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Further applications of photocatalysis were limited by the high recombination probability of photo-induced electron–hole pairs in traditional titanium dioxide nanoparticles (TiO2 NPs). Herein, we modified them with rare earth metal via a facile sol–gel method, using tetrabutyl titanate as a precursor and terbium (III) nitrate hexahydrate as terbium (Tb) source. The resulting samples with different Tb doping amounts (from 0 to 2%) have been characterized by X-ray diffraction, UV–visible diffuse reflectance spectroscopy, X-ray photo-electron spectroscopy and a scanning electron microscope. The photocatalytic performance of Tb-doped TiO2 was evaluated by the degradation of methylene blue. The effects of Tb doping amount and initial pH value of solution were investigated in detail. The composite with Tb doping amount of 1.0 wt% showed the highest photocatalytic performance. It exhibited approximately three times enhancement in photocatalytic activity with a reaction rate constant of 0.2314 h−1 when compared with that of commercial P25 (0.0827 h−1). In addition, it presented low toxicity on zebrafishes with 96 h-LC50 of 23.2 mg l−1, and has been proved to be reusable for at least four cycles without significant loss of photocatalytic activity. A probable photocatalytic mechanism of Tb-doped TiO2 was proposed according to the active species trapping experiments. The high photocatalytic performance, excellent reusability and low toxicity of Tb-doped TiO2 indicated that it is a promising candidate material in the future treatment of dye wastewater.

ABSTRACT:Detecting the land cover changes is an important application of multi-temporal synthetic aperture radar (SAR) images. This study puts forward a novel SAR change detection method which has two-steps: change detector construction and change threshold selection. For change detector construction, considering the SAR intensity images follow the gamma distribution, the conditional probabilities of the binary hypothesis test are provided, then the log likelihood ratio (LLR) combined with the log ratio (LR) to construct a detector which can enhance the degree of change to calculate the diversity degree convenient between the two images; for change threshold selection, owing to the characteristic that the curve about the ratio value of adjacent grey-level (GL) values in normalized difference map, the normalized difference map can be segmented in three parts by two thresholds selected which correspond to the regions of unchanged, backscatter enhanced and weakened separately. And as this, the change areas can be also determined simultaneously. The experimental results on different areas and sensors indicate that the proposed algorithm is effective and feasible.

Abstract. Urban ecological space is a significant factor for sustainable urban development and ecological civilization construction. Traditional urban ecological space analysis mainly used medium-resolution image data at large scales and used high-resolution images at a typical urban scale. Few studies focused on the high-precision ecological space analysis at a national urban scale. In this study, high-precision urban boundary and land cover data were utilized to analyze the urban ecological space change and its reason from 2016 to 2017. Ecological space was extracted and merged from high-precision land cover data, which came from the National Geoinformation Survey data of China. Results showed that in 2017, the total urban ecological space area of 338 prefecture-level cities in China was 8514.2 square kilometers, accounting for 22.4% of the total urban area, which was far below the threshold of 40% for evaluating the urban green coverage in China. Urban ecological space of 184 cities declined. There were four principal reasons for the decrease of urban ecological space. First, the green space supporting the buildings was occupied. Second, the green landscape space near rivers and lakes was occupied. Third, blocks of woodland were occupied. Fourth, the water area was occupied. The reduced urban ecological space was mainly changed into construction sites, structures, and buildings. Urban ecological space of China was seriously insufficient, and it was heavily occupied. Adequate ecological space should be preserved not only in new urban development areas but also in the old urban areas to ensure people a more comfortable living environment.

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