Zhenning Liu

One-Step Synthesis of Single-Layer MnO2 Nanosheets with Multi-Role Sodium Dodecyl Sulfate for High-Performance Pseudocapacitors

A template-free, one-step and one-phase synthesis of single-layer MnO2 nanosheets has been developed via a redox reaction between KMnO4 and sodium dodecyl sulfate (SDS). The successful formation of single-layer MnO2 nanosheets has been confirmed by the characteristic absorption around 374 nm and the typical thickness of ~0.95 nm. The slow redox reaction controlled by the gradual hydrolysis of SDS is found to be the key factor for the successful formation of single-layer nanosheets. SDS not only serves as the precursor of dodecanol to reduce KMnO4 , but also aids the formation of single-layer MnO2 nanosheets as a structure-inducing agent. The resultant single-layer MnO2 nanosheets possess superior specific capacitance, which can be attributed to the extended surface and high porosity of MnO2 nanosheets on the electrode. The MnO2 nanosheets also show excellent durability, retaining 91% of the starting capacitance after 10 000 charge/discharge cycles. Moreover, the symmetric pseudocapacitor based on the synthesized single-layer MnO2 nanosheets exhibits a high specific capacitance, indicating great potential for real energy storage. Therefore, it has been demonstrated for the first time that a single readily available reagent, SDS, can play multiple roles in reducing KMnO4 to conveniently yield single-layer MnO2 nanosheets as a high-performance pseudocapacitive material.

Synthesis of a conjugated porous Co(II) porphyrinylene–ethynylene framework through alkyne metathesis and its catalytic activity study

The development of efficient catalysts for the oxygen reduction reaction (ORR) is crucial for a number of emerging technologies, to counter energy and environment crises. Herein, we report an alkyne metathesis polymerization protocol to synthesize a conjugated microporous metalloporphyrin-based framework containing interconnected ORR catalytic centers. A simple composite of the framework and carbon black shows excellent ORR electrocatalytic activity and specificity through a four-electron reduction mechanism under both acidic and alkaline conditions. The pyrolysis of the catalyst, which is commonly involved in the preparation of ORR catalytic systems, is not necessary. Compared to monomeric metalloporphyrins, the framework shows enhanced ORR catalytic activity, presumably due to the porous and conjugated nature of the framework structure, which allows better exposure of the catalytically active sites, and efficient electron/mass transport. More importantly, the composite electrocatalyst exhibits superior durability and methanol tolerance over commercial Pt/C and metalloporphyrin monomers. Given the highly structural tunability of conjugated microporous polymers, it is conceivable that such a non-pyrolytic approach could enable the systematic exploration of the structure–activity relationship of organic framework-based ORR catalysts and eventually lead to the development of cost-effective replacements for Pt/C.

Macroscopic porous MnO2 aerogels for supercapacitor electrodes

A supercapacitor electrode has been fabricated from macroscopic porous MnO2 aerogels, and has demonstrated an enhanced specific capacitance, a high rate capability and excellent cycling durability. The improvement of supercapacitive performance can be attributed to the macro interconnected channels in the aerogel structure, which can not only facilitate mass transfer and reduce dead volume, but also provide an additional benefit of relieving stress.

Graphene-Supported Silver Nanoparticles for pH-Neutral Electrocatalytic Oxygen Reduction

In order to improve the electrocatalysis of oxygen reduction and reduce the captive cost of microbial fuel cell (MFC), graphene-supported catalyst of silver nanoparticles (Ag/RG) was prepared and its activity toward oxygen reduction reaction (ORR) in pH-neutral condition was examined. The Ag/RG catalyst was prepared by chemical reduction of aqueous silver ions to silver nanoparticles on the surface of reduced graphene (RG), which was obtained from graphene oxide (GO) precursor synthesized via classic Hummers method using graphite as starting material. The results demonstrated that aqueous co-reduction method could yield high-quality Ag/RG catalyst, in which Ag nanoparticles were dispersed on the graphene surface with average diameter of 13 nm as revealed by XRD and TEM examination. The XPS results suggested the presence of polar oxygen-containing functional groups on the graphene sheets could provide the nuclei to form Ag nano-structure. The CV results showed that Ag/RG was active of catalyzing ORR electrochemically in pH-neutral electrolyte. Since Ag costs much less than Pt, Ag/RG is expected to hold remarkable potential as a promising alternative to promote the commercialization of MFC for practical application.

Recent advances in the development of functionalized carbon nanotubes: a versatile vector for drug delivery

Carbon nanotubes (CNTs) possess unique physical and chemical properties and can serve as a platform for transporting a variety of bioactive molecules, such as drugs, proteins, and genes, given appropriate surface modifications. Here, we present an overview of the progress in applying CNTs as therapeutic agent carriers. Drugs can be attached to CNTs either through supramolecular chemistry to form noncovalent assembly or via covalent linkage to the functional groups preinstalled on CNTs. In addition to surface loading, packing of molecules inside the internal cavity of CNTs to protect less stable entities has also been achieved. Besides drugs, the high specific surface area of CNTs can also allow the installation of multiple molecules with different functions, e.g. target recognition and optical imaging, simultaneously to achieve synergistic effects. The drug release process tends to be gradual and sustained after being attached to CNTs, and could be tuned by various factors, such as pH, diameter of CNTs, and target recognition. The content throughout this review is mainly focused on the different protocols of loading drugs onto or into CNTs as well as how to control the drug release.

