Experimental and theoretical exploration of bismuth oxyhalide (BiOX, X = Cl, Br, I) nanoparticles in thermoelectric, optoelectronic, and photocatalytic applications

Abstract

Here, we performed first-principles density functional theory (DFT) modeling coupled with the Boltzmann transport equation to explore hydrothermally synthesized bismuth oxyhalides (BiOX, X = Cl, Br, I) nanoparticles. The correlation between BiOX crystallographic and elastic properties was established from the equation of state and elastic tensor simulations. The phonon calculations inferred the dynamical stability and infrared activity of BiOX. The Raman absorptions were reproduced in Raman tensor simulations. The field emission scanning electron microscopy revealed average particle sizes of 154, 221, and 71 nm for BiOCl, BiOBr, and BiOI, respectively. The elemental identification and chemical state analysis were performed with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The diffuse reflectance-derived indirect electronic band gaps of BiOCl (3.54 eV), BiOBr (2.83 eV), and BiOI (1.85 eV) were modeled from the hybrid Heyd–Scuseria–Ernzerhof screened and tuned approach with long-range van der Waals interaction and relativistic spin–orbit coupling. The effective mass analysis revealed that holes in BiOCl and BiOBr are heavier than electrons, whereas the opposite holds in BiOI. High degree of anisotropy was revealed in lattice thermal transport in BiOX. The thermoelectric figure of merit ZT turned out to be 0.51, 0.76, and 1.49 near 990 K in BiOCl, BiOBr, and BiOI, respectively, indicating them as promising thermoelectric materials. The photoluminescence emissions of BiOCl, BiOBr, and BiOI were detected in the opto-electronically favorable visible ranges of 366–521, 335–658, and 393–658 nm, respectively. The theoretical electronic band alignment analysis of BiOX facilitated the straddling of the relevant redox potentials, supporting the photocatalytic degradation of rhodamine B dye. In essence, this work provides comprehensive information on functional properties of BiOX nanoparticles relevant in thermoelectric, optoelectronic, and photocatalytic applications with a combined DFT-experimental approach.