Fengyu Qu

Hierarchical SnO2 Nanostructures Made of Intermingled Ultrathin Nanosheets for Environmental Remediation, Smart Gas Sensor, and Supercapacitor Applications

In this paper, the hierarchical SnO2 nanostructures (HTNs) were prepared by a facile hydrothermal process. The prepared HTNs were characterized in detail by various analytical techniques that reveal the well-crystallinity with tetragonal rutile structure of SnO2 for the as-prepared material. By detailed experiments, interestingly, it was observed that the shapes and sizes of as-prepared HTNs could be tailored by varying the precursor concentration and reaction time. The synthesized HTNs were used as the efficient photocatalysts for the photocatalytic degradation of methylene blue (MB) under light illumination which showed almost complete degradation (∼99%) of MB dye in 20 min. The observed degradation for MB dye was higher than other commonly used dyes, i.e. methyl orange (MO; 96% in 50 min) and Rhodamine B (RhB; 97% in 40 min.). Further, the prepared HTNs were used as the effective gas sensing material to examine a series of volatile gases, such as ethanol, ammonia, benzene, acetone, toluene, methanol, diethyl ether, and methanol. By the detailed experiments, it was observed that the prepared HTNs exhibited tremendous gas sensing performance toward ethanol. Finally, because of the unique morphology and the fast ion and electron transfer characteristics, the prepared HTNs show excellent supercapacitor performances.

High-performance energy-storage devices based on WO3 nanowire arrays/carbon cloth integrated electrodes

Ordered WO3 nanowire arrays on carbon cloth (WNCC) conductive substrates are successfully prepared by a facile hydrothermal method. The as-prepared samples were characterized by XRD, SEM and TEM and directly functionalized as supercapacitor (SC) and lithium-ion battery (LIB) electrodes without using any ancillary materials such as carbon black or binder. The unique structural features endow them with excellent electrochemical performance. The SCs demonstrate high specific capacitance of 521 F g−1 at 1 A g−1 and 5.21 F cm−2 at 10 A cm−2 and excellent cyclic performance with nearly 100% capacity retention after 2000 cycles at a current density of 3 A g−1. All-solid-state SCs based on the integrated electrodes are also presented, exhibiting high flexibility without obvious performance declination at different bending states. A high capacity of 662 mA h g−1 after 140 cycles at a 0.28 C rate and excellent rate capabilities are also obtained for LIBs due to the unique structures of the integrated electrodes.

Facile synthesis and electrochemical properties of CoMn2O4 anodes for high capacity lithium-ion batteries

Manganese-based oxides have been proven to be promising materials for applications in high voltage and high energy density Li-ion batteries. In this work, by using hydrothermally synthesized β-MnO2 nanorods as the templates, we prepared single-crystalline CoMn2O4 nano/submicrorods with diameters of about 100 nm and lengths up to tens of micrometers. The electrochemical tests showed that the CoMn2O4 products have a reversible capacity of 512 mA h g−1 at a current density of 200 mA g−1 with a coulombic efficiency of 98% after 100 cycles. A specific capacity of about 400 mA h g−1 was obtained even at a current density as high as 1000 mA g−1, exhibiting a high reversibility and a good capacity retention. This study suggests that CoMn2O4 nano/submicrorods are promising anode materials for high performance lithium-ion batteries.

Towards three-dimensional hierarchical ZnO nanofiber@Ni(OH)2 nanoflake core–shell heterostructures for high-performance asymmetric supercapacitors

The design and synthesis of unique core–shell heterostructures for high-performance supercapacitors have exerted a tremendous fascination and have recently attracted intensive attention. In this paper, a three-dimensional ZnO@Ni(OH)2 core–shell heterostructure is controllably synthesized through an electrospinning method combined with a hydrothermal approach. The as-prepared ZnO@Ni(OH)2 heterostructures are investigated for their use as electrodes for supercapacitors, which exhibit excellent electrochemical performances such as ultrahigh specific capacitance (2218 F g−1 at 2 mV s−1) and superior rate capability even at a high scan rate. Moreover, the assembled asymmetric supercapacitor with the as-obtained ZnO@Ni(OH)2 hybrid as the positive electrode and the porous carbon microfibers as the negative electrode yields a high energy density of 57.6 W h kg−1 with a power density of 129.7 W kg−1. Hence, the ZnO@Ni(OH)2 hybrid holds great promise for high-performance energy storage applications.

Hydrothermally Grown ZnO Micro/Nanotube Arrays and Their Properties

We reported the optical and wettability properties of aligned zinc oxide micro/nanotube arrays, which were synthesized on zinc foil via a simple hydrothermal method. As-synthesized ZnO micro/nanotubes have uniform growth directions along the [0001] orientations with diameters in the range of 100–700 nm. These micro/nanotubes showed a strong emission peak at 387 nm and two weak emission peaks at 422 and 485 nm, respectively, and have the hydrophobic properties with a contact angle of 121°. Single ZnO micro/nanotube-based field-effect transistor was also fabricated, which shows typical n-type semiconducting behavior.

