H2O2 Ratiometric Electrochemical Sensors Based on Nanospheres Derived from Ferrocence-Modified Covalent Organic Frameworks

A uniform nanosphere derived from ferrocencemodified covalent-organic frameworks (COFETTA-TPAL-FC(COOH)(2)) with 200 nm in diameter was prepared by dehydration condensation reaction between 4,4',4',4'- (ethane-1,1,2,2-tetrayl) tetraaniline and terephthalaldehyde in the presence of electroactive Fc(COOH)(2). The Fc(COOH)(2) was embedded into the layers of COFETTA-TPAL to result in the formation of nanospheres, which increased the specific surface area of the available COFETTA-TPAL to provide more active sites due to the increase in interlayer distance. The Fc(COOH)(2) could interact with H2O2 which might undergo self-disproportionation process to produce O-2 and be reduced into H2O simultaneously, whereas the generated O-2 was directly reduced into H2O by COFETTA-TPAL. The reduction peak current of the generated O-2 at -0.5 V (j(-0.5 V)) was gradually enhanced, whereas that of Fc(COOH)(2) around 0.45 V (j(0.45 V)) was decreased with continuous adding of H2O2. Thus, the COFETTA-TPAL-Fc(COOH)(2) nanospheres were used to fabricate a "on-off" nonenzymatic H2O2 ratiometric electrochemical sensor. The proposed "on-off" ratiometric electrochemical sensor showed good performance with a wide linear range of 1.1-500 mu M, high sensitivity of 0.009 mu M-1, and lower detection limit of 0.33 mu M. The work would offer insights for design and preparation of electroactive COF and accelerate the practical application of COF in electroanalysis.