC) material Al2O3:Eu3+, which facilitate the light harvesting of solar cells via converting near infrared (NIR) and ultraviolet (UV) radiation to visible emission, respectively. Moreover, the TiO2:G layer provides faster electron transport from TiO2 to FTO for the high carrier mobility of G. Moreover, the one-dimensional nanorod structure can offer direct electrical pathways for photogenerated electrons as well as enhance the light scattering capabilities of photoanodes. This study indicates that the TiO2:G/TiO2:Er3+,Yb3+ NRs/TiO2:Al2O3:Eu3+ hierarchical structure has the potential to improve the performance of DSSCs.

Dye-sensitized solar cells (DSSCs) have attracted extensive attention as one of the promising alternatives to silicon solar cells. However, DSSCs have a maximum absorption in the visible light of solar spectrum, which confines their power conversion efficiency. Lots of research efforts have been focused on extending light absorption to enhance the conversion efficiency. Rare earth ion doped up/down conversion materials is an available approach to compensate for the non-absorbable wavelength region of DSSCs via converting ultraviolet and near-infrared radiation to visible emission. In addition to the light-harvesting enhancement, light-scattering effect and recombination loss can also be achieved in DSSCs by utilizing upconversion (UC) or downconversion (DC) materials. Moreover, the introduction of UC or DC facilitates to improve the stability of solar cells. In this review paper, the performance of dye-sensitized solar cells based on up or down conversion materials will be introduced.

•Hollow cubic Zn2SnO4 were fabricated by a facile one-pot hydrothermal method.•The cubic morphology changed from smooth to roughly hollow surface by calcination.•Zn2SnO4 showed different selectivity on the photodegradation of RhB, MO and MB.•The calcination significantly influenced the photocatalytic activity of samples.Hollow cubic Zn2SnO4 sub-microstructures (ZTOs) were fabricated via a one-pot hydrothermal method. The samples were carefully characterized and the experimental results show that the as-prepared ZTOs possess hollow cubic morphology with the length of 500 nm and a relatively rough surface which may endow them high surface areas. The photocatalytic activities were evaluated by the degradation of methylene blue (MB), methylene orange (MO), and rhodamine B (RhB) and the results exhibit a much higher selectivity to the degradation of MB (95%) by Zn2SnO4 than that of MO (70%), RhB (81%) and ZnSn(OH)6 (MB 20%) in 20 min.

TiO2 nanorods arrays (TiO2 NRAs):Eu3+, Tb3+ decorated with Cs2CO3/CdS grown on carbon textiles coated with a TiO2–graphene (TiO2-G) thin film (TiO2-G/TiO2 NRAs:Eu3+, Tb3+/Cs2CO3/CdS) was fabricated. The as-prepared sample exhibits an excellent photodegradation performance under xenon (Xe) lamp light irradiation. The result indicates that the presence of Eu3+, Tb3+ can be excited by ultraviolet light to produce a high intensity visibe light absorbed by CdS, which can generate more photogenerated electron hole pairs. In addition, the presence of graphene is an important factor in accelerating the transferring of photogenerated electron to carbon textiles for photocatalytic reaction. This work can offer an alternative route for designing a hybrid structure system to utilize effectively broad-spectrum solar light and suppress the recombination of photogenerated electron–hole pairs.

Molybdenum dioxide (MoO2) nanoparticles with the size of 200 nm in diameter were synthesized by a facile hydrothermal method. The nanoparticles were directly functionalized as supercapacitors (SCs) electrodes and photocatalysts. The electrochemical studies showed that the SCs demonstrated high capacitance of 621 F g−1, which was 3 times larger than previous reports. Furthermore, they exhibited good cyclic performance with 90% capacity retention after 1000 cycles at a current density of 1 A g−1. The photocatalytic activities were evaluated by the degradation of methylene blue (MB) and rhodamine B (RhB), respectively, and the nanoparticles demonstrated preferred selectivity on the degradation of RhB (70%) than that of MB (30%).

