Efficient magnetic hybrid ZnO-based photocatalysts for visible-light-driven removal of toxic cyanobacteria blooms and cyanotoxins

A hybrid magnetic-ZnO-based photocatalyst platform is designed for the efficient and simultaneous sunlight-driven photoremoval of cyanobacteria and mineralization of cyanotoxins (anatoxin-A). The photocatalyst killing ability was evaluated against two types of microalgae with different morpholo-gy and toxicity, Spirulina platensis paracas and Anabaena flos-aquae. The hybrid photocatalyst Ni@ZnO@ZnS-Spirulina was synthetized by means of a multistep process using Spirulina as bio-template. The effects of reactor geometry, magnetic actuation, and concordant architecture on pho-tokilling ability were tested. Moreover, the prepared photocatalysts were demonstrated to be effective for the anatoxin-A degradation under artificial sunlight. In the interest of reducing waste content and optimizing resources, photocatalyst recycling after their useful lifetime has ended is proposed through the fabrication of microalgal biofuel-pellets. This inexpensive circular process involves mul-ti-functional algae-based photocatalysts applied to the simultaneous destruction of algae blooms and cyanotoxins and then recycled to close the circle through cultivating biotemplates

X-ray imaging of the magnetic configuration of a three-dimensional artificial spin ice building block

The extension of artificial spin systems to the third dimension offers advances in functionalities and opportunities for technological applications. One of the main challenges facing their realization is the fabrication of three-dimensional geometries with nanoscale resolution. In this work, we combine two-photon lithography with deformation-free pyrolysis and a GdCo coating to create a three-dimensional (3D) tripod structure that represents a building block of an 3D artificial spin ice, surrounded by a two-dimensional magnetic film. We map the three-dimensional magnetic configuration of the structure and its surroundings using soft x-ray magnetic laminography. In this way, we determine the magnetic configuration of the tripod nanostructure to be in the low-energy two-in-one-out spin ice state, observed at the 2D vertex of a kagome ice and predicted for three-dimensional vertices of magnetic buckyball structures. In contrast to isolated vertices, the degeneracy of this state can be lifted by the surrounding film, which also offers a route toward the controlled injection of emergent charges. This demonstration of the building block of a 3D spin system represents the first step toward the realization and understanding of more complex 3D artificial spin systems.ISSN:2166-532

Direct observation of spin correlations in an artificial triangular lattice Ising spin system with grazing-incidence small-angle neutron scattering

The triangular lattice with Ising magnetic moments is an archetypical example of geometric frustration. In the case of dipolar-coupled out-of-plane moments, the geometric frustration results in a disordered classical spin-liquid state at higher temperatures while the system is predicted to transition to an anti-ferromagnetic stripe ground state at low temperatures. In this work we fabricate artificial triangular Ising spin systems without and with uniaxial in-plane compression to tune the nature and temperature of the correlations. We probe the energy scale and nature of magnetic correlations by grazing-incidence small-angle neutron scattering. In particular, we apply a newly-developed empirical structure-factor model to describe the measured short-range correlated spin-liquid state, and find good agreement with theoretical predictions. We demonstrate that grazing-incidence neutron scattering on our high-quality samples, in conjunction with detailed modeling of the scattering using the Distorted Wave Born Approximation, can be used to experimentally quantify the spin-liquid-like correlations in highly-frustrated artificial spin systems.ISSN:2055-6756ISSN:2055-676