Adsorption of 2,4,6-trichlorophenol by magnetic mesoporous SiO2 and the adsorption capacity regeneration by UV photolysis

The adsorption of 2,4,6-trichlorophenol (2,4,6-TCP) on synthesized magnetic mesoporous silica (Fe3O4/SiO2/m-SiO2, MMS) composites and the regeneration of its adsorption capacity through direct UV photolysis was performed in this work. MMS exhibited good performance in removing 2,4,6-TCP from aqueous solutions. The adsorption ratio of 2,4,6-TCP was determined to be influenced by aquatic pH, dissolved humic acids, ionic strength, temperature, and the loaded adsorbents. The adsorption isotherm fit the Freundlich and Polanyi–Manes model better than the Langmuir model, which indicated that the adsorption of 2,4,6-TCP was more likely a pore-filling process. The calculated adsorbed capacity for 2,4,6-TCP on MMS was 55 mg/g. Direct UV photolysis could decompose the adsorbed 2,4,6-TCP and later regenerate the adsorption capacity of MMS to a certain degree; however, the outer mesoporous silica layer was not UV-persistent, and large parts of the mesoporous silica layer were also shown to be corrupted from the Fe3O4/SiO2 core. Therefore, after long duration UV irradiation, the adsorption of 2,4,6-TCP on regenerated MMS was much lower than on freshly synthesized MMS. These results suggest that the photostability of magnetic core-shell-like nanocomposites should be investigated because parts of the composites might leach into the bulk phase during practical use and cause potential environmental risks, similar to other well-known nanomaterials.