Phase-controlled synthesis of polymorphic MnO2 structures for electrochemical energy storage

Manganese dioxide (MnO2) with α-, β- and δ-type structures was controllably synthesized by hydrothermal treatment of an acidic solution of KMnO4 containing different concentrations of ions at 160 °C. The effects of metallic cations, H+ and anions on the structures and morphologies of MnO2 were investigated systematically. The experimental results indicated that cations played a significant part in the formation of MnO2 with different structures. When K+ ions were in competition with H+ ions in solution, different MnO2 structures were formed. α-MnO2 was formed when the amount of K+ was higher than the amount of H+, whereas a higher amount of H+ was favorable for the growth of β-MnO2 structures. When the concentration of K+ was much greater than that of H+, δ-MnO2 was obtained. Possible formation mechanisms are proposed based on a series of controlled experiments. The electrochemical properties of supercapacitors based on different types of MnO2 electrodes were investigated in detail. The specific capacitance measured for MnO2 strongly depended on the crystallographic structure and decreased in the order α-MnO2 > δ-MnO2 > β-MnO2 at a current density of 0.5 A g−1. A specific capacitance of 535 F g−1 was obtained for α-MnO2, but was only 155 F g−1 for β-MnO2. α-MnO2 was more suitable for use as the working electrode at high current densities. Both α- and δ-MnO2 had a poor cycling performance after 3000 cycles, whereas β-MnO2 showed good stability, maintaining a cycling efficiency of 80% after under the same conditions.

Facile synthesis of ultralong MnO2 nanowires as high performance supercapacitor electrodes and photocatalysts with enhanced photocatalytic activities

A simple hydrothermal route was developed for the synthesis of uniform α-MnO2 nanowires using a controllable redox reaction in a MnCl2–KMnO4 aqueous solution system. Electrochemical properties of the resulting products as an electrode were investigated by cyclic voltammetry, chronopotentiometry and electrochemical impedance tests. The electrode can provide a specific capacitance of 180 F g−1 at a current density of 1.0 A g−1. After 2000 cycles, the specific capacitance was maintained above 78%. Besides, the as-synthesized products were also used as the photocatalyst for the photocatalytic degradation of several dye molecules. The results show almost complete degradation (~99%) of Congo red dye molecules in 30 min. Such ultralong MnO2 nanowires are expected to have potential applications in wastewater treatment and energy storage.

Acid degradable ZnO quantum dots as a platform for targeted delivery of an anticancer drug

Efficacious chemotherapy mainly hinges on the tumor-specific delivery of anticancer drugs. Herein we report a successful fabrication of highly photoluminescent and water dispersible ZnO quantum dotsvia a new ligand exchange free strategy. In addition to bioimaging, ZnO QDs have also been evaluated as a platform for targeted and pH responsive intracellular delivery of an anticancer drug. The cancer targeting feature is endowed by conjugating folic acid on to the surface of ZnO–NH2 QDs via an amidation reaction. Doxorubicin (DOX) is then successfully loaded onto the folic acid functionalized ZnO QDs by capitalizing on its marked tendency towards the formation of metal complexes. Drug loaded ZnO-FA QDs remain stable at physiological pH but readily disintegrate in the mildly acidic intracellular environment of cancer cells as validated by a drug release profile, confocal microscopy and a cell-cytotoxicity assay. Compared to the conventional drug nanovector, ZnO-FA QDs themselves manifest a significant therapeutic activity after reaching their targeted site, therefore, combined DOX and ZnO QDs can be more efficacious than either alone. Hence, this approach provides a valuable ZnO QDs-based nanovector that can simultaneously realize targeting, diagnosis, and therapy of cancer cells.

Synthesis of mesoporous carbon fibers with a high adsorption capacity for bulky dye molecules

The mesoporous carbon fibers, of about 400 to 900 nm in diameter, have been synthesized by an electrospinning method with PF resin and PVP as carbon sources and triblock copolymer Pluronic P123 and tetraethyl orthosilicate (TEOS) as mesoporous templates. All materials have large surface areas (1215–2092 m2 g−1), high pore volumes (0.66–1.37 cm3 g−1), and mesoporous structure (with pore sizes of 2.31–2.64, 3.79–3.86, and 5.68–5.70 nm). The adsorption capability of four dyes, methylthionine chloride, methyl orange, rhodamine B, and congo red have been investigated. All the adsorption isotherms fit the typical Langmuir adsorption model well. The mesoporous carbon fibers show high adsorption capacity for these bulky dye molecules. The adsorption amount is mainly determined by the surface area, pore size and the structure/size matching between adsorbent and adsorbate. With the highest BET surface area, C-3.5 (with 3.5 g TEOS) exhibits the highest adsorption amount (1044 mg g−1).

A high energy density all-solid-state asymmetric supercapacitor based on MoS2/graphene nanosheets and MnO2/graphene hybrid electrodes

An asymmetric supercapacitor (ASC) with high energy density is designed using flower-like MoS2 and MnO2 grown on graphene nanosheets (GNS) as the negative and positive electrodes, respectively. In this paper, flower-like MoS2/GNS and MnO2/GNS electrodes were controllably synthesized through a hydrothermal approach. The prepared MoS2/GNS hybrid displays a typical crinkly and rippled structure with ultrathin MoS2 nanosheets uniformly grown on the surface of graphene. Additionally, the MoS2/GNS electrode exhibits superior electrochemical performance, such as high specific capacitance (320 F g−1 at 2 A g−1). The MoS2/GNS electrode holds great promise as a negative electrode for an ASC due to its high specific capacitance and wide operation window in negative potential. The assembled all-solid-state ASC delivers a remarkable energy density of 78.9 W h kg−1 at a power density of 284.1 W kg−1. Thus the MoS2/GNS hybrid is a promising electrode material for next-generation storage systems.