Regulating Oxygen Configuration in Hierarchically Porous Carbon Nanosheets for High-Rate and Durable Na+ Storage.

Surface oxygen functionalities (particularly C-O configuration) in carbon materials have negative influence on their electrical conductivity and Na+ storage performance. Herein, we propose a concept from surface chemistry to regulate the oxygen configuration in hierarchically porous carbon nanosheets (HPCNS). It is demonstrated that the C-O/C=O ratio in HPCNS reduces from 1.49 to 0.43 and its graphitization degree increases by increasing the carbonization temperature under a reduction atmosphere. Remarkably, such high graphitization degree and low C-O content of the HPCNS-800 are favorable for promoting its electron/ion transfer kinetics, thus endowing it with high-rate (323.6 mAh g-1 at 0.05 A g-1 and 138.5 mAh g-1 at 20.0 A g-1 ) and durable (96 % capacity retention over 5700 cycles at 10.0 A g-1 ) Na+ storage performance. This work permits the optimization of heteroatom configurations in carbon for superior Na+ storage.

Porous α-Fe2O3 nanoparticles encapsulated within reduced graphene oxide as superior anode for lithium-ion battery.

A facile route for the controllable synthesis of porous α-Fe2O3 supported by three-dimensional reduced graphene oxide (rGO) is presented. The synergistic effect between α-Fe2O3 and rGO can increase the electrolyte infiltration and improve lithium ion diffusion as well. Moreover, the combination of rGO nanosheets can increase the available surface area to provide more active sites and prevent α-Fe2O3 nanoparticles from agglomeration during the cycling process to ensure its long-term cycle performance. Consequently, the α-Fe2O3/rGO nanocomposites exhibit higher reversible specific capacity (1418.2 mAh g-1 at 0.1 A g-1), better rate capability (kept 804.5 mAh g-1 at 5.0 A g-1) and cycling stability than the α-Fe2O3 nanoparticles. Owing to the superior electrochemical performance, the α-Fe2O3/rGO nanocomposites might have a great potential as anode for lithium-ion batteries.

A sand composite with surface gel coating containing alkylamine toward the removal and immobilization of complex metal ions from electroplating wastewater.

SiO2 gel was formed on the grain surface of silica sand by hydrolysis and condensation of tetraethyl orthosilicate in water with the addition of 1-butylamine. The resultant product was a composite consisting of sand grains with mesoporous silica coating containing alkylamine inside. This composite exhibited basicity in the wastewater from copper electroplating due to its release of amine. As a result, the strongly acidic wastewater was neutralized and the co-precipitation of complex metal ions occurred. It was shown that up to 12 major metal ions in the wastewater could be simultaneously removed under static condition at room temperature by using the sand composite. The Fe and Cu in the wastewater could be removed completely, while the concentrations of Al, Cd, Ti, V, and Zn in the wastewater were reduced by two to three orders of magnitude. After the removal of multiple metal ions from the electroplating wastewater, the used sand was further applied as a raw material for making a silicate glass. The glass was chemically stable and thus the heavy metal ions from the wastewater were immobilized.

Three-dimensional biogenic C-doped Bi2MoO6/In2O3-ZnO Z-scheme heterojunctions derived from a layered precursor.

Novel 3D biogenic C-doped Bi2MoO6/In2O3-ZnO Z-scheme heterojunctions were synthesized for the first time, using cotton fiber as template. The as-prepared samples showed excellent adsorption and photodegradation performance toward the hazardous antibiotic doxycycline under simulated sunlight irradiation. The morphology, phase composition and in situ carbon doping could be precisely controlled by adjusting processing parameters. The carbon doping in Bi2MoO6/In2O3-ZnO was derived from the cotton template, and the carbon content could be varied in the range 0.9-4.4 wt.% via controlling the heat treatment temperature. The sample with Bi2MoO6/In2O3-ZnO molar ratio of 1:2 and carbon content of 1.1 wt.% exhibited the highest photocatalytic activity toward doxycycline degradation, which was 3.6 and 4.3 times higher than those of pure Bi2MoO6 and ZnInAl-CLDH (calcined layered double hydroxides), respectively. It is believed that the Z-scheme heterojunction with C-doping, the 3D hierarchically micro-meso-macro porous structure, as well as the high adsorption capacity, contributed significantly to the enhanced photocatalytic activity.

