Two-Dimensional Bi₂WO₆ Nanosheets as a Robust Catalyst toward Photocyclization

Abstract

The present work describes the improved photocatalytic activity of cetyl trimethylammonium bromide (CTAB)-assisted Bi2WO6 (CBTH) toward the synthesis of bioactive benzazoles. X-ray diffraction analysis of CBTH suggests that crystal growth has occurred along the (200) plane, whereas field-emission scanning electron microscopy images confirm two-dimensional rose bud morphology and high-resolution transmission electron microscopy analysis suggests the formation of thin nanosheets possessing an orthorhombic structure. Temperature-programmed desorption of ammonia and Py-IR measurements indicate substantial acidity with the generation of Brønsted acid sites on the surface of CBTH. Raman spectra of CBTH also corroborate these observations with the formation of defects within [Bi2O2]2+ layers, resulting in decreased thickness and shapes of nanoplates. These beneficial properties are explored toward the photochemical synthesis of benzazoles using a 35 W tungsten lamp and a CBTH photocatalyst, resulting in better yields at lesser exposure time. It is observed that the catalytic activity is retained up to five consecutive cycles with marginal decrease in % yield. Such a feature can be ascribed to the photostability of the photocatalyst even after continuous exposure to light, implying that the surface active sites remained unaltered as evident from the X-ray photoelectron spectroscopy analysis of pre- and post-characterization of CBTH. Moreover, decrease in the surface hydroxyl groups after five catalytic cycles also accounts for the generation of enhanced Brønsted sites owing to the presence of Bi–O on the surface of CBTH. It exhibits better catalytic activity as compared to other photocatalysts employed for the synthesis of benzazoles. Thus, CBTH serves as a robust photocatalyst for the facile synthesis of these heterocycles in a sustainable manner.

2D Oxide Nanomaterials to Address the Energy Transition and Catalysis

“…Bi 2 WO 6 nanosheets were reported as a robust catalyst in photocyclization, specifically the synthesis of bioactive benzazoles (in the presence of cetyl trimethylammonium bromide) . As described in Section , ultrathin TiO 2 nanosheets were found to show high H 2 evolution rates, due to the exposed (001) facets of the layer.…”

Progress in Photocatalytic Synthesis of Benzimidazoles

“…Acidic MMT promoted the adsorption of aldehydes on the catalyst and the subsequent condensation of aldehydes with amines to form imines, while activated CdSe favored the generation of a biradical on imine intermediate, consequently facilitating the formation of BIs. Another visible‐light photocatalyst developed by Chikate et al [42] . for BIs synthesis is cetyl trimethylammonium bromide (CTAB)‐assisted Bi 2 WO 6 nanosheets (CBTH).…”

“… Photocatalytic synthesis of BIs based on (a) CdSe/MMT, [41] (b) CBTH, [42] and (c) Cu/Cu 2 O@C 3 N 4 [43] …”

Recent Trends in the Synthesis of Benzimidazoles From o‐Phenylenediamine via Nanoparticles and Green Strategies Using Transition Metal Catalysts

“…The catalyst activates the α-C─H bond of aliphatic primary amines (44) and forms imine via trans-amination with N-substituted o-phenylenediamines (43). Subsequent transimination and intramolecular cyclization form benzimidazoline, which later gets oxidized to afford the desired product (Scheme 16) [58].…”

“…In another attempt, Jakhade et al . explored the use of cetyltrimethylammonium bromide, CTAB‐assisted Bi 2 WO 6 (CBTH, 15 mg), as a photocatalyst in the reaction (Scheme ) . The catalyst showed resistance to photo‐corrosion and severe conditions.…”