Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Lignin materials are abundant and among the most important potential sources for biofuel production. Development of an efficient lignin degradation process has considerable potential for the production of a variety of chemicals, including bioethanol. However, lignin degradation using current methods is inefficient. Given their immense environmental adaptability and biochemical versatility, bacterial could be used as a valuable tool for the rapid degradation of lignin. Kraft lignin (KL) is a polymer by-product of the pulp and paper industry resulting from alkaline sulfide treatment of lignocellulose, and it has been widely used for lignin-related studies. Beta-proteobacterium Cupriavidus basilensis B-8 isolated from erosive bamboo slips displayed substantial KL degradation capability. With initial concentrations of 0.5–6 g L-1, at least 31.3% KL could be degraded in 7 days. The maximum degradation rate was 44.4% at the initial concentration of 2 g L-1. The optimum pH and temperature for KL degradation were 7.0 and 30°C, respectively. Manganese peroxidase (MnP) and laccase (Lac) demonstrated their greatest level of activity, 1685.3 U L-1 and 815.6 U L-1, at the third and fourth days, respectively. Many small molecule intermediates were formed during the process of KL degradation, as determined using GC-MS analysis. In order to perform metabolic reconstruction of lignin degradation in this bacterium, a draft genome sequence for C. basilensis B-8 was generated. Genomic analysis focused on the catabolic potential of this bacterium against several lignin-derived compounds. These analyses together with sequence comparisons predicted the existence of three major metabolic pathways: β-ketoadipate, phenol degradation, and gentisate pathways. These results confirmed the capability of C. basilensis B-8 to promote KL degradation. Whole genomic sequencing and systematic analysis of the C. basilensis B-8 genome identified degradation steps and intermediates from this bacterial-mediated KL degradation method. Our findings provide a theoretical basis for research into the mechanisms of lignin degradation as well as a practical basis for biofuel production using lignin materials.

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Characterization and genomic analysis of kraft lignin biodegradation by the beta-proteobacterium Cupriavidus basilensis B-8

We demonstrate a controllable electromagnetic wave reflector/absorber for different polarizations with metamaterial involving electromagnetic resonant structures coupled with diodes. Through biasing at different voltages to turn ON and OFF the diodes, we are able to switch the structure between nearly total reflection and total absorption of a particularly polarized incident wave. By arranging orthogonally orientated resonant cells, the metamaterial can react to different polarized waves by selectively biasing the corresponding diodes. Both numerical simulations and microwave measurements have verified the performance.

Switchable metamaterial reflector/absorber for different polarized electromagnetic waves

Abstract Metasurfaces as optically thin composite layers can be modeled as electric and magnetic surface current sheets flowing in the layer volume in the metasurface plane. In the most general linear metasurface, the electric surface current can be induced by both incident electric and magnetic fields. Likewise, magnetic polarization and magnetic current can be induced also by external electric field. Metasurfaces which exhibit magnetoelectric coupling are called bianisotropic metasurfaces. In this review, we explain the role of bianisotropic properties in realizing various metasurface devices and overview the state-of-the-art of research in this field. Interestingly, engineered bianisotropic response is seen to be required for realization of many key field transformations, such as anomalous refraction, asymmetric reflection, polarization transformation, isolation, and more. Moreover, we summarize previously reported findings on uniform and gradient bianisotropic metasurfaces and envision novel and prospective research directions in this field.

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Bianisotropic metasurfaces: physics and applications

Lignin is the most abundant aromatic substrate on Earth and its valorization technologies are still under developed. Depolymerization and fragmentation are the predominant preparatory strategies for valorization of lignin to chemicals and fuels. However, due to the structural heterogeneity of lignin, depolymerization and fragmentation typically result in diverse product species, which require extensive separation and purification procedures to obtain target products. For lignin valorization, bacterial-based systems have attracted increasing attention because of their diverse metabolisms, which can be used to funnel multiple lignin-based compounds into specific target products. Here, recent advances in lignin valorization using bacteria are critically reviewed, including lignin-degrading bacteria that are able to degrade lignin and use lignin-associated aromatics, various associated metabolic pathways, and application of bacterial cultures for lignin valorization. This review will provide insight into the recent breakthroughs and future trends of lignin valorization based on bacterial systems.

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Recent advances in lignin valorization with bacterial cultures: microorganisms, metabolic pathways, and bio-products

Aims: The aim was to obtain evidences for lignin degradation by unicellular bacterium Comamonas sp. B-9.



