Bismuth Oxy-halide (BiOBrmI(1-m)) solid solutions for the photodegradation of methylene blue dye under solar and UV-light irradiation.

Abstract

Continuous discharge of textile wastes such as dyes into the water bodies deteriorates the quality of water. Therefore, the removal of these materials from the wastewater should be a priority due to their carcinogenic properties, which pose a health hazard to both human beings and aquatic life. The use of advanced oxidation processes (AOPs) for example heterogeneous photocatalysis has been broadly studied due to their efficacy in the removal of such organic contaminants. Engineering of the bandgap via doping is among the strategies for enhancing the photocatalytic performance of the nanomaterials and the fact that bismuth oxy-halide (BiOM, (M = Br, Cl, I)) can be modified to form solid solutions make them suitable candidates for this study. This dissertation describes the synthesis, characterization, and applicability of BiOBrmI(1- m)solid solutions materials. The materials were prepared through a simple hydrothermal method at 160 °C. The applicability of the prepared materials was examined through the photocatalytic degradation of Methylene blue (MB) dye under solar and UV-light irradiation. The particle size and morphology of the synthesized solid solutions were obtained by scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. X-ray diffractometer (XRD) patterns revealed the structural features of the prepared materials. The optical properties such as absorption edge, energy bandgap, and photodegradation studies were obtained by the UV-Vis spectrophotometer. The Brunauer-Emmett-Teller (BET) was applied to determine the surface area and the pore size distribution of the materials. Vibrational modes of the materials were determined using Raman spectroscopy. From SEM analysis, BiOBr displayed ultrathin plates-like structures that are large and thick with variable dimensions. BiOBr0.2I0.8, BiOBr0.4I0.6, BiOBr0.6I0.4, and BiOBr0.8I0.2 showed flake-like structures as the morphology, whereas BiOI displayed flower-like structures as the morphology. The formation of flakes and flower-like structure is due to the microplates undergoing self-assembly to form 3-dimensional structures. Energy-dispersive X-ray spectroscopy (EDAX) study confirmed the existence of Bi, O, Br, and I. The XRD peaks corresponding to (102) planes shifted to the lower diffraction angle with an increase in the composition of iodide. From the optical properties analysis, the bandgap was tailored from 2.59 to 1.96 eV via doping. The BET surface area of BiOBr, BiOBr0.6I0.4, and BiOI was found to be 0.517, 3.249, and 1.890 xvii m2 /g, respectively. The photodegradation of MB was monitored through color and COD reduction. After 3 h of solar and UV irradiation, the degradation efficiencies over BiOBr0.6I0.4 were 99 and 88%, respectively. The stability of the BiOBrmI(1-m) solid solution was revealed by the reusability of BiOBr0.6I0.4 for 5 cycles with degradation percentage decreasing to 82% after the 5 th cycle. From the scavenging experiment, it was confirmed that superoxide (O2 • ⁻) and photogenerated holes (h+ ) were liable for the degradation of MB. From the study, it can be established that bismuth oxyhalide solid solution is an effective material in the treatment of MB under irradiation from solar and UV-light and thus holds huge promise in environmental remediation.