Removal of Azo Dyes from Water by Combined Techniques of Adsorption, Desorption, and Electrolysis Based on a Supramolecular Sorbent

In this work, adsorption and desorption of azo dye-Congo red on a supramolecular sorbent (SiO2-CD) were studied. Static adsorption study showed that the adsorption of Congo red onto SiO2-CD obeyed Langmuir's model. The sorbent may be easily regenerated by using beta-cyclodextrin (beta-CD) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as a desorption agent. The desorption efficiency of Congo red was strongly dependent on the concentration of the desorption agent and the temperature. The electrochemical degradation of dye solutions revealed that the average current efficiency (ACE) was sharply increased with dye concentration. The combination of above three techniques dramatically increased the concentration of the dye by a factor of 30, improved the removal (approaching 80% color removal), and enhanced ACE by over 50%. These findings suggest that an organic combination of adsorption, condensation, and electrochemical degradation techniques can achieve a satisfactory outcome for the degradation of low-concentration dye effluents with large volume.