S. Majumder

A highly sensitive non-enzymatic hydrogen peroxide and hydrazine electrochemical sensor based on 3D micro-snowflake architectures of α-Fe2O3

In the present work, well crystalline 3D micro-snowflake structured α-Fe2O3 has been successfully synthesized on a large scale via a simple hydrothermal reaction by hydrolysis of a K3Fe(CN)6 precursor. The structure, composition, purity and morphology of the synthesized α-Fe2O3 samples are examined using powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy and Mossbauer spectroscopy. The FESEM and TEM images reveal that the sample exhibits a micro-snowflake like shape having six-fold symmetry with symmetric branching along each arm consisting of a long central trunk and secondary branches. The 3D micro-snowflake structured α-Fe2O3 embedded ITO electrode exhibits high selectivity and sensitivity for electrochemical probing of hydrogen peroxide (H2O2) and hydrazine (N2H4) with a very low detection limit in a wide linear range. Amperometric measurements show a sensitivity of 7.16 μA mM−1 cm−2 in a wide linear range from 0.1 to 5.5 mM with the lowest detection limit of 0.01 mM (S/N = 3) towards H2O2 sensing. The sample also exhibits a sensitivity of 24.03 μA mM−1 cm−2 in the linear range between 50 μM and 1340 μM with the lowest detection limit of 5 μM towards hydrazine detection. The excellent electrochemical activity of the sample is rendered to the presence of a large number of catalytic sites in the sample due to its 3D micro-snowflake like architecture. Good reproducibility, stability and selectivity suggest its suitability for the fabrication of H2O2 and hydrazine sensors.

Enhancement of photoluminescence emission and anomalous photoconductivity properties of Fe3O4@SiO2 core–shell microspheres

In this manuscript we report the successful synthesis of both pristine Fe3O4 and the Fe3O4@SiO2 core@shell structure. From SEM images we observe that each Fe3O4 microsphere is composed of a large number of smaller nanoballs. We have extensively studied the photoluminescence and photoconductivity properties of both pristine and SiO2 coated Fe3O4 particles for the first time. An enhancement in photoluminescence emission is observed in the Fe3O4@SiO2 core@shell samples, whereas a reduced and negative photoconductivity is observed in the same sample. SiO2 coating reduces the concentrations of non-radiative trap levels at the interfaces of the core and shell, thereby resulting in the enhancement of photoluminescence intensity in the core–shell particles. An exponential rise and decay in photocurrent is observed upon UV irradiation in the ON and OFF state, respectively, for Fe3O4, whereas for Fe3O4@SiO2, we observe a transient rise in the photocurrent and this photocurrent is not stable. We have explained this unusual behavior of photocurrent.