Enhanced visible-light-active photocatalysts: incorporating bismuth tungstate into graphitic carbon nitride for an efficient condensation reaction†

Abstract

Visible-light active heterogeneous photocatalysts offer various advantages owing to their ability to exploit clean, renewable, and economically viable visible light as a driving force. This study aims to develop such photocatalysts by incorporating various loadings (10, 20, and 30 wt%) of bismuth tungstate (Bi₂WO₆ or BWO) into graphitic carbon nitride (g-C₃N₄ or CN) nanosheets. The CN nanosheets and BWO nanomaterials are synthesized using an eco-friendly hydrothermal method. The objective is to evaluate the photocatalytic activity of these catalysts for the Knoevenagel condensation reaction under 12 W blue LED light (low power), aiming to outperform the activity of pure CN. Various characterization methods, including XRD, UV-vis DRS, FTIR, PL, XPS, and TEM, are employed to analyze the catalysts. The study specifically focuses on the performance of the various BWO loading percentages on CN nanosheets. Among those, 20 wt% BWO loaded CN achieves a yield of 80% with minimal activity decline over five recyclability cycles. Furthermore, this study identifies that BWO/CN follows a Z-scheme pathway, enhancing the photocatalytic performance and facilitating organic transformations. Scavenging experiments confirm the formation of radicals during photocatalysis, validating the proposed mechanism and providing crucial mechanistic insights. Ultimately, this research seeks to highlight BWO/CN as a promising, environmentally friendly photoactive substance with significant potential for effective photocatalytic use. To our knowledge, this is the first study to use BWO/CN catalysts for the Knoevenagel condensation reaction under blue LED irradiation.