Photoinduced Oxidation Of Water To Oxygen In The Ionic Liquid Bmimbf_4 As The Counter Reaction In The Fabrication Ofexceptionally Long Semiconducting Silver-tetracyanoquinodimethane Nanowires

摘要

The synthesis of exceptionally long semiconducting silver tetracyanoquinodimethane (AgTCNQ) nanowires has been achieved in the room temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF_4) by photochemical reduction of TCNQ to TCNQ~-, coupled with use of benzyl alcohol as the sacrificial electron donor. The presence of Ag(I) in the ionic liquid allows formation of mm length AgTCNQ nanowires onto both conducting and insulating surfaces, via a nucleation and diffusion-controlled growth mechanism. Remarkably, photocrystallization also can be achieved using adventitious or deliberately added water present in the ionic liquid as the sacrificial electron donor. In this case, oxidation of water produces O_2 as the counter reaction in the photoreduction of TCNQ. In contrast, irradiation in "dried" ionic liquids fails to induce any detectable photochemistry. Molecular structural differences, relative to the situation encountered in more conventional solvent media, are believed to account for the more favorable kinetics available for oxidization of water in ionic liquids. Water assisted photocrystallization in viscous BMIMBF_4 where diffusion rate are slow leads to slow growth of AgTCNQ, thereby allowing easy manipulation of AgTCNQ morphology from small nanoparticles to extremely long single nanowires by tuning the irradiation and ripening time. Infrared and Raman spectroscopic data, elemental analysis, and scanning electron microscopic images all confirm the formation of highly pure AgTCNQ nanomaterials. This study highlights the significant role that water present as an adventitious impurity may play in photochemical studies in ionic liquids and also suggests that ionic liquids may provide a favorable environment for photochemically based water splitting.