Methods and Results: Comamonas sp. B-9 was inoculated into kraft lignin-mineral salt medium (KL-MSM) at pH 7·0 and 30°C for 7 days of incubation. The bacterial growth, chemical oxygen demand (COD) reduction, secretion of ligninolytic enzymes and productions of low-molecular-weight compounds revealed that Comamonas sp. B-9 was able to degrade kraft lignin (KL). COD in KL-MSM reduced by 32% after 7 days of incubation. The maximum activities of manganese peroxidase (MnP) of 2903·2 U l−1 and laccase (Lac) of 1250 U l−1 were observed at 4th and 6th day, respectively. The low-molecular-weight compounds such as ethanediol, 3, 5-dimethyl-benzaldehyde and phenethyl alcohol were formed in the degradation of KL by Comamonas sp. B-9 based on GC-MS analysis.



Conclusions:  This study confirmed that Comamonas sp. B-9 could utilize KL as a sole carbon source and degrade KL to low-molecular-weight compounds.



Significance and Impact of the Study: Comamonas sp. B-9 may be useful in the utilization and bioconversion of lignin and lignin-derived aromatic compounds in biotechnological applications. Meanwhile, using Comamonas sp. B-9 in treatment of wastewater in pulp and paper industry is a meaningful work.

https://sfamjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2672.2012.05275.x

Biodegradation of kraft lignin by a bacterial strain Comamonas sp. B-9 isolated from eroded bamboo slips.

In this paper, two kinds of bi-layered chiral metamaterials were proposed to enhance the asymmetric transmission effects for circular polarized electromagnetic waves which are only found in planar chiral metamaterials according to previous studies. It was found that the magnitude of the asymmetric transmission parameters mainly depends on the distances between the two metal layers. With appropriate distance, the asymmetric transmission parameter for circular polarized electromagnetic waves can increase to 0.6. Moreover, both proposed configurations show no asymmetric transmission for linear polarized electromagnetic waves which is widely studied in other bi-layered metamaterials.

Giant asymmetric transmission of circular polarization in layer-by-layer chiral metamaterials

The three-dimensional (3D) and two-dimensional (2D) chiral metamaterials (CMMs) have been proved to exhibit circular dichroism and circular conversion dichroism, respectively. The layer-by-layer chiral metamaterials, as a category of 3D CMMs, are expected to show the same properties as bulk 3D structures (e.g. helices). However, in this paper, we demonstrated that the layer-by-layer CMMs exhibit circular dichroism and circular conversion dichroism simultaneously by using both theoretical and experimental methods. This work showed that asymmetric transmissions of circular polarizations can also be observed in layer-by-layer CMMs. Moreover, we provided some necessary requirements for the existing of asymmetric transmissions in layer-by-layer CMMs.

Electromagnetic manifestation of chirality in layer-by-layer chiral metamaterials

In this paper, a kind of bi-layered asymmetrical split ring metamaterial was proposed as a circular polarization converter. Simulations and experiments at the microwave regime showed that the proposed structures can achieve the conversions from right-handed circularly polarized electromagnetic waves to left-handed ones and the reversed conversions in the opposite propagating direction. The linear to circular polarization transmission coefficients and the surface currents were investigated to understand the mechanism of the circular polarization conversions. Moreover, we optimized the proposed metamaterials by increasing the distance between the two metal layers. The proposed circular polarization converters have applications in microwave wave plates and metamaterial antennas.

Circular polarization converters based on bi-layered asymmetrical split ring metamaterials

We studied numerically the transmission properties of a kind of layer-by-layer nonchiral metamaterial. Simulation results show that under certain off-normal incidence, giant circular polarization conversion occurs for both the right and left circularly polarized waves with a roughly 1 GHz operation band. Meanwhile, the copolarization transmissions are almost suppressed to zero, leading to the high purity circular polarization transformation. This phenomenon of giant circular polarization conversion is assumed to suffer from the strong magnetic response, which is illustrated by the surface current distributions of the structure. Compared with chiral structures, this nonchiral structure is easier to design and fabricate and is expected to be used as a promising circular polarization transformer.

Yu Zheng

Papers

Biodegradation of kraft lignin by a bacterial strain Comamonas sp. B-9 isolated from eroded bamboo slips.

Giant asymmetric transmission of circular polarization in layer-by-layer chiral metamaterials

Electromagnetic manifestation of chirality in layer-by-layer chiral metamaterials

Circular polarization converters based on bi-layered asymmetrical split ring metamaterials

Giant circular polarization conversion in layer-by-layer nonchiral metamaterial