3D KIT-6 silica: A robust, recyclable adsorbent for the removal of organic dyes from water

Abstract

Mesoporous silica materials like MCM-41 and SBA-15 are well-established adsorbents in many applications, yet KIT-6 stands out due to its unique three-dimensional interconnected pore network and exceptional thermal and hydrothermal stability. This study highlights KIT-6 as a tunable adsorbent for removing various dyes from wastewater, with pore sizes adjustable from 5.9 to 8.6 nm by varying hydrothermal synthesis temperatures (60–120 °C). The relationship between synthesis temperature and the structural and physicochemical properties of KIT-6 was elucidated through powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), nitrogen physisorption, thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FT-IR). Adsorption performance was evaluated for cationic and anionic dyes. KIT-6 synthesized at 80 °C demonstrated superior capacity for cationic dyes, achieving 227 mg g⁻¹ for rhodamine B (RhB) and over 200 mg g⁻¹ for malachite green, methylene blue, and crystal violet, outperforming previously reported silica-based mesoporous materials under comparable conditions. Conversely, KIT-6 showed negligible affinity for anionic dyes (e.g., sunset yellow, quinoline yellow, methyl orange), except for congo red, which exhibited an exceptional capacity of ∼432 mg g⁻¹, likely due to the presence of amine groups in its molecular structure. Notably, the remarkable thermal stability of KIT-6 enabled sustainable reuse of the adsorbent. The RhB-adsorbed KIT-6 was easily regenerated by combusting the adsorbate via a thermal treatment in air. The regenerated KIT-6 retained over 85% of its pristine RhB adsorption capacity after five adsorption-regeneration cycles. These findings introduce KIT-6 as a highly effective and recyclable adsorbent for the dye removal in wastewater treatment.