Observations of atmospheric air ions at most geographic areas have been undertaken, but there are still very few observations at middle-latitude semi-arid areas throughout the world. To quantify characteristics of small air ions in semiarid areas of China, measurements of small air ions and particulate matter (PM 10 ) were conducted at 16 different sites in Xi'an (34°26′N, 108°94'E), China, from August 2009 to July 2010 along with meteorological parameters. The influences of meteorological parameters and PM 10 concentration on small air ions as well as their influence mechanisms were discussed in detail. The results showed that both spatial and temporal distributions of small ions were uneven in Xi'an city. Spatially, the concentration of small ions increased gradually from city center to the suburbs. The mean annual concentration of small negative ions was in the range of 200-400 cm -3 with the mean value of 261 ± 39 cm -3 at urban areas, while more than 500 cm -3 at suburban areas. Significant seasonal variations of small ions were observed with highest level in summer, followed by spring and autumn, and lowest in winter at various types of sites. The positive correlations were found between small ions concentration and temperature as well as relative humidity, while negative correlation between the small ions concentration and PM 10 concentration. Air ions concentration was also applied to the assessment of air quality in Xi'an. The assessment results indicated that the air quality was better at suburban areas than at urban areas, suggesting that the unipolarity model is reasonable to indicate air cleanness.

In this paper, the covalent organic polymer of enaminone was modified by thiourea, and the covalent organic polymer of thiourea (CTOP) was synthesized by simple solvothermal method. At 25 ℃, the adsorption capacity of the polymer for trivalent gold ion is 2372.7 mg/g. In the mixed aqueous solution of divalent cadmium ion, trivalent gold ion, divalent copper ion, divalent cobalt ion and divalent nickel ion, CTOP can only adsorb trivalent gold ion, which indicates that CTOP has high selective adsorption performance for trivalent gold ion. In addition, CTOP material still maintains high adsorption performance after five adsorption cycles, which proves that the adsorption material has good reusability. According to the experimental results of adsorption kinetics and thermodynamics, the adsorption process of CTOP for trivalent gold ions conforms to the quasi second order adsorption model and Langmuir adsorption model, that is, the adsorption process of CTOP for trivalent gold ions is single-layer chemical adsorption. CTOP not only has strong adsorption and selectivity to Au (Ⅲ), but also has good reusability. Therefore, it is an ideal environmental functional material, which can be used to separate and enrich trivalent gold ions in wastewater.

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