Distribution, source, risk and phytoremediation of polycyclic aromatic hydrocarbons (PAHs) in typical urban landscape waters recharged by reclaimed water.

A park that had used reclaimed water as the sole water supply for fourteen years, was selected to analyze the distribution, sources and risks of 16 priority polycyclic aromatic hydrocarbons (PAHs) in waters and sediments. The effects of phytoremediation were investigated in waterbodies classified as phytoremediation, transitional and non-phytoremediation areas. Diagnostic ratio (DR) and principal component analysis (PCA) were used to analyze the sources of PAHs, while risk quotient (RQ) was used as risk assessment tool. Results showed that ∑PAH concentrations in sediments ranged from 29.4 to 1245.6 ng‧g-1, with average of 354.3 ng‧g-1, corresponding to a moderate pollution level. The concentration of PAHs in water ranged from 10.6 to 326.3 ng‧L-1, with average of 147.2 ng‧L-1, corresponding to a low pollution level. The ∑PAHs in sediments showed a downward trend from northwest to southeast along with the water flow direction, with average values of 459.5, 362.9 and 246.1 ng‧L-1 in the upstream, midstream and downstream, respectively. In contrast, PAH concentrations in water were consistent with recreational activities in the urban park area. There were 95% of water samples and 72% of sediment samples obtaining the Ant/(Ant + Phe) > 0.1 and Flu/(Flu + Pyr) > 0.5, indicating that coal combustion was the major source of PAHs in both the water and sediment. The RQ∑PAH(NCs) values in water and sediment were all between 1 and 800, while RQ∑PAH(MPCs) reached equal to 0, suggesting that ∑PAHs presented a low ecological risk. Acenaphthene accounted for 28.4% of RQ(NCs), and became the most risk PAH in water column. Aquatic plants effectively removed high-ring PAHs from water and middle-ring PAHs from sediments, reducing the overall risks posed by PAHs.

Self-powered ultraviolet MSM photodetectors with high responsivity enabled by a lateral n+/n- homojunction from opposite polarity domains.

We report a GaN-based self-powered metal-semiconductor-metal (MSM)-type ultraviolet (UV) photodetector (PD) by employing a "lateral polarity structure (LPS)" grown on the sapphire substrate. An in-plane internal electric field and different Schottky barrier heights at a metal/semiconductor interface lead to efficient carrier separation and self-powered UV detection. A dark current of 6.8nA/cm2 and detectivity of 1.0×1012 Jones were obtained without applied bias. A high photo-to-dark current ratio of 1.2×104 and peak responsivity of 933.7 mA/W were achieved for the lateral polarity structure-photodetector (LPS-PD) under -10V. The enhanced performance of the LPS-PD was ascribed to the polarization-induced carrier separation as demonstrated by the lateral band diagram.