Thickness-dependent ultrafast charge-carrier dynamics and coherent acoustic phonon oscillations in mechanically exfoliated PdSe2 flakes.

Recently, palladium diselenide (PdSe2) has emerged as a promising material with potential applications in electronic and optoelectronic devices due to its intriguing electronic and optical properties. The performance of the device is strongly dependent on the charge-carrier dynamics and the related hot phonon behavior. Here, we investigate the photoexcited-carrier dynamics and coherent acoustic phonon (CAP) oscillations in mechanically exfoliated PdSe2 flakes with a thickness ranging from 10.6 nm to 54 nm using time-resolved non-degenerate pump-probe transient reflection (TR) spectroscopy. The results imply that the CAP frequency is thickness-dependent. Polarization-resolved transient reflection (PRTR) measurements reveal the isotropic charge-carrier relaxation dynamics and the CAP frequency in the 10.6 nm region. In addition, the deformation potential (DP) mechanism dominates the generation of the CAP. Moreover, a sound velocity of 6.78 × 103 m s-1 is extracted from the variation of the oscillation period with the flake thickness and the delay time of the acoustic echo. These results provide insight into the ultrafast optical coherent acoustic phonon and optoelectronic properties of PdSe2 and may open new possibilities for PdSe2 applications in THz-frequency mechanical resonators.

High-efficiency harvesting of microalgae enabled by chitosan-coated magnetic biochar.

Magnetic flocculation which uses magnetic particles is an emerging technology for harvesting microalgae. However, the potential modification and use of cost-effective and sustainable biochar-based composites is still in its infancy. As such, this study aimed to compare the harvesting efficiency of peanut shell biochar (BC), biochar modified with FeCl3 (FeBC), and biochar dual-modified with chitosan and FeCl3 (CTS@FeBC) on microalgae. The results showed CTS@FeBC exhibited significantly higher microalgae harvesting efficiency compared to BC and FeBC. Both acidic and alkaline conditions were favorable for harvesting microalgae by CTS@FeBC. At pH 2 and pH 12, the harvesting efficiency reached 96.9% and 98.8% within 2 min, respectively. The primary adsorption mechanism of CTS@FeBC on microalgae mainly involved electrostatic attraction and sweeping flocculation. Furthermore, CTS@FeBC also showed good biocompatibility and reusability. This study clearly demonstrated a promising technique for microalgae harvesting using biochar-based materials, offering valuable insights and potential applications in sustainable bioresource management.

Integrated culture and harvest systems for improved microalgal biomass production and wastewater treatment.

Microalgae cultivation in wastewater has received much attention as an environmentally sustainable approach. However, commercial application of this technique is challenging due to the low biomass output and high harvesting costs. Recently, integrated culture and harvest systems including microalgae biofilm, membrane photobioreactor, microalgae-fungi co-culture, microalgae-activated sludge co-culture, and microalgae auto-flocculation have been explored for efficiently coupling microalgal biomass production with wastewater purification. In such systems, the cultivation of microalgae and the separation of algal cells from wastewater are performed in the same reactor, enabling microalgae grown in the cultivation system to reach higher concentration, thus greatly improving the efficiency of biomass production and wastewater purification. Additionally, the design of such innovative systems also allows for microalgae cells to be harvested more efficiently. This review summarizes the mechanisms, characteristics, applications, and development trends of the various integrated systems and discusses their potential for broad applications, which worth further research.

Efficient microalgal lipid production driven by salt stress and phytohormones synergistically.

In this study, a novel method of coupling phytohormones with saline wastewater was proposed to drive efficient microalgal lipid production. All the six phytohormones effectively promoted microalgae growth in saline wastewater, and further increased the microalgal lipid content based on salt stress, so as to achieve a large increase in microalgal lipid productivity. Among the phytohormones used, abscisic acid had the most significant promoting effect. Under the synergistic effect of 20 g/L salt and 20 mg/L abscisic acid, the microalgal lipid productivity reached 3.7 times that of the control. Transcriptome analysis showed that differentially expressed genes (DEGs) of microalgae in saline wastewater were mainly up-regulated under the effects of phytohormones except brassinolide. Common DEGs analysis showed that phytohormones all regulated the expression of genes related to DNA repair and substance synthesis. In conclusion, synergistic effect of salt stress and phytohormones can greatly improve the microalgal lipid production efficiency.

