Fluorescence sensing of formaldehyde based on the catalytic reaction of MnO<sub>2</sub> nanowires modulated by different crystal structures

Abstract

α -, β -, γ -, δ -MnO2 nanowires with different crystal structures were synthesized by a hydrothermal method. Employing o -phenylenediamine (OPD) as the substrate, the fluorogenic reactions catalyzed by these MnO2 nanowires were detailedly studied. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), mass spectrometry and electrochemical methods were employed to probe the catalytic fluorogenic reaction. Experimental results revealed that, the activity of the catalytic fluorogenic reaction of β -MnO2 nanowires towards OPD was best, compared with that of other MnO2 nanowires with different crystal structures. On the basis of these findings, taken together the condensation reaction forming the Schiff base between the –CHO group of formaldehyde and –NH2 group of OPD, a novel, highly selective and sensitive catalytic fluorogenic sensing system was successfully established and employed for detecting formaldehyde in foods.