A range of bifunctional vermiculite-based adsorbents for simultaneous removal of Congo red and permanganate

It remains a challenge to design and prepare multifunctional low-cost adsorbents to dispose of diverse pollutants in wastewater. Herein, a series of bifunctional vermiculite-based adsorbents named DDPA-Vt as well as DDPU-Vt, are constructed via gemini surfactants containing pyridine-amide/pyridine-urea groups as modifiers. The morphology, physicochemistry and structure of organo-Vts are confirmed by multifarious probe methods thoroughly. The organo-Vts for the retention of anionic dye (Congo red (CR)) together with heavy metal (permanganate (MnO₄^-)) are investigated in single/mixed components in depth. More importantly, the maximum adsorption capacities are up to 504/822 mg/g for CR and 279/371 mg/g for MnO₄^- onto DDPA-Vt/DDPU-Vt, respectively. Pseudo-second-order kinetic model and Freundlich isotherm model could be depicted the adsorption processes. Competing anions have little effect on the adsorption of MnO₄^-, demonstrating that the organo-Vt could selectively removal MnO₄^-. Co-adsorption tests display that organo-Vt are still effective retention to CR and MnO₄^-, especially onto DDPU-Vt. The adsorption mechanism along with adsorptivity-structure relationship betwixt organo-Vt and pollutants are elucidated via characterization of the spent organo-Vts and DFT calculation: (i) π-π, NH-π, hydrophobic and electrostatic interactions are the mechanism for uptake of CR. (ii) Electrostatic interaction and coordination are the driving forces for retention of MnO₄^-. (iii) The diverse nitrogen-containing groups on the pyridine ring and the spacer have synergistic effects on CR and MnO₄^- retention. (iv) The greater preference of DDPU-Vt for pollutants is based on the stronger nitrogen atom-donating ability on the urea group. This work displays the potential of organo-Vt in the removal of multi-component sewage, and reclaims a prominent way for the simultaneous removal of anionic pollutants.