Mechanisms and application of microalgae on removing emerging contaminants from wastewater: A review.

This study reviews the development of the ability of microalgae to remove emerging contaminants (ECs) from wastewater. Contaminant removal by microalgae-based systems (MBSs) includes biosorption, bioaccumulation, biodegradation, photolysis, hydrolysis, and volatilization. Usually, the existence of ECs can inhibit microalgae growth and reduce their removal ability. Therefore, three methods (acclimation, co-metabolism, and algal-bacterial consortia) are proposed in this paper to improve the removal performance of ECs by microalgae. Finally, due to the high removal performance of contaminants from wastewater by algal-bacterial consortia systems, three kinds of algal-bacterial consortia applications (algal-bacterial activatedsludge, algal-bacterial biofilm reactor, and algal-bacterial constructed wetland system) are recommended in this paper. These applications are promising for ECs removal. But most of them are still in their infancy, and limited research has been conducted on operational mechanisms and removal processes. Extra research is needed to clarify the applicability and cost-effectiveness of hybrid processes.

Tunable Optical Rotation in Twisted Black Phosphorus.

Black phosphorus (BP) is a typical two-dimensional (2D) layered material with strong in-plane anisotropy and large birefringence, making it possible to manipulate the light field with atomically controlled devices for various optoelectronic and photonic applications-for instance, atomic thickness waveplates. The twist angle in twisted black phosphorus (TBP) can be presented as a new tunable dimension to control BP's optical anisotropy. Here, we report a large and tunable optical rotation effect in TBP, the result of regulating the twist angle and BP thickness. To accurately study the optical rotation and the impact of the twist angle, we developed a new method to prepare TBP. A lab-made polarimeter microscope was used to visualize the optical rotation mapping of TBP. A large polarization-plane rotation (PORA) of 0.49° per atomic layer was observed from an air/BP/SiO2/Si Fabry-Pérot cavity at 600 nm, an order of magnitude higher than the PORA of 0.05° per atomic layer reported earlier. For the same thickness, the PORA of TBP can be tuned from 0.48° to 7.75° based on the twist angle from 0° to 90°. Our work provides an efficient method to investigate the anisotropy of 2D materials and their heterojunctions. TBP could help us design novel optical and optoelectronic devices such as tunable nanoscale polarization controllers.

Layer contribution to optical signals of van der Waals heterostructures.

The optical signals (such as Raman scattering, absorption, reflection) of van der Waals heterostructures (vdWHs) are very important for structural analysis and the application of optoelectronic devices. However, there is still a lack of research on the effect of each layer of two-dimensional materials on the optical signals of vdWHs. Here, we investigated the contribution from different layers to the optical signal of vdWHs by using angle-resolved polarized Raman spectroscopy (ARPRS) and angle-dependent reflection spectroscopy. A suitable theoretical model for the optical signal of vdWHs generated by different layers was developed, and vdWHs stacked by different two-dimensional (2D) materials were analyzed. The results revealed a strong dependence of the relative strengths of the optical signals of the upper and lower layers on the thicknesses of 2D materials and the SiO2 layer on the Si/SiO2 substrate. Interestingly, on the 285 nm SiO2/Si substrate, the contribution to the optical signal by the underlying 2D material was much greater than that by the upper layer. Furthermore, optical signals originating from different layers of twisted black phosphorus (BP) for different twist angles were studied. There is great significance for optical spectroscopy to study vdWHs, as well as the development of better twisted 2D materials and moiré physics.

A gate-tunable symmetric bipolar junction transistor fabricated via femtosecond laser processing.

