Making Chitin Work in an Electrochemical Environment with Non-Noble, Moderately Electropositive Metals: Production of Sensors and Batteries

Due to adsorption of all metal ions (and some non-metals like As, Sb), metal complexes and metal-rich small (oxide, carbonate, oxalate) particles alike, chitin does remove these M spe-cies from a solution or from moist sediments, depleting the solution down to pMol/l levels except for alkali metals, or Mg. Chitin retains substantial metal ions from solutions < 1 nMol/l. Accordingly, there is a (concentration gradient-caused) voltage between two identi-cal pure metal or -alloy electrodes of which one is wrapped by chitin. While 10 min will do to obtain reproducible adsorption on chitin, electrochemical measurements show that the voltage forming between a chitin-surrounded and an identical bare metal electrode keeps on changing for 24 hours except for Ni. Preliminary experiments showed that dried arthropods produce similar results as previously purified chitin(proteins and metal carbonates removed during workup). On chitin exist on-equivalent binding sites the former of which are quickly populated and the metal ions then pass to the latter. However, these latter sites are still lo-cated next to the surface of chitin: upon addition of an appropriate ligand, voltage will mas-sively increase within 1 – 2 min which shows that even sizable ligand ions (glycinate, phe-nolic carboxylic acids like caffeic acid) can still access the metal ions in aq. solution. Chitin does catalyze ligand glycinate oxidation by introduced air oxygen next to cobalt electrodes. Multimetal electrode chitin-modified sensor systems, batteries and designs of fuel cells are discussed. This does agree with results concerning adsorption on surface of living crayfish and crickets and means that the latter can be involved in investigation protocols for environmental pollu-tants. Except for a longer lag time, electrochemical data are easier to obtain than analyzing metal contents on a chitin interface. Voltage does increase rapidly when there is addition of either a ligand, some species connecting a metal ion to the chitin surface by some molecular or ionic bridge or of an anion which does form hardly soluble salts (e.g., to set M levels in solution similar to those in the open environment) and keeps up for several days until the chitin gets saturated with the metal ion. Oxidation of ligand (glycinate) or reduction of pre-cipitating agent (iodate) both change the voltage but with different signs. Effects of SCN- addition suggest possible photoactivation of signals, too.