Functionalized TEVS-EGDMA microspheres for efficient cadmium(II) removal: Synthesis, characterization, and adsorption performance

The development of new functionalized adsorbents in the form of polymeric microspheres, based on triethoxyvinylsilane (TEVS) and ethylene glycol dimethacrylate (EGDMA), has been achieved. These adsorbents were created by incorporating coumarin additives, synthesized in an environmentally friendly manner, into the TEVS-EGDMA polymer matrix. This includes coumarin-3-carboxylic acid and its ester derivatives (CRM1-4). The newly developed adsorbents (TEVS-EGDMA-CRM1, TEVS-EGDMA-CRM2, TEVS-EGDMA-CRM3, and TEVS-EGDMA-CRM4) have been applied for the removal of Cd(II) from aqueous solutions. The material was characterized using spectral techniques like pH_zpc, ATR-FTIR, SEM with EDS, DSC, and specific surface area (S_BET). The maximum adsorption capacity for Cd(II) is 58.73, 59.03, 59.16, 63.07 and 64.26 mg/g at pH 6.5, pH_zpc 6.16, 6.28, 6.40, 6.49, and 6.63, and equilibration time of 240 min, respectively. The addition of coumarins to the microspheres improves the thermal resistance of samples. The kinetics are well-fitted by the pseudo-second-order kinetic model (R² > 0.99). The equilibrium adsorption data are fitted by the Langmuir, Freundlich and Dubinin-Raduskevich isotherms. The adsorption capacities calculated from the Langmuir model agree with the experimental results.