Two-dimensional (2D) bipolar junction transistors (BJTs) with van der Waals heterostructures play an important role in the development of future nanoelectronics. Herein, a convenient method is introduced for fabricating a symmetric bipolar junction transistor (SBJT), constructed from black phosphorus and MoS2, with femtosecond laser processing. This SBJT exhibits good bidirectional current amplification owing to its symmetric structure. We placed a top gate on one side of the SBJT to change the difference in the major carrier concentration between the emitter and collector in order to further investigate the effects of electrostatic doping on the device performance. The SBJT can also act as a gate-tunable phototransistor with good photodetectivity and photocurrent gain of ß = ∼21. Scanning photocurrent images were used to determine the mechanism governing photocurrent amplification in the phototransistor. These results promote the development of the applications of multifunctional nanoelectronics based on 2D materials.

Carrier Engineering in Polarization-Sensitive Black Phosphorus van der Waals Junctions.

van der Waals p-n heterostructures based on p-type black phosphorus (BP) integrated with other two-dimensional (2D) layered materials have shown potential applications in electronic and optoelectronic devices, including logic rectifiers and polarization-sensitive photodetectors. However, the engineering of carriers transport anisotropy, which is related to the linear dichroism, have not yet been investigated. Here, we demonstrate a novel van der Waals device of orientation-perpendicular BP homojunction based on the anisotropic band structures between the armchair and zigzag directions. The structure exhibits good gate-tunable diode-like rectification characteristics caused by the barrier between the two perpendicular crystal orientations. Moreover, we demonstrate that the unique mechanisms of the polarization-sensitivity properties of this junction are involved with the linear dichroism and the anisotropic carriers transport engineering. These results were verified by the scanning photocurrent images experiments. This work paves the way for 2D anisotropic layered materials for next-generation electronic and optoelectronic devices.

Black-Phosphorus-Based Orientation-Induced Diodes.

Despite many decades of research of diodes, which are fundamental components of electronic and photoelectronic devices with p-n or Schottky junctions using bulk or 2D materials, stereotyped architectures and complex technological processing (doping and multiple material operations) have limited future development. Here, a novel rectification device, an orientation-induced diode, assembled using only few-layered black phosphorus (BP) is investigated. The key to its realization is to utilize the remarkable anisotropy of BP in low dimensions and change the charge-transport conditions abruptly along the different crystal orientations. Rectification ratios of 6.8, 22, and 115 can be achieved in cruciform BP, cross-stacked BP junctions, and BP junctions stacked with vertical orientations, respectively. The underlying physical processes and mechanisms can be explained using "orientation barrier" band theory. The theoretical results are experimentally confirmed using localized scanning photocurrent imaging. These orientation-induced optoelectronic devices open possibilities for 2D anisotropic materials with a new degree of freedom to improve modulation in diodes.

Understanding strategy of nitrate and urea assimilation in a Chinese strain of Aureococcus anophagefferens through RNA-seq analysis.

Aureococcus anophagefferens is a harmful alga that dominates plankton communities during brown tides in North America, Africa, and Asia. Here, RNA-seq technology was used to profile the transcriptome of a Chinese strain of A. anophagefferens that was grown on urea, nitrate, and a mixture of urea and nitrate, and that was under N-replete, limited and recovery conditions to understand the molecular mechanisms that underlie nitrate and urea utilization. The number of differentially expressed genes between urea-grown and mixture N-grown cells were much less than those between urea-grown and nitrate-grown cells. Compared with nitrate-grown cells, mixture N-grown cells contained much lower levels of transcripts encoding proteins that are involved in nitrate transport and assimilation. Together with profiles of nutrient changes in media, these results suggest that A. anophagefferens primarily feeds on urea instead of nitrate when urea and nitrate co-exist. Furthermore, we noted that transcripts upregulated by nitrate and N-limitation included those encoding proteins involved in amino acid and nucleotide transport, degradation of amides and cyanates, and nitrate assimilation pathway. The data suggest that A. anophagefferens possesses an ability to utilize a variety of dissolved organic nitrogen. Moreover, transcripts for synthesis of proteins, glutamate-derived amino acids, spermines and sterols were upregulated by urea. Transcripts encoding key enzymes that are involved in the ornithine-urea and TCA cycles were differentially regulated by urea and nitrogen concentration, which suggests that the OUC may be linked to the TCA cycle and involved in reallocation of intracellular carbon and nitrogen. These genes regulated by urea may be crucial for the rapid proliferation of A. anophagefferens when urea is provided as the N source.