Electrospun Silicon Dioxide and Bismuth Silicate Nanofibers for Sensing and Photocatalysis Applications

Abstract

Metal oxide nanofibers were fabricated using electrospinning technique. Electrical measurements were used as a diagnostic tool for gas sensing application. Photocatalytic activity of metal oxide nanofibers was measured for degradation of organic contaminants in water. The synthesized metal oxide nanofibers were of titanium dioxide (TiO2), silicon dioxide (SiO2), bismuth modified silicon dioxide (Bi-modified SiO2) and bismuth silicate (Bi4(SiO3)4). The diameters of fabricated nanofibers were ~150 – 200 nm and length is of several micrometers. AC impedance spectroscopy of TiO2 nanofibers was performed in the temperature range of 333 K – 513 K. Dielectric loss peak in loss tangent confirmed the presence of relaxing dipoles. The AC conductance as a function of frequency obeys the Jonscher’s power law. The effect of metal (Ti, Ni, and Au) electrodes on humidity sensing properties of TiO2 nanofibers was investigated from 40% – 90% relative humidity (RH) at room temperature. TiO2 nanofibers RH sensor with Ti-electrode had higher sensitivity of 7.53 MΩ/∆%RH, fast response and recovery time of 3 s and 5 s, respectively, as compared to other electrode sensors. SiO2 nanofibers RH sensor was also investigated and it had sensitivity of 9.40 MΩ/∆%RH, quick response and recovery time of 5 s and 3 s, respectively. All sensors were stable, having good reproducibility and low hysteresis values. Oxygen sensing properties of SiO2, Bi-modified SiO2 and Bi4(SiO3)4 nanofibers were investigated by changing the oxygen concentration inside the chamber using different gas flow rates. The performance of the sensors was evaluated from 298 K – 400 K in oxygen rich environment. SiO2, Bi-modified SiO2 and Bi4(SiO3)4 nanofibers oxygen sensors had response time of 58 s, 51 s and 49 s, respectively (error < 5 %). The photodegradation of cationic (methylene blue (MB) and Safranin O (SO)) and anionic (methyl orange (MO)) dyes were performed using photocatalyst i.e. SiO2, Bi-modified SiO2 and Bi4(SiO3)4 nanofibers. The photodegradation rate of SiO2 photocatalyst increased from 0.008 min-1 - 0.085 min-1 (MO), 0.071 min-1 – 0.312 min-1 (SO) and 0.081 min-1 – 0.231 min-1 (MB) with increasing Bi contents from 1 % to 10 %. In case of Bi4(SiO3)4 nanofibers photocatalyst the photodegradation rate was 0.273 min-1, 0.409 min-1 and 0.406 min-1 for MO, SO and MB respectively.