Synthesis of bentonite/SiO₂/magnetite nanostructure as an efficient adsorbent for Bisphenol A removal from waters

Bisphenol-A (BPA) is a conventional plasticizer and is considered a chemical of concern due to its potential for endocrine disruption. Therefore, bentonite (Bnt) clay-based silicon dioxide magnetic composite (Bnt/SiO₂/Mag) was synthesized and used as an effective adsorbent for BPA removal from aqueous solutions. The factorial design study was applied for screening the experimental design of parameters. The isotherm modeling results indicated that the equilibrium data fitted to the non-linear Langmuir isotherm model with adoption capacity 276.5 mg g⁻¹. The kinetic findings exhibited good suitability of pseudo-second-order (PSO) model with rate-limiting step involved in the chemical adsorption. The ΔG data between − 16.46 and − 18.02 kJ/mol for a temperature range of 293–323 K confirmed that the BPA adsorption process was taken place spontaneously. The ΔH parameter (−32.3 kJ/mol) characterized the exothermic nature of the adsorption process as the ΔS parameter (−53.44 J/mol.K) showed the reduced randomness at the solution-adsorbent interface after the adsorption process. The BPA adsorption can occur with a combination of different mechanisms including the filling of interlayer holes, electrostatic attraction, hydrogen bonds and π-π interaction. The cycling performance test demonstrated that Bnt/SiO₂/Mag composite adsorbent still showed reasonable performance (70/75%) until five time-adsorption/desorption cycling. The results also designated that Bnt/SiO₂/Mag composite can be valued as an alternative sorbent for the adsorption of BPA from water.