Frontiers of Materials Science (v.12, #1)

Graphene: from synthesis to engineering to biosensor applications by Jagpreet Singh; Aditi Rathi; Mohit Rawat; Manoj Gupta (1-20).
Graphene is a fascinating material of recent origin whose first isolation was being made possible through micromechanical cleavage of a graphite crystal. Owing to its fascinating properties, graphene has garnered significant attention in the research community for multiple applications. A number of methods have been employed for the synthesis of single-layer and multi-layer graphene. The extraordinary properties of graphene such as its Hall effect at room temperature, high surface area, tunable bandgap, high charge mobility and excellent electrical, conducting and thermal properties allow for the development of sensors of various types and also opened the doors for its use in nanoelectronics, supercapacitors and batteries. Biological aspects of graphene have also been investigated with particular emphasis on its toxicity and drug delivery. In this review, many of the salient aspects of graphene, such as from synthesis to its applications, primarily focusing on sensor applications which are of current interest, are covered.
Keywords: graphene; nanoelectronics; Hall effect; tunable bandgap; supercapacitors; sensors; catalysis

Heterogeneous Fenton-like discoloration of methyl orange using Fe3O4/MWCNTs as catalyst: combination mechanism and affecting parameters by Huan-Yan Xu; Yuan Wang; Tian-Nuo Shi; Hang Zhao; Qu Tan; Bo-Chao Zhao; Xiu-Lan He; Shu-Yan Qi (21-33).
Multi-walled carbon nanotubes (MWCNTs) can act not only as a support for Fe3O4 nanoparticles (NPs) but also as a coworker with synergistic effect, accordingly improving the heterogeneous Fenton-like efficiency of Fe3O4 NPs. In this study, Fe3O4 NPs were in situ anchored onto MWCNTs by a moderate co-precipitation method and the as-prepared Fe3O4/MWCNTs nanocomposites were employed as the highly efficient Fenton-like catalysts. The analyses of XRD, FTIR, Raman, FESEM, TEM and HRTEM results indicated the formation of Fe3O4 crystals in Fe3O4/MWCNTs nanocomposites prepared at different conditions and the interaction between Fe3O4 NPs and MWCNTs. Over a wide pH range, the surface of modified MWCNTs possessed negative charges. Based on these results, the possible combination mechanism between Fe3O4 NPs and MWCNTs was discussed and proposed. Moreover, the effects of preparation and catalytic conditions on the Fenton-like catalytic efficiency were investigated in order to gain further insight into the heterogeneous Fenton-like reaction catalyzed by Fe3O4/MWCNTs nanocomposites.
Keywords: MWCNTs; Fe3O4 NPs; Fenton-like catalyst; combination mechanism; affecting parameters

Heterogeneous Fenton-like discoloration of methyl orange using Fe3O4/MWCNTs as catalyst: kinetics and Fenton-like mechanism by Huan-Yan Xu; Yuan Wang; Tian-Nuo Shi; Hang Zhao; Qu Tan; Bo-Chao Zhao; Xiu-Lan He; Shu-Yan Qi (34-44).
The kinetics and Fenton-like mechanism are two challenging tasks for heterogeneous Fenton-like catalytic oxidation of organic pollutants. In this study, three kinetic models were used for the kinetic studies of Fe3O4/MWCNTs-H2O2 Fenton-like reaction for MO degradation. The results indicated that this reaction followed the first-order kinetic model. The relationship of reaction rate constant and temperature followed the Arrhenius equation. The activation energy and frequency factor of this system were calculated as 8.2 kJ·mol-1 and 2.72 s-1, respectively. The quantifications of Fe ions dissolution and •OH radicals generation confirmed that the homogeneous and heterogeneous catalyses were involved in Fe3O4/MWCNTs-H2O2 Fenton-like reaction. The reaction rate constant was closely related with Fe ions dissolution and •OH radicals generation. Fe3O4/MWCNTs nanocomposites had typical ferromagnetic property and could be easily separated from solution by an external magnet after being used. Furthermore, Fe3O4/MWCNTs nanocomposites exhibited good stability and recyclability. Finally, the Fenton-like mechanisms on homogeneous and heterogeneous catalyses were described.
Keywords: MWCNTs; Fe3O4 NPs; kinetics; •OH radicals; Fenton-like mechanism

Hierarchical nano-on-micro copper with enhanced catalytic activity towards electro-oxidation of hydrazine by Xiaodong Yan; Yuan Liu; Kyle R. Scheel; Yong Li; Yunhua Yu; Xiaoping Yang; Zhonghua Peng (45-52).
The electrochemical properties of catalyst materials are highly dependent on the materials structure and architecture. Herein, nano-on-micro Cu electrodes are fabricated by growing Cu microcrystals on Ni foam substrate, followed by introducing Cu nanocrystals onto the surface of the Cu microcrystals. The introduction of Cu nanocrystals onto the surface of Cu microcrystals is shown to dramatically increase the electrochemically active surface area and thus significantly enhances the catalytic activity of the catalyst electrode towards electro-oxidation of hydrazine. The onset potential (-1.04 V vs. Ag/AgCl) of the nano-on-micro Cu electrode is lower than those of the reported Cu-based catalysts under similar testing conditions, and a current density of 16 mA·cm-2, which is 2 times that of the microsized Cu electrode, is achieved at a potential of -0.95 V vs. Ag/AgCl. Moreover, the nano-on-micro Cu electrode demonstrates good long-term stability.
Keywords: electrocatalysis; hydrazine oxidation; copper; nanocrystal; hierarchical architecture

