Allelopathic effects of Ulva pertusa, Corallina pilulifera and Sargassum thunbergii on the growth of the dinoflagellates Heterosigma akashiwo and Alexandrium tamarense

The allelopathic effects of fresh tissue, dry powder and aqueous extracts of three macroalgae, Ulva pertusa, Corallina pilulifera and Sargassum thunbergii, on the growth of the dinoflagellates Heterosigma akashiwo and Alexandrium tamarense were evaluated using coexistence culture systems in which concentrations of the three macroalga were varied. The results of the coexistence assay showed that the growth of the two microalgae was strongly inhibited by using fresh tissue, dry powder and aqueous extracts of the three macroalga; the allelochemicals were lethal to H. akashiwo at relatively higher concentrations of the three macroalga. The macroalgae showing the most allelopathic effect on H. akashiwo and A. tamarense using fresh tissue were U. pertusa and S. thunbergii, using dry powder were S. thunbergii and U. pertusa, and using aqueous extracts were U. pertusa and C. pilulifera. We also examined the potential allelopathic effect on the two microalgae of culture filtrate of the three macroalga; culture medium filtrate initially exhibited no inhibitory effects when first added but inhibitory effects became apparent under semi-continuous addition, which suggested that continuous release of small quantities of rapidly degradable allelochemicals from the fresh macroalgal tissue were essential to effectively inhibit the growth of the two microalgae

Room-Temperature Ordered Spin Structures in Cluster-Assembled Single V@Si₁₂ Sheets

Since most of the existing pristine two-dimensional (2D) materials are either intrinsically nonmagnetic or magnetic with small magnetic moment per unit cell and weak strength of magnetic coupling, introducing transition metal atoms in various nanosheets has been widely used for achieving a desired 2D magnetic material. However, the problem of surface clustering for the doped transition metal atoms is still challenging. Here we demonstrate via first-principles calculations that the recently experimentally characterized endohedral silicon cage V@Si₁₂ clusters can construct two types of single cluster sheets exhibiting hexagonal porous or honeycomb-like framework with regularly and separately distributed V atoms. For the ground state of these two sheets, the preferred magnetic coupling is found to be ferromagnetic due to a free-electron-mediated mechanism. By using external strain, the magnetic moments and strength of magnetic coupling for these two sheets can be deliberately tuned, which would be propitious to their advanced applications. More attractively, our first-principles molecular dynamics simulations show that both the structure and strength of ferromagnetic coupling for the pristine porous sheet are stable enough to survive at room temperature. The insights obtained in this work highlight a new avenue to achieve 2D silicon-based spintronics nanomaterials

From the ZnO Hollow Cage Clusters to ZnO Nanoporous Phases: A First-Principles Bottom-Up Prediction

A family of Zn_<i>k</i>O_<i>k</i> (<i>k</i> = 12, 16) cluster-assembled solid phases with novel structures and properties has been characterized utilizing a bottom-up approach with density functional calculations. Geometries, stabilities, equation of states, phase transitions, and electronic properties of these ZnO polymorphs have been systematically investigated. First-principles molecular dynamics (FPMD) study of the two selected building blocks, Zn₁₂O₁₂ and Zn₁₆O₁₆, with hollow cage structure and large HOMO–LUMO gap shows that both of them are thermodynamically stable enough to survive up to at least 500 K. Via the coalescence of building blocks, we find that the Zn₁₂O₁₂ cages are able to form eight stable phases by four types of Zn₁₂O₁₂–Zn₁₂O₁₂ interactions, and the Zn₁₆O₁₆ cages can bind into three phases by the Zn₁₆O₁₆–Zn₁₆O₁₆ links of H′, C′, and S′. Among these phases, six ones are reported for the first time. This has greatly extended the family of ZnO nanoporous phases. Notably, some of these phases are even more stable than the synthesized metastable rocksalt ZnO polymorph. The hollow cage structure of the corresponding building block Zn_<i>k</i>O_<i>k</i> is well preserved in all of them, which leads to their low-density nanoporous and high flexibility features. In addition the electronic integrity (wide-energy gap) of the individual Zn_<i>k</i>O_<i>k</i> is also retained. Our calculation reveals that they are all semiconductor with a large direct or indirect band gap. The insights obtained in this work are likely to be general in II–VI semiconductor compounds and will be helpful for extending the range of properties and applications of ZnO materials

Mechanically Strong Multifilament Fibers Spun from Cellulose Solution via Inducing Formation of Nanofibers

Mechanically strong cellulose fibers spun with environmentally friendly technology have been under tremendous consideration in the textile industry. Here, by inducing the nanofibrous structure formation, a novel cellulose fiber with high strength has been designed and spun successfully on a lab-scale spinning machine. The cellulose–NaOH–urea solution containing 0.5 wt % LiOH was regenerated in 15 wt % phytic acid/5 wt % Na₂SO₄ aqueous solution at 5 °C, in which the alkali–urea complex as shell on the cellulose chain was destroyed, so the naked stiff macromolecules aggregated sufficiently in a parallel manner to form nanofibers with apparent average diameter of 25 nm. The cellulose fibers consisting of the nanofibers exhibited high degree of orientation with Herman’s parameter of 0.9 and excellent mechanical properties with tensile strength of 3.5 cN/dtex in the dry state and 2.5 cN/dtex in the wet state, as well as low fibrillation. This work provided a novel approach to produce high-quality cellulose multifilament with nanofibrous structure, showing a great potential in the material processing