The First-principles Study on the Rectification of Molecular Junctions Based on the Alkyl-chain-modified[2,5?]Bipyrimidinyl(biphenyl isocyanide)gold(Ⅰ)

Using density functional theory(DFT)combined with nonequilibrium Green?s function investigates the electron-transport properties of several molecular junctions based on the[2,5?]bipyrimidinyl(biphenyl isocyanide)gold(Ⅰ)molecule(BPM-Au(Ⅰ)CN-BP),which is modified by one to three alkyl groups forming BPM-Au(Ⅰ)CN-BP(CH2)n.The asymmetric current-voltage characteristics have been obtained for the molecular junctions.Rectifying performance of Au/S-BPM-Au(I)CN-BP-S/Au molecular junction can be regulated by introducing alkyl chain.The M1 molecular junction exhibits the best rectifying effect.Its maximum rectifying ratio is 2109,which is about 150 times more than that of the molecular junction based on the original M.Moreover,all the systems modified by alkyl group have obvious negative differential resistance behavior(NDR).The current-voltage(Ⅰ-Ⅴ)curves of all the systems in this work are illustrated by transmission spectra.

Photocatalytic reduction of organic pollutant under visible light by green route synthesized gold nanoparticles

We report a rapid method of green chemistry approach for synthesis of gold nanoparticles（AuNPs）using Lagerstroemia speciosa leaf extract（LSE）. L. speciosa plant extract is known for its effective treatment of diabetes and kidney related problems. The green synthesis of Au NPs was complete within 30 min at 25°C. The same could also be achieved within 2 min at a higher reaction temperature（80°C）. Both UV–visible spectroscopy and transmission electron microscopy results suggest that the morphology and size distribution of Au NPs are dependent on the pH of gold solution,gold concentration,volume of LSE,and reaction time and temperature. Comparison between Fourier transform infrared spectroscopy（FT-IR）spectra of LSE and the synthesized Au NPs indicate an active role of polyphenolic functional groups（from gallotannins,lagerstroemin,and corosolic acid）in the green synthesis and capping of Au NPs. The green route synthesized Au NPs show strong photocatalytic activity in the reduction of dyes viz.,methylene blue,methyl orange,bromophenol blue and bromocresol green,and 4-nitrophenol under visible light in the presence of Na BH4. The non-toxic and cost effective LSE mediated Au NPs synthesis proposed in this study is extremely rapid compared to the other reported methods that require hours to days for complete synthesis of Au NPs using various plant extracts. Strong and stable photocatalytic behavior makes Au NPs attractive in environmental applications,particularly in the reduction of organic pollutants in wastewater.