Mg-doped ZnO nanorods with different contents have been fabricated on various substrates by hydrothermal method. The effects of Mg-contents and different substrates on structural and optical properties are analyzed by scanning electron microscopy, X-ray diffraction, photoluminescence (PL) spectra, energy dispersive X-ray spectroscopy and Raman spectroscopy. The results reveal that the Mg-doped ZnO nanorods possess good crystalline quality and morphology when the molar ratio of Mg/Zn is 1. The PL spectra show that the UV emissions have an obvious blue shift with the increase of Mg-content. The results of investigation for the samples grown on different substrates show that the crystal quality and morphology of the samples grown on ZnO layer are perfect, and the UV emission also occurs blue shift owing to the effects of different substrates.

Polyhedral Zn2SnO4 (ZTO) have been successfully fabricated with a facile hydrothermal method. Their morphologies, gas sensing and photocatalytic properties were carefully studied. The morphologies were found to be dependent on the growth time. Morphologies achieved include cubes and octahedrons with the reaction time of 16 h and 36 h. A plausible mechanism for the formation of octahedral ZTO microstructure was proposed. The gas sensing properties of triethylamine (TEA) for ZTO microstructures showed that the sensor response (S = Ra/Rg) reach to be 37 at 100 ppm, which is much larger than the previous reports. Furthermore, the detection limit can be down to 5 ppm-level with a response value about 11 at 200 °C. For the photocatalytic performance, the octahedral ZTO structures (24 h) exhibited faster photocatalytic degradation efficiency toward methylene blue (MB) than others (16 h and 36 h) which can be ascribed to their specific octahedral structures.

Zn-doped SnO2 hierarchical architectures (ZSHAs) with controllable size have been prepared using a facile hydrothermal method, which are composed of two dimensional (2D) nanosheets with a thickness of about 40 nm. The properties of ZSHAs have been explored by gas sensing and photocatalysis testing. A sensor response (S = Ra/Rg) of 43 can be achieved at 100 ppm glycol, and the detection limit can reach down to the 5 ppm level with a response of about 5, combined with a low operating temperature of 240 °C, suggesting a promising application of ZSHAs in glycol gas sensing. Besides, the photocatalytic activities of ZSHAs have been evaluated by the degradation measurement of methylene blue (MB), methylene orange (MO), and rhodamine B (RhB). As a result, the ZSHAs demonstrate a much higher selectivity on the degradation of MB (91%) than that of MO (40%) and RhB (60%) in 60 min of measurement.

High quality ZnO microwires have been fabricated by chemical vapor deposition method. Ultraviolet photodetector based on heterojunction of n-ZnO (individual microwire)/p-GaN film was fabricated. The current–voltage characteristic of the photodetector was investigated, which showed that the heterojunction had rectifying behavior with rectification ratio (Iforward/Ireverse) of about 6.3 × 102 at 4 V. The photoresponse spectrum displayed a sharp cut-off at the wavelength of 380 nm, and the photoresponsivity was as high as 0.45 A W−1 at 0 V and 1.3 A W−1 at 2.5 V reverse bias. The ultraviolet-visible rejection ratio (R370 nm/R450 nm) is three orders of magnitude under zero bias.

Bismuth sulfide (Bi2S3) microflowers have been successfully fabricated through a one-pot hydrothermal method. The structures and morphologies of the as-obtained products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Raman spectroscopy. The experimental results show that Bi2S3 microflowers are composed of many microrods with lengths of 18–20 μm. Metal/semiconductor/metal (MSM) sandwich structures are fabricated, and the current–voltage (I–V) characteristics exhibit a clear back-to-back Schottky-diode behavior. The galvanostatic charge–discharge performance illustrates that the prepared Bi2S3 microflowers exhibit good performance for discharge efficiency at current densities from 1 mA cm−2 to 10 mA cm−2. Furthermore, the as-synthesized Bi2S3 microflowers are also used as the efficient UV-light photocatalysts for the photocatalytic degradation of methylene orange (MO) under light illumination, which shows almost complete degradation (∼95%) of MO dye.