Electrostatically Assembled Magnetite Nanoparticles/Graphene Foam as a Binder-Free Anode for Lithium Ion Battery.

Lithium ion batteries (LIBs) are promising candidates for energy storage, with the development of novel anode materials. We report the fabrication of Fe3O4 nanoparticles/graphene foam via electrostatic assembly and directly utilize it as a binder-free anode for LIBs. Owing to the integrated effect of the well-dispersed Fe3O4 nanoparticles and the conductive graphene foam network, such composite exhibited remarkable electrochemical performances. It delivered a large reversible specific capacity reaching to ∼1198 mAh g-1 at a current density of 100 mA g-1, a good rate capacity, and an excellent cyclic stability over 400 cycles. This work demonstrated a facile methodology to design and construct high-performance anode materials for LIBs.

High efficiency photocatalysis for pollutant degradation with MoS2/C3N4 heterostructures.

Porous graphitic carbon nitride was synthesized by controllable thermal polymerization of urea in air. Their textural, electrical, and optical properties were tuned by varying the heating rate. The presence of proper residual oxygen in carbon nitride matrix had enhanced light absorption and inhibited the recombination of charge carriers. Furthermore, the MoS2 nanosheets were coupled into the carbon nitride to form MoS2/C3N4 heterostructures via a facile ultrasonic chemical method. The optimized MoS2/C3N4 heterostructure with 0.05 wt % MoS2 showed a reaction rate constant as high as 0.301 min(-1), which was 3.6 times that of bare carbon nitride. As analyzed by SEM, TEM, UV-vis absorption, PL and photoelectrochemical measurements, intimate contact interface, extended light response range, enhanced separation speed of charge carriers, and high photocurrent density upon MoS2 coupling led to the photocatalytic promotion of the MoS2/C3N4 heterostructures. In this architecture, MoS2 served as electron trapper to extend the lifetime of separated electron-hole pairs. Meanwhile, the accumulated holes on the surface of carbon nitride oxidized the organic dye directly, which was a predominant process in the photodegradation of organic pollutants in water treatment. The promotional mechanisms and principles reported here would have great significance in heterogeneous photocatalysis.

Hierarchical hollow α-Fe2O3/ZnFe2O4/Mn2O3 Janus micromotors as dynamic and efficient microcleaners for enhanced photo-Fenton elimination of organic pollutants.

Micro/nanomotors that can promote mass transport have attracted more and more research concern in the photocatalysis field. Here we first report a newly-designed hierarchical α-Fe2O3/ZnFe2O4/Mn2O3 magnetic micromotor as a heterogeneous photocatalyst for the degradation of cationic dye methylene blue (MB) from wastewater. The resulting three-dimensional (3D) flower-like hollow Janus micromotors are fabricated through a green and scalable strategy, in which each component has different functions. ZnFe2O4 microspheres serve as a magnetic scaffold for the nucleation and growth of α-Fe2O3 nanosheets and for the recycling of the micromachine. α-Fe2O3 nanosheets have shown great potential as an ideal semiconductor material for the photocatalytic decontamination of pollutants. Mn2O3 nanoparticles are mainly utilized as a catalyst to produce O2 bubbles to propel the autonomic movement of the micromotors in the presence of H2O2 fuel and also as a Fenton-like catalyst to decompose H2O2 to generate reactive oxygen species. Furthermore, the resultant micromotors exhibited linear-like motion form with an average speed of 189.1 µm s-1 in 5 wt% H2O2 solution. Moreover, the self-driven micromotors exhibited a superior catalytic degradation property toward MB, which was attributed to the synergistic effect of heterogeneous photocatalyst and the boosted micro-mixing and mass transfer caused by the vigorous motion of the micro-actuator. The possible degradation intermediates and passways of MB by α-Fe2O3/ZnFe2O4/Mn2O3 micromotor were identified with time of flight mass spectroscopy (TOF-MS). The 3D Janus micromotors have the potential to be used as a high-efficiency and active heterogeneous photocatalyst for the degradation of organic pollutants.

