pH-Mediated Collective and Selective Solar Photocatalysis by a Series of Layered Aurivillius Perovskites

Abstract

Semiconductor photocatalysis under natural sunlight is an emergent area in contemporary materials research, which has attracted considerable attention toward the development of catalysts for environmental remediation using solar energy. A series of five-layer Aurivillius-phase perovskites, Bi 5 ATi 4 FeO 18 (A = Ca, Sr, and Pb), are synthesized for the first time. Rietveld refinements of the powder X-ray diffraction data indicated orthorhombic structure for the Aurivillius phases with Fe largely occupying the central octahedral layer, whereas the divalent cations (Ca, Sr, and Pb) are statistically distributed over the cubo-octahedral A-sites of the perovskite. The compounds with visible-light-absorbing ability ( E g ranging from ∼2.0 to 2.2 eV) not only exhibit excellent collective photocatalytic degradation of rhodamine B–methylene blue (MB) and rhodamine B–rhodamine 6G mixture at pH 2 but also show almost 100% photocatalytic selective degradation of MB from the rhodamine B–MB mixture at pH 11 under natural solar irradiation. The selectivity in the alkaline medium is believed to originate from the combined effect of the photocatalytic degradation of MB by the Aurivillius-phase perovskites and the photolysis of MB. Although a substantial decrease in MB adsorption from the mixed dye solution (MB + RhB) together with slower MB photolysis at the neutral pH makes the selective MB degradation sluggish, the compounds showed excellent photocatalytic degradation activity and chemical oxygen demand removal efficacy toward individual RhB (at pH 2) and MB (at pH 11) under sunlight irradiation. The catalysts are exceptionally stable and retain good crystallinity even after five successive cyclic runs without any noticeable loss of activity in both the acidic and alkaline media. The present work provides an important insight into the development of layered perovskite photocatalysts for collective degradation of multiple pollutants and selective removal of one or multiple pollutants from a mixture. The later idea may open up new possibilities for recovery/purification of useful chemical substances from the contaminated medium through selective photocatalysis.

Interplay between Mesocrystals of CaTiO3 and Edge Sulfur Atom Enriched MoS2 on Reduced Graphene Oxide Nanosheets: Enhanced Photocatalytic Performance under Sunlight Irradiation

“…It is well known that PL spectroscopy studies the efficacy of the photogenerated charge separation and recombination in terms of PL intensity for different nanocomposites. A relatively lower PL intensity indicates the slow or ineffective recombination of electrons and holes, which implies better separation of the photogenerated charges, resulting in an enhancement of the photocatalytic activity . As depicted in Figure d, CT mesocrystals and CTMG nanocomposites show multiple PL emissions centered around 360 nm, when excited at 310 nm.…”

Cation disorder and octahedral distortion control of internal electric field, band bending and carrier lifetime in Aurivillius perovskite solid solutions for enhanced photocatalytic activity

“…As reported in previous studies that the ∆ values gradually decreases in the order, terminal > preterminal > central octahedral layer for the five-layer Aurivillius phase perovskites in a given series of compounds, is consistent with the second-order Jahn-Teller (SOJT) distortion of d 0 cations in these compounds. [66][67][68] The increase in local octahedral distortion enhances the extent of adsorption of dye molecules on the catalyst surface. Further, the axial distortion parameter, defined as,…”

Progress and Perspectives on Aurivillius-Type Layered Ferroelectric Oxides in Binary Bi4Ti3O12-BiFeO3 System for Multifunctional Applications

“…As the wastewater is contaminated with multiple dyes rather than a single dye, it is desirable to test the efficiency of a catalyst toward the collective removal of multiple dyes from a mixture. Naresh et al [206] reported that a series of five-layer Bi 5 AFeTi 4 O 18 (A = Ca, Sr, and Pb) compounds not only exhibited collective photocatalytic degradation of RhB-methylene blue and RhB-rhodamine 6G mixture at pH = 2, but also showed almost 100% photo-catalytic selective degradation of methylene blue from the RhB-methylene blue mixture at pH = 11 under natural solar irradiation. In addition, size, morphology, surface area, etc., of a catalyst may greatly affect its catalytic performance.…”