Highly-ordered ridged TiO2 nanotube (TNT) arrays have been fabricated by a simple anodic method. Their structures have been systematically investigated using X-ray diffractometer, scanning electron microscope, energy dispersive spectrometer and HRTEM, and the results clearly presented the ridged morphologies with the outer diameters of about 200 nm. We also found that the annealing procedure induced the phase transformation from amorphous phase to anatase phase. The room-temperature photoluminescence (PL) properties were studied, and the much stronger PL emission for the anatase phase was observed compared to the amorphous counterparts. Furthermore, the broad emission for the anatase phase could be decomposed of three peaks locating at 540, 622 and 773 nm, respectively. The oxygen vacancies and the trapping of free excitons by TiO6 octahedra near defects are the key factors to cause these peaks.

Anatase TiO2 nanotube arrays with rod-formed walls have been fabricated using a one-step anodic oxidation method for the first time. XRD, Raman spectroscopy, SEM, and HRTEM analysis were used for the structural characterization of the synthesized nanostructures. Their photocatalytic and field emission (FE) properties were also systematically investigated, and the experimental results indicated that the crystallization of the starting polycrystalline nanostructures turned into a better anatase phase after the annealed process. The photocatalytic properties showed that the nanostructures with optimized crystallization demonstrated faster degradation rate than the as-prepared polycrystalline counterparts, which would be caused by the improved crystallinity. Furthermore, the dependence of the FE properties on the distances between the anodes and the samples was investigated and the results revealed that the annealed samples have higher field enhancement factor β compared to the as-prepared nanostructures. The formation mechanism of this novel rod-formed TiO2 nanotubes is also briefly discussed.

Fe nanotubes with different outer diameters (55 nm, 80 nm, 200 nm) have been successfully fabricated into the anodic alumina membranes (AAMs) by direct-current electrochemical deposition technique, and their nanotube-core/alumina-sheath nanocables were further realized with a simple chemical etching method. X-ray diffraction, scanning electron microscopy and transmission electron microscopy analyses show that the Fe nanotube core is single crystalline along [110] crystal direction, and the sheath is an amorphous alumina. Such a new nanostructure may be suitable for two-dimensional ferromagnetic structural materials and the diameter of the nanocables can be modulated by controlling the experimental conditions, and the formation mechanism was explored. Our experimental results provide a useful way for fabricating low-cost and large-scale metal nanocables, which are of important applications in modern nanoelectronics.Highlights► Fe nanotubes with different outer diameters (55 nm, 80 nm, 200 nm) were fabricated. ► The nanotubes were deposited directly into in anodic alumina membranes. ► Fe nanotubes are single crystalline along [110]. ► The crystal direction is independent of the outer diameter. ► The nanocables were realized according to the adjustment of the etching time.

•Rice husks as a sustainable silica source for hierarchical flower-like metal silicate.•The interconnected ultrathin nanosheets structure and high specific surface area.•The maximum adsorption capacity of magnesium silicate is 557.9 mg/g for Pb2+.•Ni NPs/SiO2 exhibited high catalytic activity and good stability for 4-NP reduction within only ∼160 s.Metal silicates have attracted extensive interests due to their unique structure and promising properties in adsorption and catalysis. However, their applications were hampered by the complex and expensive synthesis. In this paper, three-dimensional (3D) hierarchical flower-like metal silicate, including magnesium silicate, zinc silicate, nickel silicate and cobalt silicate, were for the first time prepared by using rice husks as a sustainable silicon source. The flower-like morphology, interconnected ultrathin nanosheets structure and high specific surface area endowed them with versatile applications. Magnesium silicate was used as an adsorbent with the maximum adsorption capacities of 557.9, 381.3, and 482.8 mg/g for Pb2+, tetracycline (TC), and UO22+, respectively. Ni nanoparticles/silica (Ni NPs/SiO2) exhibited high catalytic activity and good stability for 4-nitrophenol (4-NP) reduction within only ∼160 s, which can be attributed to the ultra-small particle size (∼6.8 nm), good dispersion and high loading capacity of Ni NPs. Considering the abundance and renewability of rice husks, metal silicate with complex architecture can be easily produced at a large scale and become a sustainable and reliable resource for multifunctional applications.