3D hierarchical LDHs-based Janus micro-actuator for detection and degradation of catechol.

Micro/nanomotors that combine the miniaturization and autonomous motion have attracted much research interest for environmental monitoring and water remediation. However, it is still challenging to develop a facile route to produce bifunctional micromotors that can simultaneously detect and remove organic pollutants from water. Herein, we developed a novel Janus micromotor with robust peroxide-like activity for simultaneously colorimetric detection and removal of catechol from water. Such laccase (Lac) functionalized Janus micromotor consisted of calcined MgAl-layered double hydroxides (MgAl-CLDHs) nanosheets and Co3O4-C nanoparticles (Lac-MgAl-CLDHs/Co3O4-C), revealing unique 3D hierarchical microstructure with highly exposed active sites. The obtained Janus micromotors exhibited autonomous motion with a maximum velocity of 171.83 ± 4.07 µm/s in the presence of 7 wt% H2O2 via a chemical propulsion mechanism based on the decomposition of H2O2 by Co3O4-C layer on the hemisphere surface of Janus micromotors. Owing to the combination of autonomous motion and high peroxide-like activity, Lac-MgAl-CLDHs/Co3O4-C Janus micromotors could sensitively detect catechol with the limit of detection of 0.24 µM. In addition, such Janus micromotors also could quickly degrade catechol by •OH generated from a Fenton-like reaction. It is a first step towards using autonomous micromotors for highly selective, sensitive, and facile detection and quick removal of catechol from water.

Ion-catalyzed synthesis of N/O co-doped carbon nanorods with hierarchical pores for high-rate Na-ion storage.

Appropriate heteroatom doping and pore structure optimization are cost-effective technologies to improve the electronic conductivity and ion diffusion kinetics of hard carbons (HCs). Here, we report an ion-catalyzed synthesis of N/O co-doped carbon nanorods (NOCNRs) with abundant hierarchical pores, achieving high-capacity and high-rate Na-ion storage (336 mA h g-1 at 0.1 A g-1 and 196 mA h g-1 at 20.0 A g-1).

Synthesis and characterization of nanostructured Fe3O4 micron-spheres and their application in removing toxic Cr ions from polluted water.

We present a simple and effective method for the synthesis of nanostructured Fe(3)O(4) micron-spheres (NFMSs) by annealing hydrothermally formed FeCO(3) spheres in argon. The phase structure, particle size, and magnetic properties of the product have been characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and by means of a superconducting quantum interference device (SQUID). The results have shown that the as-obtained NFMSs have a diameter of about 5 µm and are composed of nanometer-sized porous lamellae. The NFMSs have a large specific surface area (135.9 m(2) g(-1)), reductive Fe(2+) incorporated into their structure, and intense magnetic properties. These properties suggest that NFMSs have potential application in removing toxic Cr(6+) ions from polluted water. At 25°C, each gram of NFMSs product can remove 43.48 mg of Cr(6+) ions, as compared to just 10.2 mg for nanometer-sized Fe(3)O(4) and 1.89 mg for micron-sized Fe(3)O(4). The enhanced removal performance can be ascribed to the structural features. Moreover, the Cr(6+) ion removal capacity of the NFMSs can reach up to 71.2 mg g(-1) at 50°C. The influencing parameters in the removal of Cr(6+) ions, such as contact time, pH, and temperature, have been evaluated. The Cr(6+)-removal mechanism has been investigated. We have found that the NFMSs product not only serves as an effective adsorbent to remove toxic Cr(6+) ions from polluted water, but also as an effective reductant in reducing the adsorbed toxic Cr(6+) ions to much less toxic Cr(3+) through the Fe(2+) incorporated into its structure.

