Probing the effect of lightly doped Iron in Bi₂S₃ nanostructures on Physiochemical properties and efficacy in anti-microbial activity

Abstract

In this study, Bi2S3 nanostructures doped with Iron (Fe) at various concentrations i.e., FexBi2-xS3 (x = 0.0, 0.4, 0.6, 0.8 wt%) were synthesized using the reverse micelle method. EDAX (Energy Dispersive Analysis of x-rays) has shown that the prepared samples are in stoichiometry without any kind of impurities. Rietveld refinement XRD (x-ray diffraction) pattern confirmed the orthorhombic crystal structure and showed good crystallinity of all the samples with increase in Fe content. The unit cell volume is found to be varied from 12.34 nm to 19.39 nm. HRTEM (High Resolution Transmission Electron Microscopy) has shown that the prepared nanostructures are nanorods and nanocylinders with high crystallinity and corroborates with our XRD results. Diffuse reflectance spectroscopy analysis indicated that the band gap has increased from 1.550 eV for pure Bi2S3 to 1.592 eV for Fe0.08Bi1.92S3 nanostructures reflecting the blue shift compared to bulk sample. The photoluminescence spectra (PL) recorded with 250 nm excitation wavelength for powder samples has shown that with increase in Iron concentration the intensity of 440 nm peak increases whereas the peaks at 470 nm and 510 nm decreases. The PL spectra is also recorded for nanostructures dispersed in liquid media and has shown that the peaks at 501 nm is observed while rest of the two peaks are quenched. Raman spectra dependent on temperature is obtained for FexBi2-xS3 (x = 0.0, 0.4, 0.6, 0.8 wt%) samples in pellet form in the range of 80 K to 280 K. All samples have shown B1g and Ag phonon modes with higher intensity. The Gruneisen parameter determined for B1g mode varies from 1.21 to 14.13 whereas for Ag mode it varies from 0.60 to 7.91 with the exception of a negative value of −3.10 for Fe0.06Bi1.94S3 sample. VSM (vibrating sample magnetometer) showed the diamagnetic behavior of Bi2S3 and ferromagnetic behaviour of FexBi2-xS3 (x = 0.0, 0.4, 0.6, 0.8 wt%) samples. The saturation magnetization is found to be reaching to a value of 127.5 emu gm−1 for 0.6 wt% of Fe doping in Bi2S3 and then decreases drastically to 40.34 emu gm−1 for 0.8 wt% Fe doping. The antibacterial efficacy showed that as Fe concentration increases, the MIC (minimal inhibitory concentration) fluctuates between 60 to 70 μg ml−1 and is found to be maximum for Fe0.08Bi1.92S3 sample. It is also found that Fe0.04Bi1.96S3 nanostructures show the lowest MIC value for Gram +ve and Gram –ve bacteria in comparison to Bi2S3 nanostructures.