Zuowan Zhou

Antimicrobial Mechanism Based on H2O2 Generation at Oxygen Vacancies in ZnO Crystals

The production of H2O2 has been taken for a crucial reason for antimicrobial activity of ZnO without light irradiation. However, how the H2O2 generates in ZnO suspension is not clear. In the present work, the comparatively detections on three kinds of ZnO, tetrapod-like ZnO whiskers (t-ZnO), nanosized ZnO particles (n-ZnO), and microsized ZnO particles (m-ZnO), showed that the antimicrobial activity of ZnO was correlated with its production of H2O2. Oxygen vacancy (V(O)) in the surface layer of ZnO crystals determined by XPS indicated that it was quite probably involved in the production of H2O2. To validate the role of V(O), the concentration of VO in t-ZnO was adjusted by heat-treatment under the atmospheres of H2, vacuum, and O2, respectively, and the H2O2 production and antimicrobial effect were detected. Consistently, the t-ZnO treated in H2, which possessed the most V(O) in its crystal, produced the most H2O2 and displayed the best antimicrobial activity. These results provide the basis for developing a more detailed mechanism for H2O2 generation catalyzed by ZnO and for taking greater advantage of this type of antimicrobial agent.

A simple strategy to achieve very low percolation threshold via the selective distribution of carbon nanotubes at the interface of polymer blends

Selective distribution of carbon nanotubes (CNTs) at the interface of immiscible polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) is achieved via a combination of adding maleic anhydride grafted ABS (ABS-g-MA) and using an appropriate processing procedure. The composite shows a much lower percolation threshold of 0.05 wt%. The value obtained here is the smallest percolation threshold reported so far, comparing with those in the literature.

Hierarchical ZnO architectures consisting of nanorods and nanosheets prepared via a solution route for photovoltaic enhancement in dye-sensitized solar cells

ZnO nanorod–nanosheet (NR–NS) hierarchical architectures grown on fluorine-doped tin oxide (FTO) coated glass substrates were prepared via a two-step solution route, which involved the growth of the ZnO nanorods on the FTO substrate, followed by a secondary growth of the ZnO nanosheet on the as-grown backbone. The characterization showed that the nanosheets composed of very small nanoparticles underwent oriented attachment by closely covering the nanorods, resulting in an enhancement of the internal surface area. The ZnO nanostructure films were applied to dye-sensitized solar cells (DSSCs). The photovoltaic results demonstrated that the short circuit current density and the energy conversion efficiency of the NR–NS hierarchical architecture DSSCs were 4.806 mA cm−2 and 1.13%, respectively, which was almost two times higher than those of nanorod only arrays. The dye desorption result and diffused reflectance spectra indicated that the dye absorption amount and light scattering within the NR–NS hierarchical architecture photoanode were higher than those for the nanorod photoanode. The significant improvement was a consequence of the enhancement of dye loading and light scattering within the NR–NS hierarchical architecture photoanode.

Gas-Induced Formation of Cu Nanoparticle as Catalyst for High-Purity Straight and Helical Carbon Nanofibers

The facile preparation of high-purity carbon nanofibers (CNFs) remains challenging due to the high complexity and low controllability in reaction. A novel approach using gas-induced formation of Cu crystals to control the growth of CNFs is developed in this study. By adjusting the atmospheric composition, controllable preparation of Cu nanoparticles (NPs) with specific size and shape is achieved, and they are further used as a catalyst for the growth of straight or helical CNFs with good selectivity and high yield. The preparation of Cu NPs and the formation of CNFs are completed by a one-step process. The inducing effect of N(2), Ar, H(2), and C(2)H(2) on the formation of Cu NPs is systematically investigated through a combined experimental and computational approach. The morphology of CNFs obtained under different conditions is rationalized in terms of Cu NP and CNF growth models. The results suggest that the shapes of CNFs, namely, straight or helical, depend closely on the size, shape, and facet activity of Cu NPs, while such a gas-inducing method offers a simple way to control the formation of Cu NPs.

Growth of Fe3O4 nanosheet arrays on graphene by a mussel-inspired polydopamine adhesive for remarkable enhancement in electromagnetic absorptions

Fe3O4 nanosheet arrays grown on both surfaces of graphene can be achieved by combining a mussel-inspired polydopamine adhesive and ethylene glycol-mediated process. Polydopamine is utilized not only as an efficient linker molecule that binds Fe3O4 nanosheets to the graphene, but also as a carbon source during heat treatment to yield the three dimensional (3D) graphene@carbon@Fe3O4 nanosheet arrays architecture. After the growth of Fe3O4 nanosheet arrays with accompanying reduction of graphene oxide into graphene, the 3D architecture exhibits outstanding microwave absorption properties. The simulated value of maximum reflection loss can reach −52.8 dB at 9.5 GHz with a sample thickness of 2.7 mm. The improved absorption capacity arises from the synergy of dielectric loss and magnetic loss, as well as the enhancement of multiple interfaces among graphene, carbon and Fe3O4 nanosheets. Furthermore, the synthesis strategy presented here can be expended as a facile approach to synthesizing related graphene-based 3D nanostructures for functional design and applications.

