Dual-Functionalized HPW/SBA-15-SH as an Efficient and Recyclable Catalyst for the Sustainable Synthesis of 9,9-Bis(4-hydroxyphenyl) fluorene

Bisphenol fluorene (BHPF) is a thermally stable and less endocrine-disrupting alternative to bisphenol A, yet its synthesis relies on homogeneous cocatalysts like concentrated H2SO4 and thiopropionic acid, which suffer from low efficiency and difficult catalyst separation. Herein, we developed a dual-functionalized heterogeneous catalyst, HPW/SBA-15-SH, by covalently anchoring thiol-grafted groups (−SH) onto SBA-15 mesoporous silica followed by immobilizing phosphotungstic acid (HPW). Comprehensive characterizations confirmed the well-preserved hexagonal mesostructure, the successful formation of Brønsted acid sites (−SO3H from HPW), and stable thiol groups. The optimized catalyst, HPW/SBA-15-SH-0.05, exhibited a high density of medium strong acid sites (122.9 μmol/g) and achieved 99.3% BHPF yield under mild conditions (110 °C, 4 h, phenol/9-fluorenone molar ratio = 4:1) without auxiliary cocatalysts, surpassing nonthiolated analogues. It also demonstrated versatility in synthesizing other bisphenols efficiently. A synergistic mechanism is proposed, wherein −SH groups facilitate intermediate activation and product desorption. This work presents a robust, recyclable, and cocatalyst-free catalytic system, offering a sustainable pathway for BHPF production and highlighting the potential of multifunctional mesoporous catalysts in condensation reactions.