Porous silica composites as efficient adsorbents for dye removal from aqueous solution

Abstract

This study aimed to analyze the feasibility of removing Alizarin red S (ARS) used as model pollutant from aqueous solutions using the preparative porous silica composites (PSCs) as adsorbents which were prepared via hydrothermal approach. The physicochemical properties of materials were characterized by means of Transmission electron microscope (TEM), Scanning electron microscope (SEM), Energy dispersive spectrometer (EDS), Brunauer-Emmett-Teller (BET) method, Barret-Joyner-Halenda (BJH) method, Fourier Transform Infrared Spectrometer (FTIR) and X-Ray Diffractometer (XRD). PSCs possessed the specific surface area were 731.6 m2/g, 420.9 m2/g, 294.6 m2/g, respectively. The presence of silica structures was confirmed by FTIR spectra. In order to confirm efficiency of composites as adsorbents and reveal adsorption mechanism, the impacts of pH, contact time, initial ARS concentration, temperature on adsorption were conducted. The adsorption experiment results showed that the adsorption efficiency of ARS onto PSC-3 was better than that of PSC-1 and PSC-2 at pH = 11. Furthermore, the adsorption kinetic models, isotherm models and thermodynamic model were analyzed for comprehensive adsorption process. The maximum adsorption capacity of PSC-3 for ARS was 43.1 mg/g. The pseudo-second-order kinetic model and Sips isotherm model were more suitable for experimental results. The adsorption process was endothermic according to the adsorption thermodynamic model. The free energy of adsorption required for ARS onto PSCs was less than 8 kJ/mol, indicating physical adsorption. What’s more, PSC-3 possessed advantages of higher adsorption capacity and shorter equilibration time. Overall, these results made it potentially applicable as an effective adsorbent for ARS dye from effluent.