Sustainable, inexpensive and easy-to-use access to the super-reductant e ˙−aq through 355 nm photoionization of the ascorbate dianion—an alternative to radiolysis or UV-C photochemistry

Abstract

We have investigated and exploited a new photochemical route to hydrated electrons, which are among the strongest reductants known and can even be used for direct carbon dioxide and nitrogen fixation. Our electron precursor is the ascorbate dianion, which we photoionize with a 355 nm laser. The method is instrumentally much simpler and far less accompanied by health and safety issues than is pulse radiolysis. Advantages over other photoionizable substrates or systems comprise the favourably long operating wavelength, at which many additives do not absorb anymore; the low price and nonexisting biohazards of this naturally occurring electron precursor; and the lack of visible absorption as well as the nonreactivity of the ionization by-product, the ascorbate radical, which greatly simplifies the mechanistic and kinetic studies of subsequent reactions. To illustrate the usefulness of this electron source, we have prepared a number of radical anions (through scavenging the electrons) including several that are inaccessible by the usual photochemical route for mechanistic or thermodynamic reasons, obtained their calibrated absorption spectra, and in one case investigated their green-light photochemistry. As proof of its applicability to environmental remediation, we have successfully utilized this electron generator to detoxify a model compound for halogenated organic waste.