Epichlorohydrin/triethylamine modified psyllium as a highly efficient adsorbent for selective adsorption of anionic dyes

To develop new green sustainable adsorbents, herein, psyllium, a polysaccharide, was transformed into a cationic material by introducing a quaternary ammonium group in its structure through a two-step process. Psyllium was epoxidized with epichlorohydrin to epoxy propyl form (EPsy) and the resulting material was reacted with triethylamine to obtain a quaternized psyllium, TPsy. TPsy demonstrates selective elimination of anionic dyes (CR and MO). The maximum % adsorption (Pr) of 93.94%, and 94.44% were reported for MO and CR (anionic dyes) respectively within 70 min. The strong adsorption of MO and CR can be attributed to electrostatic attraction and hydrogen bonding. The adsorption process adhered to the pseudo-second-order kinetics indicating chemisorption and Langmuir isotherm suggesting monolayer adsorption, exhibiting a maximum adsorption capacity (qm) of 223.71 mg/g for MO and 260.41 mg/g for CR. TPsy is regenerable even after twelve adsorption-desorption cycles with cumulative q of 903.97 mg/g and 932.83 mg/g for MO and CR respectively. Our study introduces a novel approach by reversing the surface charge of psyllium (anionic, PZC = 2.25) through quaternization to TPsy (cationic, PZC = 6.23), which significantly enhances its efficiency as an anionic dye adsorbent.