Frontiers of Materials Science (v.12, #4)

Rare-earth coordination polymer micro/nanomaterials: Preparation, properties and applications by Honghong Zou; Lei Wang; Chenghui Zeng; Xiaolei Gao; Qingqing Wang; Shengliang Zhong (327-347).
Rare-earth coordination polymers (RECPs), as a family member of coordination polymers (CPs), have been prepared and studied widely. Thanks to their characteristic properties and functions, RECPs have already been used in various application fields ranging from catalysis to drug delivery. In recent years, CPs with tunable morphologies and sizes have drawn increasing interest and attractive attention. This review presents the recent research progress of RECP micro/nanomaterials, and emphasizes the preparation, properties and broad applications of these fascinating materials.
Keywords: coordination polymer; metal–organic framework; rare earth; nanomaterials

Fe nanowire array with strong shape anisotropy was employed as the soft phase in Nd-Fe-B based nanocomposites. The effects of the Fe nanowire distribution on magnetic properties of the nanocomposites were investigated by micromagnetic simulation. The results indicate that the shape anisotropy of Fe wires added in the same direction as the uniaxial magnetocrystalline anisotropy of the hard phase cannot increase the coercivity of the nanocomposite. When the nanowires are distributed perpendicular to the easy axis of the hard phase, the shape anisotropy of soft phase can retard the moments from rotating to the full reversed direction, leading to enhanced coercivity. In addition, with increasing the nanowire diameter, the coercivity of the nanocomposite decreases, but the dipolar interaction shows different roles in magnetic reversal of nanocomposite for different distributions of nanowires. The current results suggest that the coercivity of the Nd2Fe14B/α-Fe nanocomposite can be enhanced by introducing the soft magnetic nanowire array with the diameter less than the exchange length and with the long axis along the direction other than the easy axis of hard phase.
Keywords: Nd2Fe14B/α-Fe nanocomposite; micromagnetic simulation; Fe nanowires; shape anisotropy; exchange coupling

In pursuing excellent supercapacitor electrodes, we designed a series of MoS2/CoS2 composites consisting of flower-liked MoS2 and octahedron-shaped CoS2 through a facile one-step hydrothermal method and investigated the electrochemical performance of the samples with various hydrothermal time. Due to the coupling of two metal species and a big amount of well-developed CoS2 and MoS2, the results indicated that the MoS2/CoS2 composites electrodes exhibited the best electrochemical performance with a large specific capacitance of 490 F/g at 2 mV/s or 400 F/g at 10 A/g among all samples as the hydrothermal time reached 48 h (MCS48). Furthermore, the retention of MCS48 is 93.1% after 10000 cycles at 10 A/g, which manifests the excellent cycling stability. The outstanding electrochemical performance of MCS48 indicates that it could be a very promising and novel energy storage material for supercapacitors in the future.
Keywords: MoS2/CoS2 composites; hydrothermal time; electrochemical properties; supercapacitors

Construction of yolk–shell Fe3O4@C nanocubes for highly stable and efficient lithium-ion storage by Ruiping Liu; Chao Zhang; Xiaofan Zhang; Fei Guo; Yue Dong; Qi Wang; Hanqing Zhao (361-367).
The yolk-shell Fe3O4@C nanocubes were successfully synthesized through carbothermic reduction process from carbon-coated α-Fe2O3 precursor. The results show that the yolk-shell Fe3O4@C nanocubes are uniformly coated with a thin carbon layer, and a clear cavity about 150 nm in width between Fe3O4 core and carbon shell are formed due to the volume shrinkage during the reduction treatment. The obtained yolk-shell Fe3O4@C nanocubes exhibit excellent cycling stability (the discharge capacity is 709.7 mA·h/g after 100 cycles at the current density of 0.1C) and rate performance (1023.4 mA·h/g at 0.1C, 932.5 mA·h/g at 0.2C, 756.1 mA·h/g at 0.5C, 405.6 mA·h/g at 1C, and 332.3 mA·h/g at 2C, and more importantly, when the current density finally backs to 0.1C, a capacity of 776.8 mA·h/g can be restored). The outstanding lithium storage properties may be attributed to the unique yolk-shell structures.
Keywords: Fe3O4 ; yolk–shell; nanocube; anode; lithium storage

