Substituent engineering in g-C_(3)N_(4)/COF heterojunctions for rapid charge separation and high photo-redox activity

The heterojunction composed of covalent organic frameworks(COFs)with adjustable structure and other photocatalysts has great potential in the field of photocatalysis.However,effectively enhancing the photocatalytic performance of organic heterojunctions by designing the structure of COFs has not been explored.Herein,TPB-TP-COFs fabricated from 1,3,5-tris(4-amino-phenyl)benzene(TPB)and terephthalaldehyde(TP)with different substituents(−H,−OH,−OCH_(3),−Br and−F groups),were applied to construct g-C_(3)N_(4)/COFs.The performance improvement of the heterojunction could be affected by substituents,and only−OCH_(3) groups can significantly improve both the photocatalytic phenol oxidation and Cr(Ⅵ)reduction.DFT calculation demonstrated that the substituents will affect the electron cloud distribution of CBM,and the location of CBM in the TPB segment is beneficial for the charge transport between TPB-TP-OCH_(3) and g-C_(3)N_(4).The enhanced charge transfer from g-C_(3)N_(4) to TPB segment and the improved light absorption of TPB-TP-OCH_(3) jointly optimize the photocatalytic redox capacity of g-C_(3)N_(4)/TPB-TP-OCH_(3).On the basis of this study,regulating the electronic effects of semiconductors played a vital role in improving photocatalytic performance in organic heterojunctions.

Spatial assessment of water quality using chemometrics in the Pearl River Estuary, China

A cruise was commissioned in the summer of 2009 to evaluate water quality in the Pearl River Estuary （PRE）. Chemometrics such as Principal Component Analysis （PCA）, Cluster analysis （CA） and Self-Organiz- ing Map （SOM） were employed to identify anthropogenic and natural influences on estuary water quality. The scores of stations in the surface layer in the first principal component （PC1） were related to NH4-N, PO4-P, NO2-N, NO3-N, TP, and Chlorophyll a while salinity, turbidity, and SiO3-Si in the second principal component （PC2）. Similarly, the scores of stations in the bottom layers in PC1 were related to PO4-P, NO2-N, NO3-N, and TP, while salinity, Chlorophyll a, NH4-N, and SiO3-Si in PC2. Results of the PCA identified the spatial distribution of the surface and bottom water quality, namely the Guangzhou urban reach, Middle reach, and Lower reach of the estuary. Both cluster analysis and PCA produced the similar results. Self-organizing map delineated the Guangzhou urban reach of the Pearl River that was mainly influenced by human activities. The middle and lower reaches of the PRE were mainly influenced by the waters in the South China Sea. The information extracted by PCA, CA, and SOM would be very useful to regional agencies in developing a strategy to carry out scientific plans for resource use based on marine system functions.