Catalytic Activity of Biomorphic α-MoO(3) in the Degradation of Methyl Violet Dye.

A network of fibers comprising orthorhombic molybdenum trioxide (α-MoO(3)) crystals were synthesized using paper as template via a biomorphic approach. The template was completely removed by annealing the sample at 600°C for 5 min. Monoclinic MoO(3) was formed and consequently converted into orthorhombic α-MoO(3) after prolonged annealing. Three milligrams of the biomorphic α-MoO(3) could degrade up to 90% of a methyl violet aqueous solution with a concentration of 20 mg/L under normal visible light. The size of the α-MoO(3) grains and the porosity of the biomorphic sample affected catalytic performance.

Storage of Lithium-Ion by Phase Engineered MoO3 Homojunctions.

With high theoretical specific capacity, the low-cost MoO3 is known to be a promising anode for lithium-ion batteries. However, low electronic conductivity and sluggish reaction kinetics have limited its ability for lithium ion storage. To improve this, the phase engineering approach is used to fabricate orthorhombic/monoclinic MoO3 (α/h-MoO3) homojunctions. The α/h-MoO3 is found to have excessive hetero-phase interface. This not only creates more active sites in the MoO3 for Li+ storage, it regulates local coordination environment and electronic structure, thus inducing a built-in electric field for boosting electron/ion transport. In using α/h-MoO3, higher capacity (1094 mAh g-1 at 0.1 A g-1) and rate performance (406 mAh g-1 at 5.0 A g-1) are obtained than when using only the single phase h-MoO3 or α-MoO3. This work provides an option to use α/h-MoO3 hetero-phase homojunction in LIBs.

Kinetic Analysis of Bio-oil Derived Hierarchically Porous Carbon for Superior Li+/Na+ Storage.

Herein, an efficient biomass utilization is proposed to prepare bio-oil-derived carbon (BODPC) with hierarchical pores and certain H/O/N functionalities for superior Li+/Na+ storage. Kinetic analyses reveal that BODPC has similar behavior in the electrochemical Li+ and Na+ storage processes, in terms of physical adsorption (Stage I), chemical redox reactions with surface functionalities (Stage II), and insertion into the graphitic interlayer (Stage III). Promisingly, BODPC exhibits a high reversible specific capacity (1881.7 mAh g-1 for Li+ and 461.0 mAh g-1 for Na+ at 0.1 A g-1), superior rate capability (674.1 mAh g-1 for Li+ and 125.7 mAh g-1 for Na+ at 5.0 A g-1), and long-term cyclability. More notably, the BODPC with highly capacitive-dominant behavior would hold great promise for the applications of high-power, durable, and safe rechargeable batteries/capacitors.

Oxygen vacancies boosted the electrochemical kinetics of Nb2O5-x for superior lithium storage.

The introduction of oxygen vacancies (OVs) into Nb2O5 can not only provide more active sites for lithium storage but also change the electronic structure of Nb2O5 to boost electron/ion transport kinetics. Consequently, the defective Nb2O5-x exhibits high lithium storage capacity, superior rate capability, and cycling stability.

Operando mechanistic and dynamic studies of N/P co-doped hard carbon nanofibers for efficient sodium storage.

In situ Raman and electrochemical results reveal that Na+ adsorbs on the surface/defective sites of N/P-HCNF and inserts randomly into its turbostratic nanodomains in the dilute state without a staged formation, which can facilitate fast Na+ diffusion kinetics for efficient sodium storage.

A versatile method for controlled synthesis of porous hollow spheres.

