Integrated adsorption and catalytic degradation of safranine T by a porous covalent triazine-based framework

Abstract

The structural features of adsorbents and the interactions between adsorbents and adsorbates dominate the removal capacity of porous materials to a certain degree. In this work, we used a bottom-up strategy to select a high-performance catalytic adsorbent with appropriate pore structure characteristics by integrating adsorption and catalytic degradation to wipe off Safranin T (ST) dye. That is, a covalent triazine framework based on tetra(4-cyanophenyl)-ethylene (CTF-TCPE) was synthesized to wipe out ST dye from aqueous solution. Systematic researches including kinetics, equilibrium adsorption and photo-catalysis studies were performed. The micro-layer and hierarchical pore structure, high surface area, large pore volume, high negative Zeta potential and the catalytic degradation of CTF-TCPE play key roles in the removal process of ST. The removal amount reaches 6743 mg g−1 in experiment, which is much higher than most experimental values of the other porous materials reported so far, as far as we know. The removal efficiency can reach as high as 99% even above 1000 ppm ST concentration. Removal process and mechanism analyses show that there are strong electrostatic interactions and π-π interactions between CTF-TCPE and ST. The desorption and kinetics experiments show that there exists catalytic degradation during the adsorption process. In high initial concentration of the dye system, partly multilayer adsorption phenomenon occurs between CTF-TCPE and ST dye. The catalytic degradation and multilayer adsorption combine to result in high removal capacity of CTF-TCPE for ST. The effects of pH and ionic strength on ST removal show that CTF-TCPE can work at wide pH and ionic strength ranges. These results indicate that CTF-TCPE is high-efficiency for removal of ST from aqueous solution. Therefore, the strategy of selecting adsorbents based on the structural characters integrating adsorption and catalytic degradation is efficient for designing and synthesizing high-performance removal materials.