Green synthesis of hybrid graphene oxide/microcrystalline cellulose aerogels and their use as superabsorbents

In this work, we developed a green synthesis method to prepare the hybrid aerogels containing graphene oxide (GO) and microcrystalline cellulose (MCC) using lithium bromide (LiBr) aqueous solution as the solvent, which insured the complete dissolution of MCC. The interaction between GO and MCC was investigated through different methods The results demonstrate that there is a strong interaction between GO and MCC molecules, which promotes the exfoliation of GO in the hybrid aerogels. The hybrid GO/MCC aerogels exhibit typical three dimensional porous structure and the pore morphology can be well adjusted by changing the content of GO. The adsorption ability of the hybrid aerogels was measured using methylene blue (MB) as an adsorbate. The results show that the adsorption ability of GO per unit mass is greatly enhanced compared with the pure GO aerogel, especially at relatively low GO content the adsorption amount of GO per unit mass is enhanced up to 2630mg/g. Further results demonstrate that the hybrid GO/MCC aerogels still obey the pseudo-second-order adsorption model, which is similar to that of the pure GO aerogel. The mechanism for the amplified adsorption ability of GO in the hybrid GO/MCC aerogels is then analyzed.

First-principles study of static polarizability, first and second hyperpolarizabilities of small-sized ZnO clusters

The static linear and nonlinear optical properties of (ZnO)N clusters of N= 2-12 are studied using finite field approach within the framework of density functional theory. Most of these clusters feature ring or cage structures in the specific size range, differing much from the wurtzite structure of bulk ZnO. The low-lying isomers with various structures possess remarkably different properties. The effect of ring structure, cluster stability, HOMO-LUMO gap, covalent/ionic bonding, etc., on the dipole moment, polarizability, first and second hyperpolarizabilites is discussed. Both the polarizability and second hyperpolarizability exhibit distinct size dependences, reflecting clearly the structural transition when the cluster grows. Our study reveals that the linear and nonlinear optical properties of ZnO clusters vary a lot in the size range studied, as a result of their structural diversity at small sizes.

Trapping carbon nanotubes at the interface of a polymer blend through adding graphene oxide: a facile strategy to reduce electrical resistivity

Graphene oxide (GO) and carbon nanotubes (CNTs) were simultaneously introduced into an immiscible polymer blend. The dispersion of fillers and the electrical resistivity of the composites were studied. The results first showed that more CNTs were trapped at the blend interface by GO. Consequently, a remarkable decrease of electrical resistivity by about 7 orders of magnitude was achieved even if the concentration of CNTs was only 0.1 wt%. Further results showed that the quaternary composites exhibited much smaller percolation threshold (0.06 wt%) compared with the ternary composites containing only CNTs (0.24 wt%).

Synergistic Enhancement of Microwave Absorption Using Hybridized Polyaniline@helical CNTs with Dual Chirality

In this study, we designed a dual-chirality hierarchical structure to achieve a synergistically enhanced effect in microwave absorption via the hybridization of nanomaterials. Herein, polyaniline (PANi) nanorods with tunable chirality are grown on helical carbon nanotubes (HCNTs), a typical nanoscale chiral structure, through in situ polymerization. The experimental results show that the hierarchical hybrids (PANi@HCNTs) exhibit distinctly dual chirality and a significant enhancement in electromagnetic (EM) losses compared to those of either pure PANi or HCNTs. The maximum reflection loss of the as-prepared hybrids can reach -32.5 dB at 8.9 GHz. Further analysis demonstrates that combinations of chiral acid-doped PANi and coiled HCNTs with molecular and nanoscale chirality lead to synergistic effects resulting from the dual chirality. The so-called cross-polarization may result in additional interactions with induced EM waves in addition to multiscaled relaxations from functional groups and interfacial polarizations, which can benefit EM absorption.

Super toughened immiscible polycarbonate/poly(L-lactide) blend achieved by simultaneous addition of compatibilizer and carbon nanotubes

Polycarbonate/poly(L-lactide) (PC/PLLA) blend exhibits great potential application in several fields, including package, toy, electronic element and automobile. However, the poor mechanical properties of the immiscible PC/PLLA blend restrict its application. In this work, a compatibilizer maleic anhydride grafted ethylene–octene copolymer (EOR-g-MAH) and functionalized carbon nanotubes (F-CNTs) were introduced into the immiscible PC/PLLA blend by simple melt-compounding processing. Mechanical property measurements showed that even at low environmental temperature (0 °C), the blend composites exhibited excellent fracture toughness, e.g. 40.9 ± 2.1 kJ m−2 at F-CNT content of 2 wt%. To better understand the toughening mechanism, the morphologies of the blend composites and the dispersion of F-CNTs and the rheological properties were systematically investigated. The results showed that with the combined effects of EOR-g-MAH and F-CNTs, the decreased PLLA particles were achieved. Most of F-CNTs selectively located in the PC matrix and some F-CNTs entered into PLLA particles. Specifically, at relatively high content (>2 wt%), F-CNTs formed percolated network structure. Then, the toughening mechanism was proposed on the basis of the morphology evolution, the formation of F-CNT network structure and the impact-fractured surface morphologies. This work demonstrated that even for the immiscible polymer blend, the super toughened blend composites could be achieved by the combined effects of compatibilizer and carbon nanotubes, and therefore it provides an alternative strategy for largely improving the fracture toughness of immiscible polymer blends.