A versatile method was developed to synthesize nickel silicate, silica, and silica-nickel composite porous hollow spheres by using silica spheres as templates. In the preparation, silica spheres were treated with a mixture of NiSO(4)·6H(2)O and NH(3)·H(2)O. The nickel-based ingredient reacted with the silica to form a shell while the alkaline solution could remove the silica core, thus forming the nickel silicate hollow spheres. After these spheres were further treated with hydrogen in reduction or with HCl in etching, they became silica-nickel hollow spheres or silica hollow spheres, respectively. The sizes of these hollow spheres depended on the concentration of the precursor. Our investigation also found that their surface properties or magnetic properties could be tailored by adjusting the fabrication parameters.

Synthesis of Zn2SnO4 nanowires and their photoluminescence properties.

Single-crystalline Zn2SnO4 nanowires were successfully synthesized on a photoresist-coated Si substrate using a facile chemical vapor deposition method. The growth of the nanowires followed a self-catalytic vapor-liquid-solid process. During annealing, the photoresist was carbonized into a complex glassy and graphite carbon structure. The immiscibility between the carbon layer and the in-situ formed Zn2SnO4 was a prime factor in the formation of the one-dimensional Zn2SnO4 nanowires. A broad blue-red emission band centered at 490.4 nm was observed in the photoluminescence spectrum of these nanowires, and it was related to the oxygen vacancies in these nanowires.

Synthesis and characterization of tetrapod-like Cu-ZnO nanowhiskers prepared by photo-reduction technique.

Tetrapod-like Cu-ZnO nanowhiskers were synthesized by a photo-reduction technique in an aqueous solution containing Cu2+ ions. The XRD and TEM analyses revealed that the as-prepared ZnO nanowhiskers were covered by Cu coating or surrounded by Cu nanoparticles. Pure Cu nanoparticles were also produced in the solution by increasing the duration of xenon irradiation. These nanoparticles were amorphous and could be converted to crystalline structure by further electron beam irradiation. The photoluminescence measurement showed that the visible emission from the Cu-coated ZnO nanowhiskers had a blue shift when compared with that of the pure ZnO.

A colorimetric strategy for ascorbic acid sensing based on the peroxidase-like activity of core-shell Fe3O4/CoFe-LDH hybrid.

A novel core-shell Fe3O4/CoFe-LDH (layered double hydroxides) hybrid as a peroxidase mimic for the colorimetric detection of ascorbic acid was first fabricated via a facile two-step route. The resulting Fe3O4/CoFe-LDH hybrid exhibited much higher peroxidase-like catalytic activity for the oxidation of 3,3',5,5'- tetramethylbenzidine (TMB) with H2O2 than the pristine Fe3O4 and CoFe-LDH nanosheets owing to the unique hierarchical architecture containing more exposed active sites and the synergistic effect between Fe3O4 and CoFe-LDH. A sensitively and selectively visual sensor for the determination of ascorbic acid (AA) was successfully constructed based on the reduction effect of AA with enediol group on the formed oxidation of TMB, which exhibited a sensitive response to AA in the range of 0.5 ∼ 10 µM with the detection limit of 0.2 µM. Additionally, the Fe3O4/CoFe-LDH magnetic hybrid could be easily recycled by applying a magnetic field. This work provided a feasible means for the fabrication of magnetic nanomaterials with encouraging prospect in biosensing, environmental monitoring and medical diagnostics.

Recovery of nickel ions from wastewater by precipitation approach using silica xerogel.

A facile route was developed to recover nickel ions from a synthetic wastewater. It involved the use of silica xerogel containing amine in the nickel sulphate solution resulting in the formation of a greenish precipitate. It was found that this precipitate was mostly amorphous Ni(OH)2 spherical aggregate composed of nanosheets. The pH level of the solution was monitored, and it was maintained in the range of 10-10.5 due to the steady release of amine from the xerogel into the waste solution. The prepared silica xerogel would provide a stable environment for the chemical precipitation of metal ions in wastewater during the whole precipitation process. The silica xerogel was collected and reused for two more cycles of recovery. The nickel removal efficiencies (99.34˜99.65%) kept unchanged and higher than those reported earlier. The collected precipitate that contained nickel hydroxide with some residual silica could be utilized as glass colorant.