Photoinducedly electrochemical preparation of Prussian blue film and electrochemical modification of the film with cetyltrimethylammonium cation

This work presents a photoinducedly electrochemical preparation of Prussian blue from a single sodium nitroprusside and insertion of cetyltrimethylammonium cations into Prussian blue as counter ions. The product of photoinducedly electrochemical reactions has a couple of voltammetric peaks at E° = 0.266 V in 0.2 mol l−1 KCl solution, the measurements of X-ray powder diffraction and FT-IR spectroscopy show that it is Prussian blue (PB). The formation mechanism of a pre-photochemical reaction and subsequent electrochemical reaction is suggested. The cyclic voltammetric treatment of the freshly as-prepared PB film in 1.0 mmol l−1 cetyltrimethylammonium (CTA) bromide solution leads to the insertion of cetyltrimethylammonium cations into the channels of Prussian blue, which substitutes for potassium ions as counter ions in Prussian blue. The Prussian blue containing CTA counter ions shows two couples of voltammetric peaks at E° = −0.106 V and E° = 0.249 V in 0.2 mol l−1 KCl solution containing 1.0 mmol l−1 cetyltrimethylammonium bromide. Compared with the electrochemical behaviors of KFeFe(CN)6 in 0.1 mol l−1 KOH alkali solution, CTAFeFe(CN)6 shows relatively durable voltammetric currents due to the hydrophobic effects of cetyltrimethylammonium. The diffusion coefficients for CTA and potassium cations were estimated to be DCTA 1.25 × 10−12 cm2 s−1, DK 2.59 × 10−12 cm2 s−1, respectively. The peak current of electro-catalytic oxidization on hydrogen peroxide showed a linear dependence from 6.59 × 10−6 to 2.20 × 10−4 mol l−1 with R = 0.99947 (n = 8). The linear regression equation was Ip (mA) = 0.82949 + 0.00594C (μmol l−1) with errors of ±7.92833 × 10−5 for the slope and ±0.01085 for the intercept with the detection limit of 1.46 × 10−6 mol l−1. Thus, it is expected to find its application in neutral or weak alkali medium for biosensors.

Research highlights
► Cetyltrimethylammonium cations work as counter ions in Prussian blue film was observed and confirmed by cyclic voltammetry, Fourier transform infrared spectroscopy, X-ray powder diffraction measurements, scanning electronic microscopy and transmission electron microscope for the first time.
► Because the cetyltrimethylammonium cations in Prussian blue film are hydrophobic, the Prussian blue film is very stable even in alkali solution, which provides a technical basis for fabrication of stable biosensors.