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Thallium (Tl) is a metal of high toxicity, and the problem of Tl pollution is being faced globally. However, environmental data on Tl are still scarce and its biogeochemical behaviors remain mostly unclear. Studies have revealed the potential transport of other heavy metal by microplastics (MPs), but there is no report on the interactions between Tl and MPs yet. Therefore, we studied the adsorption of Tl by the three most commonly detected MPs, i.e., polyethylene (PE), polystyrene (PS), and polypropylene (PP) in fresh and seawater. We considered the effects of particle size, pH and competitive cations on adsorption capacity. The results showed PS has the highest adsorption capacity for Tl which was mainly through surface complexation. PS showed the lowest crystallinity and had the most oxygen-containing functional groups among the studied MPs. The adsorption of Tl on PE and PP was dominated by physical adsorption. The adsorptions exhibited significant salinity and pH dependence. Dominant cations in seawater competed with Tl ions for adsorption sites on MPs. With the increase in pH, the deprotonation of the carboxyl functional groups on MPs was enhanced, which increased the effective adsorption sites and promoted the adsorption of Tl. However, the adsorption capacity of the studied MPs for Tl was much lower than the corresponding capacity of natural minerals (clay, iron and manganese oxides) previously reported. Therefore, MPs may not be the main factors affecting the environmental behavior of Tl. This study provides valuable information for the study of thallium’s environmental behavior and ecological risk assessment.

Microstructure and dielectric performance of graphite oxide (GO)/polyimide (PI) composites were investigated. Graphite oxide was prepared by hummer method [1] through which graphite flakes were oxidized by concentrated sulfuric acid, potassium permanganate and hydrogen peroxide. Polyimide was synthesized with pyromellitic dianhydride (PMDA) and 4,4-diamino-diphenyl ether (ODA) in N,N-dimethylformamide (DMF) solution. GO/PI composite film was fabricated via coating process. The experimental results showed that the dielectric constant ε r increased gradually with GO content before reaching the percolation threshold. The value of dielectric constant ε r was 68 at 1000 Hz for the composite containing 1wt% of GO, which was 19 times larger than that of the pure PI. The dielectric loss tanδ was 0.6 for the composite containing 1 wt% GO. When the GO content reached 2 wt%, both of the ε r and tanδ values increased substantially, indicating formation of conducting pathway between GO particles. The results implied that when GO content was at a low level, the insulating PI served as electrons barrier layer between GO and prevented electrons from transferring from one GO to another under an external field. As a result, the measured ε r value increased with GO content, while the tanδ remained low. However, when GO filler loading reached a higher level and was in the vicinity of a critical concentration, GO was so close to each other and the conducting pathway could be developed in PI, leading to remarkable growth of ε r and tanδ.