One-pot synthesis of Au@TiO2 yolk-shell nanoparticles with enhanced photocatalytic activity under visible light

Natural biological systems often use hollow structures to decrease reflection and achieve high solar light utilization. Herein, bio-inspired Au@TiO2 yolk-shell nanoparticles (NPs) have been designed to combine the advantages of noble metal coupling and hollow structures, and subsequently synthesized via a facile one-pot hydrothermal approach. The Au@TiO2 yolk-shell NPs not only exhibit reduced reflectance by multiple reflections and scattering within the hollow NPs, but also show enhanced photocatalytic activity in Rhodamine B (RhB) degradation by simultaneously improving light harvesting, charge separation and reaction site accessibility. Specifically, compared to the commercial TiO2 (P25), Au/TiO2 hybrid and Au@TiO2 core-shell NPs, the Au@TiO2 yolk-shell NPs demonstrate lower reflectance over a broader range and superior photocatalytic activity with more than 98.1% of RhB decomposed within 4h under visible light. The bio-inspired nanostructure, as well as the facile and scalable fabrication approach, will open a new avenue to the rational design and preparation of efficient photocatalysts for pollutant removal.

Controllable growth of Au@TiO2 yolk–shell nanoparticles and their geometry parameter effects on photocatalytic activity

Yolk–shell nanoparticles (NPs) have attracted significant interest due to their decreased reflection and high solar light utilization. Herein, we precisely and independently controlled the geometrical parameters of the cavity diameter, shell thickness, and Au core diameter in the Au@TiO2 yolk–shell NPs using the hydrothermal method. Furthermore, the photocatalytic activities of these samples were systematically evaluated by the photocatalytic degradation of Rhodamine B (RhB). Smaller cavity size, thinner TiO2 shell, and medium AuNP diameter were found to facilitate more efficient photocatalysis. Overall, Au@TiO2 yolk–shell NPs with a cavity diameter of 121 nm, Au core diameter of 50 nm, and shell thickness of 26 nm demonstrated highest photocatalytic activity. These results are important for understanding the effects of the geometrical parameters of Au@TiO2 yolk–shell NPs on the photocatalytic performance and for designing novel yolk–shell nanostructures.

Bioinspired self-standing macroporous Au/ZnO sponges for enhanced photocatalysis

A self-standing macroporous noble metal-zinc oxide (ZnO) sponge of robust 3D network has been fabricated through in-situ growth method. The key to the construction of the bioinspired sponge lies in the choice of commercial polyurethane sponge (CPS) with interconnected and junction-free macroporous structure as the skeleton to support Au/ZnO nanorods (Au/ZnONRs). The resultant Au/ZnO/CPS not only exhibits hierarchical structures representing physical features of CPS, but also demonstrates durable superior photocatalytic activity and hydrogen generation capability. In addition, we have adopted various irradiations to investigate the effect of UV light and visible light on the photocatalytic performance of Au/ZnO/CPS individually. In detail, the photocatalytic properties of Au/ZnO/CPS and ZnO/CPS have been monitored and compared under irradiations of different wavelengths (200-1100, 350-780, 200-420 and 420-780 nm) for 90 min to reveal the effect of irradiation wavelength on the activity of photocatalysts. A possible mechanism between irradiation wavelength and photocatalytic degradation efficiency is proposed. The facile in-situ growth approach presented herein can be easily scaled up, affording a convenient method for the preparation of self-standing 3D macroporous materials, which holds great potential for the application in both environmental purification and solar-to-hydrogen energy conversion.

MnO2 aerogels for highly efficient oxidative degradation of Rhodamine B

High-efficiency oxidative degradation of Rhodamine B (RhB) is demonstrated with manganese dioxide (MnO2) aerogels. The MnO2 aerogels are fabricated by an ice-templating approach from MnO2 nanosheet colloids, which have been synthesized by redox reaction between MnCl2 and KMnO4 in sodium dodecyl sulfate (SDS) aqueous solution. The obtained self-standing MnO2 aerogels show a three dimensional (3D) structure of a percolating network with open pores ranging from hundreds of nanometers to tens of micrometers. The oxidative degradation efficiency of MnO2 aerogels is compared with ultrathin MnO2 nanosheets and commercial MnO2 powder, and the effects of concentration of MnO2 aerogels as well as pH on the degradation efficiency are also investigated. Typically, the MnO2 aerogels show an excellent oxidative degradation performance of RhB (97.6% removed within 10 min) in acidic solution (pH 2.5), which can be attributed to the large open pores and high surface areas of the aerogels. Furthermore, the MnO2 aerogels also exhibit good capability in the degradation of methylene blue (MB) under acidic conditions. It is believed that MnO2 aerogels hold great promise for future applications in organic pollutant removal with virtues of high efficiency, low cost and environmental friendliness.

ZnO nanodisks decorated with Au nanorods for enhanced photocurrent generation and photocatalytic activity

A facile approach for the preparation of Au nanorod/ZnO nanodisks (AuNR/ZnONDKs) through in situ nucleation and growth of ZnO in AuNR colloidal solution was developed. This is the first report of AuNRs modified on the ZnO surface. Furthermore, the aspect ratios of AuNRs in nanohybrids of AuNR/ZnONDKs were also tuned to achieve tunable and broad LSPR bands for an optimized photocatalytic performance. All of the resultant AuNR/ZnONDK nanohybrids with exposed AuNRs exhibit much higher photocatalytic activity and photocurrent generation compared to commercial ZnO (C-ZnO). In particular, AuNR-707/ZnONDKs express a swift and steady photocurrent of 0.33 mA cm−2, which is 16.5 times higher than the photocurrent generated by C-ZnO. The facile approach presented here opens up a new avenue for the rational design and preparation of high-performance photocatalysts for the future applications in both environmental purification and photoelectric conversion.