The counter electrode (CE) prominence in dye-sensitized solar cells (DSSCs) is undisputed with research geared towards replacement of Pt with viable substitutes with exceptional conductivity and catalytic activity. Herein, we report the replaceable CE with better performance than that of Pt-based electrode. The chemistry between the graphene oxide and ice templates leads to cellular formation of reduced graphene oxide that achieves greater conductivity to the CE. The simultaneous growth of active edge-oriented MoS2 on the CE through CVD possesses high reflectivity. High reflective MoS2 trends to increase the electroactivity by absorbing more photons from the source to dye molecules. Thus, the synergistic effect of two materials was found to showcase better photovoltaic performance of 7.6% against 7.3% for traditional platinum CE.
Keywords: dye-sensitized solar cell; graphene oxide; molybdenum disulfide; counter electrode

Electrospun titania fibers by incorporating graphene/Ag hybrids for the improved visible-light photocatalysis by Zhongchi Wang; Gongsheng Song; Jianle Xu; Qiang Fu; Chunxu Pan (379-391).
A novel graphene/Ag nanoparticles (NPs) hybrid (prepared by a physical method (PM)) was incorporated into electrospun TiO2 fibers to improve visible-lightdriven photocatalytic properties. The experimental study revealed that the graphene/Ag NPs (PM) hybrid not only decreased the bandgap energy of TiO2, but also enhanced its light response in the visible region due to the surface plasmon resonance (SPR) effect. In addition, compared with those of TiO2 fibers incorporating the graphene/Ag NPs hybrid (prepared by a chemical method (CM)), TiO2-graphene/Ag NPs (PM) fibers exhibited a higher surface photocurrent density and superior photocatalytic performance, i.e., the visible-light-driven photocatalytic activity was enhanced by 2 times. The main reasons include a lower surface defect density of the graphene/Ag NPs (PM) hybrid, a smaller particle size (10 nm) and a higher dispersity of Ag NPs, which promote the rapid transfer of photoexcited charge carriers and inhibit the recombination of photogenerated electrons and holes. It is expected that this kind of ternary electrospun fibers will be a promising candidate for applications in water splitting, solar cells, CO2 conversion and optoelectronic devices, etc.
Keywords: TiO2–graphene/Ag; electrospining; photocatalysis

Nitrogen ion irradiation effect on enhancing photocatalytic performance of CdTe/ZnO heterostructures by Yazi Wang; Wei Li; Yimeng Feng; Shasha Lv; Mingyang Li; Zhengcao Li (392-404).
To deal with the increasingly deteriorating environment problems, more and more harsh requirements are put forward for photocatalysis application. Building semiconductor heterostructures has been proven to be an efficient way to enhance photocatalytic performance. A kind of CdTe/ZnO heterostructures were synthesized by a hydrothermal and successive ionic layer absorption and reaction (SILAR) method and achieved obviously efficient photocatalytic performance. Moreover, after the N ion irradiation treatment, the photocatalytic activity was further enhanced, which can be ascribed to the introduction of oxygen vacancy defects. The photocatalytic performance enhancement mechanism by coupling constructing heterostructures and ion irradiation are further studied to give us an overall understanding on ZnO nanowires.
Keywords: N ion irradiation; CdTe/ZnO heterostructures; photocatalytic performance

Enhanced visible-light-driven photocatalysis of Bi2YO4Cl heterostructures functionallized by bimetallic RhNi nanoparticles by Palepu Teja Ravindar; Vidya Sagar Choppella; Anil Kumar Mokshagundam; M. Kiruba; Sunil G. Babu; Korupolu Raghu Babu; L. John Berchmans; Gosipathala Sreedhar (405-414).
Bismuth-based Sillen-Aurivillius compounds are being explored as efficient photocatalyst materials for the degradation of organic pollutants due to their unique layered structure that favours effective separation of electron-hole pairs. In this work, we synthesized Sillen-Aurivillius-related Bi2YO4Cl with the bandgap of 2.5 eV by a simple solid-state reaction and sensitized with rhodium nickel (RhNi) nanoparticles (NPs) to form the RhNi/Bi2YO4Cl heterostructure. Photocatalytic activities of BiOCl, Bi2YO4Cl and the RhNi/Bi2YO4Cl heterostructure were examined for the degradation of rhodamine- 6G under visible-light illumination. Results demonstrated that the photocatalytic dye degradation efficiency of RhNi/Bi2YO4Cl heterostructures is higher than those of BiOCl and Bi2YO4Cl, attributed to the synergistic molecular-scale alloying effect of bimetallic RhNi NPs. The plausible mechanism for the degradation of rhodamine-6G and the effective electron-hole pair utilization mechanism were discussed.
Keywords: BiOCl; Bi2YO4Cl; RhNi catalyst; rhodamine-6G; photocatalysis

