Tunable sulfonate-functionalized silsesquioxane-based hybrid networks for efficient gold recovery and selective adsorption of cationic dyes

Abstract

The novel ionic hybrid networks PCS-SOS-x (x = 1, 2, 3; where x denotes the molar percentage of vinyl groups contributed by sodium styrenesulfonate (SSS) relative to total vinyl groups: 25 % (x = 1), 50 % (x = 2), 75 % (x = 3)) were designed and synthesized via ‘thiol-ene’ click reaction using different ratios of octamercaptopropyl silsesquioxane (SQ-SH₈), octavinylsilsesquioxane (OVS), and SSS as the precursors. The photo-induced ‘thiol-ene’ reaction is mild and efficient, and does not require expensive metal catalysts. Hybrid networks can be formed in 1 min under UV light. PCS-SOS-x (x = 1, 2, 3) was fully characterized using various techniques, including FTIR, solid-state ¹³C and ²⁹Si NMR, TGA, SEM, EDS, and XPS. Benefiting from sulfonate groups (-SO₃Na) and the sulfur atoms with strong electronegativity and hydrophilicity, PCS-SOS-x (x = 1, 2, 3) can be utilized as efficient ionic hybrid absorbents to capture Au (III) ions and cationic dyes from wastewater. PCS-SOS-1 exhibited a high adsorption capacity of 1192 mg/g and good selectivity for gold ions. Moreover, due to the situ generation of Au (0) during the adsorption of Au (III) ions, PCS-SOS-1-Au (PCS-SOS-1 loaded with Au) acted as an excellent catalyst for the degradation of methylene blue (MB). PCS-SOS-3 showed a good adsorption capacity for the cationic dye methylene blue (MB), achieving a maximum equilibrium adsorption capacity of 883 mg/g. The networks also exhibited good selectivity and a rapid adsorption rate for MB within 7 min in a mixture of MB and Methyl Orange (MO) dye aqueous solution. To address the poor recoverability and processability of the insoluble PCS-SOS-1 powders in industrial production applications, an electrospun film (PCS-SOS-PAN) was successfully fabricated by incorporating the powders into polyacrylonitrile (PAN). The removal efficiency of the PCS-SOS-PAN towards Au (III) was achieved up to 95 % in 60 min. This work offers an innovative wastewater treatment and purification approach using silsesquioxane-based networks.