Isotherm and kinetic modeling of Cr(VI) removal with quaternary ammonium functionalized silica

In this study, we focused on the efficiency of Cr(VI) adsorption on quaternary ammonium functionalized silica. Additionally, kinetic and isothermal models have been successfully performed. We began by synthesizing the siliceous material through sol-gel process. The incorporation of ammonium groups into the siliceous structure was confirmed via FTIR spectroscopy. The textural characterization reveals that the synthesized adsorbent exhibits a high surface area with two types of porosity: micropores and mesopores. SEM analysis revealed heterogeneous particle morphology, with sizes ranging from 2 to 53.4 μm. Additionally, the point of zero charge was determined to be 2.4. We investigated the influence of various parameters on adsorption, including pH, adsorbent dosage, initial concentration, and temperature. The optimal pH for adsorption was found to be 2.0. The functionalized silica successfully removed 99% of Cr(VI) from solutions with concentrations below 50 mg/L. Furthermore, a notable adsorption capacity of 57 mg/g was noticed at 298 K. The material demonstrated effective regeneration through four cycles of reuse. For isotherm modeling, we used a non-linear approach with the PUPAIM library in R software. Kinetic modeling was performed using the PUPAK library. Statistical parameters were obtained for models with two, three, and four parameters, indicating that both Khan and Redlich–Peterson models fit well the data. Kinetic analysis showed that a pseudo-second-order model effectively described the initial chromium ion adsorption kinetics, followed by a diffusion phase beginning at 225 min. Moreover, the hybrid material exhibited antibacterial activity against various tested bacteria, even after being loaded with chromium ions.