Synthesis of Thermally Stable Psyllium Husk/4,4´-Diphenylmethane Diisocyanate-Based Polyurethanes for Effective and Selective Removal of Cationic Dyes

Abstract

Dye-laden toxic wastewater generated from textile industries creates a huge problem of toxicity and disposal. Novel research involves biopolymer-based adsorption as the most commonly used remedial method. Herein, a novel psyllium-based polyurethane foam (Psy-PUF) adsorbent was synthesized through polyaddition reaction with 4,4´-Diphenylmethane Diisocyanate (MDI) in the presence of 1,4-diazabicyclo (2.2.2) octane (DABCO 33-LV, as the catalyst), triethanolamine (as the co-catalyst), silicone oil (as a surfactant), and orange peel powder (as a filler) to eliminate dye pollutants. Psy-PUF was characterized using several techniques. The TGA (Thermogravimetric analysis) showed the significant thermal stability of the synthesized Psy-PUF with the final decomposition temperature of 841 °C showing a tremendous increase compared to 601.9 °C for untreated psyllium. Psy-PUF was studied as an adsorbent in binary dye mixtures including cationic and anionic dyes, and the best-adsorbed dyes i.e., malachite green (MG) and crystal violet (CV) were studied. Psy-PUF demonstrated rapid adsorption with 56.38% (MG) and 61.02% (CV) adsorbed only within 20 min, reaching 96.04% and 93.58% for MG and CV, respectively, within 60 min. The adsorption of MG and CV followed pseudo-second-order kinetics with respective R² values of 0.98747 and 0.98685. Moreover, the adsorption behavior of Psy-PUF aligned with the Langmuir isotherm, indicating q_m of 229.35 mg. g⁻¹ for MG and 223.71 mg. g⁻¹ for CV. Psy-PUF exhibited remarkable regeneration for up to ten cycles with cumulative adsorption capacities (q_max) of 801.4 mg. g⁻¹ and 760.3 mg. g⁻¹ for MG and CV. Thus Psy-PUF is an economically viable, eco-friendly, biodegradable, and recyclable adsorbent, for removing harmful cationic dyes.

Graphical abstract