Synthesis of sillenite-type Bi36Fe2O57 and elemental bismuth with visible-light photocatalytic activity for water treatment by Chuan Deng; Xianxian Wei; Ruixiang Liu; Yajie Du; Lei Pan; Xiang Zhong; Jianhua Song (415-425).
With Fe(NO3)3·9H2O and Bi(NO3)3·5H2O as raw materials, different sillenite-type compounds and elemental bismuth were prepared by a facile one-pot solvothermal method using H2O, C2H5OH, (CH2OH)2 and C3H8O3 as solvents, respectively. The structure, morphology, elemental compositions and properties of samples were examined by XRD, SEM, TEM, ICP, XPS, N2 adsorption and desorption, UV-vis DRS and PL. The photocatalytic activities of different samples were evaluated by the photodegradation of RhB under visible-light irradiation (λ > 400 nm), and results show that Bi36Fe2O57 prepared using C2H5OH as the solvent owns the optimum performance. In order to explore the reaction mechanism, an additional experiment was designed to investigate the main active species during the photodegradation process via dissolving different trapping agents in the reaction solution before light irradiation. The results show that superoxide radical anions play a major role in this system since the RhB degradation was significantly suppressed after the addition of benzoquinone.
Keywords: photocatalysis; sillenite; elemental Bi; Bi36Fe2O57

In the present study, a series of regeneration conditions and the regeneration mechanism of modified lake sediment biochar (Fe-KOH/LSB) catalysts for low-temperature catalytic hydrolysis of carbon disulfide (CS2) were investigated. The results showed that Rm-WNA method had the best regeneration effect. Under optimal regeneration conditions, the sulfur capacity (13.86 mg[S]/g[catalyst]) of regenerated Fe- KOH/LSB was close to that of fresh Fe-KOH/LSB (14.88 mg[S]/g[catalyst]). The water washing process could wash away a small number of sulfates and a large number of alkaline groups. TG-DTA and DRTFIR results indicated that the nitrogen sweeping process could decompose Fe2(SO4)3 into Fe2O3, which partially recovered the catalytic and the adsorptive abilities. CO2-TPD results indicated that the alkali steeping process offer -OH groups, further improving the catalytic and the adsorptive abilities. After 3 times-regeneration, the sulfur capacity of Fe-KOH/LSB reached 13.31 mg[S]/g[catalyst], indicating that the Rm-WNA method had good stability for the recovery of the catalytic activity. BET, XPS and XRD results revealed that the decrease of the sulfur capacity for regeneration was attributed to the decrease of the adsorptive abilities of C and SiO2.
Keywords: regeneration condition; modified lake sediment; regeneration mechanism; biochar; catalytic hydrolysis; carbon disulfide

Nerve guidance conduits (NGCs) can provide suitable microenvironment for nerve repair and promote the proliferation and migration of Schwann cells (SCs). Thus, we developed nerve guidance conduits (NGCs) with polypyrrole-coated polycaprolactone nanoyarns (PPy-PCL-NYs) as fillers in this study. PCL-NYs with the oriented structure were prepared with a double-needle electrospinning system and then PPy was coated on PCL-NYs via the in situ chemical polymerization. Subsequently, PCL nanofibers were collected around nanoyarns by the conventional electrospinning process as the outer layer to obtain PPy-PCL-NY nerve guidance conduits (PPy-PCLNY NGCs). PPy-PCL-NYs were analyzed by SEM, FTIR and XPS. Results showed that PPy was homogeneously and uniformly deposited on the surface of PCL-NY. Strain-stress curves and the Young’s modulus of PPy-PCL-NYs were investigated compared with those of non-coated PCL-NYs. Studies on biocompatibility with SCs indicated that PPy-PCL-NY NGCs were more conducive to the proliferation of SCs than PCL-NY NGCs. In summary, PPy-PCL-NY NGCs show the promising potential for nerve tissue engineering repair and regeneration.
Keywords: electrospinning; Schwann cell (SC); polypyrrole (PPy); polycaprolactone nanoyarn (PCL-NY); nerve guidance conduit (NGC)