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

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 perform either adsorption or degradation of pollutants leading to sluggish pollutant removal process. With the aim of developing “super-mop”, we have synthesized Eu3+ incorporated Bi2SiO5 with high surface area. Eu3+ incorporation led to rapid formation and stabilization of orthorhombic/monoclinic phase Bi2SiO5 by inducing asymmetry in the structure at significantly lower temperature compared to earlier reports. Further, 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 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 removal of a wide range of pollutants from aqueous medium through adsorption process with initial rates as high as 3.25 mg g-1 min-1. To illustrate, the material was able to adsorb >60 percent of pollutants within first five minutes of contact with 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 presence of higher number of oxygen defects acted as excellent sites for temporary trapping of electrons to generate the reactive radical species responsible for photocatalytic degradation.