Mo-doped Na3V2(PO4)3@C composites for high stable sodium ion battery cathode by Xiaoxiao Wang; Wanwan Wang; Baichuan Zhu; Fangfang Qian; Zhen Fang (53-63).
NASICON-type Na3V2(PO4)3 (NVP) with superior electrochemical performance has attracted enormous attention with the development of sodium ion batteries. The structural aggregation as well as poor conductivity of NVP hinder its application in high rate perforamance cathode with long stablity. In this paper, Na3V2-x Mo x (PO4)3@C was successfully prepared through two steps method, including sol-gel and solid state thermal reduction. The optimal doping amount of Mo was defined by experiment. When x was 0.15, the Na3V1.85Mo0.15(PO4)3@C sample has the best cycle performance and rate performance. The discharge capacity of Na3V1.85Mo0.15(PO4)3@C could reach 117.26 mA·h·g-1 at 0.1 C. The discharge capacity retention was found to be 94.5% after 600 cycles at 5 C.
Keywords: storage materials; doping; electrochemical reactions; Na ion battery

In this work three different mesoporous TiO2 film electrodes were prepared and used for the immobilization of Cytochrome c (Cyt-c). Films prepared via a standard sol-gel route (SG-films) were compared with commercially available benchmark nanotitania materials, namely P25 Degussa (P25-films) and Dyesol nanopaste (Dyesol films). Their properties, film deposition characteristics and their abilities to adsorb protein molecules in a stable and functional way were examined. We investigated whether it is possible, rather than preparing TiO2 films using multistep, lengthy and not always reproducible sol-gel procedures, to use commercially available nanotitania materials and produce reproducible films faster that exhibit all the properties that make TiO2 films ideal for protein immobilization. Although these materials are formulated primarily for dye-sensitized solar cell applications, in this study we found out that protein immobilization is facile and remarkably stable on all of them. We also investigated their electrochemical properties by using cyclic voltammetry and spectroelectrochemistry and found out that not only direct reduction of Fe(III)-heme to Fe(II)-heme of immobilized Cyt-c was possible on all films but that the adsorbed protein remained electroactive.
Keywords: TiO2 films; spectroelectrochemistry; cyclic voltammetry; Cytochrome c

Enhancement of thermal properties of conventional heat transfer fluids has become one of the important technical challenges. Since nanofluids offer a promising help in this regard, development of simpler and hassle free routes for their synthesis is of utmost importance. Synthesis of nanofluids using a hassle free route with greener chemicals has been reported. The single-step chemical approach reported here overcomes the drawbacks of the two-step procedures in the synthesis of nanofluids. The resulting Newtonian nanofluids prepared contained cuboctahedral particles of cuprous oxide and exhibited a thermal conductivity of 2.852 W·m-1·K-1. Polyvinylpyrrolidone (PVP) used during the synthesis acted as a stabilizing agent rendering the nanofluid a stability of 9 weeks.
Keywords: cuprous oxide; nanofluids; thermal conductivity; viscosity

In the present study, β-cyclodextrin-grafted chitosan nanoparticles (β-CD-g-CS NPs) were prepared using a new ionic gelation strategy involving a synergistic effect of NaCl (150 mmol/L), 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES, 10 mmol/L), and water bath sonication. This new strategy afforded smaller and more monodisperse β-CD-g-CS NPs vs. the classical ionic gelation method. New HA/β-CD-g-CS NPs were also prepared using the above-mentioned strategy by adding hyaluronic acid (HA) to the β-CD-g-CS copolymer at different weight ratios until the ZP values conversion. The best result was obtained with the weight ratio of w(HA):w(β-CD-g-CS) = 2:1 and furnished new spherical and smooth HA/β-CD-g-CS NPs. Furthermore, the stability of β- CD-g-CS NPs and HA/β-CD-g-CS NPs at 4°C in physiological medium (pH 7.4) was compared for 3 weeks period and showed that HA/β-CD-g-CS NPs were more stable all maintaining their monodispersity and high negative ZP values compared to β-CD-g-CS NPs. Finally, preliminary study of HA/β-CD-g-CS NPs as carrier for the controlled release of the anticancer drug doxorubicin was investigated. These new HA/β-CD-g-CS NPs can potentially be used as drug delivery and targeting systems for cancer treatment.
Keywords: β-cyclodextrin-grafted chitosan; hyaluronic acid; ionic gelation; drug delivery; physicochemical parameters control

Evaluation of hydrogels for soft tissue adhesives in vitro and in vivo analyses by Liu Yuan; Wenshuai Fan; Linyingjun Han; Changan Guo; Zuoqin Yan; Meifang Zhu; Xiumei Mo (95-104).
In this study, natural materials (sodium alginate, dextran, gelatin and carboxymethyl chitosan) were modified to get aldehyde components and amino components. Upon mixing the two-component solutions together, four kinds of Schiff base hydrogels formed successfully within 5-300 s and could seal the wound tissue. The cytotoxicity tests of hydrogel extraction solution confirmed that the hydrogels are nontoxic materials. The adhesive ability was evaluated in vivo by measuring the adhesive strength after sealing the skin incisions on the back of rats. All the hydrogels showed higher adhesive strength than that of commercial fibrin glue and the blank control. The histological staining observation by hematoxylin and eosin staining (HE) and Masson’s trichrome staining (MTC) methods suggested that the hydrogels had good biocompatibility and biodegradation in vivo. They have only normal initial inflammation to skin tissue and could improve the formation of new collagen in the incision section. So, the prepared hydrogels were both safe and effective tissue adhesive, which had the great potentials to be used as skin tissue adhesive.
Keywords: Schiff’s base; injectable; hydrogels; tissue adhesive