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•The advanced Bi-based photocatalytic semiconductors are introduced.•Main challenges for applying Bi-based compounds in photocatalysis are concluded.•Possible approaches to overcome ...these challenges are suggested.•Future work about Bi-based photocatalytic semiconductors are listed.
Bismuth-based semiconductors are a unique and promising group of recently developed advanced photocatalytic materials. They have been widely applied in several areas including the generation of H2 by splitting water, decomposition of organic and inorganic pollutants in both wastewater and polluted air, and organic synthesis through harvesting the energy of light. The electronic structure of bismuth-based semiconductors confers them with a suitable band gap for visible-light response and a well-dispersed valence band composed of hybrid orbitals of Bi6s and O2p, making them a promising candidate when compared to other metal oxide semiconductors. In addition, they are simple to operate and prepare with controlled morphologies, making them attractive as potential photocatalysts. The purposes of this review are (1) summarization of advanced bismuth-based compounds that have been applied to date, (2) statement of challenges facing this material and possible approaches to overcome them, and (3) suggestions for future work.
Remote sensing satellite sensors feature a tradeoff between the spatial, temporal, and spectral resolutions. In this paper, we propose an integrated framework for the spatio-temporal-spectral fusion ...of remote sensing images. There are two main advantages of the proposed integrated fusion framework: it can accomplish different kinds of fusion tasks, such as multiview spatial fusion, spatio-spectral fusion, and spatio-temporal fusion, based on a single unified model, and it can achieve the integrated fusion of multisource observations to obtain high spatio-temporal-spectral resolution images, without limitations on the number of remote sensing sensors. The proposed integrated fusion framework was comprehensively tested and verified in a variety of image fusion experiments. In the experiments, a number of different remote sensing satellites were utilized, including IKONOS, the Enhanced Thematic Mapper Plus (ETM+), the Moderate Resolution Imaging Spectroradiometer (MODIS), the Hyperspectral Digital Imagery Collection Experiment (HYDICE), and Système Pour l' Observation de la Terre-5 (SPOT-5). The experimental results confirm the effectiveness of the proposed method.
•This paper provided a holistic review of the pansharpening methods.•The methods were evaluated from a new perspective based on meta-analysis.•The CS-based methods, MRA-based methods, and VO-based ...methods were reviewed.
In this paper, the development of pansharpening methods from traditional understanding to the current understanding is comprehensively reviewed. Furthermore, the performance of the different categories of pansharpening methods developed between 2000 and 2016 is evaluated based on the idea of meta-analysis. This is innovatively performed by making a statistical analysis of the studies ever published. In the proposed scheme, based on strict selection criteria, 48 representative articles, which were selected from more than 1000 articles, were applied for the statistical analysis. This paper aims to provide a holistic review of the pansharpening methods, and highlights the development process from the traditional understanding to the current understanding. In addition, the experiments were implemented from a new perspective based on the idea of meta-analysis.
Photocatalysis holds great promise as an efficient and sustainable oxidation technology for application in wastewater treatment. Rapid progress developing novel materials has propelled photocatalysis ...to the forefront of sustainable wastewater treatments. This review presents the latest progress on applications of photocatalytic wastewater treatment. Our focus is on strategies for improving performance. Challenges and outlooks in this promising field are also discussed. We hope this review will help researchers design low-cost and high-efficiency photocatalysts for water treatment.
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•A novel BiOBr/Ti3C2 heterojunction photocatalyst was successfully synthesized.•BiOBr/Ti3C2 with suitable band positions for both water purification and splitting.•BiOBr/Ti3C2 ...exhibited enhanced visible-light-induced photocatalytic activity.
Transition metal carbides (MXenes), a new two-dimensional material, are an emerging research area. In this work, an MXene (Ti3C2) was combined with a photoactive material (BiOBr), and as-prepared composite exhibited excellent photocatalytic activities in both water detoxification and water splitting. It was found that Ti3C2 with excellent conductivity, served as a reservoir for photogenerated holes in the composite. Furthermore, photogenerated electrons on the conduction band of BiOBr were blocked from being transferred to Ti3C2, as the work function of Ti3C2 was more negative compared to the conduction-band potential of BiOBr. This phenomenon facilitated the separation of photogenerated charge carriers and promoted the photocatalytic activity in both water detoxification and water splitting. This work provides not only a new protocol for designing MXene-family materials for high-performance photocatalysts, but also a new mechanism to explain the charge separation in enhanced photocatalysis.
•This paper proposes a simple and effective spatial-spectral (SESS) method.•SESS fuses spectral and multi-scale spatial features of coastal wetlands.•SESS achieves better classification results than ...other state-of-the-art methods.•The first paper to use China ZY1-02D satellite data in mapping coastal wetlands.
