Silica-enhanced agarose monolith as a highly porous and robust adsorbent for the removal of cationic dyes from wastewater

A silica-enhanced agarose monolith adsorbent was synthesized and evaluated as a highly porous and robust adsorbent for the removal of Janus Green B (JGB) as a cationic dye from aqueous solutions. For this purpose, the molded agarose monolith adsorbent was reinforced by incorporating silica into its structure. The effects of sample volume, pH, contact time, and stirring speed on the removal efficiency of the sorbent were optimized using a response surface methodology with a central composite design. Under the optimal conditions, the monolith achieved satisfactory removal efficiencies greater than 98% for JGB. The maximum adsorption capacity of the agarose-silica adsorbent for 200 mg L^− 1 of JGB was approximately 60 mg g^− 1. Structural and morphological characterization was performed using Fourier transform infrared spectroscopy, scanning electronic microscopy and, energy-dispersive X-ray spectroscopy. The monolith exhibited excellent regenerable properties, with a removal efficiency exceeding 96% after three times of usages. Equilibrium adsorption data showed better agreement with the Freundlich isotherm model compared to Langmuir. This work demonstrated the enhanced physical stability and high porosity of the agarose-silica monoliths for the efficient removal of JGB cationic dye from real-life water and wastewater samples.