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Size-selected polyynes synthesized by submerged arc discharge in water

Polyynes are linear sp-carbon chains of finite length consisting in a sequence of alternated single and triple bonds and displaying appealing optical and electronic properties. A simple, low cost and scalable production technique for polyynes is the submerged arc discharge (SAD) in liquid, which so far, has been mainly exploited in organic solvents. In this work, we investigated in detail SAD in water as a cheap and non-toxic solvent for the production of polyynes. The role of process parameters such as current (10-25 A) and voltage (20-25 V) in the production yield have been investigated, as well as polyynes stability. Polyynes terminated by hydrogen (CnH2: n=6-16) were identified by High-Performance Liquid Chromatography (HPLC) coupled with UV-Visible absorption spectroscopy and with the support of density functional theory (DFT) calculations. Size-selected polyynes separated by HPLC were analyzed by surface enhanced Raman spectroscopy (SERS). The formation process was monitored by in situ SERS using an immersed fiber-optic Raman probe and employing Ag nanoparticles directly produced in the solution by SAD.