This paper proposes a simple and effective spatial-spectral (SESS) method for mapping large-scale coastal wetlands using China ZY1-02D satellite hyperspectral data. First, the improved sparse subspace clustering algorithm is implemented to select presentative bands, and then the multi-scale low-rank decomposition algorithm is employed to extract multi-scale spatial features. After that, the extracted spatial and selected spectral features are stacked and fused using presented Landmark-neighborhood preserving embedding algorithm. Finally, the low-dimensional fused features are classified with two popular classifiers (i.e., random forest and support vector machine) to map coastal wetlands. Experiments results show that the SESS obtains the highest classification accuracy of 96.92% and 94.84% on Yellow River Delta and Yancheng coastal wetlands of China, respectively, exhibiting good capability in accurately identifying complicated ground objects. This paper is the first attempt to investigate the potentials of China ZY1-02D satellite hyperspectral data, and the SESS can also be applied into other hyperspectral data.
Two-dimensional (2D) Ti3C2 MXenes have aroused tremendous attention as frontier materials for energy storage, solar energy conversion, and environmental remediation because they exhibit high ...elemental abundance in the earth, a unique layered microstructure, abundant surface functional groups, and prominent electrical conductivity and optical properties. The present study summarizes and discusses the most recent advancements in the synthesis methods of Ti3C2 MXenes; the routes of intercalation, exfoliation, and cutting for multilayered Ti3C2 to obtain its delaminated compounds and quantum dots; and their photocatalysis applications. Given the differences of applied Ti3C2 on morphology and size, high-efficiency Ti3C2-based Schottky junction photocatalysts and its derivative photocatalysts are generalized and discussed. The advantages of Ti3C2 MXenes in synthesizing high-efficiency photocatalysts are analyzed, consisting of electronic acceptor, substrate, light harvesting, cocatalyst, and precursor. Lastly, the lingering challenges and directions for the subsequent Ti3C2-based photocatalyst development are proposed.
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Solar-driven evaporation is capable of efficiently and conveniently generating steam from water, which has been developed in the novel applications of evaporation power generation, ...steam sterilization, and fresh water extraction from seawater. It has been confirmed to be promising to reduce energy shortage and water scarcity. In this review, the design points of evaporators are summarized and integrated, and the main factors for the efficiency and long-term performance of evaporators are discussed (e.g., the selection of photothermal materials and the development of key components to achieve high-performance evaporation). Furthermore, the possibilities, opportunities, and challenges of solar-driven evaporation in energy conversion are described by exemplifying the latest research progress.
Due to the limitation of hyperspectral sensors and optical imaging systems, there are several irreconcilable conflicts between high spatial resolution and high spectral resolution of hyperspectral ...images (HSIs). Therefore, HSI super-resolution (SR) is regarded as an important preprocessing task for subsequent applications. In this letter, we use sparse representation to analyze the spectral and spatial feature of HSIs. Considering the sparse characteristic of spectral unmixing and high pattern repeatability of spatial-spectral blocks, we proposed a novel HSI SR framework utilizing spectral mixture analysis and spatial-spectral group sparsity. By simultaneously combining the sparsity and the nonlocal self-similarity of the images in the spatial and spectral domains, the method not only maintains the spectral consistency but also produces plenty of image details. Experiments on three hyperspectral data sets confirm that the proposed method is robust to noise and achieves better results than traditional methods.
The China GaoFen-5 (GF-5) satellite sensor, which was launched in 2018, collects hyperspectral data with 330 spectral bands, a 30 m spatial resolution, and 60 km swath width. Its competitive ...advantages compared to other on-orbit or planned sensors are its number of bands, spectral resolution, and swath width. Unfortunately, its applications may be undermined by its relatively low spatial resolution. Therefore, the data fusion of GF-5 with high spatial resolution multispectral data is required to further enhance its spatial resolution while preserving its spectral fidelity. This paper conducted a comprehensive evaluation study of fusing GF-5 hyperspectral data with three typical multispectral data sources (i.e., GF-1, GF-2 and Sentinel-2A (S2A)), based on quantitative metrics, classification accuracy, and computational efficiency. Datasets on three study areas of China were utilized to design numerous experiments, and the performances of nine state-of-the-art fusion methods were compared. Experimental results show that LANARAS (this method was proposed by lanaras et al.), Adaptive Gram–Schmidt (GSA), and modulation transfer function (MTF)-generalized Laplacian pyramid (GLP) methods are more suitable for fusing GF-5 with GF-1 data, MTF-GLP and GSA methods are recommended for fusing GF-5 with GF-2 data, and GSA and smoothing filtered-based intensity modulation (SFIM) can be used to fuse GF-5 with S2A data.
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