Defect induced “super mop” like behaviour of Eu3+-doped hierarchical Bi2SiO5 nanoparticles for improved catalytic and adsorptive behaviour

Abstract

Development of “super-mops”, i.e., materials that are able to rapidly adsorb and degrade pollutants from water bodies, is a necessity for sustaining the marine ecosystem. But, most materials can either adsorb or degrade pollutants leading to a sluggish pollutant removal process. With the aim of developing a “super-mop”, we have synthesized Eu³⁺ incorporated Bi₂SiO₅ with high surface area. Eu³⁺ incorporation led to the rapid formation and stabilization of orthorhombic/monoclinic phase Bi₂SiO₅ by inducing asymmetry in the structure at significantly lower temperatures compared to earlier reports. Furthermore, partial reduction of Eu³⁺ to Eu²⁺ due to reaction conditions resulted in defects in the system by creation of oxygen deficient regions on the surface. These promoted the self-assembly of the initially formed nanoflakes into hierarchical microflowers. The as-synthesized materials, particularly after 1.5 percent Eu³⁺ incorporation, showed high efficiency in the removal of a wide range of pollutants from aqueous media through the adsorption process with an initial rate as high as 3.25 mg g⁻¹ min⁻¹. To illustrate, the material was able to adsorb >60 percent of pollutants within the first five minutes of contact with the aqueous solution. Eu³⁺ incorporation also significantly improved (∼5 times enhancement in rate constant) the photocatalytic activity of Bi₂SiO₅ by suppressing the degree of recombination as Eu³⁺ present in the material can effectively trap the photo-excited electrons to produce Eu²⁺, which thereafter rapidly de-traps to efficiently produce reactive radicals, and the oxygen defects, which are present in large number, acted as excellent sites for temporary trapping of electrons to generate the reactive radical species responsible for photocatalytic degradation.