Anatase TiO2 nanotube arrays with rod-formed walls have been fabricated using a one-step anodic oxidation method for the first time. XRD, Raman spectroscopy, SEM, and HRTEM analysis were used for the structural characterization of the synthesized nanostructures. Their photocatalytic and field emission (FE) properties were also systematically investigated, and the experimental results indicated that the crystallization of the starting polycrystalline nanostructures turned into a better anatase phase after the annealed process. The photocatalytic properties showed that the nanostructures with optimized crystallization demonstrated faster degradation rate than the as-prepared polycrystalline counterparts, which would be caused by the improved crystallinity. Furthermore, the dependence of the FE properties on the distances between the anodes and the samples was investigated and the results revealed that the annealed samples have higher field enhancement factor β compared to the as-prepared nanostructures. The formation mechanism of this novel rod-formed TiO2 nanotubes is also briefly discussed.

The core–shell structure has been extensively utilized to develop new functional materials and become a research focus in materials science recently. Over the past decades, the requirements of high-capacity, high-rate, long cycle-life and superior safety have been the main driving force for the advance of cathode materials for lithium-ion batteries (LIBs). Correspondingly, the concept of the core–shell structure is introduced to prepare the above desired cathodes. After that, the concentration-gradient structure is further exploited to overcome the drawbacks of the core–shell structure. The co-precipitation route is more suitable for synthesizing core–shell and concentration-gradient structures compared with other methods, such as sol–gel and spray-drying. More importantly, it is capable of producing large-scale cathodes in the domain of LIBs. In this review, we first illustrate the design principles and formation mechanism of core–shell and concentration-gradient cathode materials; then the recent advances in co-precipitation preparation core–shell and concentration-gradient cathodes for high-energy, high-power, long-life and safe LIBs are summarized. Moreover the structural evolution during cycles to uncover the origin of these improved performances is also analysed. Based on these achievements thus gained, we propose a new strategy to enhance the performances of cathodes. Finally, the remaining challenges including fundamental investigation, commercialized application and present possible solutions are also discussed.

Manganese dioxide (MnO2) nanoarchitectures including microspheres assembled by nanosheets and hollow urchins assembled by nanorods have been successfully synthesized using a facile and efficient hydrothermal method at 150 °C. The effects of concentrations of the reactants and reaction time on the structures and morphologies of MnO2 were systematically investigated. The experimental results showed that the morphologies of MnO2 transformed into nanosheet-assembled microspheres (10 min) from nanorod-assembled hollow urchins (5 min) by tuning the suitable reaction time. The nanorod-assembled hollow urchins experienced the morphology transformation cycle from urchin to a disordered structure to urchin with the extension of the reaction time. Furthermore, the nanorods with different diameters and lengths were formed with different concentrations of reactants at the same reaction time (8 h). The MnO2 nanorods fabricated with 0.59 g KMnO4 showed a maximum specific capacitance (198 F g−1) with a good rate capability and excellent cycling stability (maintained 94% after 2000 cycles). Furthermore, the nanosheet-assembled microspheres exhibited the higher specific capacitance of 131 F g−1 at 1 A g−1 with a long-term cycling stability for the samples at different reaction times. These results indicated their promising applications as high-performance supercapacitor electrodes and provided a generic guideline in developing different nanostructured electrode materials for electrochemical energy storage.

The development of advanced adsorbents with high adsorption capacity and fast adsorption rates is one of the most important issues for water treatment. Herein, oxygen vacancy-rich WOx/C inorganic–organic hybrid nanowire networks were prepared by a one-pot and high yield solvothermal method. With their unique intercrossed hierarchical structure and abundant active sites, the WOx/C networks exhibited high adsorption capacities of ∼1224.7 and 1188.3 mg g−1 for the removal of Pb2+ and MB, respectively. Moreover, the adsorption equilibriums of Pb2+ and MB onto WOx/C networks can be achieved within only ∼1 min, which were among the fastest of those previously reported for Pb2+ and MB adsorbents. These unexpected ultrafast and high adsorption capacities are attributed not only to the unique network nanostructure, but also to the enriched oxygen vacancies onto which small carbonaceous molecules can attach with high affinities, which may serve as anchoring sites for Pb2+ ions or dyes. The removal mechanism of Pb2+ and MB on WOx/C can be attributed to ion exchange, π–π interaction, hydrogen bonding and/or electrostatic attraction. This study not only provides a new strategy to design inorganic–organic hybrid adsorbents, but also demonstrates its prospective application in adsorptive removal and/or recovery of heavy metals and organic pollutants on a large scale.