Post Transition Metals Doped Bismuth Oxyhalides for Photocatalysts Applications using Computational and Experimental Approaches

Abstract

Bismuth oxyhalides (BiOX) are layered materials with unique physicochemical and optical properties. This study investigates the characteristics of BiOX (X= F, Cl, Br, I) crystals using first-principles calculations. The effect of post transition metals (In, Sn, Tl) doping and co-doping with Br atom on the electronic and optical properties of BiOCl was analyzed using the density functional theory (DFT) method. The molecular interaction of different dyes with water and adsorption behaviors on [001] BiOCl surface were investigated via DFT and Monte Carlo dynamics simulations (MCDS). The electronic properties analysis shows BiOX has a different energy band gap which varies with the halogen atom, BiOF has a wide band gap, and BiOI has a narrow band gap. Phonon dispersion studies confirmed the geometric stability of optimized BiOX structures, while thermodynamic evaluations re vealed that BiOX exhibits hard material characteristics at higher temperatures but softer characteristics at lower temperatures. The electronic band structure indicates that doping introduces additional extrinsic electronic states within the energy band gap. Partial density of states (PDOS) analysis confirms that the extrinsic band within the forbidden energy gap arises from the dopants. Consequently, doping with post transition metals and co-doping with bromine have enhanced the electronic and optical properties of the BiOCl crystal. The molecular interaction analysis of dye interactions with water revealed a stable electronic structure in an aqueous medium. Based on the assessed energy gaps, methylene blue (MB) proves to be a stronger electron donor compared to methyl orange (MO) and methyl red (MR). Conversely, MO exhibits a greater electron-accepting capacity. The electrophilic ity index result shows that MB interacts more with BiOCl crystals than MO and MR dye. The 2D-reduced density gradient graph and 3D isosurfaces of the non-covalent interaction analysis confirm repulsive, attractive, and weak interactions. The molecular electrostatic potential map analysis of the dyes revealed regions of varying potential values indicating both nucleophilic and electrophilic sites. MCDS results shows MO has a higher adsorption energy of-89.34 kcal/mol than MB and MR. Similarly, the experimental results show that the synthesized samples have a nanosheet with a layered structure. The absorption intensity of the Sn-doped samples exhibited a redshift and relatively had a higher excitation lifetime compared to pristine BiOCl. Furthermore, the electronic band gaps obtained from the com putational and experimental results are consistent with each other. In conclusion, this study will help to create more effective and customized adsorbent materials for dye removal appli cations, advancing environmental remediation technologies.